Crustal anisotropy from tectonic tremor in Guerrero, Mexico

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AbstractWe present new shear wave anisotropy measurements in the continental crust in northern Guerrero obtained from tectonic tremor. Measurements of crustal anisotropy had not been performed in this area due to the lack of seismicity. However, tectonic tremor activity is abundant and offers an opportunity to determine anisotropy parameters. Polarization and splitting analyses were performed using broadband three‐component seismograms. Results show that splitting times range between 0.07 and 0.36 s. These values are similar to the splitting magnitudes typically observed in the continental crust. The state of stress in the continental crust was investigated by inverting focal mechanisms determined in this study, and also from previous structural geology studies. Unfortunately, no stress measurements were possible in the area where tectonic tremor occurs. It was determined that, to the south of the study area, near the Pacific coast, and to the north, in the volcanic arc, the maximum compressive stress shows a general E‐W trend. The fast polarization directions are oriented NE‐SW and are oblique to the observed maximum compressive stress surrounding the study area. Thus, the relationship between the maximum compressive stress and the observed anisotropic pattern cannot be conclusively established. Several factors such as nonlinear strain in the continental crust as a result of Slow Slip Events, variations of pore fluid pressure, deep crustal mineralogy, and/or upper crust foliations and schistosity could be inducing the observed anisotropy pattern. In general, the fast axes tend to parallel the regional Laramide and Tertiary folds‐and‐thrusts which strike NNE‐SSW. This system of folds‐and‐thrusts is highly foliated in low‐grade schist and seems likely to control the anisotropic structure observed within the tectonic tremor region in Guerrero.