Temporal change in seismic wave attenuation using highly stable vibration sources

Ryoya Ikuta,Koshun Yamaoka,Shuhei Tsuji

doi:10.1186/s40623-022-01570-0

Abstract

We developed a method to detect attenuation changes during seismic wave propagation excited by precisely controlled artificial seismic sources, namely Accurately Controlled Routinely Operated Signal System (ACROSS), and applied it to monitor the temporal changes for in situ data collected by previous studies. Our method, together with the use of the ACROSS sources, is less susceptible to noise level changes, from which conventional methods such as envelope calculation suffer. The method utilizes the noise level that is independently estimated in the frequency domain and eliminates the influence of the noise from the observed signal. For performance testing, we applied this method to a dataset that was obtained in an experiment at Awaji Island, Japan, from 2000 to 2001. We detected a change in amplitude caused by rainfall, variation in atmospheric temperature, and coseismic ground motions. Among them, coseismic changes are of particular interest because there are limited studies on coseismic attenuation change, in contrast to many studies on coseismic velocity decrease. At the 2000 Western Tottori earthquake (MW = 6.6, epicenter distance of 165 km), a sudden decrease in amplitude of up to 5% was observed. The coseismic amplitude reduction and its anisotropic characteristics, which showed a larger reduction in the direction of the major axis of velocity decrease, were consistent with the opening of fluid-filled cracks, as proposed by previous studies. The Delta {Q}^{-1} corresponding to the amplitude change gives similar values to those reported in previous studies using natural earthquakes.Graphical

Highlights

Temporal changes in the propagation property of seismic waves have been studied using both seismic velocity and attenuation
We demonstrate a method to estimate the temporal variation in the amplitude by removing the noise variation effect, which is independently obtained during the observation of the Accurately Controlled Routinely Operated Signal System (ACROSS) source
The amplitude change was obtained by calculating the ratio of the power of the transfer function of each period to that of the reference time

Summary

Introduction

Temporal changes in the propagation property of seismic waves have been studied using both seismic velocity and attenuation. Experiments with artificial seismic sources (Ikuta et al 2002; Yang et al 2014; Tsuji et al 2018) were conducted to identify coseismic velocity changes with better resolution. In most cases the seismic velocity decreases during the earthquakes and recovers gradually over time. These phenomena are accounted for by the fracturing of subsurface rock (Sawazaki et al 2009; Nakata and Snieder 2011) and/or crack opening by stress (Grêt et al 2006; Silver et al 2007) or pore pressure changes (Ikuta and Yamaoka 2004; Sawazaki and Snieder 2013) caused by the strong ground motions of earthquakes

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Discussion

Conclusion