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Potential Shallow Slip and Energy-Deficient Radiation During the 2022 M7.6 Coalcomán, Mexico Earthquake

Description: 

Conventional wisdom for large earthquakes at the subduction interface in Mexico has been that slip stops short of the trench, usually at a depth of ~10km. This has certainly been true for M7+ events in the last ~25 years for which slip models constrained by teleseismic and regional seismic and geodetic data exist. Because shallow slip, or its absence, directly impacts the resulting tsunami, this view has had a strong influence on how tsunami hazards are quantified in the country. However, there is paleoseismic evidence of significant tsunamis which can likely only be explained by near-trench slip. In the northern reaches of the subduction zone, there is also compelling evidence that the 1995 M8 Jalisco earthquake included slip to the trench. Here we present a source analysis of the 2022 M7.6 Coalcoman earthquake in Michoacan using teleseismic, regional strong motion, high-rate GNSS, InSAR, and tsunami data. We will show that the slip pattern abuts the southern terminus of the 1995 rupture, and moreover that there is potentially a modest amount of slip at near-trench-depths. We will show a number of different tests that rely on modeling tide gauges near the event using high-resolution bathymetry and confirm that this shallow slip is a necessary feature of the slip model. Additionally, we will show that the radiated energy of the event is significantly less than what is expected both globally and regionally for an event of this size. This is consistent with shallow near-trench slip which typically radiates poorly at high frequencies. Finally, we will discuss the implications of the source properties both from a hazards and a seismotectonics standpoint.

Session: Active Faults in the Caribbean and Central America

Type: Oral

Date: 4/20/2023

Presentation Time: 03:00 PM (local time)

Presenting Author: Diego Melgar

Student Presenter: No

Invited Presentation: 

Authors