Geologic Hazards

  1. Asthenosphere
    Under the lithosphere, it is the weak upper mantle where isostatic adjustments are made, magma generated and seismic waves strongly attenuated.
  2. Attenuation
    A reduction in the aomplitude of seismic waves produced by divergence, scattering, reflection, and absorption
  3. Avalanche
    A large mass of snow, ice, soil, rock, or mixtures of these materials, falling, sliding, or flowing very rapidly due to gravity
  4. Body-Wave Magnitude (Mb)
    Magnitude of an earthquake as estimated from the amplitude of body waves
  5. Crown
    The material that is still in place and adjacent to the highest parts of the main scarp of a landslide
  6. Differential Settlement
    The uneven lowering of different parts of an engineered structure, often resulting in damage to the structure
  7. Dilatency
    The increase in volume of rocks due to elastic and nonelastic changes during deformation
  8. Elastic Rebound Theory
    A theory proposed by Reid to explain the cause of earthquakes
  9. Epicenter
    Point on Earth's surface directly above the focus (hypocenter)
  10. Factor of Safety
    A measure of the stability of the slope in which the resisting forces are compared to the driving forces. If the resisting forces is equal to or less than the driving forces the slope will fail.
  11. Fall
    A very rapid downward movement of rock or earth that travels most of the distance through the air, either by free fall, leaps and bounds, or rolling.
  12. Fault Creep
    Slow ground displacement usually occuring without accompanying earthquakes. It may be of tectonic origin or result from oil or groundwater withdrawal.
  13. Fault Scarp
    A steep slope formed directly by movement along a fault and representing the exposed surface of the fault before erosion and weathering modify it.
  14. Fault-Line Scarp
    A steep slope formed by differential erosion along a fault line.
  15. Flow
    Movement within the displaced mass of rock or soil that continually deforms it. Slip surface are not generally visible
  16. Focus (hypocenter)
    The place where earthquake rupture originates
  17. ground Lurching
    The movement of an unsupported cliff or stream bank towards the free face during an earthquake. A series of more or less paralles cracks are formed, separating the ground into blocks.
  18. Ground Shattering
    Bedrock or soil on a ridge top that has been thoroughly pulverized due to high accelerations over many cycles of earthquake shattering
  19. Growth Fault
    A fault that moves contemporaneously with deposition causing the throw (amount of vertical displacement) to increase with depth and the strata to be thicker on the downthrown side as compared to the upthrown side.
  20. Head scarp or Main Scarp
    A steep surface on the undisturbed ground at the top of the slide, which is the upper slip surface
  21. Hydrocompaction
    The process whereby soils collapse when they are wetted, it may also be called hydroconsolidation
  22. Intensity
    A measure of the effects of an earthquake at a particular place. Observed effects are the damage to human structures, ground disturbances, and animal reactions.
  23. INtensity Scale
    A descriptive way to assess earthquake intensity. The scale used is the Modified Mercalli Intensity Scale.
  24. Lateral Spread
    Movement of a fractured mass laterally, often along a basal shear surface or zone of plastic flow
  25. Liquefaction
    The sudden large decrease of shearing resistance of a cohesionless soil cause by collapse of the structure by a shock (such as an earthquake), and associated with an increase of pore pressure.
  26. Lithosphere
    Composed of the Earth's crust and part of the upper mantle, it is approximately 100km thick and is relatively strong as compared to the underlying asthenosphere
  27. Local Magnitude (ML)
    Local or richter magnitude is the log10 of the minimum seismic wave amplitude (in thousandths of a millimeter) recorded on a standard seismograph at a distance of 100 km from the earthquake epicenter.
  28. Magnitude
    A measure of the strength of an earthquake or the strain energy released by it. Four common types are Richter (or local), body wave, surface wave, and moment magnitude.
  29. Microseism
    A more or less continuous motion in the Earth unrelated to earthquakes, with a period of 1 - 9 seconds.
  30. Moment Magnitude (M)
    The magnitude of an earthquake estimated by using the seismic moment
  31. Period
    The interval of time required for the completion of a cyclic motion or recurring event.
  32. Recurrence Interval
    The average time interval between earthquake occurences of equal magnitude on the same fault.
  33. Rigidity
    The ratio of the shearing stress to the amoung of angular rotation it produces in a rock sample
  34. Rotational Slide or Slump
    Landslide movement due to forces that cause a turning moment about a point above the center of gravity of the unit. The slip surface is concave upwards.
  35. Sand Boil
    A cone-shaped deposit of sand formed during an earthquake when subsurface sand layers liquefy and then are blown to the surface through cracks.
  36. Seiche
    A wave oscillation of the surface of water in an enclosed basin (such as a lake or bay) initiated by an earthquake or changes in atmospheric pressure.
  37. Seismic Moment (Mo)
    A measure of earthquake size that depends on the rock rigidity, amount of slip, and area of rupture.
  38. Settlement
    The gradual downward movement of a structure due to compression of the soil below the foundation
  39. Soil Creep
    A gradual, steady downhill movement of soil and loose rock material
  40. Subsidence
    A localized mass movement that involves the gradual downward settling or sinking of the Earth's surface.
  41. Surface-Wave Magnitude (Ms)
    Magnitude of an earthquake estimated from measurements of the amplitude of surface waves.
  42. Toe
    The outermost margin of a displaced landslide material, farthest away from the head scarp.
  43. Topple
    Slope movement due to forces that cause an overturning moment about a pivot point below the center of gravity of the unit.
  44. Translational Slide
    Landslide movement that occurs predominantly along planar or gently undulating surfaces.
  45. Triggered Creep
    Creep that occurs on a fault which has been triggered by a strong earthquake on some other fault.
  46. Tsunami
    Gravitational sea wave produced by large-scale, short duration earthquake on ocean floor, submarine earth movement, subsidence, or volcanic eruption.
Card Set
Geologic Hazards
Geologic Hazard Terms