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All Journal IJOG : Indonesian Journal on Geoscience Journal of Mathematical and Fundamental Sciences Journal of Engineering and Technological Sciences Jurnal Geologi dan Sumberdaya Mineral (Journal of Geology and Mineral Resources) Jurnal Geofisika Indonesian Journal on Geoscience Indonesian Journal on Geoscience Jurnal Geologi dan Sumberdaya Mineral (Journal of Geology and Mineral Resources) Jurnal Meteorologi dan Geofisika
Afnimar
Faculty Of Mining And Petroleum Engineering, Institut Teknologi Bandung,
Astronomy Chemistry Earth & Planetary Sciences Education Energy Engineering Environmental Science Mathematics Physics

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Estimation of SH-Wave Amplification in the Bandung Basin Using Haskell’s Method Afnimar, A.
Journal of Engineering and Technological Sciences Vol 46, No 1 (2014)
Publisher : ITB Journal Publisher, LPPM ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (414.286 KB) | DOI: 10.5614/j.eng.technol.sci.2014.46.1.6

Abstract

The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell’s method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks.
MIKROZONASI BAHAYA GEMPA BUMI DI WILAYAH KOTA BANDUNG BERDASARKAN DATA MIKROTREMOR Marjiyono, Marjiyono; Afnimar, Afnimar
Jurnal Geologi dan Sumberdaya Mineral Vol 21, No 1 (2011): Jurnal Sumber Daya Geologi
Publisher : Pusat Survei Geologi

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (220.942 KB)

Abstract

Bandung is one of the metropolitan city which rapidly developed and tectonically located in the vicinity of active tectonic lines. The surface geology condition of this region vary from very soft sediments to hard volcanic rocks. The soft sediment area has potential to experience amplification when an earthquake occure. Characterization of surface geology is necessary to identify vulnerability level in order to mitigate the earthquakes hazard in this region. In this regard, we have conducted microtremor measurements in 97 sites which are spread throughout the city of Bandung. Data processing is based on the Nakamura method (HVSR) to obtain the value of amplification factor. The results show the value of amplification factor ranged from 2.1 to 17, with the highest amplification factor distribution in the southeastern of the research area. Distribution of this very high amplification factors are broadly corresponded with lacustrine sediment (lake sediment). The amplification factor scores were then used as the basis in determining the level of relative vulnerability to earthquake hazards.Keywords : microtremor, effect of surface geology, amplification factor, Nakamura methods.
The Drop of Relative Velocity Variation and Coherence Values Prior to Sinabung 2013 Eruptions Suparman, Yasa; Afnimar, Afnimar; Syahbana, Devy Kamil
Indonesian Journal on Geoscience Vol 8, No 1 (2021)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (901.025 KB) | DOI: 10.17014/ijog.8.1.109-117

Abstract

DOI: 10.17014/ijog.8.1.109-117The cross-correlations of ambient seismic noise at Sinabung Volcano were analyzed from February 2013 to February 2014. Many eruptions occurred during these periods, started on 15 September 2013. Looking at the variations in the coda of the correlations, two types of measurements can be distinguished associated to two types of changes: relative velocity variation and waveform decoherence. The drop of relative velocity variations and waveform decoherence were observed for each station pair of Sinabung one to two months before the first eruption. These changes in accordance to the deformation of the Sinabung edifice were estimated from geodetic measurements, since an analysis of baseline change between GPS stations indicated an inflation of the volcanic edifice prior to September 2013 eruption. The monitoring of relative velocity variations and decoherence provides insights into the ongoing processes in the volcanic edifice to assist in determining the level of volcanic activity.
The Drop of Relative Velocity Variation and Coherence Values Prior to Sinabung 2013 Eruptions Suparman, Yasa; Afnimar, Afnimar; Syahbana, Devy Kamil
Indonesian Journal on Geoscience Vol 8, No 1 (2021)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.8.1.109-117

