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Several large earthquakes, the largest of which measured 9.0 on the Richter scale, caused a tsunami and widespread devastation to much of north-east Japan and caused damage and an ongoing crisis at the Fukushima nuclear power plant.
Couple of quotes on the ‘supermoon’ theory first:
John S Whalley, Geoscience Programme Manager, University of Portsmouth, said:
“There is no established correlation between variations in the orbit of the moon and either the number or magnitude of earthquakes. It is all too easy, with hindsight, to link major earthquakes to variations in all sort of parameters. The real test is to look at the vast numbers of earthquakes of all magnitudes that occur on a daily basis worldwide. (There was a line I read this morning suggesting that in Japan alone there is a seismic event every 5 minutes.) Any correlation with the lunar orbit would have to be established on the basis of this population of earthquakes, not on individual high magnitude events. I need hardly add that no such correlation has been established.”
Prof. George Helffrich, Seismologist, University of Bristol
“Complete nonsense. The moon has no significant effect on earthquake triggering. If the moon triggers *big* earthquakes, it would trigger the many of millions of times more *small* earthquakes that happen daily. There is no time dependence of those; hence no moon effect.”
Dr Richard Phillips, Lecturer in Tectonics & Geochronology, University of Leeds, said:
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
“The nuclear power stations automatically switch off. They then need to be rapidly cooled. One power station failed to cool sufficiently but the stations are robust and there is no expectation that any leaks will occur. Once checks have being undertaken the stations should be back online in a few days.”
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth?
“Japan and its islands sit on a complicated plate boundary that includes the Pacific Plate, the Eurasian plate, the North American plate and the Philippine plate. For this earthquake, it occurred because the Pacific Plate is being pushed underneath the Eurasian plate to the west. Japan sits above this plate boundary.”
Similarities/differences to 2004 Indonesian quake/tsunami
“The earthquake occurred along a subduction zone and was a megathrust, similar in style to that for the Banda Ache earthquake on Boxing Day 2004. The sea floor would have been rapidly uplifted creating a 10m high tsunami. Because the epicentre was only 80 miles offshore Japan, it has had a dramatic effect. Unlike Indonesia though, Japan is better prepared in terms of building codes and what to do in the event of an earthquake and/or tsunami.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“It’s hard to predict what will happen in Hawaii – it should be arriving in the next 30-40 mins. The main problem will be for low lying islands in the Pacific – they will be less prepared and have no access to high ground. Although the tsunami loses energy as it travels, it does not need to be high to cause significant problems in low lying areas.”
How does strength of quake compare with 2004 quake?
“The Indonesian earthquake was larger (9.1) but at 8.9 this one is comparable in energy released and ground shaking.”
Why was Tokyo Bay not inundated?
“Tokyo was not affected because Tokyo sits in an embayment that faces away from the direction in which the tsunami is travelling. Also, the main tsunami wave will be travelling to the south east – toward Hawaii and many low lying islands.”
How big is an 8.9 earthquake? Are there any analogies we can draw?
“8,000 times more powerful than the recent Christchurch earthquake.”
Why is this effect so large? Why is the effect of this so widespread?
“The strain has been building up on the plate boundary and ultimately needs releasing. A number of foreshocks occurred over two days but they were insufficient to reduce the strain. The result was the 6th largest earthquake since records began in 1900. The effects in Japan are so widespread because the fault plane that ruptured was 400km long and several tens of km’s wide. That means that the tsunami may have started out as a 10m high wave and about 400km long! That will propagate across the Pacific.”
Dr Lisa McNeil, senior lecturer in geology at the University of Southampton, said:
What are the different types of tsunami? What are the names of them? How are they different?
“There aren’t really different types of tsunami. There are differences between those generated by large earthquakes (such as the one today in Japan) and those generated by a submarine landslide or underwater volcano eruption. The former (large earthquake) is a linear source for the wave – these tend to cause damage significant distances from the earthquake that generated them, e.g., around the margins of the Pacific Ocean in this case.”
Is the any relation to Christ Church earthquake?
“No. Earthquakes happen regularly on active faults around the world, so it is not surprising to have a magnitude 6.3 earthquake (in New Zealand) followed several weeks later by a magnitude 8-9 earthquake somewhere else.”
How big is an 8.9 earthquake? Are there any analogies we can draw?
