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Towards an Updated Quaternary Fault Map of Puerto Rico

Description: 

Puerto Rico is the largest landmass of the Puerto Rico-Virgin Islands microplate, along the Caribbean–North American plate boundary between the Puerto Rico trench oblique subduction zone and the Muertos Trough incipient subduction zone. Despite recent seismicity and geodetic deformation that record ~3 mm/yr of left-lateral slip across the island, the locations of Quaternary faults accommodating deformation throughout the island are still mostly uncertain. The preservation of recent faulting in the landscape is masked by moderate-to-slow fault slip rates (<1 mm/yr) and distributed faulting, humid tropical weathering, steep topography resulting in frequent landsliding over large parts of the island, and extensive agricultural activity and urbanization near the coastlines and in river valleys. Many of the previously identified potentially active faults are in the arid southwestern region of the island. We present new remote neotectonic mapping of historical imagery from the 1950s-60s and recent 1-m lidar data, integrated with field observations, to create an updated active fault map of Puerto Rico. We focus on faults that offset younger geomorphic surfaces, with age estimates constrained by previous geologic mapping and our landscape interpretations. We also map fault-related features that may represent active deformation in regions where younger geomorphic surfaces are not present. Scarps along the South Lajas, Salinas, Cerro Goden, Great Southern Puerto Rico, and San Marcos faults record vertical and sometimes lateral motion. More subtle fault-related features, such as sag ponds, linear ridges and valleys, and laterally offset channels are present along the Punta Montalva, San Marcos, and Cerro Goden faults. Together, these new observations, integrated with recent fault studies, provide the foundation for an updated Quaternary fault map of Puerto Rico. Future studies will focus on constraining fault slip rates and earthquake recurrence intervals.

Session: Active Faults in the Caribbean and Central America

Type: Oral

Date: 4/20/2023

Presentation Time: 10:15 AM (local time)

Presenting Author: Jessica A. T. Jobe

Student Presenter: No

Invited Presentation: 

Authors