Secular and coseismic changes in S-wave velocity detected using ACROSS in the Tokai region

Earth, Planets and Space

Koshun Yamaoka¹  Toshiki Watanabe¹  Takahiro Kunitomo¹  Ryoya Ikuta²  Shuhei Tsuji³  Yasuhiro Yoshida⁴  Akio Katsumata⁵ 

[1] Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University;Faculty of Science, Shizuoka University;Graduate School of Environmental Studies, Nagoya University;Meteorological College;Meteorological Research Institute;

关键词: Seismic wave velocity change;    Coseismic change;    Secular change;    Artificial seismic source;    ACROSS;    2011 Tohoku earthquake;   

DOI  :  10.1186/s40623-018-0917-2

来源: DOAJ

【 摘 要 】

Abstract We discovered a secular change in the travel time of direct S-waves over a 10-year observation period by means of continuous operation of an artificial and stable seismic source, called Accurately Controlled Routinely Operated Signal System (ACROSS), which is deployed in the central part of Japan along the Nankai Trough. We used 13 High Sensitivity Seismograph Network Japan (Hi-net) stations around the ACROSS source to monitor the temporal variation in travel time. Green’s functions were calculated for each station daily from March 29, 2007, through October 30, 2017. Secular advance in the temporal variation in travel time was seen for the whole operation period, in addition to a steplike delay associated with the 2011 Tohoku earthquake. We estimated the rate of secular change and the amount of coseismic step by modeling the transfer function of S-waves with a linear trend and the coseismic step of the 2011 Tohoku earthquake. Distance dependences of the travel time changes can be explained as a combination of common bias and dispersion for each station, for both the secular and coseismic changes. This can be interpreted as a randomly distributed change in seismic velocity over the range of the observation region. An azimuthal dependence exists for both changes and shows larger changes in the NE–SW direction than in the NW–SE direction from the ACROSS source.

【 授权许可】

Unknown