“The earthquake magnitude scale is logarithmic. For each unit increase (e.g., from 8 to 9) the earthquake releases about 30 times more energy, so this is a major increase in the potential impact. Useful analogies are the earthquake that took place offshore Chile last February – this was a magnitude 8.8, so similar in size and is the same kind of earthquake (subduction zone). The 2004 earthquake in the eastern Indian Ocean was larger, with a magnitude of 9.1-9.2.”
Why is this effect so large? Why is the effect of this so widespread?
“We are still waiting to see the impact of the earthquake and tsunami on both Japan and other countries around the Pacific Ocean. But these large magnitude earthquakes on subduction zones take place mostly under water. The movement of the seafloor from the earthquake often generates a tsunami and this is what has the widespread impact – so the tsunami can travel 1000’s km and cause damage and loss of life very far from the earthquake.”
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
“I do not know details of any impact on nuclear plants in Japan. In general, Japan is particularly advanced in the area of automatic systems which shut down, for example, gas pipelines to prevent fires and transport systems.”
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“The subduction zone is the Japan Trench and it is where the Pacific plate subducts beneath the N. American plate (beneath Honshu island). The fault, which is the boundary between these two plates, extends from close to Tokyo in the south to the island of Hokkaido in the North and continues north to Kamchatcka, known as the Kuril Trench. Although the fault line is very long, only sections (segments) of the fault rupture in each earthquake. There are also other subduction zones around Japan, e.g, the Nankai Trough to the SW of Tokyo. Each of these subduction zones have had tsunami-generating earthquakes with magnitudes >8 in the past, but this is the largest magnitude earthquake since they have been instrumentally recorded on this subduction zone. It is difficult to be precise about the magnitudes of earlier earthquakes in Japan’s historic record.”
Similarities/differences to 2004 Indonesian quake/tsunami
“See above for comparisons of the magnitude of the 2 earthquakes. Correspondingly we would expect the tsunami for today’s Japanese earthquake to be smaller than that generated by the 2004 earthquake.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“I do not know the estimated wave heights but a good resource is NOAA’s Pacific Tsunami Warning Center. There is a widespread warning in effect for coastlines around the Pacific Ocean and the tsunami will be measurable on the eastern side of the Pacific Ocean (N, C and S America). Hawaii, in the centre of the Pacific, will record the tsunami as it travels across and will then be able to provide more accurate warnings.”
How does strength of quake compare with 2004 quake?
“See above for comments on this earthquake compared to the 2004 earthquake.”
Why was Tokyo Bay not inundated?
“I have not seen the data. In general, tsunami are strongly affected by the shape of thecoastline and by the shape (water depth) of the seafloor close to the coastline.”
Prof. George Helffrich, University of Bristol Earth Sciences:
What are the different types of tsunami? What are the names of them? How are they different?
“No different types, no different names.”
Is there any relation to the Christchurch earthquake?
“No. Most earthquakes happen on plate boundaries. Both the Christchurch and the Japan earthquakes did, too.”
How big is an 8.9 earthquake? Are there any analogies we can draw?
“About 1/3 – 1/2 the size of the 2004 Sumatran earthquake.”
Why is this effect so large? Why is the effect of this so widespread?
“When an earthquake happens under or near the seafloor, and the seafloor is permanently deformed, a tsunami forms. The water displaced by rock moves elsewhere — the tsunami. The larger the earthquake, the larger the displacement and thus the greater the tsunami. When an earthquake faces an open ocean basin, the effect can be widespread.”
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
“Yes. Japan, in particular, has an Earthquake Early Warning system in place. As earthquakes happen, seismic stations calculate the size and warn subscribers of impending shaking. Electrical generation utilities, transport (railways and highway authorities), are subscribers and are instantly informed before the seismic waves arrive. They take responses appropriate to the size of the disturbance.”
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“Pacific under the Eurasian plate”
Similarities/differences to 2004 Indonesian quake/tsunami
“Smaller. Tsunami is propagating across the Pacific, but there is monitoring infrastructure in place (open ocean buoys), unlike the Indian Ocean in 2004.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“Difficult to predict. The wave is about 1 meter high in the open ocean but when it reaches coastlines, the detailed shape and bathymetry can amplify the wave height significantly. The tsunami already passed Wake Island — 1 foot of height. Local effects matter A LOT.”
How does strength of quake compare with 2004 quake?
“1/3 – 1/2 the strength.”
Why was Tokyo Bay not inundated?
“Not facing the propagating wave front; wrong shape.”
