Canadian Magnitudes of Earthquakes and Nuclear Explosions in South-Western North America

Canadian seismograph network mean body-wave and surface-wave magnitudes are computed for 28 earthquakes and 28 nuclear explosions in south-western North America to test the effectiveness of the surface- vs body-wave discriminant between earthquakes and explosions for purely continental paths. For the present Canadian network, the magnitude threshold of discrimination is about m 4.5. A comparison is made between these and other (intercontinental) surface- vs body-wave relationships by normalizing all data to standard magnitudes. Surface-wave attenuation for intercontinental paths limits the effectiveness of the discriminant to magnitudes about 1.0 higher than the same recording techniques can achieve for intracontinental paths.