Table of contents

The Southeast Asian Conference on Geophysics (SEACG) is a biannual event held by the Geophysical Engineering Department, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung (ITB), Indonesia. The SEACG has been successfully conducted since 2016, and several selected papers have been published in the IOP Conference Series: Earth and Environmental Science. The first (2016) and second (2018) conferences were held offline in Bali, Indonesia, while the third conference (2020) was held virtually due to the Covid19 pandemic. Along with the end of the Covid19 pandemic, the current event (2022) is being run as a hybrid conference (physical and virtual), live from Bandung, Indonesia.

The conference theme of the SEACG 2022 is "Great Challenges and Opportunities of Geophysics Today and Future." The program lasts two days, from August 9, 2022, to August 10, 2022, and is sponsored by the Institute of Research and Community Services, ITB. There are 11 invited international speakers (30-minute duration) and 88 contributed speakers (20 min duration) who presented their ideas. With five panel rooms, 35 contributed speakers delivered offline presentations and 53 virtually via Zoom. The speakers, both invited and contributed, presented and introduced new geophysical insights and techniques.

The panel discussion featured intriguing topics and invited speakers from various institutions, such as Institut Teknologi Bandung – Indonesia (Dr.rer.nat. R. Mohammad Rachmat Sule, Dr. Tedi Yudistira, Prof. Sri Widiyantoro, Prof. Wahyu Srigutomo, and Prof. Wawan Gunawan Abdul Kadir), CSIRO – Australia (Dr. Erdinc Saygin), Australian National University – Australia (Prof. Phil Cummins), University of Tokyo – Japan (Prof. Takeshi Tsuji), JGI, Inc. – Japan (Moeto Fujisawa, M.Sc.), Ocean University of China – China (Dr. Zhijun Du), and Institut de Physique du Globe de Paris – France (Dr. Jean-Philippe Metaxian). The event was opened by Dr. Fatkhan (the Head of the Geophysical Engineering Master and Doctorate Degree Program, ITB) and closed by Dr. Warsa (the Head of the Geophysical Engineering Bachelor Degree Program, ITB).

The SEACG 2022 provided a platform for academics, professionals, and students to discuss and promote scientific results related to recent advancements in geophysical methods and related sciences. The conference covered various session topics, such as Fault and Deformation Study, Passive Seismic, Environmental Geophysics, Geophysical Approaches in Hydrocarbon, Geophysical Approaches in Geothermal, Advance Geophysics, Vulcanology, Tomography, Seismic Hazards, Geomagnetic, and Seismology.

We would thank the organization's team members, the reviewers, and the faculty staff. They have worked very hard to make this event possible. We wish all attendees of SEACG 2022 have an exciting experience and enjoy the moment in this scientific forum.

List of Organizing Committee, Documentation are available in this pdf.

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

• Type of peer review: Single Anonymous

• Conference submission management system: Morressier

• Number of submissions received: 53

• Number of submissions sent for review: 53

• Number of submissions accepted: 49

• Acceptance Rate (Submissions Accepted / Submissions Received × 100): 92.5

• Average number of reviews per paper: 1.03

• Total number of reviewers involved: 13

• Contact person for queries:

Name: Indra Gunawan

Email: indra.gunawan@itb.ac.id

Affiliation: Institut Teknologi Bandung - Geophysical Engineering

The Matano fault in central Sulawesi is one of the major strike-slip faults that accommodate the rapid left-lateral slip between the Pacific and Australian plates. The Matano fault has a high seismic potential of producing large (M_w ≥7) earthquakes. However, the Matano fault was less studied, unlike the Palu-Koro fault. This paper presents preliminary results of our active fault investigation in the eastern Matano fault which may help in understanding the neotectonics and earthquake hazard in central Sulawesi. The late Quaternary deformation of the eastern Matano fault is evidenced by deformed young geomorphic surfaces. The fault shows predominantly left-lateral motion and has steeply dipping fault plane. The eastern portion of the Matano fault may form a seismic gap that potentially host the next surface-rupturing earthquake.

Renun Segment is located in the center of the Sumatran Fault, parallel to the Famous Toba Lake Volcano. The fault cuts the thick, and vast Young Toba Tuffs (YTT) deposited ∼74,000 years ago during the supervolcano eruptions. It shows a series of noticeable dextral strike-slip offsets of the river valleys that deeply incised the tuffs. Our study will determine the geological slip rate in this location by measuring river-valley offsets in the Dolok Sanggul area using UAV photogrammetry and DEMNAS images. Detail morphology shows a fault lineament, monocline, and anticline structure. Three rivers about a hundred meters deep cross perpendicular to the fault line and have 585±83 meters dextral offset. This amount is only half of the other dextral offsets on the northern and southern parts of the site. Hence, the slip rate is also a half slower, approximately 7±1 mm/yr. This indicates that the other half of the slip budget is accommodated by the Samosir Fault in the center of Toba Lake.

Yogyakarta has experienced two devastating earthquake disasters: May 26, 2006, Mw6.4, and the penultimate event, June 10, 1867 Mw7.7. The active fault that is thought to be responsible for the two earthquake events is the Opak Fault. However, the Opak Fault has still not been thoroughly well mapped yet. The lack of a high-resolution image, dense vegetation cover, high sediment flux from the Merapi volcano, and human activities eroding the original landscape challenge studying the on-land fault in this area. Our recent study, however, indicates that the Opak Fault is not the only active fault that can cause a major disaster, but another fault strand exists in the area. We mapped the fault using the best available data of DEMNAS assisted by more detailed DEM and Orthophoto, developed from drone survey, and we also conducted Earth Resistivity Tomography (ERT) survey. We found that inferred new active fault is oriented East-West across the center of the high-populated city. The fault runs parallel and close to the famous Mataram channel (Selokan Mataram). The fault is likely continue the previously recognized Dengkeng Fault, east of the Opak fault. The fault strand is indicated by morphological lineaments and a few steam offsets. Our ERT 2D sections have revealed the fault zone in several locations along the inferred fault line. The fault line cut the Young Quaternary rocks; hence, it is an active fault. Further studies are needed to get further details of this newly recognized active fault, such as conducting paleoseismological studies, detailed seismological survey, geodetic GPS measurement, and acquiring a high-resolution image acquisition survey (LiDAR – Light Detection and Ranging Survey).

The Ambon fault in the northern Banda Arc has capability of generating M_w 6.9 earthquake. The Ambon fault poses a significant seismic hazard to Ambon Island because the fault is located near populous areas, the Ambon City. Recent seismicity in Ambon Island and surrounding areas indicates that this region is actively deforming. Ambon Island has experienced many damaging earthquakes since the 17^th century. However, the potential seismic hazard on this island remains enigmatic due to the lack of detailed geological information, such as fault traces, slip rate, and paleoseismic history. This study reports the preliminary results of tectonic geomorphic investigations and ground-penetrating radar (GPR) surveys on the Ambon fault. Tectonic geomorphic features, such as fault scarps, warped surfaces, and sag ponds indicate the late Quaternary activity of the Ambon fault. The Ambon fault predominantly shows a normal sense of motion with a dip of ~60-70°. The Ambon fault is related to the extensional tectonics in the Banda Sea.

