ABSTRACT
Ground failure, consisting of cracking and distributed deformation, was common in gently sloping alluvial areas during the January 17, 1994, Northridge, California, earthquake. The mechanism of ground failure was ambiguous in many locations because it was not accompanied by venting of liquefied material. To resolve this ambiguity, we conducted detailed geotechnical investigations at four sites. The investigations indicate that three of the sites are underlain by liquefiable materials that should have liquefied at the observed levels of ground shaking. At the fourth site where no liquefiable material is present, we infer that dynamic shear failure of a weak clay layer caused ground failure. The experience with ground failure during the Northridge earthquake suggests that geologically based regional mapping of areas of high liquefaction susceptibility in alluvial fan environments may be more challenging than in fluvial environments.(AU)
