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ABSTRACT CyberShake is a high-performance computing workflow for kinematic fault-rupture and earthquake ground-motion simulation developed by the Statewide California Earthquake Center to facilitate physics-based probabilistic seismic hazard assessment (PSHA). CyberShake exploits seismic reciprocity for wave propagation by computing strain green tensors along fault planes, which in turn are convolved with rupture models to generate surface seismograms. Combined with a faultwide hypocentral variation of each simulated rupture, this procedure allows for generating ground-motion synthetics that account for realistic source variability. This study validates the platform’s kinematic modeling of physics-based seismic wave propagation simulations in Southwest Iceland as the first step toward migrating CyberShake from its original study region in California. Specifically, we have implemented CyberShake workflows to model 2103 fault ruptures and simulate the corresponding two horizontal components of ground-motion velocity on a 5 km grid of 625 stations in Southwest Iceland. A 500-yr-long earthquake rupture forecast consisting of 223 hypothetical finite-fault sources of Mw 5–7 was generated using a physics-based model of the bookshelf fault system of the Southwest Iceland transform zone. For each station, every reciprocal simulation uses 0–1 Hz Gaussian point sources polarized along two horizontal grid directions. Comparison of the results in the form of rotation-invariant synthetic pseudoacceleration spectral response values at 3, 4, and 5 s periods are in good agreement with the Icelandic strong motion data set and a suite of empirical Bayesian ground-motion prediction equations (GMPEs). The vast majority of the physics-based simulations fall within one standard deviation of the mean GMPE predictions, previously estimated for the area. At large magnitudes for which no data exist in Iceland, the synthetic data set may play an important role in constraining GMPEs for future applications. Our results comprise the first step toward comprehensive and physics-based PSHA for Southwest Iceland.
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Reduced-order modelling for complex three-dimensional seismic wave propagation
SUMMARY Elastodynamic Green’s functions are an essential ingredient in seismology as they form the connection between direct observations of seismic waves and the earthquake source. They are also fundamental to various seismological techniques including physics-based ground motion prediction and kinematic or dynamic source inversions. In regions with established 3-D models of the Earth’s elastic structure, such as southern California, 3-D Green’s functions can be computed using numerical simulations of seismic wave propagation. However, such simulations are computationally expensive, which poses challenges for real-time ground motion prediction and uncertainty quantification in source inversions. In this study, we address these challenges by using a reduced-order model (ROM) approach that enables the rapid evaluation of approximate Green’s functions. The ROM technique developed approximates three-component time-dependent surface velocity wavefields obtained from numerical simulations of seismic wave propagation. We apply our ROM approach to a 50 km $$\times$$ 40 km area in greater Los Angeles accounting for topography, site effects, 3-D subsurface velocity structure, and viscoelastic attenuation. The ROM constructed for this region enables rapid computation ($$\approx 0.0001$$ CPU hr) of complete, high-resolution (500 m spacing), 0.5 Hz surface velocity wavefields that are accurate for a shortest wavelength of 1.0 km for a single elementary moment tensor source. Using leave-one-out cross validation, we measure the accuracy of our Green’s functions for the CVM-S velocity model in both the time domain and frequency domain. Averaged across all sources, receivers, and time steps, the error in the rapid seismograms is less than 0.01 cm s−1. We demonstrate that the ROM can accurately and rapidly reproduce simulated seismograms for generalized moment tensor sources in our region, as well as kinematic sources by using a finite fault model of the 1987 $$M_\mathrm{ W}$$ 5.9 Whittier Narrows earthquake as an example. We envision that rapid, accurate Green’s functions from reduced-order modelling for complex 3-D seismic wave propagation simulations will be useful for constructing real-time ground motion synthetics and source inversions with high spatial resolution.
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- PAR ID:
- 10573625
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 241
- Issue:
- 1
- ISSN:
- 0956-540X
- Format(s):
- Medium: X Size: p. 526-548
- Size(s):
- p. 526-548
- Sponsoring Org:
- National Science Foundation
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