Lab 3: Earthquakes

liquifaction

When loose, water-saturated sediment (like sand/fill) loses strength and acts like a liquid during shaking.

Triassic age (200 million years old)

faults leftover from breakup of Pangaea

Hypocenter depths range from…

1 to 8 miles with over 90% deeper than 3 miles

P-wave

The fastest seismic wave; it arrives first at a seismograph station; always start at 0 seconds 

S-wave

Arrives second; causes more damage because it has a larger amplitude ("bigger range").

Seismic waves

vibrations of energy caused by the sudden breaking of rock in the Earth's crust (earthquakes), volcanic eruptions, or explosions, propagating through the Earth's interior and along its surface.

transform plate boundaries

friction of plates moving past each other creates earthquakes

convergent plate boundaries

reverse faults

divergent plate boundaries

normal faults

hypocenter

the position where the strain energy stored in the rock is first released, marking the point where the fault begins to rupture

epicenter

The point on Earth's surface directly above where an earthquake starts.

the lithosphere is brittle

it bends until it breaks

incipient fractures

A joint or fracture which does not continue through the specimen or at least not seen with the naked eye.

no strain

strain build-up

rupture with elastic rebound

strain released

most earthquakes occur

along plate boundaries

Normal Fault

where the hanging wall moved down relative to the footwall

tensional stress

the type of stress that creates normal faults (pulling apart)

hanging wall

upside down shoe

foot wall

looks like a shoe

the plate boundary most commonly associated with normal faults? FUN

divergent FOOT UP NORMAL

reverse fault

where the hanging wall moves up relative to the footwall

compressional stress

the type of stress that creates reverse faults (pushing together)

the plate boundary most commonly associated with reverse faults

convergent

strike-slip fault

a fault where blocks move horizontally past each other; it has no hanging wall or footwall

Shear stress

type of stress that creates strike-slip faults

the plate boundary most commonly associated with strike-slip faults (San Andreas)

transform

triangulation

The process of using 3 seismograph stations to locate an earthquake's epicenter.

S-P interval

The time difference between P and S waves; it increases the further you are from the epicenter.

Artificial Fill (AF)

Man-made ground material (sand/rocks) that is the least stable and most prone to liquefaction.

wando formation

A dense, clay-rich natural deposit that is more stable during an earthquake than artificial fill.

intraplate earthquake

An earthquake that occurs away from a plate boundary (e.g., the 1886 Charleston Earthquake).

seismic joint

A rubber seam or gap in a building designed to let sections flex and move independently during shaking.

earthquake bolts

metal rods/plates added to old buildings to pull walls back to square and provide structural support