Deep ocean seismology



Recent measurements of seismic noise on the ocean bottom have revealed surprisingly low levels at frequencies greater than 3 Hz (Figure 1). In some instances values for frequencies of 3 to 15 Hz are comparable to, or lower than, values from the best continental seismic stations. This would be of little significance if, as is generally observed with most continental instruments, the only phases to have such frequencies were the result of local earthquakes. Actual observations, however, indicate that two classes of teleseismic (distant) phases have substantial signal-to-noise (S/N) ratios at high frequencies when observed in the low noise environment of the deep oceans.