Bedrock detection based on seismic interferometry using ambient noise in Singapore

The city-state of Singapore principally sits on granite bedrock known as the Bukit Timah formation. The Bukit Timah granite outcrops in the centre of Singapore, but it is buried below quaternary sediments known as the Old Alluvium formation in the east and north. Bedrock depth and faults in the shallow surface influence the stability of structures built above it, while the depth to bedrock constrains the water storage capacity and sub-soil water movement. Seismic methods are needed to image bedrock depth, however explosive methods are forbidden in the densely populated urban environment of Singapore. Passive seismic based on seismic interferometry is nondestructive and can provide us estimated detection depth. We apply the passive surface wave method based on seismic interferometry to the whole of Singapore island using a 1 month deployment of short-period nodes, to obtain the 3D velocity structure. We also obtain more detailed information in the Old Alluvium sediments by applying the MASW (multi-channel analysis of surface waves) method to linear geophone arrays. By analyzing the results from both tomography and MASW, we show that the granite bedrock beneath the Old Alluvium sediments is deeper than existing geological model suggests, which potentially increases the storage volume for fresh water in the deep underground acquifer.