Kenta Ohara , Yuji Yagi, Ryo Okuwaki 

A large non-double-couple component of a tectonic earthquake indicates that its rupture likely was complex and likely involved multiple faults. Detailed source models of such earthquakes can add to our understanding of earthquake source complexity. The 2007 Martinique earthquake in the Caribbean Sea is one of the largest recent earthquakes with a known large non-double-couple component. It was an intermediate depth intraslab earthquake within the South America plate where it is subducting beneath the Caribbean plate. We applied potency density tensor inversion (PDTI) to teleseismic P waves generated by the 2007 Martinique earthquake to model its source processes and focal mechanism distribution. We identified two focal mechanisms: a strike-slip mechanism with a north–south T axis, and a down-dip extension (DDE) mechanism with an east–west T axis. Rupture by the DDE mechanism was predominant in the northern part of the source region and strike-slip rupture in the southern part. These two focal mechanisms had approximately parallel P axes and approximately orthogonal T axes. The seismic moments released by both types of rupture were almost equal. These results indicate that the 2007 Martinique earthquake had a large non-double-couple component. We identified five sub-events with two predominant directions of rupture propagation: two strike-slip sub-events propagated to the southeast and three DDE sub-events propagated to the east. Although the directions of propagation were consistent for each focal mechanism, each sub-event appears to have occurred in isolation. For example, the rupture of one DDE sub-event propagated from the edge of the source region back towards the hypocentre. Complex ruptures that include multiple sub-events may be influenced by high pore fluid pressure associated with slab dehydration. Our results show that PDTI can produce stable estimates of complex seismic source processes and provide useful information about the sources of complex intermediate depth intraslab earthquakes for which fault geometry assumptions are difficult.