Detection of seismic anisotropy from seismic data recorded at SMNH01 station of KiK-net using seismic interferometry and empirical mode decomposition

Abstract

This study uses deconvolution of earthquakes registered at the SMNH01 station of KiK-net, which is located in Japan, to identify the presence of: (a) anisotropic layers and (b) waves which could have been induced by motion of fluid, crack propagation and local fault activation. The SMNH01 station has a borehole which is equipped with triaxial accelerometers installed at surface and at 100 m of depth. By deconvolving seismic events registered at surface and at 100 m of depth, anisotropic layers are identified. To interpret interferograms, the following tools are utilized: (a) a one dimensional (1D) isotropic layered medium, (b) empirical mode decomposition and (c) an orthorhombic model. From the empirical mode decomposition, genuine resonances or tremors are identified along directions that are subparallel to the horizontal stress orientations that seem to bisect an effective orthogonal-conjugate fracture set. The strong changes in the amplitude of the main descending deconvolved wave could be mainly due to the combined influence of: motion of fluids through fractures on the spatial scale of meters, recurrent seismic events, evolving anisotropy, dilation and temperature variations. This wave travels from the surface of the earth to the receiver located at 100 m of depth. The detected anisotropy could be associated with the presence of layers constituted by naturally fractured basalt, which are situated beneath the soil. Such anisotropic layers could have orthorhombic symmetry or lower. This study has implications in the exploration and production of natural resources.