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A systematic test of the hypothesis that the b value varies with depth in California
Author(s) -
Gerstenberger Matt,
Wiemer Stefan,
Giardini Domenico
Publication year - 2001
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 - 10.1029/2000gl012026
Subject(s) - crust , geology , seismology , range (aeronautics) , upper crust , geodesy , geophysics , materials science , composite material
We spatially map the shallow to deep b value ratio in the crust in California. Previous studies of the frequency magnitude distribution, as a function of depth, for selected crustal regions indicated that b decreases from b > 1.1 in the 0–5 km depth range to b < 0.8 in the depth range 7–15 km. Our detailed mapping confirms that this pattern can be established at the 99% significance level for about 32% of the entire seismically active crust. About 2% of the crust displays the opposite b ‐gradient. One such area is the San Francisco Bay Area. We speculate that differences in stress levels are the main factor controlling the depth dependency of b . These results confirm that the b value should not always be considered a constant in studies such as seismic hazard estimations.