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ATOC 185 (71)
Lecture

# NATTYD lecture 1.docx

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School
Department
Atmospheric & Oceanic Sciences
Course
ATOC 185
Professor
Semester
Fall

Description
9/11/2012 7:40:00 AM Earthquake  shaking/vibration of ground  rocks undergo deformation and break suddenly along a fault. (rocks break in a brittle fashion and then get offset.) Earth’s surface made of tectonic plates, which are always in constant morning. (egg – crust of earth, shell of egg) made of cold material and breaks brittly. (dropped egg, cracks  (plate) boundaries between pieces which are tectonic plates, they are mobile). Plate tectonics  Constant movement of the plates Divergent Convergent Transform Question: The most powerful and destructive earthquakes occur: A. along divergent plate boundaries B. along convergent plate boundaries (subduction zones) Divergent margins Magma is injected into crack (boundary between two plates), plates are forced apart, cools and becomes new crust. Spreading rate, 1 – 15 cm per year. Example: Atlantic ocean is a divergent margin, being torn, the two plates are separating continuously at a rate of several cm/y. Example 2: Red sea, like the atlantic ocean except its younger, started to spread apart much more recently. Arabian plate, volcanism is evident as a result of rifting. Middle of red sea in submarine, hydrothermal springs, magma being erupted by volcanoes, along that specific margin of Red Sea. Convergent margins (subduction zones) Instead of two plates moving apart, when you have two plates coming together, the friction with the plates rubbing off each other, earthquakes are very large and frequent. Oceanic plate dives/slides beneath continental plate, recycling material back into mantle of earth  process known as subduction. Subduction environments  large earthquakes. Older denser goes down, younger less denser above. Convergent margins II If two continental plates collide, do not subduct  they are too buoyant. Intense compression with crustal shortening and thickening occur, large destructive earthquakes also are generated in this situation. (crust becomes thick). Example: Alps in Europe/Himalayas Thickness of continental crust in Himalayas: 5 km Normal oceanic crust from sea floor to mantle, is normally 5 km - thinnest Thickness – 100 km India has been driving north into the rest of Asia, by creating the Himalayas. Transform margins/Transform plate boundary The third type of plate margin is called a transform boundary. Chile/Alaska/Indonesia/Japan  potential good papers. Pacific Rim of Fire This notorious zone is characterized by SUBDUCTION ZONES Earthquakes here are violent Friction from subduction produces large destructive earthquakes. Faults associated with earthquakes Linear planes of weakness along earth, when rocks break fast, earthquake happens. Three types of dominantly vertical faults Normal fault: Generated in an area where things are being torn apart (divergent), it is the result of tensional forces/rifting. Pulling rock apart. Reverse and thrust faults are the result of: horizontal compression. Faults whose movement is dominantly horizontal These faults are termed strike slip faults Use upper block to evaluate if moving left or right relative to the lower block They are a small scale version of transform tec
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