A new velocity field for El Salvador derived from combined InSAR and GNSS data

Abstract

The country of El Salvador lies on an active tectonic margin, where the Cocos plate is subducting under the Caribbean plate. A crustal fault system, the El Salvador Fault Zone (ESFZ), crosses the country from East to West through the Central American Volcanic Arc, accommodating more than 1 cm/yr of differential deformation between the Chortís block and the volcanic forearc sliver. Here we use GNSS and interferometric synthetic aperture radar (InSAR) data to measure interseismic ground deformation across ESFZ. We have processed and updated GNSS data in more than 110 continuous and episodic stations in the region. GNSS results have been useful for determining the broad pattern of the tectonic signal in the area. However, they are scarce and unable to characterise complex behaviour in the intra-fault basins.SAR data acquired by the ALOS PALSAR L-band satellite (2006-2011), for both the ascending and descending tracks covering El Salvador, were used to form interferograms with a Small Baseline (SBAS) approach. The time series and average velocity were computed. The average coherence obtained for the area is overall good, and the results are coherent with the regional tectonics.