Velocity changes related with the Earth tide
Takano, T., T. Nishimura, H. Nakahara, Y. Ohta, and S. Tanaka (2014), Seismic velocity changes caused by the Earth tide: Ambient noise correlation analyses of small‐array data, Geophys. Res. Lett., 41, 6131-6136, doi: 10.1002/2014GL060690. [PDF]
We develop a novel method to estimate seismic velocity changes caused by the Earth tide by noise correlations. We calculate cross-correlations of ambient noise recorded at a temporal small array composed of seven seismometers in northeastern Japan. We stack noise correlations for the dilatational and contractional episodes that are predicted from theoretical tidal volumetric strains. Noise correlations of the two episodes are highly correlated, but tiny differences are found in their phases. The phase differences are explained by seismic velocity changes of −0.2%, which are interpreted to be caused by opening/closure of cracks or pores in the shallow subsurface due to the tidal strain.