«Earthquakes and Volcanoes»
Theoretical
presentation
«Η σεισμικότητα της Κρήτης και
δράσεις ενημέρωσης του ΜΦΙΚ»
Δρ Χαρ. Φασουλάς
Τμημ. Γεωποικιλότητας
Μουσείο Φυσικής Ιστορίας Κρήτης
Πανεπιστήμιο Κρήτης
An earthquake is a
natural phenomenon,
like tornados or rain,
originated in Earth’s
internal!
Earth interior
Earth’s interior consists of several layers: the crust (divided in
continental and oceanic), the mantle and the core (internal
and external)
Crust
Mantle
Lithosphere
The most outer part of mantle that is in continuous contact
with crust, together with crust consist earth’s lithosphere.
Lithosphere actually “floats” over the molten materials of
mantle.
Lithosphere
Mantle
Lithospheric plates
Lithosphere is fragmented into several pieces called
lithospheric or tectonic plates. Plates displace apart each other
in three ways.
Plate displacement
Over 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 drift
Continental 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 earthquakes
Plate 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
epicenters
Earthquakes
An earthquake is a
sudden tremor of the
earth that is usually
caused by fault activity
and the consequent
rock displacement by
them.
Fault
Rock displacement
Epicenter
Waves
Energy is released in
the form of seismic
waves during
earthquakes
Fault scarp
Focus
Mediterranean seismicity
The area of Mediterranean is located at the boundary
between African and Eurasian plates, which is the reason
for its high seismicity.
Seismic risk
A seismic risk may be induced in an area from rock
displacement and seismic wave propagation following an
earthquake.
Plates and volcanoes
Volcanoes, in most cases, occur near plate boundaries
because there crust can break leaving space to magma to
raise from the mantle to the surface.
Α
Γ
Β
Thus, volcanoes occur in the areas where to plates approach (Α)
or move apart (Β) each other. Also, occur in plates interior at the
areas called hot spots.
Volcano distribution
Most volcanoes occur thus near plate boundaries like in
the area of Mediterranean or around Pacific ocean (Ring of
fire).
Types of volcanoes
Volcanoes bring lava on the earth surface forming rocks in
small hills or mountains. Depending on the chemical
composition of lava several volcano types:
Scoria cones
Shield-volcano
Stato-volcano
Volcanic risk
Risks 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, Sicily
Acknowledgments
This 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 Earth
Additional 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.