Skip to Main Content
Book Chapter

Toward an integrated understanding of Holocene fault activity in western Puerto Rico: Constraints from high-resolution seismic and sidescan sonar data

By
Nancy R. Grindlay
Nancy R. Grindlay
1
Center for Marine Science and Department of Earth Sciences, University of North Carolina at Wilmington, Wilmington, North Carolina 28409, USA
Search for other works by this author on:
Lewis J. Abrams
Lewis J. Abrams
1
Center for Marine Science and Department of Earth Sciences, University of North Carolina at Wilmington, Wilmington, North Carolina 28409, USA
Search for other works by this author on:
Luke Del Greco
Luke Del Greco
1
Center for Marine Science and Department of Earth Sciences, University of North Carolina at Wilmington, Wilmington, North Carolina 28409, USA
Search for other works by this author on:
Paul Mann
Paul Mann
2
Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas 78759-8500, USA
Search for other works by this author on:
Published:
January 01, 2005

It has been postulated that the western boundary of the Puerto Rico–Virgin Islands microplate lies within the Mona Passage and extends onland into southwestern Puerto Rico. This region is seismically active, averaging one event of magnitude 2.0 or larger per day, and over 150 events of magnitude 3.0 or greater occurred during the past five years. Moreover, there have been at least 13 historical events of intensity VI (MM) or greater in the past 500 years. We conducted a high-resolution seismic and sidescan sonar survey of the insular shelf of western and southern Puerto Rico during May 2000 in an effort to identify Holocene faults and to further assess the seismic hazard in the region. We focus on an ∼175 km2 part of the surveyed area offshore of western Puerto Rico, extending from Punta Higuero to Boquerón Bay. This area was targeted as a likely place to image recent faults, because multi-channel seismic profiles offshore western Puerto Rico show numerous WNW-trending normal and strike-slip faults that offset Oligocene-Pliocene age carbonate rocks and underlying Cretaceous basement rocks. Analyses of these data identify three zones of active deformation within the survey area: (1) the Cerro Goden fault zone; (2) the Punta Algarrobo/Mayagüez fault zone that lies offshore the city of Mayagüez; and; (3) the Punta Guanajibo/Punta Arenas fault zone. Two of the offshore fault zones, the Cerro Goden and Punta Algarrobo, show strong correlation with fault zones onland, Cerro Goden and Cordillera, respectively. Many of the mapped faults offshore appear to reactivate older WNW-trending basement structures and show evidence of some component of right-lateral motion that is consistent with geodetic measurements. The offshore deformation zones are also associated with headlands and linear NW-SE magnetization lows (serpentinite dikes?) mapped offshore. Elongate outcrops of serpentinite in western Puerto Rico are colinear with the fault zones we have mapped offshore, suggesting that either the presence of serpentinite has localized fault activity or that fault activity has remobilized serpentinite. This offshore study improves assessments of the seismic hazard in Puerto Rico by identifying targets for onshore paleoseismic studies and by better defining the total length of offshore Holocene faults.

You do not currently have access to this article.

Figures & Tables

Contents

GSA Special Papers

Active Tectonics and Seismic Hazards of Puerto Rico, the Virgin Islands, and Offshore Areas

Paul Mann
Paul Mann
Search for other works by this author on:
Geological Society of America
Volume
385
ISBN print:
9780813723853
Publication date:
January 01, 2005

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal