A receiver function study of crustal properties in the Lesser Antilles Arc

Abstract:

In the present study, we report the crustal thickness and mechanical properties along the Lesser Antilles Arc by employing receiver function technique. To do so, we collected teleseismic data, available in the IRIS online database, recorded by several broadband stations that have been deployed in the arc. The selected events have epicentral distances from 30° to 90°, and magnitudes of 5.7 or larger. Unfortunately, we were only able to apply the method to 9 of the 25 stations deployed in the arc, due to nosy data (possibly because of the effects of strong winds, waves and tides), recording problems, and short recording periods. We used the recordings from P-to-S conversion in order to estimate the crustal thickness by depth staking the computed receiver functions. We also analyzed crustal reverberations found in some stations to estimate the crustal thickness and the average crustal Vp/Vs ratio, as well as the Poisson’s ratio, by applying H-k matrix-search methodology. We found large variations in the crustal thickness along the arc: the thinnest crust (~22 km) was found in Barbuda Island at the northern-exterior section of the arc, while the thickest crust (~36.8 km) was found in Anguilla Island at the northern-central section of the arc. In general, the northern sections of the arc have a thicker crust with a mean value of ~29 km, while the southern sections have a thinner crust with a mean value ~23 km, and this might be related to the general asymmetry of the arc (the northern part is much more active and complex than the southern part). Poisson’s ratio estimated along the arc vary from 0.266 (Vp/Vs=1.777) to 0.3 (Vp/Vs=1.87) which are relatively consistent with mafic island arc origin, although the carbonatic cover of the island might influence the lower values in the range, while higher values could be associated to the old Cretaceous basement of some of the northern islands. We hope to be able collect more information from relatively new stations of the West Indies IPGP to better estimate the crustal properties of the arc and further understand the role of the subduction asymmetry in the arc crustal topography and, eventually, characterize the isostasy of the arc using gravimetric data.