1. Postdoctoral Fellow, Dept. of Civil and Environment Engineering, Univ. of Western Ontario, London, ON, Canada N6A 5B9.
2. Professor, Dept. of Civil and Environment Engineering, Univ. of Western Ontario, London, ON, Canada N6A 5B9 (corresponding author).
3. Professor, Dept. of Geography, Univ. of Western Ontario, London, ON, Canada N6A 5C2.