Combination of Passive Seismic (HVSR) and Active Seismic (MASW) Methods to Obtain Shear Wave Velocity Model of Subsurface in Majalengka

Majalengka is a district in West Java which is located close to local faults and subduction zone, so that made this area has a high enough risk of earthquake hazards. Engineering Seismology Team of Meteorology Climatology and Geophysics Agency has been carried out microtremor and MASW survey in Majalengka. The combination of HVSR and MASW inversion methods is applied to obtain the value of the shear wave velocity (Vs), a combination of the two methods is expected to overcome the deficiency of each method. Results of the distribution of the value of the shear wave velocity can explain the subsurface conditions related to a vulnerability in the study area to seismic hazards. The results of HVSR and MASW inversion are 1-D (Vs) profiles at each measurement point, after that interpolated to obtain a 3-D Vs30 model. The results showed that Vs30 values in Majalengka District varied around 80 - 1500 m/s. Layers with low (Vs) values were relatively thick dominant in the north and northwest regions of the study area, soil types in this area were mostly composed of medium soils, a small part was composed of soft soil layers and rock layers. Therefore, in theory, the disaster in the north and northwest regions has a relatively higher vulnerability compared to other regions in Majalengka District. (paper)