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2013
Symithe, SJ, Calais E, Haase JS, Freed AM, Douilly R.  2013.  Coseismic slip distribution of the 2010 m 7.0 Haiti earthquake and resulting stress changes on regional faults. Bulletin of the Seismological Society of America. 103:2326-2343.   10.1785/0120120306   AbstractWebsite

The 12 January 2010 M-w 7.0 Haiti earthquake ruptured the previously unmapped Leogane fault, a secondary transpressional structure located close to the Enriquillo fault, the major fault system assumed to be the primary source of seismic hazard for southern Haiti. In the absence of a precise aftershock catalog, previous estimations of coseismic slip had to infer the rupture geometry from geodetic and/or seismological data. Here we use a catalog of precisely relocated aftershocks beginning one month after the event and covering the following 5 months to constrain the rupture geometry, estimate a slip distribution from an inversion of Global Positional Systems (GPS), Interferometric Synthetic Aperture Radar (InSAR) and coastal uplift data, and calculate the resulting changes of Coulomb failure stress on neighboring faults. The relocated aftershocks confirm a north-dipping structure consistent with the Leogane fault, as inferred from previous slip inversions, but with two subfaults, each corresponding to a major slip patch. The rupture increased Coulomb stresses on the shallow Enriquillo fault parallel to the Leogane rupture surface and to the west (Miragoane area) and east (Port-au-Prince). Results show that the cluster of reverse faulting earthquakes observed further to the west, coincident with the offshore Trois Baies fault, are triggered by an increase in Coulomb stress. Other major regional faults did not experience a significant change in stress. The increase of stress on faults such as the Enriquillo are a concern, as this could advance the timing of future events on this fault, still capable of magnitude 7 or greater earthquakes.

Douilly, R, Haase JS, Ellsworth WL, Bouin MP, Calais E, Symithe SJ, Armbruster JG, de Lepinay BM, Deschamps A, Mildor SL, Meremonte ME, Hough SE.  2013.  Crustal structure and fault geometry of the 2010 Haiti earthquake from temporary seismometer deployments. Bulletin of the Seismological Society of America. 103:2305-2325.   10.1785/0120120303   AbstractWebsite

Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 M-w 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Leogane fault, a north-dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean-bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Leogane fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first-motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.