Table of contents

Preface

This issue of Journal IOP Conference Series: Earth and Environmental Science contains the outstanding papers presented at Southeast Asian Conference on Geophysics (SEACG) 2016. The SEACG is the first event which was organized by Department of Geophysical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung. It was held on August 31^st until September 3^rd, 2016 in Bali – a small beautiful island and a part of Indonesia archipelago.

This conference provided a venue for collaboration, sharing and developing new ideas and technologies. The SEACG created an opportunity for academics, professionals, and students to promote and discuss the scientific results related to recent development in geophysical methods and related science. Topics to be during the conference including: (1) rock- and paleomagnetism; (2) near-surface geophysics; (3) geophysical approaches in hydrocarbon exploration; (4) geophysical approaches in geothermal exploration; (5) microseismic for new and renewable energy exploration; (6) environmental geophysics; (7) volcanology; (8) earthquake seismology; (9) exploration seismology; (10) current developments on potential method; (11) development and new approaches.

The main objective of this conference is to lead to develop new ideas and technologies in geophysical methods and related science. This year, our theme was "Development of Geophysical Methods for Sustainable Energy and Environments", presented by the invited speakers. The invited speakers are Prof. Jeannot Trampert (Univ. Utrecht), Prof. James M. Russell (Brown Univ.), Prof. Toshifumi Matsuoka (Kyoto University), Prof. Sri Widiyantoro (ITB). Prof. Djoko Santoso (ITB), Dr. Satria Bijaksana (ITB), and Dr. Haposan Napitupulu (Government).

The organizing committee would like to thank the sponsors of this conference: Institute of Research and Community Services-ITB, Faculty of Mining and Petroleum Engineering ITB, The SATREPS Program of Gundih CCS Pilot Project. We would like to express our sincere thanks to all authors and presenters for their valuable research. We hope to see you again during the next event SEACG 2018 which will be held in Labuan Bajo, Indonesia.

List of Committee

All papers published in this volume of IOP Conference Series: Earth and Environmental Science have been peer reviewed through processes administered by the proceedings Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

The measurement of magnetic susceptibility and the content of gold (Au) on sediments in the Bombana Gold Mining Area (BGMA) has been done. The samples analyzed totaled 121 samples. The magnetic susceptibility values was measured using Low Field MS2B Bartington Susceptibility meter, while the contents of gold (Au) was measured using X-Ray Nitton. Generally, the lower the value of magnetic susceptibility, contents of gold (Au) on the sediment is higher. Based on this result, the magnetic susceptibility can be used as one of the parameters and/or the alternative methods on the exploration of gold in BGMA.

Magnetic susceptibility of soil affected by hydrocarbon was studied through cored soil samples in two zones (Zone One and Zone Two) of an oil field in Wonocolo Village, East Java. We also collected soil samples as the background from a residential area near the oil field (Zone Three). The Zone One, consisted two cores near producing well; the Zone Two consisted two cores obtained from near a dry hole well and a discontinued well; and the Zone Three consisted two cores to validate the initial soil magnetic susceptibility value in this area. The hydrocarbon content measurement was also done for the upper part of each cores using distillation method to identify the correlation between magnetic susceptibility and hydrocarbon content. From magnetic susceptibility measurement in dual frequency, samples from the Zone One and Zone Two have magnetic susceptibility range from 6,1 × 10^-8 m³kg^-1 - 160 × 10^-8 m³kg^-1 and 15,7 × 10^-8 m³kg^-1 - 417,9 × 10^-8 m³kg^-1, respectively. Whereas background samples from Zone Three have magnetic susceptibility range from 4,8 × 10^-8 m³kg^-1 to 81,1 × 10^-8 m³kg^-1. We found low χ_fd (%) in samples with high magnetic susceptibility values, shown that there was no indication of superparamagnetic minerals in the samples. The hydrocarbon content measurement shows the value range of 8% - 14% only exists in the upper part of all cores in Zone One and one core in Zone Two. From this analysis, we assume that other than the volume of the hydrocarbon content in soil, the period of petroleum hydrocarbon deposition in soil and the fossil fuel combustion generated in the study site could differently increase the soil magnetic susceptibility value in this area. Positive correlation between the two parameters hopefully could contribute to develop environmental magnetic methods for detecting oil spills in soil, especially to remediate former hydrocarbon exploration and production area.

Geologic observations and paleo magnetic studies of the western and eastern Palu Bay was undertaken, in order to study the extent of rotated areas and to develop constraints on tectonic models concerning the formation of this bay. Characteristic of remanent magentization (ChRM) results from Palu bay, the western show that; yield a pole at -39.116^°N, 119.895^°E with R=13.99, α₉₅ =0,42, D_m/I_m=61.76/-26.7 and the Eastern Palu bay show that; yield a pole at -81.855^°N, 52.913^°E, R=8.99, α₉₅=0.29, D_m/I_m =67.1/-5.42. The granitic rocks in these areas are dominated by granite and Monzonit-Quartz in composition, with high-K calc-alkaline photasik (KAP) and show metaluminous-peraluminous affinity. This suggests that the rotational motion on both sides of the bay are similar during the Neogen.

Self-Potential (SP) method is frequently used to identify subsurface structures based on electrical properties. For fixed geometry problems, SP method is related to simple geometrical shapes of causative bodies such as a sphere, cylinder, and sheet. This approach is implemented to determine the value of parameters such as shape, depth, polarization angle, and electric dipole moment. In this study, the technique was applied for investigation of fault, where the fault is considered as resembling the shape of a sheet representing dike or fault. The investigated fault is located at Pinggirsari village, Bandung regency, West Java, Indonesia. The observed SP anomalies that were measured allegedly above the fault were inverted to estimate all the fault parameters through inverse modeling scheme using the Levenberg-Marquardt method. The inversion scheme was first tested on a synthetic model, where a close agreement between the test parameters and the calculated parameters was achieved. Finally, the schema was carried out to invert the real observed SP anomalies. The results show that the presence of the fault was detected beneath the surface having electric dipole moment K = 41.5 mV, half-fault dimension a = 34 m, depth of the sheet's center h = 14.6 m, the location of the fault's center x_o = 478.25 m, and the polarization angle to the horizontal plane θ = 334.52° in a clockwise direction.

The interest of this study was to prove the existence of geological contact to field models with presences of outcrops as references. The physical relief of the outcrops can be determined by geological events of faulting, fracture, and folding. Geological contact plays important roles in environmental studies. 2-D resistivity imaging is the best method used for identifying the geological structures of study area located in Guar Jentik, Perlis and Bukit Kukus, Kedah. Besides that, seismic refraction method also applied at the study area. Results from both methods were integrated to get data correlation. There is good correlation produced which have successfully proved the existence of the faults and contact zones in study areas. Resistivity result shows that first study area has two main zones, red mudstone with resistivity value of 1 Ωm – 100 Ωm, sandstone with resistivity value of 2000 Ωm – 9000 Ωm, and Seismic refraction has provided the result on velocity of each zone, mudstone zone is 200 m/s -1800 m/s and sandstone zone is >2000 m/s. The geological contact of fault is determined between the red mudstone zone and sandstone zone. In the second study area, the fracture was found within chert zone and contact zone is located between the chert zone and mudstone zone. In addition, the fold is found to form in the chert zone. Mudstone zone has resistivity value of 1 Ωm – 1500 m/s and chert zone has resistivity value of 2600 Ωm – 35000 Ωm. The first layer of the seismic section is consisting of mudstone with a velocity of <800 m/s and the velocity obtained for the second layer was generally >1200 m/s is interpreted as chert zones.

