David P. Sahara

Bandung Institute of Technology | ITB · Faculty of Mining and Petroleum Engineering

This study describes a systematic analysis of breakout occurrence, variation of breakout orientation and fracture characteristics. We infer the impact of fracture networks on the development of breakouts from detailed analysis of 1221 borehole elongation pairs in the vicinity of 1871 natural fractures observed in the crystalline section of the GPK4...

Damage distribution and evolution have a significant effect on borehole stress concentrations. To model the complex fracturing process and inelastic deformation in the development of the borehole breakout, we implement a continuum damage mechanics (CDM) concept that takes tensile and compressive failure mechanisms into account. The proposed approac...

A stress transfer modeling revealed the stress heterogeneity and its correlation with the seismicity pattern in the bifurcation zone of the Great Sumatran Fault (GSF), where the GSF is divided into two separate sub-parallel segments up to 35 km apart, i.e. Angkola and Barumun, forming a strike-slip duplex at around equator. The analysis was conduct...

On September 26, 2019, a significant, Mw 6.5, earthquake shook Ambon region, Indonesia, causing severe damage on the Island(s) of Ambon. Due to the complexity of the fault network and in-situ stress field it was, up to now, not possible to define the fault plane using data from the BMKG regional seismic network. In this study, we analyze the fault...

Realizing an effective earthquake early warning system (EEWS) in the case of extensive regions and noisy signals is challenging, particularly in East Java, Indonesia. This letter proposes the rapid detection of the p-wave arrival and determination of the earthquake's hypocenter and magnitude using deep learning. The Ncheck algorithm is used for noi...

Research on strain anomalies and large earthquakes based on temporal and spatial crustal activities has been rapidly growing due to data availability, especially in Japan and Indonesia. However, many research works used local-scale case studies that focused on a specific earthquake characteristic using knowledge-driven techniques, such as crustal d...

In the case of mining in an inclined intrusion using the block caving method, the highest stress is usually concentrated in the seismogenic and abutment zones, especially in the front of the sloping area. In an inclined intrusion of more than 40°, the seismometer network is usually distributed in the facility area where the footwall area is also lo...

The Lembang Fault is located about eight km north of Bandung City, the capital city of the West Java province of Indonesia, with about 8.79 million people (dated 2020). Several studies state that the Lembang fault is an active fault with a maximum magnitude of 6.5 to 7. In terms of earthquake disaster mitigation, distinguishing characteristics of s...

This study’s research aim has been to clearly reveal the geometry of the Molucca Sea Plate subduction zone beneath Sulawesi’s north arm, the relationship between the subduction zone and volcanic activity in Halmahera, and analyze the depths of the upper arch of the double subduction of the Molucca Sea Plate. The use of travel time tomography made i...

Java Island is one of the areas with a population density of 1,171 people/km ² , which is relatively high compared to other regions in Indonesia. The tectonic setting of the Java region is affected by the interaction of tectonic plate subduction between the Indo-Australian Plate and the Eurasian Plate which moves at the rate of 67 mm/year. In addit...

Recent borehole seismic deployments conducted along the Baribis Fault in northwestern Java reveal that it may be active. In this study, we exploit these data to locate proximal earthquakes using a relative relocation technique, estimate their moment magnitudes using a spectral fitting method and compute their focal mechanisms via waveform inversion...

A destructive earthquake with magnitude Mw 6.5 occurred in Ambon, Indonesia, on 26 September 2019. This earthquake generated an aftershock sequence. In this study, we determined the location of the aftershock sequence using a non-linear algorithm from the Non-Linear Location (NonLinLoc) program. The catalog and waveform data were collected using 11...

A volcano-Tectonic earthquake, commonly referred to as VT, is an earthquake caused by magma intrusion that increases the pressure below the volcano’s surface. The accumulation of stress that continuously affects the elasticity of rocks causes fractures when the elasticity limit of rocks is exceeded. VT is one of the earthquakes used as a parameter...

This study intends to evaluate the possible correlation between the correlation dimension (DC) and the seismic moment rate for different late Quaternary active fault data, shallow crustal earthquakes, and GPS on the island of Sumatra Probabilistic Seismic Hazard Analysis (PSHA). The seismicity smoothing was applied to estimate the DC of active faul...

