Pepen Supendi - Academia.edu (original) (raw)

Papers by Pepen Supendi

Geomatics, Natural Hazards and Risk

The Seismic Record

We reveal the existence of a previously unknown fault that generated the Mw 7.3 Flores Sea earthq... more We reveal the existence of a previously unknown fault that generated the Mw 7.3 Flores Sea earthquake, which occurred on 14 December 2021, approximately 100 km to the north of Flores Island, in one of the most complex tectonic settings in Indonesia. We use a double-difference method to relocate the hypocenters of the mainshock and aftershocks, determine focal mechanisms using waveform inversion, and then analyze stress changes to estimate the fault type and stress transfer. Our relocated hypocenters show that this earthquake sequence ruptured on at least three segments: the source mechanism of the mainshock exhibits dextral strike-slip motion (strike N72°W and dip 78° NE) on a west–east-trending fault that we call the Kalaotoa fault, whereas rupture of the other two segments located to the west and east of the mainshock (striking west-northwest and southeast, respectively) may have been triggered by this earthquake. The Coulomb stress change imparted by the rupture of these segments...

Additional file 1. Additional figures and tables.

IOP Conference Series: Earth and Environmental Science, 2021

Shear-wave splitting (SWS), or the propagation of two independent shear waves, can be used as an ... more 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 distribution related to the rupture zone of the 2018 Lombok earthquake. After applying instrument correction to the data, the waveform data were then windowed in each P and S arrival time. To determine the SWS parameters, we performed rotation in each horizontal seismogram components. The horizontal components were rotated from azimuth 0° to 180° with an increment of 1°. Cross-correlation coefficient (CCC) was determined for each rotation angle. The polarization direction and the SWS delay time were chosen from the parameters shown in the highest value of CCC.

&lt;p&gt;The Southeast Asia (SEA) region is tectonically very active as it accomm... more &lt;p&gt;The Southeast Asia (SEA) region is tectonically very active as it accommodates the northward movement of the Indo-Australian plate in the south and the westward movement of the Philippine Sea plate in the east. Borneo and Sulawesi are located in the centre of SEA, which is our area of interest. Borneo has an intraplate setting, while Sulawesi is situated above several microplate boundaries. For that reason, Sulawesi is seismically and volcanically more active than Borneo. The tectonic link and evolution between the two islands are not well understood as we are missing some fundamental knowledge, such as the variations in their crustal thickness and structure. This includes the provenance of their respective lithosphere, which may have Eurasian and/or East Gondwana origin.&lt;/p&gt;&lt;p&gt;Here, we show the results obtained from the receiver function (RF) study on seismic stations in the region to have a better understanding of the crust and mantle lithosphere beneath the two islands. The RF study includes H-k stacking, time-depth migration of the RF and inversion to estimate crustal thickness and the shear speed variation with depth. The finding from this study shows that the crust in Sulawesi is much more complex than that of Borneo. The crustal thickness gradually changes throughout Borneo, with northern Borneo having an overall thicker crust than other parts of the island. In Sulawesi, the crustal thickness is much more varied across small distances, especially along the northern and southern arms of the island.&lt;/p&gt;&lt;p&gt;We also show some results from the Virtual Deep Seismic Sounding (VDSS) method, which we only applied to the seismic stations in northern Borneo. We used VDSS on Northern Borneo to learn more about its complex tectonic history, such as the two subduction episodes and a continent-continent collision in a recent geological time scale. Our finding reveals a band of alternating thick and thin crust striking NE-SW in this region, which we believed resulted from extensional tectonics related to the Sulu Sea basin opening in the Miocene.&lt;/p&gt;

Physics of the Earth and Planetary Interiors, 2022

E3S Web of Conferences, 2020

On December 15, 2017, and January 23, 2018, there were destructive earthquakes to the south of We... more On December 15, 2017, and January 23, 2018, there were destructive earthquakes to the south of West Java, Indonesia, with Mw 6.9 and Mw 6.1, respectively. We have determined the hypocenter location for both mainshocks through re-picking of the Pand S-wave arrival times recorded by the Agency for Meteorology, Climatology, and Geophysics (BMKG) seismic stations in West Java and its vicinity. We have then relocated the aftershocks for both events. We have also conducted focal mechanism analysis to estimate the type of fault slip. Our results show the 2017 and 2018 events occurred in the intra-slab at 108.6 km and 46.5 km depths, respectively. The focal mechanism solution shows a thrust fault type with the strike direction almost perpendicular to the trench for the 2017 event, and it is almost parallel to the trench for the 2018 event.

