Calculation of raypaths and wavepaths from traveltime tables for the tomographic estimation of transmission velocities

A method of estimating seismic transmission velocities by determining seismic wavepaths from traveltime tables comprising the steps of:

• obtaining seismic data representing seismic pulses produced by sources and detected by receivers;
• selecting the earliest traveltimes of waves transmitted between different source and receiver locations for a region of interest which includes any region which may influence a wavepath;
• selecting a velocity model that describes transmission velocities in the region of interest;
• extrapolating traveltimes from each source position to each point in the region of interest and traveltimes from each receiver location in each point in the region of interest;
• adding together the extrapolated traveltimes from the source and receiver to each point in the region of interest to quantify the path of a wave between one source and one receiver;
• determining all points in the region of interest whose total traveltimes are less than half a wavelength greater than a predetermined minimum traveltime;
• retaining a representative raypath that passes through the center of the region for each source and receiver location;
• and
• improving said model of velocities by tomographic means to increase the match between the recorded and modeled traveltimes along the representative raypaths.

An apparatus for improving estimating seismic transmission velocities by determining seismic wavepaths from traveltime tables comprising:

• means for obtaining seismic data representing seismic pulses produced by sources and detected by receivers;
• means for selecting the earliest traveltimes of waves transmitted between different source and receiver locations for a region of interest which includes any region which may influence a wavepath;
• means for selecting a velocity model that describes transmission velocities in the region of interest;
• means for extrapolating traveltimes from each source position to each point in the region of interest and traveltimes from each receiver location to each point in the region of interest;
• means for adding together the extrapolated traveltimes from the source and receiver to each point in the region of interest to quantify the path of a wave between one source and one receiver;
• means for determining all points in the region of interest whose traveltimes are less than half a wavelength greater than a predetermined minimum traveltime;
• means for retaining a representative raypath that passes through the center of the region for each source and receiver location;
• and
• means for improving said model of velocities by tomographic means to increase the match between the recorded and modeled traveltimes along the representative raypaths.