Large Scale Observations and Modeling of Strain Partitioning in
Guatemala from SAR Interferometry.
Abstract
The zone of interaction between the Cocos (CO), Caribbean (CA) and North
America (NA) plates in Guatemala is defined by the sub-parallel Motagua
and Polochic strike-slip faults, a series of north-south-trending
extensional grabens immediately south of the Motagua Fault, the Middle
America trench, and faults within the Middle America volcanic arc.
Historical earthquakes associated with these faults include the
destructive 1976 Mw 7.5 earthquake along the Motagua fault and the 2012
Mw 7.5 Champerico thrust earthquake. The latest published GPS-based
present-day kinematic model of the region shows that about two-thirds of
the strain accumulation from the NA/CA relative motion concentrates on
the Motagua fault and one third across the Polochic fault, suggesting
that slip varies with time as a result of mechanical interactions within
the Motagua-Polochic fault system. As part of the efforts to quantify
the present-day kinematics and slip behavior of these faults, we use
interferometric synthetic aperture radar (InSAR) to measure the strain
rates across faults in Guatemala and to constrain slip partitioning
among them. We processed L-band ALOS-1 images spanning from 2006 to
2011, and C-band Sentinel-1 images spanning from 2015 to 2019, from
ascending and descending tracks covering the Polochic and Motagua
faults, the Ipala and Guatemala City grabens, and part of the volcanic
arc to the south. We are using the New Small temporal and spatial
baselines (NSBAS) workflow to compute the interferograms, make
tropospheric and ionospheric corrections, and perform time-series
analysis. We present the first InSAR-based maps of interseismic velocity
for this region, which will contribute to the refinement of interseismic
locking estimates across the Motagua-Polochic fault system, the
subduction zone, and other nearby faults.