Achmad Fajar Narotama Sarjan

University of Mataram

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Trends

Author Order

Document Type

Co-Authors

Andri Dian Nugraha

Bandung Institute of Technology

Zulfakriza Zulfakriza

Bandung Institute of Technology

Sri Widiyantoro

Bandung Institute of Technology

Muzli Muzli

Meteorological, Climatological, And Geophysical Agency

David P. Sahara

Bandung Institute of Technology

Shengji Wei

Earth Observatory of Singapore

Haunan Afif

Bandung Institute of Technology

Awali Priyono

Bandung Institute of Technology

Nanang T. Puspito

Bandung Institute of Technology

Billy Sugiartono Prabowo

Bandung Institute of Technology

Cooperative Institutions

Bandung Institute of Technology

Meteorological, Climatological, And Geophysical Agency

National Research and Innovation Agency

Ministry of Natural Resources and Environment

Australian National University

The University of Tokyo

Indonesian Institute of Sciences

Pertamina (Indonesia)

University of Cambridge

John Wiley & Sons (United States)

Author Statistics

Papers

Citation

H-Index

i-10 index

Research Field

Determination of Shear Wave Splitting Parameters in 2018 Lombok Earthquake Using Rotation Correlation Method: Preliminary Result

IOP Conference Series Earth and Environmental Science (2021)

Annisa Trisnia Sasmi Andri Dian Nugraha Muzli Muzli Sri Widiyantoro Zulfakriza Zulfakriza

Abstract 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.

Seismogram

Shear wave splitting

10.1088/1755-1315/873/1/012101

Cite

Citations (1)

Delineation of Upper Crustal Structure Beneath the Island of Lombok, Indonesia, Using Ambient Seismic Noise Tomography

Frontiers in Earth Science (2021)

Achmad Fajar Narotama Sarjan Zulfakriza Zulfakriza Andri Dian Nugraha Shindy Rosalia Shengji Wei

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 and broadband sensors. There are 185 Rayleigh waves retrieved from cross-correlating the vertical components of the seismograms. We used frequency-time analysis (FTAN) to acquire the interstation group velocity from the dispersion curves. Group velocity was obtained for the period range of 1 s to 6 s. The group velocity maps were generated using the subspace inversion method and Fast Marching Method (FMM) to trace ray-paths of the surface waves through a heterogeneous medium. To extract the shear wave velocity (Vs) from the Rayleigh wave group velocity maps, we utilize the Neighborhood Algorithm (NA) method. The 2-D tomographic maps provide good resolution in the center and eastern parts of Lombok. The tomograms show prominent features with a low shear velocity that appears up to 4 km depth beneath Rinjani Volcano, Northern Lombok, and Eastern Lombok. We suggest these low velocity anomalies are associated with Quaternary volcanic products, including the Holocene pyroclastic deposits of Samalas Volcano (the ancient Rinjani Volcano) which erupted in 1257. The northeast of Rinjani Volcano is characterized by higher Vs, and we suggest this may be due to the presence of igneous intrusive rock at depth.

Ambient noise level

Group velocity

Seismic Tomography

Rayleigh Wave

Seismogram

10.3389/feart.2021.560428

Cite

Citations (14)

Shear Wave Splitting of the 2018 Lombok Earthquake Aftershock Area, Indonesia

Research Square (Research Square) (2022)

Annisa Trisnia Sasmi Andri Dian Nugraha Muzli Muzli Sri Widiyantoro Syuhada Syuhada

Abstract 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, using 16 seismographic stations. The steps taken to obtain the SWS parameters are event selection, windowing using short time Fourier transform, and rotation-correlation process. The results of the SWS analysis indicate that the fast polarization directions probably have a linkage with the local fault system and the fault related to the Lombok earthquake rupture zone.

