Seismic velocity structure in southern Hokkaido deduced from ocean-bottom seismographic and land observations *

1. Institute of Seismology and Volcanology, Faculty of Science, Hokkaido University, 2. Department of Terrestrial Magnetism, Carnegie Institution of Washington, 3. Marine Works Japan LTD, 4. Kochi University, 5. National Institute of Advanced Industrial Science and Technology, 6. Meteorological Research Institute, 7. Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University