1. Department of Geology and Geophysics; University of Wisconsin-Madison; 1215 Dayton,; Madison; Wisconsin; 53706; USA
2. Departamento de Geomagnetismo y Exploracion, Instituto de Geofisica; Universidad Nacional Autonoma de Mexico; 04510; Mexico City; Mexico
3. DGOT, SisVoc; Universidad de Guadalajara; Avenida Maestros y Mariano Barcenas,; 93106; Guadalajara; Mexico