# Multiple and Escape Arrival Techniques for Geophysical Imaging and Inversion

Escape arrivals methods solve problem of computing multiple arrivals, based on high frequency approximations to the wave equation. These non-viscosity solutions, which contain swallowtails and overlaps, are required to accurately perform seismic inversion, since first arrivals may not contain the most energy. The methods rely on recasting the time-dependent Lagrangian characteristic equations in phase space as time-dependent Eulerian Liouville equations. These are then converted into coupled boundary value equations which, using variants of Ordered Upwind Methods, compute all arrivals from all possible sources simultaneously.