The Mechanisms of Tsunami Amplification and the Earthquake Source of the 2021 M7 Acapulco, Mexico, Earthquake

Abstract

Here we show a slip model for the 2021 M7 Acapulco, Mexico, earthquake produced by inversion of strong motion, GNSS, tide gauge, and InSAR data. The earthquake occurs within the Guerrero gap, identified as a region of concern for its seismogenic potential and paucity of large events. We find that rupture was compact, constrained to depths between 10 and 20 km and consistent of two main slip patches. The slip model leaves a broad swath of the megathrust unbroken. Whether the event signals a reactivation of large earthquakes in the region remains unknown. We find that tide gauge recordings inside Acapulco Bay for the M7 1962 earthquake and the 2021 event are strikingly similar, we interpret this as weak evidence that 2021 is a repeat of 1962. We also produce a high resolution hydrodynamic model of the resulting tsunami using the slip model as initial condition and place special emphasis in understanding the long duration (~17 hr) of waves inside the bay. We find that simple bay resonance alone does not account for the features of the event. Rather it is a complex interaction with shelf modes and edge waves which continuously re-excite the bay resonance that leads to the protracted tsunami disturbances. Furthermore, we find that significant currents in excess of 1 m/s occur in localized portions of the bay even when wave amplitudes remain small.

Study of the rupture processes of the 1989 (Mw 6.9) and 2021 (Mw 7.0) Guerrero earthquakes using teleseismic records: Sismotectonic implications

“…The slip model of the 2021 event was also determined by Melgar et al (2022) using strong motion, GNSS, tide gauge, and InSAR data. In the slip model determined by Melgar et al (2022), two maximum slip zones are observed: a zone of maximum slip in the downdip portion of the rupture zone and another in the updip part.…”

“…The slip model of the 2021 event was also determined by Melgar et al (2022) using strong motion, GNSS, tide gauge, and InSAR data. In the slip model determined by Melgar et al (2022), two maximum slip zones are observed: a zone of maximum slip in the downdip portion of the rupture zone and another in the updip part. In the model determined in this study, a zone of maximum slip is observed in the downdip zone and slip corresponding to approximately 20% of the maximum slip is observed in the updip area.…”

“…However, in the 300 independent runs there are models that have slip values in the updip zone that correspond to 45% of the maximum slip. Melgar et al (2022) determine an asperity in the updip zone that corresponds to approximately 40% of their maximum slip. On the other hand, the slip model determined here with teleseismic data defines an asperity in the downdip region of the fault, which is consistent with the source zone defined by Melgar et al (2022).…”

“…Melgar et al (2022) determine an asperity in the updip zone that corresponds to approximately 40% of their maximum slip. On the other hand, the slip model determined here with teleseismic data defines an asperity in the downdip region of the fault, which is consistent with the source zone defined by Melgar et al (2022). However, Melgar et al (2022) determine a second asperity in the updip area.…”

“…These 1962 earthquakes generated small tsunamis and neither of the two events caused damage (Merino et al, 1962;Ortiz et al, 2000). Recently, Melgar et al (2022) determined a slip model of the Acapulco 2021 event using strong motion, GNSS (Global Navigation Satellite System), tide gauge and InSAR (Interferometric Synthetic Aperture Radar) data. They determined that two asperities broke in this event.…”