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Plate TectonicsPlate Tectonics

Earth qqqqqquakes

!

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What are we going to look What are we going to look at?at?

How do earthquakes

form?

Where do earthquakes

happen?

Variety of magnitude?

What are EQs like?

Differences between

LIC & HIC

Personal management

of EQs

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To experience the drama of plate tectonics -- the jostling of the giant plates that carry continents and oceans -- try this experiment: Sit in a comfortable chair, hold your hand out, and watch your fingernails grow. That's about the average speed of a tectonic plate. But wait around long enough, and even the tortoise crawl of plate tectonics will have dramatic and deadly consequences. Though plate tectonics is a global phenomenon and virtually invisible to us in our daily lives, it introduces enormous stresses in the crust where we live. From time to time, stressed-out crust releases the stress in sudden fits: earthquakes.

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Most earthquakes happen near the boundaries of tectonic plates, both where the plates spread apart and where they crunch or grind together But large temblors also strike from time to time in the normally stable interior of continents.

Movement of body waves away from the focus of

the earthquake. The epicentre is the location on the surface directly

above the earthquake's focus.

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As you see the UK is not As you see the UK is not immuneimmune

Earthquake hits North YorkshireThe British Geological Survey (BGS) said the 3.6-magnitude quake struck 9km north-west of Ripon in North Yorkshire just after 2100 GMT on Monday (Jan 3rd 2011)

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But as you can see – 3.6 is not But as you can see – 3.6 is not very big – and there are 100s of very big – and there are 100s of

thousands every yearthousands every year

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More frequently than time to time, actually. If you imagine the Earth as a giant bell, it's ringing with earthquakes every second of the day -- from the many imperceptible clinks of microquakes to the deafening gong of very occasional but "great" earthquakes (those of magnitude 8.0 or greater). It is estimated that there several million temblors, most undetectable, happen every day.

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These are all the earthquakes of magnitude These are all the earthquakes of magnitude 7.0 or greater for 2010. You can see where 7.0 or greater for 2010. You can see where they are concentrated – but even tho’ these they are concentrated – but even tho’ these are quite severe, deaths only occurred 5 of are quite severe, deaths only occurred 5 of them.them.

Red >7.5 – with !! means deathsBlue<7.5 or wheelchair is <7.5 + deaths

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What do earthquakes feel What do earthquakes feel like?like?

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There are 2 types of waves in There are 2 types of waves in an earthquakean earthquake

Body waves and surface waves. Body waves travel outward in all directions, including downward, from the quake's focus -- that is, the particular spot where the fault first began to rupture. Surface waves, by contrast, are confined to the upper few hundred miles of the crust. They travel parallel to the surface, like ripples on the surface of a pond. They are also slower than body waves.

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Following an earthquake …Following an earthquake …..the body waves (P-wave) strike first and are the fastest kind. People often report a sound like a train just before they feel a quake, which is the P-wave moving as an acoustic wave in the air. Then the secondary, or S-waves, arrive. A person in a building perceives the arrival of S-waves as a sudden powerful jolt, as if a giant has pounded his fist down on the roof. Finally, the surface waves strike. In very strong earthquakes, the up-and-down and back-and-forth motions caused by surface waves can make the ground appear to roll like the surface of the ocean, and can literally topple buildings over.

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In Washington State 2001In Washington State 2001

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In Washington State 2001In Washington State 2001

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In Washington State 2001In Washington State 2001

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How do we measure How do we measure earthquakes?earthquakes?

The scale you usually hear about is the Richter Scale.This uses data from a seismograph (see below) and combines it with the distance from the epicentre (the middle of the earthquake)

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What do the numbers mean?What do the numbers mean?Each number is a power of 10!So a 2 is 10 x bigger than 1And a 4 is 10x bigger than 3 and is 1000 x bigger than a 1So while 6 is moderate, a 7 is x10 bigger and getting serious and an 8 is x100 bigger than a 6 and very bad indeed!But Richter only really works within about 500 km of the epicentre, so there are now more accurate way to measure.But news programmes still tend to stick to Richter as everyone knows about it!

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Ground-shaking is not the only Ground-shaking is not the only hazardhazard

Some times the shaking is so violent, that boulders can be thrown into the airAlso landslides. In 1692, in Jamaica, the whole town of Port Royal slid into the sea and came to rest 15 metres below the surface. Mud quickly covered it up.When it was investigated in 1959, they found a buried copper kettle ( a big pot with a lid) together with it contents, turtle soup.

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Groundshaking is not the only Groundshaking is not the only hazardhazard

Sometimes whole chunks of land moveNear San Francisco, you can still see where a piece of fence was moved sidewaysIn Alaska, some land rose 10 metres and the sea floor dropped nearly 15 metres!

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Ground-shaking is not the only Ground-shaking is not the only hazardhazard

Also earth-slides and mudslides can happen.If a sugar bowl has been sitting around and you shake it, the sugar grains stay stuck together.But if you continue shaking it side to side, the grains split up and look a bit like a liquid moving – and this is what can happen to the soil, and like a liquid it can run down slopes and envelop villages and so on

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ReviewReview

What is the first thing you might notice about an earthquake?Second?Then?Afterwards, besides collapsed building, what are some other effects?

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HomeworkHomeworkGo through the slides and make sure you know what it might be likeThen imagine there is a biggish earthquake where you live – as you have seen it could happen!Then write an short article for the local paper telling what it was like.You might also want to include one or 2 of the ‘effects’e.g. A crack 1 metre deep and 10 metres long appears in the road outside Sainsbury's. The road was closed for a week while repairs were made