Japanese disaster felt in Borders

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some 12 minutes after the massive earthquake occurred off the eastern coast of Japan in the early hours of Friday morning, sensitive scientific instruments in the Borders were registering the shock waves.

The sixth largest earthquake ever recorded since seismographic records began in 1900 triggered a giant tsunami that laid waste to towns and villages along a vast coastal area of Honshu and is now estimated to have killed more than 10,000 people.

Measuring 8.9 on the Richter scale, the earthquake was 8,000 times bigger than the recent Christchurch earthquake in New Zealand and is believed to have actually shifted Japan several metres closer to the United States.

One of the British Geological Survey’s (BGS) measuring stations is the Eskdalemuir Geophysical Observatory near Langholm.

Eskdalemuir Observatory is owned by the Natural Environment Research Council (NERC) and is located in the upper reaches of the White Esk valley.

Operated by the BGS, as a centre for geophysical and meteorological measurement, it provides information on the long-term monitoring of the geomagnetic field in the UK – important to navigation – as well as recording global earthquake activity.

Its seismic array also provides the British contribution to the monitoring of compliance under the Comprehensive Nuclear Test Ban Treaty.

The work at the observatory, built in 1908, contributes to an international network which allows earthquake locations to be pin-pointed. The observatory is also the principal means of detecting the many small earthquakes which occur in Scotland.

It also detected the crash of the Pan Am 747 airliner at Lockerbie in 1988 and recordings of the observed time of impact was presented as evidence at the subsequent court hearings and enquiries.

At 5.58am our time on Friday, an alarm went off at the observatory signalling an earthquake somewhere in the world.

Experts at the BGS say it has ruptured a 400–500km long segment of the tectonic plate boundary east of northern Honshu.

The earth’s crust is made up of numerous separate plates which rub up against each other as a result of stresses and the build-up of pressure, and it is the energy released by this which causes earthquakes.

The reason the Japanese earthquake caused a tsunami was that its epicentre was at sea and the shifting of the plates, which may have been by as much as 5–10m, caused an uplift of the sea floor above the rupture zone by several metres.

In this instance, the Eurasian plate has moved up over the Pacific Plate. Japan lies along the fault line where these two plates meet.

BGS seismologist Davie Galloway says a series of global monitoring stations such as the one at Eskdalemuir all recorded the earthquake and from the information obtained, such as the time differences between the various shock waves, it was possible to work out the exact location and depth at which it struck.

“Centres such as the one at Eskdalemuir let us build up a picture of what is happening seismically around the world. Around 95 per cent of all earthquakes occur along the plate margins, where energy is released when these plates bump up against each other,” he explained to TheSouthern this week.

The UK sits roughly in the middle of what is termed the Eurasian plate, but does not lie along a major fault line like Japan, New Zealand or Chile – the latter the site of the biggest-ever earthquake, recorded in 1960 in Chile and measuring 9.5.

As well as coping with the devastation caused by last week’s quake, Japan could face thousands of aftershocks over the coming months. The largest so far of these measured a magnitude of 7.1.

Friday’s earthquake is the largest to have affected Japan in the last century and much bigger than anything else in living memory in Japan.

The largest previously was the 1923 Kanto earthquake, which measured 7.9 – 30 times less powerful than the one on Friday.

Mr Galloway explained that, while not prone to the size of earthquakes around the Pacific Ocean’s notorious ‘Ring of Fire’ fault lines, the UK and surrounding waters were still subject to between 150 and 200 earthquakes each year.

“The nearest plate boundary to us here in the UK is the Mid-Atlantic Ridge and, although we’re quite far away from that, we still have to take into account the threat from earthquakes when it comes to things like designing and building sensitive structures such as nuclear power stations,” he said.

Mr Galloway says data collected by the observatory at Eskdalemuir will be among that shared with scientists in Japan.