Professor Philip Woodworth, from the National Oceanography Centre in Liverpool and Visiting Professor at the University of Liverpool’s School of Environmental Sciences, said:
“There is considerable experience with tsunamis in the Pacific Ocean which is well equipped with sea level monitoring stations and telecommunications systems as well as seismic instrumentation. The distances between earthquakes and population centres are larger than in other ocean basins so warnings to distant shores can be made in good time, and often the progress of the tsunami waves can be followed by means of the coastal sea level stations and deep ocean instruments called DART buoys. In that way, locations like Hawaii or the Asian and American Pacific coasts can receive good warning. As for Japan itself, however, the earthquake occurred close to the coast and the warnings of a possible tsunami would have been based on the seismic data alone. Again, experience with such ‘local tsunamis’ in the past means that Japan will have as good a warning system in place as could be hoped for.”
Dr Ken McCaffrey, Reader in the Department of Earth Sciences, Durham University, said:
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“Pacific plate is being subducted under Eurasian plates – size of fault – well plate boundary is 40,000 km – Pacific ‘Ring of fire’.
“Size of this individual fault is hard to predict but by comparison with Sumatra system – likely to be about 1000km long.”
Similarities/differences to 2004 Indonesian quake/tsunami
“Very similar – tectonic setting .”
How bad will it be in Hawaii, Pacific islands, Australia?
“Really depends on local seafloor conditions how bad it gets when wave hits the local continental shelf.”
Could waves reach US west coast and if so how bad?
“Yes they will – same answer applies depends on local conditions.”
How does strength of quake compare with 2004 quake?
“Slightly smaller.”
Why was Tokyo Bay not inundated?
“Again local geography will have dictated how the wave impacts – may have been shielded from a wave coming from this particular direction.”
Dr John Elliott, Department of Earth Sciences, University of Oxford, said:
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“The pacific plate is subducting underneath the Eurasian plate on which Japan sits. That is to say, the pacific plate is forced beneath Japan and disappears into the earth. The point at which it goes under is 200 km of the east coast of Japan.”
Similarities/differences to 2004 Indonesian quake/tsunami
“This is the same type of earthquake (Great Subduction earthquake) in which the oceanic plate is being forced underneath another plate that has islands above it. The tsunamis appear to be similarly large, indicating that there has been significant slip on the fault near the sea bed.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“I cannot comment on how bad the tsunami will be in Hawaii, Pacific Islands and Austrailia other than genral comments that it will have less impact than in Japan as they are further away, the amplitudes of the sea surface die down with distance. However, low lying areas could be affected, particularity on islands. Waves will reach the US Coast, but will not be anywhere near as high as Japan, and therefore will not go inland as much.”
How does strength of quake compare with 2004 quake?
“The strength of the earthquake is a few times smaller than the the Summatra 2004 earthquake (Magnitude 9.1 vesus this Japan one at 8.9). The fault is likely to have broken a few hundred kilometres north-south. The Summatra 2044 one broke 1200 km.”
Why was Tokyo Bay not inundated?
“Tokyo bay is not inundated because the bay is protected by a piece of mainland – a penisula. The fault which broke runs north-south, so the tsunami has the most impact on shorelines running north-south (i.e. most of the east coast of Japan). However, Tokyo bay is protected by a piece of land, and the open channel into the bay is in the south which is in the wrong direction to allow the wave to propagate into it.”
What are the different types of tsunami? What are the names of them? How are they different?
“There aren’t really different ‘types’ of tsunami – mainly different causes – earthquakes, landslides, volcanic eruptions, meteorite impacts.”
Is there any relation to Christ Church earthquake?
“There is no relation to the Christchurch earthquake – these earthquakes were ‘relatively’ small and a long way away.”
How big is an 8.9 earthquake? Are there any analogies we can draw?
” A magnitude 8.9 earthquake is likely to break a fault 500 km long and 40 km wide. The slip on the fault underground in parts could be man metres to a couple of tens of metres. It would have taken tens of seconds to break the fault that size.”
Why is this effect so large? Why is the effect of this so widespread?
“The effect is so widespread, because the earthquake is so large (although there have been similarly sized earthquakes around the Pacific in the last 100 years.) The fault is likely to have ruptured almost a quarter of the length of Japan’s main Island length. Therefore the tsunami affects a large area. The open Pacific ocean allows it to spread right across to the US and Chile.”
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
“I do not have specific information on the Nuclear Plant safety systems.”
