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
How many seismographs do you need to locate the epicentr
Total of three or more
Magnitude
The amount to energy that is generated during an earth wake but it depends on which scale is used
Richter magnitude scale
Developed by Charles richter in 1935 and basked p the amplitude of the highest recorded magnitude
Amplitude in Richter scale
-each level produces 10x mor amplitude the;magnitude before, so the amplitude of a magnitude 3 is 10 times higher than 4
Energy in the Richter scale
The scale is logarithmic
-each level produces 32x more amplitude than the magnitude before
—a magnitude of 5 is 32x32 times higher than that of a 3
Momentum magnitude scale
The difference between moment magnitude and the Cale is the addition of more data: fault surface area and wave length of displacement
Earthquake intensity scale
scale 1-7 depending on effect of quake
Shaking and rupture
Surface waves often cause ru
Tires at the surface (not to mention destruction of urban areas-producing a fault surface called a fault scarp
Liquefaction
We mentioned it in soils: too much water in the rock/sediments May liquefy in response to seismic waves (sensitivty)
Sand boil
Sand mixed with water liquefies during quakes and often water is ejected out of the ground forming sand/mud holes
Landslide
On hills where the rock/soil strength is overcome by the shaking rockslides occur
-mount Huascaran shook and a large part (rock and ice) collapsed burying the city of Yungay, Peru killing >20k people in 1970
Earthquakes cause
- Liauficatoon
- Sand/mud boiling
- Landslides
- Fires and disease
- Tsunami
Tsunami
Japanese for large harbor waves, are gigantic waves generated by:
-vertical displacement from subsea earthquakes
-large subsea landslides
-extraterrestrial impacts
—-third largetst earthquake December 26, 2004 Indonesia magnitude 9.0-9.1 earthquake, displacement was about 15 m along 1200 km to the WSW and caused tsunami waves and triggering quakes as far as Ak killing about 230 k people
Tsunami characteristics
Avg speed-713 km (>500 km/hr)
Save length: >100 km, shortens as you near the beach
Wave heigh on impact: increases near the shore, up to 30 meters, largest was from a land slide at 524 meters
More than one wave: first not always the last
Seismic risk is analyzed by
Geology-tyE of rocks determine how seismic waves move through
Seismology- recent seismic activity
Paleosiesmology- faulting reforged in the rock record
Geodesy-tectonic plate movement as recorded by gas satellites
What tells us about the history of a fault and frequency of quakes
Regions faults in rock record along with defending the age of the rocks
Precursors to earthquakes
- foreshocks
- deformation of the ground
- emission of radon (Rn) gas
- seismic gaps
- anomalous animal behavior
What to do to prepare for an earthquake
-practice duck voter and hold
-education: is your house ready?
—chimney reinforced?
—house securely attached to foundation
—heavy house items secure
—cover windows with Mylar
—water/gas heater fastened
During and after an earthquake
Be aware of how seismic waves hit(p then s)
- remain calm-crouch under a desk/table or stand in a strong doorway
- wait until shaking is done
- check on family members
- check for gas leaks/fire
Volcanic seismic waves
Tremors and harmonics
Seismic waves produced by volcanoes
Shallower often with harmonic tremor waves
How many volcanic eruptions per year
50-60
20k lives lost in the last 20 years
Where are the most active volcanoes
Japan, Mexico, Phillipeans, and Indonesia
Famous historical eruptions
- August 27 1883 itAly
- Vesuvius: precursors earthquake in Feb 63 ad, many tremors in the days before, eruption 73 AD Death toll: 300 body casts 3360-10k dead
- Krakatoa: precursors earthquakes up to 3 months prior, venting steam may 1883, erupted August 27 1883 death toll: official 36,417 but prolly around 120k