HR: 0800h
AN: NG31A-0855    [Abstracts]
TI: Study of Low-Frequency Earth motions from Earthquakes and a Hurricane using a Modified Standard Seismometer
AU: * Peters, R D
EM: peters\_rd@mercer.edu
AB: The modification of a WWSSN Sprengnether vertical seismometer has resulted in significantly improved performance at low frequencies. Instead of being used as a velocity detector as originally designed, the Faraday subsystem is made to function as an actuator to provide a type of force feedback. Added to the instrument to detect ground motions is an array form of the author's symmetric differential capacitive (SDC) sensor. The feedback circuit is not conventional, but rather is used to eliminate long-term drift by placing between sensor and actuator an operational amplifier integrator having a time constant of several thousand seconds. Signal to noise ratio at low frequencies is increased, since the modified instrument does not suffer from the 20dB/decade falloff in sensitivity that characterizes conventional force-feedback seismometers. A Hanning-windowed FFT algorithm is employed in the analysis of recorded earthquakes, including that of the very large Indonesia earthquake (M 7.9) of 25 July 2004. The improved low frequency response allows the study of the free oscillations of the Earth that accompany large earthquakes. Data will be provided showing oscillations with spectral components in the vicinity of 1 mHz, that frequently have been observed with this instrument to occur both before as well as after an earthquake. Additionally, microseisms and other interesting data will be shown from records collected by the instrument as Hurricane Charley moved across Florida and up the eastern seaboard.
UR: http://physics.mercer.edu/hpage/peters.html
DE: 7260 Theory and modeling
DE: 7200 SEISMOLOGY
DE: 3210 Modeling
DE: 3220 Nonlinear dynamics
SC: Nonlinear Geophysics [NG]
MN: 2004 AGU Fall Meeting