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Using Geodetically-Derived Strain Rates in Future US National Seismic Hazard Models

Description: 

Geodetic data are now being used in developing the US National Seismic Hazard Map (NSHM) to estimate slip rates on crustal faults using various kinematic models that relate long-term fault slip rates to surface velocities. However, best practices for using geodetic data in the hazard models are still under consideration and challenges remain, especially in areas of diffuse faulting and distributed off-fault deformation, in inferring fault slip rates using geodetic data. Due to a lack of confidence in off-fault strain rate estimates generated by models of geodetic data, these off-fault rates were not used in the 2014 or 2023 NSHM hazard calculations. An alternative approach that was not adopted in 2023 NSHM is to use geodetically-derived strain rates directly, without introducing a kinematic model for surface velocities. Such an approach was adopted for the 2022 release of the New Zealand national seismic hazard model in which slip deficit rates on faults were inverted directly from strain rate observations. In this study, we address two major challenges of working with strain rates: 1. Strain rate inferences are non-unique, and the uncertainties are not well understood, and 2. Methods to infer slip deficit rate on faults directly from strain rate are underdeveloped. To address the first problem, we systematically compute and compare strain rate maps and uncertainties in the western US using suites of different methods for computing strain rates from geodetically-derived velocities. The methods include fitting non-parametric basis functions and elastic basis functions to geodetic data. We also conduct inversions of strain rate observations for slip deficit rates on all western US seismic hazard model faults (2023 NSHM fault model) using a viscoelastic earthquake cycle model that accounts for time-dependent viscoelastic mantle flow due to periodic locking and unlocking of the faults. We explore the uncertainty in slip deficit rate estimates introduced by uncertainties in strain rate observations and viscoelastic cycle model parameters.

Session: USGS National Seismic Hazard Models: 2023 and Beyond [Poster]

Type: Poster

Date: 4/18/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Nicolás Castro-Perdomo

Student Presenter: Yes

Invited Presentation: 

Authors