Figure 1. Map showing locations and focal mechanisms of the earthquakes analyzed in this study. Gray zone delineates Mexican Volcanic Belt. Isodepth contours of the Benioff zone (modified from Singh and Mortera, 1991; Pardo and Suarez, 1995) are marked (dashed where inferred). LVIG and PNIG are seismic stations at Laguna Verde nuclear power plant and Pinotepa Nacional, respectively. Seismograms from TUIG, located on a noisy site, are not used in the analysis. SCIG recorded only three of the events listed in Table 1. A to D refer to the four groups into which the events have been divided. Straight dashed lines, denoted A to D, from the trench to LVIG indicate the locations of the vertical sections on which the events are projected in Figure 4.