Near surface velocity imaging with the resistivity inverted from shallow transient electromagnetic sounding

摘要

Contrasting the resistivity profile inverted from the shallow transient electromagnetic sounding(STEM) with the stratum velocity observed by mini-logging at the same line showed that the coherence of the shallow structure of stratum velocity and the layered resistivity is perfect, and the relationship between stratum velocity and resistivity is non-linear. Based on Faust formula, the method in which the stratum velocity is approached as a polynomial function of resistivity and depth in logarithm domain was put forward. By the use of the stratum velocity from mini-logging and the resistivity from STEM the coefficients were calculated with conjugate gradient method, so the experiential formula of stratum velocity as a function of resistivity and depth was derived, with this formula the velocity was imaged upon the resistivity profile. The result is important and valuable to the identification of the low velocity boundary, and also helpful to the establishment of velocity model for seismic static correction.