Earthquakes, Tsunamis, and a Modern Journey to the Center of the Earth

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Earthquakes, Tsunamis, and a Modern Journey to
the Center of the Earth Michael
Wysession Professor of Geophysics, Dept of Earth
and Planetary Sciences Washington University, St.
Louis, Missouri
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PLATE
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Plate Tectonics, The Basic Idea
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Locations of the Major Tectonic Plates
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The ACTION happens at the boundaries between
plates!!
Plate Tectonics I Ocean seafloor is created at
mid-ocean ridges, where plates move apart.
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Plate Tectonics II Ocean seafloor is eventually
destroyed at subduction zones, where it sinks
back into the mantle.
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A Global Map of Earthquakes Also Shows the Plate
Boundaries
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Japanese Folklore Earthquakes caused by giant
Namazu.
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Following the 1755 Lisbon earthquake on All
Saints Day, the Spanish Inquisition burned
people at the stake to atone for the citys sins.
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The San Andreas Fault
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Can you read this?
Rosetta Stone
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Can you read this?
In the reign of the young one who has succeeded
his father in the kingship, lord of diadems, most
glorious, who has established Egypt and is pious
towards the gods, triumphant over his enemies,
who has restored the civilized life of men, lord
of the Thirty Years Festivals, even as Ptah the
Great, a king like Ra, great king of the Upper
and Lower countries, offspring of the Gods
Philopatores, one whom Ptah has approved, to whom
Ra has given victory, the living image of Amun,
son of Ra, PTOLEMY, LIVING FOR EVER, BELOVED OF
PTAH, in the ninth year, when Aetos son of Aetos
was priest of Alexander, and the Gods Soteres,
and the Gods Adelphoi, and the Gods Euergetai,
and the Gods Philopatores and the God Epiphanes
Eucharistos Pyrrha daughter of Philinos being
Athlophoros of Berenike Euergetis, Areia daughter
of Diogenes being Kanephoros of Arsinoe
Philadelphos Irene daughter of Ptolemy being
Priestess of Arsinoe Philopator the fourth of
the month of Xandikos, according to the Egyptians
the 18th Mekhir . Translated Text of the
Rosetta Stone
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Can you read this?
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Seismologists read seismograms to learn about
the earth.
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For a large earthquake, seismic waves will
continue to circle the Earth for weeks, making it
reverberate like a gong.
Courtesy of J. Tromp
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For a large earthquake, seismic waves will
continue to circle the Earth for weeks, making it
reverberate like a gong. (Earths lowest
fundamental note, with a period of 54 minutes,
is an E, twenty octaves below middle E on a
piano.)
Courtesy of J. Tromp
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Seismic Tomography Has Allowed Us to Explore
the Interior of Our Planet.
Courtesy of A. Dziewonski
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This is what parts of California used to look
like..
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Seismic Imaging Reveals the Most Likely Places to
Find Oil and Natural Gas.
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It also will also reveal the locations of the
next big source of energy, methane gas hydrates.
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Seismic Tomography tells us what happens to Ocean
Seafloor after it sinks back into the mantle.
? ? ? ? ? ? ? ?
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Subduction of ancient Pacific seafloor beneath
North America
Courtesy of Van Heijst et al.
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Subduction of ancient Pacific seafloor beneath
North America .and Notice the Mid-Atlantic
Ridge.
Courtesy of Van Heijst et al.
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DOWNWELLING UPWELLING
Courtesy of P. Tackley
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Map of the Base of the Mantle
Blue Graveyard of Subducted Ocean Seafloor Red
Birthplace of Super-Plumes
Blue Graveyard of Subducted Ocean Seafloor Red
Birthplace of Mega-Plumes
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Fantasy Writers Idea of the Core-Mantle
Boundary.
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Artists Idea of the Core-Mantle Boundary.
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Scientists Idea of the Core-Mantle Boundary.
Courtesy of E. Garnero
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Magnetic Field Lines in Earths Iron Core
Courtesy of G. Glatzmaier
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Magnetic Field Lines in Earths Iron Core The
Field FLIPS RANDOMLY Every Few 100,000 Years (or
so)!
Courtesy of G. Glatzmaier
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Magnetic Field Lines in Earths Iron Core The
Field FLIPS RANDOMLY Every Few 100,000 Years (or
so)!
Courtesy of G. Glatzmaier
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Magnetic Field Lines in Earths Iron Core The
Field FLIPS RANDOMLY Every Few 100,000 Years (or
so)!
Courtesy of G. Glatzmaier
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Magnetic Field Lines in Earths Iron Core The
Field Strength has recently decreased by 10. Are
we beginning a new field reversal??
Courtesy of G. Glatzmaier
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There are other things besides earthquakes that
make waves!!
