Characteristics and Spatial Distribution of Vs30 Based on Microtremor Inversion and MASW Data through Landform Unit in Yogyakarta, Indonesia

The Yogyakarta region is located in the earthquake-prone areas of Indonesia. An earthquake hazard can be assessed by identifying the site conditions from Vs30 to estimate the potential amplification of ground shaking. Site conditions are affected by the earth surface relief and material composition. The landform is characterized by differences in geomorphological structures and processes, relief/topography, and material. This research aims to analyze the characteristics and spatial distribution of Vs30 based on MASW and microtremor inversion for each landform unit in the Yogyakarta region. We collected 545 microtremor and MASW responses from field measurements. Data inversion was performed to obtain a 1D Vs30 model and estimate the Vs30 value. The results are presented in the Vs30 spatial distribution map and site classification. They show that the value of Vs30 is varied in a range of 140 – 1092 m/s. The site classification ranges from SE to SB. The Vs30 value tends to be similar to the USGS model, except in the karst landform in the Gunungkidul area. Here, the site class ranges from SC to SB, while the USGS model ranges from SD to SC. Based on the landform analysis, the higher average values of Vs30 are for karst, followed by structural, denudational, volcanic, fluvial, marine, and aeolian landforms. This difference indicates that local conditions significantly affect the Vs30. The higher the elevation and the steeper the slope, the larger the Vs30 value. Moreover, the higher values of Vs30 are determined by harder and solid/consolidated material.