## What is/are First Arrival Traveltime?

First Arrival Traveltime - The fast sweeping method (FSM) has been widely used in computing the first-arrival traveltimes for anisotropic media because it does not need to expand the wave front from the point of the smallest traveltime.^{[1]}Accurate picking of head-wave arrival times is an important component of first-arrival traveltime tomography.

^{[2]}Thereafter, inversion was performed using a 2D ray-based tomography algorithm to minimize first-arrival traveltime misfits by inverting the seismic velocities and the vertical position of the refractors.

^{[3]}After preprocessing, including receiver geometry correction, moveout correction, component rotation, and energy transformation from three dimensions to two dimensions, preconditioned first-arrival traveltime tomography based on an improved scattering-integral algorithm is applied to construct an initial P-wave velocity model.

^{[4]}First-arrival traveltime tomography (FATT) is used to delineate shallow velocity structures to identify static effects in oil exploration as well as to characterize the near surface for geotechnical purposes.

^{[5]}As a synthetic test example, we infer porosity fields using crosshole ground-penetrating radar (GPR) first-arrival traveltimes.

^{[6]}The velocity distribution for the surrounding rock can be obtained by the first-arrival traveltime tomography of the transmitted waves in the coal mining face.

^{[7]}A non-iterative first-arrival traveltime inversion method (NFTI) is proposed for building smooth velocity models using seismic diving waves observed on irregular surface.

^{[8]}First, a uniform prior distribution is used to reflect the lack of prior knowledge of model parameters, and inversions are performed using the straight-ray model with first-arrival traveltime data, the finite-difference time-domain (FDTD) model with first-arrival traveltime data, and the FDTD model with waveform data, respectively.

^{[9]}The first arrival traveltimes are then picked and inverted to generate the P-wave velocity tomogram.

^{[10]}The first arrival traveltime is calculated efficiently using the dynamic programming scheme, and the source-side propagating direction of the local plane-wave can be obtained using the traveltime field gradient.

^{[11]}

## velocity model building

First-arrival traveltime tomography is one of the most used velocity model building techniques especially in sparse wide-angle acquisitions for deep crustal seismic imaging cases.^{[1]}Accurate simulation of first-arrival traveltimes is the foundation of seismic depth imaging and macro velocity model building for full waveform inversion.

^{[2]}

## near surface velocity

First-arrival traveltime tomography is an essential method for obtaining near-surface velocity models.^{[1]}