Microearthquake seismicity and focal mechanisms at the Rodriguez Triple Junction in the Indian Ocean using ocean bottom seismometers

Hypocenters and focal mechanisms of microearthquakes have been investigated at the Rodriguez Triple Junction in the Indian Ocean. Little was known on microearthquake activity in this region. We deployed 18 ocean bottom seismographs during the KH93-3 cruise of the R/V Hakuho-Maru (Ocean Research Institute, University of Tokyo) from July 30 to August 20, 1993. We obtained 579 well-constrained hypocenters and 13 focal mechanisms. Microearthquakes were found to be active along all of the three ridges: the Central Indian Ridge, the Southeastern Indian Ridge, and the Southwestern Indian Ridge. Especially at the triple junction there was an earthquake swarm within narrow area of approximately 15 × 5 km². All of the 13 focal mechanisms showed normal or strike-slip faultings, which means that the extensional stress field characterizes this region.