Description: Ground shaking is the earthquake effect that results in the vast majority of damage. Several factors control how ground motion interacts with structures, making the hazard of ground shaking difficult to predict. Seismic waves propagating through the earth’s crust are responsible for the ground vibrations normally felt during an earthquake. Seismic waves can vibrate in any direction and at different frequencies, depending on the frequency content of the earthquake, its rupture mechanism, the distance from the earthquake source, or epicenter, to an affected site, and the path and material through which the waves are moving. All of San Diego County is located within Seismic Zone 4 (Sec. 1629.4.1 of the CBC), which is the highest Seismic Zone, and like most of Southern California, is subject to ground shaking. In 1997, the Uniform Building Code incorporated Near-Source Zones for calculating base shear, which accounts for high ground motion and damage that have been observed within a few kilometers of historic earthquake ruptures. These Near-Source Zones were developed by the Strong Ground Motion Ad-Hoc Subcommittee of the Seismology Committee of the Structural Engineers Association of California (SEAOC). Several Near-Source Zones occur in the County. Active faults (faults which are known to have been active during Holocene time within the past 11,000 years) in the unincorporated portion of the County were classified as A or B in accordance with the criteria specified in 1997 UBC Table 16-U (DMG, 1998). Type A faults are capable of producing magnitude 7.0 earthquakes or greater and have a high rate of seismic activity (a slip rate of at least 5 millimeters per year). Segments of the San Jacinto and Elsinore fault zones are included in this category. Near-source velocity effects need to be considered in the design of buildings within 15 kilometers of a Type A fault. Type B faults are the majority of the rest of the seismogenic faults in California, and segments of the San Jacinto, Elsinore, and Rose Canyon fault zones are included in this category. Near-source velocity effects need to be considered in the design of buildings within 10 kilometers of a Type B fault.
Service Item Id: d0310a4ca2164843ae1960cd81ae1b98
Copyright Text: 1997 Uniform Building Code. County of San Diego, Planning & Development Services, LUEG-GIS Service