Sensors Developed in the US for Low Frequency Seismology

1. Sensors Developed in the US for Low Frequency Seismology W. E. Farrell Science Applications International Corp

2. Topics • Summary • Motivation • Nuclear test detection • Physics and geophysics • Geotech KS series • Other Geotech sensors • Academic projects

3. Summary • The principal driver for 1/2 century of development of LP sensors has been nuclear test monitoring • The heyday lasted a long time, 1958-2000 • Currently here seems to be little interest within DoD or DoE for R&D in LP sensors • Much innovation came from University programs • Academics partly rode on the shirt tails of the test detection funding, but were focused on fundamental problems • NSF and private foundation money was key to these programs • AFOSR was a supporter in the early years • Sensor R&D in universities tapered off through the 70s • Perception that available technology good enough?

4. Motivation - Nuclear Test Detection • The problem of nuclear test detection has generated the most money for R&D in long period sensors • Berkner Report 1959 • Mb:Ms discriminant requires good SNR in the .1-.03Hz range • Lower frequency data required for estimating shallow earth structure, but ultra low frequencies were not a concern • Borehole packaging deemed critical • DARPA & Vela Uniform • See Farrell, 1985, Sensors, Systems & Arrays • AFTAC • Sponsored sensor R&D related to its monitoring mission • DOE

5. Motivation - Physics and Geophysics • Fundamental research in physics & geophysics has been an equally important driver of progress • Dicke • Theories of gravity • Lock-in amplifiers, capacitor pickoff & electrostatic feedback • IDA • Systematic observation of free oscillations for splitting and Q(r) • Inherited and applied Dicke approach • Superconducting gravity meter • “Zero” drift would lead to data in the tectonic frequency band • A few in service as seismometers • Strain meters

6. Geotech KS series

7. Other Geotech sensors

8. Academic projects