Land subsidence has been historically detected and observed using the Global Positioning System (GPS) observations since the year 2000. At present, the Interferometric Synthetic Aperture Radar (InSAR) method is used to monitor the ongoing subsidence in the Bandung Basin. Due to its significant subsidence rate, reaching up to -20 cm/year, much evidence of its impact has been found in this area, e.g., damaged buildings. This study aims to develop a land subsidence fragility curve for damaged buildings, which is very beneficial for estimating economic losses and developing a risk map of land subsidence. The study area will be focused on Bandung District Area. Field surveys are carried out in areas that experience large land subsidence. More than 200 buildings are surveyed to estimate the damage to buildings due to land subsidence. Damage classification is divided into four categories: heavy, medium, low, and no subsidence. The classification is based on subsidence slope and cracks in the building. Survey results showed that damage occurred in all these categories. The modeling of the fragility curve shows the tendency of the increasing subsidence slope to cause more severe damage. However, this study only shows the preliminary result of a land subsidence fragility curve in the Bandung district and will be further investigated for optimal results.

There are various considerations in determining whether a field is said to have geothermal potential or not. One of them is the appearance of shallow faults in the area. This shallow fault can function as a permeable layer that is used as a fluid flow path in the geothermal system. Due to the emergence of manifestations around Mount Pandan in the Gondang area, Bojonegoro, seismic refraction measurements are also needed that can support and validate the geothermal potential in the area with the hope of shallow faults that are visible through the interpretation of seismic wave propagation velocity. This measurement produces an anomaly that is thought to be a shallow fault on the track that passes through the main fault, namely on tracks 1, 2, and 5, not far from the manifestation of the Banyukuning hot spring. This is also reinforced by direct observation of the surface conditions as a result of the appearance of shallow faults.

The gravity method has been widely used in tectonic studies and the determination of geological structures. Besides land surveys, gravity data can also be measured by using satellites. However, the gravity data obtained from the satellite is usually not as good as the land survey. For example, the satellite data provided by Topex has a resolution of 1-minute grids, while the land survey could have a higher resolution. It means the gravity data obtained from the satellite cannot be as detailed as the land survey. To understand the relationship between both data, we calculate the correlation on the CBA, regional, and residual map. We also compared the maps qualitatively with geological data. During our investigation in the Timor Leste area, it was found that the correlation value between the CBA, regional, and residual from both data (land survey and satellite) is 0.703, 0.722, and 0.015 sequentially. The CBA and regional of both gravity data have the best agreement, but the residual nearly doesn't have any correlation. This result is because the satellite data has 1-minute grids in resolution, which means the spacing between the gravity data is roughly about 1800 m. With that spacing, the full wavelength that can be observed is more than 3600 m, so anomalies in lower wavelengths usually associated with shallow depths are not good enough to be appropriately measured. Vice versa, the longer wavelengths will be sufficiently provided by satellite. The long-wavelength of gravity data has considerable potential to be used in investigating regional anomalies, such as basement and general geologic mapping. Our results also show that the regional gravity anomaly has high compatibility with geological data.

Landslide is a natural disaster which often occurs in Indonesia. Based on National Disaster Management Agency (BNPB), there were 1,321 landslide incidents which occurred in 2021. Labuan Bulan Hill located on high susceptibility landslide seen from Landslide Susceptibility Zone of Brebes Regency, furthermore, soil tensile cracks presence with 5 - 50 cm width and 15 - 125 cm height at upper slope. In this study, the identification of subsurface lithologies and potential slip plane was carried out using geoelectric survey method with Wenner – Schlumberger configuration. The Wenner – Schlumberger configuration has deeper penetration than other geoelectric survey configurations. Geoelectric surveys are carried out on two lines with 240 m length and 5 m electrode space. Geoelectric line is made parallel and perpendicular with slope direction to estimate subsurface conditions easier with the help of tensile cracks presence in the surface. Results of measurements identified that the upper layer consists of poorly graded silty sand with 285 Ωm – 1700 Ωm resistivity, the second layer is a moderate - highly weathered volcanic breccia with 129 Ωm – 285 Ωm resistivity, and the third layer is fresh – slightly weathered volcanic breccia with 285 Ωm – 1388 Ωm resistivity. A fresh – slightly weathered volcanic breccia layer was identified as potential slip plane with 20 – 30 m depth.

The landslide occurred in Sumampir of Purbalingga Regency has reached 120 m in length and 50 m in width. This landslide is suspected to be a retrogressive landslide, which was manned by a landslide associated with the cliffs of the Brangkal River. This landslide is interpreted as progressive development of a landslide associated with Brangkal river bank failures, which continues to enlarge to the dimensions as measured currently. The main active landslide has a steep scarp of along 60 m with a height of up to 8 m, with several transverse tensile cracks were found in between the scarp and above the crown. These tensile cracks have caused partial subsidence on the side of the village road that crosses it. In order to determine the existence of slip surface that have developed since the first landslide formed until the last one, an integrated technique of geoelectric resistivity and borehole logging has been applied. This integrated technique was then used to reconstruct the landslide progression retrogressively towards the top. The results of the geoelectric resistivity analyses indicated that there are four stages of slip surface formation. The first slip surface is located at 80 m south of the village road, which is defined to be the initial of a retrogressive landslide. The second slip surface located at 40 m from the village road is possible to be a former landslide damaged the prior village road. The third slip surface is formed at a distance of 15 m from the village road, which is a landslide considered to have caused the bridge to collapse. The fourth slip surface is located at the side of the village road, which is the last landslide causing the concrete slab of the bridge moved 15 m to the south. The average depth of the slip surface is about 8 m. This depth has been confirmed using borehole logging data, by obtaining a relatively hard weathered claystone layers at a depth of 6-8 m.

In the past decade, cross-correlations of ambient seismic noise have been exploited in various applications to model the shallow-to-deep structure of Earth's interior through tomographic inversions. The stack of cross-correlations between a 2-station pair represents empirical Green's function and comprises the information of the subsurface structure between those stations. In practice, noise correlation function (NCF) is analyzed to reconstruct surface wave group or phase velocity dispersion; then, the dispersion data is used to model shear-wave velocity (Vs). This study presents a case for temporary seismic networks deployed in the Jakarta Basin; we applied a two-step routine to obtain a representative 1D Vs profile beneath an array. First, we extracted our array's average phase velocity dispersion based on the relationship between NCF's spectra and the Bessel function. Then, we invert for the 1D depth profile of Vs using a transdimensional Bayesian inversion to allow for exploring a number of layers in parameterizations. We successfully generate a 1D Vs profile up to 5 km depth reflecting the regional stratigraphy of the Jakarta Basin. In general, a sedimentary basin fill covers the area reaching a depth of 650 m. We suggest that this simple routine can be undertaken for other ambient noise cross-correlation cases; such a 1D depth profile would be beneficial to be used as a reference model.

Lake Toba is located on the Sumatra Island, Indonesia. The subduction of the Indo-Australian plate dominates the tectonic setting in this region underneath the Eurasian plate. This area has active seismicity, especially from the subduction process in the West. Most rocks in Lake Toba are tuff sediments. This study's objective is to map the vulnerability index that can be used to identify high damage areas in the region if an intense event occurs. We use 24 three-component seismometers installed around Lake Toba. We gathered good quality recording data for one day on each station. Next, we divided our data into 1 hour and performed the time to frequency domain using the fast Fourier transform. Lastly, we divided the horizontal and vertical components and extracted some parameters such as dominant frequency value and its amplitude. The dominant frequency value ranged from 0.18 to 27.6 Hz, H/V amplification was found to be between 2.84 and 11.9, and shear wave velocity (Vs30) was found to be between 240 and 760 m/s, and the soil vulnerability index (Kg) was found to be between 0.42-43.4. The study area's highest vulnerability is in the southeast, whereas the study area's lowest vulnerability is located in the West and North East.

