iPlex Lunch spring-2012

Five years ago, Central Panama was considered relatively aseismic compared to the other Central American countries. Our recent tectonic geomorphic mapping and paleoseismic trenching studies in central Panama have led to a paradigm shift in the neotectonic deformation and seismic hazard of this Caribbean-bounding country. To date, we have conducted strip mapping and 2-D and 3-D trenching studies of several crustal faults, including the Gatún, Limón, and Pedro Miguel faults, and have demonstrated that each fault has had multiple Holocene surface ruptures. The Gatún fault is a left-lateral, E-W-trending strike-slip fault that forms the southern margin of the Sierra Maestra. The fault is at least 40-50 km long from the Gatún Lake eastward to the San Blás Islands, and possibly another 50 km westward across Gatún Lake into the interior of Panama. Our trenching studies indicate a sinistral slip rate of 6.0±3.0 mm/yr, with three 0.7-1.0 m displacement events in the last ~500 years, and the most recent event (MRE) likely in 1849. The Limón fault is a N-S-trending, right-lateral strike slip fault, about 28 km long, terminating to the north at the Gatún fault, and possibly stepping onto the Pedro Miguel fault at its southern end. From our trenching studies we determined a dextral slip rate of 5.0±1.0 mm/yr, at least three surface ruptures in the past ~950 to 1500 years, average displacement per event of about 2 meters, and the MRE possibly in 1873. The Pedro Miguel fault may be the southern extension of the Limón fault, extending 48 km N-S from the south end of the Limón fault at the Chagres River to the Pacific Ocean, and likely another 12 km south to Taboga Island, where it may be responsible for the island’s uplift. Based on our trenching studies, the Pedro Miguel fault has a dextral slip rate of 5.0±2.0 mm/yr, producing three surface-rupturing events in the past ~1500 years totaling at least 8.1 meters displacement, with the last event, a 3.0±0.2 meter rupture, on May 2, 1621.