Shallow S-wave Velocity Profile Estimation using Surface Velocity and Microtremor HVSR with a Linear Velocity Increase Approach

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

Shallow S-wave Velocity Profile Estimation using Surface Velocity and Microtremor HVSR with a Linear Velocity Increase Approach

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

Estimation of SH-Wave Amplification in the Bandung Basin Using Haskellâs Method

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\u27s Method

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\u27s 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

Development of an Inversion Method for Low Velocity Medium

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

Source Processes of the March 2007 Singkarak Earthquakes Inferred from Teleseismic Data

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

Estimation of S-wave Velocity Structures by Using Microtremor Array Measurements for Subsurface Modeling in Jakarta

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)

Seismologi

Buku seimologi ini adalah buku pertama yang berbahasa Indonesia untuk memenuhi kebutuhan buku acuan dasar bagi tingkat sarjana dan pascasarjana perguruan tinggi. Selain untuk para mahasiswa, buku ini juga bisa dijadikan acuan dasar bagi para seismologis di luar kampus. Buku ini bersifat dasar, pendahuluan atau pengenalan. Tentu saja lebih sederhana dibandingkan dengan referensi-referensi yang dipakai. Oleh karena itu, rumus matematika tidak diturunkan secara rinci. Bagi pembaca yang ingin lebih tahu tentang rinciannya, bisa membaca lebih rinci pada buku-buku referensi. Pengertian-pengertian dasar tentang gelombang seismik, mekanisme fokus, ukuran kekuatan gempa (magnitudo, energi, dan intensitas) menjadi hal yang pokok dalam buku ini. Selain itu, ditekankan juga teknik-teknik dasar dalam beberapa hal seperti pembuatan mekanisme fokus, penentuan episenter dan lain-lain

Seismologi

Buku seismologi ini adalah buku pertama yang berbahasa indonesia untuk memenuhi kebutuhan buku acuan dasar bagi tingkat sarjana dan mungkin bisa untuk pascasarjana perguruan tinggi. Selain untuk para mahasiswa, buku ini juga bisa dijadikan acuan dasar bagi para seimologis diluar kampus. acuan dasar di atas berarti buku ini bersifat dasar, pendahuluan atau pengenalan. Tentu saja lebih sederhana lagi dibandingkan dengan referensi-referensi yang dipakai. Oleh karena itu, rumus matematika tidak diturunkan secara rinci, bahkan ada rumus jadinya saja dan lebih ditekankan pada penggunaannya. Bagi pembaca yang ingin lebih tahu tentang rinciannya, bisa membaca lebih rinci pada buku-buku referensi. pengeritan-pengertian dasar tentang gelombang seismik, mekanisme fokus, ukuran kekuatan gempa (magnitudo, energi, dan intensitas) menjadi hal yang pokok dalam buku ini. Selain itu, ditekankan juga teknik-teknik dasar dalam beberapa hal seperti pembuatan mekanisme fokus, penentuan episenter, dan lain-lain