Sumatra Island is an island located in the subduction zone of the Indo-Australian plate towards Eurasia. The geological structure on the island of Sumatra is the Semangko Fault. There is active volcanic activity, such as the Bukit Barisan Mountains, which makes Sumatra Island vulnerable to volcanic eruptions. The study was conducted in Lake Toba, North Sumatra, using earthquake data from the IRIS station. The purpose of this study is to investigate the amplitude in determining the presence of fluid reservoirs (magma) and to analyze the volcanics of the Lake Toba region using the Low Frequency Passive Seismic (LFPS) method by utilizing attributes such as maximum amplitude Vertical-to-Horizontal Spectral Ratio (VHSR), maximum amplitude of Power Spectral Density (PSD) Z, and the maximum amplitude spectrum of the Z component, which are used as indicators to connect the subsurface fluid reservoir by looking at the spectrum curve. Previous research has linked the presence of a reservoir to the peak amplitude spectrum in the vertical component in the frequency range 1-6 Hz. Based on the research results from the analysis of all attribute parameters obtained, the maximum anomaly of the maximum VHSR amplitude spectrum, the maximum PSD Z amplitude, and the maximum Z component amplitude spectrum indicate that the location with the highest subsurface fluid reservoir potential is in the Northwest-Southeast around Lake Toba and Samosir island. These results support previous research. Volcanic activity in Lake Toba is relatively lower because the amplitude spectrum values of all attribute parameters are not too high.

lobal warming, the impact of greenhouse-gases emission has triggered climate change and caused various geological and hydro-meteorological disasters in the world. Most countries have carried out decarbonization efforts following the Paris Agreement, which aims to reduce carbon emissions from 29% of domestic effort up to 41% with international support by 2030. Sustainable Development Goal number 13 states combating climate change is a globally accepted framework adopted by the Indonesian Ministry of Development Planning. One aspect of decarbonization efforts involves establishing successful CCS/CCUS facilities, which requires readiness of geological carbon storage (GCS). The GCS has limited capacity, locate specifically underneath, and must consider nearby faulting system to avoid leakage and uncontrollable behavior after the injection phase of the liquefied (high-pressure) carbon. This study optimizes gravity dataset analysis to identify the existing faults and characterize the initial stage of proposed GCS in the northern part of East Java, Indonesia. Synthetic modeling of a strike slip fault was conducted to support data interpretation. The GCS characterizations, which include shape, depth, and storage capacity estimations, are inferred through 3D gravity inverse modeling. This study deduced the presence of a large-scale anticline closure without any intersecting of strike-slip fault in the area. The existing fault system is identified as the Baribis-Kendeng Reverse Fault Zone, trending west-east, and intersected by a sinistral strike-slip fault in the northeast-southwest direction. The study area is suggested as a potential GCS location with low-risk of leakage, located adjacent to the Central Processing Plant Gundih and Sukowati in East Java, Indonesia

The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in the implementation process, with the occurrence of cracks cavities conditions in the headrace tunnel locations. We applied the cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties of the formations between two boreholes in this case inferred cracks cavities condition. The seismic source is inside the borehole "a sparker" and the receivers "hydrophones" are in an adjacent one, the sparker is lowered into the borehole one step at the time. Seismic waves, propagating in the tunnel wall rock, spread widely, and are reflected and refracted when encountering interfaces between rocks with different acoustic impedances. Reflected waves returning to the receivers are recorded. After the processing of the first arrivals of the P waves we obtain a cross section of the seismic velocities in between the two wellbores. With the cross-hole seismic tomography, the basis could be provided to the tunnel construction and parameter adjustments to guarantee the construction safety. Our result shown that there is a weak zone above the tunnel with low Vp zone (~1.2 km/s) may be related to weak zone (may be fracture, unconsolidated rock, and fluid-filled rock or landslide caving). Checker-board resolution test is also conducted to determine the tomogram areas that are reliable to be interpreted. Our challenges are we have poor resolution due to not enough raypath. The Cross-hole seismic tomography can effectively and safely guide the excavation of the tunnel section working surface in combination with reconstructed images and excavation technology.

The study using time-lapse microgravity (TLM) data can be helpfull to understand near surface variation caused by hidrological variation. Shallow groundwater variation can be highly correlated with density variation as time-lapse microgravity source, because the changes are very close to the surface. For several days (or weeks or months), we can observe density variation in the near surface caused by the changes of water saturated zones. The time-lapse of density variation for several days can be simplified as groundwater table changes. The purpose of this work is to study time-lapse microgravity application for groundwater level estimation. Using numerical example, we utilize lateral variation of time-lapse microgravity signal and also surface topography. In order to do the estimation groundwater level for second TLM survey, we need the groundwater level data from first survey (and vice versa). After numerical example, we applied the algorithm in the study area of (5 × 5) km square in the Blora regency. The shallow groundwater level (0 to 14 meters below the surface) are observed after the second (2016) microgravity survey. From this work, we constrained the model using second groundwater level data. After iterative calculation of using TLM anomaly (value in the range of -80 to +80 microGal) with surface topography variation (in the range 90 to 230 meters), we get the estimation the first (2014) groundwater level variation in the range of -7 to 7 meters from the second (2016) groundwater level data.

The Gedebage district in Bandung city has experienced a vast physical development in recent years. Previous geodetic studies showed that the area undergoes high-rate land subsidence. The subsurface soil of the Gedebage area has remarkably high compressibility, void ratio, and water content. A thick sequence of soft organic clay of 20-27 m exists, making the area prone to subside. As the district continues to develop, it is important to predict the future rate of land subsidence in the area. This paper aims to analyze the contribution of groundwater exploitation to the land subsidence rate. A combination of 1-dimensional Terzaghi consolidation analytical analysis and numerical modeling was employed in this study. Groundwater level data up to 2015 was used, and hydrostatic condition was assumed to occur in 1986. Results show that the Gedebage area has subsided as much as 161 cm since 1986. Modeling results are consistent with geodetic survey results. It is predicted that the land subsidence will slow down in the next 40 years, provided that the groundwater level remains stable.

Ground Penetrating Radar (GPR) is a geophysical method that widely used and developed in a lot of fields because of the non-destructiveness and relatively high resolution of the method. Despite all that, this method can produce a biased result because of factors that could affect the anomaly. To prevent those, advanced analytical methods are used, one of them is frequency characteristic analysis technique. Frequency characteristic technique used GPR's frequency content to then analyze it in frequency and time domain. The result is quantified in various characters of frequency. This technique is used to help identify steam vents in geothermal environment in Darajat, Garut. Finite difference time domain (FDTD) method is used to generate a synthetic model then we applied frequency characteristic technique to analyzed and compared with the field data to identify the property of steam vent. Based on the result, frequency characteristic technique can be used to help identify presence of a steam vent.

