Earthquake Activity Flashcards
Earthquake Formation
- Two plates move alongside eachother (convection currents)
- The plates get stuck and a build up of stress forms
- Released pressure at the focus.
- Seismic waves from the focus travel through the crust to the surface causing earthquake.
Define:
-Focus
-Epicentre
-Shallow focus
-Intermediate focus
-Deep focus
-Point at which the pressure is released from crust
-The Point immediately above focus on surface
-(0-70km deep) greatest damage
-(70-300km deep) milder
-(300-700km deep) weak
Convergant Plate boundaries
Massive friction, layers of rock at subduction zone, rough edges of rock lock together while subducting, stress builds up which eventually breaks , releasing tension this can lead to large earthquakes and potential tsunamis
Divergent plate boundaries
Occur along fractures along mid ocean ridges, weak quakes
Transform plate boundaries
Sliding plates, stress builds up as they try to push past eachother, energy is released, powerful quakes, e.g San Andreas Fault
Seismograph
Seismologists (people who measure s activity) use this to detect and record earthquake activity, measure INTENSITY of seismic waves, generate graph called seismogram
Body waves Vs
Surface waves
Body waves - Travel through inner layers of earth, arriving at different times
Surface waves - Last to arrive and travel at the slowest speed, moving like ripples along the surface, most damage done.
The Richter Scale
Records magnitude of s activity, seismograph readings to calculate mag, open ended scale (no limit)
Mercalli Scale
Measures the intensity of quake from table of events, Roman numerals, Intensity I - not severe damage
Intensity XII - extremely severe damage
- Less accurate than richter as other things can impact the degree of destruction such as poor build quality
Earthquake prediction, Dating patterns
Previous earthquake activity along fault lines predict likelihood, magnitude and intensity of next quake,
look at patterns, seismic gaps etc
Electromagnetic fields Prediction
Changes in these fields near fault lines, satellite laser beams and other sensors placed within crust pick up these changes.
Gas Emissions
Rising levels of radon gas can indicate…, Radioactive gas found in rocks and soils. Can be released shortly before quakes by subterranean movements, easily detected by instruments
Reducing the impact of earthquakes
(Come up with how? for each in your head)
- Early warning systems (seismographs)
- Earthquake drills (practice)
- Power stations kept far from fault lines
- Earthquake proof buildings
How to earthquake proof a building
- Shock absorbers
- Base isolator
- Moat
- Cross bracing
- fireproof windows
- Shear core
- Weights on roof
Case study: Haiti
- 2010
- 70% lived under poverty
- Few building regulations made impacts worse
- 7.0 Mag
- Epicentre approx 25km from Port-au-Prince
- At least 52 aftershocks
Short term effects of Haiti quake
- 3.5 M people affected
- 230,000 deaths, 300,000 injuries
- 250,000 homes destroyed (1.5m left homeless)
- Shortage of clean water
- Overcrowded hospital
- 4,000 escape prison and cause havoc
Long term effects Haiti
- Contaminated water lead to cholera epidemic which claimed almost 6,000 lives
- Unemployment rose to 20%
- Landmark buildings destroyed like the presidents palace and cathedral
Japan 2011 Tsunami
- 9.0 magnitude
- 72km from coast
- Eurasian jolted upwards creating megathrust with 24km deep focus
- Ocean rose more than 10 metres while travelling 500 km/h
- flooded 561 km²
Japan short term effects
- 16,000 deaths
- 25,000 injured
- contaminated water
- 4.4 Million with no electricity
Long term effects Japan
- 2,500 still missing
- 125,000 buildings collapsed
- Fukushima nuclear power plant, 3 explosions evacuated 20km radius (exclusion zone)
