4. VALUE OF THE REPORT

Prior to publication of this report, several agencies have requested data from us or asked for assistance in interpreting our findings for engineering or surveying purposes. Briefly, these include the following:

• The National Geodetic Survey has so far received and filled about 100 requests for new heights and coordinates in southern California from the restored network.

• Caltrans used the pre- and post-earthquake elevation changes to assess subsidence and deformation associated with tunneling for the Metropolitan Transit Authority's subway extension [Satalich, 1996]. Such use of the restored network will continue as the MTA expands, and thus the restored leveling network promises to improve the safety of the drilling operations.

• NASA's Jet Propulsion Laboratory has requested and received our map of long-term subsidence in metropolitan Los Angeles to evaluate and interpret deformation inferred from a new generation of radar satellites, which measure height change by forming an interferogram with three successive radar images of the topography [e.g., Massonnet, et al., 1993].

• The City of Simi Valley has used the anomalous BM listing and the sites of liquefaction and landslides to assess damage and urban reconstruction issues. The U.S. Geological Survey prepared a set of deformation profiles and maps with the surface street grid included at their request, which aided the Simi Valley deliberations.

• The California Seismic Safety Commission requested and received a preliminary version of the map to compare elevation change measured by surveying with the distribution of ground cracking mapped by its members and independent geologists. The Commission seeks to evaluate the extent and cost of damage to the built environment directly attributable to surface faulting in a blind earthquake.

• Scientists at the U.S. Geological Survey and the California Institute of Technology used the coseismic elevation changes developed in this report to study the earthquake source and rupture propagation. This effort has lead to improved models of earthquake hazards, and a better understanding of the causes of earthquake shaking [Wald, Heaton, & Hudnut, 1996].

• Geologists at the U.S. Geological Survey are using the coseismic elevation changes along with detailed surface mapping to determine if ground cracks in the Granada Hills were caused by slip on a fault or by shaking and liquefaction.