Time-depth conversion is one of the keys to successful drilling with a specific target. However, if the drilling target is incorrectly defined, it can cause significant material losses. For example, several cases found that the hydrocarbon depth was deeper than the expected target. As a result, the well will be considered dry even though it still has hydrocarbon reserves. In this study, we intend to develop 3D check shot modeling in which check shot and formation marker data are referred to and taken at the well to obtain a precise time-depth relationship to overcome this problem. The well data with check shot available that can be used for velocity modeling, for the time-depth conversion process is very limited. However, in development fields with dozens or even hundreds of wells, the time-to-depth conversion process becomes a challenge where it is not enough when using one single velocity. In addition, the velocity model must accommodate lateral heterogeneity so the depth structure map can match the well formation markers. On the other hand, seismic data can indirectly measure subsurface velocities vertically and horizontally. This research combines well-check shot data with seismic semblance velocity data to build a velocity model calibrated by well data. The time-to-depth conversion process with the calibrated velocity model has an average residual of less than 5 meters compared to only using check shot data, with an average residual is 25-meters.

Many factors can drive seismic anisotropy, whether it is the intrinsic condition of rock, external force, or longwave anisotropy. Saturated fluid, as one of the reservoir's intrinsic elements, is known to trigger an anisotropic effect in far offset seismic with Vertical Transverse Isotropic character. Anisotropy on seismic presents as hockey stick curving that a combination of two-parameter could correct during move-out: V_NMO and the elliptical anisotropy η parameter. This research means observing how the saturated fluid within the reservoir contributes to the observed anisotropy in seismic. Rock physics modelling (RPM) and fluid substitution (FRM) are conducted to investigate the saturated fluid effect at a particular temperature and pressure that reflects the deep-water environment. The anisotropy parameter is extracted by applying Tsvankin 4^th Order NMO to obtain the elliptical anisotropy η parameter. Based on synthetic seismic modelling with VTI Rüger Reflectivity, saturated fluid has an effect on far offset seismic as a manifestation of seismic anisotropy η. In this case of a deep-water environment, gas saturated sand needs the most considerable η correction, followed by oil and water-saturated. Although the η value difference is relatively small and easily dismissed as insignificant, saturated fluid indeed does contribute to the observed seismic anisotropy.

For good interpretation and modelling, knowledge about the effects of anisotropy and its relationship with reservoir properties is needed. Related to this issue, this study evaluated the effects of porosity on the anisotropy parameters for sand reservoirs deposited in the upper slope fan facies. The study objects are obtained from core plug samples of sand reservoirs in the deep-water Kutai Basin. Core plug samples were collected from 13602.5 ft to 13704.5 MD depth. The ε, γ, δ, and η anisotropy parameters data were obtained by ultrasonic measurements, and porosity data were obtained by laboratory measurement with Coreval 700 apparatus and Boyle's law. The analysis results show that the relationship of the anisotropy parameters with porosity appears when high-porosity sandstone and low-porosity sandstone are separated. The plots of anisotropy ε, γ, and δ, show trends for greywacke, with increasing anisotropy value the porosity increases. The effect of porosity on the high porosity (29%-37%) sandstone shows a steeper change than on the lower porosity (12%-13%) sandstone. The analysis also shows that the higher composition of lithic mineral grain reduces the effect of anisotropy on porosity.

Kutai basin hydrocarbon's potential is not only in the delta area but extends to the deepwater area of East Kalimantan. The result of the integration method based on petrophysical, inversion, and seismic multiattribute aim to delineate the gas reservoir potential zone in the research area. The reservoir rocks consist of graywacke to sublitharenite of Upper Miocene sandstone with an average shale volume content 19%, porosity 23%, and water saturation 55%. The reservoir gas is reflected in the Vp/Vs ratio range of 1.58 to 1.8, the Poisson ratio value of 0.17 to 0.3 GPa, and the incompressibility value of 8 to 22 Gpa*g/cc. The distribution potential reservoir zone is indicated by the low acoustic impedance anomaly value of 4000 to 7500 m/s*gr/cm3, high RMS attribute anomaly value of 2000 to 10000, and distribution of low shale volume, high porosity, and low incompressibility will be estimated by using multi-attribute linear regression and probabilistic neural network methods that concentrated on the upper slope fan in the southern area.

In general, there are two types of processes using the gravity method, that is the basic processes and the advanced processes. The basic process includes Gravity Meter reading conversion until the gravity corrections process. While the advanced process is a process to put an edge on the geological appearance of the research area that is already in the form of a map. The advanced process includes map filtering and inversion modeling. This advanced processing of gravity data is very useful, one of which is to separate regional anomalies and local anomalies, while inversion modeling is useful for knowing the approximate location of the anomaly depth. What will be applied to the software is advanced processing, because in its application this processing is required in every geophysical research and requires data processing support tools. However, for now, gravity data processing software, especially for the filtering and data modeling process is available as a licensed software. Where not everyone can access it because of limited costs and those who are still in the learning stage in lectures need practicing to process the geophysical data. The purpose of implementing this filtering process and inversion modeling is to provide access to gravity data processing for free and open source so that it can make it easier for students to process the data while practicing in the field, and in the future this software can be the basis for learning and development in the field of geophysical computing. This research was made using a descriptive method with a complete step and explanation of the creating and applying of the geophysical data processing into a software, so the detail processes inside it can be known. A literature study was also conducted to determine the basic formula that will be used as a reference in calculating gravity data in order to obtain the expected processing and modeling results. After that, the final step is to apply all of the components in a program to create a software based on MATLAB for the final result of this research. This software will containing map filtering and inverse modeling for gravity data which can be used for data processing.

The magnetotelluric method is a geophysical method commonly used to map subsurface resistivity. The subsurface's true resistivity is generated by inversion of the magnetotelluric data. Inversions carried out using conventional methods such as linear and global approaches have several limitations including the need for an initial model, models trapped in local minima, a large number of iterations and long computation time. To overcome the drawbacks, this paper proposes to invert one-dimensional magnetotelluric data using one of the deep learning methods, the convolutional neural network, which is heavily inspired by the human nervous system. This method starts by training the network with large amounts of data. The trained network is then used for inversion by receiving input in the form of apparent resistivity data and generating true resistivity and thickness values instantly. This method has been tested on synthetic data with curves of type A, H, K, and Q. The inversion results show that the convolutional neural network could approach the true resistivity and thickness values with a fairly small error and extremely fast computation time without initial model guess and iteration.

This research applied the geoelectric method to determine the presence of aquifer layers in Bumi Harapan village. This method can determine the value of subsurface resistivity, and from this value, will know the lithology based on the distribution of subsurface resistivity. The lithology results will be described in the form of resistivity logs to make it easier to find the groundwater layer and its depth. Subsurface lithology obtained structures in the form of topsoil, clayey sand, sandy clay and clay. The layers suspected as groundwater layers are sandy clay and clayey sand. The results of the presence of average groundwater at a depth of 4 - 9 meters with sandy clay and clayey sand in the fourth and fifth layers were also found at a depth of 90 - 100 meters below the ground surface. The results of the resistivity values that are thought to be the groundwater layer are found to be 125 – 317 Ωm. Formation factor in determining the type of soil layer as an estimate of groundwater potential Below the surface. The formation factor in this study was found to be in the range of 1.7-8 with a type of aquifer layer to a medium aquifer.

