Large scale observations and strain partitioning analysis in Guatemala from SAR interferometry

Abstract

The interaction between the Cocos, Caribbean, and North America plates in Central America results in complex deformation mostly accommodated by the sub-parallel Motagua and Polochic left-lateral faults, north-south-trending extensional grabens south of the Motagua Fault, the Middle America subduction zone, and right-lateral faults along the Middle America volcanic arc. Large earthquakes associated with these faults include the destructive 1976 Mw 7.5 earthquake along the Motagua fault and the 2012 Mw 7.5 Champerico subduction thrust earthquake. The most recent GPS-based elastic-kinematic models of the region show that about 80% of the strain accumulation from the North America/Caribbean plates relative motion concentrates on the Motagua fault and 20% across the Polochic fault, with significant internal stretching of the Caribbean plate between Honduras and western Guatemala, a decreasing strike-slip rate from east to west along the volcanic arc, and lateral variations of coupling along the subduction zone. We propose the use of Synthetic Aperture Radar Interferometry (InSAR) to measure slip rates along faults in Guatemala, strain partitioning among them and potential internal deformation within blocks. We analyze Sentinel-1 radar images spanning from 2015 to 2020, from ascending and descending tracks, covering the whole Guatemala region. We use Distributed Scatterers (DS) Interferometry techniques adapted to large Sentinel-1 data sets to better assess and mitigate the various sources of noise. We present the first InSAR-based maps of interseismic velocity for this region, analyze these InSAR results over the whole surface covered by the tracks and along key profiles across main faults for a first comparison with GPS data and the GPS-based block model. The DS results show an overall good agreement with predictions from the GPS-based block model. These InSAR results along with GPS data will be used to refine the block model and estimate the lateral variations of interseismic slip deficit rates along major faults, as well as internal deformation within the western Caribbean plate.