Tsunami Causes and consequences. Geography Tsunami Causes and consequences. Hazard prevention, warning, perceptions of risk and risk reduction.

Contents Tectonic explanation for the 2011Japan tsunami Warning systems for tsunami Perception of risk Tectonics of the tsunami 10/11/2017 Tsunami

March 11 2011: the basic facts The tsunami that struck the coast of Japan hit roughly thirty minutes after the magnitude-9.0 Tohoku earthquake. The quake, which ruptured about 130km from Japan's northeastern coastline, occurred when one tectonic plate sprang violently upward as the friction between the two plates was overcome. 10/11/2017 Tsunami

March 11 2011 This caused a 480km section of the seafloor to spring upward, generating the tsunami. The waves were reported to reach three stories high. The disaster is estimated to have killed approximately 20,000 people. 10/11/2017 Tsunami

Pacific Ring of Fire & tsunamis 9.0 epicentre in sea 11 March 2011 Japan tsunami triggered by magnitude 9.0 earthquake in the sea where the Pacific plate was subducted under a micro plate connected to the Eurasian plate Eurasian Plate Pacific Plate The Ring of Fire is a string of volcanoes and sites of seismic activity, or earthquakes, around the edges of the Pacific Ocean. Roughly 90% of all earthquakes occur along the Ring of Fire, and the ring is dotted with 75% of all active volcanoes on Earth.    The Ring of Fire isn’t quite a circular ring. It is shaped more like a 40,000-kilometer (25,000-mile) horseshoe. A string of 452 volcanoes stretches from the southern tip of South America, up along the coast of North America, across the Bering Strait, down through Japan, and into New Zealand. Several active and dormant volcanoes in Antarctica, however, “close” the ring. Hot Spots The Ring of Fire is also home to hot spots, areas deep within the Earth’s mantle from which heat rises. This heatfacilitates the melting of rock in the brittle, upper portion of the mantle. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.  Hot spots are not generally associated with the interaction or movement of Earth’s tectonic plates. For this reason, many geologists do not consider hot spot volcanoes part of the Ring of Fire. 10/11/2017 Tsunami

Warning systems were put in place after the 2004 Boxing Day tsunami 10/11/2017 Tsunami

The devastation in Japan was swift The devastation in Japan was swift. The monster wave arrived less than two hours after the quake — the world's fifth-largest on record. However, an ocean away, calculations were under way to see what the tsunami would do over the coming hours. 10/11/2017 Tsunami

Bobbing sentinels Quake-triggered tsunamis can race across the Pacific at speeds of 970 kph or more, inflicting tremendous damage when they finally reach shore, according to the U.S. National Oceanic and Atmospheric Administration (NOAA). To help detect and characterize these destructive waves, NOAA has deployed a phalanx of sentinel buoys. The first six Deep-Ocean Assessment and Reporting of Tsunami (DART) buoys were put out in 2001, and 32 were in place throughout the Pacific by 2008. (NOAA has deployed 39 DART buoys worldwide.) 10/11/2017 Tsunami

Bobbing sentinels Each DART station consists of a floating buoy moored to a monitoring instrument on the ocean floor. This sensor measures temperature and pressure every 15 seconds, detecting tsunamis by the pressure changes they cause. The device converts pressure readings into estimates of sea-surface height, giving researchers an idea of how big the coming waves will be. These monitoring devices relay their readings to the surface buoys, which beam the information to scientists in real time. Researchers combine this information with seismic information about the quake and data from tidal gauges along various coasts to gain an integrated, detailed picture of any incoming tsunami. 10/11/2017 Tsunami

Perception of risk Perceptions survey: “Surveys conducted a year before the March tsunami and then afterward reveal a potentially deadly shift in perception among citizens in western Japan, Satoko Oki, an assistant professor at the Earthquake Research Institute, University of Tokyo, said here today (Dec. 5) at the annual meeting of the American Geophysical Union.” http://www.livescience.com/17311-japan-tsunami-danger-misperception-agu.html 10/11/2017 Tsunami

Perceptions (2) When participants in the online, representative survey were asked, 'What height of a tsunami would you consider dangerous?' in March 2010, 70.8 percent of respondents said that less-than-10 feet (3 meters) was dangerous. This was the correct answer, according to Oki. "A 2-meter-high [7-foot] tsunami can completely destroy your house," she said. But in the later survey, conducted in April 2011, fewer — 45.7 percent — of survey respondents responded correctly. Likewise, when asked, 'At what estimated height of tsunami would you evacuate?' 60.9 percent said less-than-3 meters (10 feet). A year later, 38.3 percent agreed with this. "So the damage lowered the risk assessment, it did not teach a lesson, but instead, it made the Japanese people more vulnerable than before," Oki said. 10/11/2017 Tsunami

Perceptions (3) She then showed headlines reporting tsunami waves measuring from 49 feet (15 meters) to the near-record 124 feet (37.9 meters) hitting the coast of Japan. After March 11, Japanese kept hearing those numbers over and over again, and they began to evaluate the danger associated with tsunamis against those numbers, she said. So, a smaller height began to seem less dangerous, even if it wasn't. To prevent this from happening in the future, Oki recommended that information available to the public should make clear the risk associated with relatively small tsunamis, including it in reports describing tsunamis like the one in March. Japanese officials are considering not including projected tsunami heights with future evacuation orders, she said. 10/11/2017 Tsunami

Tectonics of the tsunami 10/11/2017 Tsunami

Pacific plate subducts under Eurasian plate 10/11/2017 Tsunami

Tectonics of the tsunami Slow quake 40 cm over 2 months 10/11/2017 Tsunami

Tectonics of the tsunami Slow quake 40 cm over 2 months 10/11/2017 Tsunami

Tectonics of the tsunami Oceanic plate subducting 10/11/2017 Tsunami

The two plates are locked together in an asperity 10/11/2017 Tsunami

Pressure builds up in the asperity due to the slow forward movement in the two month long “slow earthquake” But some areas near to the asperity were only partly locked together. 10/11/2017 Tsunami

Tectonics of the tsunami This produced the 40cm movement over two months and accounted for the slow quake Slow quake 40 cm over 2 months 10/11/2017 Tsunami

In the asperity the 40cm movement has now added to the pressure build-up 10/11/2017 Tsunami

The compressed elasticity is like a coiled up spring and when enough pressure has been built up to overrcome the locked asperity… 10/11/2017 Tsunami

… it jumps forward 10/11/2017 Tsunami

This takes place over a 480 km section of continental plate which is the seabed 10/11/2017 Tsunami

This caused an upward flip of the continental plate 10/11/2017 Tsunami

Water depth here is 6 km and the water is massively displaced over 480 km 10/11/2017 Tsunami

The TSUNAMI is not like a normal wave on the surface of the ocean but a fast-travelling transfer of energy from rock to water: effectively a SHOCK-WAVE 10/11/2017 Tsunami

(sequence begins 14.04 mins into film ) 30 minutes warning time https://www.youtube.com/watch?v=alJo5m1y0uM (sequence begins 14.04 mins into film ) 10/11/2017 Tsunami