Annual Meeting - SCEC.org

Poster Abstracts | Group 1 – CME/PetaSHA
initialization. Further code enhancements are highly required to meet the novel challenges that
emerge when running at the largest scales.
We ported and optimized the AWP-Olsen code for use on the 504 teraflops TACC’s Ranger
machine. Special algorithms have been implemented into the code for easy adaptation on different
TeraGrid platforms, which proven to be highly effective for use. The optimizations are adjusted at
run-time depending on system characteristics. Additional options are also added to selectively
decimate the output spatially or/and temporally.
Scaling the reads of initial conditions is a challenging task due to its extraordinary size and highly
discontinuous distribution. We have implemented MPI-IO for both source and media initialization.
The parallelization and integration of these routines involves first determining the layout of the
physical cells that describes physical velocity information and the sources that provide fault
information to processors in a manner that can be used by the IO routines. Based on the precalculated
information, linear abstract data types for both files are created. Each processor can
access its local data linearly with the aforementioned customized MPI-IO data types. Temporal
source partitioning for the source data has also been introduced to prevent a memory buffer
overflow, which may occur when a large amount of source nodes are allocated in a single
processor. The initial parallel mesh initialization has already shown a time reduction from previous
15 hours to less than minute. Further tests are under way for different compilers and large data
sets.
Furthermore, we implemented an application-initiated check-pointing facility to prepare multipleday
ShakeOut-D mesh initialization on three SDSC BG/L racks. This IBM-based restart library
feature is at system-level, where no application-level restart capability is available. This provided
an initial insight of the type of fault tolerance feature needed for petascale computing.
1-021
SEARCHING FOR 3D WAVE-PROPAGATION EFFECTS IN SOUTHERN
CALIFORNIA Ely GP
Ground motions in southern California can be significantly influenced by three-dimensional basin
wave-propagation effects. Amplification due to focusing was observed in Santa Monica during the
1994 Northridge event. Simulations of large events on the southern San Andreas within the SCEC
Community Velocity Model (CVM) find large amplifications at Whittier Narrows due to basinguided
waves. We have begun a study to search for similar basin effects in southern California,
using a series 3D wave-propagation simulations over a suite of potential source scenarios. Selection
of scenarios is being guided by the Uniform California Earthquake Rupture Forecast, as well as
CyberShake--an effort to estimate probabilistic seismic hazard based on 3D simulations.
Simulations will be performed up to 0.5 Hz using the Support Operator Rupture Dynamics (SORD)
code and kinematic finite-fault sources, with fault geometry (often non-planar) from the SCEC
Community Fault Model. Waves will be propagated through the SCEC-CVM as well as the SCEC-
CVMH (Harvard version) with comparisons helping to address uncertainty in the basin effect
results. Selected scenarios will recomputed with dynamic rupture sources.
1-022
WEBSIMS: A PYTHON-BASED WEB APPLICATION FOR STORING, EXPLORING
AND DISSEMINATING 4D EARTHQUAKE SIMULATION DATA Ely GP, and Olsen KB
WebSims aims to provide a tool for cataloging, exploring, comparing and sharing four-dimensional
results of large numerical earthquake simulations. Users may extract time histories or two-
78 | Southern California Earthquake Center