The University of Saskatchewan Seismograph Network
Funk, Craig W
This thesis discusses the work completed on the University of Saskatchewan Seismograph Network (USSN). The main thrust of the work was the development of an automatic seismic data monitoring algorithm and interactive computer packages which are used to analyze digitally recorded earthquakes. Currently the monitoring package detects two earthquakes, on average, daily. Seven earthquakes within 1500 km of the USSN were detected between the period of September and December of 1991. The interactive computer packages are used to provide earthquake information such as location, magnitude, and spectral parameters. Instrument calibration is a vital component of the analysis package. A reliable calibration function has been derived for the system by studying the instrument response to known ground-motions, which were introduced into the seismometers electronically. A direct benefit of the USSN will be a better understanding of seismicity in Saskatchewan and the rest of western Canada. The utility of the network is evaluated by studying the magnitudes of earthquakes which can be reliably recorded. The event resolvibility is limited by the background noise level, whereas the maximum recordable event size is controlled by the inherent limitations of the seismographs. The recording range of the instrumentation is v established using results from both an ambient background noise study and instrument calibration experiments. The investigation shows that earthquakes from southern Saskatchewan, which have magnitudes between 2.5 and 4.0, can be reliably recorded (based on the present seismograph configuration) . Accurate earthquake location requires a keen understanding of the seismic velocity variations within the crust and upper mantle (a crustal model). Earthquake data recorded by the USSN were interpretated to develop a crustal model for the Saskatoon area. The study used seismograms recorded between epicentral distances of 200 and 11 000 km. The interpretation shows that the depth to the base of the crust (Moho), under Saskatoon, is 46 km. Refractions along the Moho, from regional distance earthquakes, have apparent P-wave velocities of 8.3 km/sec. The P-wave velocity in the upper crust is 6.16 km/sec. The crust, in this area, is found to be complicated, based on the teleseismic and local earthquake data. P-waves from teleseismic earthquakes show travel time deviations as large as 0.4 sec, which may be related to the fractured nature of the crust. The existence of an inter-crustal discontinuity is suggested by seismograms from a local earthquake. The observed P-wave refractions are consistent with a horizon at 20 km depth, which has a dip of 4.5 deg, and a P-wave velocity of 6.6 km/sec.