Crustal Structure and Fault Geometry of the 2010 Haiti Earthquake from Temporary Seismometer Deployments

Abstract

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 Léogâne 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 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. We use first-motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.Online Material: Tables of hypocenter locations and focal mechanisms, and Figure showing azimuthal variation with respect to travel-time residuals.

Crustal structure of western Hispaniola (Haiti) from a teleseismic receiver function study

“…The variability of the Moho depths we image in the Southern Peninsula may reflect the large differences in the LIP thickness identified in previous studies between the oceanic crust and the areas with more or less of underplated material (Diebold et al, 1981;Mauffret and Leroy, 1997;Leroy et al, 2000;Mauffret et al, 2001). In our results the mean Vp/Vs ratio is 1.80 ± 0.03, consistent with previous studies (Douilly et al, 2013) and the geology of the Southern Peninsula (Calmus, 1983;Bien-Aimé Momplaisir, 1986). The northern limit of the LIP crustal domain is given by the Moho depth calculated at the station LGNH (34.6 km; Fig.…”

“…In addition, Douilly et al (2013) provide a velocity model for the crust in the southern part of Haiti, and show that the mean Vp/Vs in this area is 1.80, which is typical for oceanic crust mafic rocks (Christensen, 1996). Velocity model and receiver functions studies made by Moreno et al (2002) and González et al (2012) show that the depth of the Moho is approximately 20 km in the south of Cuba.…”

“…Several geological field studies have led to a description of the shallow structure and stratigraphy of the island of Hispaniola (e.g., Mann et al, 1995;Pubellier et al, 2000). The Mw 7.0 2010 Haiti earthquake prompted several geological and geophysical studies to constrain the fault geometry and the crustal structure in the area of the mainshock (e.g., Douilly et al, 2013). However, our knowledge of the mid-and lower-crustal tectonics remains very limited in the absence of whole crustal geophysical studies in Haiti.…”

“…We estimate the depth of the shallow discontinuity easily visible in the RFs of the group b assuming that the upper crust has an average Vp of 5.8 km/s and an average Vp/Vs ratio of 1.77. These average properties are derived from the P velocity model in Haiti of Douilly et al (2013). This discontinuity is thus estimated at~9.7 km depth.…”

A more accurate relocation of the 2013 M s7.0 Lushan, Sichuan, China, earthquake sequence, and the seismogenic structure analysis

“…Chiarabba and Frepoli (1997) combined the VELEST and HYPOINVERSE methods to yield an improved velocity structure (VELEST) and performed a joint earthquake location (HYPOINVERSE) analysis for central and southern Italy. Douilly et al (2013) used the VELEST method to find the inverse velocity structure and obtain station corrections for the seismogenic zone of the 2010 Haiti earthquake, and then applied the HypoDD method to obtain more accurate earthquake locations for the Haiti sequence. Building from these studies, we adopt a combined earthquake relocation approach, consisting of several established methods that are employed in a stepwise process, with the goal of providing more precise relocations for the 2013 M s 7.0 Lushan earthquake sequence.…”