Figure F50. Comparison of depth vs. two-way traveltime (TWT) relationships. A. Site 1140 traveltimes based on the sum of transit times from the sonic tool agree very well with results from the well seismic tool (WST), which measures one-way traveltimes directly. TWTs from discrete samples are underestimated in basement because they are biased toward high values (Fig. F49). B. TWTs for Site 1139 from the downhole sonic log and from discrete samples disagree strongly because of low data quality and data gaps. We acquired no WST data at Site 1139.