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Analysis of H/V Ratio Curve to Estimate Seismic Hazard Vulnerability in Lombok Island, West Nusa Tenggara, Indonesia Muhammad Randy Caesario Harsuko; Zulfakriza Z.; Andri Dian Nugraha; Muzli Muzli; David Prambudi Sahara; Nanang T Puspito; Yayan M Husni; Billy S Prabowo; Achmad Fajar Narotama Sarjan
Jurnal Geofisika Vol 18 No 1 (2020): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.36435/jgf.v18i1.432

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.

Seismicity Pattern of the Great Sumatran Fault System from Hypocenter Relocation of Regional Seismic Network Ade Surya Putra; Andri Dian Nugraha; David Prambudi Sahara; Zulfakriza Zulfakriza; Antonius Nanang Tyasbudi Puspito; Faiz Muttaqy; Pepen Supendi; Daryono Daryono
Indonesian Journal on Geoscience Vol 10, No 1 (2023)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.10.1.83-95

The seismicity pattern along the Great Sumatran Fault (GSF) was analyzed during April 2009 - December 2017 period with magnitude of >3.0 and depth of < 30 km. Of 752 preliminary absolute locations, 695 were successfully relocated using double-difference method to provide an improved view of seismicity, sharpening locations and interpretations of seismogenic features throughout the region. The relocation results depict a pattern of significant increase on small to intermediate earthquakes occurring in a shallow part of northern Sumatra, i.e. the Aceh and Seulimeum segments, as well as in central Sumatra, i.e. the Toru and Barumun. This increase was interpreted due to indications of creeping that reduce or prevent stress build-up on these segments. Meanwhile, few segments, i.e. the Tripa segment in the northern part, then Suliti and Siulak segments in the central part, and Manna segment in the southern part of Sumatra show the least activities over the period. These segments were identified as lock asperity, which caused accumulating stress that could be released as an earthquake. The behaviour of these locking segments can be related to the seismic gap along the GSF which has not experienced major earthquakes (M>7) since 2000, making the densely populated area around these segments potentially have a great seismic hazard in the future.

Reducing Numerical Dispersion with High-Order Finite Difference to Increase Seismic Wave Energy: - Syamsurizal Rizal; Awali Priyono; Andri Dian Nugraha; Mochamad Apri; Mochamad Agus Moelyadi; David Prambudi Sahara
Journal of Engineering and Technological Sciences Vol. 55 No. 4 (2023)
Publisher : Directorate for Research and Community Services, Institut Teknologi Bandung

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.eng.technol.sci.2023.55.4.5

The numerical dispersion of 2D acoustic wave modeling has become an interesting subject in wave modeling in producing better subsurface images. Numerical dispersion is often caused by error accumulation with increased grid size in wave modeling. Wave modeling with high-order finite differences was carried out to reduce the numerical error. This study focused on variations in the numerical order to suppress the dispersion due to numerical errors. The wave equation used in modeling was discretized to higher orders for the spatial term, while the time term was discretized up to the second order, with every layer unabsorbed. The results showed that high-order FD was effective in reducing numerical dispersion. Thus, subsurface layers could be distinguished and observed clearly. However, from the modeling results, the wave energy decreased with increasing distance, so the layer interfaces were unclear. To increase the wave energy, we propose a new source in modeling. Furthermore, to reduce the computational time we propose a proportional grid after numerical dispersion has disappeared. This method can effectively increase the energy of reflected and transmitted waves at a certain depth. The results also showed that the computational time of high-order FD is relatively low, so this method can be used in solving dispersion problems.

Seismicity Pattern of the Great Sumatran Fault System from Hypocenter Relocation of Regional Seismic Network Ade Surya Putra; Andri Dian Nugraha; David Prambudi Sahara; Zulfakriza Zulfakriza; Antonius Nanang Tyasbudi Puspito; Faiz Muttaqy; Pepen Supendi; Daryono Daryono
Indonesian Journal on Geoscience Vol. 10 No. 1 (2023)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.10.1.83-95

The seismicity pattern along the Great Sumatran Fault (GSF) was analyzed during April 2009 - December 2017 period with magnitude of >3.0 and depth of < 30 km. Of 752 preliminary absolute locations, 695 were successfully relocated using double-difference method to provide an improved view of seismicity, sharpening locations and interpretations of seismogenic features throughout the region. The relocation results depict a pattern of significant increase on small to intermediate earthquakes occurring in a shallow part of northern Sumatra, i.e. the Aceh and Seulimeum segments, as well as in central Sumatra, i.e. the Toru and Barumun. This increase was interpreted due to indications of creeping that reduce or prevent stress build-up on these segments. Meanwhile, few segments, i.e. the Tripa segment in the northern part, then Suliti and Siulak segments in the central part, and Manna segment in the southern part of Sumatra show the least activities over the period. These segments were identified as lock asperity, which caused accumulating stress that could be released as an earthquake. The behaviour of these locking segments can be related to the seismic gap along the GSF which has not experienced major earthquakes (M>7) since 2000, making the densely populated area around these segments potentially have a great seismic hazard in the future.

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