SCEC Award Number 14061 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Prediction uncertainty in kinematic source inversion
Name Organization
Jean-Paul Ampuero California Institute of Technology
Other Participants Zacharie Duputel
SCEC Priorities 2a, 3c, 6b SCEC Groups Seismology, Geodesy, SIV
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
We recently developed a general approach to explicitly handle Earth model inadequacies when computing geodetic predictions (forward models) in earthquake source inversion problems. We extended this new formalism to seismic predictions. Using this new approach, we can move from traditional deterministic approaches to more appropriate stochastic forward modeling approaches, enabling more rigorous quantification of uncertainties in fault slip inverse problems. In addition, prediction uncertainty dictates the relative weighting between geodetic, tsunami and seismic dataset for a given earthquake source problem. These advances lay the groundwork for a new generation of kinematic source models based on a general formalism that rigorously quantifies and incorporates the impact of uncertainties in fault slip inverse problems.

We applied this new formalism to actual observations in two cases using a Bayesian sampling approach: (1) the study of fault coupling along the San Andreas Fault and (2) the recent 2014 Mw=8.1 Pisagua earthquake. In these two cases, we derived the slip posterior probability density function using a Bayesian approach, including a full description of the data covariance and accounting for uncertainty in the elastic structure of the crust.
Intellectual Merit Our research attempts to enable a new generation of kinematic earthquake source model that are more resistant to over-fitting of data, provide a physical basis for the relative weighting between disparate data sets, and include more realistic estimates of uncertainty on inferred model parameters. This effort exploits recent advances in Bayesian earthquake source modeling and new massively parallel computational approaches using GPUs. The benefits of this approach include improving the sharpness of our images of seismic and aseismic fault slip processes - thereby directly impacting both our models for fault mechanics and inferences of seismic hazard.

Our research addresses the following SCEC4 research priorities and requirements:
• 2a: The tools we developed support the “improvement of earthquake catalogs, including non-point-source source descriptions” by providing a general framework to have realistic error estimates on point-source and finite-fault model parameters.
• 3c: Our results support “theoretical and numerical modeling of specific fault resistance mechanisms for seismic radiation and rupture propagation”, by assessing the reliability of seismological constraints on such processes.
• 6b: By providing better constraints on the earthquake rupture, our results contribute to “modeling of ruptures that includes realistic dynamic weakening mechanisms, off-fault plastic deformation, and is constrained by source inversions”, and to “produce physically consistent rupture models for broadband ground motion simulation.”

Our research directly addresses a priority for FARM: “propose source-inversion methods with minimal assumptions, and provide robust uncertainty quantification of inferred source parameters”. It also relates to Computational Science disciplinary activities: “provide tools and algorithms for uncertainty quantification in large-scale inversion and forward-modeling studies”, and Seismology disciplinary activities: “develop strategies for robust uncertainty quantification in finite-fault rupture models”.
Broader Impacts This project provided training and research opportunities for a postdoctoral scholar, Zacharie Duputel, who is now hired as a CNRS researcher in France. He continues to lead this project, especially through regular visits to Caltech. The multidisciplinary research addressed herein gathered together geodesists, seismologists and computational scientists.

The algorithms and methods developed here are now directly applicable to other crustal deformation problems such as models of volcano deformation or to rapid source estimations problems for warning purposes. As we have done in the past, all of our developed tools will be documented and openly available to the geophysical community as open source. Open source software for 3D kinematic rupture was developed, incorporated in the spectral element code SPECFEM3D, distributed and maintained online through the Computational Infrastructure for Geophysics.
Exemplary Figure Figure 3: From Duputel et al. (in prep). Probabilistic slip model of the April 1st, 2015 Mw 8.1 Pisagua earthquake inferred from InSAR, GPS, tsunami and strong motion data, accounting for uncertainty in the Earth model. Arrows and their associated 95% error ellipses indicate the slip direction and uncertainty. Red star is the inverted hypocenter location. Gray lines are a posterior set of 1000 rupture fronts shown every 10 sec. Bottom left inset shows the posterior ensemble of moment rate functions.