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Application of ISC-PPSM to Subduction Zone Seismicity in South and Central America

Session: Subduction Processes Along Latin America Subduction Zones I

Type: Oral

Date: 4/19/2021

Presentation Time: 10:30 AM Pacific

Description: 

The precise depth of shallow earthquakes that occur outside the aperture dense seismic networks remains poorly constrained in both local and regional earthquakes. Even in well instrumented subduction zone settings this can lead to a lack of depth resolution for earthquakes occurring offshore. Earthquake locations and moment tensor solutions for these earthquakes can therefore often be set to a fixed depth, while significant variations can be seen between the moment tensors reported. In order to address these uncertainties, we report the earthquake depth and moment tensor uncertainties inferred for shallow (<40 km) subduction zone earthquakes in South and Central America, using the techniques of the newly implemented ISC-PPSM (International Seismological Centre – Probabilistic Point Source Model) catalogue. ISC-PPSM is a global earthquake catalogue which employs a Bayesian inversion strategy to jointly solve for the earthquake moment tensor, source time function (STF) and depth. This allows the trade-offs between STF and depth to be investigated, while quantifying the uncertainty in the earthquake moment tensor. This inversion strategy allows new depth resolution to be added, especially to relatively shallow earthquakes, where tele-seismically observed depth phases would otherwise be subsumed into the STF. Earthquake depths determined in this way will then be used to inform the depth of earthquakes in the ISC-bulletin, where the depth would otherwise be uncertain or unconstrained. The ensemble of earthquake point source solutions produced also allows the error in the earthquake mechanism to be quantified. In this study, probabilistic moment tensor solutions for moderate magnitude (Mw 5.8 – 7.0) earthquakes are compared to the geometry of the subducting slab in order to estimate the portion of offshore seismicity that occurs directly on the subduction zone interface, and add potential constraints to the roughness of the subduction interface.

Presenting Author: Thomas I. M. Garth

Student Presenter: No

Authors