Definition and Paleoseismology of the Active, Left-Lateral Enriquillo-Plantain Garden Fault Zone Based on High-Resolution Chirp Profiles: Lakes Azuey and Mirogoane, Haiti

Abstract:

In July 2014, we obtained a total of 94 km of high-resolution Chirp profiles from the 129 km2, brackish Lake Azuey and 37 km of profiles from the 14 km2, fresh water Lake Mirogoane that both straddle the active trace of the Enriquillo-Plantain Garden fault zone (EPGFZ) of Haiti. 80% of the grid on Azuey and 85% on Mirogoane was dedicated to north-south profiles of the EPGFZ. In Azuey we defined the linear and east-west-striking fault trace in deformed Holocene sediments along with its landfalls west of Lake Azuey in Haiti and east of Lake Azuey in the Dominican Republic. All profiles showed the fault to be a sub-vertical flower structure whose active traces could be traced on Chirp data to a depth of 30 m below the lake floor. Previous workers have suggested that this fault ruptured during a large November, 1751, earthquake with a parallel and elongate felt zone. We hypothesize the most recent break of the fault several meters below the lake floor to have formed during the 1751 event but plan a coring program to precisely constrain the timing of historical and prehistorical events based on syn-faulting colluvial wedges observed on Chirp profiles. Our survey of Mirogoane confirmed its rhomboidal pull-apart structure with the basin center at a depth of 42-8 m making this basin the deepest lake in the Caribbean region. Deformational features include active folds at the lake bottom, large oblique-slip normal faults at an angle to the bounding east-west faults, and 30 m of recognizable stratigraphy. The 7 m of Holocene cored in the basin center in 1988 is observed to be highly deformed and locally folded and overlies with angular unconformity a well stratified and more folded lower basinal unit. Historical events are proposed to have ruptured on or near this segment of the EPGFZ in 1701 and 1770.