MAPPING LIQUEFIABLE LAYER THICKNESS FOR SEISMIC HAZARD ASSESSMENT

Investigations of liquefaction sites, combining subsurface mapping and evaluation of liquefaction damage, are summarized for four areas in S an Francisco affected by 1906 and 1989 earthquakes, where more than 95 0 borehole and sounding records were collected and analyzed. The maps developed from this database provide a comprehensive picture of subsur face conditions with substantial practical value. Postliquefaction set tlement, horizontal displacement caused by lateral spread, and earthqu ake damage to buried pipelines are shown to be related closely with th e thickness of underlying liquefiable soil. The influence of surface a nd liquefiable layer thicknesses on liquefaction damage is evaluated. Mapping liquefiable layer thickness is shown to be an excellent means of locating areas of potentially severe liquefaction, which is adapted easily to geographic information systems (GIS) for planning and desig n purposes.