The research was conducted using Resistivity and Ground Penetrating Radar (GPR) methods in detecting in-filled cavities and air-filled cavities. The importance of this study is to see the difference in conductivity value of the in-filled and air-filled cavity. The first study location in which the known target is air-cavity located at School of Language, Literacies, and Translation (SoLLAT). The next study location is at Desasiswa Bakti Permai, which the known target is a bunker with both were located at Universiti Sains Malaysia, Penang and the last location is at Gua Musang, Kelantan with suspected in-filled cavity. The result from Gua Musang is compared with both of the results that have been done at Universiti Sains Malaysia. The resistivity value of the first location that indicates the possible tunnel is about 500 Ωm to 800 Ωm and the conductivity value is about 0.0017 S/m. The resistivity value for the second location located at Desasiswa Bakti Permai that indicates the bunker is about 50 Ωm to 250 Ωm and the conductivity value is about 0.1104 S/m. The resistivity value from Gua Musang is about 50 Ωm to 100 Ωm and the conductivity value is about 0.0101 S/m. The velocity of the in-filled cavities is much lower compared with the velocity of the air-filled cavities. Based on the characteristics, Gua Musang area was dominated with in-filled cavities.

Rock lithology influences the electrical properties representing soils or rocks. Electrical conductivity value can be measured using geophysical methods like Ground Penetrating Radar (GPR) and 2-D resistivity imaging. The objective of this survey is to integrate GPR, 2-D resistivity imaging and borehole log based on the conductivity value with soil description and N-value from borehole. Borehole is conducted in the middle of the survey line at a distance of 20 m. GPR method used 250 MHz frequency antenna. The result was filtered using Band Pass, Time Varying Gain and DC removal. 2-D resistivity imaging used two arrays; Wenner-Schlumberger and pole-dipole with total distance of 40 m and 1 m minimum electrode spacing using ABEM SAS4000. The results of both arrays are represented in the form of inversion models. Electrical conductivity values for GPR are calculated based on the conductivity values obtained by 2-D resistivity imaging. The conductivity values calculated from GPR are in good agreement with the values from 2-D resistivity imaging method. Electrical conductivity for the top soil is 0.7 – 3.0 mS/m with no soil description and N-value due to imprecise sample of the loose soil condition. The results showed that soil composed of loose silty gravel with some sand at the depth of 1.81 – 2.99 m has higher value of conductivity (0.4 – 3.0 mS/m) while soil dominated by very stiff sandy silt with some rock fragment (gravel) at the depth of 3 – 3.5 m has lower conductivity values of 0.4 mS/m to 0.7 mS/m. Soil having low electrical conductivity is probably due to the stiff condition (minimum water content) confirmed by greater N-value. Integration of geophysical methods and geotechnical method is a success and the geophysical parameters can be used in understanding soil condition.

Outcrop studies are a fascinating part of geology as it evidently shows the aftermath of how the earth forming processes billion years ago. Outcrops do not cover majority of the Earth's land surface as it is covered by soils or vegetation thus cannot be seen clearly. In Kedah, Malaysia, there are many outcrops exposed in the state. The aim of this research studies was to correlate the parameters of geophysical survey with the properties of the Permian facies of Semanggol Formation in Kedah. The Permian facies consists of bedded chert and claystone. Two geophysical technique, electrical resistivity tomography (ERT) and seismic refraction tomography (SRT) were applied at the same line on top of the outcrop at Bukit Kukus beside Kulim – Baling (Kedah) road. The arrays used for ERT are Pole–dipole and Wenner–Schlumberger. The spacing between electrodes for ERT is 1.5 m while the geophone spacing for SRT is 2 m. Both ERT and SRT line is 60 m and 46 m respectively. Based on the results of both geophysical techniques, relating the porosity and permeability (poroperm) with geophysical parameters, it can be concluded that the bedded chert of low poroperm having seismic velocity and resistivity values at range of 1500 m/s – 2500 m/s and 1400 Ωm – 45000 Ωm. Whereas for claystone, it is very soft and laminated, concluding having high poroperm with seismic velocity between 600 m/s – 1200 m/s and resistivity values between 400 Ωm – 1000 Ωm.

Lembang and Cimandiri fault are active faults in West Java that thread people near the faults with earthquake and surface deformation risk. To determine the deformation, GPS measurements around Lembang and Cimandiri fault was conducted then the data was processed to get the horizontal velocity at each GPS stations by Graduate Research of Earthquake and Active Tectonics (GREAT) Department of Geodesy and Geomatics Engineering Study Program, ITB. The purpose of this study is to model the displacement distribution as deformation parameter in the area along Lembang and Cimandiri fault using 2-dimensional boundary element method (BEM) using the horizontal velocity that has been corrected by the effect of Sunda plate horizontal movement as the input. The assumptions that used at the modeling stage are the deformation occurs in homogeneous and isotropic medium, and the stresses that acted on faults are in elastostatic condition. The results of modeling show that Lembang fault had left-lateral slip component and divided into two segments. A lineament oriented in southwest-northeast direction is observed near Tangkuban Perahu Mountain separating the eastern and the western segments of Lembang fault. The displacement pattern of Cimandiri fault shows that Cimandiri fault is divided into the eastern segment with right-lateral slip component and the western segment with left-lateral slip component separated by a northwest-southeast oriented lineament at the western part of Gede Pangrango Mountain. The displacement value between Lembang and Cimandiri fault is nearly zero indicating that Lembang and Cimandiri fault are not connected each other and this area is relatively safe for infrastructure development.

Based on field study, Sedati Mud Volcano located in a line with Gunung Anyar Mud Volcano and occurred by increased pressure in the compression area and rapid loss of gas. The combination of both fast-growing constructions of infrastructures and the presence of the mud volcanoes brings new challenges in Sidoarjo city. The purpose of this scientific research is to determine the sedimentary thickness around Sedati mud volcano. Only a few data show real amplitude spectrum, which represent high contrast impedance. At some point, there are several peaks indicating the presence of contrast impedance between layers. Based on 20 processed data, Sedati Mud Volcano has a 30 – 70m engineering bedrock thickness and natural frequency between 0.5 until 14.4 Hz. The enhancement of natural frequency tends to occur along decrement of layer thickness in the upper basement layer. The result shows the natural frequency parameter and its amplification is slightly variated around Sedati Mud Volcano, as caused by sedimentary lateral depth variation and/or the presence of variation on existing rock. Further analysis indicates a fault inside the area of mud volcano as possible reason behind the occurring mudflow.

The role of geophysics in Environmental Earth Sciences and Engineering is considered. In the developing era, geophysics has mainly contributed in investigation of new constructions such as tunnels, road, dams and high-rise buildings. This study was carried out to assess the foundation depths around a construction site in the Southern Industrial & Logistics Clusters (SiLC), Nusajaya, Johor using 2-D resistivity method. The 2-D resistivity method was carried out with a view to characterize different subsurface geological and to provide the engineering and environmental geophysical characterization of the study area. Measurements of eight 2-D resistivity profile using Pole-dipole array with 2 m minimum electrode spacing was taken with the use of ABEM Terrameter SAS4000 and ES10-64C selector. The results are presented as inversion model resistivity with the outline of the survey line. The inversion model resistivity from L1-L8 obtained is characterized by resistivity range of 1-8000 ohm-m. This range indicates the occurrence of silt, clay, sandy clay and sand whose ranges are; 10-100 ohm-m, 1-100 ohm-m, 100-800 ohm-m and 100-3000 ohm-m respectively. However, there was a boulder with range of >5000 ohm-m and saturated zone (1-20 ohm-m) which may indicate the weak zones of the study area. The 2-D resistivity method is not intended to replace borings, except in specific cases where information gathered would be sufficient to address the intended engineering and environmental purpose.

Bukit Bunuh is the most popular area of suspected meteorite impact crater. In the history of meteorite impact hitting the earth, Bukit Bunuh has complex crater of a rebound zone of positive magnetic anomaly value. This study area was located at Lenggong, Perak of peninsular Malaysia. The crater rim extended 5 km outwards with a clear subdued zone and immediately surround by a positive magnetic residual crater rim zone. A recent study was done to enhance the magnetic interpretation towards meteorite impact crater on this study area. The result obtained is being correlated with boreholes data to determine the range of local magnetic value. For the magnetic survey, the equipment used is Geometric G-856 Proton Precision magnetometers with the aids of other tools such as compass and GPS. In advance, the using of proton precision magnetometer causes it able in measures the magnetic fields separately within interval of second. Also, 18 boreholes are accumulated at study area to enhance the interpretation. The additional boreholes data had successfully described the structure of the impact crater at Bukit Bunuh in detailed where it is an eroded impact crater. Correlations with borehole records enlighten the results acquired from magnetic methods to be more reliable. A better insight of magnetic interpretation of Bukit Bunuh impact crater was done with the aid of geotechnical methods.