This file contains a 3D distribution of Vp, Vs and Vp/Vs ratios of the source region of the 2018 ... more This file contains a 3D distribution of Vp, Vs and Vp/Vs ratios of the source region of the 2018 Lombok earthquake sequence, Indonesia and also relocated earthquake location. Please refer to: H. Afif, A.D. Nugraha, M. Muzli, S. Widiyantoro, Z. Zulfakriza, S. Wei, D.P. Sahara, A. Riyanto, T. Greenfield, N.T. Puspito, A. Priyono, A.T. Sasmi, P. Supendi, A. Ardianto, D.K. Syahbana, S. Rosalia, A. Cipta, and Y.M. Husni (2021), Local earthquake tomography of the source region of the 2018 Lombok earthquake sequence, Indonesia, Geophysical Journal International (submitted).

Supplementary material "SASSY21: A 3-D seismic structural... more Supplementary material "SASSY21: A 3-D seismic structural model of the lithosphere and underlying mantle beneath Southeast Asia from multi-scale adjoint waveform tomography" by Wehner, D., Blom, N., Rawlinson, R., Daryono, Böhm, C., Miller, M.S., Supendi, P. and Widiyantoro, S., submitted for publication in Journal Geophysical Research - Solid Earth. The material contains: The final model, SASSY21, as NetCDF and HDF5 files, with the former being readable by e.g. xarray and the latter suitable for viewing with ParaView and interaction with Salvus. We further provide SASSY21 in CSV format. A Jupyter Notebook (embrace_the_sass.ipynb) with a minimum working example on how to interact with each file format mentioned above. A 3-D model fly-through.

Seismological Research Letters, 2022

Beginning on 30 June 2021, hundreds of earthquakes were detected beneath Semangko Bay in southern... more Beginning on 30 June 2021, hundreds of earthquakes were detected beneath Semangko Bay in southernmost Sumatra, which is located adjacent to the Sunda Strait, a narrow sea passage that separates the islands of Java and Sumatra. A number of these earthquakes were large enough to be felt by people living in the city of Lampung, some 100 km to the east. In terms of magnitude and temporal distribution, the earthquakes did not follow a typical mainshock–aftershock sequence because the onset was marked by a cluster of five earthquakes with local magnitudes that ranged between 4.2 and 4.6, followed by a rapid decay in the number of detected events. We have relocated 254 of the 258 earthquakes that were recorded between 30 June and 14 July 2021, with a local magnitude range between ML 0.9 and 4.6, using the double-difference relocation method (hypoDD); focal mechanisms were also determined for a subset of events with a magnitude >4. Our results show that the seismicity pattern and focal m...

Lombok is one of the islands in the transitional zone from the Sunda Arc to the Banda Arc, Indone... more Lombok is one of the islands in the transitional zone from the Sunda Arc to the Banda Arc, Indonesia. In the mid-2018, the island of Lombok was shaken by a series of strong earthquakes, started with a magnitude 6.4 earthquake on July 29, 2018 followed by earthquakes on August 5 (M 7.0), August 9 (M 5.9), and August 19 (M 6.3 and 6.9). Some researchers suggested that this phenomenon occurred due to a segmentation rupture in the northern part of Lombok Island. This study aims to obtain information on the distribution of the Lombok earthquake rupture zone 2018, through Shear Wave Splitting (SWS) study. Splitting, or S-wave separation, occurs when the S-wave passes through an anisotropic medium. The S wave is split into fast and slow S waves with almost orthogonal polarizations and has parameters such as delay time and polarization direction of the fast S wave. To determine the SWS parameters, we used a Lombok earthquake aftershock data set recorded from 4 August to 9 September 2018, us...

