UK SMC: Answers to questions from journalists provided by the UK Science Media Centre…
Is there any relation to Christchurch earthquake?
Prof. Dr. Polat Gülkan, President of the IAEE (International Association for Earthquake Engineering) and a member of the Editorial Board for Earthquake Engineering and Structural Dynamics, says:
“In terms of causality, none. They are both on the same so called Pacific Ring of Fire belt but are so far from one another that it’s a very remote possibility that one triggered the other. The Christ Church event was M6.3, so this M8.9 one packed about 8,000times more energy but was much further removed from any urban area, so its effects in terms of ground shaking were milder. The tsunami waves are really one way of transporting the energy released by the earthquake to points farther.”
Dr John Elliott, Department of Earth Sciences, University of Oxford, says:
“There is no relation to the Christchurch earthquake – these earthquakes were ‘relatively’ small and a long way away.”
Dr David Rothery, Open University, Volcano Dynamics Group, says:
“No”.
Dr Lisa McNeil, senior lecturer in geology at the University of Southampton, says:
“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.”
Prof. George Helffrich, University of Bristol Earth Sciences says:
“No. Most earthquakes happen on plate boundaries. Both the Christchurch and the Japan earthquakes did, too.”
Dr Alex Densmore, Department of Geography and Institute of Hazard, Risk and Resilience, Durham University, said:
“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.
What are the different types of tsunami? What are the names of them? How are they different?
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.
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.”
Prof. Dr. Polat Gülkan, President of the IAEE (International Association for Earthquake Engineering) and a member of the Editorial Board for Earthquake Engineering and Structural Dynamics, says:
“I think there’s only one kind of (and one name for) a tsunami, a travelling sea wave that is triggered by the sudden vertical shift of the bottom of the sea. They are known to be triggered also by submarine landslides, but those are of smaller size and consequences. Tsunami is a Japanese word.”
Dr Lisa McNeil, senior lecturer in geology at the University of Southampton, says:
“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.”
Dr David Rothery says:
“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).”
Dr Dan Faulkner says:
“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.”
Dr Alex Densmore says:
“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.
How big is an 8.9 earthquake? Are there any analogies we can draw?
Prof. Dr. Polat Gülkan says:
“Earthquakes seldom come any larger than that. The Richter scale has no upper limit (it’s open-ended). I believe that the M9.1 earthquake in Chile in 1960 is still not been eclipsed, but I heard them say this M8.9 was the 5th largest ever recorded.”
Dr John Elliott says:
” 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.”
Dr David Rothery says:
“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).”
Dr Lisa McNeil says:
“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.”
Dr Richard Phillips says:
“8,000 times more powerful than the recent Christchurch earthquake.”
Prof. George Helffrich says:
“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?
Prof. Dr. Polat Gülkan says:
“Tsunami waves rush in every direction, and pack a lot of energy in them. They destroy all sea front facilities in their way, and also run up and inward on land. We are talking of unimaginably large volumes of water that have been excited to move across the oceans.”
Dr John Elliott says:
“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.”
Dr Lisa McNeil says:
“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.”
Prof. George Helffrich says:
“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.”
Dr David Rothery says:
“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.”
Dr Richard Phillips says:
“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.”
What about the nuclear plants affected? Are there special systems in place to stop earthquake damage to plants?
Prof. Dr. Polat Gülkan says:
“Yes. All nuclear facilities have primary and secondary safety systems that kick into effect when the ground motion exceeds pre-set limits. The general principle is to stop the controlled nuclear reaction in the reactor and then go through very careful inspections to ensure that all is safe.”
Dr Richard Phillips, Lecturer in Tectonics & Geochronology, University of Leeds, said:
“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.”
Prof. George Helffrich says:
“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?
Dr Lisa McNeil says:
“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.”
Dr Alex Densmore says:
“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.
Prof. Dr. Polat Gülkan says:
“The earth has about 20 major plates that cover it and that shift gradually relative to one another. Some of them subduct (dive under) others they touch. Others just slide past their neighbors. That’s what has been happening near Japan.”
Dr Richard Phillips says:
“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.”
Dr David Rothery says:
“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.”
Dr Ken McCaffrey, Reader in the Department of Earth Sciences, Durham University, says:
“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.”
Dr Dan Faulkner, a structural geologist from the University of Liverpool’s School of Environmental Sciences, says:
“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.”
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.”
Similarities/differences to 2004 Indonesian quake/tsunami:
Prof. George Helffrich says:
“Smaller. Tsunami is propagating across the Pacific, but there is monitoring infrastructure in place (open ocean buoys), unlike the Indian Ocean in 2004.”
Prof. Dr. Polat Gülkan says:
“Very similar, I think.”
Dr John Elliott says:
“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.”
“The strength of the earthquake is a few times smaller than the the Sumatra 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.”
Dr Richard Phillips says:
“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.”
Dr David Rothery says:
“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 does strength of quake compare with 2004 quake?
Prof. Dr. Polat Gülkan says:
“The Indian Ocean earthquake? They’re in the same league.”
Dr Richard Phillips says:
“The Indonesian earthquake was larger (9.1) but at 8.9 this one is comparable in energy released and ground shaking.”
Prof. George Helffrich says:
“1/3 – 1/2 the strength.”
Dr Dan Faulkner says:
“They are both classed as ‘great earthquakes’ but the 2004 event probably released about 10 times more energy than the Japanese earthquake.”
Dr David Rothery says:
“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?
Dr David Rothery says:
“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.”
Dr John Elliott says:
“Tokyo bay is not inundated because the bay is protected by a piece of mainland – a peninsula. 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.”
Prof. Dr. Polat Gülkan says:
“The shape of the coastline plays a major role here. If land obstructs the path of the wave, it can’t affect what lies behind it.”
Dr Richard Phillips says:
“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.”
Prof. George Helffrich says:
“Not facing the propagating wave front; wrong shape.”
Dr Phillips is available for interview, as is Dr Roger Clark who has done some monitoring of underground nuclear explosions in the USSR. To speak to either please call us or Hannah Isom at the University of Leeds, 0113 343 5764, h.isom@leeds.ac.uk.