Analysis of the Stress Field and Orientation of Anisotropic Structures by Mean of the Shear Wave Splitting Technique in the tres Virgenes Volcanic Complex, Baja California, Mexico
Abstract
An analytical approach is performed to estimate the parameters: fast shear wave polarization Ø and time delay δt of microearthquakes recorded from two seismic arrays in the Tres Virgenes Volcanic Complex, Baja California Mexico, during 2009 and 2012 by mean of the shear wave splitting technique, which is based in the cross correlation method. The observation of fast shear wave polarization and time delay parameters allowed us to analyze the change in the stress level and the direction of the principal stresses in the area, of importance to verify the behavior of the current geothermal field located in the studied area. The seismic data set is analyzed by means of time graphs, hodograms and rose diagrams, showing some concordances and slight changes between the years 2009 and 2012. Observations of time delay between the fast (S1) and slow (S2) shear wave phases show a clear increment, having values between 0.002 s to 0.1 s in 2009, meanwhile the values of 2012 have a range that surpass the 0.1 s reaching up to 0.15 s, manifesting a possible increment in the thickness of the anisotropic layer during 2012. The polarization directions in the rose diagrams analyzed for every seismic station are more consistent in the data set of 2012, maintaining in the most cases the main polarizations directions of NW - SE and NE - SW unlike the seismic data set of 2009, meaning a persistent influence of structures aligned due to the increased stress field during 2012. Our results of polarization directions are consistent with the studies of focal mechanisms carried out in 2006 and previous structural geological studies, however our studies show how the local stress level has changed from 2009 to 2012, affecting the orientations of the main geological structures and incorporating secondary polarization directions, proving to be the shear wave splitting technique more sensitive to the changes of the orientation of the structures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T13G0309C
- Keywords:
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- 1242 Seismic cycle related deformations;
- GEODESY AND GRAVITYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 8118 Dynamics and mechanics of faulting;
- TECTONOPHYSICSDE: 8164 Stresses: crust and lithosphere;
- TECTONOPHYSICS