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Gutenberg–Richter law for deep earthquakes revisited: A dual-mechanism hypothesis

Zhan, Zhongwen (2017) Gutenberg–Richter law for deep earthquakes revisited: A dual-mechanism hypothesis. Earth and Planetary Science Letters, 461 . pp. 1-7. ISSN 0012-821X. doi:10.1016/j.epsl.2016.12.030.

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Deep earthquake b values appear to vary with slab thermal state and earthquake magnitude. The physical reason for the variations and the relation with deep rupture mechanisms are still unclear. Here I confirm the spatial variations of b value and the dependence on slab temperature using about 40 yr of data from the Global Centroid Moment Tensor catalog. A new bimodal pattern is observed for the 500–700 km depth range: b is close to 1 in the cold Tonga slab, while in warmer slabs (e.g., South America, Japan–Kuril, Izu–Bonin–Mariana), b is close to 0.5 for intermediate magnitudes (M_w 5.3–6.5) and increases to ∼1 for large magnitudes (M_w > 6.5). To explain these observations, I propose a dual-mechanism hypothesis in which deep earthquakes nucleate only within the metastable olivine wedge (MOW), but can rupture outside MOW by a different mechanism. The fractal dimension of earthquake size distribution changes from 2 to 1 as the thermally controlled MOW thickness decreases, and back to 2 as the mechanism outside MOW dominates.

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Zhan, Zhongwen0000-0002-5586-2607
Additional Information:© 2016 Elsevier B.V. Received 26 August 2016, Revised 26 November 2016, Accepted 22 December 2016, Available online 5 January 2017. I thank Hiroo Kanamori, Jean Paul Ampuero, Yanbin Wang, and Victor Tsai for constructive discussions. Comments and suggestions from two anonymous reviewers help clarify the manuscript significantly. Data used in this study are from the Global Centroid Moment Tensor Project,, last accessed on August 11th, 2016.
Group:Seismological Laboratory
Subject Keywords:deep earthquakes; Gutenberg–Richter law; frequency–magnitude distribution
Record Number:CaltechAUTHORS:20170109-091608305
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Official Citation:Zhongwen Zhan, Gutenberg–Richter law for deep earthquakes revisited: A dual-mechanism hypothesis, Earth and Planetary Science Letters, Volume 461, 1 March 2017, Pages 1-7, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73324
Deposited By: Tony Diaz
Deposited On:09 Jan 2017 21:14
Last Modified:11 Nov 2021 05:14

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