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Earthquakes Michel Van Camp Royal Observatory of Belgium www.seismology.be Photo: T. Lecocq Earthquakes may be very destructive: e.g. Haïti Pctures: Roger Bilham, U. Colorado Why do earthquake occur? An earthquake: causes vibrations in the Earth Duck from Théocrite, ©J.-L. & P. Coudray Duck: from Théocrite, ©J.-L. & P. Coudray How does our Earth look like??? Depth: 6400 km = distance Brussels-New York Solid inner core Liquid outer core Solid mantle Crust (fragile, brittle) © Peyo The Earth’s crust: Like the cracked shell of an egg ! © Tyler and Morgan If the Earth had the same size of an egg, Then the crust would be as thin as the shell of the egg! The different « pieces » Or « tectonic plates » Nord-America Carabbean plate Eurasian Pacific African Pacific Nazca SouthAmerica IndoAustralian Antarctica map: © Royal Observatory of Belgium What causes an Earthquake? At plate boundaries: Deformations until it breaks During the rupture, the earthquake is caused by a sudden or abrupt movement when two blocks (or « plates ») slide past each other http://www.iris.edu/gifs/animations/faults.htm Click on the picture …Earthquakes are also caused by volcanic eruptions, explosions (bombs, gas, quarry blasts) or mine collapse, or even trains, concerts, … Between 2 plates: fault line Plates may slide alongside each other (« strike slip fault ») © Istanbul Technical University http://www.iris.edu/gifs/animations/faults.htm GEER Association Imperial Valley, 1979, U. Colorado Other faults… Plates are colliding: « thrust (or reverse) fault » http://www.iris.edu/gifs/animations/faults.htm © IDEERS Campine http://www.iris.edu/gifs/animations/faults.htm Maas valley (Bree) © Observatoire Royalde Belgique Kim Clijsters is from Opitter, along that normal fault Plates are diverging: “normal fault” Different pieces or “tectonic plates” North-America Between plates: faults Most of the Earthquakes take Place along those faults Carrabean Plate Eurasian Pacific Africaine Pacific Nazca SouthAmérican IndoAustralian Antarctic map: © Royal Observatory of Belgium Carabbean plate (Carabbean sea) © Walt Disney Imagineering map: © Royal Observatory of Belgium © Studio 100 8 km = 4000 earthquakes during 1 million years Carte © googlemap Borah Peak, Basin and Range http://en.wikipedia.org/wiki/File:Borah1983.JPG At some locations, earthquakes change landscape !!! (unfortunately causing shocks) How measuring an earthquake? With a sismometer! © Peyo Click on the picture © Peyo Belgian seismic network Uccle www.seismology.be Some stations: Membach, Rochefort, Princess Elisabeth ? 2 remote earthquakes as seen in Belgium (here: Membach) Chili, Magnitude 8.8 Haiti, Magnitude 7.0 from IFFO-RME What to do during an Earthquake ? During the earthquake: In case of electrical system damage or gas is leaking: Drop, Cover, Hold turn off electricity, gas Near the seashore: Move inland to higher ground immediately and stay there Stay away from damaged areas