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