Large Active Faults and the Wharton Basin Intraplate Earthquakes in the Eastern Indian Ocean

In recent years, great earthquakes occurred within the Wharton Basin in the eastern Indian Ocean, and they have been associated with active faulting on the ancient oceanic crust. Large seismogenic faults were thought to be the fault reactivation on the ancient oceanic crust, but these phenomena are still unclear and require examination. This study used high-quality multibeam bathymetry and multichannel seismic data collected over the northern Ninetyeast Ridge to investigate detailed fault geometry, structure, and activity. We recognized 12 large linear active faults by integrating bathymetry maps and multichannel seismic reflection profiles. Our results showed that these faults have high angles, and they all displaced the basement and propagated to the seafloor with distinct fault scarps. They trended NWW-SEE with a spacing of 10 – 40 km and were parallel to each other and the nearby subfault of the 2012 great intraplate earthquake, suggesting similar stress fields. These faults are also in agreement with the orientations of magnetic isochrons, implying their formation by seafloor spreading. Furthermore, regarding the strike-slip focal mechanism of 2012 earthquakes, we proposed that these faults were created early by a normal spreading process and then evolved into a strike-slip pattern since the ancient oceanic crust approached the subduction zones.