Transcript 5a. Dr. Andy Bach: Japan, Tectonics, & 2011 Tsunami

Tectonics, Earthquakes and Tsunamis:
Japan 2011
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Crust 43 miles or 70 km thick
Sial = silica and aluminum – light
Sima = silica and magnesium – heavy
Isostasy = sial crust float atop
sima mantle
Fig. 8.2
sima
sima
sial
p = density g/cm3
Continental drift
Sea-floor spreading
Ring of Fire
Black dots = major EQ
Red dots = active volcano
Fig. 8.5
Convergent Boundaries
-Massive earthquakes
Bellingham
Plate
Motion
-Subduction
or Seattle
Land motion
Land motion
Plate
Motion
-Trench
-Orogony
-Volcanism
sial
-Accretion
Sial – andesite or rhyolite magma
Fig. 9.12
p =2.9
p =3.3
Pacific Plate moving
toward the NW,
colliding with the
Euraisian Plate
Convergent Boundaries
-Ocean to ocean
-Island arc
May 23, 2006
Chuginadak Island
In the Pacific Northwest, two of the earth’s tectonic plates collide, and the boundary
between them is a 600-mile-long fault called the Cascadia Subduction Zone (CSZ).
Here the Juan de Fuca Plate and the North American plate converge at the rate of 1-2
inches per year (3-4 cm/yr), causing stress to accumulate on the fault (called a
megathrust) that extends from Northern California to Vancouver Island. Earthquakes are
caused by the abrupt release of this slowly accumulated stress.
Energy release
increases by 30X
for each unit.
So a M9 is 900X
more powerful
than a M7.
2011 Tohoku earthquake
or the Great East Japan Earthquake
or the 311 Earthquake
Occurred on March 11, 2011 (311) at 2:46 pm
- Magnitude of 9.0 on the subduction zone, ~20 mi deep
- shaking lasted ~6 minutes
- 7.2 M foreshock event on 9 March
- >800 aftershocks of magnitude 4.5 M or greater, 3 over 7 M
- Japan moved 2.4 m (7.9 ft) closer to North America
- 400 km (250 mi) of coastline dropped vertically 0.6 m (2.0 ft)
- Pacific plate may have moved westward by up to 20 m (66 ft)
- shifted the Earth's axis between 10-25 cm (4-10 in)
- Earth's rotation increased, shortening the day by 1.8 microseconds
due to the redistribution of Earth's mass
- caused seafloor to rise 5-8 meters over180-km area, generating
a tsunami
2011 Tohoku earthquake
upthrust seafloor 5-8 meters over180-km area, generating
a huge tsunami that propagated across the Pacific Basin
- Struck Japanese coast 10-100 minutes after earthquake
- Wave height was varied due to underwater topography and
proximity to epicenter.
38.9 meters (128 ft) was estimated at Omoe peninsula, Miyako city,
Iwate prefecture
Most of Japan’s coast had heights 3-7 m (9-24 ft),
- much higher than predicted (how??)…
- many protective seawalls were overwhelmed
Washed inland up to 10 miles, especially up river valleys
- well beyond elevation of wave due to momentum.
2 m in Chile (opposite side of Pacific), Friday Harbor 4-6”
2011 Tohoku earthquake - Human and Economic Impacts
National Police Agency reports 15,854 deaths, 26,992 injured,
and 3,155 people missing.
129,225 buildings totally collapsed, 254,204 buildings 'half collapsed',
and another 691,766 buildings partially damaged
230,000 automobiles were dadestroyed
Estimated damages $14.5 to $34.6 billion U.S.
Ports, roads, cities, farms and farmland destroyed
- number of nuclear accidents, 3 meltdowns at
Fukushima Daiichi Nuclear Power Plant complex
- 100,000’s still evacuated
Subduction Zone Earthquakes
The effects of a great (magnitude 9.0) earthquakes will reach far inland.
Shaking is strongest closest to epicenter
- patterns irregular based on bedrock geology/interference
- can expect up to 5 minutes of shaking.
Prolonged shaking can cause structure collapse, landslides,
disruption of lifeline services, and tsunami generation.
