MULTICOMPONENT STRAIN SEISMOGRAPH
Abstract
Phase responses of the strain seismographs indicate appreciable deviations from theory. However, good cancellation of Rayleigh waves with combinations of strain and inertial seismographs indicates acceptable phase match. Unpredicted phase discrepancies of approximately 5 degrees in the 0.8 cps galvanometers of the strain seismographs can be eliminated by a simple conversion to a 3 cps system. Uncertainties in the phase response of the calibrators on the strain seismometers can be resolved by installing a monitor at the calibrator. The main effort on the program has been shifted toward evaluating the directional capabilities of the strain-inertial combinations in the long-period spectrum. A combination of long-period strain and inertial seismographs with matched frequency responses has been designed and is being put into operation at WMSO. The technique of detecting long-period (15-20 sec) surface waves masked either by microseisms or by surface waves from another event is demonstrated using 6 sec surface waves from the short-period strain directional array. To minimize off-line summing of data from individual seismographs of the eight-component short-period strain directional array, the data will be summed on-line and recorded on a Develocorder at WMSO. This system will be an operational prototype of a strain system capable of enhancing short- period signals. The transition to on-line operation is nearly complete. A comparison of the plastic-cased borehole and the steel-cased borehole indicates that the latter is not responding properly to earth strain. Theoretical expressions for displacement and differential displacement due to incident SV waves have been derived.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 20, 1967
- Accession Number
- AD0807662
Entities
People
- B. W. Girard
- J. R. Sherwin
- R. C. Shopland
- R. H. Kirklin
Organizations
- Geotech Instruments (United States)