Estimated relative abundance of landslides in the San Francisco Bay region, California

Relative slope stability and land-use planning in the San Francisco Bay region, California

“…Many complex interrelated factors contribute to the generation of landslides. Engineering geologists may spend months preparing analyses of soil and rock strength parameters (Early and Skempton, 1972), location of preexisting faults and fractures (Warn, 1966), precipitation records (Prior and Stephens, 1972), slope geometry, the orientation of the bedding planes in relation to slopes (Radbruch and Weiler, 1963;Briggs, 1974), and other factors to determine the causes of individual landslides. Many of the factors and processes that lead to landsliding are summarized in table 4.…”

“…Many interesting examples of the widely divergent form and style of relative slope stability and landslide susceptibility maps have been published in recent years. These include maps of parts of California by Blanc and Cleveland (1968); Johnson and Ellen (1968); Johnson and Lobo Guerrero (1968); Rogers (1971); Radbruch and Wentworth (1971); Brabb, Pampeyan, and Bonilla (1972); Rice and Strand (1972); Huffman ( , 1972Huffman ( , 1973; Burnett (1972); Radbruch and Crowther (1973); McGill (1973); Rice (1973); Williams (1973); Saul (1973); Morton, Miller, and Fife (1973); Bishop and Knox (1973); ; Frame (197 4); Bedrossian (197 4); and Anderson (1974). For other parts of the United States, maps have been prepared by Bailey (1971), Van Horn (1972), Williams (1972), Scott (1972), Maberry (1972), Miller (1973), Simpson (1973a, b), Dobrovolny and Schmoll (1974), and Pomeroy and Davies (1975), among others.…”

“…It has long been known in the bay region and elsewhere that certain bedrock units are more susceptible to landsliding than others, because of their physical and chemical characteristics, as well as the type and thickness of soil that tend to develop over them. Thus, two adjacent areas that appear to be similar may differ greatly in landslide susceptibility because of the type of underlying bedrock (Kachadoorian, 1956(Kachadoorian, , 1959Radbruch and Weiler, 1963;Radbruch and Case, 1967;Brabb and others, 1971;Frame, 1974;Anderson, 1974). We have discussed the characteristics of various bedrock units with geologists at the U.S. Geological Survey who have mapped the bedrock geology in the area during the past five years.…”

“…These maps provide a generalized regional representation of the relative stability of slopes in the San Francisco Bay region. They are based on more data and are at a larger scale (1:125,000) than an earlier map at a scale of 1:500,000 showing the estimated :relative abundance of landslides in the San Francisco Bay region (Radbruch and Wentworth, 1971). However, the slope stability maps are of smaller scale and are not based on as much information as previously published, more detailed relative slope stability maps that cover smaller areas, such as that by Brabb, Pampeyan, and :&onilla (1972) at a scale of 1:62,500 for San Mateo County, Frame (1974) for the Mount Sizer area in Santa Clara County at a scale of 1:12,000, Rogers (1971) and for part of the Santa Cruz Mountains in Santa Clara County at a scale of 1:12,000, Rice and Strand (1972) and.Huffman (1971) at a scale of 1:24,000 for parts of the San Francisco Bay region, and others shown on the slope stability index map ( fig.…”

Natural conditions that control landsliding in the San Francisco Bay region: An analysis based on data from the 1968-69 and 1972-73 rainy seasons

“…This characteristic permitted Radbruch and Wentworth (1971) to prepare a generalized map of estimated landslide abundance for the bay region. T. H. Nilsen and R. H. Wright (unpub.…”