Lateral spreading is the horizontal displacement of soil — typically toward a free face such as a riverbank, shoreline, or excavation — caused by liquefaction or cyclic softening during an earthquake. It is a major cause of damage to bridges, pipelines, and waterfront structures.
Lateral spreading is the horizontal displacement of soil masses caused by earthquake-induced liquefaction or cyclic softening. It occurs when a sloping ground surface, or a level surface adjacent to a free face (such as a riverbank, shoreline, or retaining wall), displaces laterally toward that free face during or after seismic shaking. The mechanism involves the loss of shear strength in the liquefied or softened soil, which allows the overlying non-liquefied crust to slide laterally. Displacements can range from a few centimeters to several meters, and the resulting ground movement can be highly damaging to structures supported on or embedded in the moving soil.
Lateral spreading is one of the most damaging forms of ground failure in earthquakes. The 1964 Alaska and Niigata earthquakes produced dramatic lateral spreading along waterfronts, with ground displacements of several meters. The 1989 Loma Prieta earthquake caused lateral spreading in the San Francisco Bay Area, damaging the Bay Bridge and other infrastructure. The 1995 Kobe earthquake produced extensive lateral spreading along the waterfront, damaging port facilities, quay walls, and lifelines. The 2010–2011 Christchurch earthquakes produced widespread lateral spreading in the eastern suburbs, damaging residential buildings, roads, and buried infrastructure. In Iran, lateral spreading potential exists in the Caspian coastal plain, Khuzestan, and other regions with shallow groundwater and loose saturated deposits, and the phenomenon was observed in the 2003 Bam earthquake (limited). The damage mechanism is typically structural: bridges lose support as abutments displace, pipelines rupture as ground moves differentially, buildings tilt or are pulled apart, and waterfront structures are pushed or rotated by the moving soil.
Lateral spreading is assessed through empirical, analytical, and numerical methods. Empirical approaches use case histories to develop correlations between displacement and parameters such as the thickness of the liquefied layer, the ground slope, the free-face geometry, and the intensity of shaking. The most widely used empirical model is that of Youd and colleagues (2002), based on the 1999 Turkey and 2001 Bhai (India) earthquakes, which estimates lateral displacement as a function of SPT resistance, ground geometry, and seismic demand. Analytical and numerical approaches use finite difference or finite element models with advanced constitutive models for liquefiable soil (such as PM4Sand, UBCSAND, or multi-yield surface models). Mitigation measures include ground improvement (densification, drainage, or solidification of the liquefiable layer), structural measures (deep foundations extending below the moving soil, or ground anchors), and geometric measures (flattening slopes, removing free faces, or providing buttresses). In practice, lateral spreading is often evaluated together with liquefaction potential, since the two phenomena share the same triggering mechanism and often occur together.