Decade-scale decrease in b value prior to the M9-class 2011 Tohoku and 2004 Sumatra quakes

• Published in: Geophysical research letters Vol. 39; no. 20
• Main Authors: NANJO, K. Z, HIRATA, N, OBARA, K, KASAHARA, K
• Format: Journal Article
• Language: English
• Published: Washington, DC American Geophysical Union 18.10.2012; John Wiley & Sons, Inc
• Subjects: Coastal environments; Earth sciences; Earth, ocean, space; Earthquakes; Exact sciences and technology; Geophysics; High performance computing; Hydrology; Indicators; Nonlinear systems; Plate tectonics; Precursors; Seismic activity; Seismic phenomena; Seismicity; Seismology; Asia; United States; Honshu; Japan; Pacific Coast; Sumatra; Western U.S; Tohoku; Hokkaido; Far East; Indonesia; Laboratory study; precursors; seismology; b value; slopes; indicators; earthquakes; North America; hypocenter; Precursor; frequency; seismicity
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2012GL052997

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 M9-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.