Earthquake prediction?

While there tends to be some kind of prior warning that a large-scale volcanic eruption is on the cards, earthquakes are a lot more difficult to pin down, so I was interested to read this news item in the Asahi Newspaper (Saturday 28th May 2011), which suggests that prediction – of major earthquakes, at least – is now a possibility.

I assume this story has been reproduced in English language news sources, but anyway, I thought it would be an interesting one to translate – any scientific inaccuracies are entirely my responsibility:

Electrons increased 40 minutes before earthquake

Forty minutes before the magnitude 9 Great East Japan Earthquake, levels of electrons in the ionosphere about three hundred kilometres above the Tohoku region of Japan showed an abnormal increase. The data was ascertained by Hokkaido University Professor Kohsuké Heki using signals from GPS equipment, and presented at a conference of the Japan Earth Satellite Association on 27th May. The same phenomenon has been observed at other large earthquakes, and has given rise to the valuable possibility of predicting earthquakes.

GPS satellite signals are influenced by electrons in the ionosphere – the larger the number of electrons, the greater the influence – and Professor Heki has checked National Geographic Society members’ GPS records from around the time of the earthquake.

As a result of this research, Heki has found that before the 11th March earthquake, electrons in the atmosphere began to increase by as much as ten per cent, at a distance of between three and four hundred kilometres from the epicentre. As soon as the earthquake began, electron levels returned to normal, although the exact mechanism of the increase is not yet clear.

It has been confirmed that just before the Chile earthquake of 2010 (magnitude 8.8), the Sumatra earthquake of 2004 (magnitude 9.1) and the Hokkaido Eastern Sea earthquake of 1994 (magnitude 8.2), increased levels of electrons were also observed in GPS records. The bigger the earthquake, the greater the breadth of the increase, although increases have not been seen for earthquakes of a magnitude below 8.

‘We hope to be able to predict earthquakes of magnitude 9 and above,’ said Professor Heki. ‘and because GPS records can be analysed using simple software, anyone can view the data.’ It is expected to be confirmed during the coming year whether or not such increases occur on occasions other than when there is an earthquake.

朝日新聞、平成２３年５月２８日

本震４０分前に電子増加

マグニチュード（M）９．０を記録した東日本大震災の発生四十分前に、東北地方の上陸約三百キロにある「電離圏」の電子が異常に増えていたことを、日置幸介北海道大教授が衛星利用測位システム（GPS）の電波から突き止めた。日本地球惑星連合大会で二十七日に発表した。他の巨大地震でも同じ現象が見られ、地震の直前予知に役立つ可能性もあり注目されている。

GPS衛星からの電波は電離圏で電子の影響を受ける。電子の数が多いほど影響も大きい。日置教授は国土地理員のGPS記録を大震災の前後について調べた。

その結果、発生約四十分前に震源三〇〇〜四〇〇キロ内の上空で電子が増え始め、最大で一割ほど増加していた。電子は地震発生後すぐ元に戻った。増加の仕組みはまだよく分からないという。

 チリ地震（二〇一〇年、M８．８）、スマトラ沖地震（〇四年、M９．１）、北海道東方沖地震（一九九四年、M８．２）の直前にもGPS記録から電子の増加が確認された。地震規模が大きいほど増加幅も大きく、M８以下の地震では増加は見られなかった。

「M９級地震の直前予知に有望。GPS記録を使って簡単なソフトで分析できるため、誰でも検証できる」と日置教授は話す。地震以外で今回のような増加が起きないことを今後、一年かけて確認するという。