Non-artifact vector P- and S-wave separation for elastic reverse time migration

Elastic reverse time migration(RTM)uses the elastic wave equation to extrapolate multicomponent seismic data to the subsurface and separate the elastic wavefield into P-and S-waves.P-and S-wave separation is a necessary step in elastic RTM to avoid crosstalk between coupled wavefields.However,the current curl-divergence operator-based separation method has a polarity reversal problem in PS imaging,and vector separation methods often have separation artifacts at the interface,which affects the quality of the imaging stack.We propose a non-artifact P-and S-wave separation method based on the first-order velocity-strain equation.This equation is used for wavefield extrapolation and separation in the first-order staggered-grid finite-difference scheme,and the storage and calculation amounts are consistent with the classical first-order velocity-stress equation.The separation equation does not calculate the partial derivatives of the elastic parameters,and thus,there is no artifact in the separated Pand S-waves.During wavefield extrapolation,the dynamic characteristics of the reflected wave undergo some changes,but the transmitted wavefield is accurate;therefore,it does not affect the dynamic characteristics of the final migration imaging.Through numerical examples of 2 D simple models,part SEAM model,BP model,and 3 D 4-layer model,different wavefield separation methods and corresponding elastic RTM imaging results are analyzed.We found that the velocity-strain based elastic RTM can image subsurface structures well,without spike artifacts caused by separation artifacts,and without polarity reversal phenomenon of the PS imaging.

A Numerical Method and its Error Estimates for the Decoupled Forward-Backward Stochastic Differential Equations

In this paper,a new numerical method for solving the decoupled forwardbackward stochastic differential equations(FBSDEs)is proposed based on some specially derived reference equations.We rigorously analyze errors of the proposed method under general situations.Then we present error estimates for each of the specific cases when some classical numerical schemes for solving the forward SDE are taken in the method;in particular,we prove that the proposed method is second-order accurate if used together with the order-2.0 weak Taylor scheme for the SDE.Some examples are also given to numerically demonstrate the accuracy of the proposed method and verify the theoretical results.

Self-consistent effective-one-body theory for spinless binaries based on post-Minkowskian approximation I:Hamiltonian and decoupled equation forψ^(B)_(4)

To build a self-consistent effective-one-body(EOB)theory,in which the Hamiltonian,radiation-reaction force and waveform for the“plus”and“cross”modes of the gravitational wave should be based on the same effective background spacetime,the key step is to look for the decoupled equation forψ^(B)_(4)=h_(+)−ih_(×),which seems a very difficult task because there are non-vanishing tetrad components of the tracefree Ricci tensor for such spacetime.Fortunately,based on an effective spacetime obtained in this paper by using the post-Minkowskian(PM)approximation,we find the decoupled equation forψ^(B)_(4)by dividing the perturbation part of the metric into the odd and even parities.With the effective metric and decoupled equation at hand,we set up a frame of self-consistent EOB model for spinless binaries.

Explicit High Order One-Step Methods for Decoupled Forward Backward Stochastic Differential Equations

By using the Feynman-Kac formula and combining with Itˆo-Taylor expansion and finite difference approximation,we first develop an explicit third order onestep method for solving decoupled forward backward stochastic differential equations.Then based on the third order one,an explicit fourth order method is further proposed.Several numerical tests are also presented to illustrate the stability and high order accuracy of the proposed methods.

Self-consistent effective-one-body theory for spinning binaries based on post-Minkowskian approximation

This study extends the research on the self-consistent effective-one-body theory of a real spinless two-body system based on the post-Minkowskian approximation(Sci.China-Phys.Mech.Astron.65,100411(2022))to the case of a binary system for the spinning black holes.An effective rotating metric and an improved Hamiltonian for the spinning black hole binaries are constructed.The decoupled equation for the null tetrad component of the gravitational perturbed Weyl tensorψ4B in the effective rotating spacetime is found with the help of the gauge transform characteristics of the Weyl tensors.The decoupled equation is then separated between radial and angular variables in the slowly rotating background spacetime,and a formal solution of ψ_(4)^(B) is obtained.On this basis,the formal expressions of the radiation reaction force and the waveform for the“plus”and“cross”modes of the gravitational wave are presented.These results,obtained in the same effective spacetime,constitute a self-consistent effective-one-body theory for the spinning black hole binaries based on the post-Minkowskian approximation.