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Concern about Earthquakes and Volcanic Eruptions

Responding to Public Questions and Misconceptions

David Morrison

May 19, 2010

Questions from the public regarding earthquakes and volcanic eruptions, answered by Dr. David Morrison

Note: These are questions (slightly edited) from the public, received during April 2010 at NASA’s Ask an Astrobiologist.

Question: Why so many strong earthquakes all of a sudden? In no past years have we had so many earthquakes in so little time.

There has been no increase in numbers or intensity of earthquakes, but there has been increased news reporting, especially when earthquakes are “close to home” for U.S. audiences. The world-wide frequency of earthquakes has been tabulated by the U.S. Geological Survey based on historical data. For the largest earthquakes (magnitude 8 and higher) there is an average of about one per year. There was one in 2009 (Sept 29 in Samoa) and there has been one so far in 2010 (Feb 27 in Chile). For Earthquakes of magnitude 7.0 to 7.9 (sometimes called “major earthquakes”), the average frequency is about one every 3 weeks. Thus earthquakes like Haiti (Jan 12, at magnitude 7.0) and Baja (Apr 4, at magnitude 7.2) are not unusual. The earthquake in Tibet on April 14, at magnitude 6.9, does not even qualify officially as a “major earthquake”, although it caused extensive damage because of poor construction practices. As summarized by the USGS, “we expect about 17 major earthquakes and one great earthquake per year.” That is close to the rate we have experienced so far in 2010.

Question: Why have there been over double the number of 4.0 magnitude earthquakes so far this year (71 as of April 12, as opposed to 30 last year) this not proof that the earths crust is shifting more rapidly than anytime in recent recorded history?

I don't understand the numbers you give for magnitude 4 earthquakes. There are more than ten thousand magnitude 4 earthquakes every year, and probably additional thousands that are undetected. (Note that the energy released by a magnitude 4 earthquake is only about one millionth that of a magnitude 8 earthquake). At this small size, many of these earthquakes are not primary tectonic events but aftershocks from major earthquakes. People are sensitized to earthquakes right now because several have been in populated regions including Haiti (January 12), Chile (February 27), and Tibet (April 14). But tectonic activity on Earth has not increased, and the crust is not shifting. I regret that so many people write to me with unwarranted fears of nature -- including tectonic activity, solar outbursts, volcanic eruptions, planet alignments, black holes, changes in Earth's rotation or magnetic fields, and many other ordinary events in astronomy and geology. This fear of nature seems to be spread by irresponsible TV "documentaries" and a proliferation of pseudoscience and conspiracy theory websites. The Internet is a powerful source for education, and some websites like Wikipedia and the public webpages of NASA and USGS are excellent, but they compete with the "noise" of poorly informed and intentionally misleading websites. People need to learn, at an early age, how to distinguish reliable information from the misinformation and disinformation that are so widespread.

Question: Is the volcano that has been erupting in Iceland a supervolcano (such as Yellowstone)? Can a very large volcano explosion be the end of humans world wide?

No, the eruption of Eyjafjallajökull, which has produced some spectacular images and disrupted airline traffic across Europe for a week, is not a particularly large eruption. It will probably rate a 2 on the Volcanic Explosivity Index (VEI). Eruptions of this size happen somewhere on the planet every few weeks. In contrast, the 1980 eruption of Mt. St. Helens produced about 1 cubic km of ash, rating a VSE of 5. The Pinatubo eruption of 1991 (VSE 6) was the second largest in the twentieth century, and it created red sunsets around the world and produced measurable global cooling lasting at least a year. The eruption of a supervolcano like Yellowstone is more than a thousand times larger yet, but even an explosion of that magnitude would not produce a mass extinction or seriously threaten human civilization. What is happening in Iceland now is a routine geological event, important to us only became of its temporary effect on air travel.

David Morrison

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David Morrison is a long-time NASA senior scientist and Committee for Skeptical Inquiry fellow. He now divides his time between the SETI Institute and the NASA Lunar Science Institute. He hosts the "Ask an Astrobiologist" column at NASA's website.