Presentation on theme: "1 Plate Tectonics Earth qqqqqquakes! EVERYONE But before that – a bit of revision from last week and I want EVERYONE to have a go!"— Presentation transcript:
1 Plate Tectonics Earth qqqqqquakes! EVERYONE But before that – a bit of revision from last week and I want EVERYONE to have a go!
2 As __ is to ___ then ___ is to ? Why? As H is to L, then E is to ? What is the rule?
3 As B is to N, then D is to ? What is the rule? As G is to E, then A is to ? What is the rule? As V is to J, then Y is to ? What is the rule?
4 Which is the Odd One Out? And why? Because it is not ……. 1. E, J, N 2. W, T, Z3. U,L,R
5 What are we going to look at? How do earthquakes form? Where do earthquakes happen? Variety of magnitude? What are EQs like? Differences between LIC & HIC Personal management of EQs
6 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.
7 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. focus epicentre 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.
8 As you see the UK is not immune Earthquake hits North Yorkshire The 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 3 rd 2011)
9 But as you can see – 3.6 is not very big – and there are 100s of thousands every year
10 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.
11 These are all the earthquakes of magnitude 7.0 or greater for 2010. You can see where they are concentrated – but even tho these are quite severe, deaths only occurred 5 of them. ! Red >7.5 – with ! means deaths Blue<7.5 or wheelchair is <7.5 + deaths
13 There are 2 types of waves in an 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.
14 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.
19 How do we measure 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)
20 What do the numbers mean? Each number is a power of 10! So a 2 is 10 x bigger than 1 And a 4 is 10x bigger than 3 and is 1000 x bigger than a 1 So 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!
21 Ground-shaking is not the only hazard Some times the shaking is so violent, that boulders can be thrown into the air Also 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.
22 Ground-shaking is not the only hazard Sometimes whole chunks of land move Near San Francisco, you can still see where a piece of fence was moved sideways In Alaska, some land rose 10 metres and the sea floor dropped nearly 15 metres!
23 Ground-shaking is not the only hazard 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
26 Homework Go through the slides and make sure you know what an earthquake might be like Then 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