Soft-sediment deformation structures in Holocene coastal gravel deposits reveal two 1.8–2.0 ka old Mw > 7.0 earthquakes in southern-central Hispaniola

TL;DR

This study identifies two large earthquakes over 1,800 years ago in Hispaniola using preserved sediment structures, improving understanding of regional seismic risk.

Contribution

The study provides new evidence of two Mw > 7.0 earthquakes in southern-central Hispaniola using high-resolution geological analysis.

Findings

Three liquefaction sequences were dated to 2332–2008, 1982–1803, and 1770–1530 cal BP.

Earthquakes likely occurred every 200 years, with magnitudes exceeding Mw 7.0.

Strike-slip fault zones are identified as the primary sources of seismic activity in the region.

Abstract

An exceptionally well-preserved outcrop of Holocene liquefaction structures in the Tortuguero Beach of southern-central Hispaniola has been investigated. We present a new high-resolution orthoimage mosaic, combined with fieldwork, sedimentary logging, structural analyses, and rock sampling for granulometric, grain-shape, and geochronological analysis to improve our understanding of the seismic hazard and the magnitude of the cyclic paleo-earthquakes occurred in this high seismically active region. Our results revealed three sedimentary sequences of deformed layers separated by undeformed sections. These metric-scale, episodic liquefaction structures resulted in an unusual negative density gradient in a coarsening upward stratified succession. Deformed layers form NNW-trending dome and basin elongated structures controlled by the present-day NE-directed regional shortening. Radiocarbon dating of the lower, intermediate, and upper sequences yielded ages (1σ) of 2332—2008, 1982—1803, and 1770—1530 cal BP, respectively. Liquefaction structures were triggered by Mw > 7 earthquakes likely occurring every 200 years. Seismic hazard modeling establishes that the primary sources of earthquakes are the large-scale, strike-slip fault zones that accommodate the collision of the Beata Ridge with southern-central Hispaniola. These fault zones probably generated the 1751 Mw 7.5 Azua earthquake, and given the recurrence of such seismic events in southern Hispaniola, they could trigger future destructive earthquakes.

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