The study location was at Bukit Kukus, Kuala Ketil, Kedah, Malaysia where the geological outcrop of this Semanggol Formation comprises of chert, mudstone, and volcanic tuff. The study was conducted using two geophysical methods, which are 2-D Resistivity and Ground Penetrating Radar (GPR). The objectives of the study are to correlate both of the geophysical methods through the value of conductivity and to identify the physical properties of rocks through the value of porosity and permeability. The data acquisition for both methods was conducted on the same line. For 2-D Resistivity method, the length of the line is 60 m with 1.5 m electrode spacing and the array used was Wenner-Schlumberger. For GPR method, the survey line was on top of the resistivity line, and the frequency of the antenna used is 250 MHz. A good correlation exists between both of the GPR signature and contour maps for resistivity from the surfer 10 software with the outcrop feature. Conductivity value from both GPR and Resistivity method was compared and the range value of conductivity obtained from GPR method almost equivalent with Resistivity method based on derivation and calculation for the sedimentary rocks, which are 0.037 to 0.574 miliSiemens per metre (mS/m) for chert and 0.186 to 10.142 miliSiemens per metre (mS/m) for mudstone. Two types of rock samples were taken, and several geotechnical tests were conducted, but only the value of permeability, K and porosity, ɸ of chert can be calculated, which are 1.95E-22 m² (original condition) and 2.27E-22 m² (dry condition) and 3 percent respectively as the sample of mudstone was damaged. The parameter of the 2-D resistivity method derived from Archie's law was used to calculate the porosity, ɸ_f value using the Formation Factor equation. The range values of porosity, ɸ_f for chert mostly in the range of 5 to 25 percent, which is 6.26 to 13.36 percent but slightly out of range for mudstone, which is 14.12 to 36.02 percent.

Water shortage is a big problem for those who live in the region with unsustainable water resource like in Kidangpananjung - a village in Cililin district West Java. With elevation of 1070 m above mean sea level, Kidangpananjung stands on crest of a hill with the geographical coordinate of 113.5^° BT, 6.97^° LS. Based on geological survey, the outcrop which found in Kidangpananjung indicates that this region consists of pyroclastic rock such as fresh tuff and andesitic breccia. Four springs are found in the foothills with elevation of ± 1040 m above mean sea level which indicates the location of water table. To map the groundwater distribution more precisely and understand the aquifer rock more accurately, geo-electrical approach was conducted. This method is chosen based on the principle that the survey target, the water saturated rock, would give a relatively low resistivity contrast than its surrounding rocks. The target aquifer is considered as confined aquifer at 30m - 40m beneath Kidangpananjung. The data acquisition was designed with two lines of wenner-alpha arrays with 235 meters length each. Two lines of profiling were chosen in order to map the underground layer and its resistivity and thicknesses. The resistivity measurements were carefully interpreted by using least-square inversion technique by using RES2DINV program. The purpose of this research is to understand the characteristics and depth of Kidangpananjung aquifer. Therefore, it can be used to be a reference in groundwater drilling in order to improve the living of the inhabitants of Kidangpananjung

2-D resistivity imaging method is widely used to delineate fault zones. The fault referred as a rock fractures or discontinuity in rock volume due to relative displacement caused by the earth movement. In this study, 2-D resistivity imaging survey conducted in Iejue, Aceh Besar locality with the aim to delineate the Seulimeum fault system for this locality. Two survey lines L1 and L2, with a total length of 1200 m each, conducted across the suspected fault using ABEM SAS4000 system with Pole-dipole array and 10 m minimum electrodes spacing. 2-D resistivity imaging profile shows the exploration depth of >320 m with resistivity range of 1-1800 Ωm. The contrast in resistivity values for both lines L1 and L2 indicates the suspected fault at distance of 550-600 m and 500-550 m respectively. Correlation of 2-D resistivity imaging analyses with a geological map of the area shows that the fault is trending in the NW-SE direction with fault lineament approaching the resistivity result. Two distinct resistivity zones identified for each survey line; a saturated zone starting at distance of 600 m toward the end of the line and high resistivity zone at distance of 0 m to 550 m. This saturated zone interpreted as a ground fluid, while the high resistivity zone represents as existing alluvium, sandstones, and volcanic sediments.

Bravo Structure is one of the Pertamina EP gas producing field in North West Java Basin region. This structure located at Subang about 10 km southeast from City Subang. The objective of this structure is a vertical compartment of carbonate due to diagenetic effect and transgression. This evident cause shale deposited and divide multi-layer carbonate reservoir. The carbonate lies at Cibulakan Formation and has three reservoirs: Z-14, Z-15, and Z-16 limestone. Since each reservoir has different pressure data and CO₂ contain, so it becomes challenges to make new interpretation and to know those compartments between reservoirs. To look up geometry distribution detailed, this structure is reinterpreted using 3D seismic (2014) and new concept depositional environment based on wells correlation and core analysis. Generating seismic interpretation using seismic inversion and attribute. Amplitude envelope and instantaneous frequency are calculated to obtain sweetness. Both of them are built by 3D volume seismic. High magnitude from amplitude envelope is used to characterize geometry distribution of carbonate while instantaneous frequency determines low frequency because of gas distribution. The result of this study suggests vertical and lateral carbonate distribution characteristics Meanwhile sweetness attribute can determine gas contain in each layer Z-14 and Z-15. Vertical distribution of Z-14 layer about 140 m (porosity 7-11%) and Z-15 about 70 m (porosity 8-13%). Finally, interpreting carbonate both Z-14 and Z-15 as shelf margin that new concept gives a chances to develop this structure and optimize reservoir management.

To have safe and economical in drilling design, an information of formation pore pressure is required. Pore pressure can be estimated from seismic data using a velocity to pore pressure transform. The objective of this paper is proposing the drilling exploration design for the case study of South Sumatra field, which is controlled by predicted pore pressure. The pore pressure is predicted by using Eaton method that used velocity from 2D seismic and was validated with well log data. The predicted pore pressure is used to design exploration drilling including casing depth and mud weight. Eaton parameter (N =1.1), shear stress (Ko= 0.6), Gardner (A = 0.198 and B = 0.268), which is used in this works, is gained from existing well data. The velocity model is derived from RMS velocity that should be converted into interval velocity. In addition, this velocity should be validated with the sonic log from existing well. The Normal Compaction Trend (NCT) from interval velocity that was combined with generated previous parameter is used for predicting pore pressure and fracturing pressure. Our experiment shows that based on pore pressure prediction, the drilling exploration design is divided into three sections. i.e. section 17-1/2", 12-1/4" and 8-1/2" and four casing sections, i.e. Casing 20', K-55, 90 ppf at 160 ft, casing 13-3/8', K-55, 54.5 ppf at 1400 ft with mud weight 8.8 - 13.7 ppg, casing 9-5/8 ', K-55, 40 ppf at 4000 ft with mud weight 9.5 - 14.0 ppg and casing 7', L-80, 26 ppf at 5500 ft with mud weight 10.4 - 14.6 ppg.

The development of unconventional shale hydrocarbon is really depending on integrating approach of wide range disciplines. The integrated approach for analysing organic-rich shale reservoirs involves calibration of core and well-log data, building petrophysical and rock-physics models, and finally characterizing the key reservoir parameters (TOC, porosity, and natural fractures) and mechanical properties evaluation from seismic data. In this research, integrated approach of geochemical, geomechanical, mineralogy, petrophysical, and geophysical analysis are carried out in Brown Shale, Central Sumatera Basin. Total Organic Carbon (TOC), maturity, and brittleness index are the main parameters used in this study to analyse the shale hydrocarbon potential. The result of geochemical analysis shows that the maturity level of shale in the interest zone in oil window, which means it can generate shale oil in early mature phase at depth of 6400 ft. Quantity of shale hydrocarbon potential is indicated by the TOC value of 0.5-1.2 wt. % (fair to good), with average of shale thickness for over 50 ft. The result of geomechanical analysis shows that brittleness index of interest zone for over 0.48 and rock strength below 10000 Psi.

