Michio Hashizume

Q of the crust beneath southwestern Honshu, Japan, derived from explosion seismic waves

Abstract The specific quality factor Q of the crust was derived from explosion seismic waves by measuring the change of spectrum ratio with distance from the source. The spectrum for two wave groups, which are supposed to be transmitted entirely in the upper crust and transmitted primarily in the lower crust, respectively, were used. The source function could be represented by a simple function with one parameter. The value of Q and the parameter were determined simultaneously by the least-squares method. The same Q value was obtained for the upper and the lower crust and was estimated to be in the range Q = 1000–2000.

Surface-wave study of the Canadian Shield

Abstract Phase and group velocities of surface waves with travel paths confined to the Canadian Shield and its surrounding areas were determined in a period range between 5 and 40 sec. The Canadian Seismic Network and three earthquakes of which source parameters are already known were used for this study. Mean phase velocities from source to receiver were determined from phase differences between the focal phases and the observed phase spectra by the single station method. Group velocities were determined by the algorithm of Dziewonski et al. They were put into a program for relocation of epicenters and regional surface-wave velocities by the least-squares method. The area under investigation was divided into six geologically significant regions. Finally, regional surface-wave velocities were inverted to obtain regional earth structures. Taking resolving power into consideration, the earth structures were assumed to have four layers, namely, uppermost crust, granitic layer, basaltic layer, and upper mantle. It was found that the shear velocities in the granitic and basaltic layers of the Canadian Shield are rather uniform laterally, differences for most of the regions are less than 0.015 km/sec. These facts may indicate the uniformness of its formation and the later crustal movements.