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Short-Period Multicomponent Strain System.

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Final rept. 16 Feb 68-15 Feb 69,

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A five-component system of matched short-period strain and inertial seismographs at Wichita Mountains Observatory WMO was expanded to include a three-component system of matched long-period strain and inertial seismographs for recording large magnitude earthquakes. An examination of film recordings of strain noise, pressure fluctuations inside and outside of the strain vault, and wind velocity at WMO suggests that the long-period LP noise observed on the strain traces is caused by wind-pressure fluctuations that are coupled more strongly through the ground or by compression of the vault structure than through leakage of air through the vault enclosure. A series of improvements reduced the noise level of the long-period strain seismographs substantially. However, study of the detection capability of the WMO LP strain seismographs shows that the environmental noise still severely limits detection. A study of the directional characteristics of the seismic noise shows that the predominant microseisms in the band 0.1 to 0.5 Hz can be partially rejected by horizontal strain-inertial seismograph combinations. From a study of S-wave enhancement, it is concluded that there is no one combination of seismograph outputs that can be used in general to provide enhancement of all recorded S waves. 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. Author

Subject Categories:

  • Seismology
  • Seismic Detection and Detectors

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