Fri. May 2, 2014 2:15 PM - 4:00 PM 502 (5F)

Convener:*Hisashi Nakahara(Solid Earth Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University), Hiroaki Sato(Central Research Institute of Electric Power Industry), Chair:Hisashi Nakahara(Solid Earth Physics Laboratory, Department of Geophysics, Graduate School of Science, Tohoku University), Hiroaki Sato(Central Research Institute of Electric Power Industry)

Microseisms and microtremors (hereafter called microtremors) are considered to be caused by ocean swells and human activities, respectively. Though they are recognized as noise to seismic observations, they can be turned into useful signal in other point of view. The nature of microtremors has been long studied. And the utilization of microtremors for engineering applications have been actively made in Japan such as the classification of site conditions based on the predominant periods, and the estimation of subsurface velocity structures by means of the spatial auto-correlation (SPAC) method and the horizontal-to-vertical (H/V) spectral ratio. These methods are now widely used all over the world in order to estimate shallow subsurface structures in terms of the prediction of strong ground motions. And in the last decade, studies on microtremors have been revitalized, mainly because seismic interferometry was developed and seismic observations became more efficient. For example, the H/V method was reinterpreted based on the theory of diffuse waves. And the centerless circular array (CCA) method was newly developed. Moreover, temporal changes in shallow subsurface structures caused by the nonlinear site effect can be detected by analyzing long-term continuous records of microtremors. In this session, we widely invite contributions on the nature of microtremors and their applications to exploration in order to understand the present status and discuss future directions of the subjects.