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The SCEC TeraShake Earthquake Simulation
Abstract
The southern portion of the San Andreas fault, between Cajon Creek and
Bombay Beach has not seen a major event since 1690, and has therefore
accumulated a slip deficit of 5-6 m. The potential for this portion of
the fault to rupture in a single M7.7 event is a major component of
seismic hazard in southern California and northern Mexico. TeraShake is
a large-scale finite-difference (fourth-order) simulation of such an
event based on Olsen's Anelastic Wave Propagation Model (AWM) code, and
conducted in the context of the Southern California Earthquake Center
Community Modeling Environment (CME). The fault geometry is taken from
the 2002 USGS National Hazard Maps. The kinematic slip function is
transported and scaled from published inversions for the 2002 Denali
(M7.9) earthquake. The three-dimensional crustal structure is the SCEC
Community Velocity model. The 600km x 300km x 80km simulation domain
extends from the Ventura Basin and Tehachapi region to the north and to
Mexicali and Tijuana to the south. It includes all major population
centers in southern California, and is modeled at 200m resolution using
a rectangular, 1.8 giganode, 3000 x 1500 x 400 mesh. The simulated
duration is 200 seconds, with a temporal resolution of 0.01seconds,
maximum frequency of 0.5Hz, for a total of 20,000 time steps. The
simulation is planned to run at the San Diego Supercomputer Center
(SDSC) on 240 processors of the IBM Power4, DataStar machine. Validation
runs conducted at one sixteenth (4D) resolution have shown that this is
the optimal configuration in the trade-off between computational and I/O
demands. The full run will consume about 18,000 CPU.hours. Each time
step produces a 21.6GByte mesh snapshot of the entire ground motion
velocity vectors. A 4D wavefield containing 2,000 time steps, amounting
to 43 Tbytes of data, will be stored at SDSC. Surface data will be
archived for every time step for synthetic seismogram engineering
analysis, totaling 1 Tbyte. The data will be registered with the SCEC
Digital Library supported by the SDSC Storage Resource Broker (SRB).
Data collections will be annotated with simulation metadata, which will
allow data discovery operations on metadata-based queries. The binary
output will be described using HDF5 headers. Each file will be
fingerprinted with MD5 checksums to preserve and validate data
integrity. Data access, management and data product derivation will be
provided through a set of SRB APIs, including java, C, web service and
data grid workflow interfaces. High resolution visualizations of the
wave propagation phenomena will be produced under diverse camera views.
The surface data will be analyzed online by remote web clients plotting
synthetic seismograms. Data mining operations, spectral analysis and
data subsetting are planned as future work. The TeraShake simulation
project has provided some insights about the cyberinfrastructure needed
to advance computational geoscience, which we will discuss.
... Using the methodologies above, subsurface structure of various levels of 3D heterogeneity can be incorporated in the simulation of the propagation of the seismic energy. The downside of these methods, however, is the relatively high computational cost that limits their use, since large scale computer systems need to be employed in order to carry out large scale simulations: e.g. the TeraShake simulation (Minster et al., 2004), the Tangshan earthquake simulations by Fu et al. (2017), etc. Furthermore, each of these methods has an intrinsic disadvantage such as numerical dispersion in the finite element method (Bonilla, 2002) or the limitation to models with weak heterogeneities in the boundary element method (Semblat, 2011). ...
An identification of the responsible faults for the destructive earthquakes of 1894 in the Atalanti region was carried out by employing a novel application of 3D finite-difference wavefield modeling. Several faults proposed in the literature were tested in detailed 3D simulations, by also utilizing a detailed local 3D velocity model, as well as the local topography. The assessment of the most probable sources for these events was based on the correlation of reported damages with the distribution of the simulated peak ground acceleration. Furthermore, the distribution of the spectral amplitudes at higher frequencies that are related to the resonant frequencies of the local buildings on that time period was also used as an indicator. The general effect of the local 3D subsurface structure on the propagation of the wavefield and the spatial distribution of the ground motion was also investigated. The Malessina fault was identified as a probable source for the main event of 20/4/1894 based on the results of the 3D modeling, whereas the 3D effect was found to be a highly contributing factor to the distribution of the simulated ground motion.
... Deep sedimentary basins in southern California form significant velocity structures in the crust. These basins are generally filled with thick (up to 12 km) sequences of relatively low velocity and density sediments that have been shown to amplify seismic waves and localize hazardous ground shaking during large earthquakes (e.g., Bonamassa and Vidale, 1991;Frankel and Vidale, 1992;Bouchon and Barker, 1996;Olsen, 2000;Graves et al., 1998;Bielak et al., 1999;Aagaard et al., 2001;Komatitisch et al., 2004;Minster et al., 2004;. Thus, the first step in our development of the USR was to generate accurate descriptions of the 3D geometry and velocity structures of the major basins. ...
... The simulation was run at SDSC on 240 processors of the IBM Power4, DataStar machine [9,10]. Validation runs conducted at one-sixteenth (4D) resolution have shown that this is the optimal configuration in the trade-off between computational and I/O demands. ...
The Southern California Earthquake Center digital library publishes scientific data generated by seismic wave propagation simulations. The output from a single simulation may be as large as 47 Terabytes of data and 400,000 files. The total size of the digital library is over 130 Terabytes with nearly three million files. We examine how this scale of simulation output can be registered into a digital library built on top of the Storage Resource Broker data grid. We also examine the multiple types of interactive services that have been developed for accessing and displaying the multi-terabyte collection.
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