Searching for blind faults: The Haiti subsurface imaging project

Abstract

On 12 January 2010, Haiti suffered a magnitude 7.0 earthquake near Port-au-Prince, which resulted in a catastrophic loss of life and infrastructure. The effects were particularly severe on the Léogâne fan delta, close to the earthquake's epicenter. Because no unambiguous rupture to the surface has been found, the suspected fault that caused the event has been labeled "blind." A geophysical team from the University of Houston has undertaken expeditions to Haiti in 2012-2014, with support from the SEG Geoscientists Without Borders program, to try to help build Haiti's geophysical capability and assist in finding subsurface evidence of the proposed blind fault. The team reconnoitered the epicentral region of the 2010 earthquake and selected sites on the Léogâne delta fan for land surveys. The team enjoyed a productive and pleasant interaction with local villagers while receiving access to survey areas and assistance with operations. The resulting 2012 seismic and gravity data provided promise for more detailed surveys that the team undertook in February 2013. Measurements indicated that the soil sediments near Léogâne are Class E - a substantial geohazard. The University of Houston team found a broad and unfaulted anticline in the overlying fan deposit that is consistent with seismogenic movement on a north-dipping reverse fault at greater depth. The axis of the subsurface anticline is in alignment with an eastwest- trending zone of localized highway damage and a coral reef that was uplifted during the 2010 earthquake. Lake sonar surveys have given some excellent images of the associated Enriquillo-Plantain Garden fault zone (EPGFZ). As a result of this work, the team plans to bring larger seismic sources to create more detailed and deeper seismic sections (land and lake) and to assist in further development of Haitian geophysical capabilities. The project has provided a remarkable learning experience for staff and students as well as for Haitian colleagues.