Events Calendar

AME Department Seminar

Speaker: Anders Petersson, Center for Applied Scientific Computing. Lawrence Livermore National Laboratory. Livermore, CA.

Talk Title: Source Estimation by Full Wave Form Inversion

Abstract: We discuss the inverse problem of determining the source parameters of a small seismic event (location, mechanism, start time, frequency), such that the wave form misfit between seismographic recordings and simulated ground motions is minimized. Our approach is based on direct numerical simulations of the elastic wave equation, allowing for complex heterogeneous material models and realistic topography. A non-linear conjugated gradient approach is applied to solve the inverse problem, where the gradient of the misfit (with respect to the source parameters) is calculated from the numerical solution of an adjoint wave equation. Numerical experiments on simple 2-D models illustrate the importance of scaling the source parameters before applying the conjugated gradient iteration, preferably using the Hessian. A procedure based on arrival times is used to generate an initial guess for the source parameters. For the cases considered here, the conjugate gradient iteration often converges in 20-50 iterations.

Solving the inverse problem requires of the order O(100) numerical solutions of the elastic wave equation. For 3-D models, such problems can only be solved on large parallel machines. We will present the capabilities of our parallel open source code WPP, which was designed to solve seismic wave propagation problems on the regional scale. A higher order accurate scheme is currently being implemented to improve the the frequency resolution and efficiency of the method. These enhancements will be important for solving the three-dimensional inverse problem, for example in geothermal applications where there is interest in using micro seismicity for imaging the geometry of a fractured network.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. This is contribution LLNL-ABS-523199.


Host: Prof. Veronica Eliasson

More Info: http://ae-www.usc.edu/seminars/index.shtml#upcoming

Location: Seaver Science Library (SSL) - 150

Audiences: Everyone Is Invited

Contact: April Mundy

Event Link: http://ae-www.usc.edu/seminars/index.shtml#upcoming