The issue of IOP Conference Series: Earth and Environmental Science contains the outstanding papers presented at International Conference on Geoscience and Earth Resources Engineering (ICGERE) 2021. Due to Covid-19 Pandemic, the 3rd ICGERE 2021 Conference was held online on 8 – 9 December 2021. List of Committees are available in this pdf.

Microseismic monitoring has been used for gathering subsurface information in Geothermal field as part of reservoir monitoring and management plan. New micro earthquake (MEQ) stations were installed in the Muara Laboh geothermal field in the end of 2019, coinciding with the first operation of Unit-1. They have been continuously used to monitor the...

The Sumatra Island, which is close to the active subduction zone between the Indo-Australian and Eurasian plates, experienced numerous earthquakes in the historical past. One of those earthquakes is the 2004 Mw 9.1 off-Sumatra earthquake, considered to be the second largest event ever recorded in history after the 1960’s Chilean earthquake (Mw 9.5)...

The Mw 6.5 Pidie Jaya strike-slip earthquake struck Pidie Jaya, Aceh, on December 7, 2016. The aftershocks lasted until January 2017. The aftershocks, which were recorded by Indonesia’s Meteorological, Climatological, and Geophysical Agency (BMKG) network on December 7–19, 2016, depicted northwest–southeast cluster orientation. While the aftershock...

The seismically active Sumatra subduction zone has generated some of the largest earthquakes in the instrumental record, and both historical accounts and paleogeodetic coral studies indicate such activity has historical recorded megathrust earthquakes and transferred stress to the surrounding, including the Great Sumatran Fault (GSF). Therefore, ev...

Subsurface images of an area with a thick volcanic layer generally cannot be well-imaged with conventional seismic exploration (seismic reflection) due to seismic wave scattering. Another method is needed to obtain an accurate subsurface image in a thick volcanic layer area. In this study, we applied ambient noise tomography (ANT) to image the shea...

The geological setting of Jakarta and its immediate surroundings are poorly understood, yet it is one of the few places in Indonesia that is impacted by earthquakes from both the Java subduction zone and active faults on land. In this study, a borehole seismic experiment with low noise characteristics was deployed to record seismic activity on the...

Hypocenter relocation is one of the keys to success in the analysis of seismicity induction in underground mines. Overburden thickness, topography, geological complexity, and mining activities can result in newly induced seismicity that can endanger the safety of underground mine workers. The relatively narrow underground mine area requires the mos...

The crust, when viewed over a long period, moves towards one another. Crusts might experience sudden slip on a fault plane and caused fractures or cracks. There are three different types of faults, normal, reverse, and strike-slip faults. Induced stress due to sudden rupture on fault planes capable of creating stress and need to be measured quantit...

Present day Molucca or Maluku sea plate in the eastern of Indonesia possesses a complex tectonic setting. This complex tectonic setting has been formed due to the collision of an actively moving Eurasian plate and Philippine sea plate toward the Maluku sea plate. At the west, Maluku sea plate is subducting beneath Sangihe arc, which began in the ea...

The island of Ambon lies on complex tectonics, part of Banda Arc which is driven by the Australia – Eurasia collision. Historical earthquake data show that an earthquake resulting the greatest tsunami in Indonesia had occurred at Ambon Island. On 26 September 2019, Ambon was shaken by an M 6.5 earthquake at a depth of 10 km (BMKG). In this study, w...

Agung is one of active volcanoes in Indonesia, located on island of Bali. Since 1963, Agung has not had significant activity, until in September 2017 the volcano was active again which was marked by increased seismic activity and eruptions in November 2017. Therefore, to analyze the dynamics and processes of active volcanic eruptions requires an un...

The Ambon Mw 6.5 earthquake on September 26th, 2019, had contributed to give severe damages and significantly increased seismicity around Ambon Island and surrounding areas. Mainshock was followed by aftershocks with spatial distribution added to the impact of destructions in this region. We investigated aftershocks sequences to reveal the effect o...