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Courtesy of IRIS
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Courtesy of P. Richards
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A DEVASTATING EVENT THE SUMATRA EARTHQUAKE OF
DECEMBER 26, 2004
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COMPLEX PLATE BOUNDARY ZONE IN SOUTHEAST
ASIA Northward motion of India deforms all of
the region Many small plates (microplates) and
blocks
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Burma Microplate
Indian Plate
Sumatra
The process of subduction that has created
Indonesia through volcanic activity, also makes
it dangerous.
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SEISMOGRAMS reveal how slip varied along the
fault plane. Most fast slip along an area 400
km long Maximum slip 20 m
Contours show time, in seconds
Courtesy of C. Ji
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Back to the idea of the Earth vibrating like a
gong..
Courtesy of M. Van Camp
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These modes of Earths vibration are still
ringing from the Sumatra earthquake!
Courtesy of R. Aster
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Aftershocks soon showed the full extent of the
rupture.
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Ruptured Quickly
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2/3 of the Total Energy Released Went Undetected
for Weeks!!
Ruptured Quietly
Ruptured Quickly
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EARTHQUAKE MAGNITUDE 9.3
2004 Sumatra Earthquake
Courtesy of IRIS
Energy released 65 1017 Joules, or 1,550,000
kilotons (1,550 megatons) of TNT, or the
equivalent of 75,000 Hiroshima bombs.
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TSUNAMI - water wave generated by earthquake
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IN DEEP OCEAN tsunami has long wavelength,
travels fast, small amplitude - doesnt affect
ships AS IT APPROACHES SHORE, it slows. Since
energy is conserved, amplitude builds up - very
damaging
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Banda Aceh Before.
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Banda Aceh Before. and After..
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Courtesy of K. Sataki
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TSUNAMI SPEED IN DEEP WATER of depth d c
(gd)1/2 g 9.8 m/s2 If d 4000 m, then c
200 m/s 720 km/hr 450 m/hr Tsunami
generated along fault, where sea floor displaced,
and spreads outward
Courtesy of K. Sataki
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Tsunami waves bend around obstacles like
islands and peninsulas in a process called
DIFFRACTION.
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The Tsunami Eventually Crossed All Oceans
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Rays Bend as the Water Depth Changes The
Density of Rays Shows the Focusing and Defocusing
due to REFRACTION
1 hour
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Seen safely from high ground, a wave of the 1960
Chilean tsunami pours into Onagawa, Japan.
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NY Times
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TSUNAMI WARNING SYSTEM
Deep ocean buoys can measure wave heights of
tsunamis.
Seismic waves travel much faster than tsunamis!
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The previous most devastating tsunami in
Indonesia was NOT caused by an earthquake.
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Giant Eruption of Krakatau in 1883.
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The tsunami from the 1650 BCE eruption of Mt.
Thera may have destroyed the Minoan culture on
Crete, giving rise to the legend of Atlantis.
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So.Could this Happen in New York?!?
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Massive landslides in places like the Canary
Islands likely cause enormous Atlantic tsunamis!
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There are Also Giant Undersea Landslides in the
Puerto Rico Trench!!!!
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An enormous tsunami from the Chixulub impact (65
million years ago) washed over North America.
Chixulub Crater
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For a copy of this presentation, please email me
at michael_at_seismo.wustl.edu or go to the IRIS
web site at http//www.iris.edu
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March 28, 2005, Aftershock Ruptured a Different
Gap
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Seismogram analyses first showed that most slip
was in the southernmost 400 km
Courtesy of C. Ji
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Initial seismograms showed fast slip in the
bottom 1/3 of the fault area. Many days of
following seismograms showed even more energy
released through ultra-slow, undetectable
slip. Maybe MANY earthquakes behave like this?
Courtesy of S. Stein and E. Okal
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Seismograms show the seismic waves wrapping
around the Earth many times.
Courtesy of R. Aster
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New 9.3 magnitude value
This one earthquake comprises more than ½ of the
total energy released by earthquakes during the
past 30 years!
Courtesy of G. Ekstrom
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VERTICAL UPLIFT HORIZONTAL
MOTION
Courtesy of C. Ji
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Changes in Length of Day (due to mass
redistribution)
Atmospheric Angular Momentum (AAM, in red) and
VLBI length of day (LOD, in blue) measurements
are strongly correlated over periods of one week
to several years (storms, atmospheric currents,
El Nino, etc.).
Ocean tides and currents modulate the Earth's
orientation on periods of a day and shorter. The
model (red) follows the VLBI measurements (blue)
closely.
Predicted change in length of day due to the
Sumatra earthquake    -2.676 microseconds (not
verifiable?)
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The change in polar motion excitation from the
earthquake is predicted to be very small, about
0.82 milliarcseconds (also not observable?).