Rupture Models of Recent Mw > 7 Thrust Earthquakes in the Guerrero-Oaxaca Region of the Mexico Subduction Zone Using Teleseismic Body Waves

We invert the teleseismic broadband (1-60 s period) ground-displacement body waveforms recorded for the 1995 M-w 7.3 Copala, the 1996 M-w 7.1 Oaxaca, the 2012 M-w 7.5 Ometepec, and the 2018 M-w 7.2 Pinotepa Nacional thrust earthquakes in the Guerrero-Oaxaca portion of the Mexico subduction zone to derive the best-fit rupture models using a sampling procedure in which input fault parameters are selected from a prescribed range of values. More than 400 independent inversions are performed for each event using random combinations of strike, rake, dip, and hypocenter depth. Waveform fits are observed to be relatively insensitive to variations in strike, rake, and focal depth but show a distinct dependence on fault dip. The lowest residuals are limited to a dip interval of about +/- 3 degrees, indicating that a relatively precise estimate of the fault dip is necessary for the optimal derivation of slip models using teleseismic body waves. The best-fit teleseismic source models obtained for the four events show varying degrees of spatial detail, with the 2012 and 2018 earthquakes exhibiting more separated slip along the fault than has been observed in rupture models derived using frequency bands covering longer periods. Areas of high-interplate slip for the four events do not overlap, suggesting an adjoining pattern of asperity zones that is consistent with prior observations in northwest Mexico and in the New Britain region of the South Pacific. Additional investigation of this type of asperity interaction for recurrent events would be beneficial, given the implications for estimating the size and location of future large subduction earthquakes.

Automated summary

The study emphasizes the importance of accurate estimation of fault dip in deriving rupture models using teleseismic body waves in the Guerrero-Oaxaca portion of the Mexico subduction zone. The best-fit teleseismic source models for different earthquake events show varying degrees of spatial detail, with non-overlapping areas of high interplate slip, suggesting an adjoining pattern of asperity zones similar to other regions. Further investigation of this type of asperity interaction for recurrent events would be beneficial for estimating the size and location of future large subduction earthquakes.