Earthquake Flashcards
(26 cards)
Earthquakes at convergent boundaries
Most powerful earthquakes occur along subduction zones, plates to lock from friction, pressure breaks rock. The subducting plate suddenly sinks => violent earthquake.
Oceanic - continental
2011 Japanese earthquake => sudden movement of Pacific plate under Eurasian plate. Eurasian plate pushed up =>tsunami, power plant meltdown
Continental - Continental
2015 Nepal earthquake Indo-Australian + Euasian 7.8. 2 plates collide, rock layers buckle up, pressure =friction, plates lock together.
The pressure builds rock breaks - sudden movement
shallow focus-highly destructive.
Earthquakes at diverging boundaries
Mozambique earthquake 2006
crust rifts apart and plumes of magma rise, causing vibrations, elastic rebound => strong earthquake
Elastic rebound
Rocks stretches until it breaks + snaps back, releasing loads of pressure
Earthquakes at transform boundaries
San Andreas fault Pacific + North American
plates slide past, friction = lock, pressure builds until rock breaks + plate jolts up => earthquake.
P waves/ primary waves
1st
travel through anything
no damage
S waves/ secondary waves
2nd
Only travels through rock
Crust moves up + down, ground shakes
Surface waves
Closest, so causes almost all damage
Crust moves up, down + side to side
Richter Scale
Records readings from seismograph.
Begins at 0 -no upper limit.
Logarithmic scale – e.g. 2.0 is 10 × stronger than 1.0.
Moment magnitude scale
Most common + accurate
Seismograph + amount of rock movement at fault.
logarithmic scale.
Mercalli scale
Subjective
12 grades- Roman numerals
Predicting earthquakes - Strainmeters
Monitor rock stress
holes 200m deep in ground, tells when rock will break
Predicting earthquakes - Tiltmeter
Shows change in slope from increased rock pressure
Predicting earthquakes - Seismometer
Records horizontal + vertical crust movement, is placed at fault lines
Predicting earthquakes - Gas emmisions
Radon is released, radioactive so easily detectable, but tells us nothing about time/location
Predicting earthquakes - Animal behaviour
Animals can sense P-waves
2011 Japan Earthquake - the earthquake
11 March 2011 9.0 magnitude 72 km off Japanese coast for 6 mins. Pacific subducted, Euarasian went up - megathrust.
Focus 24km below ocean floor, whch rose 10m=> tsunami which travelled 10km inland
2011 Japan Earthquake - Effects
15,897 killed
120,000+ buildings destroyed
1.5 million without safe drinking water
2011 Japan Earthquake - Powerplant
Generators at the Fukushima Daiichi Nuclear Power Plant generators flooded – cooling system fails-reactors overheat =>20 km radius evacuation zone
2011 Japan Earthquake - Aftermath
Early warning system upgraded.
€200 billion to the Japanese economy.
Radiation still being released into the Pacific
Earthquake negative effects - Infrastructure damage
Seismic waves make buildings + bridges to sway + collapse.
Falling debris crushes + suffocates people => significant loss of life
Earthquake negative effects - tsunami - how it works
1 plate rises, other subducts=> excess water hump spreads out in all direcions u to 970km/h. When tsunami hits land, friction slows it + quadruples in height before crashing
Earthquake negative effects - Liquifaction
Groundwater water saturates soi until it liquifies, can’t support anything, so buildings collapse + pipes sink/break
