REMOTE MAPPING AND LANDSCAPE MORPHOLOGY OF POTENTIALLY ACTIVE FAULTS IN PUERTO RICO

Puerto Rico is situated along the Caribbean:North American plate boundary between two subduction zones. Despite recent widespread seismicity and geodetic deformation that indicates ~3 mm/yr of left-lateral compressional slip across the island, the character of the Quaternary fault network that accommodates active deformation remains mostly unknown. Preservation of faulting in the landscape is complicated by moderate-to-slow fault slip rates and diffuse faulting, a humid climate, rugged topography resulting in frequent landsliding over parts of the island, and extensive anthropogenic modification near the coastlines and valleys. Most of the previously identified potentially seismogenic faults are in the arid southwestern region of the island. Here, we review existing constraints on the fault network and present new remote neotectonic mapping of historical imagery and 1-m lidar data, coupled with landscape morphology and field observations, to develop an updated active fault map of Puerto Rico. We focus on fault zones that offset younger geomorphic surfaces. In addition, we delineate fault-related features in the landscape that may represent active deformation in regions where younger geomorphic surfaces are not present. Clear fault scarps recording vertical and lateral motion are mapped along the South Lajas, Salinas, Cerro Goden, Great Southern Puerto Rico, and San Marcos faults. Subtle fault-related features, such as areas of ponding, linear ridges and valleys, and laterally offset channels are present along the Punta Montalva, Cerro Goden, San Marcos, and Great Northern Puerto Rico faults. The preliminary active fault map will be integrated with other onshore and offshore datasets to develop models of how recent deformation is accommodated across the island and broader region (a geologic deformation model), in addition to serving as a foundation for geologic databases that inform the 2025 U.S. National Seismic Hazard Model update for Puerto Rico and the U.S. Virgin Islands.