Instantaneous Seismic Attributes and Response Characteristics of Active Faults

Active fault detection is not only the foundation for the fault activity evaluation, but also the basis for prevention of natural earthquake disasters. The shallow seismic exploration is one of the effective methods for active fault detection. This study aims to further improve the fault activity evaluation with shallow seismic methods. We construct theoretical models of active fault of different fracture zone widths, apply the finite difference method of two-dimensional viscoelastic wave equation to simulate wave field response characteristics, use Hilbert transform method to extract the attributes of instantaneous frequency and instantaneous phase, and analyze the performance in the field of anti-noise and effect of practical applications of method. The results show: Combination of the vertical travel time section and seismic attributes can effectively obtain the response characteristics of active faults which cut through the Quaternary and achieve the evaluation of fault activity; However, when coherent noise reaches thirty percent, it is difficult to trace and identify the weak reflection signals in the Quaternary by the vertical travel time section and instantaneous frequency section, but instantaneous phase attributes can still effectively trace and identify the weak reflection signals with a high anti-noise ability. In the practical determination of active faults, both the vertical travel time section, instantaneous frequency section and instantaneous phase section can determine the existence of faults.The instantaneous phase attribute is the most obvious and prominent to show the characteristics of faults or fracture zones which cut through the Quaternary, whereas the vertical travel time section takes the second place.It is concluded that the instantaneous phase attribute is an important and effective seismic attribute to determine the fault activity.