7.3.6: Engineering Against Ground Displacement

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Overview

Up to this point, the main hazard discussed has been ground shaking. The Alquist-Priolo Act in California seeks to avoid construction on active fault traces (see chapter 14 for details). A large displacement of several feet, particularly vertical (dip-slip) displacement, will probably destroy a building constructed across the fault, but building foundations can be designed to survive displacements of a foot or less. It makes no difference whether the displacement is caused by faulting, ground subsidence, or incipient landslides. An example of building destruction in Fengyuan City due to the 1999 Chi-Chi, Taiwan, earthquake is shown in Figure 12-15. The upthrown hanging wall is to the left, and footwall is to the right. The fault itself is close to the base of the scarp. Buildings along the hanging wall of the Chelungpu fault were totally destroyed.

Pipelines can be made flexible, and underground utility cables can have slack built-in at fault crossings. The Trans-Alaska Oil Pipeline was built across a major strike-slip fault that underwent several feet of displacement in an earthquake in November 2002. After a paleoseismic study led by Lloyd Cluff of Pacific Gas and Electric Co., the pipeline was designed to accommodate strike-slip surface displacement. It survived the earthquake virtually undamaged and with no spillage of crude oil.

I recently served as a consultant on a housing development where there was potential for small-scale, distributed faulting on a large part of the property. The likelihood of a surface-rupturing earthquake was present but relatively low. The geologist determined the maximum amount of displacement expected based on backhoe excavations, and the geotechnical engineer (Jonathan Bray of the University of California Berkeley) designed building foundations that would withstand that displacement without significant damage.