High-resolution back-projection at regional distance: application to the Haiti

9 A catastrophic Mw 7 earthquake ruptured on January 12th 2010 on a complex fault 10 system near Port-au-Prince, Haiti. Offshore rupture is suggested by aftershock 11 locations and marine geophysics studies but its extent remains difficult to define using 12 geodetic and teleseismic observations. Here we perform the multi-taper MUSIC 13 analysis, a high-resolution array technique, at regional distance with recordings from 14 the Venezuela National Seismic Network to resolve high frequency (about 0.4 Hz) 15 aspects of the earthquake process. Our results indicate westward rupture with two 16 subevents, roughly 35 km apart. In comparison, a lower frequency finite source 17 inversion, with fault geometry based on new geologic and aftershock data, shows two 18 slip patches with centroids 21 km apart. Apparent source time functions from 19 USArray further constrain the inter-subevent time delay, implying a rupture speed of 20 3.3 km/s. The tips of the slip zones coincide with subevents imaged by back21 projections. The different subevent locations found by back-projection and source 22 inversion suggest spatial complementarity between high and low frequency source 23 radiation, consistent with high frequency radiation originating from rupture arrest 24 phases at the edges of main slip areas. The CMT solution and a geodetic-only 25 inversion have similar moment, indicating most of the moment released is captured by 26 geodetic observations, and no additional rupture is required beyond where it is imaged 27 in our preferred model. Our results demonstrate the contribution of back-projections 28 of regional seismic array data for earthquakes down to M≈7, especially when 29 incomplete coverage of seismic and geodetic data imply large uncertainties in source 30 inversions. 31