Along‐Arc Heterogeneity in Local Seismicity across the Lesser Antilles Subduction Zone from a Dense Ocean‐Bottom Seismometer Network

Abstract

The Lesser Antilles arc is only one of two subduction zones where slow‐spreading Atlantic lithosphere is consumed. Slow‐spreading may result in the Atlantic lithosphere being more pervasively and heterogeneously hydrated than fast‐spreading Pacific lithosphere, thus affecting the flux of fluids into the deep mantle. Understanding the distribution of seismicity can help unravel the effect of fluids on geodynamic and seismogenic processes. However, a detailed view of local seismicity across the whole Lesser Antilles subduction zone is lacking. Using a temporary ocean‐bottom seismic network we invert for hypocenters and 1D velocity model. A systematic search yields a 27 km thick crust, reflecting average arc and back‐arc structures. We find abundant intraslab seismicity beneath Martinique and Dominica, which may relate to the subducted Marathon and/or Mercurius Fracture Zones. Pervasive seismicity in the cold mantle wedge corner and thrust seismicity deep on the subducting plate interface suggest an unusually wide megathrust seismogenic zone reaching ∼65 km depth. Our results provide an excellent framework for future understanding of regional seismic hazard in eastern Caribbean and the volatile cycling beneath the Lesser Antilles arc.

Inferring Interseismic Coupling Along the Lesser Antilles Arc: A Bayesian Approach

“…Since then, more detailed models of the subduction interface have become available, allowing us to better account for the influence of fault geometry in the inversion process. Here we test two different fault geometries: the Slab2 model (Hayes et al, 2018) and a more recent model developed by Bie et al (2020). We discretize the subduction interface into triangular elements, which vary in size from 2,500 km 2 (i.e., ∼70 km side-length) below the islands, to 11,500 km 2 (i.e, ∼150 km side-length) along the shallow parts of the fault.…”

“…Figure 8 shows the mean and mode posterior coupling estimates for both geometries, as well as three depth profiles along sections of the arc, in order to highlight the differences in slab geometries. The geometry proposed by Bie et al (2020) fits the local seismicity (i.e., the CDSA catalog) better and might therefore better represent the actual geometry of the Lesser Antilles slab. We however find that the difference of mean interseismic coupling between the two geometries is very small and that the two models are in very good agreement.…”

“…For instance, in the central part of the subduction zone, the global Slab2 model (Hayes et al., 2018) estimates the slab surface to be up to 70 km shallower than the Bie et al. (2020) model.…”

“…Bie et al. (2020) also observe pervasive seismicity in the cold mantle wedge corner, suggesting a deep decoupling depth between the slab and the upper‐plate mantle (Wada & Wang, 2009). This, in combination with the occurrence of the 2017 Martinique thrust event at 51 km depth suggests that the seismogenic zone may reach as far as ∼65 km depth.…”

Earthquakes and extreme rainfall induce long term permeability enhancement of volcanic island hydrogeological systems

“…The Lesser Antilles slow-spreading subduction zone 31 is characterized by a relatively old subducting plate (80 Ma), with a subduction rate of 19 mm/year 32 , 33 . Martinique Island is the largest volcanic island (1080 km 2 ) of the Lesser Antilles archipelago, with a volcanic activity, mainly andesitic, for at least 25 Ma 34 .…”