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Generic dependence of the frequency‐size distribution of earthquakes on depth and its relation to the strength profile of the crust
Author(s) -
Spada M.,
Tormann T.,
Wiemer S.,
Enescu B.
Publication year - 2013
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 - 10.1029/2012gl054198
Subject(s) - crust , geology , differential stress , brittleness , seismology , differential (mechanical device) , upper crust , fault (geology) , magnitude (astronomy) , continental crust , stress (linguistics) , geodesy , geophysics , deformation (meteorology) , physics , linguistics , oceanography , philosophy , astronomy , thermodynamics
We explore the idea that the relative size distribution of earthquakes, quantified using the so‐called b ‐value, is negatively correlated with differential stress. Because the maximum possible differential stress increases linearly in the brittle upper crust, we expect to find a decrease of b with depth. We test this expectation for seven continental areas around the world, each of which is described by a regional earthquake catalog. We find a monotonic decrease in b ‐value between 5 and 15 km depth. The decrease stops near the brittle‐ductile transition. We specifically focus on the high‐quality catalogs of earthquakes in California to perform a sensitivity test with respect to depth uncertainty; we also estimate the probability‐depth gradient for the occurrence of a target magnitude event and study the behavior of b with depth in near‐ and off‐fault zones. We also translate the observed b ‐depth gradients into b ‐differential stress gradients. Our findings suggest that b ‐values are negatively correlated with differential stress and hus have the potential to act as stress meters in the Earth's crust.