HR: 0935h
AN: NS21A-06 INVITED    [Abstracts]
TI: The use of Near-surface Geophysics in Evaluating and Assessing Natural Hazards
AU: * Pellerin, L
EM: pellerin@ak.net
AF: Green Engineering, Inc, 6543 Brayton Drive, Suite B, Anchorage, AK 99507, United States
AB: The list of natural hazards that transform the physical environmental is extensive: earthquakes, tsunamis, floods, volcanoes, lahars, landslides and debris flows, avalanches, karst/cavern collapse, heavy-metal contamination, permafrost, liquefaction, and magnetic storms. Because these events or conditions can have significant negative impact on health and infrastructure, the need for knowledge about and education of natural hazards is important. Near-surface geophysics can contribute in significant ways to both the knowledge base and wider understanding of these hazards. The discipline encompasses a wide range of methodologies, some of which are described below. A post-tsunami helicopter electromagnetic (EM) survey along the coasts of Aceh, northern Sumatra was used to discriminate between fresh-water and saltwater aquifers., saltwater intrusion occurred close to the coast as a result of the tsunami and deep saltwater occurrences particularly around 30 m depth were mapped up to several kilometers inland. Based on the survey results recommendations were made to locate shallow hand-dug wells and medium depth (60m) water wells. Utilizing airborne EM and magnetic measurements, a detailed assessment of the internal distribution of altered zones within an active volcano; Mount Rainier (NW USA) showed that alteration is much more restricted than had been inferred from surficial exposures alone. The study also suggested that the collapse of fresh, unaltered portions of the volcano is possible, and no flank of the volcano can be considered immune from lahars during eruption. Ground penetrating radar (GPR) has been used worldwide in a variety of applications from geotechnical investigations related to geologic hazards. These include assessment of transportation infrastructure, which maybe be damaged due to a natural hazard, study of the movement of rock glaciers in the Swiss Alps, and search and recovery of avalanche victims. Permafrost is widespread in polar areas and cold mountain terrain. GPR, electrical resistivity and EM methods have been used successfully to map permafrost and massive ground ice. The stability of these materials has impact on building and development within these regions. Mass movements in lowland permafrost terrain, which have implications for climate change, are being monitoring with thermal borehole measurements. Whether in times of flood or draught, understanding our watersheds is an important use of near surface geophysics. Satellite-based remote sensing methods are used to efficiently obtain soil moisture measurements over large regions. Ground-based conductivity meters are used to map soil types that play a fundamental role affecting the pattern of stream flow response. Synthetic Aperture Radar (SAR) is used to directly measure surface deformation, which can be related to subsurface hydrological conditions, aseismic deformation or landslides. Resolution of fine as 2mm/year can be obtained from satellite-based measurements. This level of resolutions aids in seismic risk assessment and allows the extent of landslides to be mapped and monitored efficiently. A series of national probabilistic seismic shaking hazard maps are being produced by the US Geological Survey using gravity, magnetic and seismic data in addition to other information. They can be used as input for many policy decisions on building codes and land use, and to estimate the probabilities of strong earthquakes, detailed maps of shaking amplification and susceptibility to liquefaction and landslides, and planning scenarios of large urban earthquakes.
DE: 0600 ELECTROMAGNETICS
DE: 0700 CRYOSPHERE (4540)
DE: 0900 EXPLORATION GEOPHYSICS
DE: 1600 GLOBAL CHANGE
DE: 7200 SEISMOLOGY
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting