Seismicity and tectonics of the southeastern Caribbean

Abstract

We present 33 new focal mechanisms for SE Caribbean earthquakes (1963–1988). We use these mechanisms, in conjunction with 28 previously available mechanisms, to distinguish between two models of plate boundary zone interaction in the SE Caribbean: the trench‐trench transform and hinge faulting model, and the right oblique collision model. Shallow (0–70 km) and intermediate (70–200 km) depth earthquakes occur in the study region; we focus on the tectonic causes of these events and the motions they delineate. The shallow earthquakes are in a broad linear zone which trends NE from the Paria Peninsula of Venezuela towards Barbados. Intermediate depth earthquakes cluster beneath and NW of the Peninsula, and deepen to the NW, perpendicular to the NE‐trending shallow events. The vertical distribution of the earthquakes suggests a slab with steep NW dip. Shallow, dextral strike slip on E‐striking faults is restricted to a 60‐km‐wide linear zone between the Gulf of Cariaco and the western margin of the Gulf of Paria. Dextral strike slip is active only as far east as the Gulf of Paria, and not within or east of Trinidad. Shallow thrust events with ENE‐striking planes, distributed between the Araya Peninsula and the Gulf of Paria, indicate collision at crustal levels between South America and Caribbean, and that folding and thrusting are still active over a 60‐km interval south of the Araya‐Paria isthmus. Active thrusting in Venezuela corroborates predictions of transpression between Caribbean and South America and discounts transtensional motions between the two plates in the SE Caribbean. The conjunction of shallow thrust, strike slip, and normal earthquakes in the Gulf of Paria at around 62.3° may be the expression of unpartitioned oblique compressive deformation in the plate boundary zone. Intermediate (165 km > h > 70 km) depth thrust and dip slip events within the NW‐dipping slab indicate that oceanic lithosphere, probably originally attached to South America, subducts to the NW beneath the Caribbean plate. Shallow normal faulting events E and NE of Trinidad are expressions of plate bending about near‐horizontal axes parallel to the Lesser Antilles subduction zone. We conclude that the earthquake mechanisms provide strong support for the right oblique collision model of Caribbean‐South American plate interaction.

Rupture history of the 1997 Cariaco, Venezuela, earthquake from teleseismic P waves

“…Plate motion is largely accommodated by right-lateral displacement along the east-west El Pilar fault (e.g., Molnar and Sykes, 1969;Perez and Aggarwal, 1981;Russo et al, 1993). The USGS National Earthquake Information Center (NEIC) located the epicenter of the 1997 Cariaco earthquake just north of the E1 Pilar fault near the towns of Cariaco and Casanay (Figure 1).…”

Probabilistic Seismic Hazard Assessment for Bridgetown-Barbados, Employing Subduction Interface Characteristic Earthquakes

“…Russo et al [12] suggest also that the northern boundary of the Eastern Caribbean-South America plate may lie as far north as the southern end of the Grenada basin. Moderate but shallow earthquakes occurred south of Tobago on 1982 (4.8 Mw) and 1997 (6.7 Mw) with right-lateral strike slip and normal faulting mechanisms, respectively [20,23].…”

“…Zones 2 and 4 cover the latitudes from 14.8º N to 20.0º N and they are characterized with a higher seismic activity than Zone 3 and 5 (from 11.0º N to 14.8º N latitude). Bengoubou-Valeruis et al [11] and Russo et al [12] attribute the differences in the seismic activity to the following reasons: (1) changes in the tectonic structures mapped by Feuillet et al [13]; (2) there being enough sediments to lubricate or decouple the two plates in the subduction zone; (3) strengthening caused by thick accretionary prism overburden which lies above the shallow reach of the subduction zone. The quiescent area coincides with the deepest part of the Barbados accretionary wedge.…”

“…This zone constitutes a subducting detached oceanic lithosphere with depth ranging from 50 km to 300 km and represents one of the most active seismogenic sources in the Eastern Caribbean [12]. The largest reported earthquakes occurred in October 21, 1766 and January 10, 1888 with magnitudes of 7.5 M w and 7.0 M w , respectively.…”

“…Russo et al [12] defined this zone as a passive margin edge in the foreland basin in north of south American continent, covering events with strike slip, mixed thrust and strike slip, and thrust mechanism around the Orinoco Delta region in Venezuela, with an average depth of 50 km and a maximum magnitude of 6.6 (M w ).…”