Probing the creep rate along the Lesser Antilles Subduction Zone through repeating earthquakes
Abstract
The Lesser Antilles Subduction Zone remains very little known, especially concerning its current mechanical state. While it currently exhibits moderate seismic activity (M<6), two major earthquakes occurred in 1839 and 1843 with an estimated magnitude of 8+ and a supposed megathrust mechanism (Feuillet et al., 2011). This interpretation contrasts with the results of a recent paper (van Rijsingen et al., 2020), which provides evidence, from GPS data, of very low coupling all along the plate interface. Here we address the problem of estimating interplate coupling by using a different observable, namely repeating earthquakes, which provide quantitative information on the local creep rate on the subduction interface. We used cross-correlation at two reference stations (in Martinique et Guadeloupe) to detect ten families of repeaters over a period of six years. The families are each composed of two to three events with magnitude between 2 and 4 and located within the supposed rupture area of the 1839 and 1843 earthquakes, offshore Martinique and north-east of Guadeloupe, respectively. We compare the resolution of the cross-correlation approach (~60 m, for signals low-pass filtered at 15 Hz) with the source size (~140 m of diameter, for M=2.5 and supposing a stress drop of 10 MPa) and conclude that each family corresponds to the re-rupturing of the same asperity. Using the model of Nadeau and Johnson (1998), we infer a local creep rate (around each asperity) which is comparable to the plate convergence rate (19 mm/year). Our observation thus points towards a loosely coupled interface surrounding the repeating earthquake asperities. The fact that repeaters are concentrated in two specific regions of the subduction leads to new questions about the heterogeneity of plate coupling. A study over a longer time span is currently carried out to complete the repertoire of repeaters and to confirm the above findings.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.T25A0167S