Dr Alex Densmore, Department of Geography and Institute of Hazard, Risk and Resilience, Durham University, said:
“The earthquake occurred where the Pacific plate is subducting under the eastern edge of the Eurasian plate. This has been going on for millions of years and the current rate of motion between the two plates is about 90 mm per year. The plates are constantly moving relative to each other, but most of the time the fault between them – the subduction zone – is stuck together. That fault is very large – it can be traced off the coast of Japan, as far south as Taiwan, and as far north as Kamchatka. The fault only moves in large earthquakes like the one today.
“Compared to the 2004 Sumatra earthquake, the earthquake today had about 60% of the ground movement, and about half of the total energy release. It’s the energy release that causes most of the damage.
“The tsunami waves have been measured at up to 1 m high at deep-ocean buoys. This is important, because tsunami waves are typically very small in the deep ocean and only reach large heights as they approach the coast. The reason for this is that waves travel much faster in deep water; as the front of the wave enters shallow water, it slows down and the waves pile up. How much they pile up depends a lot on the topography of the ocean floor off the coast. The areas that are most at risk are those places where offshore topography is very steep, where the continental shelf is very narrow, and where the waves can be focused toward a single point – for example, into a large bay. The orientation of the coast, compared to the direction in which the waves are travelling, is also important. So the effects, and the hazard, can vary tremendously from place to place.
“The waves will definitely reach the west coast of the US but at the moment NOAA has issued an advisory rather than a direct warning. The expected arrival time in Hawaii is about 0300 (1300 UK time) and it will take several more hours to reach the US mainland. Its height was measured at 1.5 m at Midway Island about an hour ago (1028 UK time).
“There is not likely to be any direct connection between today’s earthquake and the recent Christchurch earthquake. They occurred many thousands of km apart, on different plate boundaries. There is, on average, one large (magnitude 8.0 or greater) earthquake in the world each year, and Japan has a long history of large earthquakes, so this is not unusual. It is likely to be, however, the largest recorded earthquake (in terms of magnitude) since historical records began with the 684 earthquake off Tokyo.
“A magnitude 8.9 earthquake is very large indeed. The total energy release is equivalent to about 6700 gigatons of TNT (6.7 million megatons), far greater than any nuclear weapon. That’s a bit misleading, though, because all of that energy doesn’t get released at the surface, so we don’t see the direct effects of it. But it gives you an idea of how powerful these events are.”
Dr Dan Faulkner, a structural geologist from the University of Liverpool’s School of Environmental Sciences, said:
“Tsunamis are produced by displacement of the seafloor. They can be produced by earthquakes, volcanic eruption or submarine landslides. Of these, earthquake tsunamis are by far the most common.
“The Japan earthquake released the approximate energy equivalent to 1.5 billion tonnes of explosives. An earthquake of this size will release more energy than all of the earthquakes of a lesser size that occur in one year.
“The earthquake will rupture a part of the subduction zone that is several hundred km long and tens of km deep. This means that although the maps show the earthquake occurring at a ‘point’ there is a zone of slip which widens the area effected by the earthquake.”
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“The earthquake occurred on the plate boundary between the Pacific and the North American plates. This subduction zone plate boundary fault runs to the north where it links with the Aleutian arc – another subduction zone that produced the 1964 Alaska earthquake, the second largest earthquake recorded since seismic records began.”
Similarities/differences to 2004 Indonesian quake/tsunami
“This is the same type of tectonic plate boundary – a subduction zone – that produced the Boxing Day 2004 earthquake.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“The main concerns relate to the nations to the south, such as the Philippines and Papua New Guinea. Waves will affect Hawaii and will reach the west coast US, but the extent and size of these is not known. The west coast US should not be badly affected.”
How does strength of quake compare with 2004 quake?
“They are both classed as ‘great earthquakes’ but the 2004 event probably released about 10 times more energy than the Japanese earthquake.”
Professor Andreas Rietbrock, seismologist from the University of Liverpool’s School of Environmental Sciences, said:
“There are two different types of tsunamis. There are distant tsunamis’ which travel through the ocean basin and hit on the other side of the Pacific Ocean. Instruments that record the progress of sea waves are placed throughout the Pacific Ocean, so there is plenty of data collected to warn us of an event. These types of tsunamis mean that distances between earthquakes and populated areas are large and warnings to the shore can be made quickly. Hawaii, therefore, has received warning of the tsunami before it has hit there. The tsunami in Japan, however, is a local one and warning times are very short.
“The earthquake was relatively shallow, therefore the displacement of the sea bed was quite big. The displacement moves the sea water, resulting in a tsunami.
