Plate boundaries & Earthquakes
seismicity (seismic event, process of earthquake)
- ** movement along fault line (most common) - a change in mineral structure - inflation of a magma chamber - volcanic eruptions - giant landslides - meteorite impact
surface waves
- R-waves - L-waves friction absorbs the waves' energy, so it feels weaker the further you are from the epicenter
magnitude methods
- Richter scale - moment magnitude
seismic waves
- body waves - p-waves - s-waves
earthquake occurrence
- discrete belts along plate boundaries - but also, some that occur at ancient plate boundaries. (most continents are continental pieces that have been fused together) - you can also get earthquakes in ocean basin from enough volcanic activity
hot spots
- fed by mantle plumes - defined by volcanoes and volcanic activity - stationary--not moving through time. (therefore can track hot spots to determine plate motions)
short-term earthquake prediction
- foreshocks - crustal strain - stress triggering
earthquake-related hazards
- landslides - liquefaction
master fault
- made of smaller interconnected faults breaking off - earthquake event doesn't always occur exactly on master fault
Mercalli scale
- measures intensity of shaking; damage - uses Roman numerals
Wadati-Benioff zone
- no earthquakes below 660-670 km - defines subducting slab via earthquake locations
3 types of convergent plate boundaries
- oceanic-oceanic - oceanic-continental - continental-continental
p-waves
- primary or compression wave - fastest wave type - moves through solids and liquids - push-pull motion - parallel to wave
s-waves
- secondary wave or shear wave - 2nd fastest wave type - moves only through solids - shaking motion is perpendicular to the wave motion
tsunami
- seismic sea wave - usually earthquake-generated - wavelength is 10-100 km - velocity is 100s of km/hr 1) offset seafloor during an earthquake 2) entire column of water displaced 3) increases overall level of water
subduction zones
-oceanic lithosphere sinks beneath converging lithosphere (oceanic or continental) - occurs with oceanic-oceanic and oceanic-continental convergent plate boundaries - deep trench - chain of volcanic islands or mountains - high mountains - broad plateaus - cause the largest earthquakes
L-waves
Lowe: snaking morion on surface of earth (horizontal plane)
earthquakes occur at...
PLATE BOUNDARIES usually at convergent plate boundaries, but occur at plate boundaries in general
R-waves
Raleigh: move in ripple motion (vertical plane) like ripples
displacement: offset or slip
amount of movement along fault - marker layers (rock layer recognizable) are offset
earthquake size
amplitude of s-waves
magnitude
amplitude related to distance of S-P time by 1) energy released (news) or 2) intensity
recurrence interval
average time between major (earthquake) events
stick-slip behavior
faults move in jumps - once movement starts, it stops quickly due to friction on the fault surface - stress builds up again --> leads to another period of movement
moment magnitude
measures energy released
divergent plate boundary
mid-ocean ridges continental rifts parallel valleys volcanoes: - little to none, EXCEPT for continental rifts earthquakes: - shallow - less frequent
supercontinents
most continental masses are connected to form one continent two most recent supercontinents: - Pangea (250 mya) - Rodinia (1000 - 750 mya)
convergent plate boundary
mountains volcanoes: - prevalent - linear belt; dense earthquakes: - broad belt - shallow to deep - diffuse zone of earthquakes at continent-continent
Richter
outdated system
distance from epicenter =
p arrival - s arrival =
hypocenter (focus)
place along fault surface where earthquake initiates
epicenter
place on surface of earth above where the earthquake occurred
transform plate boundary
plates sliding past each other volcanoes: - none earthquakes: - shallow - form narrow linear belt
earthquakes
rapid release of energy that causes earth to shake
long-term earthquake prediction
recurrence interval
earthquakes occur due to...
stress buildups
fault initiation
tectonic stresses force rock to break - rocks bend slightly: elastic strain - continued stress leads to growth of cracks --> cracks eventually rupture --> earthquake energy released
mantle plumes
upwelling of deep hot mantle material
liquefaction
wet layers of sediment most hazardous 1) higher pore pressure reduces friction 2) sand flows up into the spaces of the cracks 3) earthquake waves liquefy water-filled sediment, and high pore pressure forces grains apart, resulting in reduced friction 4) newly liquefied sediments flow like a slurry 5) causes land to slump and flow