Attenuation of Short-period P-waves and Q in the Mantle

Q for short-period P-waves in the mantle has been investigated, based on the spectral analysis of the initial P phases of two earthquakes. Amplitude spectrums in the epicentral range between 21 and 103 degrees have been calculated, compensating for the propagation effects through the total seismic path. Amplitude-distance relations over the frequency range between 0.3 and 1.3cps show that the rate of diminution of amplitude with epicentral distance is independent of frequency. From this observational results it follows that the intrinsic Q value becomes greater with depth between about 700 and 2500km, and also with increasing frequency. The frequency independency of Q theory is inappropriate within the frequency range between 0.3 and 1.3cps. It is also shown that the source asymmetry is not masked by the propagation effects except the stations near the nodal line for these frequencies.