T89 Recent Advances in Paleoseismology and Neotectonics of Eastern and Central North America and Northern Caribbean I

Monday, 1 November 2010
8:00 AM - 12:00 PM
Mile High Ballroom 2AB/3AB

PALEOSEISMOLOGY AND EARTHQUAKE HAZARD IN THE CARIBBEAN

Paper number: T89-1
Program: Technical Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

Throughout the Caribbean region most major seismogenic structures are offshore and inaccessible for typical paleoseismic studies. However, where onshore faults have been studied, faulted Holocene sediments record past earthquakes, and the active tectonics are expressed in the geomorphology of young landforms. Over the last 15 years, we have conducted paleosesimic research in the Dominican Republic (DR), Puerto Rico (PR), Trinidad, Jamaica, and in Haiti following the catastrophic earthquake of 12 January 2010. Our studies of the Septentrional Fault (SF) in DR show that the most recent rupture on the SF east of Santiago, in the central part of the Cibao Valley, occurred ~800 years ago and was associated with a minimum of 4.6m of displacement, suggestive of a M>7.5 earthquake. Historical earthquakes in 1562 and 1842 did not rupture the SF east of Santiago. Offset Holocene stream terraces suggest a SF slip rate of 6-12 mm/yr, indicating that this fault accommodates about one-half of the ~19 mm/yr geodetically determined total plate-boundary motion.

Near PR, the major structures of the North American-Caribbean plate boundary are offshore. However, our mapping and paleoseismic studies show that repeated Holocene surface rupture has occurred on a previously unknown fault in the Lajas Valley of southwestern PR. Excavations across this scarp exposed faulted alluvium and evidence for two, and possibly three earthquakes. Radiocarbon ages suggest that at least two earthquakes occurred on this fault in the last 5 ka.

Trinidad is located along the plate boundary between the South American and Caribbean plates. Geodetic studies suggest that a significant fraction of the plate-boundary motion is accommodated across the Central Range Fault (CRF) in central Trinidad where our excavations show the most recent surface rupture occurred 550-2710 years BP.

In Jamaica and Haiti we studied the Enriquillo-Plantain Garden Fault (EPGF). In Jamaica, we see evidence of repeated surface ruptures in the Quaternary, and in Haiti our work shows that the EPGF did not rupture to the surface on 12 Jan 2010, but has produced repeated, large earthquakes in the Quaternary. We measured offsets of 1.3-3.3m on small stream channels across the EPGF, which we associate with the most recent earthquake, most likely the historical earthquake of either 1751 or 1770.