Prototype landslide hazard map of the conterminous United States
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Geology topics
Publications and source records attributed to L.M. Highland.
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As a result of population pressures, hillsides in the world's urban areas are being developed at an accelerating rate. This development increases the risk for urban landslides triggered by rainfall or earthquake activity. To counter this risk, four approaches have been employed by landslide managers and urban planners: (1) restricting development in landslide-prone areas; (2) implementing and enforcing excavation, grading, and construction codes; (3) protecting existing developments by physical mitigation measures and (4) developing and installing monitoring and warning systems. Where they have been utilized, these approaches generally have been effective in reducing the risk due to landslide hazards. In addition to these practices, landslide insurance holds promise as a mitigative measure by reducing the financial impact of landslides on individual property owners. Until recently, however, such insurance has not been widely available and, where it is available, it is so expensive that it has been little used. ?? Springer-Verlag 2006.
Land-use planners have an important role in reducing losses from debris-flow hazards. For that reason, the U.S. Geological Survey (USGS) and the American Planning Association (APA) have developed a strategy to make information about landslide and debris-flow hazards available to local planners so that they can incorporate this information into the planning process. A guidebook for planners and active training and technical support are the centerpieces of this strategy. The strategy that the USGS is using, which enlists the support of a professional society such as the APA to develop the guidebook and communicate with its members, may be a useful example for other countries to follow. ?? 2003 Millpress.
The mammoth Slumgullion landslide in southwestern Colorado is the largest actively moving landslide in Colorado and, perhaps, the entire country. To learn more about how and why landslides move the way they do, scientists at the U.S Geological Survey (USGS) have observed and monitored the remarkably regular movement of this landslide for more than 30 years. Located near Lake City in the San Juan Mountains, Slumgullion was chosen for a comprehensive study of landslide processes because part of the landslide appears to have been moving continuously for the past 300 years, transporting material hundreds of meters downslope, and because the slide has the potential to threaten life and property. Surface features of the landslide, such as folds and faults within the sliding mass, are constantly changing, either being created or destroyed by the continuous movement of the landslide. Current evaluation of hazards includes possible landslide. Current evaluation of hazards includes possible landslide damage to State Highway 149 and recreational areas in the vicinity of Lake San Cristobal. The mountains of Colorado, and the Rocky Mountains in general, have one of the highest levels of landslide hazard in the nation. In a typical year, landslides hazard in the nation. In a typical year, landslides cause several fatalities and millions of dollars in damage to highways, pipelines, buildings, and forests in Colorado. To reduce such losses we need to understand why landslides occur and how they behave once they form. The Slumgullion landslide, an ideal natural laboratory, offers a unique opportunity to carefully observe and monitor the movement of a large, active landslide. In 1990, soon after the State of Colorado assigned high priority to hazard evaluation of the Slumgullion landslide, the USGS began an intensive study as part of its Landslide Hazards Reduction Program.
Slope instability along a new highway bypass in Golden, Colorado, became a major concern in 1993. Rains and snowmelt accelerated movement of a landslide that had begun to develop before the bypass was opened to traffic in July of 1991. The downslope movement of earth materials increased significantly in 1993. During the first few months of the year, the landslide pushed onto the west shoulder of the road and crumpled the pavement beneath the south-bound lane. As we prepare this article (September, 1993), the slide continues to encroach onto the highway, posing a persistent problem despite repeated efforts to slow or stop its movement. As this article will show, permanent solutions to landslide problems of this kind are difficult to obtain.
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This map is one of a series of seismicity maps produced by the U.S. Geological Survey that show earthquake data of individual states or groups of states at the scale of 1:1,000,000. This map shows only those earthquakes with epicenters located within the boundaries of New York, even though earthquakes in nearby states or countries may have been felt or may have caused damage in New York.
This map is one of a series of seismicity maps produced by the U. S. Geological Survey that show earthquake data of individual states or groups of states at the scale of 1:1,000,000. This map shows only those earthquakes with epicenters located within the boundaries of Vermont, even though earthquakes in nearby states or countries may have been felt or may have caused damage in Vermont. The data in table 1 were used to compile the seismicity map; these data are a corrected, expanded, and updated (through 1983) version of the data used by Algermissen (1969) for a study of seismic risk in the United States. The locations and intensities of some earthquakes were revised and intensities were assigned where none had been before. Many earthquakes were added to the original list from new data sources as well as from some old data sources that had not been previously used. The data in table 1 represent best estimates of the location of the epicenter, magnitude, and intensity of each earthquake on the basis of historical and current information. Some of the aftershocks from large earthquakes are listed, but not all, especially for earthquakes that occurred before seismic instruments were universally used. The latitude and longitude coordinates of each epicenter were rounded to the nearest tenth of a degree and sorted so that all identical locations were grouped and counted. These locations are represented on the map by a triangle. The number of earthquakes at each location is shown on the map by the arabic number to the right of the triangle. A Roman numeral to the 1eft of a triangle is the maximum Modified Mercalli intensity (Wood and Neumann, 1931) of all earthquakes at that geographic location. The absence of an intensity value indicates that no intensities have been assigned to earthquakes at that location. The year shown below each triangle is the latest year for which the maximum intensity was recorded.