The shear wave splitting technique as a methodology to retrieve temporary variations of induced stress

Abstract

Shear wave splitting studies have represented a good methodology to characterize anisotropic structures both in volcanic and tectonic environments from the analysis of regional and local seismic sources. In contrast, observations due to stress-induced and temporally varying anisotropy (here called TEV) have been more difficult to ensure without doubting that the anisotropic effects could be due to structural alignments instead. This occurs because the anisotropic ray-paths between the seismic sources and the analyzed seismic stations may be affected by structural alignments with different orientations. Based on analysis of previous works, three different scenarios based on the station-event configuration are proposed with the aim of having a better control of the anisotropic measurements. The knowledge of the structural features of the study area, the hypocentral spatial delimitation of the seismic events analyzed as well as their azimuthal variation with respect to the station studied, would allow assessing what would be the best scenario to retrieve temporally induced stress from spatiotemporal variations of the splitting parameters. Therefore, in this work, two previously studied local volcanic areas are evaluated to discern in which cases the groups of seismic events analyzed would be more feasible to retrieve temporary induced stress. These areas are conformed by structural complexities and marked by tectonic and geothermal effects. The anisotropic parameters obtained from some seismic events are strategically analyzed by statistical tests and temporary behaviors, taking into account the structural features of the study area. It is possible to observe that different seismic groups analyzed are more feasible to retrieve TEV effects than other, while others seismic groups are more feasible to be influenced by anisotropic structures.