STRAIN PARTITIONING ACROSS THE POLOCHIC-MOTAGUA FAULT SYSTEM, GUATEMALA: INSIGHTS FROM KINEMATIC MODELING

The Polochic-Motagua Fault System (PMFS) in eastern Guatemala is part of the sinistral transform plate boundary between the North American plate (NA) and the Caribbean plate (CA). New kinematic models have been generated to provide a better understanding of how strain is accommodated across the PMFS and its interaction with the Swan Fault and the Volcanic Arc Fault (VA). This study utilizes 2D Finite Element Analysis (FEA) to simulate the block movements of the NA and CA plates. The model moves the CA plate eastward relative to the NA plate at a velocity of 20 mm/yr. Several variations of the model are compared with GPS data in order to analyze the results. The initial interpretation assumes the VA fault as a through-going fault indicating the maximum slip on the eastern side of the VA fault reaching up to 17 mm/yr, which is higher than the 10 mm/yr observed by GPS measurements. Results also show that any model that does not connect the PMFS with the Swan Fault results in low slip rates ranging from 0 mm/yr to 7 mm/yr on the PMFS. These results are in disagreement with GPS data showing slip rates decreasing from 20 mm/yr along the eastern to 0 mm/yr along the western segment of the fault system. A more detailed and realistic fault system geometry can be inferred through comparison with GPS data. Models which best fit the GPS data connect the Swan Fault and the PMFS, and the VA Fault is inferred to be a segmented fault within a weak zone. This modeling approach allows refinement of current structural models and can help us to better understand strain partitioning in the PMFS and aid in future seismic hazard assessments in this area.