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Microscopic and macroscopic physics of earthquakes

Kanamori, Hiroo and Heaton, Thomas H. (2000) Microscopic and macroscopic physics of earthquakes. In: Geocomplexity and the Physics of Earthquakes. Geophysical Monograph. No.120. American Geophysical Union , Washington, DC, pp. 147-163. ISBN 9780875909783.

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Frictional melting and fluid pressurization can play a key role in rupture dynamics of large earthquakes. For faulting under frictional stress σ_ƒ, the temperature increases with σ_ƒ and the earthquake magnitude, M_w. If the thickness of the heated zone, w, is of the order of a few mm, then, even for a modest σ_ƒ, the temperature rise, ΔT, would exceed 1000° for earthquakes with M_w = 5 to 6, and melting is likely to occur, and reduce friction during faulting. If fluid exists in a fault zone, a modest ΔT of 100 to 200° would likely increase the pore pressure enough to significantly reduce friction for earthquakes with M_w = 3 to 4. The microscopic state of stress can be tied to macroscopic seismic parameters such as the seismic moment, M_0, and the radiated energy, E_R, by averaging the stresses in the microscopic states. Since the thermal process is important only for large earthquakes, the dynamics of small and large earthquakes can be very different. This difference is reflected in the observed relation between the scaled energy ẽ = E_R/M_0 and M_W. The observed ẽ for large earthquakes is 10 to 100 times larger than for small earthquakes. Mature fault zones such as the San Andreas are at relatively moderate stress levels, but the stress in the plate interior can be high. Once slip exceeds a threshold, runaway rupture could occur, and could explain the anomalous magnitude-frequency relationship observed for some mature faults. The thermally controlled slip mechanism would produce a non-linear behavior, and under certain circumstances, the slip behavior at the same location may vary from event to event. Also, slip velocity during a large earthquake could be faster than what one would extrapolate from smaller earthquakes.

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Kanamori, Hiroo0000-0001-8219-9428
Heaton, Thomas H.0000-0003-3363-2197
Additional Information:© 2000 American Geophysical Union. We thank Kenshiro Otsuki for sharing his insight into cataclasites and pseudotachylytes with us. Discussions with Rachel Abercrombie helped us assess the accuracy of energy measurements for small earthquakes. We benefited from the comments on the early version of the manuscript by Yoshio Fukao, Masayuki Kikuchi, Minoru Takeo, and Emily Brodsky. We also thank Toshihiko Shimamoto, Lee Silver, and Yuri Fialko for helpful discussions at various stages of this work. We thank Masataka Ando and Hisao Ito for allowing us to use some of their unpublished figures. This research was partially supported by the U. S. Geological Survey grant 99HQGR0035. Contribution #8635, Division of Geological and Planetary Sciences, California Institute of Technology.
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Caltech Division of Geological and Planetary Sciences8635
Series Name:Geophysical Monograph
Issue or Number:120
Record Number:CaltechAUTHORS:20121121-084449316
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Official Citation:Kanamori, H., and T. H. Heaton (2000), Microscopic and macroscopic physics of earthquakes, in Geocomplexity and the Physics of Earthquakes, Geophys. Monogr. Ser., vol. 120, edited by J. B. Rundle, D. L. Turcotte, and W. Klein, pp. 147–163, AGU, Washington, D. C., doi:10.1029/GM120p0147
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:35595
Deposited By: Tony Diaz
Deposited On:26 Nov 2012 22:27
Last Modified:09 Nov 2021 23:16

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