A Highly Accurate Traveltime Approximation for Large-offset Reflections over Layered VTI Models

Summary Modern high-fold large-offset studies in exploration seismology require a highly accurate traveltime approximation as an essential part of many data processing and inversion algorithms. However, the accuracy of conventional traveltime approximations –designed for homogeneous media and used in layered media by employing Dix-type effective parameters– is limited to small offsets. To address this problem, we first calculate the correct asymptote of exact traveltime at infinity, then propose a new traveltime approximation for horizontally layered VTI media that is highly accurate from zero to infinite offsets. Among its potential applications, we show how it can be used to estimate model parameters from reflections traveltimes beneath a known high-velocity layer.