This paper describes a method to determine anisotropy parameter by shear wave splitting of crosswell seismic data. The purpose of this work is to present a section of anisotropy to be used in detecting hydrocarbon. Splitted S-waves were detected by picking the traveltimes of S-fast and S-slow on SH and SV components, respectively. Polarization method was done on the 3-C crosswell data using hodogram analysis, so that from these three components we can observe P-, SH- and SV-waves. Tomography of SH- and SV-wave of crosswell seismic were run to produce SH and SV tomograms. Due to the azimuth randomness of the 3-C receivers, an azimuth and inclination correction were implemented on the data, and some preconditioning were applied to enhance the quality of the firstbreaks including deconvolution, bandpass filtering and fx-decon. The traveltimes were picked on SH and SV components, furthermore to be inversed using traveltime tomography algorithm. In this work, a case study was carried out to the seismic data collected on inter-bedded sand-shale layers. The results of this work are SH- and SV-wave tomograms and the anisotropy section. We conclude that this method is effectively presenting an anisotropy section to be used for reservoir recognition.

Hydrocarbon Microtremor Analysis is a low-frequency passive seismic method which derives a quick look estimates new hydrocarbon reservoir prospect area. This method based on the empirical study which investigated an increasing of spectra anomaly between 2 – 4 Hz above the reservoir. We determined five attributes on low-frequency band of microtremors including Power Spectral Density integral of vertical component (PSD-IZ), Power Spectral Density (PSD) on 3 Hz frequency, frequency shifting, the spectral ratio of vertical and horizontal components (V/H) maximum and integral of spectral ratio of vertical and horizontal components (V/H). We deployed 105 points of measurement spreading in our suspect area. We used time series data that recorded from particle velocity of three components with 80 minutes duration and 100 Hz of the sampling frequency. The noise identification analysis in each station data set has been made from the measurement location, considering the suspect area had different local cultural noise. We proceed attributes for each data acquired from all station then used the interpolated map using a standard kriging algorithm spatially. As a result, each attribute analysis and spatial attribute map are combined to identify and estimate a good prospect of the hydrocarbon reservoir.

Pore pressure prediction in the planning of the drilling well commonly carried out using seismic stacking velocity and Normal Compaction Trend (NCT) analysis with Eaton's equation. There are other parameters that correlate to pore pressure, i.e. density, P-impedance, S-impedance, and Vp/Vs ratio. The aims of this study are to predict pore pressure distribution from 2D pre and post-stack seismic data of South Sumatera field by applying the Probabilistic Neural Network (PNN). The pre-stack seismic inversion, which resulted in the elastic parameters such as Density (ρ), Vp/Vs ratio, P-impedance (Zp), S-impedance (Zs), is used as input for PNN training. In another hand, the post-stack seismic data, which resulted in the following parameters such as the average frequency, absolute integrated amplitude, apparent polarity, and dominant frequency, is also used to predict the lateral distribution of pore pressure. Our data training using PNN with pre-stack seismic data provided the best correlation up to 98% compared with the post-stack seismic data. Our prediction, in general, provides the pore pressure model and in detail provides over-pressure. The advantage of PNN shows vertical resolution as good as seismic resolution and provides more helpful information for a further drilling operation.

Rock properties analysis (porosity, permeability, elastic modulus, and wave velocity) of the rock is important to note as one of the methods to determine the characteristics of the reservoir rock. Rock properties can calculated in conventional (laboratory), indirect (inversion of seismic waves), and digital computation (Digital Rock Physics). This paper will introduce and discuss the digital calculation/simulation and empirical equation to predict the value of the rock properties from reservoir sandstone. The data used is the samples of the data sandstone core (reservoir) subsurface in an oil field. The research method is to combine the data from a thin layer, a digital image of rocks in three-dimensional (μ-CT-Scan), and empirical approaches of the equations of permeability on rocks and Lattice Boltzmann equation. Digital image of a scanned using μ-CT-Scan used to determine value rock properties and pore structure at the microscale and visualize the shape of the pores of rock samples in 3D. The method combined with rock physics can be powerful tools for determining rock properties from small rock fragments.

Integrated analysis of geochemical, rock mechanic and geophysics were carried out to characterize and map the unconventional reservoir shale hydrocarbon in Baong field, North Sumatera Basin, which is proven with the large potential hydrocarbon, particularly in the sand reservoir. The new challenge of this field is the present of thick shale layer, which is offering the new concept of an unconventional reservoir. The shale layer has the double role as source rock and reservoir. In this work, we performed geochemical analysis on the core data to determine the Total Organic Carbon (TOC), mineralogy, Tmax, and Kerogen type. In term of rock mechanic, the Rock Strength was calculated to determine the hardness and brittleness index. While for petrophysical analysis, we performed multi-linear regression of log data to estimate TOC relationship with the seismic attribute. In term of geophysics, we carried out seismic inversion to produce acoustic impedance, which is useful to map shale distribution. Our analysis shows that the target of shale layer has TOC range from 2 up to 3.5 wt.% with brittleness index of 0.48. Based on the predicted Tmax, this shale layer is categorized into early mature phase and classified into II Kerogen type, which means it has a potential to produce oil. The shale layer was indicated by the result of acoustic impedance inversion which has a value for over 25000 ft/s *g/cc and Rock Strength less than 3000 Psi.

The processing of microseismic data requires reliable software for imaging the condition of subsurface related to occurring microseismicity. In general, the currently available software is only specific for certain processing module and developed by the different developer. However, the software with integrated processing modules will give a better value because the users can use it easier and faster. We developed GMSTech (Ganesha Microseismic Technology), a C# language-based standing-alone software consisting several modules for processing of microseismic data. Its function is to solve a non-linear inverse problem and imaging the subsurface. C# library is supported by ILNumerics to reduce time consumption and give good visualization. In this preliminary result, we will present four developed modules: (1) hypocenter determination, (2) moment magnitude calculation, and (3) 3D seismic tomography. In the first module, we provide four methods for locating the microseismic events that can be chosen by a user independently: simulated annealing method, guided grid-search method, Geiger's method, and joint hypocenter determination (JHD). The second module can be used for calculating moment magnitude using Brune method and to estimate the released energy of the event. At last, we also provided the module of 3-D seismic tomography for imaging the velocity structures based on delay time tomography. We demonstrated the software using both a synthetic data and a real data from a certain geothermal field in Indonesia. The results for all modules are reliable and remarkable, reviewed statistically by RMS error. We will keep examining the software using another set of data and developing further modules of processing.

Microseismic monitoring and constraining its hypocenters in and around hydrocarbon reservoirs provides insight into induced deformation related to hydraulic fracturing. In this study, we used data from a single vertical array of sensors in a borehole, providing measures of arrival times and polarizations. Microseismic events are located using 1-D velocity models and arrival times of P- and S-waves. However, in the case of all the sensors being deployed in a near-vertical borehole, there is a high ambiguity in the source location. Herein, we applied a procedure using azimuth of P-wave particle motion to constrain and improve the source location. We used a dataset acquired during 1-day of fracture stimulation at a CBM field in Indonesia. We applied five steps of location procedure to investigate microseismic events induced by these hydraulic fracturing activities. First, arrival times for 1584 candidate events were manually picked. Then we refined the arrival times using energy ratio method to obtain high consistency picking. Using these arrival times, we estimated back-azimuth using P-wave polarization analysis. We also added the combination of polarities analysis to remove 180^° ambiguity. In the end, we determined hypocenter locations using grid-search method that guided in the back-azimuth trace area to minimize the misfit function of arrival times. We have successfully removed the ambiguity and produced a good solution for hypocenter locations as indicated statistically by small RMS. Most of the events clusters highlight coherent structures around the treatment well site and revealed faults. The same procedure can be applied to various other cases such as microseismic monitoring in the field of geothermal and shale gas/oil exploration, also CCS (Carbon Capture and Storage) development.

