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Poster Abstracts | Group 2 – Tectonic Geodesy
Angeles, in early 2005. Up to 6 cm of vertical deformation affecting seven GPS sites, centered on the
site LONG, can be seen in both GPS and InSAR data. This has been interpreted as a
hydrogeological response of an aquifer to high rainfall in the spring of 2005 by other authors (e.g.
N. King et al., 2007, JGR). We assess here the effects and potential data improvements that arise
from the integration of meteorological data into our GPS processing, and hence the proportion of
the InSAR signal that has a tropospheric origin.
We find that the inclusion of meteorological data in GPS data processing corrects for a persistent
vertical bias in GPS station coordinates and improves the repeatability of tropospheric delay
estimates. In addition, we find that the observed InSAR signal in the
San Gabriel Valley spanning the period of uplift in 2005 cannot be solely interpreted as a
hydrological uplift but includes significant contributions from tropospheric delay. This
tropospheric phase contribution could result in an overestimate of peak aquifer uplift by as much
as 30% if left unaccounted for.
2-028
MITIGATION OF TROPOSPHERIC EFFECTS ON SITE VELOCITIES OF THE BAY
AREA REGIONAL DEFORMATION NETWORK (BARD) Houlié N, Funning GJ, Friday J,
Gardner J, Burgmann R, and Romanowicz B
The BARD network is a permanent GPS network comprising 40 GPS sites, installed since 1994 in
northern California (Romanowicz et al., 1994). Originally started as a collaborative effort of
different Bay Area institutions, since the establishment of the Plate Boundary Observatory, it is
now focused on real-time data acquisition from stations operated by UC Berkeley, with plans for
expansion in collaboration with USGS/Menlo Park. The BARD network streams data to the
Berkeley Seismological Laboratory in real-time (sampling rates of 1s and 15s, depending on the
site). All sites transmit data using Frame Relay technology which improves reliability in case of
earthquake occurrence. Data are archived at the Northern California Earthquake Data Center
(NCEDC, http://www.ncedc.org) and are freely available (Neuhauser et al., 2001). The BARD
network is currently able to provide high precision (error < 1mm/yr) velocities over most of
northern California.
In the vicinity of San Francisco Bay, however, heterogeneous tropospheric effects can scatter site
coordinates significantly (amplitudes ~5 mm) during a single day of measurements. Such effects
can be seen when comparing sites from either side of the Bay, or between the Bay and the Great
Valley, further inland. With seven sites located less than 15 km from the Hayward fault, the BARD
network is well suited for constraining the slip amplitude (currently ~5 mm/yr of creep) along the
fault's length; however in order to detect small changes in creep rate, such as slip transients, such
tropospheric effects need to be mitigated. We will show recent developments, completed over the
past year, designed to improve the estimation of troposphere delay over the BARD network by
incorporating additional constraints from ground- and air-based meteorological measurements
into our processing.
2-029
INSTANTANEOUS DEFORMATION FROM CONTINUOUS GPS: CONTRIBUTIONS
FROM QUASI-PERIODIC LOADS Bennett RA
Continuous GPS (CGPS) coordinate time-series are known to experience repeating deformation
signals with seasonal and other periods. It is unlikely that these signals represent perfect sinusoids
with temporally constant amplitude. A complete understanding of these "quasi-periodic" motions
152 | Southern California Earthquake Center