Use of the mantle magnitude M_m for the reassessment of the moment of historical earthquakes - II: Intermediate and deep events

We extend to the case of intermediate and deep earthquakes our application of the mantle magnitude M_m to historical events. Because of the general lack of quantitative studies of deep earthquakes before the initiation of the Centroid Moment Tensor databank in 1977, we regard as historical all non-shallow earthquakes up to and including 1976. An analysis of 57 records from 41 events, using the Uppsala Wiechert seismometer and various long-period instruments at Pasadena, yields new moment estimates for 28 events whose moments had not previously been published. Our results correlate poorly with available traditional magnitudes, as would be expected from early saturation effects for magnitude scales measured at relatively high frequencies. They also suggest that large events (10²⁸ dyn-cm and greater) take place in the 100-200 km depth range, but that the depth interval 350-520 km features few if any large earthquakes.