Indonesia is situated in Southeast Asia's active tectonic zone, influenced by the movement of four plates: the Eurasian Plate in the south, the Eurasian Plate in the north, the Philippine Plate, and the Pacific Plate in the northeast. The Tomography approach was used in this work to obtain a stable solution, which was achieved through regularization. Least Square and Hybrid Lsqr are the inversion methods employed. This research aimed to use the IR Tools Package Irhybrid LSQR to investigate inversion tomography with regulatory approaches in 3D. In this study, Matlab is used to perform inversion tomography. Two types of data, real and synthetic, are employed at this stage. The study's genuine data came from earthquake catalogues from BMKG, MARAMEX, DOMERAPI, and BPPTKG, with depths ranging from 0-658 km and recorded between 20 December 2013 - 6 September 2020, with an area boundary of 110.1 – 110.8. LS -7.8–7.2 BT. The red colour represents the magma reservoir area according to the inversion data. Hybrid LSQR is an iterative approach that is considered stable enough to be used in tomography. When applied to tomographic coding and compared to the most widely used inversion method, Least Square, the results obtained in the least Square have a higher value than Hybrid LSQR.

The Synthetic Aperture Radar (SAR) sensors onboard satellites are leading in advance to monitor physical changes of volcano edifices such as deformation. A few days of temporal resolution imageries provided by Sentinel-1 SAR make it possible to monitor volcanoes worldwide in near-real-time monitoring. The Sentinel-1 constellation produces a large amount of SAR images valuable for monitoring volcano deformation and hazard mitigation. However, processing the Interferometric SAR (InSAR) for a large SAR dataset is time-consuming and requires high-performance computers. Overcoming the problem, the Center for Observation & Modelling of Earthquakes, Volcanoes & Tectonics (COMET) created a program called Looking Inside the Continents from Space of Sentinel Aperture Radar (LiCSAR) integrated to InSAR time-series analysis of LiCSBAS InSAR to process and calculate the interferogram deformation in time series efficiently. This study presents the LiCSBAS observation for volcanic activities at Mts. Sinabung and Agung in North Sumatra and Bali, respectively. We have observed the activities of both volcanoes from 2015 to 2022. We have analyzed 1824 and 848 interferograms of Mt. Sinabung and Mt. Agung, respectively. The LiCSBAS InSAR time-series analysis was successfully processed for Mts. Sinabung and Agung despite being located under tropics. Velocity deformation of Mt. Sinabung is dominated by uplift around the summit, consistent with measurement by the Center for Volcanology and Geological Hazard Mitigation (CVGHM). In the period of January to March 2017, the lava dome measurement using laser distance meter showed an increase from 1.2 Mm³ to 1.7 Mm³, while LiCSBAS detected an uplift movement of 14 mm. On the contrary, the deformation of Mt. Agung at the summit of lava dome is 3 mm/yr indicate uplift, while subsidence is observed around the crater.

Indonesia's archipelago formed by the tectonic evolution proceeded with subduction, which was accompanied by volcanism. The systematic subduction zones produce the magmatic arcs with different periods since the Permian up to the Tertiary. However, only the recent Quaternary volcanic arc is recognized and lacked of information about the ancient volcanic environment. Calderas are a crucial feature in any volcanic environment due to the prospect site of geological resources. The Gravity and Magnetic methods are commonly used for preliminary study in almost any cases due to their light-weight, low-cost, and ability to map a wide area rapidly. The inverse-modeling scheme was invoked to estimate the sub-surface situation during the interpretation processes. The study intended to show the ability of both gravity and magnetic method for delineating of caldera-like environment including geological resources prospective site identification. According to the research, a northwest-southeast dextral strike-slip fault found in the area and belongs to the Pamanukan-Cilacap Fault Zone (PCFZ). A circular caldera-like anomaly delineated and interpreted as the ring fault of an ancient volcanic caldera in the study area. Several high gravity anomalies found within the caldera rims are interpreted as lava domes or intrusion rocks, while the high-density found following the outer part of the ring-fault terrain is interpreted as the buried lava. The ancient eruption point inferred around Majenang city, thus the study area proposed as the Majenang Caldera. A mineralization zone identified around the study area, which is comparable with the Cihonje people's gold mining site as the proven prospective area.

The characteristic of explosion earthquakes associated with lava avalanche at Sinabung volcano from October to December 2014 is investigated. The 1-component short-period seismometers which are Sukanalu (SKN), Laukawar (KWR), and Kebayaken (KBY) are used. All stations are located about 3-9 km away from the summit. The result shows the characteristics of these waveforms as follows; the amplitude increases rapidly to maximum for about 2-5 s, then the amplitude is almost constant for about 30-40 s followed by the gradual decrease of amplitude for about 40-50 s. Most of explosion earthquakes have a dominant frequency at about 1-4 Hz. The result also observed that the energy of explosion earthquake changes with lapse time and much stable for longer duration compared with explosion earthquake study at different volcano. Our result suggests that the explosion earthquake at Sinabung volcano may have a different waveform generation and/or mechanism to the general explosion earthquake at different volcano.

Tangkuban Parahu is an active volcano in Indonesia that is part of the Quaternary Sunda volcanic arc. We used the vertical component of waveform recorded by 55 temporary seismic stations deployed around Tangkuban Parahu volcano from October 2021 to February 2022 to gain a thorough understanding of its seismic structure. To extract empirical Green's functions, we computed cross-correlations of the vertical component of continuous record data. The empirical Green's function was extracted from the daily data series, and the cross-correlation data from each day was stacked into a single inter-station cross-correlation data set. The empirical Green's Function is seen at the band period 1-10 s. In this preliminary result, we obtained the Rayleigh wave group velocity map in period 1 s. The result shows a low-velocity value around the crater surrounded by high velocities. The low velocity is related to the weak zone or fluid presence.

Semeru is the highest volcano on the island of Java and one of Indonesia's volcanoes that has a potential threat of pyroclastic flows. The eruption of Semeru often shows a transition pattern between explosive and effusive styles. An increased eruptive activity occurred in 2021 with series of explosions dominated the first two thirds of the year and then transition to series of pyroclastic flows in December 2021. On 4 December 2021, a dome collapse triggered significant pyroclastic flows that reached a maximum distance of 16 km from the crater and resulted in 51 casualties. In this paper, we aimed to study the dynamics of magma movement from depth to the surface and assessing the style transition of the eruptions between explosive and effusive activity from visual, seismic and deformation monitoring data. We analyzed Semeru volcano monitoring data throughout the year 2021. The volcanic activity monitoring system of Semeru volcano consists of 4 seismic stations, 5 deformation stations (2 tiltmeters and 3 GPS stations), and 2 Web Camera/CCTV. Our analysis on seismic data indicates that the series of large pyroclastic flows were triggered by excess pressure at shallow depths a few hours before the events. Deep volcanic earthquakes are relatively increased after the collapse of the lava dome or pyroclastic flows, possibly caused by the sudden decrease in hydrostatic pressure of the rock mass around the magma pocket, thus triggering gas expansion. Deformation monitoring using a tiltmeter at Argosuko and Jawar stations indicates inflation of a deep source since 15 August 2021. Since 7 November 2021, tiltmeter measurement has shown deep source deflation patterns which indicate magma movement from the deep reservoir to a shallower reservoir. After 21 November, inflation of the deep source was observed again, indicating an increase in magma supply from the deep pocket. The results of the pressure source modeling from GPS vector data in the period before the eruption, 1 November – 4 December 2021, showed an anomaly in the form of an increased volume at a depth of > 1.7 km of about 0.84 million/m3. Between 5 December and 31 December 2021, after the 4 December pyroclastic flow, the deformation modeling indicates the transition of the pressure source from a depth of 1.7 km to 8 km. In addition, we also observed a decrease in volume of 5.6 million/m3. The deformation pattern at shallow depths showed a deflationary pattern indicating a decrease in magma overpressure.