Enhanced Geothermal system assessment conducted to have a better understanding of characteristics of fracture caused by a fluid injection in the geothermal reservoir. Fluid injection may cause microseismic occur. These events allow us to map and characterize fractures in the geothermal system. Fractures play important role at the geothermal system due to its ability to increase permeability for fluid movement within the reservoir. In this study, we combined tomographic inversion method and fuzzy clustering to identify fracture characteristics at the EIF Geothermal Field. Tomography helped in delineating fluid-filled fractures with high permeability area which shown by lower velocity Vs anomaly than Vp and higher Vp/Vs ratio. Fuzzy clustering allowed us to map microseismic movement and estimate suitable locations for the future well injections or productions.

Development of geothermal production can be conducted in several ways, one of them analyses the fracture or crack and structure within the reservoir. Due to low permeability and porosity value within the reservoir in geothermal field. This crack or fracture provide porosity for fluid storage and permeability for fluid movement and play a major role in production from this kind of reservoir. Structure and polarization direction can be derived from anisotropy parameter and seismic velocity parameter in geothermal field. In this study, we used micro-earthquake data of 1,067 events that were recorded by the average of 15 stations during almost 1-year measurement. We used anisotropy parameter using 3-D shear-wave splitting (SWS) tomography method to represent the distribution of anisotropy medium around the geothermal field. Two parameters produced from the S-wave analysis, which is polarization direction and delay time between fast S-wave and slow S-wave. To determine SWS parameters, we used a rotation of horizontal seismogram including N-S component and E-W component. Furthermore, we used short-time fourier transform (STFT) to calculate lag time and time window based on wave periods. Two horizontal components have been rotated from azimuth 0^° to 180^° with an increment of 1^°. Cross-correlation coefficient used every azimuth of two horizontal components based on delay time with predetermined time window obtained by STFT. When cross-correlation coefficient is high, the corresponding value of delay time and azimuth are chosen as the polarization direction and delay time of SWS. Normalized time different divided by total ray length was used to determine the distribution of crack density. Through correlation of seismic velocity model, crack density, and 3-D anisotropy tomography, we can delineate a geothermal reservoir model. Our results show, high degree of anisotropy and crack density occur in the northern and eastern part of "PR" geothermal field for further development. The result had good correlation with high production of geothermal activities.

The joint inversion of geophysical data can reduce the ambiguity of model parameters. Joint Inversion of Magnetotelluric (MT) and Transient Electromagnetic (TEM) data was performed to get detailed information of subsurface structure. Whereas TEM data is sensitive to describe in the shallow structure, while the deeper structure is related to MT data. We derived the joint inversion scheme from the second order of Marquardt algorithm using singular value decomposition (SVD). The detailed analyses of the model parameters are performed by damping factors, V-matrix, damped error bounds and importances value. The joint models parameters with damping factor and importances value above 0.9 indicate that the associated eigen parameters are well-resolved.

Time Domain Electromagnetic (TDEM) method uses electromagnetic wave to detect resistivity or conductivity difference of lithology in the subsurface, measured in the time domain. TDEM method has been developed in decades. There are forward modeling and inversion programs have been made. The purpose of making the forward modeling programs is to calculate TDEM response so that data acquisition parameters can be chosen correctly. The inversion program is for synthesizing geological model from measured TDEM data. Several TDEM programs have been made, but the procedures require heavy and complex computation, which need high computer specification and lot of calculation time. Nowadays program that used less complex computation and faster calculation is needed to match field data acquisition productivity. To achieve faster and more accurate process, we use Born Approximation of the apparent conductivity for the forward modeling program and Levenberg-Marquardt algorithm for the inversion program. We use many circumstances in testing our programs, from one layer to multi layers by varying the resistivity or thickness of lithology and compared with a validated program, EMUPLUS. At the end of the test, inversion of real data is taken as confirmation that the program can be used to process real TDEM data. Inversion results of both synthetic and real TDEM data show pleasant results. These test results indicate that our program can be used as daily forward modeling program for determining data field acquisition parameters and do the inversion procedure for synthetic and real TDEM data.

Underground cavities or voids detection is essential especially when it comes to building construction. By knowing the presence of void lying underground, one could consider whether the subsidence is likely to be prevented or not. Ground penetrating radar is a high-frequency electromagnetic sounding technique that has been developed to investigate the shallow subsurface using the contrast of dielectric properties. This geophysical method is suitable to be used to detect and locate voids beneath the surface especially those that lie in shallow depth. This research focused on how GPR could be implemented as void detector using model simulation or forward modelling. The models applied in the forward modelling process are to be made as similar as the real condition in the case study location which took place in Tahura Japan Cave, Bandung, Indonesia. Forward modelling needs to be done so in the future, we might use the modelling results as the references in measuring real GPR data in the location. We used three models that we considered fairly representative to prove that GPR is capable of detecting and locating voids underneath the ground. This research resulted in the different amplitude region around the considerably homogeneous region. The different amplitude region is characterized having an arc shape and is considered to be air which is known as the key component of voids.

In this paper, we simulated frequency responses of subsurface due to incident SH wave by using discrete wave number method (DWM: Aki-Larner Method). It is useful in constructing the models of the non-uniform subsurface. We estimated subsurface profile based on the resonance frequency of HVSR method comparing with frequency responses obtained from SH waves incident by DWM. The only information from HVSR is the resonance-frequency of the ground. Although what obtained from the numerical analysis by DWM is a response function, it coincides with the response of the surface ground if the input motion is a white noise and the ground behaviour is a liner. In this case, the peak of response function can be considered to be a resonance frequency of the ground. Therefore, we here compared the peak frequencies of HVSR curve and response functions. To estimate the resonance frequency of ground by HVSR, the single observations of microtremor at 161 sites were carried out by using the three-component accelerometer with a data logger, GPL-6A3P, in the study area of Ende Regency that is one of five regencies in East Nusa Tenggara Province on the island of Flores, Indonesia. The results show that site response in Ende area varies the resonance frequencies span 0.7-1.4 Hz. For DWM, we assume simple two layered media with irregular boundary aimed at making a simple ground profile of the study area. The two-layered model is composed of a 'soft basin' on engineering bedrock. We varied the depth and the shear wave velocity of the basin and calculated response functions by using DWM. Then we selected the best fit parameters by comparing the resonance frequency of H/V result. Finally, we proposed a possible non-uniform ground model in the study area.

A 3D soil profiling system for effective design of countermeasures for a damaged or potentially damaged river levee is developed. This system consists of a 3D integrated seismic and electric measurement tool and a 3D visualization system of its soil properties such as hydraulic and mechanical properties estimated from the geophysical data. For a quick survey, the 3D measurement tool is a sensor belt with both geophones and electrodes to be able to measure seismic and electric data simultaneously. S-wave velocity and resistivity data acquired by this tool are converted to soil properties such as hydraulic and mechanical properties and support a countermeasure design of levee. In this study, we introduce the experimental result of the 3D soil profiling by using the integrated seismic and electric measurement tool in the field.

Particle Swarm Optimization (PSO) is one of nature-inspired optimization algorithms that adopts swarm (insects, school of fish, flock of birds etc.) behaviour in search for food or common target in a collaborative manner. The particles (or agents) in the swarm learn from their neighbours as well as themselves regarding the promising area in the search space. The information is then used to update their position in order to reach the target. The search algorithm of a particle is dictated by the best position of that particle during the process (individual learning term) and the best particle in its surroundings (social learning term) at a particular iteration. In terms of optimization, the particles are models defined by their parameters, while the promising area in the model space is characterized by a low misfit associated with optimum models. Being a global search approach, PSO is suitable for nonlinear inverse problem resolution. The algorithm was applied to a simple minimization problem for illustration purpose. The application of PSO in geophysical inverse problem is demonstrated by inversion of synthetic magnetotelluric (MT) data associated with simple 1D models with satisfactory results in terms of model recovery as well as data misfit.

