Near-surface fault detection using high-resolution shear wave reflection seismics at the CO2CRC Otway Project site, Australia

High-resolution, near-surface, shear wave reflection seismic measurements were carried out in November 2013 at the CO2CRC Otway Project site, Victoria, Australia, with the aim to determine whether and, if so, where deeper faults reach the near subsurface. From a previous P wave 3-D reflection seismic data set that was concentrated on a reservoir at 2 km depth, we can only interpret faults up to 400m below sea level. For the future monitoring in the overburden of the CO2 reservoir it is important to know whether and how the faults continue in the subsurface. We prove that two regional fault zones do in fact reach the surface instead of dying out at depth. Individual first-break signatures in the shot gathers along the profiles support this interpretation. However, this finding does not imply perforce communication between the reservoir and the surface in the framework of CO2 injection. The shear wave seismic sections are complementary to existing P wave volumes. They image with high resolution (better than 3m vertically) different tectonic structures. Similar structures also outcrop on the southern coast of the Otway Basin. Both the seismic and the outcrops evidence the complex youngest structural history of the area.