Temporal Clustering of Global Seismic Moment Release Over the Past 115 Years: Is Mother Nature Out of Control?
A series recent devastating earthquakes have stirred up widespread debates in the general public and even the geoscientific community about whether the Earth has entered a (probably unprecedented in human history) period of high seismic activity, and associated speculations about the physical or even spiritual causes of such a perception. Such a controversy was mostly the result of the absence of an earthquake catalog that accurately logged all the large earthquakes occurred over a long period of time. In this study we compare several global seismic catalogs and determine temporal variation of seismic moment release (M0) rate since 1895. The NGDC (National Geophysical Data Center) earthquake catalog shows that over the 115-year period of 1895-2010, the annual M0 for a total of 27 years is larger than 10 Zetta Newton*Meters (ZNM). Fifteen of the 27 years are clustered in the period of 1897-1918 (i.e., 15/21 = 71% of the years), 8 years are in the period of 1939-1965 (31%), and 4 years are in the period of 2004-2010.25 (60%). The first active period lasted 19 years, while the second period lasted 26 years. The second period has the largest peak amplitude (about 200 ZNM), which is about 3-4 times larger than that of the first and third period. Virtually all of the four catalogs used in the study show a significant increase in the annual seismic moment release starting from 1994 relative to the period of 1978-1993, during which all the catalogs show that no earthquake is greater than 8.3. This increase was followed by a more dramatic increase starting from 2004 represented by the Sumatra (2004) and other high-profile earthquakes such as those in Wenchuan (China, 2008), Haiti (2010), and Chile (2010). Based on the Harvard CMT catalog, over the 17-year period from 1994 to 2010, only five years had a moment release that is lower than the highest value in the 16 year period from 1978 to 1993. We test the statistical significance of the temporal variation by generating 100 million pairs of random-number sets using a random number generator, and found that the probability for such a temporal variation to be random is only about 0.00047%. Therefore, the increase in moment release since 1994 is unlikely a random phenomenon, a conclusion that is similar to a previous study for the period of increased earthquake activity during 1950-1965 [Bufe and Perkins, 2005]. The data presented above suggest that while the Earth has been more seismically active since 1994 relative to the 15 or so year period before, the recent activity has not been unprecedentedly higher than the other two active periods during the past 115 years. Thus Mother Nature is not "out of control", if the term implies that it is suffering from an all-time-high in earthquake activity.
S. S. Gao and K. H. Liu, "Temporal Clustering of Global Seismic Moment Release Over the Past 115 Years: Is Mother Nature Out of Control?," American Geophysical Union (AGU), Aug 2010.
AGU Joint Assembly (2010; Aug. 8-12, Foz do Iguassu, Brazil)
Geosciences and Geological and Petroleum Engineering
Keywords and Phrases
Seismology; Seismicity And Tectonics
Article - Conference proceedings
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