Seminars & Events

Computing, Environment and Life Sciences and University of Chicago
"From M8 to CyberShake: Using Large-Scale Numerical Simulations to Improve Seismic Hazard Models"

DATE: April 18, 2011
TIME: 11:00 AM - 12:00 PM
SPEAKER: Thomas H. Jordan, Center Director, Southern California Earthquake Center (SCEC)
LOCATION: Building 240 Conference Room 1404, Argonne National Laboratory
HOST: Rick Stevens and Daniel Katz

Description:
Abstract. A seismic hazard model computes the probability that earthquake ground motions at a geographic site will exceed some specified shaking intensity during a fixed interval of time. The National Seismic Hazard Model (NSHM), which is regularly updated by the USGS for all U.S. territories, is the basic source of seismological information used by decision-makers at the local, state, and federal levels for earthquake risk assessment, seismic safety engineering, and disaster preparedness. The NSHM is currently limited by uncertainties in long-term earthquake rupture forecasts, the paucity of near-field recordings of large earthquakes, and the variability arising from fault rupture complexity and wave propagation through highly heterogeneous crustal structures. This presentation will describe how large-scale, physics-based simulations of earthquakes can improve seismic hazard mapping by addressing these limitations.
Interdisciplinary teams organized by the Southern California Earthquake Center (SCEC) have used the Oak Ridge and Argonne Leadership Computing Facilities, as well as NSF supercomputers, to model a complete spectrum of earthquakes in Southern California. The M8 production runs on NCCS Jaguar have simulated magnitude-8 earthquakes on the San Andreas fault with 4D outer/inner scale ratios approaching 1017, fully representing the strong seismic shaking from a “wall-to-wall” rupture up to frequencies of 2 Hz. The computational advantages of seismic reciprocity, which expresses the reversal symmetries of linear wave propagation, have been employed to develop a new type of physics-based seismic hazard model called CyberShake. In its current implementation, CyberShake can generate and manipulate suites of synthetic time-histories large enough (~108 seismograms) for the probabilistic mapping of shaking intensities throughout the Los Angeles region. The physics-based model predicts long-period shaking intensities in the highly-populated sedimentary basins that are substantially higher than empirical models such as the NSHM, primarily due to the strong coupling between rupture directivity and basin excitation. SCEC plans to scale CyberShake up to a 1-Hz statewide seismic hazard model—an exascale computational problem—to coincide with the next release of the NSHM in 2013.
In addition to their utility for long-term hazard mapping, numerical simulations can be used to improve operational earthquake forecasting, which provides short-term earthquake probabilities using seismic triggering models, and earthquake early warning systems, which predict imminent shaking during an event. These applications offer new and urgent computational challenges, including requirements for robust, on-demand supercomputing and rapid access to very large data sets.
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