Seismic raytracing method and apparatus

A remote exploration apparatus for investigation of a subsurface structure for the presence of a portion of the structure having commercially valuable properties, said apparatus forming a system comprising:

• a seismic wave generator;
• a seismic wave detector capable of generating a seismic signal representative of a seismic wave affected by said subsurface structure;
• numerical simulation means for modeling said subsurface structure and generating a synthetic seismic signal resulting from a synthetic seismic generator;
• comparison means for generating a difference indicator comparing said synthetic seismic signal and said seismic signal, wherein said model generally represents at least a portion of said subsurface structure when said difference is small;
• means for further exploring said subsurface structure when said simulation means for modeling includes said portion of the structure and when said comparison means generates said small difference;
• and
• wherein said numerical simulation means comprises means for calculating paired rays from a synthetic seismic wave.

A seismic signal analysis method for evaluating a property of a substructure contained within a structure, which method comprises the steps of:

• a) impressing a wave on the structure from a wave source located spaced apart from said substructure;
• b) placing a plurality of detectors each capable of sensing at least a portion of said wave affected by said substructure and producing a data signal, wherein at least one of said detectors is spaced apart from said wave source;
• c) detecting a plurality of said data signals from said sensors to form an actual sensed data set, wherein the amplitudes of said data signals are above a first threshold level;
• d) constructing an initial numerical model of at said structure;
• e) calculating synthetic waves and a synthetic ray data set from said model, wherein said calculations are limited to synthetic discrete rays having greater than a second threshold amplitude wherein said calculating also comprises simultaneous paired calculating of synthetic discrete rays, wherein said paired rays are state-space vector representations located nearly adjacent to each other;
• f) comparing said calculated data set with said actual data set;
• g) perturbing said theoretical model based upon said comparison;
• and
• h) repeating steps e, f, and g until said comparing step indicates an acceptable accuracy value.