1. Department of Civil Engineering, Universidad de Concepción, P.O. Box 160-C, Concepción, Chile.
2. Department of Civil Engineering, University of Toronto, 35 St. George Street, Toronto, Ontario M5S 1A4, Canada.
3. Netlab, Centre for Urban and Community Studies, University of Toronto, 455 Spadina Avenue, Fourth Floor, Toronto, Ontario M5S 2G8, Canada.