2010 Jan 12 Haiti Earthquake

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Launched: January 29, 2010
Updated: January 31, 2010
Strong Motion Seismology Group

An earthquake of Mw 7.1 (Global CMT Project) occurred approximately 25 km west of Port-au-Prince, the capital of Haiti at 21:53:10 UTC on January 12, 2010. According to the USGS preliminary report, the event was located in the boundary region separating the Caribbean and North American plates. The northern Caribbean plate boundary near Haiti is dominant by left-lateral strike slip and compression accommodated by two principal surface faults: the Septentrional fault system and the Enriquillo-Plaintain Garden fault system, both of which are east-west trending strike slip fault systems. According to the focal mechanism ( Global CMT Project) and hypocenter location (USGS) the January 12 event corresponds to the left-lateral strike slip faulting on the Enriquillo-Plaintain Garden fault system. This event was a catastrophic earthquake that caused severe damage and casualties in the Port-au-Prince area. Nearly 170,000 people died and about three million people were affected by this event.

To investigate the source process of this earthquake, we have performed both the the moment tensor analysis and the finite fault inversion using the methods of Kikuchi and Kanamori (1982, 1991) and Kikuchi et al. (2003), and the teleseismic displacement records observed at FDSN stations from IRIS DMC. The 44 vertical components of the body-wave data at epicentral distances of 35-100 deg. were used in the inversion (Fig. 1). We fixed the epicenter at lat=18.457 N, lon=-72.533 E, as reported by USGS, and search for the focal depth to minimize the waveform fit. We used the result of the moment tensor analysis and the assumption that the earthquake was generated by the faulting on the Enriquillo-Plaintain Garden fault system with the east-west orientation to select the nodal plain for the finite fault inversion (strike=259.0 deg., dip=71.0 deg.). The fault size was assumed to be 40km x 25 km basing on the scaling relation for inland crustal earthquakes derived by Irikura and Miyake (2001). The rupture initiation point was assumed to be located at a depth of 12.5 km. (Fig. 2).

In the obtained slip distribution over the fault plane, we can find a single asperity. The peak slip of around 5.0 m appears on the upper part of the fault plane around and above the hypocenter. The total rupture duration is estimated to be 16 s. The results of the inversion are summarized in Fig. 3 and the surface projection of the obtained slip distribution is shown in the Fig. 4 together with the aftershocks and the location of the highly damaged city of the Port-au-Prince. According to these results, the fault slip propagated from the hypocenter in both the westward and eastward directions. However, the extension towards the east (towards the city of Port-au-Prince) is predominant (Fig. 4).

Fig.1. Stations used for the teleseismic waveform inversion.

Fig. 2. Distribution of aftershocks (orange dots) and location of the mainshock (red star).

The USGS updated location of the January 12, 2010 Haiti earthquake (red star). Orange circles correspond to aftershocks within the first 24 hours reported by USGS. The black rectangle corresponds to the fault plane assumed for the inversion.

Fig. 3. Source time function, point source solution, slip distribution, and comparison of the observed and synthetic displacement waveforms.

Fig. 4. Surface projection of the slip distribution superimposed on GEBCO08. The orange circles correspond to the aftershocks within the first 24 hours reported by USGS.

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