HR: 1330h
AN: S12A-0368    [PDF]
TI: Calibration of Alyeska Seismographs for the Denali Fault Earthquake of 3 November 2002
AU: * Evans, J R
EM: jrevans@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS-977, Menlo Park, CA 94025 United States
AU: Jensen, E G
EM: gjensen@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS-977, Menlo Park, CA 94025 United States
AU: Stephens, C D
EM: cdstephens@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, MS-977, Menlo Park, CA 94025 United States
AU: Nyman, D J
EM: nymandj@djna.com
AF: D. J. Nyman \& Associates, 12337 Jones Road, Suite 232, Houston, TX 77070 United States
AU: Hamilton, R C
EM: rchamilton@sbcglobal.net
AF: Consultant, 10226 Sugar Hill Dr, Houston, TX 77042 United States
AB: Several of the most important records yet obtained of a large continental strike slip earthquake were produced by some of the 11 strong-motion seismographs operated by the Alyeska Pipeline Service Company, six of which recorded the event along the 800-mile Trans-Alaska Pipeline System corridor. These 200 sample/s instruments were designed for detecting strong shaking and generating alarms for the Pipeline Control System, evaluating the potential for damage to the pipeline and supporting facilities, and guiding shutdown, inspection, and other emergency responses in the event of strong shaking. While these instruments, particularly the one at Pump Station 10 (PS10), less than 3 km from the Denali fault, were very well placed to record the {\bf Mw}7.9 event of 03 November 2002 and its rare examples of high-velocity, low-acceleration records from likely supershear rupture in a large event, they were not intended for seismological and engineering use at very low frequencies and require retrospective calibration for optimal application at these periods. In particular, they require calibration for the accurate recovery of permanent displacements and computing the responses of structures affected by long-period motions. Calibration of the 0.1- to 40-Hz 4-pole Butterworth bandpass filters and Honeywell Sundstrand Q-Flex$^{\rm TM}$ QA1100$^{\rm TM}$ and QA1200$^{\rm TM}$ accelerometers from a nearly identical spare Alyeska instrument demonstrated that the low-cut corner frequency differed by 10 to 16% from the nominal value which can cause as much as 20% variation in the recovery of displacement signals from acceleration records. Therefore, we are retrieving the PS10 instrument and both of the neighboring Alyeska instruments in September, 2003, and calibrating their filters, amplifiers, and accelerometers in an effort to recover the most accurate ground motions to about 0.05 Hz, and possibly below. We will verify instrument orientations in the field, test instrument and site noise levels and baseline stability, test their ability to recover known displacements and displacement waveforms, measure their sensitivities, measure their static and dynamic linearity, measure filter corner frequencies and the filters' (fairly significant) sensitivities to temperature, and measure the vault and recording-room temperature responses during the Autumn of 2003 as a surrogate for the Autumn for 2002.
DE: 7209 Earthquake dynamics and mechanics
DE: 7294 Instruments and techniques
DE: 8010 Fractures and faults
SC: Seismology [S]
MN: 2003 Fall Meeting