Affiliation:
1. Department of Earth and Planetary Sciences School of Science Tokyo Institute of Technology Tokyo Japan
Abstract
AbstractWhile the Earth (rocky planet) can be approximated as an elastic body, it also possesses anelasticity, Q−1, which causes energy dissipation (intrinsic attenuation) during deformation. Rock deformation experiments have demonstrated that Q−1 shows a marked amplitude dependency for strain of >∼10−6, but seismic‐waves‐induced strain is generally much smaller than the threshold value. Therefore, all seismological analyses have assumed amplitude‐independent attenuation. However, theoretical models of dislocation‐induced attenuation have predicted amplitude‐dependent attenuation under high temperatures and pressures equivalent to the crustal and uppermost mantle conditions. This study investigates whether attenuation is actually independent of seismic‐wave amplitudes by a systematic analysis of a large number of spectral amplitudes of co‐located earthquake pairs with different observed amplitudes. We assume the ω2 source and circular crack models to correct for the source parameters of earthquakes. The obtained results suggest that amplitude‐dependent attenuation is required to explain the observations, which contradicts a long‐standing recognition that amplitude‐dependent attenuation is negligible for the propagation of seismic waves. Our model calculation further suggests that Q−1 is proportional to the seismic amplitude, A, whereby Q−1 ∝ A0.1–0.2, which introduces attenuation variations along a given raypath, with significantly enhanced attenuation near the hypocenter. Our result highlights the need to revisit and potentially rethink current models of the physical mechanisms influencing intrinsic attenuation.
Funder
Japan Society for the Promotion of Science
Ministry of Education, Culture, Sports, Science and Technology
Publisher
American Geophysical Union (AGU)