Cubadak area in Pasaman Regency, West Sumatra, Indonesia is one of many potential geothermal areas in Indonesia. This paper deals with resistivity structure beneath Cubadak area obtained from magnetotelluric data. The subsurface resistivity image of Cubadak reveals the components of Cubadak geothermal system clearly such as the altered clay having very low resistivity values, the possible reservoir zone having intermediate resistivity values underlying the altered clay as well as the indication of geological structures controlling the system. The top boundaries of the reservoir vary from elevation of 250 m to -500 m above sea level.

Controlled-Source Audio-frequency Magnetotellurics (CSAMT) is a frequency domain sounding technique employing typically a grounded electric dipole as the primary electromagnetic (EM) source to infer the subsurface resistivity distribution. The use of an artificial source provides coherent signals with higher signal-to-noise ratio and overcomes the problems with randomness and fluctuation of the natural EM fields used in MT. However, being an extension of MT, the CSAMT data still uses apparent resistivity and phase for data representation. The finite transmitter-receiver distance in CSAMT leads to a somewhat "distorted" response of the subsurface compared to MT data. We propose a simple technique to present CSAMT data as an apparent resistivity pseudo-section with more meaningful information for qualitative interpretation. Tests with synthetic and field CSAMT data showed that the simple technique is valid only for sounding curves exhibiting a transition from high – low – high resistivity (i.e. H-type) prevailing in data from a geothermal prospect. For quantitative interpretation, we recommend the use of the full-solution of CSAMT modelling since our technique is not valid for more general cases.

Indonesia has 40% of the world's potential geothermal resources with estimated capacity of 28,910 MW. Generally, the characteristic of the geothermal system in Indonesia is liquid-dominated systems, which driven by volcanic activities. In geothermal exploration, electromagnetic methods are used to map structures that could host potential reservoirs and source rocks. We want to know the responses of a geothermal system using synthetic data of Audio-magnetotelluric (AMT) and Magnetotelluric (MT). Due to frequency range, AMT and MT data can resolve the shallow and deeper structure, respectively. 1-D models have been performed using AMT and MT data. The results indicate that AMT and MT data give detailed conductivity distribution of geothermal structure.

East Flores is part of Nusa Tenggara island belongs to volcanic arc zone, hence the active volcanoes surround the area about 60 × 50 square km. It is located at latitude south 8^° 30', and longitude east 122^° 45'. Geologically, the rock is mostly of volcanic material since Miocene age. The Intriguing question is where the volcanic feeder, pyroclastic, and how it vanish in subsurface. The magnetic data acquisitions were executed on land for 500 meter interval and denser through the bay surrounded by volcanoes. The combine reduction to pole and forward modelling is apply for serve interpretation using forward modelling technique. The two interpretation sections, show the body of magmatic may present at depth about 2 to 3 km. The observation show no significant decreasing or loosening of magnetic anomaly although near the active volcano. We suggest the thermal anomaly is just disturbing magnetic data in near surface but not in the depth one. Meanwhile the reduction to pole's section could distinguish the two group of rock. In assuming the layer is flat. The inferred peak of magmatic body near the existing volcano; and the active demagnetization associated through evidence of hot spring and inferred fault structure.

Mt. Pandan is one of the volcano that state as dormant volcano. On the other hand, Smyth et al. (2008) defined that Mt. Pandan is an active volcano. This volcano is apart a volcanic chain in Java island which is trending east-west along the island. This volcanic chain known as present day volcanic arc. Mt. Wilis is located in the south and it relatively much bigger compare to Mt. Pandan. There were earthquakes activity experienced in the surrounding Mt. Pandan area in the past several years. This event is interesting, because Mt. Pandan is not classify as the active volcano according to the list of volcanoes in Indonesia. On the otherhand Smyth et. al. (2008) mentioned that G. Pandan as modern volcanic which is located in Kendeng Zone of East Java. Gravity measurement around Mt. Pandan area was done in order to understand subsurface structure of Mt. Pandan. Gravity interpretation results shows that there is a low density structure beneath Mt. Pandan. It could be interpreted as existing of magma body below the surface. Some indication of submagmatic activities were found as hot spring and warm ground. Therefore it could be concluded that there is a possibility of magmatic activity below the Mt. Pandan.

Many geophysical methods at various scales have been applied to understand the internal structure beneath Merapi volcano and its magmatic process. As part of the DOMERAPI project, a seismic experiment was conducted from October 2013 to mid April 2015 in order to determine the deep magma source beneath the volcano through seismic travel-time tomography. The earthquake events were identified and picked manually and carefully to determine the hypocenters. They were then relocated to get precise hypocenter locations before running the seismic tomographic imaging. The data from the BMKG network from the same period of time as mentioned above were also incorporated to minimize azimuthal gap, because the majority of events occurred outside the DOMERAPI network. The checkerboard resolution test result depicts that the area around the network can be well resolved. Compared to previous studies, our result shows a higher resolution at shallow depths, i.e., less than 35 km and a low velocity material imaged to ascend diagonally from the deeper area.

Mt. Merapi is one of the most active and hazardous volcanoes not only in Indonesia but also in the world. Having a height of about 2968 meter above sea level it contains an active lava dome, which regularly produces pyroclastic flows and is categorized as a stratovolcano. It erupts on average every 2-5 years, in which thousands of people live on the flanks of the volcano. The last eruption occurred on 26 October 2010 and after the large eruption in 2010 the characteristic of Mt. Merapi was changed. Due to its uniqueness, Merapi is closely monitored by the many geoscientists, particularly through volcanological surveys.This study is concerned with the application of ambient noise tomography (ANT) to create Rayleigh wave group velocity maps around Mt. Merapi. The continuous data set is taken from the DOMERAPI project, which consists of temporary seismic array of 40 broadband seismometers for approximately ten months. The resulting group velocity maps of Rayleigh wave show an anomaly pattern that agrees with previous geological and geophysical study results. A pronounced, positive anomaly is clearly imaged with direction about 152^°N beneath Mt. Merapi through to Mt. Merbabu. In addition, negative anomalies are observed in its east and west flanks.

Continuous development in the area of Jatinangor campus is becoming one of the problems threatening the groundwater supply. To support the availability of groundwater in the area of Jatinangor campus, a geophysical investigation with the geo-electric method is conducted to determine the condition of the subsurface based on the value of resistivity of rock. Based on Bandung's regional geological map of Silitonga in 2003, rocks in the Jatinangor area consist of volcanic rock breccia, tuffs, and lapilli that makes it possible to contain the groundwater. 32 stations of 1-Dimensional (DC sounding) geo-electric measurement using Schlumberger configuration are performed in Jatinangor area. We integrated the results of measurement with geological and hydrogeological observation information with the aim of producing images of subsurface rocks and distribution models. Based on the model, the type of aquifer contained in the study area as well as its potential reserve can be determined. This research aims to know the potential groundwater zone region to support the availability of groundwater for Jatinangor education region. Furthermore, the results are expected to provide insights in implementing conservation strategies for Jatinangor educational area, Sumedang Regency.

The research was conducted using 2-D resistivity in verifying Paleozoic aquifer. Since most geologic materials behave as electrical insulators, surface measurements of earth resistivity are controlled by the electrolytic ability of interstitial water. The subsurface distribution of water is controlled by the porosity of the formations. The study area is at Bukit Chondong, Beseri, Perlis. Bukit Chondong is made of sedimentary rock which mostly is sandstone. Bukit Chondong is from uppermost of the Kubang Pasu Formation that represented by a thick unit of grey mudstone interbedded with sandstone. The Kubang Pasu Formation was influenced by shallow marine during the early age. Paleocurrent and fossils traces were found on the mudstone at the study area. The area is suspected to be a Paleozoic aquifer because the sandstone can be a productive aquifer with diffuse flow. The water movement in sandstone is through the fractures and joints. Most of the water stores and transmits in sandstone. The interbedded sandstone and mudstone is one of the aquifer characteristic. Sandstone and mudstone are water-bearing rocks and low-permeable rocks respectively. The data was processed according to the geological information of the study area since there was an outcrop. The study area have low resistivity value which both sandstone and mudstone give less than 800 Ohm-m due to the water content (Sulphide and clay).

