Multicomponent Strain Seismograph
Quarterly rept. no. 7, 1 Jan-31 Mar 1967
GEOTECH GARLAND TX
Pagination or Media Count:
Eleven seismograph channels at WMSO were converted to a 3-cycle system, resulting in a significant improvement in matching of phase response of strain-inertial combinations. A substantial increase in utility of the short- period strain directional array data was achieved by a transition from offline summing to online summing of strain and inertial signals. A combination of long- period horizontal strain and inertial seismographs with matched frequency responses was put into operation at WMSO to evaluate its directional capabilities. An equivalent inertial magnification of 12K at 25 seconds has been achieved with the long-period strain seismograph. Magnifications of 50K-100K are required to reject long-period microseisms effectively. A comparison of the steel-cased borehole and the plastic-cased borehole indicates that 6-second microseisms are recorded with approximately 30 percent less amplitude in the steel-cased borehole. Further comparison will be made by interchanging seismometers in the two boreholes. Relative theoretical values of displacement and differential displacement have been computed for incident longitudinal waves as part of the study of wave discrimination.