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Lecture 2

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Environmental Science
Nick Eyles

EESA06 Lecture 2 Page 1 EESA06 Lecture 2 The deepest mine in the world is 4km underground, any deeper it will be too hot, hole will begin to close due to temperature and movement Geophysics – application of physics to the world Earthquakes – generate energy - Fault plane – surface (between moving bocks) which blocks have moved, we feel as an earthquake - Focus – is where the energy is released, the trigger of the earthquake, always underground, can predict how much damage it can do – how deep down the focus is - Epicenter – directly above the focus on the earth’s surface - Seismic risk assessment – gauge any movement along any fault, looks at fault scarp & fault trace - Fault scarp – cliff, bluff, the steep slope that results after earthquake (ex: 1891 Japan) - Fault trace – fairly straight lines, many river valleys along traces of faults o Morphological – what shapes on earth’s surface created by faults - Not all faults create earthquakes, some “creep” don’t result in earthquake, the “lock” ones create earthquakes Waves: - Body waves – goes thru the interior o Primary and Secondary waves - Surface waves – go around the surface - Primary waves – the quickest 7km/sec, compression + extension spring o can go thru fluids, go all the way thru the interior of planet, thru the core o Refraction effects create “shadow zones” – no direct P waves - Secondary waves - are smaller 5km/sec, wave on a rope o Cannot go thru fluids, stops at core, very large shadow zone Earth Core: - Outer most part of core is liquid – preventing s-waves, refracting p-waves - Inner core is solid Seismograph station – closer to focus = time lag of arrival of P&S waves not much, farther from focus = time lag from P&S wave is bigger - Allow to determine where the epicenter was - Networks was setup to determine nuclear bomb testing Major Epicenters – Circum-Pacific belt (most damaging, deepest), Indonesian belt, Mediterranean- Himalayan belt (where India is colliding with China) - Deep focus earthquakes - Along the plate margins - Deepest earthquake is 7km down - Shallow-focus earthquakes, where plates are diverging, mid ocean drifts - Low magnitude earthquakes, magma coming up - Earthquakes can be in the middle of continents - Intracratonic earthquakes – are very difficult to explain and predict (ex: Toronto) Ancient China used missing farm animals to predict earthquakes Using Heat Flow measurements to map mantle structure and plumes (very hot rock) - Black lines are continents – cooler areas - White lines are the plate boundaries – higher heat flow below the oceans EESA06 Lecture 2 Page 2 Picture of the Core by Julain Lowman - Large plumes protruding from the core - Green slabs going down into core - Plates are moving around due to convection in this interior Rift valley on ridge crest (in textbook!) – seems like a conveyer belt - Hot mantle rising and cold mantle sinking -
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