Earthquake swarms commonly come approximately active tectonic and volcanic area. Interestingly, the swarm events occurred ~23 km southwest from Mt. Salak-Bogor, West Java, Indonesia, from August 10 to November 24, 2019, and were recorded by local/regional network of the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG). Our prev...

The inland seismic activity in Great Sumatran Fault (GSF) has significantly increased over the past several decades after the occurrence of historical large interplate earthquakes along the plate boundary. This condition led to some occurrences of historical intraplate earthquakes along Sumatran fault. To quantitatively examine the physical mechani...

Shear-wave splitting (SWS), or the propagation of two independent shear waves, can be used as an indicator of seismic anisotropy. In this study, we utilize this concept using aftershock data of the 2018 Lombok earthquake which had been acquired in period of August 4 – September 9, 2018. The goal of this research is to better understand the crack di...

Coseismic changes in principal stress orientation in the northern Sumatra subduction zone due to two giant megathrust earthquakes there in 2004 and 2005 are estimated to investigate the in-situ stress. The two megathrust earthquakes, the 2004 Sumatra-Andaman and the 2005 Nias-Simeulue events, are both among the 11 largest earthquakes ever recorded....

The Banyumas Basin is a tertiary sedimentary basin located in southern Central Java, Indonesia. Due to the presence of volcanic deposits, 2-D seismic reflection methods cannot provide a good estimation of the sediment thickness and the subsurface geology structure in this area. In this study, the passive seismic tomography (PST) method was applied...

This study provides an attempt to analyze the pre-eruptive seismicity events for volcano eruption forecasting. After more than 50 years of slumber, Agung volcano on Bali Island erupted explosively, starting on November 21, 2017. The eruption was preceded by almost 2 months of significant increase of recorded seismicity, herein defined as “seismic c...

We develop and present a three-dimensional (3D) seismic velocity model of the source region of the 2018 Lombok, Indonesia earthquakes by employing local earthquake tomography. The data consist of 28,728 P- and 20,713 S-wave arrival times from 3,259 events which were recorded by 20 local seismic stations. The results show that most of the significan...

Local seismic tomography is a well-known and commonly used method for obtaining detailed information about the internal structure of volcanoes. The eruption of Mt. Agung in 2017 was a vital opportunity scientifically because it is the first eruption that had sufficient seismic observation networks to carry out local seismic tomography at this volca...

A seismic hazard study and analysis of the megathrust source off the west coast of North Sumatra, Indonesia, were conducted based on the estimated horizontal crustal strain using the surface displacement data. This area was selected due to the availability of pre- and co-seismic Global Positioning System (GPS) data for the 2005 Nias–Simeulue Mw 8.6...

A seismic hazard study and analysis of the megathrust source off the west coast of North Sumatra, Indonesia, were conducted based on the estimated horizontal crustal strain using the surface displacement data. This area was selected due to the availability of pre- and co-seismic Global Positioning System (GPS) data for the 2005 Nias–Simeulue Mw 8.6...

Shallow earthquake produced by intra-island fault in a populated region could be a catastrophic disaster. Java island is the most populated area specifically in Western Java since there include Jakarta, the capital city of Indonesia. Cimandiri, Lembang and Baribis fault as main intra-island fault are considered to be responsible due to some shallow...

We have successfully conducted the first ambient noise tomography on the island of Lombok, Indonesia using local waveform data observed at 20 temporary stations. Ambient noise tomography was used to delineate the seismic velocity structure in the upper crust. The waveform data were recorded from August 3rd to September 9th, 2018, using short-period...

Local earthquake data was used to determine a three-dimensional (3D) seismic attenuation structure around the aftershock source region of the 2018 Lombok earthquake in Indonesia. The aftershocks were recorded by 13 seismic stations from August 4 to September 9, 2018. The selected data consist of 6,281 P-wave t ∗ values from 914 events, which had go...

Subsurface images of an area with a thick volcanic layer generally can not be well-imaged with conventional seismic exploration (seismic reflection) due to seismic wave scattering. Another method is needed to obtain an accurate subsurface image in a thick volcanic layer area. In this study, we applied Ambient Noise Tomography (ANT) to image the she...

