Raymond C. Wilson

Real-Time Landslide Warning During Heavy Rainfall

A real-time system for issuing warnings of landslides during major storms is being developed for the San Francisco Bay region, California. The system is based on empirical and theoretical relations between rainfall and landslide initiation, geologic determination of areas susceptible to landslides, real-time monitoring of a regional network of telemetering rain gages, and National Weather Service precipitation forecasts. This system was used to issue warnings during the storms of 12 to 21 February 1986, which produced 800 millimeters of rainfall in the region. Although analysis after the storms suggests that modifications and additional development are needed, the system successfully predicted the times of major landslide events. It could be used as a prototype for systems in other landslide-prone regions.

The Borah Peak, Idaho Earthquake of October 28, 1983—Liquefaction

The most pervasive and damaging effects of liquefaction generated by the 1983 Borah Peak, Idaho earthquake occurred in the Big Lost River and Thousand Springs Valleys above Mackay Reservoir. Less severe effects occurred in the Big Lost River Valley south of Mackay Reservoir and in the Pahsimeroi Valley. Nearly all of the liquefaction effects developed in floodplain alluvium of late Holocene age. However, the sediment that liquefied beneath the alluvial fans on the east side of the Thousand Springs Valley was deposited in late Pleistocene time. The distance from the fault to the farthest effect of liquefaction was unusually short for an M S = 7.2 event. The distribution of liquefaction effects were consistent, however, with the distribution of MMI intensity and estimated peak ground motion parameters, both of which attenuated more rapidly than is generally expected for an earthquake of this type and magnitude.

The Borah Peak, Idaho earthquake of October 28, 1983: Landslides

The Borah Peak, Idaho earthquake caused several hundred landslides throughout an area of about 4,200 km2. The most numerous landslides were rock falls and rock slides, which occurred where slopes contained conspicuous, through-going, open fractures or were composed of weakly cemented rocks. The earthquake also produced several slumps and cracks in man-made fill, several soil liquefaction phenomena, a large debris flow, a large mud flow, and a few ground failures of other types. The most significant landslide damage was in Challis, where rock falls damaged at least 3 houses and 2 automobiles.