Southeast Indian Ocean-Ridge earthquake sequences from cross-correlation analysis of hydroacoustic data.

Parameters of earthquake sequences, for instance location and timing of foreshocks and aftershocks, are critical for understanding dynamics of mid-ocean ridge and transform faults. Whole sequences including small earthquakes in the ocean cannot be well recorded by land-based seismometers due to large epicentral distances. Recent hydroacoustic studies have demonstrated that T waves are very effective in detecting small submarine earthquakes because of little energy loss during propagation in Sound Fixing and Ranging channel. For example, an (2006 March 6, 40.11°S/78.49°E) transform-fault earthquake occurred at the Southeastern Indian Ocean Ridge, but National Earthquake Information Center only reported three aftershocks in the first following week. We applied cross-correlation method to hydroacoustic data from the International Monitoring System arrays in the Indian Ocean to examine the whole earthquake sequence. We detected 14 aftershocks and none foreshock for the earthquake and locations of these aftershocks show an irregular pattern. From the observation, we suggest that the feature could be caused by complicated transcurrent plate-boundary dynamics between two overlapped spreading ridges that is possibly explained by the bookshelf faulting model. [ABSTRACT FROM AUTHOR]