Geophysics and Tectonics Seminar winter-2019

The 2010 M7.0 Haiti earthquake was the first major earthquake in southern Haiti in 250 years. As this event could represent the beginning of a new period of active seismicity in the region, and in consideration of how vulnerable the population is to earthquake damage, it is important to understand the nature of this event and how it has influenced seismic hazards in the region. Most significantly, geodetic data showed that the 2010 earthquake occurred on the secondary Léogâne thrust fault (two fault segments), not the Enriquillo Fault, the major strike-slip fault in the region, despite it being only a few kilometers away. Following the earthquake, several groups had installed temporary seismic stations to record aftershocks and we used this combined dataset to clearly delineate the Léogâne 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. Using this dataset, we also investigated a detailed 3D crustal structure of this region. Our results showed a pronounced low velocity zone across the Léogâne fault, which is consistent with the sedimentary basin location from the geologic map. We also observed a southeast low velocity zone, which is consistent with a predefined structure in the morphology. In addition, we used a finite element model to simulate scenarios of the 2010 Haiti earthquake to understand why the rupture did not jump to the nearby Enriquillo fault. Our model successfully replicated rupture propagation along the two segments of the Léogâne fault, and indicated that a significant increase in stress had occurred on the top and to the west of the Enriquillo fault. These work provide information that can be used in future studies focusing on how changes in material properties can affect rupture propagation, which is useful to assess the seismic hazard that Haiti is currently facing.