Dynamic of the volcanic activity of La Soufrière volcano (Guadeloupe, Lesser Antillles): Evidence for shallow fluid seismic sources

Abstract:

La Soufrière is one of the many hazardous volcanoes in the inner arc of Lesser Antilles. Located South

of Basse-Terre island, it is the only active volcano of 

the Guadeloupe archipelago. Since the last significant magmatic eruption in 1535 AD, the

activity has been exculsively phreatic. 

Since 1992 and the abrupt renewal of seismic and fumarollic activities, 

the Guadeloupe Volcanological and Seismological Observatory (OVSG-IPGP) has 

recorded a progressive increasing of

seismicity and degassing that led scientists and authorities to set the alert level ``Vigilance''

and hold it until today.

According to the recent geophysical, geochemical and geological studies, the current volcanic activity 

of la Soufrière volcano seems to be exclusively associated to the 

hydrothermal system, while the link with seismic activity is still poorly studied.

In this context of possible pre-eruptive unrest, we investigated the spatial and

temporal variations of the seismicity recorded between 1981 and 2013. From

a consistent seismological framework coupling spectral, statistical, signal processing,

clustering, and inverse problems methods, we demonstrate that this seismicity

is largely generated by shallow hydrothermal fluid sources located in a complex 

plumbing system. Spatial variations of Vp/Vs ratio and B-value in seismogenic structures

allow us to document three main seismic zones associated to : (1) migration of magmatic

gas, (2) the storage and mixing of underground water and gas and (3) the shallow migration

of hydrothermal fluids in high fractured and heterogeneous system. Waveform analysis revealed

a low number of significant families consistent with fracturing process, and the temporal

evolution of multiplet activities highlighted several variations associated with surface 

manifestations and brutal dynamic changes after major local tectonic earthquakes of 

Les Saintes (21 November 2004, Mw=6.3), its main aftershock (14 February 2005, Mw=5.7) and 

the last major earthquake of la Martinique (29 November 2007, Mw=7.4).