Identification ground layer structure of land subsidence sensitive area in semarang city with horizontal to vertical spectral ratio method

Abstract

Semarang City is located in the northern coastal plain of Java which is geologically composed of alluvial deposits and the land subsidence sensitive area. The drilling data and various research indicates that not all layers of lithology are soft layers supporting the land subsidence. However, vertical distribution of the soft layer is still unclear. One the other side, an analysis regarding this kind of research can be done based on microtremor by using Horizontal to Vertical Spectral Ratio (HVSR). The goals of this research are to determine the layer which contribute to land subsidence based on Vs and Vp/Vs profile in Semarang City. Based Vs and Vp/Vs profile can be obtained some conclusion that the lithology layer with Vs less than 1000 meter/second and Vp/Vs less than 1.7 is the dominant lithology in high rate of land subsidence. Compare to drilling data, this lithology is composed by clay, silt and sandy clay that has the low bearing capacity.