Neotectonic Mapping of Puerto Rico

Abstract

Puerto Rico is part of the Puerto Rico-Virgin Islands microplate, along the Caribbean–North American plate boundary between the Puerto Rico trench subduction zone and the Muertos Trough incipient subduction zone. Despite recent seismicity and geodetically constrained deformation of ~3 mm/yr of left-lateral shear across the island, Quaternary fault locations remain largely uncertain. Preservation of recent faulting in the landscape is masked by distributed faulting, high weathering rates of the tropical climate, steep topography, widespread landsliding, and extensive agriculture, deforestation, and urbanization throughout the island. We present an updated active fault map of Puerto Rico, created through neotectonic mapping using historical aerial imagery from the 1930s-60s and < 1-m lidar topography, integrated with field observations, to create an updated active fault map of Puerto Rico. We focus on faults that offset younger geomorphic surfaces, with ages estimated by geologic mapping, optically stimulated luminescence (OSL) and radiocarbon dating, and morphologic interpretations. We present new evidence for Quaternary activity on seven faults, including the South Lajas, Salinas, Punta Montalva, Great Southern Puerto Rico, Cerro Goden, Parguera, and San Marcos faults. We find that active faulting occurs preferentially near the southern and western coasts and in part spatially coincides with preexisting bedrock faults, possibly reflecting reactivation of some older faults in the modern strain field.

Keywords

• faulting
• geomorphology
• lidar
• Puerto Rico
• neotectonics