Short-Period Multicomponent Strain System.
Abstract
A vertical strain seismograph and companion inertial seismograph were installed and operated at Houlton, Maine as a logical follow-up on the successful enhancement of P waves at Garland, Texas. Cultural noise at Garland was suppressed approximately 10 dB in the frequency range 1 to 3 Hz and noncultural microseisms at Houlton were suppressed an average of 10 dB in the frequency range 0.12 to 0.7 Hz. At both sites, lack of suppression of the microseisms near 1 Hz is attributed to either a low ratio of seismic signal-to-system noise; a complex mixture of seismic waves; or a threshold microseismic noise level below which the mechanical regime (composed of the country rock, the borehole casing, and the seismometer) does not respond properly to either the particle displacement or the differential particle displacement. The measurement of strain over a larger interval is recommended in order to increase the differential displacement acted upon by the seismometer, as well as to increase the ratio of microseisms-to-system noise. The relative merits of the technique of frequency filtering to enhance P waves was compared to the technique of combining vertical inertial and vertical strain seismograph outputs. In contrast to the successful application of the latter technique, frequency filtering not only failed to suppress microseisms in the frequency range of the P waves, but also attenuated first motion and distorted the P wave. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- May 30, 1969
- Accession Number
- AD0853413
Entities
People
- Richard H. Kirklin
- Robert C. Shopland
Organizations
- Geotech Instruments (United States)