Test 2 Flashcards
1906 earthquake
Richter magnitude: 8.3
700 dead prolly closer 28-30k
400-524 million in losses 6-8 bill in 2009 dollars
Earthquake definition
A rapid release of energy as strain (fractures/faults) due to stress (usually tectonic)
-energy in waves
Hypocenter
(Focus)
The source
Epicenter
Is location of focus
-movement along faults
Where do quakes occur?
Plate boundaries -convergent -divergent -transform Interplate boundaries -new Madrid zone -Virginia, US 2011
Elastic rebound theory
-natural way earthquakes happen
Hf Reid suggested based on research done on the 1906 quake
- Rocks on both sides deform from stress
- Rocks bend and store elastic energy
- Stress overcomes strength of rocks
- MOVEMENT occurs along the fault line
Manmade Causes of an earthquake
Crustal loading (building a reservoir) —Hoover dam 1930s 600 quakes in 10 years after construction Deep water disposal —Rocky Mountains Arsenal 1962-2965 (M4 quakes) pumped waste fluids into a well into fractured metamorphic rock Nuclear explosions (subsurface - Nevada test site)
Fault
A fracture upon which displacement (movement) is observed
Two sides of the fault
Foot wall: stand on
Hanging wall: hang from
Normal fault versus reverse fault versus reverse thrust fault
Foot wall goes Up:Normal (FUN)
Foot wall goes Down >45:Reverse (FDR)
Foot wall goes Down <45: Reverse thrust (FDR)
Strikeslip Fault
Surface - no foot wall or hanging wall
Defined by relative movement as seen across the fault
Fault zones
Divided into segments
Fault segments
Based on related seismic events
Active faults
Must have shown movement within the last 10,000 years
Foreshock
Caused by slippage along the Fault surface hours or days before the earthquake
Aftershocks
refer to continued movements or adjustments along the fault, or connected faults hours to months or maybe years after the quake
Seismology
The science of studying earthquakes (seismic) waves
Two kinds of seismic waves
- Body waves
- travel through the earth at varying velocities depending on the type of rock or stat of matter - Surface waves
- waves which reach the surface move in particular waves. These waves do all the shaking and damage
Two types of body waves
- P waves (compressional waves)
- p waves push and pull in the direction
- they are moving (propagation)
- they are fastest (first waves on seismogram)
- they move through solid, liquid, and gas - S waves (shear waves)
- these waves move vertically perpendicular to the direction they’re traveling (propagation)
- they do not travel through liquid
- they arrive second on seisogram
Two types of surface waves
- Rayleigh waves (r waves )
- roll as they progress along the surface - Love waves (l waves)
- like S waves they move perpendicular to the direction they are traveling, but horizontally
How are waves affected by the material they move through
Weaker the rock/sediment = seismic waves are amplified (increased)
Seismograph
- record seismic waves as they occur
- the writing instrument (today electromagnetically) is separate vroom the instrument and so records as the machine shakes with the waves
- the result is a seismogram
What are seismogram measured in
Amplitude
Time
How a seismogram works
- Seismic waves from an earthquake move out concentrically from the focus and arrive at distant seismographic stations at different times
- Because p waves travel faster than S waves, the interval between their arrival times increases with distance
- By matching the observed interval to known travel-time curves, a seismologist can determine the distance from the station to the quake epicenter