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Group 1 – CDM | Poster Abstracts
distribution constraint. The resulting coseismic slip model has a similar distribution to previously
published slip models with a chi-square value of 371.
1-105
FRICTION PARAMETERS INFERRED FROM NUCLEATION OF AFTERSLIP
FOLLOWING THE 2003 TOKACHI-OKI EARTHQUAKE Fukuda J, Johnson KM, Larson
KM, and Miyazaki S
We use high-rate GPS measurements of postseismic deformation in the first five hours following
the 2003 Tokachi-oki earthquake located off-shore of Hokkaido, Japan to estimate frictional
parameters of the afterslip zone on the subduction interface. The data show little motion
immediately after the earthquake with sudden acceleration at about 1.2 hours after the mainshock.
We interpret the delayed acceleration as nucleation of afterslip. We model the GPS time series
using a spring-slider system obeying a rate-state friction law. An inversion method is developed to
estimate the posterior probability distributions of critical slip distance, D_c, a*sigma, and (ab)*sigma,
where a and b are friction parameters and sigma is effective normal stress. The estimated
values of D_c, a*sigma, and (a-b)*sigma are 1.1*10^(-3) m, 0.32 MPa, and 0.217 MPa, respectively.
Estimated D_c is 10 to 10^3 times larger than laboratory values. Estimated (a-b)*sigma is consistent
with previous estimates from afterslip models.
1-106
THE 2008 WELLS EARTHQUAKE, NEVADA FROM ENVISAT ASAR DATA Nee P, and
Funning GJ
An earthquake of magnitude 6.0 struck Wells, Nevada on February 21st, 2008 at 6:16AM PST. The
epicenter was located approximately 10 km northeast of the city of Wells with a depth of 6.7 km
according to the Nevada Seismological Laboratory. Over 20 buildings were reported severely
damaged, over 700 buildings lightly damaged and more than three people were injured (NEIC). It
was Nevada's most destructive earthquake since the magnitude 7.1 earthquake in December, 1954
near Dixie Valley.
The Wells earthquake epicenter is covered by four Envisat ASAR tracks with multiple coseismic
pairs of images on each. One descending pair from track 127 (baseline 210 m, spanning 140 days)
and one ascending pair from track 220 (27 m, 140 days) were used in our analysis. Interferograms
were processed using ROI_PAC and a digital elevation model from the Shuttle Radar Topography
Mission. Our data show a four-fringe deformation signal in both pairs, which implies
approximately 12 cm of peak downward displacement of the ground. We subsample our data
using a quadtree decomposition and run inverse elastic dislocation models using the 'okinv' code
in order to find a best-fitting set of fault parameters. We obtain a satisfactory fit to data with both
nodal planes; however we prefer the model with a SE-dipping fault (strike 31, dip 33, rake -97,
depth 3.2-9.8 km, Mw 6.0), which has a smaller misfit to data and agrees with aftershock locations,
which also favor a SE dip (http://www.seismo.unr.edu/feature/2008/Preliminary_relocations1.pdf). This
preliminary model has dip of 33 degrees which is shallower than that obtained by seismic
waveform inversion (e.g. global CMT, UC Berkeley).
1-107
PYLITH: A FINITE-ELEMENT CODE FOR MODELING QUASI-STATIC AND
DYNAMIC CRUSTAL DEFORMATION Aagaard B, Williams CA, and Knepley MG
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