SHORT-PERIOD MULTICOMPONENT STRAIN SYSTEM
Quarterly rept. no. 2, 1 Jun-31 Aug 1968
GEOTECH GARLAND TX
Pagination or Media Count:
The PPP phase from a magnitude 8.2 earthquake was enhanced by suppressing 20-sec Rayleigh waves with the short-period vertical strain and vertical inertial seismograph combination at WMO. Signal enhancement by use of a continuous real-time spectral display of suppressed noise at WMO is not feasible in the frequency band 0.2-4.0 Hz because of a lack of time continuity of the spectral windows. True coherence of the seismic noise at WMO in the region of 1 Hz will remain indeterminable unless the ratio of seismic noise to system noise is substantially increased. Seismic noise at Garland, Texas, has been effectively suppressed by a matched combination of vertical strain and vertical inertial seismographs. In three independent series of field tests at WMO using two vertical strain seismometers in separate boreholes, loss of motion between fixed and free ends of the seismometer was approximately the same 22 percent. A comparison of motion produced at the fixed and free ends of the horizontal strain seismometer using an improved calibrator indicates an apparent loss of motion of about 20 percent between end points as compared with losses of 35 to 80 percent measured with the original calibrators.