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Proposed Updates to the Finite-Fault Model Depiction for Shakemap Computations

Description: 

The U.S. Geological Survey’s ShakeMap product relies on estimates of rupture geometry to provide accurate predictions of shaking intensity for large-magnitude earthquakes. We approximate the extent of the complex slip distribution with a quadrilateral (known as the “ShakeMap polygon”) to compute fault-to-site based distances (e.g., Joyner-Boore distance, source-rupture distance, and other measures), which must be approximated from a point-source distance when a slip model is not yet available. Currently, the rapid finite-fault model we routinely produce at the National Earthquake Information Center (NEIC) following significant (M7+) earthquakes is constrained to be a single planar fault model, which is generally sufficient for rapid shaking and impact estimation purposes. However, even simplistic planar fault models may have multiple spatially separate slip asperities with dimensions poorly approximated by a single quadrilateral. Furthermore, as we enhance the NEIC finite-fault product methodology to allow more complex rupture orientations within the rapid response time frame (e.g., models that accommodate varying dip from the Slab2 subduction zone models), we aim to update the associated ShakeMap polygon computations to allow for non-planar orientations. In this presentation, we explore new methods for approximating the ruptured portions of the fault responsible for strong motion radiation from finite-fault models to improve downstream ShakeMap shaking estimates. We provide examples of the impact these changes can have on shaking estimates, including for locations where station coverage may moderate the importance of constraining fault-finiteness.

Session: ShakeMap-related Research, Development, Operations, Applications and Uses [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Dara E. Goldberg

Student Presenter: No

Invited Presentation: 

Authors