Abstract

DOI: 10.17014/ijog.8.1.109-117The cross-correlations of ambient seismic noise at Sinabung Volcano were analyzed from February 2013 to February 2014. Many eruptions occurred during these periods, started on 15 September 2013. Looking at the variations in the coda of the correlations, two types of measurements can be distinguished associated to two types of changes: relative velocity variation and waveform decoherence. The drop of relative velocity variations and waveform decoherence were observed for each station pair of Sinabung one to two months before the first eruption. These changes in accordance to the deformation of the Sinabung edifice were estimated from geodetic measurements, since an analysis of baseline change between GPS stations indicated an inflation of the volcanic edifice prior to September 2013 eruption. The monitoring of relative velocity variations and decoherence provides insights into the ongoing processes in the volcanic edifice to assist in determining the level of volcanic activity.
Estimation of SH-Wave Amplification in the Bandung Basin Using Haskell’s Method A. Afnimar
Journal of Engineering and Technological Sciences Vol. 46 No. 1 (2014)
Publisher : Institute 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.2014.46.1.6

Abstract

The Bandung basin is a large basin in Indonesia surrounded by mountains that are associated with faults. There is the possibility of earthquakes generated by these faults shaking populated areas in the basin. The consequences will be worse because the shaking is amplified by the sediment layer of the basin. We have estimated the amplification of SH-waves generated by the Lembang fault using Haskell's method for multilayer models. The pattern of amplification is a decreasing value with increasing distance from the Lembang fault. This pattern is valid for low-frequency incident waves. For higher-frequency incident waves, the pattern looks more complicated. Fortunately, there are many areas with low amplification values. Hopefully, this result will help the local government in making decisions regarding construction planning in this region. Of course, the final objective is to reduce earthquake risks.
The Drop of Relative Velocity Variation and Coherence Values Prior to Sinabung 2013 Eruptions Yasa Suparman; Afnimar Afnimar; Devy Kamil Syahbana
Indonesian Journal on Geoscience Vol 8, No 1 (2021)
Publisher : Geological Agency

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.17014/ijog.8.1.109-117

Abstract

DOI: 10.17014/ijog.8.1.109-117The cross-correlations of ambient seismic noise at Sinabung Volcano were analyzed from February 2013 to February 2014. Many eruptions occurred during these periods, started on 15 September 2013. Looking at the variations in the coda of the correlations, two types of measurements can be distinguished associated to two types of changes: relative velocity variation and waveform decoherence. The drop of relative velocity variations and waveform decoherence were observed for each station pair of Sinabung one to two months before the first eruption. These changes in accordance to the deformation of the Sinabung edifice were estimated from geodetic measurements, since an analysis of baseline change between GPS stations indicated an inflation of the volcanic edifice prior to September 2013 eruption. The monitoring of relative velocity variations and decoherence provides insights into the ongoing processes in the volcanic edifice to assist in determining the level of volcanic activity.
Estimation of S-wave Velocity Structures by Using Microtremor Array Measurements for Subsurface Modeling in Jakarta Mohamad Ridwan; A. Afnimar; Sri Widiyantoro; Masyhur Irsyam; Hiroaki Yamanaka
Journal of Mathematical and Fundamental Sciences Vol. 46 No. 3 (2014)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2014.46.3.9

Abstract

Jakarta  is located on  a  thick sedimentary  layer that  potentially has a very  high  seismic  wave  amplification.  However,  the  available information concerning the  subsurface model and bedrock depth  is insufficient  for a seismic hazard  analysis.  In  this  study,  a  microtremor  array  method  was  applied  to estimate the geometry and S-wave velocity of the sedimentary layer. The spatial autocorrelation  (SPAC)  method  was  applied  to  estimate  the  dispersion  curve, while  the S-wave  velocity  was  estimated  using  a  genetic  algorithm  approach. The  analysis  of  the  1D  and  2D  S-wave  velocity  profiles  shows  that  along  a north-south  line,  the  sedimentary  layer  is  thicker  towards  the  north.  It  has  a positive  correlation  with  a  geological  cross section  derived  from  a borehole down to  a depth of  about 300 m. The SPT data from  the  BMKG site  were used to  verify  the  1D  S-wave  velocity  profile.  They  show  a  good agreement. The microtremor analysis  reached  the engineering bedrock  in a  range from 359  to 608  m  as  depicted by a  cross section  in  the  north-south  direction. The site class was also estimated at each site, based on the average S-wave velocity until 30 m depth. The sites UI to ISTN belong to class  D (medium soil),  while BMKG and ANCL belong to class E (soft soil).
Development of an Inversion Method for Low Velocity Medium A. Afnimar; Andri Dian Nugraha; Ahmad Syahputra
Journal of Mathematical and Fundamental Sciences Vol. 45 No. 1 (2013)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2013.45.1.8

