We propose a procedure to characterize the dynamic behavior of subsurface crack systems on the basis of triaxial doublet analysis, which estimates precise relative source location of microseismic doublets in the downhole 3-component measurement. A doublet is a pair or a group of microseismicity with very similar waveforms despite different origination times, and is thought to express stress release on the same or similar structural plane in a crack system. We explain the concept and procedure of triaxial doublet analysis using the cross-spectrum and spectral matrix, and show that this analysis provides information on the structural plane related to a subsurface crack system. We also analyze the focal mechanism of microseismicity by combining a moment tensor analysis and a grid test. An understanding of both the structural plane and the moment tensor of the events allows an estimation of whether the structural plane of a crack system behaves as a single crack or multiple cracks. The dynamic behavior of a crack system is then characterized using independent information from tectonic stress measurement, well logging, etc., in addition to information from the focal mechanism analysis and the triaxial doublet analysis. The microseismic events associated with hydraulic fracturing in the Yunomori and Ogachi HDR fields of Japan are analyzed. The results of the experiments demonstrate the feasibility and validity of the proposed procedure. Based on the orientation of the structural planes, both fields appear to be controlled by the preexisting structure.