Transcript here - Research at UVU

The December 26, 2004 Mw 9.0
Western Sumatra Earthquake
and Tsunami
Michael Bunds
Department of Earth Science
Utah Valley State College
The Earthquake’s Statistics
Magnitude 9.0 (Mw)
Sunday, December 26, 2004 at 00:58:53 (UTC)
Sunday, December 26, 2004 at 7:58:53 AM local time at epicenter
Saturday, December 25, 2004 at 5:58:53 PM Mountain Standard
Time
Energy Released = 2 x 1017 Joules
Equivalent to 475 megatons of TNT or 23,000 Hiroshima
bombs
Tsunami energy estimate = 1014 Joules (10 Hiroshima bombs)
Over 225,000 fatalities, 5 million homeless people in Indian
Ocean – most as a result of earthquake-induced tsunami
The Earthquake in Historical Context
Four Largest Earthquakes on Record
1. M 9.5 Chile, 1960
2. M 9.2 Prince William Sound, Alaska 1964
3. M 9.1 Andreanof Islands, Alaska, 1957
4. M 9.0 Kamchatka, 1952
5. M 9.0 Sumatra, 2004
10 of 11 largest
on subduction
zone
megathrusts
surrounding
Pacific Ocean
Most deadly
tsunami
recorded history
4
3
2
5
1
RUSSIA
Asia
CHINA
INDIA
Sri Lanka
Phuket
Epicenter
Sumatra
Sri Lanka
Banda
Aceh
Phuket
Epicenter
Southeast Asia
Tectonic
Setting
U.S.G.S
Subduction Zone
Destructive historical
tsunamis at the
western coast of
Sumatra
1797/02/10 M>8.0 Central part
of the western Sumatra.
Padang was flooded by
powerful waves. More then
300 fatalities.
1833/11/24 M=8.8-9.2 South
coast of the western Sumatra.
Huge tidal wave flooded all
southern part of the western
Sumatra. Numerous victims.
1843/01/05 M=7.2 Terrible
wave came from the southeast and flooded all the coast
of the Nias Island. Many
fatalities.
1861/02/16 M>8.2 Several
thousand fatalities.
What is an
Earthquake?
Ground
shaking caused
by a sudden
release of
energy within
Earth.
Most result
from slip on a
fault.
Elastic Rebound
epicenter
hypocenter
fault
Hypocenter and Epicenter
Andaman Isl.
Sumatra
Original Position
200 to 500 years later
Overriding crust
flexes 10 to 50 meters,
storing energy to be
released in
earthquake
During earthquake
Overriding crust
snaps back to original
position
200 – 250 km wide
areas uplift and
subside
Uplift
Subsidence
Aftershocks
(yellow
circles)
outline
ruptured
area on fault
~1200 km by 200 km
area of fault
ruptured
M9.0
Epicenter
U.S.G.S
Expected
Areas of
Uplift and
Subsidence
Andaman
Islands
Probable
area of
uplift
Probable
area of
subsidence
U.S.G.S
Andaman
Islands
Probable
tectonic
uplift from
earthquake
Before
After
Before
After
Andaman
Islands
Probable
tectonic
uplift from
earthquake
Submerged
coral reef
Emergent
coral reef
earthobservatory.nasa.gov
Probable Tectonic Subsidence in Banda Aceh, Sumatra
Comparison
of Sumatra
Earthquake
Fault
Rupture Area
to Cascadia
Subduction
Zone
Seismicity
in Area
1900 – 2002,
M>6
U.S.G.S
Seafloor Displacement in Earthquake
Vertical uplift
5 m max.
Horizontal movement
11 m max.
Cal Tech
Generalized Tsunami Wave
Characteristics
• Usually more than one wave is created
• In open ocean
–
–
–
–
Wavelength: 200 to 250 km (dist. between wave peaks)
Wave height: 0.5 m
Speed: 700 km/hr
Period: 17 minutes (time between wave peaks)
• Near shore
–
–
–
–
Wavelength: 10 km
Wave height: meters to tens of meters
Speed: 36 km/hr
Period: 17 minutes (time between wave peaks)
Waves Compress as They Near Land
Waveheight increases
Wavelength decreases
But tsunamis do not break like the pictured wind waves
Wind waves
are tall and
short
wavelength
Tsunamis
often are no
taller than
wind
waves, but
involve
much more
water due
to long
wavelength
Usual water level
Low Water Preceding Tsunami Wave in Sri Lanka
earthobservatory.nasa.gov
earthobservatory.nasa.gov
Sri Lanka
People Collecting Fish During Low Water
Preceding a Tsunami. Oahu, Hawaii, 1957
U.S.G.S
Variations in Tsunami Intensity
An individual tsunami can have vastly
different heights in different places
depending upon:
– Distance and direction from source
– Wave source directivity (most wave energy was
directed east and west)
– Configuration of local seafloor and
coastline
– Shielding by other landmasses
Calculated Maximum Water Height
A. Piatenesi, Tsunami
Research Lab, Russia
Sumatran Tsunami Maximum
Heights
Sumatra, north-west coast
10-15 m
Sri Lanka, east coast
5-10 m
Thailand (incl. Phuket)
3-10 m
India, east coast
5-6 m
Andaman Islands
>5m
Kenya
2-3 m
Additional Factor: In Thailand and Sumatra tsunami closely
coincided with highest tide for the month
Sri Lanka
Banda
Aceh
Phuket
Epicenter
Southeast Asia
earthobservatory.nasa.gov
Sri
Lanka
Banda Aceh
Banda Aceh, Sumatra
before
after
Banda Aceh, Sumatra
earthobservatory.nasa.gov
before
after
Banda Aceh, Sumatra
earthobservatory.nasa.gov
before
after
Banda Aceh, Sumatra
earthobservatory.nasa.gov
Banda
Aceh,
Sumatra
(before)
Banda
Aceh,
Sumatra
(after)
earthobservatory.nasa.gov
before
Khao Lak
after
earthobservatory.nasa.gov
Banda Aceh, Sumatra
(before)
earthobservatory.nasa.gov
Banda Aceh, Sumatra
(after)
earthobservatory.nasa.gov
Banda Aceh, Sumatra
(before)
earthobservatory.nasa.gov
Banda Aceh, Sumatra
(after)
earthobservatory.nasa.gov
Lessons and Conclusions
• The earthquake and tsunami were not
surprises
• Great earthquakes and tsunamis are rare
but devastating
• Tsunami warning systems can save many
lives
• If you are at the beach and you feel an
earthquake, head for higher ground
immediately