Randall D. Peters
Department of Physics
Mercer University

Wednesday, November 3, 2004, 4:30 pm
Willet Science Center 101

Seismic Instrument Evolution with a
Focus on Applied Physics

Especially because of interest in the vibrations generated by earthquakes, instruments to monitor earth motions are highly diverse.  For example, the attached pictures of a support-constrained pendulum (http://www.earthquakerose.com) involve an instrument with artistic attributes, as opposed to having practical value to seismologists.  It stands in contrast to several of the great geoscience advances of the last century.  Several of these involved physicists, who are expected to also make major contributions to future developments.  In spite of a major technological improvement to general-purpose instruments (the introduction of force feedback methods in the 1970’s), there remains a great need for improved instrument sensitivity at low frequencies.  Peters attended the IRIS Broadband Seismometer workshop of March 2004, which was concerned with design issues for a “new-generation, ultra-quiet, mHz-20 Hz seismic sensor.”  (http://www.iris.edu/stations/seisWorkshop04/seisWorkshop.htm) He believes the objectives of this workshop can best be met by paying closer attention to the importance of newly-learned physics, such as the noise generated by defect structures in the springs employed by inertial sensors.  This seminar will focus on advances made possible through the synergy of (i) a recently-patented sensor working in concert with (ii) powerful, though inexpensive personal computers, interfaced to (iii) versatile, yet user-friendly data acquisition and processing hardware/software.  A newly-developed instrument will be described, in which a classic seismometer (LaCoste spring WWSSN instrument, manufactured by Sprengnether) was modified by (i) replacing the original sensor (Faraday law type) with a capacitive array, and (ii) using a form of force feedback that does not suffer from the low frequency loss in sensitivity that is characteristic of conventional instruments.  Sample data will be shown of some important earth motions recorded by it, but which have rarely been seen by conventional instruments.  These motions include low frequency (mHz, eigenmode ‘hums’) and the records to be shown will not be limited to earthquake data; they will include microseisms and wind excitations observed during the passage of some recent hurricanes.