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

Abstract

ABSTRACT We present a slip model for the 2021 M 7 Acapulco, Mexico, earthquake produced by inversion 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 7 1962 earthquake 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 (∼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 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.