Paleoseismic Trenching Reveals Multiple Recent Earthquakes on the Great Southern Puerto Rico Fault Zone
Description:
The Puerto Rico-Virgin Islands (PRVI) microplate is located within the broad deformation zone of the North Caribbean Plate Boundary. Active faults onshore Puerto Rico are accommodating northeastward PRVI motion, including the Great Southern Puerto Rico fault zone (GSPRFZ). On the southern coastal plain, the GSPRFZ is an active right-lateral normal northwest-trending fault. Quaternary landforms record ~4–8 m of oblique displacement on the GSPRFZ, but the number and timing of individual surface-rupturing earthquakes remains unconstrained. To address this, we excavated a paleoseismic trench across the GSPRFZ at a site where a single, ~1.5-m-tall south-side-down scarp crosses a Quaternary alluvial fan surface ~200 m along strike from an exposure of a bedrock fault zone. In the trench exposure, we documented faulted fluvial and colluvial deposits, two generations of fissure fill, and un-faulted colluvium. The primary fault in the trench was sub-vertical and branched into a ~0.5–2.5-m-wide zone of faults and fissures near the surface. The fault geometries and juxtaposition of different deposits across the fault zone suggest a significant component of strike slip, consistent with the geomorphic expression. Based on the trench observations and correlations with regional deposit ages, we interpret that the GSPRFZ has hosted at least two surface-rupturing earthquakes in the latest Pleistocene to Holocene, pending numerical chronology data (radiocarbon and luminescence dating). This dated exposure, along with existing data from prior paleoseismic trenches on the GSPRFZ and Salinas faults, will provide the first numerical constraints on GSPRFZ rupture history.
Session: The Landscape Record of Earthquakes and Faulting [Poster]
Type: Poster
Date: 4/16/2025
Presentation Time: 08:00 AM (local time)
Presenting Author: Emerson
Student Presenter: No
Invited Presentation:
Poster Number: 7
Authors
Emerson Lynch Presenting Author Corresponding Author elynch@usgs.gov U.S. Geological Survey |
Jessica Jobe jjobe@usgs.gov U.S. Geological Survey |
Rich Briggs rbriggs@usgs.gov U.S. Geological Survey |
Christopher DuRoss cduross@usgs.gov U.S. Geological Survey |
Sylvia Nicovich snicovich@usgs.gov U.S. Geological Survey |
Catherine Hanagan chanagan@usgs.gov U.S. Geological Survey |
M. Morow Tan m.tan@colorado.edu University of Colorado Boulder |
Victor Ortega Díaz victor.ortega4@upr.edu University of Puerto Rico, Mayagüez |
Harrison Gray hgray@usgs.gov U.S. Geological Survey |
Laura E Strickland lstrickland@usgs.gov U.S. Geological Survey, Denver, Colorado, United States |
K. Stephen Hughes kenneth.hughes@upr.edu University of Puerto Rico, Mayagüez, Mayagüez, Puerto Rico, United States |
Alberto M López Venegas alberto.lopez3@upr.edu University of Puerto Rico, Mayagüez, Mayagüez, Puerto Rico, United States |
Paleoseismic Trenching Reveals Multiple Recent Earthquakes on the Great Southern Puerto Rico Fault Zone
Category
The Landscape Record of Earthquakes and Faulting