REGIONAL MAPPER is a menu-driven system in BASIC for computing and plotting (1) time, depth, and average velocity to geologic horizons; (2) interval time, thickness, and interval velocity of formations; and (3) subcropping and onlapping intervals at unconformities. The system consists of FILER, TRAVERSER, REFILER, and PLOTTER. A control point (sequential file) is a shot point with velocity analysis or a well with velocity check shot survey. Reflection time to and code number of seismic horizons are filed by digitizing table from record sections. TRAVERSER starts at a point of geologic control and, in traversing to another, parallels seismic events, records loss of horizons by onlap and truncation, and stores reflection time for geologic horizons at traversed points. REFIL R reads sequential files and writes a random-access file for PLOTTER.

Permafrost and buried canyons cause velocity anomalies that complicate depth mapping. At a control point, depth (Z) is from seismically derived velocity (Z_s) and from velocity interpolated between wells (Z_w). The depth difference (D) has a non-random component (D_nr) and an areally random component (D_r). A plot of D for a base horizon below the velocity anomalies is contoured with smoothing to form a D_nr surface showing the effect of permafrost and paleocanyons. Estimated depth to base horizon is the sum of Z_w and D_nr. For deeper horizons, depth is that of the base horizon plus a thickness derived by the "layer cake" method.

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