Abstract.Seismograms recorded in Mexico City reveal that the amplitudes of seismic waves whose wavepaths pass below Popocat•petl, presently an volcano, before reaching the city are diminished by a factor of about one-third at frequencies greater than i Hz as compared to those which do not cross the volcano. The high attenuation of seismic waves below the volcano may be attributed to the presence of magma and partial melting of rocks. Q of shear waves below the volcano is roughly estimated as 60. A consequence of the large attenuation of high-frequency seismic waves is a decrease in the seismic hazard to low-rise buildings in Mexico City from intraplate earthquakes whose wavepaths cross the volcano.

We relocated 52 events of 2.5 ≤ Mc ≤ 3.6 from a seismic sequence of over 250 events that occurred during July-December 2012 southwest of the Linares area, northeastern Mexico. To examine this swarm four seismic stations were installed in the region and operated during different time periods from September to December. Relocation of the swarm showed that the earthquake hypocentral depths were at 8 (±5) km, and the time residuals had values ≤ 0.38 s. The fault plane solutions were generated for individual earthquakes and through the use of the composite mechanism technique. The focal mechanism solutions show pure reverse faulting; the SW dipping NNW - SSE trending nodal plane is the inferred fault plane (strike ~150°, dip ~50° and rake ~67°), which reveals that maximum horizontal stress (SHmax > Shmin > Sv) predominates in the area.

A parameterized source and path effects inversion method based on the use of global optimization techniques is presented. We applied this method on velocity data from various seismic events collected between August, 2005 and April, 2007 in Mexico by the regional MesoAmerican Subduction Experiment (MASE) seismic network and other stations from the permanent Mexican Seismological Survey Network (SSN). The source, path and site parameters corresponding to the S wave amplitude spectra of 219 velocity seismic records (162 from MASE and 57 from SSN) were estimated by means of a generalized inversion approach. The simultaneously inverted parameters from the records of 55 stations shows a significant agreement between the observed and calculated spectra, which supports their realiability. Nakamura’s method was used to compute an initial guess for the generalized inversion. Comparisons between Nakamura’s technique and parameterized source and path effects inversion by using simulated annealing method were also established. Finally, a frecuency dependent attenuation relationship for the study area was computed by using a genetic algorithm inversion approach.