Several recent examples demonstrate implementation of results from earthquake geodesy towards evaluating earthquake related damage to societal infrastructure. For the 1992 Landers earthquake (Mw=7.3), the 1992 Cape Mendocino earthquake (Mw=7.0) and for the 1994 Northridge earthquake (Mw=6.7) in California, reports have assisted surveyors and engineers in identifying damaged structures and changes in the ground surface that can affect many infrastructure systems. The 1992 Landers earthquake sequence produced up to 6 meters of permanent ground movement (e.g., Murray et al., 1993; Hudnut et al., 1994) and although the largest ground displacement occurred in sparsely populated areas, urban areas such as Palm Springs and San Bernardino permanently shifted by 5 to 30 cm. The 1992 Cape Mendocino earthquake affected an area along the northern California coast (Oppenheimer et al., 1993; Stein et al., 1993; Murray et al., in press), causing nearly one meter uplift of shallowly submerged shoals, as well as substantial deformation of flood plains (Stein et al., 1993).
The 1994 Northridge earthquake caused permanent ground uplift of up to half a meter, primarily affecting the heavily populated San Fernando Valley near Los Angeles (USGS & SCEC, 1994). Investigations of flood plain boundary shifts, water reservoir tilting, and damage to engineered structures and systems can detect subtle damage inflicted by the static deformation and shaking effects of an earthquake. Numerous crucial water delivery and removal systems cross the San Fernando Valley and the earthquake tilted and deformed these systems. Such ground tilting can potentially affect the hydraulic gradients of these systems. Nine days after the earthquake, a report on preliminary GPS displacement field estimates was distributed by e-mail and given to State and Local surveyors and engineers to help them evaluate potential problems (Hudnut and Murray, 1994). For all three earthquakes, these reports have been provided to other Federal, State, and Local government agencies as a basis for potentially issuing notices to mariners, redefining flood plain boundaries, identifying changes in surveying control networks (that are the basis for defining land boundaries), and identifying disturbed or damaged engineered structures. Also, the information provided in these reports helps other agencies in planning resurveys of vertical and horizontal survey control networks, and bathymetric surveys of coastal waterways and ports, thereby facilitating more efficient use of public funds.