Integrated Analysis of the 2020 Mw 7.4 La Crucecita, Oaxaca, Mexico, Earthquake from Joint Inversion of Geodetic and Seismic Observations

Abstract

ABSTRACT On 23 June 2020, a major thrust faulting earthquake ruptured the megathrust near a sharp transition of the plate boundary beneath the Mexico subduction zone, overlapping the rupture area of the 1965 Mw 7.5 (Ms 7.6) event. A joint inversion of geodetic and seismic observations and prediction of coastal uplifts indicate a compact rupture with a peak slip of ∼3.6 m. The cumulative seismic moment is 1.41×1020  N·m within 20 s of coseismic rupture, giving a moment magnitude of Mw 7.4. The rupture propagated with a relatively high rupture speed (∼3.5 km/s) downdip at depths from 20 to 30 km, terminating at the edge of a slow slip region. The energy-related static stress drop is ∼8.1 MPa. The aftershock distribution and the region where slow slip events occurred show a clear complementary relationship with the coseismic rupture zone of the 2020 Oaxaca event. The high-stress drop and associated deep compact rupture pattern suggest a homogeneous asperity with high strength beneath the Oaxaca region. Comparisons of rupture areas, mechanisms, and seismic waveforms show that the 2020 Mw 7.4 Oaxaca earthquake is a quasi-repeat of the 1965 earthquake. The inferred recurrence interval is ∼55 yr. Static stress transfer from mainshock may trigger near trench aftershocks but has small loading on the megathrust interface in the Tehuantepec seismic gap.