SPATIO-TEMPORAL ANALYSIS OF SEISMIC VELOCITIES IN GUERRERO, MEXICO

Abstract:

In this work we present an analysis of the seismic velocity structure of the northern parts of Guerrero Oaxaca. The spatial structure was determined from the group velocity of Rayleigh waves for the years 2005 to 2012. The estimation of velocity changes in time was done by applying the Coda Seismic Interferometry technique from 2009 to 2012. The study was made with 8 stations from the National Seismological Service of Mexico (SSN), 38 MASE (MesoAmerican Subduction Experiment) stations and 13 from the GGAP project (a set of seismic mini arrays).

SSE’s have been detected in both states, but with very different behaviors. In Guerrero they occur every 4 years with magnitudes ~ 7.5 Mw (e.g. Kostoglodov et al., 2010). In Oaxaca they occur every year with an average magnitude of 6.5 Mw (Brudzinski et al., 2007). We found a correlation of seismic velocity variations for periods between 15s – 20s (depths above the plate interface) related to the SSE activity in both states. Specifically, seismic velocity changes were observed in the Guerrero Sweet Spot during the 2009 - 2010 SSE in Guerrero and 2012 SSE in Oaxaca.

The space results were consistent with other studies that highlight the fluids presence close to the interface. These measures show, low resistivity (Jödicke et al., 2006), pore pressure (Rivet et al., 2013) and high Vp/Vs ratio (Kim et al., 2010). We assume that identified negative anomalies in the group velocity are attributed to the fluids, since they are prominent in all tomograms specifically in the last filter (25s) where this anomaly has an expansion attributed to its migration.