Active 650-km Long Fault System and Xolapa Sliver in Southern Mexico

Ekaterina Kazachkina,Krzysztof Gaidzik,Nathalie Cotte,Andrea Walpersdorf,Jose Antonio Santiago,Vladimir Kostoglodov,Allen Husker,Maria Teresa Ramirez-Herrera

doi:10.3389/feart.2020.00155

Abstract

New estimates of long-term velocities of permanent GPS stations in Southern Mexico reveal that the geologically discernible ~650 km long shear zone, which strikes parallel to the Middle America trench, is active. This left-lateral strike-slip La Venta-Chacalapa (LVC) fault system is apparently associated with a motion of the Xolapa terrain, and at the present time is the northern boundary of a ~110 – 160 km wide forearc sliver with a sinistral motion of 3 – 6 mm/yr with respect to the North America plate. This sliver is the major tectonic feature in the Guerrero and Oaxaca regions, which accommodates most of the oblique component of the convergence between the Cocos and North America plates. Previous studies based purely on the moment tensor coseismic slips exceedingly overestimated the sliver inland extent and allocated its northern margin on or to the north of the Trans-Mexican Volcanic Belt. While the LVC fault system probably slips slowly over geologic scale time, and there is not any historic evidence of large earthquakes on the fault so far, its seismic potential could be very high assuming a feasible order of ~103 years recurrence cycle. A detailed analysis of long-term position time series of permanent GPS stations in the Guerrero and Oaxaca states, Southern Mexico discards previous models and provides clear evidence of an active LVC fault zone bounding the Xolapa forearc sliver. The southeastward motion of this sliver may have persisted for the last ~8-10 Myr and played an important role in the tectonic evolution of the region.

Highlights

The existence of a forearc sliver with contemporary sinistral motion with respect to the stable North America plate should be expected as a result of the strain partitioning produced by oblique subduction of the Cocos plate (CO)
Long-lasting GPS observations and geomorphology studies in the Guerrero–Oaxaca area of the Mexican subduction zone show that, despite the almost complete absence of historic and instrumentally recorded seismicity in the western La Venta–Chacalapa (LVC) fault zone, this mainly left-lateral shear zone is a complex and active system of numerous distributed strike-slip faults that accommodates strain partitioning produced by oblique subduction of the CO
The average velocity of the sinistral motion of the Xolapa sliver predicted from the slip vectors of subduction thrust earthquakes (∼5.4–6.3 mm/year) is consistent with the direct GPS observed trench parallel velocity component across the LVC fault (5–6 mm/year in Guerrero)

Summary

INTRODUCTION

The existence of a forearc sliver with contemporary sinistral motion with respect to the stable North America plate (wrt NA) should be expected as a result of the strain partitioning produced by oblique subduction of the Cocos plate (CO). The modeled fits to the observed Vss data show strike-slip displacement on the surface produced by the creeping fault at the depth more than 10 km while its shallower section is locked These models cannot constrain the fault coupling depth, but they highlight the slower strikeslip motion (∼3 mm/year) on the LVC fault zone within the Guerrero seismic gap compared to the adjacent areas (∼5 mm/year). The LVF location may be considered as a trace of active LVC fault system (Ramírez-Herrera et al, 2018) in western Guerrero mainly because the northern boundary of TABLE 1 | Secular velocities of the GPS stations (VSE , VSN, east and north components referenced to the fixed North America plate), and corresponding standard errors (σVsE , σVsN); trench parallel velocities (Vss) with standard errors (σVss) and azimuth of trench normal (θTn, clockwise from North); T1 and T2 are the start and end limits of the fitting time span, respectively

SS σ VSS θ Tn

CONCLUSION