Molucca Sea is one of the areas with a high level of seismicity in Indonesia due to its location between three plates. The activities of them forming a quite unique subduction zone. The Eurasian Plate (Sangihe Microplate) move to the East and The Philippine Sea Plate (Halmahera Microplate) continues to Westward caused The Molucca Sea Microplate to be pressed, and subducts in two opposite directions modelat the same time forming an inverted "U". This research used 3663 hypocenters and 9 BMKG stations in the last 5 years (2016 - 2021) with a magnitude of 3 - 8 Mw and a depth of 3 - 630 kilometers. Seismic inversion of travel time tomography is used to produce 2D models of the subduction zone around The Molucca Sea. The distribution of high ΔVp values is ranging from 3.5% to 4% is associated with a solid medium, like The Sangihe Plate, Halmahera Plate, and The Molucca Sea Plate subduction slab. While the low ΔVp is ranging from 1.8% to 2% is associated with the destruction zone and the presence of thermal fluids such as magma or partial melting (the presence of volcanoes). The 3D model is based on the Gaussian Process Regression principle using magnitude and depth data as initial model parameters. Plotting of the thrust faults at the front of the two arcs, namely The West Sangihe Thrust Fault and The East Halmahera Thrust Fault. It can be seen that the subduction under The Sangihe Microplate is deeper (627.2 kilometers) has the average subduction angle of 45.3° compared to the subduction under The Halmahera Microplate (280.0 kilometers) has the average subduction angle of 35.8°

The Palu Koro Fault, which frequently causes solid and destructive earthquakes, is the most exciting aspect of Central Sulawesi's tectonics. We used local earthquake data from the area in this preliminary study. Our preliminary investigation entails analyzing local seismic data and estimating the velocity structure and hypocenter location using a tomographic approach that employs P-wave arrival times from the Agency for Meteorology, Climatology, and Geophysics earthquake observation network from 2010 to 2019. We use a 1-D initial velocity structural model in this tomographic inversion method, and the results are evaluated using the checkerboard test, derivative weight sum, and ray hit count. To the west and east of the Palu Koro Fault area, preliminary tomographic inversion results show a relatively high seismic velocity. These areas are interpreted as West Sulawesi Mandala and East Sulawesi Mandala Poso Fault and Wekuli Fault. The low-velocity anomaly is found near the Palu Koro Fault. Because of the high-speed thrusting, the relocated hypocenters also clustered around the Palu Koro Fault area. In the following activity, we will determine the speed structure of the S wave, which is expected to provide better geological information in the interpretation.

Bengkulu is located in the southern region of Sumatra, where the Indo-Australian and Eurasian plates are subducted. As a consequence of the subduction, seismicity in the area increases, as well as volcanic activity and the appearance of structures such as the Sumatran and the Mentawai faults. Seismic velocity structures were reconstructed using earthquake tomography in Bengkulu and the surrounding areas using data from the International Seismological Center (ISC) and the Meteorology, Climatology, and Geophysics Agency (BMKG). The earthquake data collection period was from January 1, 2010 to December 31, 2018. 19 stations recorded 1721 earthquakes. LOTOS-12 is used to do a tomography inversion, starting with a 1D velocity model and wadati's Vp/Vs ratio and iteratively inverting for Vp, Vs, and Vp/Vs ratios. The bending algorithm is used to calculate the arrival time, and the LSQR method is used to invert it. The Checkerboard Resolution Test (CRT) yielded Tomography results. The results revealed the existence of zones with low-velocity anomalies and low-values of Vp/Vs ratios, indicating the presence of weak zones caused by Sumatra faults, Mentawai faults, and other local faults. Low-velocity anomalies with high-values of Vp/Vs ratios are related to volcanic activity, hereas high-velocity anomalies are associated with the existence of subduction plates and compact rocks. The low-velocity anomalies in the fore-arc at 30-50 km depths coincide with fluid circulation caused by slab dehydration.

The Hawaiian Islands are a prominent place to conduct seismicity research. Geologically, occurring earthquakes in this region are unique since it is caused by the presence of a hot spot rather than the common fault activity. The research was conducted using a tomography method called Surface Wave Tomography. The goals of this study are to produce tomographic images of the Hawaiian Islands and to test the accuracy of the Automated Surface-Wave Phase-Velocity Measuring System (ASWMS). ASWMS employs a cross-correlation process to calculate the phase delay between stations, then Eikonal equation to invert the slowness vector to obtain apparent phase velocities, and lastly Helmholtz equation to correct the amplitude to obtain structural phase velocities. The teleseismic data used in this study were collected from stations located throughout the Hawaiian Islands between 2004 and 2009. This study discovered a low-velocity anomaly beneath the Hawaiian Islands with a value of 3.8 – 3.9 km/s, indicating the presence of a low-velocity body. The decrease in velocity with increasing depth suggests an increase in temperature associated with the path that magma takes from the Earth's mantle to the Earth's crust beneath the Hawaiian Islands.

Tomography was a non-destructive method for investigating the internal structure of an object, usually used to find internal anomalies caused by differences in the physical parameters. The fresnel volume tomography method was an alternative method for reconstructing the image of an object using travel times, whereas this method did not use a ray path in its calculations. In calculating the fresnel zone, the finite difference method which was the solution to the equation of wave propagation was used. The frequency of the waves was also considered, here we used ultrasonic waves with a frequency of 1 Mhz for the inverse modelling process. The reconstruction algorithm we used was Modified Simultaneous Iterative Reconstruction Technique for Fresnel volume. The application of the inversion of synthetic data resulted in an estimation of a velocity model that has good imaging quality and similarity with the synthetic model.

The Australian continent is divided into tectonic blocks, including Archaean and Proterozoic units in the western and central part, and Phanerozoic units in the eastern part. Surface wave tomography is an effective method of getting information about velocity variations in a particular region. Surface wave tomography was used in this project to map the subsurface of the Australian continent down to a depth of 100 km with the ASWMS (Automated Surface-Wave Phase-Velocity Measuring System). From 2010 to 2015, we gathered waveform data from 767 events and 219 permanent and temporal seismic stations dispersed across Australia. We selected a set of events that has a minimum magnitude of 6. Rayleigh wave extraction and cross-correlation between two nearby stations are among the first processing processes. Following that, the apparent phase-velocity value is calculated using the Eikonal and tomographic inversion. To generate a tomographic map with a true structural phase velocity, each phase velocity data is stacked with amplitude correction. According to current tomographic imaging studies, low-velocity values under Australia tend to be dispersed easterly, with Rayleigh velocity ranging from 3.7 to 3.9 km/s. The tectonic history and evolution of eastern Australia are related to a sequence of orogenic events that are pushing toward the continent's eastern boundary.