Shear wave splitting

Transform fault

10.21203/rs.3.rs-1317712/v1

Cite

Citations (0)

Hypocenter and Magnitude Analysis of Aftershocks of the 2018 Lombok, Indonesia, Earthquakes Using Local Seismographic Networks

Seismological Research Letters (2020)

Annisa Trisnia Sasmi Andri Dian Nugraha Muzli Muzli Sri Widiyantoro Zulfakriza Zulfakriza

Abstract 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 in the northern Lombok area. In this study, we attempt to reveal the possible cause of the sequences of the 2018 Lombok earthquakes based on aftershock monitoring data. Twenty stations were deployed to record earthquake waveform data from 4 August to 9 September 2018. In total, 3259 events were identified using 28,728 P- and 20,713 S-wave arrival times during the monitoring. The aftershock hypocenters were determined using a nonlinear approach and relocated using double-difference method. The moment magnitude (Mw) of each event was determined by fitting the displacement spectrum amplitude using a Brune-type model. The magnitudes of the aftershocks range from Mw 1.7 to 6.7. The seismicity pattern reveals three clusters located in the Flores oceanic crust, which fit well with the occurrences of the four events with Mw>6. We interpret these events as the main rupture area of the 2018 Lombok earthquake sequence. Furthermore, an aseismic zone in the vicinity of Rinjani extending toward the northwestern part of Lombok was observed. We propose that the crust in this area has elevated temperatures and is highly fractured thus inhibiting the generation of large earthquakes. The aseismic nature is therefore an artifact of the detection threshold of our network (Mw 4.6).

Hypocenter

10.1785/0220190348

Cite

Citations (31)

Shear wave splitting of the 2018 Lombok earthquake aftershock area, Indonesia

Geoscience Letters (2023)

Annisa Trisnia Sasmi Andri Dian Nugraha Muzli Muzli Sri Widiyantoro Syuhada Syuhada

Abstract 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 moment magnitude (M w ) 6.4 earthquake on July 29, 2018 followed by earthquakes on August 5 (M w 7.0), August 9 (M w 5.9), and August 19 (M w 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 fault zone 2018 and also to understand the character of seismic anisotropy around the Lombok earthquake fault 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, using 16 seismographic stations. The steps taken to obtain the SWS parameters are event selection, windowing using short time Fourier transform, and rotation-correlation process. The results of the SWS analysis indicate that the fast polarization directions probably have a linkage with the local fault system and the fault related to the Lombok earthquake fault zone.

Shear wave splitting

Moment magnitude scale

Transform fault

10.1186/s40562-022-00258-3

Cite

Citations (1)

Review of the 2018 Lombok Earthquake, Indonesia, and Its Impact from Previous Studies

Achmad Fajar Narotama Sarjan Ismail Hoesain Muchtaranda

A series of strong earthquakes struck Lombok Island on 29 July (M 6.4), 5 August (M 7.0), 9 August (M 5.9), and 19 August (M 6.3 and M. 6.9) 2018 which led to severe damage with more than 500 deaths, 1,833 injured and devastated 186,010 houses (National Disaster Mitigation Agency).Lombok Island is categories as a vulnerable to earthquake zone because located between the Eurasian and Indo-Australian subduction trenches and in the northern part of Lombok lies the Flores back-arc thrust.Lombok Island are also flanked by two strike slip fault system in the west and east side of the Island.Rinjani volcanic complex are also located in the northern side of Lombok.In this manuscript, the 2018 Lombok Earthquake from previous studies were reviewed.The seismic activity and vulnerability from previous study were discussed to make preventive effort and mitigation option in the future.

10.2991/978-94-6463-088-6_9

Cite

Citations (0)

Understanding of Shallow Structure in Mataram, Lombok, Indonesia by using High Frequency of Ambient Seismic Noise

AGU Fall Meeting Abstracts (2020)

Zulfakriza Zulfakriza Andri Dian Nugraha M. R. C. Harsuko Shindy Rosalia Achmad Fajar Narotama Sarjan

Ambient noise level

Source

Cite

Citations (0)

Modeling of subsurface structures in Telomoyo Volcano geothermal area, Magelang using 1-D magnetotelluric method

AIP conference proceedings (2017)

Achmad Fajar Narotama Sarjan Sintia Windhi Niasari

There are some of geothermal prospects around Java Island. One of them are located in Telomoyo Volcano area, Magelang, Central Java. The existence of hot spring manifestations in Telomoyo Volcano area shows the presence of geothermal system. The upflow zone of this geothermal system was formed in the caldera of Telomoyo Volcano area, while the outflow zone was formed around Candi Umbul. In addition, from the geological map shows a geological structure assumed as a normal fault with southwest-northeast orientation that was caused by the volcanic activity. The aim of this research is to give a brief introduction about subsurface resistivity beneath Telomoyo Volcano area using 1-D magnetotelluric forward model. Thus, we can determine the possibility of data that will obtained during the acquisition process based on the geological model that was made. The apparent resistivity, phase, and period values were obtained from the forward modeling process. The result from this study is a 1-D resistivity section with synthetics curves of each geothermal model. In each model the presence of clay cap characterized by a low resistivity layer. A layer below the clay cap with a medium resistivity value interpreted as the reservoir of this geothermal system. The heat source of this geothermal area is characterized by a low resistivity that is located at depth 4000-5500m. This study is still in progress to acquire the exact values of resistivity from each layer from the field data acquisition in Telomoyo Volcano area, Magelang.

