A Comparison of 1-D S-wave Velocity Profile Resulting from Microtremor Array Method and Lithology Profile from Borehole Data in Jakarta

Abstract

The subsurface investigation is very important in seismic hazard assessment for the city scale because it greatly affects the propagation of seismic waves on the surface related to the amplification phenomenon caused by the thickness and hardness of the surface sediment. Local geology and geotechnical conditions for seismic hazard analysis are represented by site class which is determined based on the value of Vs30 or NSPT30, besides that it is also necessary to know the depth of the bedrock. In general, the availability of these data in the cities in Indonesia is very limited, so it is necessary to conduct a field survey which is one of the methods using the microtremor array survey method. This paper has presented the results of subsurface investigations in Kembangan Jakarta using the microtremor array method and their comparison with borehole data that was carried out at adjacent locations. The analysis results of those methods show a positive correlation between the 1-D shear wave velocity profile and lithology where the top layer has low S-wave velocity (Vs) correlated with soft rock. The S-wave velocity increases with depth which is correlated with hard rock that is indicated by lithology as hard sandstone. The results of this study are very useful for applying the array microtremor method in other cities considering it is very simple in operation.