Geologists in the UK trace readings from Japan earthquake

The magnitude 8.9 earthquake east of Honshu on 11/3/11 was recorded on a SEIS-UK seismometer.

It shows three traces that measure movement of Earth's surface in the vertical, north-south and east-west direction. SEIS-UK is part of the Natural Environment Research Council's Geophysical Equipment Facility.

Dr Richard England, senior lecturer in Geophysics at the University of Leicester, said: "Today's earthquake that occurred off the coast of Japan is unusually large. Only 1 or 2 earthquakes of this magnitude occur each year and when they occur they are not normally as close to the surface.

"While Japan is well prepared for even this type of earthquake, it will be some time before the full extent of the damage is known. Most of the devastation will have been caused by the resulting tsunami from the movement of the seafloor at the epicentre of the earthquake.

"The tsunami will be travelling out across the Pacific Ocean and warnings have been issued for the Hawaiian islands, the Philippines, the west coast of north and south America and the east coast of Australasia. Because the tsunami waves travel relatively slowly there will be time to evacuate coastal areas but low lying Pacific Ocean islands will be particularly at risk.

"In Japan the immediate danger will now be from continuing aftershocks. There was a M 7.1 event this morning which would normally be considered a strong earthquake. These 'smaller' events will still have the potential to generate small tsunami and further shake buildings and infrastructure already damaged, further delaying rescue and relief efforts. The aftershocks could continue for some time.

"Parallels have been drawn with the December 2004 earthquake off Sumatra. This earthquake is not quite as large but the cause, sudden movement along a subduction zone is the same. In this case the Eurasian plate has moved over the Pacific plate."

Are these events becoming more common? Dr England says the answer to this is, no.

"The timing of Earthquakes is not predictable, although seismologists are getting better at being able to determine which areas are most at risk. The December 2004 event raised awareness of the possibility of major earthquakes and the devastating effects they can have on communities. As a result they are much better reported so everyone takes more notice when they occur."