Modeled maximum tsunami height along the south coast of Java. Please refer to: Widiyantoro, S., G... more Modeled maximum tsunami height along the south coast of Java. Please refer to: Widiyantoro, S., Gunawan, E., Muhari, A., Rawlinson, N., Mori, J., Hanifa, N.R., Susilo, S., Supendi, P., Shiddiqi, H.A., Nugraha, A. D., Putra, H. E. (2020). Seismic gaps south of Java, Indonesia: Implications for megathrust earthquakes and tsunamis, Scientific Reports (submitted).

Geoscience Letters, 2021

The geological setting of Jakarta and its immediate surroundings are poorly understood, yet it is... more 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 ~ E-W oriented Baribis Fault, which is ~ 130 km long, passes to the south of Jakarta, and is only ~ 20 km away at its nearest point. A primary objective of this study is to determine whether this fault is seismically active, and therefore, whether it might pose a threat to nearby population centers, including Jakarta in particular. A total of seven broadband instruments that spanned Jakarta and the surrounding region were installed between the end of July 2019 and August 2020, during which time we were able to detect and locate 91 earthquakes. Two earthquakes were located close to the Baribis Fault line, one of which was felt in Bekasi (so...

We carried out a tsunami simulation of the 2011 (Mw 9.0) Tohoku earthquake. We analyze the tsunam... more We carried out a tsunami simulation of the 2011 (Mw 9.0) Tohoku earthquake. We analyze the tsunami run-up modeling by applying additional variables to seismic moment and moment magnitude equation to find out what extent it affects of sub-faults strike direction and landslide energy to tsunami propagation. To investigate the accuracy of run-up and inundation of the tsunami, we processed and analyzed the mainshock and aftershocks by applying scaling law method and inundation equation. We applied the aftershocks data to determine the wide area of the fault. The fault is divided into several sub-faults to make simulation design and scaling formulation adjustment. Each of sub-faults strike direction on simulation design has a different energy one another, which is determined by the strike direction of each fault position. Furthermore, we calculated the affects of submarine landslides on tsunami propagation. To obtain the variable of resultant energy of earthquake and landslide it perform...

Seismological Research Letters, 2021

The 26 September 2019 Mw 6.5 Ambon earthquake has been the largest instrumentally recorded event ... more The 26 September 2019 Mw 6.5 Ambon earthquake has been the largest instrumentally recorded event to occur in Ambon, the capital city of Maluku Islands, eastern Indonesia, and ruptured a previously unmapped active fault. In this study, we use seismic and geodetic data to investigate the source characteristics of the event. Our results show that the rupture process was complex in both the rupture initiation and slip directions. In addition, the rupture was mostly strike-slip motion with normal component and pure reverse slip in the north of the inverted fault. Our analysis of campaign and continuous Global Positioning System (GPS) velocity fields estimates that the fault has a 4.9 [4.0, 5.5] mm/yr slip rate with an earthquake recurrence interval of 115 [102, 141] yr. In addition, a comparison of the horizontal strain-rate tensor derived from GPS velocity fields with historical earthquake data shows that Ambon Island and the nearby regions have a high strain accumulation rate correlate...

Geoscience Letters, 2020

Mt. Agung, located in Karangasem-Bali, Indonesia, had a significant increase of swarm earthquakes... more 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 Geophysics of Indonesia (BMKG) between September 14 to October 20, 2017. P-and S-wave phases of the swarm events had been manually picked. In total, 804 events in the time period of September 14 to October 20, 2017 were successfully determined. To improve the location precision, the double-difference relocation method was performed. We identified most of the events as Volcano-Tectonic type A (VT-A) earthquakes and located between Mt. Batur and Mt. Agung. Those events form a cluster striking in NE-SW direction at a depth between 2 and 20 km. Focal mechanism solutions for selected events below Mt. Agung show a thrust and strike-slip faulting regime. Interesting...