TDEM (Time Domain Electromagnetic) method is a sounding geophysical method using electromagnetic wave generated by the electrical current source to image cross section of earth's subsurface. TDEM using galvanic source (grounded wire) is one of TDEM acquisition technique which has flexible properties for the complex topography of measurement area. Three-dimensional forward and inversion modeling technique of TDEM with galvanic source still develops until now. Three-dimensional modeling is required because three-dimentional structure can influence TDEM signal which has a dimension of z-axis direction only. In this paper, We have been developing a 3D forward modeling program applying finite difference time domain method for 3D subsurface models. We can assess a distribution of TDEM synthetic data affected by 3D model. Using this 3D TDEM modeling program synthetic data has been generated as the function of transmitter and receiver position in 3D model space. Furthermore, this program can be used to simulate a conductivity change of reservoir model as consideration of reservoir monitoring implementation.

In hydrology context, sediment can be interpreted as inorganic and organic material that is transported by, suspended in, or deposited by streams. It is important to know the function of soil, stream discharge, land-cover features, weather conditions and land-use activities. Sediment load carried by streams and rivers can be composed either of fine materials, mostly silts, and clays, or coarse materials such as sand. One product of sediment is dissolved load consists of indistinct material in solution moving downstream. It is produced by chemical weathering processes and does not move out of the water. To investigate the dissolved sediment, we have applied the floating of Time Domain Electromagnetic (TDEM) method. The acquisition of TDEM data has been performed use tires and small ship as innovation measurements. The calculated data model using Occam and Marquardt Algorithms. The responses of data show the sedimentation has less resistive compare the surrounding structures. This innovation is very helpful to know the environmental condition, especially in the water.

Currently available worldwide gravity anomaly data provides a high-resolution (2'×2') of Complete Spherical Bouguer Anomaly (CSBA) based on the available information of the Earth gravity field from surface and satellite measurements. The data has not only been provided and processed thoroughly but it also has been claimed to be appropriate for various geophysical applications. Therefore, the analysis of gravity anomaly is becoming increasingly significant for the earth sciences as a whole and assisting both shallow and deep geological problems. Earth gravity anomaly has to be analyzed carefully as it has very complex data due to anomaly mixing of the density masses spread over the Earth horizontally and vertically. The bigger the spatial coverage of data (e.g. global scale data), the more severe the data from anomaly mixing due to various wavelength. BEMD is an empirical method supposedly suitable with highly oscillation-mixing data. It can effectively isolate each local anomaly in details and is analogized as successively reverse moving average with local windowing. BEMD is designed to reduce multi-component, non-linear gravity field data to a series of single local anomaly contributions. Anomaly from a single body was assumed as a mono-component signal. The main advantage of BEMD processing techniques is to present the subtle details in the data which are not clearly identified in anomaly maps, without specifying any prior information about the nature of the source bodies. As the result, we have identified regional anomalies due to the drift of continental and oceanic masses considered as crust-regional anomaly (CRA). We remove the CRA from the CBA to provide surface-residual anomaly (SRA) where shallow geologic bodies reveal. Meanwhile, the CRA itself can be used as reference to reduce this high magnitude anomaly from any measurement data to exhibit only shallow body anomaly. Further analysis can be carried out to build a general understanding of the details and parameters of the shallower or deeper causative body distributions.

The lack of computational tools, i.e. software, often hinders the proper teaching and application of geophysical data processing in academic institutions in Indonesia. Although there are academic licensing options for commercial software, such options are still way beyond the financial capability of some academic institutions. Academic community members (both lecturers and students) are supposed to be creative and resourceful to overcome such situation. Therefore, capability for writing computer programs or codes is a necessity. However, there are also many computer programs and even software that are freely available on the internet. Generally, the utility of the freely distributed software is limited for demonstration only or for visualizing and exchanging data. The paper discusses the utility of Geosoft's Oasis Montaj Viewer along with USGS GX programs that are available for free. Useful gravity and magnetic advanced data processing (i.e. gradient calculation, spectral analysis etc.) can be performed "correctly" without any approximation that sometimes leads to dubious results and interpretation.

Indonesia is conducting research on CO2 sequestration and monitoring in Gundih area. Geophysical methods are applied in the study area as monitoring technologies of CO2 storage in the subsurface. In this paper, we will describe data quality and baseline geophysical survey (2014 and 2016) as part of time-lapse microgravity (TLM) data acquisition. The same set of two relative gravimeters (Scintrex CG5) were used in 2014 and 2016 gravity data acquisition to provide TLM map. TLM can be useful to monitor the mass increase and decrease due to significant activities in the reservoir, but for this project TLM signal (caused by the CO2 injection in Gundih's reservoir) estimated very small. Considering current project status, no injection yet, the data acquisition in 2014 and 2016 will be analysed to help us understand non-target anomalies in near surface. Preliminary analysis of gravity differences between 2014 and 2016 shows correlation pattern of time-lapse microgravity with land use in the study area. Rice fields and villages in the Western part of the study area correlate with negative TLM anomalies and forest area in the Eastern part of the study area correlate with positive TLM anomalies.

While a large number of reservoirs have been explored using P-waves seismic data, P-wave seismic survey ceases to provide adequate result in seismically and geologically challenging areas, like gas cloud, shallow drilling hazards, strong multiples, highly fractured, anisotropy. Most of these reservoir problems can be addressed using P and PS seismic data combination. Multicomponent seismic survey records both P-wave and S-wave unlike conventional survey that only records compressional P-wave. Under certain conditions, conventional energy source can be used to record P and PS data using the fact that compressional wave energy partly converts into shear waves at the reflector. Shear component can be recorded using down going P-wave and upcoming S-wave by placing a horizontal component geophone on the ocean floor. A synthetic model is created based on real data to analyze the effect of gas cloud existence to PP and PS wave reflections which has a similar characteristic to Sub-Volcanic imaging. The challenge within the multicomponent seismic is the different travel time between P-wave and S-wave, therefore the converted-wave seismic data should be processed with different approach. This research will provide a method to determine an optimum converted point known as Common Conversion Point (CCP) that can solve the Asymmetrical Conversion Point of PS data. The value of γ (Vp/Vs) is essential to estimate the right CCP that will be used in converted-wave seismic processing. This research will also continue to the advanced processing method of converted-wave seismic by applying Joint Inversion to PP&PS seismic. Joint Inversion is a simultaneous model-based inversion that estimates the P&S-wave impedance which are consistent with the PP&PS amplitude data. The result reveals a more complex structure mirrored in PS data below the gas cloud area. Through estimated γ section resulted from Joint Inversion, we receive a better imaging improvement below gas cloud area tribute to the converted-wave seismic as additional constrain.

The main objective in inverting seismic data is to estimate layer characteristics instead of layer boundaries. It is about getting as much as layer boundaries as seismically permitted with correct position and amplitude. However, the number of layers identified by seismic inversion methods is relatively in small number. Meaning, inversion methods tend to thicken the layers due to band-limited of seismic data and wavelet inaccuracy. It is well-accepted that sparse-layer inversion has the ability in recovering full RC series that are permittable seismically yet it tends to produce blocky impedance. Sparse-layer inversion is also computationally extensive because of large amount of competing relectivity model. In this paper, we test sparse optimisation inversion performance using gaussian dense-layer simulation instead of sparse-layer model.

The development of a user-friendly Common Reflection Surface (CRS) Stack software that has been built by implementing Graphical User Interface (GUI) is described in this paper. The original CRS-Stack software developed by WIT Consortium is compiled in the unix/linux environment, which is not a user-friendly software, so that a user must write the commands and parameters manually in a script file. Due to this limitation, the CRS-Stack become a non popular method, although applying this method is actually a promising way in order to obtain better seismic sections, which have better reflector continuity and S/N ratio. After obtaining successful results that have been tested by using several seismic data belong to oil companies in Indonesia, it comes to an idea to develop a user-friendly software in our own laboratory. Graphical User Interface (GUI) is a type of user interface that allows people to interact with computer programs in a better way. Rather than typing commands and module parameters, GUI allows the users to use computer programs in much simple and easy. Thus, GUI can transform the text-based interface into graphical icons and visual indicators. The use of complicated seismic unix shell script can be avoided. The Java Swing GUI library is used to develop this CRS-Stack GUI. Every shell script that represents each seismic process is invoked from Java environment. Besides developing interactive GUI to perform CRS-Stack processing, this CRS-Stack GUI is design to help geophysicists to manage a project with complex seismic processing procedures. The CRS-Stack GUI software is composed by input directory, operators, and output directory, which are defined as a seismic data processing workflow. The CRS-Stack processing workflow involves four steps; i.e. automatic CMP stack, initial CRS-Stack, optimized CRS-Stack, and CRS-Stack Supergather. Those operations are visualized in an informative flowchart with self explanatory system to guide the user inputting the parameter values for each operation. The knowledge of CRS-Stack processing procedure is still preserved in the software, which is easy and efficient to be learned. The software will still be developed in the future. Any new innovative seismic processing workflow will also be added into this GUI software.

