Tectonics, Earthquakes and Tsunamis:Japan 2011 • Andy.Bach@wwu.edu
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 sial p = density g/cm3 sima
Continental drift Sea-floor spreading Black dots = major EQ Red dots = active volcano Ring of Fire
Fig. 8.5 Convergent Boundaries • Subduction • Massive earthquakes • Trench • Orogony • Volcanism • sial • Accretion Bellingham or Seattle Plate Motion Land motion Land motion Plate Motion 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. While larger magnitudes do produce more shaking, death tolls are all about location and planning. Recent Major Earthquakes 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
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 inland- not 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.
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. 3. 2.
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 burial) data, historical documentation from tsunami arrival times in Japan, and Native Legends all reveal the Cascadia Earthquake occurred at ~9 PM on January 26, 1700. http://www.pnsn.org/HIST_CAT/SRL76-2Ludwin.pdf Spruce stumps from trees that were submerged in Willapa Bay following the 1700 Cascadia earthquake. http://pubs.usgs.gov/pp/pp1707/pp1707.pdf