Annual Meeting - SCEC.org

Poster Abstracts | Group 1 – CDM
We have developed open-source finite-element software for 2-D and 3-D dynamic and quasi-static
modeling of crustal deformation. This software, PyLith (current release is version 1.3), combines
the quasi-static viscoelastic modeling functionality of PyLith 0.8 and its predecessors (LithoMop
and Tecton) and the wave propagation modeling functionality of EqSim. The target applications
contain spatial scales ranging from tens of meters to hundreds of kilometers with temporal scales
for dynamic modeling ranging from milliseconds to minutes and temporal scales for quasi-static
modeling ranging from minutes to hundreds of years. PyLith is part of the NSF funded
Computational Infrastructure for Geodynamics (CIG) and runs on a wide variety of platforms
(laptops, workstations, and Beowulf clusters). It uses a suite of general, parallel, graph data
structures called Sieve for storing and manipulating finite-element meshes. This permits use of a
variety of 2-D and 3-D cell types including triangles, quadrilaterals, hexahedra, and tetrahedra.
Current features include kinematic fault ruptures, Dirichlet (displacement or velocity), Neumann
(traction), and absorbing boundary conditions, linear elastic, generalized Maxwell, and Maxwell
linear viscoelastic materials, gravitational body forces, and automatic time step selection for quasistatic
problems. Future releases will add dynamic fault interface conditions (employing fault
constitutive models), additional viscoelastic and viscoplastic materials, and automated calculation
of suites of Green's functions. We also plan to extend PyLith to allow coupling multiple
simultaneous simulations. For example, this could include (1) coupling an interseismic deformation
simulation to a spontaneous earthquake rupture simulation (each using subsets of the software), (2)
coupling a spontaneous earthquake rupture simulation to a global wave propagation simulation,
or (3) coupling a short-term crustal deformation simulation to a mantle convection simulation and
an orogenesis and basin formation simulation.
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CO-SEISMIC DISPLACEMENT FROM THE MW7.9 SICHUAN EARTHQUAKE
DERIVED FROM ALOS RADAR INTERFEROMETRY Tong X, Sandwell DT, and Mellors
R
On May 12th 2008, a Mw 7.9 earthquake struck Wenchuan county, Sichuan Province in China. The
causalities include approximately 70,000 dead and 374,000 injured. The rupture accompanying the
events extended over 270 km toward the northeast, and is a result of the convergent tectonic
movement associated with Longmen Shan fault.
We assemble ALOS PALSAR data including 6 tracks, totally 36 frames, to map the co-seismic
displacement with a full coverage of 400 km by 400 km of the fault zone. We use SIOSAR to
process the dataset, including pre-processing, SAR image focusing, matching the slave scenes to
the master scenes, phase calculating, and topographic correcting. The code has been revised to
apply more precise orbit information to remove the phase discontinuity of adjacent frames along a
single track. More, the topographic phase has been shifted according to cross correlation to
improve the phase correction. So far, we have processed 4 tracks and the interferogram of track 473
is consistent with those of the other groups. However, we found a trending error in the phase of
the track 471. In the future, two more tracks will be analyzed to get the complete displacement
field. Either pixel offset measurements or ScanSAR mode interferometry is required to acquire the
3 dimensional displacement field. GPS displacement measurements, especially in the large ground
motion area, will support the analysis on co-seismic and post-seismic deformation. Models of postseismic
deformation, driven by the co-seismic stress perturbation, will provide important
estimation of seismic hazards from future earthquakes and aftershocks.
126 | Southern California Earthquake Center