Abstract

The main problem with the inversion of a low velocity medium is the application of an appropriate ray tracing method after choosing a suitable model parameterization. Block parameterization is not suitable, because it is not capable of representing the velocity model well. A large amount of blocks with a small grid size are needed to express the model well, but in that case, a ray coverage problem will be encountered. A knot-point parameterization model is better suited than a block model, because it can express the velocity model well, while the number of variables is much smaller. Ray calculation using the pseudo-bending method is not appropriate for the velocity model because of an instability problem at high velocity gradients. The crucial problem of this method involves the initial ray-path that is optimized in order to obtain the "true" ray, but does not satisfy the Fermat principle. These problems can be solved by applying the eikonal-solver method, because this can handle high-velocity gradients and does not need an initial ray path. Using a suitable model parameterization and appropriate ray tracing method, the inversion can obtain good results that fit the desired output. Applying a block model and the pseudo-bending method will not produce the desired output.
Characteristics of Earthquake-Generated Tsunamis in Indonesia Based on Source Parameter Analysis Sugeng Pribadi; A. Afnimar; Nanang T. Puspito; Gunawan Ibrahim
Journal of Mathematical and Fundamental Sciences Vol. 45 No. 2 (2013)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2013.45.2.8

Abstract

We have characterized 27 earthquake-generated tsunamis from 1991 to 2012 in Indonesia, based on source parameter analysis. This includes the focal mechanism derived by W phase inversion analysis, the ratio (Θ) between the seismic energy (E) and the seismic moment (Mo), the moment magnitude (Mw), the rupture duration (To) and the distance of the hypocenter to the trench. Most of the earthquakes (24 events) were tsunamigenic earthquakes with various fault types, a shallow focal depth (12 km ≤ D ≤ 77.8 km), a small to large magnitude (6.6 ≤ Mw ≤ 9.0), a low ratio of seismic energy to seismic moment (-5.8 < Θ < -4.9), a short to long rupture duration (27 s ≤ To ≤ 257 s), a small to large tsunami height (0.1 m ≤ H ≤ 50.9 m) and a short to long distance from the hypocenter to the trench (10 km < HT ≤ 230 km). Three tsunami earthquakes were characterized by a thrust fault mechanism, a very shallow depth (D ≤ 20 km), a moderate magnitude (7.5 ≤ Mw ≤ 7.8), a very low ratio of seismic energy to seismic moment (Θ ≤ -5.8), a long rupture duration (99 s ≤ To ≤ 135 s), a large tsunami height (7.4 m ≤ H ≤ 14 m) and a short distance from the hypocenter to the trench (HT ≤ 20 km).
Source Processes of the March 2007 Singkarak Earthquakes Inferred from Teleseismic Data A. Afnimar; Reiji Kobayashi; Danny Hilman Natawidjaja
Journal of Mathematical and Fundamental Sciences Vol. 46 No. 2 (2014)
Publisher : Institute for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2014.46.2.4

Abstract

The rupture processes of two sequentialearthquakes have been inverted from teleseismic data. The first event released a total seismic moment of 7.9×1018 Nm (Mw 6.5) and the slip distribution shows three asperities, 1.5 m at the shallowside, 0.7 m at the rightsouth-east deep side and 0.5 m atthe north-west deep side. The second event had one asperity with 1.7 m slip and released a seismic moment of 7.5×1018 Nm (Mw 6.5). In both cases, maximum slip occurred above the hypocenter which was responsible for the surface displacement pattern.
Co-Authors Ahmad Syahputra Aji Suteja Andi Muhamad Pramatadie Andri Dian Nugraha Danny Hilman Natawidjaja Devy Kamil Syahbana Gunawan Ibrahim Hiroaki Yamanaka Hiroaki Yamanaka Iman Fatchurochman Indra Gunawan M. Ramdhan M. Taufik Gunawan Marjiyono Marjiyono Marjiyono Marjiyono, Marjiyono Masyhur Irsyam Mohamad Ridwan Muhammad Fahmi Nugraha mutiah, siti Nanang T. Puspito Nova Heryandoko Rahmat Setyo Yuliatmoko Reiji Kobayashi Santia Ardi M Sri Widiyantoro Sugeng Pribadi Suparman, Yasa Syahbana, Devy Kamil Wawan Gunawan, A.K Yasa Suparman