2011 Foreshocks, Aftershocks in Japan: Lessons for the Future?


Magnitude of earthquakes (M5-6=small yellow circles, M6-7 orange circles, M7+ large red circles) off the coast of Honshu, 9-14 March.

Geologist Chris Rowan's Scientific American article, "Japan earthquake: The explainer" clarifies some very important points about Japan's earthquakes {highly recommended reading.} Can we learn from this?

Take a look at these data of foreshocks and aftershocks. It tells an extraordinary story: on March 9, there was an earthquake of magnitude greater than 7.0, followed by dozens of weaker events (magnitude 5 to 6) over the next 48 hours, just before the major event on March 11 at close to magnitude 9.0.

The data also show dramatically the nearly 300 aftershocks reported in the news media, some of which approached magnitude 7.0. I am not a geologist, but wonder whether these data can help us better predict future events similar to Friday's tsunami?

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There is no known way to predict earthquakes except in generalities.

And how can anyone "predict future events that led to Friday's tsunami", as you ask...??? Doesn't make sense.

The problem is that there are plenty of M7 quakes that are followed by M5-6 aftershocks without a subsequent M8.9. There are even more M5-6 quakes that are not aftershocks, but turn out to be the main shock. And there have been numerous large quakes (1976 Tangshan for an example) that have provided little or no foreshock data.

Retrospective analysis is the only way to determine when there are foreshocks for a major quake. In that sense, Yogi Berra spoke for seismologists everywhere:

It's tough to make predictions, especially about the future.

Note: The phrase you referred to was inadvertently used via an earlier draft, now corrected.