Seismological Observations on Amplitude-Dependent Energy Dissipation in the Crust and Uppermost Mantle

The amplitude-dependent seismic attenuation in the crust and uppermost mantle was investigated using spectral analysis of crustal and intraslab earthquakes that occurred in two areas in northeastern Japan. P-wave attenuation ($Q^{-1}$) was found to be weakly proportional to amplitude ($A$) in both areas, following the relationship, $Q^{-1}\mathit{\propto }{A}^n$. Quantitative analysis reveals that amplitude-dependent attenuation is more pronounced in the uppermost mantle (n ∼ 0.16) than in the crust (n ∼ 0.05). This depth-dependent behavior of attenuation may be attributed to increasing temperature and pressure, which enhance dislocation density and mobility. Our findings challenge the common assumption of amplitude-independent attenuation. Although we infer dislocation mechanisms as the primary cause of the amplitude-dependent energy dissipation, further experimental studies under high temperature and pressure conditions are necessary for better understanding of the complex nature of seismic attenuation and the underlying processes.