“The tsunami today was the same size as the earthquake in Chile, in 2010.”
Dr Andy Gibson, School of Earth and Environmental Sciences, University of Portsmouth, said:
“The actual quake itself is smaller than the 2004 Event. That had a magnitude estimates at between 9-9.4.
“Tsunami waves will travel until their energy is dissipated into the ocean or until they make landfall.
“The pattern of inundation of tsunami wave is often very complex – it will be affected by the direction of the wave relative to the shore, the shape of the coast, the shape of the seabed offshore, the tide and many other factors. It is very difficult to predict exactly how the wave will affect each coastline.
“As with the Indonesian Tsunami, the impact very much depended upon the lie of the land and the height and direction of the wave. In those areas seriously affected by high waves, the water may pick up debris and other objects. The combined mass of water and debris has a much more damaging effect than water alone.”
Dr David Rothery, Open University, Volcano Dynamics Group, said:
Can we have a bit more detail on the geology, i.e. which plate is subducting under which plate, size and nature of fault and so forth
“Pacific Plate subducting below the Eurasian plate (Japan is at the E edge of the Eurasian plate. The average rate of convergence is about 9 cm per year, but motion is not smooth. Plates rub past each other in a stick-slip fashion. While stuck the strain builds up, and then in the ‘slip’ event the strain is suddenly released. There was probably several metres of slippage in one instant, along a 100 km extent of fault in this example.”
Similarities/differences to 2004 Indonesian quake/tsunami
“Very similar. 2004 was Indian Plate going below Eurasian plate at a subduction zone called the Sunda trench below Sumatra. The quake was mag 9.1 at 40 km. whereas today’s was mag 8.9 at 25 km. Both displaced seawater, so damage from tsunami waves was worse (and far more widespread) than from the quake itself.”
How bad will it be in Hawaii, Pacific islands, Australia? Could waves reach US west coast and if so how bad?
“By the time the Mail goes to press we will already know. Could be run-ups of several metres above sealevel on many pacific coasts.”
How does strength of quake compare with 2004 quake?
“8.9 at 25 km depth as opposed to 9.1 at 30 km depth. Slightly weaker, but still about the 6th biggest earthquake since 1900.”
Why was Tokyo Bay not inundated?
“Relatively sheltered. How waves affect shores depends on shape of coastline and underwater topography. I think Tokyo bay also has some tsunami walls designed to take the force of out waves.”
What are the different types of tsunami? What are the names of them? How are they different?
“There are no specific names for types. A tsunami is a series of waves. The first to arrive is not necessarily the biggest. The first significant thing to arrive could be a wave trough rather than a wave crest, in which case the sea recedes before rising. If a wave crest is the first arrival, it might be a large breaking wave or it could be just a rapid rise in sealevel so the land is flooded by water rushing in (but not a foaming, breaker of a wave).”
Is the any relation to Christchurch earthquake?
“No.”
How big is an 8.9 earthquake? Are there any analogies we can draw?
“In an average year only 1 quake exceeds 8.0. This was big. Slightly less powerful than the 9.1 that caused the 26 Dec 2004 Indian tsunami. Biggest recorded was 9.5 (Chile 1965).”
Why is this effect so large? Why is the effect of this so widespread?
“Tsunami waves pass unimpeded across oceans, and become higher when they reach shallow water. They lose some power as they radiate away from the source, but until their travel is impeded by hitting a big island or a continental coast they remain potentially dangerous.”
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
“I am sure there are!”
Professor Andreas Rietbrock, seismologist from the University of Liverpool’s School of Environmental Sciences, said:
“The magnitude 8.9 Japan earthquake is one of the largest earthquakes recorded worldwide in the last 100 years and the strongest one ever recorded in Japan. This quake is comparable to the 2010, Maule, Chile earthquake, which was a magnitude 8.8 at a larger depth of 35km. Today’s event occurred along the Japanese subduction zone where the Pacific and North American plates collide. The hypocentre is located close to the seabed at about 25km promoting a significant tsunami. The earthquake was preceded with a number of foreshocks and numerous aftershocks are currently happening.”
Dr Dan Faulkner, a structural geologist from the University of Liverpool’s School of Environmental Sciences, said:
“The earthquake that occurred off the east coast of the island of Honshu in Japan this morning had a magnitude of 8.9. This earthquake was preceded by a number of large foreshocks that started on the 9 March. Earthquakes of this type can produce very large displacements of the seafloor that displace huge volumes of water, resulting in devastating tsunamis. Although Japan is well prepared for earthquakes, events of this size would still be expected to produce significant damage from the shaking. Additionally, in this case, the damage resulting from the tsunami is likely to cause significant additional problems. Large aftershocks from this earthquake are to be expected in the coming days and weeks.”
