Noise-based seismic velocity changes by using 9-component cross-correlation tensors with an application to Mt. Fuji, Japan
Abstract:Dynamic and static stress changes often result in changes of seismic velocities (e.g. Brenguier et al., 2008; 2014). In Mt. Fuji volcanic region, the 2011 Tohoku-oki earthquake and a Mw 5.9 earthquake occurred 4 days after the Tohoku-oki earthquake radically perturbed the stress field (e.g., Kato et al., 2013; Miyazawa, 2011; Toda, et al., 2011). The area is thus an adequate location to consider the influence of stresses changes caused by two earthquakes.
In this study, we conducted seismic interferometry to estimate seismic velocity change following Brenguier et al. (2008) in the frequency range from 0.1 to 0.9 Hz. We used seismic data from November 2010 to October 2011 in 18 seismic stations around Mt. Fuji. While many previous studies investigated cross-correlation of the vertical-vertical component to obtain the time resolution of approximately a few days, here we attempted to improve the temporal resolution of the measurements. We calculated 9-component noise cross-correlation tensors from three-component seismic records and stacked the changes to obtain the seismic velocity change between two stations.
After these procedure, we successfully distinguished the seismic velocity changes by the Tohoku-oki earthquake and the Mw 5.9 earthquake. Coseismic velocity drops are followed by recovery. Velocity changes are large in the station pairs crossing the vicinity of the summit of Mt. Fuji. In contrast, the velocity changes are not significant away from the summit. In addition, the seismic velocity changes by the Tohoku-Oki earthquake are larger than those by the Mw 5.9 earthquake. Since the pattern of velocity changes is not consistent with the static stress changes in the area, we interpret that these differences are due to the damage caused by the dynamic stress from the Tohoku-oki earthquake that did not yet recover by the time of the Mw 5.9 earthquake.