Faults

• Earthquakes begin on a fault plane

• movement will not proceed smoothly away from the fault

• due to Changes along the length and depth of the fault

http://www.astigan.com/wp-content/uploads/2009/01/san-andreas-fault-can-produce-huge-earthquake-in-california_5106.jpg

• Amount of friction along the fault cause irregular movement– Rock type– Strength of fault– Natural barriers to movement

• Direction of fault roughness of fault surface

Strike slip faulting

• Faulting in which the movement is horizontal

• associated with shearing, are surfaces where rock bodies slide past one another horizontally, with no vertical movement.

Normal faults caused by tensional forces pulling the rock apart. The result is a fault in which the hanging wall (upper block of rock) has moved downward relative to the footwall.

• Reverse faults caused by compressional forces squeezing the rock until it breaks.

• the hanging wall will move upward relative to the footwall. Wikipedia

Stick slip: a sporadic motion of fits and starts

• As energy builds up, the rock on either side of the fault will store the energy until its force exceeds the strength of the fault

Movement along the fault will continue until the failure reaches an area where the strength of the rock is great

enough to prevent further rupture

Some of the energy in the rock will be released• by frictional heating on the fault, • the crushing of the rock, • and the propagation of earthquake waves

Liquefaction

• Does not cause earthquakes • is the result of an earthquake with a magnitude of 5.0 or

greater• Only occurs in highly saturated sand or clay soils• Vibrations cause the soil particles to lose contact with

one another and so the soil takes on the characteristics of a liquid– AKA: quicksand or quickclay– http://video.google.com/videoplay?docid=32116389448553990&

ei=LXf6Sem8CpS6qAOxirS8Bg&q=liquefaction+earthquake&hl=en

– http://www.youtube.com/watch?v=ngxG49Lf6co

When does liquefaction occur in relation to quakes?

• Takes time for pressures to buildup underground

• Quicksand is heavy, thick fluid moves slowly

• Liquefaction, sand boiling and other associated phenomena are not apparent during the shaking but after

• More distance = longer duration period for shaking

3 ways to induce Liquefaction

1. Seismically: caused by seismic waves

2. Mechanically: caused by vibrations from trains, motor vehicles, tractors

3. Hydrologically: caused when ground water pressures increase due to rising stream levels during flooding conditions

Hyrdologically

• This type most commonly occurs on properties protected by levees where rivers can rise to levels above the surface

• Sand boils become active during river flood stages

• Tractors and trains etc… crossing over sand fissures during times of high water table can cause highways to sag, tracks get out of parallel and farm equipment to sink into the ground

Vocab• Consolidated: tightly packed,

composed of particles that are not easily separated

• Lifeline: a service that is vital to the life of the community. Include: transportation systems, communication systems, water supply lines, electric power lines, and petroleum or natural gas lines

• Liquefaction: the process in which a solid (soil) takes on the characteristics of a liquid as a result of an increase in pore pressure and a reduction in stress

• Sand boil: a forcible ejection of sand and water from saturated soil, caused by and earthquake or heavy flooding.

• Saturated: having absorbed water to the point that all the spaces between the particles are filled, and no water can enter

• Unconsolidated: loosely arranged, not cemented together, so particles separate easily.

• Ground Water: subsurface or underground water