Annual Meeting - SCEC.org

Poster Abstracts | Group 2 – Tectonic Geodesy
provide a clearer picture of how the instruments respond to true geophysical signals, such as
episodic tremor and slip; and (3) comparison of the detection levels of borehole and longbase
strainmeters, borehole seismometers, and (when available) co-located surface-mounted broadband
seismometers.
2-024
PBO NUCLEUS: THE HOME STRETCH Blume F, Boyce E, Miller MM, Eriksson SC, and
Borsa A
Tectonic and earthquake research in the US has experienced a quiet revolution over the last decade
precipitated by the recognition that slow-motion faulting events can both trigger and be triggered
by regular earthquakes. Transient motion has now been found in essentially all tectonic
environments, and the detection and analysis of such events is the first-order science target of the
EarthScope Project. Because of this and a host of other fundamental tectonics questions that can be
answered only with long-duration geodetic time series, the incipient 1400-station EarthScope Plate
Boundary Observatory (PBO) network has been designed to leverage 445 existing continuous GPS
stations whose measurements extend back over a decade. The irreplaceable recording history of
these stations will accelerate EarthScope scientific return by providing the highest possible
resolution. This resolution will be used to detect and understand transients, to determine the threedimensional
velocity field (particularly vertical motion), and to improve measurement precision by
understanding the complex noise sources inherent in GPS. The PBO Nucleus project supports the
operation, maintenance and hardware upgrades of a subset of the six western U.S. geodetic
networks until they are subsumed by PBO. Uninterrupted data flow from these stations will
effectively double the time-series length of PBO over the expected life of EarthScope, and has
created, for the first time, a single GPS-based geodetic network in the US. The other existing sites
remain in operation under support from non-NSF sources (e.g. the USGS), and EarthScope
continues to benefit from their continued operation On the grounds of relevance to EarthScope
science goals, geographic distribution and data quality, 209 of the 432 existing stations were
selected as the nucleus upon which to build PBO. Conversion of these stations to a PBO-compatible
mode of operation was begun under previous funding, and as a result data now flow directly to
PBO archives and processing centers while maintenance, operations, and meta-data requirements
are continue to be upgraded to PBO standards. At the end of this project all 209 stations will be
fully incorporated into PBO, meeting all standards for new PBO construction including data
communications and land use permits. Funds for operation of these stations have been included in
planned budgets for PBO after the construction phase ends and PBO begins an operational phase
in 2008.
2-025
HETEROGENEOUS RUPTURE OF 2008 WENCHUAN, CHINA EARTHQUAKE
CONSTRAINED BY JOINTED INVERTING SEISMIC AND INSAR DATA Ji C, Lu Z,
Hudnut KW, Liu J, and Shao G
We study the rupture process of the 2008 Wenchuan earthquake using both seismic and INSAR
data and explore an unprecedented complex rupture process. The rupture of this event occurred
simultaneously on two parallel faults which intersect each other and extend unilaterally to over 250
km. The entire rupture exended over 100 sec. We observed the strong dynamic interaction between
the two faults. The rupture initiated at the low angle Pengguan fault at a depth around 11 km
below the intersection of Pengguan and high angle Beichuan faults and then triggered the
Beichuan fault 10 s later. The rupture continued on Pengguan fault for another 30 sec with slip
gradually changing from pure thrust to oblique motion and then ceased 90 km northeast of the
epicenter. The rupture on Beichuan fault had similar change in slip direction but extend a much
150 | Southern California Earthquake Center