HR: 0800h
AN: G21B-1268    [Abstracts]
TI: First Results From PBO Strainmeters On The Olympic Peninsula And Vancouver Island, Canada.
AU: * Hodgkinson, K
EM: hodgkinson@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Anderson, G
EM: anderson@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Dittmann, T
EM: dittmann@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Gladwin, M
EM: mike@gtsmtechnologies.com
AF: GTSM Technologies, PO Box 178, Kenmore, 4069 Australia
AU: Hasting, M
EM: hasting@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Johnson, W
EM: johnson@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Mee, M
EM: marie@gtsmtechnologies.com
AF: GTSM Technologies, PO Box 178, Kenmore, 4069 Australia
AU: Mueller, B
EM: mueller@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Venator, S
EM: venator@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AU: Wright, J
EM: wright@unavco.org
AF: UNAVCO, 6350 Nautilus Drive, Boulder, CO 80301 United States
AB: The Plate Boundary Observatory installed six Gladwin Tensor Strainmeters (GTSMs) on the Olympic peninsula in June and July 2005. Four boreholes are currently being drilled on Vancouver Island, Canada, with strainmeter installation planned for autumn 2005. Initial results from the strainmeters on the Olympic Peninsula indicate that all are measuring an accumulation of strain and that the phase and amplitudes of the M2 and O1 Earth tides and teleseisms are resolvable at some of the strainmeters after two months of operation. These six strainmeters and the four in Vancouver Island are well placed to capture any strain transients produced by the expected Cascadia slow earthquake. GTSMs, installed at depths of up to 250 m, measure changes in strain with a precision 1 ppb over periods of hours to months. They therefore bridge the spectrum of deformation not measurable by GPS or seismometers. GTSMs record strain at sample rates of 20 samples/second, 1 sample/second and 1 sample per 600 seconds. Rainfall, pore pressure atmospheric pressure, temperature and seismic data are also measured at the strainmeter site. The strain and environmental data flow at hourly intervals to UNAVCO's Boulder Data Collection Center (BDCC) via VSAT. At the BDCC it is converted to miniSEED and sent to the Northern California Earthquake Data Center (NCEDC) and to IRIS's Data Management Center (IRIS DMC) for archival via SEEDLink. In addition the raw data, in the data logger native format, are transferred to the archives via LDM. The strain data are processed at UNAVCO's Borehole Strainmeter Analysis Center (BSMAC), located at the PASSCAL Instrument Center at New Mexico Tech, in Socorro, NM. On arrival at the BSMAC the 1 sample/sec data are reviewed and spurious data and signals known to be introduced by non-tectonic activity are identified. The 1 sample/sec strain data are then reduced to 300-second interval in a multi-stage decimation process using minimum-phase decimate by 2, 3 and 5 causal filters. The data from each of the four gages within the strainmeter are then combined into areal and shear strains. Before strain transients or tectonic signals can be isolated in strain measurements three sets of corrections must be applied; an Earth tide correction, an atmospheric pressure correction and a borehole relaxation grout-curing correction. The Earth tides and the relation between atmospheric pressure and strain change are determined simultaneously for each gage from lowpass-filtered clean data using the program BAYTAP-G. The borehole-relaxation and grout-curing trend are modeled for each gage using a double exponential plus linear term. The parameters that describe these corrections are recalculated every 3 months. The time series corrections can then be generated for any sample interval over any time period. The final processing step is the conversion of the 300-second gage and tensor strain data into XML format, which also contains data quality and processing information. The XML files are archived along with the raw data at the DMC and NCEDC.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1294 Instruments and techniques
DE: 8150 Plate boundary: general (3040)
SC: Geodesy [G]
MN: Fall Meeting 2005