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Possible seasonality in large deep-focus earthquakes

Zhan, Zhongwen and Shearer, Peter M. (2015) Possible seasonality in large deep-focus earthquakes. Geophysical Research Letters, 42 (18). pp. 7366-7373. ISSN 0094-8276.

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Large deep-focus earthquakes (magnitude > 7.0, depth > 500 km) have exhibited strong seasonality in their occurrence times since the beginning of global earthquake catalogs. Of 60 such events from 1900 to the present, 42 have occurred in the middle half of each year. The seasonality appears strongest in the northwest Pacific subduction zones and weakest in the Tonga region. Taken at face value, the surplus of northern hemisphere summer events is statistically significant, but due to the ex post facto hypothesis testing, the absence of seasonality in smaller deep earthquakes, and the lack of a known physical triggering mechanism, we cannot rule out that the observed seasonality is just random chance. However, we can make a testable prediction of seasonality in future large deep-focus earthquakes, which, given likely earthquake occurrence rates, should be verified or falsified within a few decades. If confirmed, deep earthquake seasonality would challenge our current understanding of deep earthquakes.

Item Type:Article
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Zhan, Zhongwen0000-0002-5586-2607
Shearer, Peter M.0000-0002-2992-7630
Additional Information:© 2015 American Geophysical Union. Received 24 JUN 2015; Accepted 19 AUG 2015; Accepted article online 21 AUG 2015; Published online 16 SEP 2015. This ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009) is freely available at The Global CMT catalog is freely available at We thank Debi Kilb, Duncan Agnew, and Clifford Frohlich for their discussions and comments on an earlier version of the manuscript. We thank Douglas Wiens and the anonymous reviewer for their helpful comments. This work was supported by National Science Foundation grant EAR-111111.
Group:Seismological Laboratory
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Record Number:CaltechAUTHORS:20151112-145239095
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Official Citation:Zhan, Z., and P. M. Shearer (2015), Possible seasonality in large deep-focus earthquakes, Geophys. Res. Lett., 42, 7366–7373, doi:10.1002/2015GL065088
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62082
Deposited By: Tony Diaz
Deposited On:18 Nov 2015 17:55
Last Modified:07 Oct 2017 03:51

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