[1] Ecole Polytech Fed Lausanne, Sch Architecture Civil & Environm Engn, Lausanne, Switzerland
[2] Univ British Columbia, Dept Math, Vancouver, BC V5Z 1M9, Canada
[3] Univ British Columbia, Dept Earth & Ocean Sci, Vancouver, BC V5Z 1M9, Canada
[4] Univ British Columbia, Dept Mech Engn, Vancouver, BC V5Z 1M9, Canada