Intro to EG and class expectations

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University of Manitoba
Geological Sciences
GEOL 2390
William M.Last

Introduction to Environmental Geology and class expectations GEOPHYSICAL TOOLS • Remember - increasing costs ◦ thus, use only after regional use of topi, geol maps etc ◦ (almost) always on local scale • Mainly ◦ seismic ■ most widely used ■ e.g. depth of bedrock ◦ gravity ◦ magnetics basics: • apply sudden pressure to surface • disturbance (pressure) moves outwards from point of impact/source in form of waves • velocity of a wave ◦ density ◦ elastic properties of material • V = (k +4/3 mu)/p • V = velocity of wave • k = bulk modulus resistance to change in volume • mu = shear modulus resistance to change in shape • p = density low V material over high V material why? density. other (non-horizontal) waves reach interface and can travel along interface but con- trolled by higher velocities • while travelling, continuous refraction up • eventually a geophone will record refraction wave 1st (before slower-moving hori- zontal wave) • plot time of arrival vs. distance • slope of first few points - define V1 • break in slope = critical distance (Cd) ◦ distance where waves going through V1 and waves going through v1 - V2 - V1 arrive at same time ◦ Depth = (Cd/2) [(V2-V1)/(V2+V1)]^0.5 • not strictly hazards course but ~40% of time • most dramatic/awesome/spectacular • significant 4 - 'headline' catchers hazard types • endogenic hazards - 'internal' earth processes ◦ ground shaking ◦ surface faulting ■ eq - induced ground failures, subsidence ◦ tsunamis (some) ◦ eruptions • exogenic hazards - external surfical processes ◦ flooding (most) ◦ landslides (most) ◦ ground failures/subsidence (most) ◦ expansive soils ◦ erosion ◦ sedimentation BUT, many/most hazards aren't hazards unless… • population lives there • urbanization remember -- our purpose • EG goal: suggest ACTION that planners/decision makers take ◦ reduce losses from hazards • to accomplish: ◦ understand processes causing hazard (fundamental step in devising methods of reducing losses) • USA 1973 ~1% of GNP (natur
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