eric calais, andrew freed, purdue univ. usa
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The January 12, 2010, Mw 7.0 earthquake in Haiti: Context and mechanism from an integrated geodetic study. Eric Calais, Andrew Freed, Purdue Univ. USA Claude Prépetit , D. Anglade , M. Saint Louis, J. Altidor , J. Macly , Bureau of Mines and Energy, Haiti - PowerPoint PPT PresentationTRANSCRIPT
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• NE Caribbean and Hispaniola = major plate boundary, 2 cm/yr relative motion
• Strike-slip + convergence partitioned between 3 major fault systems
• Apparent low level of seismic activity in Haiti in past ~40 years.
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Hispaniola has been the locus of major historical earthquakes(locations poorly constrained until 1946)
Ali et al., 2008
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Interseismic GPS measurements show left-lateral shear (~18 mm/yr) + plate boundary-normal shortening (~5 mm/yr)
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Interseismic GPS velocities + block modeling => slip rates on major active faults (e.g. Manaker et al., 2008)
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• Enriquillo fault = 6 mm/an• Last major earthquake = 250 years• Accumulated slip deficit = 6 x 250 = 1.5 m• Potential for Mw=7.1
• Septentrional fault = 12+-2 mm/an• Last major earthquake in DR = 770-960 years• Accumulated slip deficit = 7-13 m• Potentiel pour Mw=7.7-8.1
Inferred slip rates provide the starting point for earthquake scenarios
Wells and Coppersmith, 1994 Wells and Coppersmith, 1994
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Mann et al, 1995
Enriquillo fault = major left-lateral strike-slip fault, vertical to high-angle south-dipping
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Prompt post-event GPS response show coseismic ground displacements: 0.8 m (near field), measurable up to ~150 km away
Coseismic pattern combines strike-slip + shortening
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Topography of the Port-au-Prince (PaP),Greissier (G), Leogane (L) area
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Surface trace of the Décrochement Sénestre Sud Haitien = Enriquillo-Plantain Garden fault
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Radar interferogram 03/09/2009 – 01/25/2010each fringe = 0.2 m of displacement in ground-satellite direction
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GPS coseismic displacements superimposed…
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The joint inversion of GPS and InSAR for a single fault geometry requires a 30 km long fault dipping 60o north, slightly oblique to the Enriquillo
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The inversion of geodetic data indicates up to 5 m of slip between depths of ~20 and 5 km, with two main patches
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This single fault model does not require slip on the Enriquillo fault and indicates that fault different from the Enriquillo was activated
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The single fault model implies that moment release was partitioned between 62% by strike-slip, 38 % dip-slip thrust
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De Lepinay et al (OBS deployment - triangles), see also Nettles and S.Hjorleifsdottir, LDEO
Aftershock studies indicate (1) locations north of the EPGFZ, (2) pure reverse faulting mechanisms on WNW-ESE trending faults
White circles = USGS PDEsColor circles = relocated aftershocksTriangles = seismic stations (OBS + onland)
White circles = USGS PDEsColor circles = relocated aftershocksTriangles = seismic stations (OBS + onland)
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Changes in Coulomb failure stresses
(aftershock locations from NRCan)
Depth = 10 km, apparent friction = 0.8, receiver faults with strike=130, dip=60,
and pure reverse motion
Depth = 10 km, apparent friction = 0.2, receiver faults with strike=85, dip=90,
and pure left-lateral motion
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Conclusions• The Mw 7.0, January 12, Haiti earthquake did not come
as a surprise:– Magnitude consistent with strain accumulation rate and
past events– Source mechanism consistent with long-term strain
accumulation• Several of its characteristics were unexpected:
– Dip angle and mechanism suggest that a fault other than the Enriquillo has ruptured.
– Rupture did not reach the surface.– Aftershocks = reverse mechanisms oblique to Enriquillo
• Implications:– Faults other that Enriquillo are active, consistent with
previous on-land and offshore geological mapping (Momplaisir:1986, Pubellier:2000).
– Changes in hazard level = work in progress.• Much work remains to be done to identify and quantify
potential earthquake sources in and around Hispaniola.
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Frankel, A.et al.,Documentation for Initial Seismic Hazard Maps for Haiti, USGS Open-File Report 2010.
Inferred slip rates are important for seismic hazard estimates (with seismicity, attenuation relations, etc..)
OAS Caribbean Disaster Management Project, http://www.oas.org/CDMP/document/seismap/
=33 % g
=3 % g
Range of above map