The Mechanisms of Tsunami Amplification and the Earthquake Source of the 2021 M 7 Acapulco, Mexico, Earthquake

We present a slip model for the 2021 M 7 Acapulco, Mexico, earthquake produced by inver-sion of strong motion, Global Navigation Satellite Systems, tide gauge, and Interferometric Synthetic Aperture Radar 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, and, 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 M 71962 earth-quake and the 2021 event are strikingly similar, thus 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 (similar to 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 that continuously re-excite the bay reso-nance that leads to the protracted tsunami disturbances. Furthermore, we find that sig-nificant currents in excess of 1 m/s occur in localized portions of the bay even when wave amplitudes remain small.

Automated summary

In this study, a slip model for the 2021 M 7 Acapulco, Mexico earthquake is presented, which was obtained by inverting strong motion, Global Navigation Satellite Systems, tide gauge, and Interferometric Synthetic Aperture Radar data. The earthquake occurred within the Guerrero gap, a region of concern for its seismogenic potential and lack of large events. The slip model indicates a compact rupture at depths between 10 and 20 km, with two main slip patches. It remains uncertain whether this event signifies a reactivation of large earthquakes in the region. Additionally, a high-resolution hydrodynamic model of the resulting tsunami is produced, highlighting the interaction of bay resonance with shelf modes and edge waves that contribute to the prolonged tsunami disturbances.