Large Earthquake Potential in the Southeast Caribbean

Abstract:

The axis of rotation describing relative motion of the Caribbean plate with respect to South America lies in Canada near Hudson’s Bay, such that the Caribbean plate moves nearly due east relative to South America [DeMets et al. 2010]. The plate motion is absorbed largely by pure strike slip motion along the El Pilar Fault in northeastern Venezuela, but in northwestern Venezuela and northeastern Colombia, the relative motion is distributed over a wide zone that extends from offshore to the northeasterly trending Mérida Andes, with the resolved component of convergence between the Caribbean and South American plates estimated at ~10 mm/yr. Recent densification of GPS networks through COLOVEN and COCONet including access to private GPS data maintained by Colombia and Venezuela allowed the development of a new GPS velocity field. The velocity field, processed with JPL’s GOA 6.2, JPL non-fiducial final orbit and clock products and VMF tropospheric products, includes over 120 continuous and campaign stations. This new velocity field along with enhanced seismic reflection profiles, and earthquake location analysis strongly suggest the existence of an active oblique subduction zone. We have also been able to use broadband data from Venezuela to search slow-slip events as an indicator of an active subduction zone. There are caveats to this hypothesis, however, including the absence of volcanism that is typically concurrent with active subduction zones and a weak historical record of great earthquakes. A single tsunami deposit dated at 1500 years before present has been identified on the southeast Yucatan peninsula. Our simulations indicate its probable origin is within our study area.

We present a new GPS-derived velocity field, which has been used to improve a regional block model [based on Mora and LaFemina, 2009-2012] and discuss the earthquake and tsunami hazards implied by this model. Based on the new geodetic constraints and our updated block model, if part of the region slipped 2.5 m (500 yrs x 5 mm/yr) in a single 200 km x 200 km rupture, the moment-magnitude of the event would exceed Mw = 8.3. We hypothesize that an active subduction zone exists and supports great earthquake events with a strong possibility of destructive tsunamis, which makes this region the one with the largest seismic hazard in the circum-Caribbean.