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extends for 500 feet in width on either side of an identified fault trace of major active faults and about 200 to 300 feet in width on either side of a minor active fault, as designated by the State. Development of a building for human occupancy is generally restricted within 50 feet of an identified fault. The Calaveras and Verona Faults are the only faults within the Planning Area that the State currendy designates as Alquist-Priolo Earthquake Fault Zones (see Figure V-5). The putpose of the Alquist-Priolo Earthquake Fault Zoning Act is to prevent construction of new buildings across known active faults in order to avoid surface fault rupture hazard. The Act prohibits placing most structures for human occupancy across traces of active faults thus mitigating damage due to surface fault rupture and not damage due to ground shaking. When construction of a building for human occupancy is proposed within an earthquake fault zone, the City requires that a developer submit a geologic report.s This study presents conclusions regarding the location and existence (or absence) of active faults at the site and also contains recommendations for detennining building setback distances from the identified faults. The City's consulting geologist reviews the reports for acceptability. The investigation of sites for the possible hazard of surface fault rupture is a difficult geologic task Many active faults are complex, consisting of multiple breaks and/or are difficult to find. Deep young alluvium deposits, for example, often prevent exploratory trenches from reaching ruptured soils making detennining a fault's location and activity difficult. In some instances fault trace investigations conclude that a given fault trace is "inferred" or "obscure" with no clear delineation of recent fault rupture. Figure V-5 includes the following fault trace types: 1. A well-located fault trace is unambiguous, easily discerned, and accurately located. 2. An approximately located fault trace may be eroded or modified. The fault-trace location is uncertain within a distance greater than 50 feet. 3. An inferred fault trace is not clearly related to surface faulting, or the surface does not indicate where the fault is located such that subsurface data are used to project its location. 4. A concealed fault has surface deposits - alluvium, colluvium,6 or landslide - covering the surface trace of the fault, burying it. Currendy, the Pleasanton Municipal Code requires that the setback from an active fault trace be 50 feet (Section 17.12.040). Most surface faulting is confined to a relatively narrow zone from a few to tens of geologist's setback recommendations could differ from a simple 50 feet from a given fault, and should 5 Geologic studies are prepared by a California-registered geologist and address faulting, slope stability, erosion, seismicity, and related hazards. Geotechnical engineering studies are prepared by California-registered engineers and address subsurface soils, drainage, and other conditions for purposes of designing foundations, pavements, retaining walls, and other improvements affected by soil conditions. 6 Colluvium is loose rock or soil at the base of a steep slope or cliff. Public Safety 082906, dean V-10 City Council 8/29/2006