Download Earthquakes

South Asia Earthquake
Last SATURDAY, October 8th, 2005
30,000 current death toll…on the
rise
• The magnitude -7.6 earthquake hit South
Asia Saturday,
• Left a wake of damage spanning at least
250 miles from Jalalabad, Afghanistan, to
the northern Indian territory.
• It was the largest earthquake ever to rock
the region!
Indonesian Tsunami
• December 2004
224,000 death toll
• Sumatra, on the western most end of the
Indonesian archipelago was the hardest
hit, losing 131-thousand people in the
region of Aceh alone.
• In all, more than 176-thousand people in
11 countries were killed.
Anatomy of an EARTHQUAKE
Rock Deformations:
o Elastic~ Earthquakes stem from this type, and
can suddenly fracture if stretched too far.
o Plastic~ Earthquakes do not come from this
type, and the earth molds like putty.
o Tectonic Plate~ Earthquakes also come from this
type, and formation and movements cause
them.
Earthquakes and Tectonic Plates!
• Plate boundaries occur in three sections:
o Circum~ Pacific Belt.
o Mediterranean Belt.
o Himalayan Belt.
More on Tectonic Plates…
o They move between 1 and 16 cm/yr. That’s as
o
o
o
fast as a fingernail grows!
Friction prevents plates from slipping past one
another
When the strain on the plates reaches a critical
value, the rock fractures and an EARTHQUAKE
ensues.
Strong rock near plate boundary is elastic, while
the edges are solid and immobile.
Earth composed of thin crust, thick
mantle, and core.
Discovery of the Crust-Mantle Boundary
• 1909 Andrija Mohrovicic discovered that
seismic waves from a distant earthquake
traveled more rapidly than those from a
nearby earthquake
• By analyzing the arrival times of the
earthquake waves to many different
seismographs, Mohrovicic identified the
boundary between the crust and mantle
• Mohrovicic discontinuity or the Moho
Mantle
• Seismic waves sped up abruptly at the
crust-mantle boundary
• Slowed down once they entered the
asthenosphere (75 and 125 kilometers)
• At the base of the asthenosphere (350
km) seismic waves sped up again
• Then again seismic wave velocities
increase again at 660 kilometers
Core
• Seismologists detect direct P and S waves
up to 150 ° from the focus of an
earthquake.
• Between 105° and 140° “shadow zone”
• No S waves arrive beyond 150° – not
transmitted through liquids
• Refraction patters of P waves  liquid
outer core and solid inner core