The Relationship of Foundation Deformation to Surface and Near-Surface Faulting Resulting from the 1992 Landers Earthquake

Abstract

Surface rupture associated with the 1992 Landers earthquake (Mw 7.3) damaged several structures in the southwest Mojave desert. Six trenches were excavated through and adjacent to three structures that were damaged by directfault displacement. Trenching insights assisted in understanding foundation failures. This investigation confirms the surface shear zones, documents subsurface fault rupture geometry, and describes the effects on those structures. The surface pattern of rupture consisted of left-stepping, right-lateral shears with local vertical components within broader zones of shearing. The trenches generally exposed poorly stratified granular materials in which faults that were previously mapped on the surface were difficult to recognize. The age and material properties of the alluvium influenced the pattern of deformation. A strong correlation was found between the geometry of faulting and the pattern of residential concrete slab deformation. These observations suggest that an adequately reinforced concrete slab with poor coupling to the ground may minimize damage due to direct surface rupturing.