The reflection imagine of seismic crosshole

Compared to surface seismic, seismic crosshole has the higher resolution; the dominant frequency of crosshole is about the decuple quantity of the former.As the result, imaging of crosshole request more accuracy than surface.Factors of VSP-CDP mapping quantity for crosshole reflection are discussed,and point out that accuracy of imaging could be evaluated by firstbreak (direct wave). A new imaging method without velocity model by extrapolating traveltime of first break is presented,which based on travel-time equation of compress wave derived in weak anisotropy media, considering the difference of reflection imaging between surface and borehole survey. Results of field data demonstrated that the new method is reliable and feasible.