HR: 0800h
AN: G51A-0072    [Abstracts]
TI: Tilt Recorded by a Portable Broadband Seismograph: The 2003 eruption of Anatahan, Northern Mariana Islands
AU: Shore, P J
EM: patrick@wups.wustl.edu
AF: Dept. of Earth and Planetary Sciences, Washington University, 1 Brookings Dr., St. Louis, MO 63130 United States
AU: * Wiens, D A
EM: doug@seismo.wustl.edu
AF: Dept. of Earth and Planetary Sciences, Washington University, 1 Brookings Dr., St. Louis, MO 63130 United States
AU: Pozgay, S
EM: spozgay@seismo.wustl.edu
AF: Dept. of Earth and Planetary Sciences, Washington University, 1 Brookings Dr., St. Louis, MO 63130 United States
AU: Sauter, A
EM: asauter@ucsd.edu
AF: Scripps Institute of Oceanography, University of California, San Diego, La Jolla, CA 92093 United States
AU: White, R
EM: rwhite@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd, Menlo Park, CA 94022 United States
AB: The horizontal components of broadband seismographs are highly sensitive to tilt, suggesting that widely deployed portable broadband seismic sensors may record important tilt information associated with volcanic eruptions. We report on a tilt episode that coincides with the first historical eruption of Anatahan volcano on May 10, 2003. The tilt was recorded by a portable PASSCAL STS-2 seismograph fortuitously deployed four days prior to the eruption as part of the Mariana Subduction Factory Imaging Experiment. The seismograph, located in an underground insulated chamber about 6 km west of the active vent, recorded continuously throughout the eruption sequence. A long-period signal with a dominant period of several hours was recorded on the EW component beginning at 06:30 GMT on May 10, which coincides with the onset of continuous volcano-tectonic (VT) seismicity and is one hour prior to the eruption time estimated by the Volcanic Ash Advisory Center based on satellite photos. The signal was much larger than a long period diurnal signal presumably resulting from temperature perturbations. A much smaller signal was recorded on the NS component, and the signal was totally absent on the vertical component, suggesting it results from tilt that is radial with respect to the active vent. An estimate of the tilt as a function of time was recovered by deconvolving to acceleration within a passband of 500-50,000 seconds, and dividing by g. The tilt signal records an initial episode of tilt down away from the volcanic center from 06:30 - 09:30 GMT, which we interpret as inflation of the shallow volcanic source. The tilt reverses and records deflation from 09:30 until 17:50, after which any large tilt signal ceases. The period of inflation corresponds to a period of numerous VT events, whereas fewer events were recorded during the deflation episode, and the VT events resumed again after the end of the deflationary tilt. The maximum tilt is about 2 microradians, although it is possible the tilt magnitude is poorly estimated since the signal is far outside the passband of the STS-2 instrument. A scenario relating the tilt to inflation volume and depth will be presented. The tilt signal is not obvious in the raw seismic records, so careful examination of broadband records of other eruptions may disclose further unrecognized tilt signals.
DE: 8414 Eruption mechanisms
DE: 8494 Instruments and techniques
DE: 7280 Volcano seismology (8419)
DE: 7294 Instruments and techniques
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting