1. School of Physics and Astronomy, University of Minnesota, 116 Church Street SE, Minneapolis, Minnesota 55455 U.S.A., vuk@umn.edu
2. Seismological Laboratory, California Institute of Technology, 1200 E. California Boulevard, MS 252‐21, Pasadena, California 91125 U.S.A.
3. Department of Geological Sciences, Indiana University, 1001 E. 10th Street, Bloomington, Indiana 47405 U.S.A.