Use of spatial autocorrelation of microtremor using L- and triangle- arrays for estimations of S-wave velocity model and soil response at ITS Surabaya

Institut Teknologi Sepuluh Nopember (ITS) Surabaya is geologically vulnerable to earthquake hazards. Therefore, preparedness is necessary to address emergencies and risks caused by earthquake at ITS Surabaya. In this study, dispersion curve were obtained through the analysis of microtremor data using the Spatial Autocorrelation (SPAC) method. Microtremor data acquisition was performed at the PLN ITS Futsal Field using L- and triangle-arrays. We successfully got dispersion curves from both arrays. The shear wave velocity (Vs) profile and the best model of Vs profile for each array were obtained by inverting the dispersion curves. By using a two-layer model, the first layer produces identical velocities with a depth of 5.44 meters for an L-array and 5.02 meters for a triangle array. In the second layer, the resulting velocities for each array have quite a difference. The best model of Vs profile for both arrays were used to analyse 1D soil response with a linear approach in the frequency domain. Parameters including Peak Ground Acceleration (PGA), 5% damped Pseudo Spectral Acceleration (PSA), and Fourier Amplitude Ratio (FAR) were obtained from the linear approach analysis that could describe the ground’s response to seismic waves. Vs influences the soil response, the higher the difference in Vs values of a layer with the layer below it (half-space), the higher the increase in PGA, PSA, and FAR.