Article Per Year (5 Year)
p-Index From 2021 - 2026
0.23
P-Index
This Author published in this journals
All Journal Journal of Mathematical and Fundamental Sciences Journal of Engineering and Technological Sciences Jurnal Geofisika
A. Afnimar
Faculty Of Mining And Petroleum Engineering, Institut Teknologi Bandung,
Astronomy Chemistry Earth & Planetary Sciences Energy Engineering Mathematics Physics

Published : 6 Documents Claim Missing Document
Claim Missing Document
Check
Articles

Found 6 Documents
Search

 1 
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.
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.
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).
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).
Stress Drop Variation di Sumatra Rahmat Setyo Yuliatmoko; Afnimar Afnimar; Indra Gunawan
Jurnal Geofisika Vol 15 No 3 (2017): Jurnal Geofisika
Publisher : Himpunan Ahli Geofisika Indonesia (HAGI)

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1512.952 KB) | DOI: 10.36435/jgf.v15i1.14

Abstract

Sumatera merupakan daerah dengan kondisi tektonik yang rumit dimana terjadi konvergensi lempeng India terhadap lempeng Eurasia dan terdapat beberapa sesar aktif. Untuk melihat keaktifan daerah Sumatera penulis menghitung stress drop di Sumatera dan membahas bagaimana kaitanya dengan tektonik secara regional. Stress drop diperoleh dengan menganalisis spektrum displacement observasi menggunakan metode inversi nonlinier Nelder Mead Simplex. Dari penelitian ini didapatkan bahwa stress drop pada daerah crustal segment Siulak menghasilkan nilai terbesar yaitu 39.26 Mpa dikarenakan daerah tersebut memiliki slip rate yang kecil jika dibandingkan dengan segment lainnya di Sumatera. Zona Ninety East Ridge menghasilkan nilai stress drop yang kecil 2.6 - 4.3 Mpa dikarenakan daerah ini merupakan daerah rekahan serta patahan. Daerah accretional wedge menghasilkan nilai stress drop tinggi 20.65 Mpa, merupakan lapisan sedimen tebal sehingga mampu menahan stress. Zona Forearc basin menghasilkan nilai stress drop kecil 0.49 Mpa karena merupakan lapisan sedimen yang mudah mengalami deformasi. Stress drop di Sumatera dipengaruhi oleh tipe tektonik, material batuan, serta slip rate masing-masing region di Sumatera.
Shallow S-wave Velocity Profile Estimation using Surface Velocity and Microtremor HVSR with a Linear Velocity Increase Approach Andi Muhamad Pramatadie; Hiroaki Yamanaka; Afnimar Afnimar
Journal of Mathematical and Fundamental Sciences Vol. 54 No. 3 (2023)
Publisher : Directorate for Research and Community Services (LPPM) ITB

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.5614/j.math.fund.sci.2023.54.3.4

Abstract

We propose a simple method for 1D S-wave velocity (Vs) profile estimation using a measured surface S-wave velocity (V1) and peak frequency of the observed microtremor horizontal-to-vertical spectral ratio (HVSR). In this method, the S-wave velocity profile is presented as linear velocity increase with depth in sediments over a bedrock layer that has a given constant S-wave velocity. Thus, the profile can be parameterized with the measured surface S-wave velocity and the velocity gradient. The gradient can be estimated based on the agreement of the peak frequencies of the observed microtremor HVSR and the theoretical ellipticity of the fundamental mode of the Rayleigh wave. We examined the applicability of the proposed method using numerical tests as well as application to actual data at five sites in the Bandung Basin, Indonesia, where observed Rayleigh wave phase velocities from microtremor array surveys were available. The applicability was confirmed in numerical tests using sample models of soil profiles in the basin. Actual application indicated the appropriateness of the estimated S-wave velocity profiles due to the similarity of their theoretical Rayleigh wave phase velocities with the observed Rayleigh wave phase velocities. Since the proposed method needs prior confirmation of the linear increase of the S-wave velocity, it is suitable for use in spatial interpolation of shallow S-wave velocity profiles with simple data acquisition.
Co-Authors Andi Muhamad Pramatadie Gunawan Ibrahim Hiroaki Yamanaka Hiroaki Yamanaka Indra Gunawan Masyhur Irsyam Mohamad Ridwan Nanang T. Puspito Rahmat Setyo Yuliatmoko Sri Widiyantoro Sugeng Pribadi