Theoretical basis of the amplitude source location method for volcano-seismic signals

摘要

The source location method using high-frequency seismic amplitudes based on the assumption of isotropic radiation of S waves has been used successfully to locate seismic events and tremor at volcanoes. This amplitude source location (ASL) method overcomes the limitations of traditional hypocenter determination methods that use onset arrival times and has great potential to improve volcano-seismic monitoring and the investigation of source processes of volcano-seismic signals. However, theoretical justification of the basic assumption used in the ASL method has not been provided in previous studies. In this study, we tested the ASL method by using seismic waveforms simulated with a finite difference method in realistic heterogeneous volcanic structures with intrinsic attenuation and topography. Our results showed that ASL determinations were successful when using waveforms characterized by multiple scattering that can be approximated by the diffusion model. We found that the energy solution of the diffusion model provided an amplitude-distance relation that is similar to that used in the ASL method. Our results suggest that the ASL method is applicable to high-frequency seismograms in highly heterogeneous media with transport mean free paths of 10(3)m or smaller and strong intrinsic attenuation. These medium parameters are consistent with those estimated at various volcanoes. Our study validates the basic assumption of the ASL method and justifies its use to locate the sources of high-frequency seismic signals observed at volcanoes.