New Advances in CyberShake PSHA Models
Abstract
The Southern California Earthquake Center (SCEC) has developed CyberShake, a software platform which performs 3D physics-based probabilistic seismic hazard analysis (PSHA) using deterministic wave propagation simulations. To reduce computational cost, CyberShake calculations are performed using reciprocity: Strain Green Tensors are convolved these with slip time histories for hundreds of thousands of individual events from an earthquake rupture forecast (ERF), typically UCERF2. Synthetic seismograms are post-processed to obtain intensity measures, which are combined with event probabilities to produce hazard curves. Typically PSHA results from hundreds of locations are interpolated to produce a regional hazard map.
In 2019, we expanded CyberShake to a large Northern California region, including the San Francisco Bay Area. PSHA calculations up to 1 Hz were performed for 869 locations of interest as part of CyberShake Study 18.8, which required 128 days of simulation on the NCSA Blue Waters and OLCF Titan supercomputers . To support simulation volumes that included most of California, we tiled three separate 3D community velocity models into a composite statewide model and applied smoothing along interfaces to minimize unrealistic reflections and refractions. To improve the representation of the near-surface velocity structure in tomographically-derived models, we inserted a geotechnical layer (GTL) in the top 500 meters by applying the Ely (2010) method on Vs30 values from the Wills et al. (2015) map. We will compare hazard results with and without the GTL to quantify its impact. Additionally, we performed CyberShake hazard calculations using an alternative ERF. The RSQSim earthquake simulator was used to generate million-year synthetic earthquake catalogs for California. Events with M≥ 6.5 are selected from the catalog to create an extended ERF, and were used to create the first fully physics-based hazard curves for California. We will present unified CyberShake results for southern, central, and northern California, comparing CyberShake PSHA results to those obtained from GMPEs. We will compare CyberShake results using UCERF2 to those with RSQSim, and discuss our future plans.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMNH23A..07C
- Keywords:
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- 4302 Geological;
- NATURAL HAZARDS;
- 4343 Preparedness and planning;
- NATURAL HAZARDS;
- 7212 Earthquake ground motions and engineering seismology;
- SEISMOLOGY