Partial CRS-Stack method is proved as an alternative method that can produce excellent subsurface image, especially if this method is applied to a seismic data that is acquired from complex subsurface structure areas. The application of this method will give a new hope in determining subsurface structures in a better way, especially if it is implemented to seismic data obtained from Indonesian region, which is dominated by complex geological structures. The Partial CRS-stack method is tested by using a seismic dataset, which is acquired from eastern part of Indonesia. Here, the continuity of reflectors cannot be seen clearly. To prove the ability of Partial CRS-stack method, its result will be compared with the result obtained from the conventional sequences. The stacked section resulted from Partial CRS-stack is much better than the result of conventional one. This could be understood, since the Partial CRS-stack method uses the information of reflectors along fresnel zone, instead conventional method that only uses information in a CDP. During its processing sequence, CRS kinematic wavefield attributes, e.g. emergence angle (α), radius curvature of normal ray (R_N) and radius curvature of normal incident point ray (R_NIP) must be determined previously, which indicates the location and behaviour of reflectors. As a conclusion, the Partial CRS-stack method is proved as a good alternative method to give better seismic sections. Because of this, the interpretation of unclear events that are seen in the conventional stack section can be avoided.

West Java, part of the Sunda Arc, has relatively high seismicity due to subduction activity and faulting. The first step of tomography study in order to infer the geometry of the structure beneath West Java is to conduct precise earthquake hypocenter determination. In this study, we used earthquake waveform data taken from the regional Meteorological, Climatological, Geophysical Agency (BMKG) network from South Sumatra to central Java. We have repicked P and S arrival times from about 800 events in the period from April 2009 to December 2015. We selected the events which have azimuthal gap < 210^° and phase more than 8. The non-linear method employed in this study used the oct-tree sampling algorithm from NonLinLoc program to determine the earthquake hypocenters. The hypocenter location results give better clustering earthquakes which are correlated well with geological structure in the study region. We also compared our results with BMKG catalog data and found that the average hypocenter location difference is about 12 km in latitude direction, 9.5 km in longitude direction, and the average focal depth difference is about 19.5 km. For future studies, we will conduct tomographic imaging to invert 3-D seismic velocity structure beneath the western part of Java.

The earthquake swarm events sequence occurred in west Halmahera, north Molucca, Indonesia for the period of October 2015 to February 2016 as reported by Meteorological, Climatological, and Geophysical Agency (BMKG) of Indonesia. There were tenths swarm events with Magnitude larger than four in the region during the period. In this study, we used the earthquake catalog data compiled by BMKG to improve the location of swarms event in west Halmahera, north Molucca, Indonesia. We relocated 86 swarm events by applying teleseismic double-difference method and 3D seismic velocity model. The focus depth of swarm events mainly concentrated at depth of 5 to 12 km at south-east of Jailolo volcano. Our preliminary interpretation the earthquake swarms may be related to the stress change around the deep magma region of the volcano.

The Sunda-Banda Arc transition zone is an active region characterized by a change in tectonic regime from subduction of Indo-Australia oceanic lithosphere along the eastern part of Sunda Arc to collision of the Australian continental crust with islands arc in the western part of the Banda Arc. This complicated tectonic setting causes this area is an ideal place to study the crustal deformation along the plate boundary. The density contrast between the Australian continental crust and Indo-Australia oceanic crust in the transition zone may cause large stresses around the boundary between them. These plate boundary forces may control the distribution pattern of the deformation in the subduction to collision transition zone. The geometry of this deformation can be investigated using shear wave splitting (seismic anisotropy) study. We conduct shear wave splitting measurements from local earthquakes recorded at 17 broadband seismic stations around the Sunda-Banda arc transition zone. The 2D delay time tomography is then applied to determine the first order approximation of lateral varying anisotropic layers due to the local effect of geological structures. We observe strong anisotropy regions which coincide with the geological features as possible causes of anisotropy in the Sunda-Banda Arc transition zone. For instance, the high anisotropy zone found in Timor Island can be related to the alignment of metamorphic and igneous rocks, whereas the high anisotropy area around Sumba Island might correspond to the interaction of Sumba basement with the Australian margin increasing the frictional strength at the plate boundary.

We have analyzed the earthquakes data in West Sumatra province to determine peak ground acceleration value. The peak ground acceleration is a parameter that describes the strength of the tremor that ever happened. This paper aims to compare the value of the peak ground acceleration by considering the b-value before and after the Padang earthquake 2009. This research was carried out in stages, starting by taking the earthquake data in West Sumatra province with boundary coordinates 0.923° LU - 2.811° LS and 97.075° - 102.261° BT, before and after the 2009 Padang earthquake with a magnitude ≥ 3 and depth of ≤ 300 km, calculation of the b-value, and ended by creating peak ground acceleration map based on Mc. Guirre empirical formula with Excel and Surfer software.

Based on earthquake data from 2002 until before Padang earthquake 2009, the b-value is 0.874 while the b-value after the Padang earthquake in 2009 to 2016 is 0.891. Considering b value, it can be known that peak ground acceleration before and after the 2009 Padang earthquake might be different. Based on the seismic data before 2009, the peak ground acceleration value of West Sumatra province is ranged from 7,002 to 308.875 gal. This value will be compared by the value of the peak ground acceleration after the Padang earthquake in 2009 which ranged from 7,946 to 372,736 gal.

Sulawesi area is located in complex tectonic pattern. High seismicity activity in the middle of Sulawesi is related to Palu Koro fault (PKF). In this study, we determined precise hypocenter around PKF by applying double-difference method. We attempt to investigate of the seismicity rate, geometry of the fault and distribution of focus depth around PKF. We first re-pick P-and S-wave arrival time of the PKF events to determine the initial hypocenter location using Hypoellipse method through updated 1-D seismic velocity. Later on, we relocated the earthquake event using double-difference method. Our preliminary results show the distribution of relocated events are located around PKF and have smaller residual time than the initial location. We will enhance the hypocenter location through updating of arrival time by applying waveform cross correlation method as input for double-difference relocation.

On February 6, 2016, an eruption occurred on the Northern Sulawesi arm, particularly Soputan volcano. One day earlier, Lokon volcano located close to Soputan volcano was decreased its status from standby to alert level by the Center for Volcanology and Geological Hazard Mitigation (CVGHM). The different reactions of two volcanoes proposed the question why the increment activity just happened in Soputan volcano. This uniqueness made us to suggest that static stress of earthquake may control the magmatic systems. We investigate here the earthquake-volcanism interaction through static stress changes by using Coulomb failure stress associated with an earthquake occurred in the Northern Molluca Sea on 25 November 2015. We slice the same dip for the each region in vertical cross sections. Therefore, the Coulomb failure stress pattern can be investigated beneath the study area. Our results suggest that Coulomb failure stress was increased by 0.3 × 10^-3 to 0.4 × 10^-3 bar below the Soputan's region. Lokon's region, the stress was reduced by -0.1 × 10^-3 to -0.4 × 10^-3 bar. The positive change may perturb magma overpressure leading to eruption and promoted volcanic earthquakes. The situation was very different that Lokon volcano ran into reduction activity and volcanic earthquakes were discourage due to stress shadow. We show that the difference volcanic response were likely controlled by static stress of the earthquake.