Magnetotellurics

Caldera

Magma chamber

Geothermal exploration

Outflow

10.1063/1.4990930

Cite

Citations (1)

Analysis of H/V Ratio Curve to Estimate Seismic Hazard Vulnerability in Lombok Island, West Nusa Tenggara, Indonesia

Jurnal Geofisika (2020)

Muhammad Randy Caesario Harsuko Zulfakriza Zulfakriza Andri Dian Nugraha Muzli Muzli David P. Sahara

In 2018, Lombok Island was hit by a series of destructive earthquakes. According to Indonesian Meteo- rological, 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 Disaster Management reported about 555 deaths, 1,833 people injured, and 186,010 houses damaged as a result of Lombok earthquake on August 5th, 2018. A number of seismometers were placed on Lombok Island from August 3rd, 2018 to October 19th, 2018 to monitor the aftershock events. There are 17 stations that record seismicity in Lombok consisting of 10 broadband sensors and 7 short period sensors. In this study, we used the Horizontal-to-Vertical Spectral Ratio (HVSR) method to analyze the risk of earthquake in the Lombok region. The basic concept of this method is to do a comparison between the horizontal component spectrum and the vertical component spectrum of a wave, where theoretically the particle movement of the horizontal component is greater than the particle movement of the vertical component on soft ground, whereas on the hard ground both components (horizontal and vertical) will be similar. H/V curve obtained from earthquake record- ings (Earthquake Horizontal-to-Vertical Ratio/EHVR) and H/V curve obtained from microtremor recordings (Microtremor Horizontal-to-Vertical Ratio/MHVR) shows good agreement and high correlation. Empirical correction of EMR (Earthquake-to-Microtremor Ratio) managed to decrease the difference of estimation of predominant frequency and amplification factor between EHVR and MHVR. Predominant frequency, amplification, and seismic vulnerability map agree with the geological condition of Lombok Island, where high value of amplification and seismic vulnerability was found on soft and thick ground. This study conclude that the maximum ground acceleration and the construction of the building should also considered when one wants to investigate the effect of an earthquake to the damage occurred, beside the site effects.

Microtremor

Seismometer

10.36435/jgf.v18i1.432

Cite

Citations (1)

Seismic Attenuation Tomography From 2018 Lombok Earthquakes, Indonesia

Frontiers in Earth Science (2021)

Awali Priyono Andri Dian Nugraha Muzli Muzli Ardianto Ardianto Atin Nur Aulia

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 good t ∗ quality in at least four stations. Our results show that the two aftershock clusters northwest and northeast of Lombok Island have different attenuation characteristics. A low P-wave quality factor (low- Qp) , low P-wave velocity ( Vp) , and high ratio of P-wave velocity and S-wave velocity ( Vp / Vs) , which coincide with a shallower earthquake (<20 km) northwest of Lombok Island, might be associated with a brittle area of basal and imbricated faults influenced by high fluid content. At the same time, the high- Qp , low Vp , and low Vp / Vs , which coincide with a deeper earthquake (>20 km) northeast of Lombok Island, might be associated with an area that lacks fluid content. The difference in fluid content between the northwest and northeast regions might be the cause of the early generation of aftershocks in the northwest area. The significant earthquake that happened on August 5, 2018, took place in a region with moderate Qp , close to the contrast of high and low- Qp and high Vp , which suggests that the earthquake started in a strong material before triggering the shallower aftershocks occurring in an area affected by fluid content. We also identified an old intrusive body on the northeast flank of the Rinjani volcano, which was characterized by a high- Qp , high-velocity, and a high Bouguer anomaly.

Seismic Tomography

10.3389/feart.2021.639692

Cite

Citations (7)