The Central and East Java region is part of the Sunda Arc which has an important role in producin... more The Central and East Java region is part of the Sunda Arc which has an important role in producing destructive earthquakes and volcanic complexes as a result of the subduction of the Indo-Australian plate under the Eurasian plate. Seismic tomography is one geophysical tool that is adaptable to understanding the mechanism process related to tectonic activity, seismicity, and volcanism. We collected a series of waveforms from 1,519 events in the period January 2009 to September 2017 and re-picked 11,192 phases for P-and S-waves at 34 stations of the BMKG network. We determined the 3-D P-and S-wave velocity structure beneath this high-risk region down to a depth of 200 km. In this study, we compare the tomographic images and relocated seismicity in order to represent the subducted slab geometry and the features in the seismic zones, i.e. the 2006 Yogyakarta earthquake zone (Opak fault), south of the mainland, and the 1994 Banyuwangi earthquake zone. Low-velocity anomalies beneath the volcanoes, i.e. Merapi, Merbabu, Kelud, Semeru, Bromo, and Ijen also imply the existence of fluid material and possible partial melting of the upper mantle which migrated from the subducted slab.

Geoscience Letters, 2019

On September 28, 2018, the Mw 7.5 earthquake occurred in Palu, Central Sulawesi, Indonesia. This ... more On September 28, 2018, the Mw 7.5 earthquake occurred in Palu, Central Sulawesi, Indonesia. This earthquake produced strong tremors, landslides, liquefaction and a tsunami and caused thousands of fatalities and damaged houses and infrastructure. We have relocated 386 of the 554 Palu aftershocks by using the double-difference relocation method (hypoDD) from September 28 to November 22, 2018. The aftershock pattern is consistent with the crustal deformation in the area and generally shows that the events have a NW–SE trending of ~ 200 km in length and ~ 50 km in width. Most of the aftershocks are located to the east of the Palu-Koro Fault Line. Since November 2, 2018, there have been hundreds of swarm earthquakes in the area of Mamasa, West Sulawesi, which is about 230 km south of the city of Palu. Some of these earthquakes were felt, and houses were even damaged. We have relocated 535 of the 556 swarm earthquakes having a magnitude of M 2 to M 5.4. Our results show that the seismicit...

AIP Conference Proceedings, 2018

Earthquake swarm are common occur around active tectonic and volcanic regions. The recent activit... more Earthquake swarm are common occur around active tectonic and volcanic regions. The recent activities of swarm event occurred around Bekancan area, North Sumatra Province, Indonesia for February 29, 2015 to July 10, 2017 recorded by BMKG local/regional network. This location close to Sinabung and Sibayak volcanoes, lead to our intriguing to analysis of source mechanism and location of the swarm event. We attempted to update hypocenter location of BMKG data catalogue by applying double-difference method. We have successfully relocated of 152 swarm events in the area. The relocated events appear about 10 km northeast of Sinabung volcano with focus depth of about 0 to 30 km (below sea level), however very close to Sibayak volcano area. Overall, the dominant frequency of the event from the closest station is about 2 to 9 Hz. So, our preliminary interpretation is the location of swarm events close to Sinabung and Sibanyak volcanoes in Bekancan area which probably related to stress change due to volcanic-tectonic activity.Earthquake swarm are common occur around active tectonic and volcanic regions. The recent activities of swarm event occurred around Bekancan area, North Sumatra Province, Indonesia for February 29, 2015 to July 10, 2017 recorded by BMKG local/regional network. This location close to Sinabung and Sibayak volcanoes, lead to our intriguing to analysis of source mechanism and location of the swarm event. We attempted to update hypocenter location of BMKG data catalogue by applying double-difference method. We have successfully relocated of 152 swarm events in the area. The relocated events appear about 10 km northeast of Sinabung volcano with focus depth of about 0 to 30 km (below sea level), however very close to Sibayak volcano area. Overall, the dominant frequency of the event from the closest station is about 2 to 9 Hz. So, our preliminary interpretation is the location of swarm events close to Sinabung and Sibanyak volcanoes in Bekancan area which probably related to stress change due to volcanic-tectoni...