Joint traveltime, waveform, and waveform envelope inversion for near-surface imaging

Abstract

The first-arrival traveltimes without large offsets constrain very shallow velocities, the waveform envelope presents low-frequency data, and the high-frequency waveform itself includes information regarding structural details. We have developed a joint traveltime, waveform, and waveform envelope (JTWE) inversion method for inverting near-surface velocity structures. By inverting three types of data, we are able to recover the low- and high-wavenumber structures and mitigate the cycle-skipping problem in waveform inversion. The calculation of traveltimes and raypaths is fast. Most of the computation effort is focused on dealing with the waveform and waveform envelope. JTWE backward propagates the waveform residual and envelope residual simultaneously to calculate the model updating gradients. This simultaneous backward-propagation strategy ensures that the computational cost of JTWE is similar to the cost of inverting waveform alone. In a synthetic experiment, we determine that JTWE mitigates the cycle-skipping problem and recovers the near-surface structures without the need for additional low-frequency data. The final results of JTWE indicate that it delivers improved results with low-velocity inclusions compared with full-waveform inversion. For field data from the Middle East, JTWE helps resolve a complex near-surface model with rugged topography and fit all three types of data.