Eastern Indonesia has a complicated structure due to the collision of the Eurasian Plate, the Pacific Plate, the Indo-Australian Plate, and the Philippine Plate, creating an active seismic zone. The Banda - Seram segment of eastern Indonesia comprises subduction, rollback, detachment, slab tear, back-arc thrust, and the Banda volcanic arc. Sri Widiyantoro did a previous study in Eastern Indonesia utilizing seismic tomography methods to detect the upper mantle and the 180-degree curved transition zone under the Banda arc. In addition, Robert Hall and Spakman's research of the upper mantle revealed the existence of a spoon-shaped mechanism in the band arc. Seismic tomography modeling, this research seeks to identify the tectonic features in Eastern Indonesia, such as partial melting, subduction, slab rips, back-arc thrust, Banda volcanic-arc, detachment, and faults, and to establish the most suitable mitigation strategies. This study uses earthquake data from the Meteorology Climatology Geophysics Agency database (BMKG) and the form of P waves. In this research from 1 January 2016 to 31 December 2020, with coordinates 1 - 12 LS and 120 - 135 BT, there were 81 recording stations and 11299 earthquake occurrences consisting of 175643 P waves and 27338 S waves. This work applies the FMTOMO method to a seismic tomographic model. This research indicates that high-velocity anomalies characterize subduction to a depth of 650 kilometers. On Buru Island, the high-velocity anomaly is diagnosed as a slab tear at a depth of more than 400 kilometers. This research identifies a 100-kilometer-deep Back-arc thrust on Wetar Island that produces shallow earthquakes. In addition, a low-velocity anomaly at a depth of 70 kilometers - 90 kilometers is characterized as partial melting due to its parallel location with the Banda volcanic arc. This study examines the connection between subduction and intense seismic and magmatic activity in Eastern Indonesia.

Indonesia is an area located in the ring of fire, which was formed as a result of the interaction between four plates, namely the Eurasian Plate on the south, the Eurasian Plate on the, the Philippine Plate, and the Pacific Plate on the northeast. The interaction between these plates causes Indonesia to have many active volcanoes and experience many geological natural disasters. In the tomographic inversion process, ill-condition problems are often found in matrix making. Therefore, a regularization technique is needed to obtain a consistent result. The regularization technique can be done using Matlab software with a package called IR Tools (Gazzola et al., 2018). In this research, inversion techniques are used in the form of Least Square and Iteratively Reweighted Norm (IRN). This study aims to analyze the tomographic inversion code with the regularization technique using the Iteratively Reweighted Norm (IRN). In this study, two types of data were used, synthetic data and real data. Based on the results, it shows that using the Least Square method has better where the resulting checkerboard is more than adequate to reconstruct the initial velocity and amplitude model, which is described more clearly and strongly. Based on the results of the real data inversion, it shows that there is a low Vp anomaly (red) in the lower area of Mt. Merapi and Mt Merbabu. Low seismic velocity anomalies are associated with magmatic zones, partial melting, or magma reservoirs. However, there is also a high seismic velocity anomaly (blue) associated with the subduction zone of the Indo-Australian Plate to the Eurasian Plate.

Central Java is a part of the Sunda Arc and has relatively high seismicity due to the subduction zone between the Indo-Australian Plate and the Eurasian Plate. This study uses double-difference tomography to image the P and S wave 3D seismic velocity structures associated with tectonic patterns due to subduction zones. The data used comes from the earthquake catalogs of BMKG, BPPTKG, DOMERAPI, and MERAMEX, with a recording period from May 2004 to December 2020. The number of earthquakes that successfully relocated was 1930 from 1937 earthquakes recorded by 285 recording stations. The results of hypocentre relocation show that seismic activity in Central Java is relatively high and originates from geological structures, including subduction zones, back-thrust, and the Opak Fault. The tomogram results of the P and S wave velocity models support each other. The high seismic velocity anomaly is associated with the subduction zone of the Indo-Australian Plate to the Eurasian Plate with a maximum resolution of up to 100 km depth. Low seismic velocity anomalies are found at the Merapi-Lawu Anomaly (MLA), the Modern Volcanic Arc (MVA), the Sumbing-Sundoro-Dieng volcanic complex, the Banyumas-Cilacap sedimentary basin, and the Kendeng Basin. A low-velocity anomaly is found at a depth of about 40-50 km and a depth of 100 km, which is associated with the process of slab dehydration and partial melting. The inversion results show the impact of the Indo-Australian Plate subduction and the Eurasian Plate on volcanic activity, seismicity, and the geological structures developed in Central Java.

Geomagnetic data from field camp surveys in Karangsambung 2005-2019 were collected and merged. Before 2020 (the restriction of Covid-19 pandemic), there are 4713 and 5984 data of field and base observation in the study area. The purpose of works in this paper are presenting the data collection, simple data processing, and simple calculation of inverse modeling. Fifteen surveys from each year of field camp data acquisition are merged with 2017 survey as reference. The data observation from proton magnetometer are corrected with geomagnetic regional field and diurnal variation (using available data from base observation). Geomagnetic model for 2.5D is calculated using SW-NE slice sections with topographic variation in the study area. The program for inverse model calculation was built to recover distribution of magnetization contrast from surface geomagnetic anomaly. The interpretation of subsurface model should be able to be analyzed and correlated with rock susceptibility and geological surface maps in the study area. From this work, the values of geomagnetic anomaly map are shown in the range of -1600 to 1600 nanoTesla, and the inverse modeling conducted over the Volcanic Breccia in the part of Bukit Brujul area, Basalts and Diabas between Geopark Karangsambung-Parangan-Sadang area, and Clay Breccia in the Sadang-Totogan area.

The presence of manifestation in the Gondang indicates a specific geological condition. Those manifestations are Banyu Kuning Hot Spring, Selo Gajah Hot Spring, and Jari Mud Burst. The purpose of this study, which was carried out near Mount Pandan, was to identify the distribution of magnetic fields and magnetic anomalies, including the patterns of potential geothermal energy distribution in the region based on its magnetism. It also aimed to explain the rock structure in the manifestation area based on susceptibility values. The survey was conducted using 94 measuring points that were randomly distributed throughout the manifestation area. The data was corrected using IGRF and diurnal correction, and it was examined using Surfer 11 to construct a contour map and Oasis Montaj to visualize 3D models. According to the processed data, the residual anomaly's value ranges from -232.1 nT until 159.4 nT. For the anomaly of residual, 2D and 3D models demonstrated low susceptibility dissemination values ranging from -0.029 until -0.0135 cgs on the manifestation zone. The high susceptibility value, which is considered an intrusion rock, has a value range of 0.011 to 0.046 cgs.

The moderate earthquake (Mw 5.9) struck eastern Manggarai and its surroundings on February 21, 2022, at 12:36:00 UTC. Although this earthquake was classified as a moderate earthquake, it produced a significant number of aftershocks. The aftershocks could be observed as the post-seismic activity, which was still well recorded until March 31, 2022. The hypocenter location of the aftershocks is updated by applying the double-difference method. The aftershock distribution is striking in west-east orientation and dipping to the south, emphasizing a geometry of faults. The strike and dip directions are consistent with the focal mechanism determined by the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG). Most aftershocks after the relocation are distributed at a depth of < 25 km; the depth of the mainshock is 21.5 km. The aftershock distribution in this study shows that the earthquake sequence propagates toward the up-dip direction. The aftershock relocation also reveals that most aftershocks are situated slightly off the main fault plane in the complex splay faults. Therefore, we conjecture that the co-seismic activity may trigger the aftershocks. In addition, this study also shows that the fault system consists of several fault segments. Our study benefits earthquake disaster mitigation, especially in mapping the segment faults of the Flores backarc thrust.

