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Transcript of «Η σεισμικότητα...
RACCE PPT Theory
Earthquakes and VolcanoesTheoretical presentation
An earthquake is a natural phenomenon, like tornados or rain, originated in Earths internal!Earth interior
Earths interior consists of several layers: the crust (divided in continental and oceanic), the mantle and the core (internal and external)CrustMantleLithosphereThe most outer part of mantle that is in continuous contact with crust, together with crust consist earths lithosphere. Lithosphere actually floats over the molten materials of mantle.
LithosphereMantleLithospheric platesLithosphere is fragmented into several pieces called lithospheric or tectonic plates. Plates displace apart each other in three ways.
Plate displacementOver heated currents of molten material within mantle, that resemble boiling water, are considered as the main reason that forces plates to move along the surface of the earth.
Continental driftContinental drift has changed continents locations and thus the image of our planet several times in geological past. Take a look at the last 200 million years
Plates and earthquakesPlate displacements induce forces into rocks that break causing earthquakes. Plate boundaries were actually mapped using the spatial distribution of earthquake epicenters, like in the Pacific Ocean.Yellow spots indicate seismic epicentersEarthquakesAn earthquake is a sudden tremor of the earth that is usually caused by fault activity and the consequent rock displacement by them.Energy is released in the form of seismic waves during earthquakes
WavesFault scarpRock displacementFocusFaultEpicenter
Mediterranean seismicityThe area of Mediterranean is located at the boundary between African and Eurasian plates, which is the reason for its high seismicity. 10Seismic riskA seismic risk may be induced in an area from rock displacement and seismic wave propagation following an earthquake.
Plates and volcanoesVolcanoes, in most cases, occur near plate boundaries because there crust can break leaving space to magma to raise from the mantle to the surface. Thus, volcanoes occur in the areas where to plates approach () or move apart () each other. Also, occur in plates interior at the areas called hot spots.
Volcano distributionMost volcanoes occur thus near plate boundaries like in the area of Mediterranean or around Pacific ocean (Ring of fire).
Types of volcanoesVolcanoes bring lava on the earth surface forming rocks in small hills or mountains. Depending on the chemical composition of lava several volcano types:
Scoria conesShield-volcanoStato-volcanoVolcanic riskRisks induced by volcanic activity may derive from lava flow, exploding materials, volcanic tephra that may travel to long distances, and poisonous gases released some times.
From 2001 Etna eruption, SicilyAcknowledgmentsThis presentation accompanies the Museum Kit of RACCE project, aiming to provide students a first introduction to earthquakes and volcanoes in order to trigger their interest and create more questions and issues for investigation and discussion.
Several figures and pictures used come from the following sources: Press & Siever: Understanding EarthAdditional data can be found in: Skinner, Porter & Park: Dynamic Earth Pavlides S.: Geology of Earthquakes
More scientific information can be also found in the Theory Booklet of the museum kit.