1. Department of Geophysics, Stanford University, 397 Panama Mall, Mitchell Earth Sciences Building, Stanford, California 94305 U.S.A., claraeyoon@gmail.com
2. Institute for Computational and Mathematical Engineering, Stanford University, 475 Via Ortega, Huang Engineering Building, Stanford, California 94305 U.S.A.
3. Now at Department of Earth and Planetary Sciences, Harvard University, 20 Oxford Street, Cambridge, Massachusetts 02138 U.S.A.
4. Department of Computer Science, Stanford University, 353 Serra Mall, Gates Computer Science Building, Stanford, California 94305 U.S.A.