Earthquake focal mechanisms are helpful in analyzing seismotectonic features in a specific area, as they can depict subsurface structures. Earthquake focal mechanism solution can result from the first polarity or moment tensor inversion method. The moment tensor inversion can produce complete information of focal mechanism solution than the first polarity method. However, the procedure is slightly more complicated, for it is based on waveform inversion. Several problems related to signal processing might arise. Strategies should be applied to overcome the difficulties and obtain reliable focal mechanism solutions. In this study, we used moment tensor inversion to produce focal mechanisms data of Palu-Koro and Matano Fault events. We processed the focal mechanism of events with a depth of less than 60 km and with a minimum magnitude of Mw 4.7. The moment tensor inversion is conducted using Isolated Asperities (ISOLA) software. Full waveform inversion of stations located near Palu-Koro and Matano Fault is applied. The cause of waveform fitting difficulties using the data in this study area and the solution are discussed. For instance, the existence of unseen signal noise and clear-yet-disturbing signals are observed. Improved solutions can be achieved by station reselection and bandpass frequency adjustment.

We analyze high-frequency receiver functions from two seismic stations to characterize the sediment properties around the eastern coast of Kalimantan. First, we compute high-frequency receiver functions from teleseismic events using the time-domain deconvolution method. The obtained receiver functions are then stacked using the H-κ stacking approach to determine the sediment properties. The computed receiver functions show the complicated waveforms for the seismic station located near Kutai Basin. These waveforms may indicate the presence of multi sedimentary layers. The H-κ stacking results suggest that the sediment is thinner in the northern part of the area (∼1.34 km depth) than in the southern part of the region (∼3.0 km depth). These results are consistent with the previous geological and geophysical studies conducted in this region. The previous works suggested that the sediment thickness around the study area can reach up to 9 km.

Determining the microseismic event location is crucial in various fields of science such as hazard mitigation, exploration of new fossil energy sources, and others. However, in determining the source location, several problems arise, namely the determination of the source location that is not appropriate due to limited data. To determine the exact location of the event requires a lot of microseismic recording data. We developed a time reverse modeling method for elastic waves. The data used is synthetic data that is generated from forward modeling which seems to originate a source that is located in subsurface at 1,300 m depth. The seismic velocity model used is a layered seismic velocity model with the assumption that every layers is unabsorbed layers. Data from the wavefield recording on the surface is propagated back to the source. From the study, this was found that the microseismic event was at a depth of 1,300 m.

Indonesia is located between three significant plate confluences that play a role in creating a subduction zone. Sumatra, one of Indonesia's provinces, is located near the collision of the Eurasian Plate, the Indo-Australian Plate, and the Pacific Plate. The Semangko Fault, the Mentawai Islands, a chain of non-volcanic forearc islands, and active faults that induce earthquakes and landslides are all produced by subduction zones on Sumatra Island. The receiver function approach was developed to identify the discontinuity limits of the Earth's structures, such as the crust and mantle, from teleseismic events. The information in this study comes from 25 temporal and 1 permanent station in West Sumatra and the time period between 2007 and 2009 from the IRIS data station. The earthquake data was taken from teleseismic earthquakes from the three components of seismic stations using criteria arc distances between 30° and 90° and magnitudes ranging from 6.0 to 10.0. This research aims to determine how crustal thickness is distributed and what effect regional geological structure has on crustal thickness. According to the early results of the study, the estimated range of crustal thickness in the research region is 27.11–32.48 km, and the range of Vp/Vs ratio values is 1.70–2.19. The direction of crustal thickness thickening in the area was likewise East-South.

The Mentawai Islands are located in the western part of Sumatra, in the Indo-Australian and Eurasian plate subduction zone. Because of these tectonic settings, the Mentawai Region has a high level of seismicity, making it particularly appealing for subsurface structure study. We used the receiver function method in this study to see response receiver function on plate subduction zone and compare the two deconvolution. This method uses the conversion of P-to-S waves, which have a larger amplitude in the radial component than vertical waves. The deconvolution technique is used to extract the two components of the receiver function signal. Water level deconvolution and iterative deconvolution were employed in this study. In practice, any deconvolution method cannot produce a suitable receiver function due to various methodologies that cannot be used in all conditions. Therefore, an evaluation is needed of each deconvolution method used to obtain the best results. This study utilizes two teleseismic stations located in the north and south of Mentawai, which were obtained through the IRIS website, and applied the Butterworth filter to obtain organized and noise-free data. The first results show that the water level is stronger than the iterative, which is more sensitive to the Gaussian filter width parameter. However, they produced almost identical results at both stations, precisely the arrival time of Ps, which was in 3-4 seconds and was followed by a low velocity.

The island of Sumatra was dominated by tectonic interaction between the Indo-Australian plate subducting beneath the Eurasian plate. Lake Toba is one of the results of the collision and had a large eruption several tens of thousands of years ago. The goal of this study was to use the receiver function approach to calculate the depth variation of the Moho layer and identify the presence of a low-velocity zone (LVZ) under Lake Toba, and then compare the results of the deconvolution method. To process data on receiver functions around Lake Toba, 31 data stations from the Lake Toba (LT) project have been chosen, with data sources coming from Geofon (Germany). Water level (frequency domain deconvolution) and iterative time-domain deconvolution are the receiver function methods employed. According to the findings, the depth of the Moho layer varies between 27.5 and 36.95 kilometres, and it thickens to the northeast of Lake Toba. The average depth of Moho is roughly 31.05 km, and the Vp/Vs ratio obtained is around 1.86 on average. The presence of a low-velocity zone was then detected at a depth of 15 km to 25 km in the A-A' section leading from northwest to southeast on the east side of Lake Toba, and at a depth of 8 km to 22 km in the B-B' section leading from southwest to northeast across Lake Toba, as indicated by low amplitude. The Investigator Fracture Zone (IFZ) beneath Lake Toba was identified as a magma reservoir and source of volcanic activity. The iterative time-domain deconvolution approach was then used to illustrate the result of the best receiver function in this investigation, which revealed that the arrival time of the Ps wave was more spiky than the result of the water level.

Mount Merapi, a stratovolcano, is the world's most active volcano, with a relatively short eruption period. Mount Merapi formed in the Java region as a result of regional tectonics dominated by the Sunda Arc, resulting in a large earthquake. Many earth scientists are interested in studying the volcano's subsurface conditions due to its relatively short eruption period and interesting geological features. The Receiver Function method was used in this study to determine the crust's depth and assess the presence of a LVZ (low velocity zone) by reprocessing receiver function data. The Receiver function is used to identify the Moho discontinuity area by converting P to S waves. A total of 100 earthquake data from 8 teleseismic stations were successfully downloaded from the IRIS website, that was distributed into sections A-A' (west side of Mount Merapi) and B-B' (east side of Mount Merapi). The processing of the receiver function data, as shown by the stacking align results, shows that the closest teleseismic station at west side of Mount Merapi has a very strong negative amplitude response, which is represented as a LVZ or magma reservoir after the arrival of P wave. To estimate the zone for LVZ, a forward modeling receiver function technique was used to find the best correlation between the Synthetic Receiver Function curve and the Receiver Function observation curve. A forward modeling receiver function technique was used to find the best correlation between the Synthetic RFcurve and the RF observation curve to estimate the zone for the LVZ. The correlation between the synthetic RF curve from Ramdhan et al's (2019) tomographic velocity model and the observed RF curve is poor. To improve the correlation, include the main signal source that affects the receiver function curve in the form of seismic wave velocity particularly Vs, LVZ Zone, thin sedimen layer or shallow reservoir, and depth of discontinuity by Suhardja et al (2019). The estimated depth of the LVZ at 10 - 17 km is thinning towards the south or towards Mount Merapi, according to the results of the synthetic receiver function curve modelling at the closest station to Mount Merapi.