(1) US Geological Survey, 6520 Mercantile Way, Suite 5 Lansing, Michigan 48911, USA Fax: +1-517-887-8937 e-mail: skhaack@usgs.gov, US;(2) US Geological Survey, MS 496, 345 Middlefield Road Menlo Park, California 94025, USA, US
Abstract:
Received, May 1999/Revised, October 1999/Accepted, October 1999