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Landslides FAQs - 22 Found

What is a landslide hazard map?

Several kinds of maps are used to depict danger from landslides. These maps may be as simple as a map that uses the locations of old landslides to indicate potential instability, or as complex as a quantitative map incorporating probabilities based on variables such as rainfall, slope angle, soil type, and levels of earthquake shaking. The term “landslide hazard map” (see specific definition below) is sometimes loosely applied to any of these. The following types of maps are used to describe and depict landslide hazards:


Landslide inventory maps show landslide locations and may show the dimensions and geographical extent of each landslide. Because one clue to the location of future landsliding is the distribution of past movement, maps that show the location and size of landslides are helpful in predicting the hazard for an area. Inventory maps do not indicate the landslide possibility in the area between the mapped landslides. For that, hazard, risk, or susceptibility maps are needed. A landslide inventory is a data set that may represent a single event, a regional event, or multiple events. Small-scale maps may show only landslide locations, whereas large-scale maps may distinguish landslide sources from deposits and classify different kinds of landslides and show other pertinent data. Examples of landslide inventory maps:



Landslide susceptibility maps describe the relative likelihood of future landsliding based solely on the intrinsic properties of a locale or site. Some organizations use the term “landslide potential map” for maps of this kind. Prior failure (from a landslide inventory), rock or soil strength, and steepness of slope are three of the more important site factors that determine susceptibility. The California Geological Survey relies on these three factors for producing its landslide susceptibility maps. However, other factors, such as fracture spacing for rock slopes, and the presence of faults and other geologic structures, are commonly used by others in preparing susceptibility maps. Examples of landslide susceptibility maps:



Landslide hazard maps indicate the possibility of landslides occurring throughout a given area. An ideal landslide hazard map shows not only the chances that a landslide may form at a particular place, but also the chance that it may travel downslope a given distance. The California Geological Survey  for example, applies the term “landslide potential map” to a specific type of hazard map that describes the likelihood of landsliding (susceptibility) jointly with the occurrence of a triggering event (opportunity).  Potential commonly is based on the three factors determining susceptibility plus an estimate or measure of the probability (likelihood of occurrence) of a triggering event such as earthquake or excessive rainfall. Examples of landslide hazard maps:



Examples of potential landslide maps:



Landslide risk maps show landslide potential along with the expected losses to life and property, should a landslide occur. Risk maps combine the probability information from a landslide hazard map with an analysis of all possible consequences (property damage, casualties, and loss of service).

Tags: Landslides, Liquefaction, Maps, Precipitation, Soils