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Poster Abstracts
THE 2011 MW 9 TOHOKU-OKI EARTHQUAKE: COMPLEXITY OF DYNAMIC RUPTURE AT THE BOTTOM
OF A SEISMOGENIC ZONE (B-075)
L. Meng, J.P. Ampuero, and A. Inbal
The 2011 Mw 9 Tohoku-Oki earthquake, recorded by over 1000 near-field stations and multiple large-aperture arrays, is by far
the best recorded earthquake in the history of seismology and provides unique opportunities to address fundamental issues in
earthquake source dynamics. We achieved high resolution source imaging of the high frequency (1 Hz) aspects of the rupture
process by back-projecting teleseismic P waves recorded by the USarray and the European seismic network. The mutually
consistent results from both arrays reveal rupture complexity with unprecedented resolution, involving phases of diverse
rupture speed and intermittent high frequency bursts within slow speed phases. The high frequency radiation is generated
mainly at the down-dip edge of the principal slip regions constrained by geodesy. Moreover, its location coincides with the
down-dip limit of interplate seismicity and encompasses regions where the background seismicity contains repeating
earthquakes. The high frequency sources initially propagated down-dip, with a slow initiation phase followed by sustained
propagation at speeds of 3 km/s. The rupture then slowed down to less than 1 km/s for 60 seconds. A rich sequence of bursts
was generated along the down-dip rim of this slow rupture front. Before the end of the slow phase an extremely fast rupture
front detached towards the North, with apparent speed of about 5 km/s . Finally a rupture front propagated towards the
South running at about 2.5 km/s for over 100 km. Key features of the rupture process are confirmed by the strong motion data
recorded by K-net and KIK-net. The energetic high frequency radiation episodes within a slow rupture phase suggests a
patchy image of the brittle-ductile transition zone, composed of discrete brittle (velocity-weakening) asperities within a ductile
(velocity-strengthening) fault zone matrix.
PARALLEL SIMULATED ANNEALING APPROACH TO SOLVE FOR UCERF3 RUPTURE RATES (B-111)
K.R. Milner, M.T. Page, and E.H. Field
We present a parallel approach to the classic simulated annealing algorithm (Kirkpatrick 1983) in order to solve for the rates of
earthquake ruptures in California’s complex fault system, being developed for the 3rd Uniform California Earthquake
Rupture Forecast (UCERF3). Through the use of distributed computing, we have achieved substantial speedup when
compared to serial simulated annealing. We will describe the parallel simulated annealing algorithm in detail, as well as the
parallelization parameters used and their effect on speedup (time to convergence, or alternatively a specified energy level) and
communications efficiency. Additionally we will discuss the correlation between performance of the parallel algorithm and
the degree of constraints on the solution. We will present scaling results to hundreds of processors, and experiences with the
MPJ Express Java Message Passing Library (Baker 2006) on the University of Southern California’s High Performance
Computing and Communications cluster.
References:
Mark Baker, Bryan Carpenter, and Aamir Shafi. MPJ Express: Towards Thread Safe Java HPC, Submitted to the IEEE
International Conference on Cluster Computing (Cluster 2006), Barcelona, Spain, 25-28 September, 2006.
S. Kirkpatrick, C. D. Gelatt, Jr., and M. P. Vecchi. Optimization by Simulated Annealing. Science 13 May 1983: 220 (4598), 671-
680. [DOI:10.1126/science.220.4598.671]
FRACTURE NETWORK CHARACTERISTICS, SEALING, AND VELOCITY STRUCTURE OF AN EXHUMED
SEISMIC FAULT ZONE; THE GOLE LARGHE FAULT ZONE, ITALIAN ALPS (A-020)
T.M. Mitchell, S.A. Smith, A. Bistacchi, M. Rempe, and G. Di Toro
The Gole Larghe Fault Zone (GLFZ) in the Italian Southern Alps has been extensively studied as a natural laboratory for
seismic faulting. Cataclasites and pseudotachylytes formed along pre-existing magmatic cooling joints over a fault zone width
of ~500m, at ambient conditions of 9-11km depth and 250-300°C. We synthesize field measurements and laboratory data
collected in the past three years that concern the architecture, sealing history, and seismic velocity and permeability structure
of the GLFZ.
The GLFZ contains three structural zones: 1) a southern damage zone ~250m wide; 2) a central zone ~100m wide bordered by
the two thickest cataclastic faults (~1m) identified to date, and; 3) a northern damage zone >150m thick. In the southern
damage zone, macroscopic fracture density (faults + joints) increases gradually from background wall-rock values towards the
central zone where it remains relatively high throughout. Despite a similar overall fracture density, the boundary between the
wall rocks and the southern damage zone defined by an abrupt transition from joints to cataclasite- and pseudotachylyte-
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