March 2011 Sendai, Japan earthquake, the Chile 2010 quake, and the
Sumatra quake of 2004.
Recent Major Earthquakes
While larger magnitudes
do produce more shaking,
death tolls are all about
location and planning.
2001 Gujarat M 7.7 > 20,000 killed
2003 Bam, Iran M 6.5 > 40,000 killed
2004 Sumatra M 9.1 ~ 230,000 killed
2005 Kashmir M 7.6 > 79,000 killed
2008 Chengdu M 8.0 ~ 90,000 killed
2010 Haiti
M 7.0 > 200,000 killed
2010 Chile
M 8.8 > 500 killed
2011 Japan
M 9.0 ~20,000 killed
Largest Earthquakes in the World Since 1900
Largest 1960 Chile
M 9.5 ~1900 dead
March in Japan was 4th
From: http://earthquake.usgs.gov/earthquakes/world/10_largest_world.php
Soft sediments can magnify shaking
- can liquefy with shaking,
- heavy things sink.
- big problem in filled areas
Earthquake shaking can be mitigated with proper engineering.
Unlikely from
an earthquake, but
100 ft waves have
been reported in small areas, near epicenter.
http://geology.com/records/biggest-tsunami.shtml
Rockfall
1720 ft wash
The largest recorded tsunami was a wave 1720 feet tall in
Lituya Bay, Alaska, 1958. Triggered by a 40 million cubic
meter landslide into a bay (over 2000 Arntzen Halls).
Spilling over
a seawall.
Tsunami is more of a surge of
water, that will flow inland
along the lowest lands, especially
rivers first.
Tsunami grinds buildings
and pushes debris inlandnot unlike dumping a
bucket of water.
Mud from sea floor, and soil erosion….used
by geologist to reconstruct past events.
http://www.youtube.com/watch?v=k4w27IczOTk
http://www.youtube.com/watch?v=iQfdl7y-blE
Lots of debris washed back out to sea,
this guy was rescued 9 miles out.
http://www.youtube.com/watch?v=PljZOj5knzo&feature=related
Tsunami in WA
As of 9:45am PST March 11,2011
From 8.9 mag. EQ in Japan
~4-6” at Friday Harbor
Neah Bay got 3-4 waves
6-12”
Westport got 3-4 waves
1-2 feet
Red line is actual data, blue
line is predicted.
From: http://tidesandcurrents.noaa.gov
Kobe 1995
Smaller
Tsunami
The earthquake in Kobe on January, 17, 1995 left 6,425
dead, injured 25,000, displaced 300,000 people, damaged or
destroyed 100,000 buildings and caused at least $132 billion
worth of damage, making it one of the most expensive
natural disasters in history.
Kobe 1995
Smaller
Tsunami
The PNW’s four kinds of earthquake sources
1. Cascadia Subduction Zone
Example: the 1700 earthquake that caused shaking and a tsunami that inundated the
Oregon coast and reached as far as Japan.
2. Intraplate
Example: the 2001 Nisqually, Washington, earthquake that affected Washington and
northwestern Oregon.
3. Volcanic
Example: the 1980 Mount St. Helens eruption-related earthquakes.
4. Crustal
Example: the 1993 Scotts Mills and Klamath Falls earthquakes Crustal
earthquakes also occur in southeastern Oregon where the crust is pulling apart.
4.
1.
2.
3.
As you can see, it's been over 310 years since the last magnitude 8+
earthquake, and the rhythm and period of massive seismic events
along that fault is typically shorter. Nine months pregnant and
overdue.
Brian Atwater
looking at tsunami
sediments
Modelled path
Geological and archeological (Ozette Village Spruce stumps from trees that were
submerged in Willapa Bay following
burial) data, historical documentation from
the 1700 Cascadia earthquake.
tsunami arrival times in Japan, and
http://pubs.usgs.gov/pp/pp1707/pp1707.pdf
Native Legends all reveal the Cascadia
Earthquake occurred at ~9 PM on January 26, 1700.
http://www.pnsn.org/HIST_CAT/SRL76-2Ludwin.pdf