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Decade‐scale decrease in b value prior to the M 9‐class 2011 Tohoku and 2004 Sumatra quakes
Author(s) -
Nanjo K. Z.,
Hirata N.,
Obara K.,
Kasahara K.
Publication year - 2012
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2012gl052997
Subject(s) - quake (natural phenomenon) , seismology , magnitude (astronomy) , geology , richter magnitude scale , induced seismicity , earthquake magnitude , scaling , mathematics , physics , geometry , astronomy
The Gutenberg‐Richter frequency‐magnitude distribution of earthquakes has become well established in seismology. The slope of the relation between frequency and magnitude ( b value) is typically 1, but it often shows variations around 1. Based on an analysis of seismicity prior to the 2011 Tohoku and 2004 Sumatra earthquakes (both in magnitude ( M ) 9 class), we show that the pronounced decade‐scale decrease in b value was a common precursor to both mega‐quakes around their hypocenters. This is the first report on M 9‐class quakes to confirm a change in b value, which has been predicted based on the results of laboratory experiments. We propose that the b value is an important indicator of an impending great earthquake, and has great potential in terms of predicting a future large quake off the Pacific coast of Hokkaido, Japan.