Your borehole seismic experiment obtains the P-wave spectra plotted in Figure 9.30 at a distance of 10 km from an earthquake. Using a ruler, crudely estimate
0 and fc from the plot. Assuming that the density is 2700 kg/m3, the P velocity
is 6 km/s, and the S velocity is 3.46 km/s, compute the moment, M0, the moment
magnitude, MW , the source radius, r, and the stress drop, σ, for this event. State
any modeling assumptions that you make. Do not confuse the source radius r in
Section 9.5 with the source–receiver distance r in equation (9.27). The recording
station is deep enough that you may assume that the effect of the free surface can
be ignored and that the rock properties are uniform between the earthquake and the
station. You may also assume that attenuation is negligible (or that the spectrum
has already been corrected for attenuation) and that the radiation pattern term is
simply its average P-wave value of 0.52.