Transcript Slide 1
Earthquakes • Movement/tremor in earths crust • Starts with a slight shake, stops and then continues • Length of shaking varies from seconds to minutes • Associated with plates boundariesparticularly subduction zones • Huge stress and rock snaps along fault line • Energy released as seismic waves A tremor or seismic wave caused by energy release along a fault line… due to stress… causes after shocks. 90% are shallow focus (70km deep) Intermediate and deep earthquakes – only at subduction zones – not as strong Main areas at plate margins 1. Pacific Ring of Fire eg. Kobe 1995 = 5,000 dead – cost $31b Chile 2010 magnitude 8.8 1. Mediterranean/Asiatic eg. Iran 1990 = 40, 000 dead Turkey 1994 = 20,000 dead – cost $7b Iran 2004 = 20,000 dead Indian-Burma 2004 Earthquake and Tsunami – 230,000 dead • Seismology the study of earthquakes. • Seismograph Instrument used to detect, measure & record seismic waves. • Seismic waves.. Primary(P) 5km per sec. through solid & molten material.(spring) • Secondary(S) 2.5km per sec. through solid material. Right angle movt. (rope) • Surface- slow.. Move side to side. Locating epicentre: Calculated by recording intervals btw. S & P waves at a seismograph station, 3 times….. 3 circles drawn & pinpoint centre. Magnitude: measured on Richter scale…. Each scale magnified by 10 for ground motion & by 30 for energy levels. Mercalli scale measures damage on a 12 point scale. Predicting earthquakes… 1. Seismic gaps… fault lines that have been quiet for a long time, likely to become active soon i.e. Patterns 2. Measure crustal stress levels – instrument placed in holes 1,5km deep can measure stress levels 3. Ground tilting - lasers 4. Swarms of foreshocks and slow tilting of the land are indicators of a quake. 5. Animal behaviour is used but not accurate. 6. Dating : study where earthquakes have occurred and monitor for energy build up & patterns. • Earthquake effects: • Death and destruction • Liquefication e.g. Mexico City anf Los Angeles • Migration – huge numbers displaced • Disease due to burst water pipes etc • Economic meltdown due to physical damage to infrastructure • Damage & injury depend on: Time of day: People indoors/outdoors, in traffic queue. Pop. Density: larger the pop. the greater the casualties. Type of structure: poorly built collapse easily. Soil type: Liquification of sand & silt (saturated & particles seperate)… flows when hit by seismic wave & destroys objects in its path. Geology: Solid rock more resistant. Magnitude & duration: stronger & longer- more damage Distance from epicentre: Further away less damage. Fire: gas pipes broken, electricity lines short, Flood: pipes broken; (lack of water to fight fire) Tsunami: ( a tidal wave) Focus under the ocean. Waves spread outwards at up to 1000km/h. Meets shallow water, piles up and creates waves up to 30m. Devastates coasts. Eg. Indonesia 2004. Satellite images help predict arrival of a tsunami. All items in houses should be fixed to walls and imovable Rubber shock absorbers and springs for buildings called seismic isolators Automatic shutters on windows to prevent flying glass and all windows should be shatterproof Flexible material that can sway should be used e.g. Reinforced Iron Bars Every floor reinforced at corners so less likely to collapse Open areas to evacuate fleeing pop. Local emergency plan Earthquake drill for the public Tsunami 26th Dec 2004 • • • • Epicenter off the west coast of Sumatra, Indonesia. depth of 30 km (19 mi) below mean sea level caused plate shifting of up to 20 m estimated 1,600 km of faultline slipped (or ruptured) about 15 m along the subduction zone where the India Plate slides (or subducts) under the overriding Burma Plate • The earthquake was caused by subduction and triggered a series of devastating tsunami along the coasts of most landmasses bordering the Indian Ocean, killing nearly 230,000 people in eleven countries, and inundating coastal communities with waves up to 30 meters high • Magnitude of between 9.1 and 9.3, second largest earthquake ever recorded. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm and triggered other earthquakes as far away as Alaska • sudden vertical rise of the seabed by several metres during the earthquake displaced massive volumes of water • In deep ocean water, tsunami waves form only a small hump, barely noticeable and harmless, which generally travels at a very high speed of 500 to 1,000 km/h • In shallow water near coastlines, a tsunami slows down to only tens of kilometres an hour but in doing so forms large destructive waves • The wave reached a height of 24 m when coming ashore along large stretches of the coastline, rising to 30 m • the total energy of the tsunami waves was equivalent to more than twice the total explosive energy used during all of World War II (including the two atomic bombs • http://www.baird.com/baird/en_html/indian_ocean/indianocean.html (Tsunami) • • http://www.pep.bc.ca/tsunamis/causes_2.htm (Tsunami) http://earthquake.usgs.gov/learning/animations/ (earthquakes) • http://earthquake.usgs.gov/learning/animations/ (all plate tectonics) Haiti Earthquake • • • • • • Haiti – Caribbean Island Poorest Country in Western World Population of 10 million Most people live on less than $1.50 a day 12 jan 2010 Earthquake measuring 7.0 on Richter Scale • Killed 230,000 people • Felt in neighbouring countries Cause • Caribbean Plate and North American Plate • Caribbean plate moves 20mm eastwards per year in relation to NAP • Had not moved in 250 yrs so huge pressure built up • Shallow quake just 13km deep and 25km fro capital of Port-au-Prince Impacts • • • • • 222,000 people dead, 300,000 injured 1.3 million homeless 90% of buildings in capital destroyed 4000 inmates escaped from prison Vital infrastructure destroyed including hospitals, transport facilities and communication systems • Port was destroyed so had to use port in Dominican Republic but connecting road was blocked for 10 days • Aftershocks hampered aid effort • Government moved people out of the capital where aid could be more effectively delivered • Aid was sent from around the world e.g. Medical supplies, tents, clothes, water etc. Long Term effects • Economic devastation – 1 in 5 jobs lost • Brazil donated $140m, UK $24 etc • Shanty Towns in port-au-prince destroyed so people returning to original villages left years previously • Economic cost close to $7b • Severe outbreak of cholera