INTRAPLATE THRUST EARTHQUAKE IN THE SOUTH CHINA SEA

To investigate the state of stress in marginal seas, we have studied the October 7, 1965 (mb = 5.9, MS = 5.6), earthquake in the center of the South China Sea. This is one of the largest events in the interior of a marginal sea since the installation of the World-Wide Standard Seismograph Network. Using body and surface wave analysis, the focal mechanism is found to be almost pure thrust faulting at a very shallow depth (about 5km) with a seismic moment of 1 x 1025 dyn cm. The mechanism indicates horizontal compression oriented N38oE. Since this event does not occur on a bathymetric feature, its mechanism may indicate the overall state of stress in the South China Sea.-Authors