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<br />1988). Computers are also used to perform complex
<br />stability analyses. Software programs for these studies
<br />are readily available for personal computers.
<br />
<br />Instrumentation
<br />Instruments such as inc1inometers, strain meters,
<br />tiltmeters, and piezometers can be used to determine
<br />the mechanics of landslide movement and to warn
<br />against impending slope failure.
<br />
<br />ANTICIPATING THE
<br />
<br />LANDSLIDE HAZARD
<br />
<br />One of the main principles of geology is that the past is
<br />the key to the future. In evaluating the landslide hazard
<br />this means that natural slope failures in the future will
<br />probably occur as a result of the same types of geologic,
<br />geomorphic, and hydrologic situations that have led to
<br />past and present slope failures. Based on this assump-
<br />tion, it is possible to estimate the types, frequency of
<br />occurrence, extent, and consequences of slope failures
<br />that may occur in the future. However, the absence of
<br />past failures in a specific area does not preclude future
<br />failures. Man-induced conditions such as changes in the
<br />natural topograpby or hydrologic conditions can create or
<br />increase the susceptibility to slope failure (\ames and
<br />the IAEG, 1984).
<br />In order to predict landslide hazards in an area, the
<br />conditions and processes that promote instability must
<br />first be identified and their relative contnllution to slope
<br />failure hazard estimated, if possible. Despite significant
<br />improvements over the past 20 years in the analysis and
<br />understanding of landslide processes, experts remain
<br />unable to accurately predict times and locations of
<br />specific landslide incidents. However, useful conclusions
<br />concerning increased probability of landsliding can
<br />be drawn by combining geological analyses with
<br />knowledge of short-and long-term meteorological condi-
<br />tions. Current technology enables persons monitoring
<br />earth movements to define those areas most susceptlllle
<br />to Iandsliding and to issue "alerts" covering time spans
<br />of hours to days when meteorological conditions known
<br />to increase or initiate certain types of landslides occur.
<br />Alerts covering longer periods of time become propor-
<br />tionately less reliable.
<br />In summary, current technology only permits the
<br />alerting of the affected. public of the increased probabili-
<br />ty of landslides in certain areas; unequivocal, site-
<br />specific predictions are presently not possible.
<br />
<br />COMMUNICATING LANDSLIDE
<br />
<br />HAZARD INFORMATION
<br />
<br />A major part of an effective landslide hazard mitigation
<br />program must be dedicated to the communication and
<br />
<br />22
<br />
<br />use of the . cal information obtained from the other
<br />parts of the program. Often individuals or groups do not
<br />take mitiga e actions because they do not understand
<br />what to do, r lack education on how to do it. The
<br />mitigation or avoidance of landslide hazards and the
<br />reduction 0 landslide losses require that the appropriate
<br />information communicated to, and effectively used by,
<br />planners, d cision-makers, and emergency response
<br />personnel.
<br />The . e use of landslide information to reduce
<br />danger, es, or other losses depends not only on
<br />the efforts the producers of the information, but also
<br />on 1) the u rs' interest, capabilities, and experience in
<br />hazard-rela activities, 2) the existence of enabling
<br />legislation thorizing and funding federal, state, and
<br />local reduction activities. 3) the availability of
<br />adequate, d tailed information in a readily usable and
<br />understan ble form, and 4) the use of good information
<br />communica . on techniques. Unless technical studies are
<br />specifically . ored, information may be used only by
<br />engineers d geologists or may be misused or not used
<br />at all in the ecision making process.
<br />
<br />Users of Landslide Hazard Information
<br />Among the tential users of landslide hazard informa-
<br />tion are pe Ie at national, state. regional, and com-
<br />munity 1 s in both the public and private sectors.
<br />Three gen categories can be identified: 1) scientists
<br />and engine who use the information directly, 2) plan-
<br />ners and d . sion-makers who consider hazards among
<br />other Iand- se and development criteria, and 3) in-
<br />terested' ns, educators, and others with little or no
<br />technical rtise. These people differ widely in the
<br />kinds of inli rmation they need and in their
<br />capabiliti s to use that information. Examples of
<br />potential u are listed in Table 2.
<br />
<br />
<br />ential users of landslide hazard
<br />n.
<br />
<br />C TY, COUNTY, AND AREA-WIDE
<br />GOVERNMENT USERS
<br />ty building, engineering, zoning, safety,
<br />nmenta1 health departments
<br />City and c ty offices of emergency services
<br />County tax assessors
<br />Local nt geologists
<br />Mayors, co ty commissioners, and city council
<br />membe
<br />Multicoun (regional) planning, development, and
<br />emerge cy preparedness agencies
<br />Municipal ngineers, planners, and administrators
<br />Police, fire and sheriff's departments
<br />Public wor departments
<br />Road dep ents
<br />
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