Dr Mike Byfield, expert in structural engineering, University of Southampton:
“How buildings survive earthquakes:
– Japan is better prepared than anywhere else in the world for severe earthquakes
– their buildings are specifically designed to withstand earthquakes – particularly the high rise buildings seen in the likes of Tokyo.
– it’s the sideways motion of an earthquake that causes buildings to collapse
– Japanese buildings have special barings and damping – like shock absorbers in cars – to take the shock of the sideways motion. It means that although their buildings may get damaged, they don’t tend to collapse – protecting the people inside. Eg – the footage inside the buildings during the earthquake shows the structure moving from side to side – they are designed to do this and withstand the earthquake.”
Preliminary report from Professor Ian Main, Professor of Seismology and Rock Physics, School of GeoSciences, University of Edinburgh:
“A magnitude 8.9 earthquake has struck the east coast of Honshu, Japan, 80 miles east of Sendai. The earthquake has triggering a large tsunami that has caused extensive damage in coastal areas of Japan, with wave heights of 1.5m already recorded by deep water sensors and onshore ‘run-up’ heights of up to 10m reported by the BBC in Honshu . A tsunami warning was made and is still in place across the Pacific, including Australia and South America.
“The level of ground shaking is expected to be strong to very strong across almost all of Japan, but the impact from the direct effects of ground shaking is likely to be less than that of the tsunami.
“The Earthquake occurred on the north-western edge of the Pacific plate, where dense oceanic lithosphere is slowly being recycled into the mantle under the Japanese islands by a process known as subduction. The earthquake mechanism is a shallow-angle thrust fault, consistent in orientation and slip direction with this tectonic process.
“The USGS have issued a red alert level for anticipated economic losses. They say “extensive damage is probable and the disaster is likely widespread”. They estimate economic losses will be less than 1% of GDP of Japan. Past events with this alert level have required a national or international level response. An orange alert level has been issued for shaking-related fatalities. This is relatively low for such a large earthquake, due to a combination of effective earthquake-resistant building codes and the relatively remote location of the earthquake offshore. Significant casualties are likely from the tsunami.
“The authorities issued an earthquake early warning, (an announcement of the earthquake having been recorded at the source made before the waves arrive), enabling some rapid-response mitigation actions to be taken, such as moving to higher ground at the coast, and automatically stopping trains and elevators temporarily.
“The area has experienced significant earthquakes in the recent past. The USGS report “the Japan Trench subduction zone has hosted 9 events of magnitude 7 or greater since 1973”, including an M 7.7 earthquake 75 km to the southwest which caused 22 fatalities and over 400 injuries.
“In the first 12 hours following the March 11 earthquake, the region has already experienced over a dozen aftershocks of M 5 or greater, the largest being M 5.7.
“The March 11 earthquake was preceded by a series of large events over the previous two days, beginning on March 9th with an M 7.2 event approximately 40 km from the March 11 earthquake, and continuing with a further 3 earthquakes greater than M 6 on the same day. These events may have triggered the magnitude 8.9 event.”
Dr David Rothery, Open University, Volcano Dynamics Group, said:
“This morning’s Japanese earthquake 05:46 GMT) measured 8.9 on the Richter scale. That is very powerful, and in an average year there is only one quake more powerful than 8.0 anywhere in the globe. At its source, it was over a thousand times more energetic than the magnitude 6.3 quake that struck Christchurch on 22 February. This one occurred about 25 km below the seabed, and the displacement of seawater caused a series of tsunami waves capable of causing far more damage than the on-land ground shaking.
“Parts of the eastern coast of Japan have already been inundated, but there is a tsunami warning in force across most of the Pacific basin. For example, the first waves are expected to reach Hawaii 7 or 8 hours after the earthquake.
“This earthquake was a consequence of the floor of the Pacific ocean being dragged under Japan as a result of plate tectonic movements. It was preceded by a nearby magnitude 7.2 quake on 9 March and there was a magnitude 7.1 aftershock at 06.25 GMT.
“The 2004 Boxing Day tsunami in the Indian ocean was caused by a magnitude 9.1 earthquake where the floor of the Indian ocean is dragged below Sumatra.”