Bedrock Depth Mapping using a Three-Dimensional Ambient Noise Tomography at Northern Singapore Island

Abstract

Summary A three-dimensional ambient noise tomography was applied to bedrock depth mapping at northern Singapore Island. Measurements were carried out over a survey footprint of approximately 700 x 400 m. Eighty cableless (nodal) seismograph units with vertical component 2 Hz geophones were deployed with a receiver spacing of 7 m. Total number of receiver locations are 3474. The GPS clock permits units to be synchronized over any distance without cables. Seismic ambient noise was recorded using a receiver spacing small enough to avoid spatial aliasing. A common midpoint spatial autocorrelation (CMP-SPAC) method was used to process ambient noise and 3D S-wave velocity (Vs) model to a depth of 60 m was obtained. We compared the resultant Vs model with 38 boring logs and summarized a relationship between Vs and depth at the top of the bedrock (GII). The Vs at the top of the bedrock linearly increased with depth and we defined the Vs of the bedrock as a function of depth. A depth to the bedrock ranges between 10 m and 60 m. The resultant Vs model and extracted bedrock depth is consistent with borehole logs. This paper summarizes, the site of investigation, data acquisition, processing and investigation results.