Herein, we applied the fault instability criterion and integrated it with the static Coulomb stress change (ΔCFS) to infer the mechanism of the 2016 Mw 6.5 Pidie Jaya earthquake and its aftershock distribution. Several possible causative faults have been proposed; however, the existence of a nearby occurrence, the 1967 mb 6.1 event, created obscuri...

This article presents earthquake catalogs of the 2019 Ambon aftershocks compiled from regional the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) and local seismic networks deployed in [1]. The final earthquake catalogs are comprised of 1,009 and 1,764 aftershocks compiled from regional [2] and local network [1], respective...

On 6 December 2016 at 22:03 UTC, a devastating magnitude 6-class strike-slip earthquake occurred along an unidentified and unmapped fault in Pidie Jaya, northern Sumatra. We analysed the possible fault using continuous Global Positioning System (GPS) observation available in the region. In our investigation, we searched for the fault source paramet...

The region of Jakarta and its vicinity is one of the least understood geological domains in Java Island, Indonesia. Yet, the region is one of the few places which are often impacted by earthquakes from the Indo-Australian Plate subduction zone as well as on land active faults. In this study, a borehole seismic experiment was designed to unravel the...

Abstract. The application of earthquake statistics, frequency-magnitude distribution (FMD), and correlation dimension (Dc) are effective approaches used to understand local seismotectonic activities. Both the b values of FMD and Dc values are significantly directly related to stress and earthquake phenomena. In this study, the correlation dimension...

Mt. Agung, located in Karangasem-Bali, Indonesia, had a significant increase of swarm earthquakes from September 2017 until the recent eruption in November 2017. To analyze the seismic swarm and its correlation with the magmatic movement, we worked on the regional seismic data recorded by Agency for Meteorology, Climatology and Geophys-ics of Indon...

In 2018, Lombok Island was hit by a series of destructive earthquakes. According to Indonesian Meteorological, Climatological, and Geophysical Agency data, about 1,973 felt earthquakes (M > 3) which shaken Lombok were recorded during August 2018 with three earthquakes with the largest magnitude of 6.9 Mw, 6.8 Mw, and 6.2 Mw. National Board for Disa...

Because of its robustness and practicality, the Horizontal-to-Vertical Spectral Ratio (HVSR) method has been widely used to obtain subsurface structure, mainly the sediment thickness that resides over bedrock. The method uses Fourier Transform to obtain frequency spectrum and calculate the H/V ratio. However, the conventional Fourier Transform meth...

The probability difference before the occurrence of a large earthquake is mapped in the northern part of Sumatra, taking the range of Region Time Length (RTL) before a major earthquake (December 26, 2004) around 15 years. By normalizing the absolute value of probability difference between two periods of RTL and before RTL, the Seismic Quiescence In...

The island of Lombok in Indonesia is located between the Indo-Australian and Eurasian subduction trenches and the Flores back-arc thrust, making it vulnerable to earthquakes. On 29 July 2018, a significant earthquake Mw 6.4 shook this region and was followed by series of major earthquakes (Mw>5.8) on 5, 9, and 19 August, which led to severe damage...

The Agung-Batur Volcanic Complex (ABVC), part of the Sunda volcanic arc, is the source of some of the most hazardous volcanic activity in Indonesia. The ABVC has undergone many small (VEI 1-2) eruptions since historical records began in the early 19th century, but Mt. Agung has experienced much larger (VEI 5) eruptions, both in the modern (1963) an...

Significant earthquakes on the island of Sumatra, Indonesia, have predominantly been earthquakes with a thrust mechanism that occurred due to the subduction process and seismotectonics near coastal cities of West and South Sumatra, which could be affected by earthquakes triggered by these seismic sources. We compared the Seismic Hazard Function (SH...

A Carbon Capture and Storage (CCS) pilot project is currently done in Gundih gas field, Central Java, Indonesia. The plan is to inject CO2 from gas production in nearby wells into a deep carbonate reservoir with the rate of 800 ton per day for 10 years. Reservoir integrity or the capability of reservoir rock to uphold the CO2 before it reaches crit...