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Science Alert: Experts Respond

Quakes in Ecuador & Japan – Expert reaction

Posted in Science Alert: Experts Respond on April 18th, 2016.

Quake EcuadorA 7.8 magnitude earthquake struck Ecuador on Saturday morning (NZT), centred near the coast, 170 km from the capital Quito.

Latest reports indicate that the quake has killed at least 235 people and injured more than 1500. The Ecuador quake comes not long after strong quakes elsewhere in the Pacific, with magnitude 6.2 and 7.0 quakes occurring in Japan just days beforehand.

The UK Science Media Centre collected the following commentary.

Dr Ilan Kelman, University College London and co-director of the NGO Risk RED (Risk Reduction Education for Disasters) which has done work on seismic safety education, said:

“The Japan and Ecuador earthquakes show how far we have come, and how far we have to go, regarding seismic safety. The comparatively low death tolls show that we can construct buildings to withstand large, shallow tremors. For me, the number of fatalities is still too high, since we know what to do to stop buildings collapsing. The challenge of disasters remains using the knowledge we have already to save even more lives.”

Professor of Planetary Geosciences at The Open University, comments:

“The earthquake in Ecuador was magnitude 7.8, which means that that shaking at its underground source was about 6 times stronger than in the magnitude 7.0 earthquake in southern Japan just over a day before. The total energy involved was probably about 20 times greater.

“This one was caused by the floor of the Pacific Ocean (the Nazca plate) being subducted below South America). The rupture was began deeper underground (about 20km) than in the recent Japan quakes, which would have lessened the shaking experienced at the ground surface. The greater damage to buildings and the probable greater loss of life in Ecuador may reflect poorer adherence to seismic building codes in the construction of buildings and bridges. There have been seven magnitude 7 or greater earthquakes within 250 km of this one since 1900.

“The epicentre of the Ecuador earthquake was onshore.  If it had been offshore, the strongest shaking would have affected a smaller area on land so the direct damage would have been less, but there would have been the potential to displace the ocean water strongly enough to cause a tsunami powerful enough to cause damage on both local and more distant coastlines.

“There is no causal relationship between the earthquakes in Ecuador and Japan. About 20 magnitude 7 earthquakes occur somewhere on the globe every year.”

On the Japan quake:

Prof David Rothery, Professor of Planetary Geosciences at The Open University:

“The magnitude 7.0 earthquake that struck Kyushu at 1625 UTC (GMT) 15 Apr was about 30 times more powerful than its magnitude 6.2 predecessor at 12:27 UTC on 14 Apr. Both sources were equally shallow (about 10km) and so the shaking at the ground surface was much stronger and more damaging during the second event.

“It is unusual but not unprecedented for a larger and more damaging earthquake to follow what was taken to be ‘the main event’. On 9 March 2011 an magnitude 7.2 earthquake in northern Japan was followed two days later by a magnitude 9.0 earthquake that caused a devastating tsunami. Fortunately this time the epicentres have been below land rather than under the sea, and no tsunamis have been triggered.

“On Kyushu there will probably continue to be aftershocks large enough to be felt for several days, but hopefully nothing more powerful than had already happened. The nearby volcano Mount Aso had a small eruption shortly after the 15 April earthquake. This almost certainly resulted from stirring up of magma and gas already present and nearly ready to erupt in the normal course of events. The earthquakes themselves do not generate fresh magma. The melting of rock is a slow process, related to events deep in the crust and the upper mantle, and is not caused by sudden slippage such as happens in an earthquake.”

From the Science Media Centre of Japan:

Associate Professor Satoko Oki, Faculty of Environment and Information Studies, Keio University, Tokyo, comments:

“Two strong earthquakes have struck southern Japan on April 14 and 16 local time. This is a developing story and the below information is current as of April 16 09:00 Japan time.
“Historically, Kyushu, or southern Japan, is an area that has had a relatively low amount of earthquake activity compared to the rest of Japan. However, the Japanese government acknowledges the region has a large number of fault lines.

About the first earthquake:

“It is believed the Hinagu Fault line caused the magnitude 6.2 (US Geological Survey) earthquake on April 14, local time.

“The Headquarters for Earthquake Research Promotion’s earthquake investigation committee believes the northwest part of Hinagu Fault line moved in this earthquake, and not the entire line.

“The April 14 earthquake experienced a particularly large amount of aftershocks recorded by the Japan Meteorological Agency. These aftershocks are relatively large for aftershocks. Normally, an aftershock is at least one value below in magnitude compared to the main earthquake. In this case, the magnitude of main shock was 7, so the largest aftershock would be expected not to exceed magnitude 6. However, this time the magnitude of the largest aftershock was as large as 6.0.

About the second earthquake:

“On April 16 01:25 local time, a magnitude 7.0 (US Geological Survey) earthquake struck southern Japan. From its size, the earthquake is being treated as a new earthquake and not an aftershock of the April 14 earthquake. This earthquake is believed to have occurred along the Futagawa Fault Zone. Further analysis has revealed the epicentre stretches from Oita prefecture to the Beppu Bay, which might indicate that the earthquake is also connected to the Beppu-Haneyama Fault Zone.

“It has not been observed for long time in Japan that an earthquake stretches over several fault lines. The Hinagu Fault Line’s northern area, a branch of the Futagawa and Hinagu Fault Zone, with aftershocks recorded around the Futagawa Fault Zone. Then, the magnitude 7.0 earthquake occurred along the Futagawa fault line. Aftershocks have been recorded beyond Mount Aso, and in the Beppu-Haneyama Fault Zone.”

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