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TitleOn the strength of subduction megathrusts / On the strength of subduction megathrusts
AuthorWang, KORCID logo
SourceActa Geologica Sinica vol. 64, no. 10, 2021 p. 3452-3465,
Alt SeriesNatural Resources Canada, Contribution Series 20210181
PublisherChinese Geophysical Society / Institute of Geology and Geophysics of Chinese Academy of Sciences
Mediapaper; on-line; digital
File formatpdf
Subjectstectonics; geophysics; Science and Technology; Nature and Environment; Health and Safety; earthquakes; earthquake magnitudes; earthquake risk; seismic risk; seismicity; tectonic environments; subduction zones; geodynamics; bedrock geology; structural features; faults; stress analyses; heat flow; pore pressures; rheology; Methodology
Illustrationsschematic cross-sections; plots; models
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 10 15
AbstractThe strength of subduction megathrusts is an important problem in geodynamics. Over the past two decades, the scientific community has made fundamental progress in understanding this problem. In this article, I briefly introduce the core scientific issues in this research, the primary methods used, and the main results. There are only two effective methods to provide macroscopic estimates of these faults` strength at large spatial scales. One method is to use forearc crustal stress observations to constrain the level of margin-normal compression which helps to estimate the strength of the megathrust. The other is to use forearc heat flow measurements to constrain the amount of frictional heating along the megathrust which also helps to estimate its strength. Research results show that these faults are extremely weak. Their effective coefficients of friction are often around 0.03, although some may be slightly higher than 0.1. The weakness of the megathrusts explains why subduction zones are not orogenic belts. Research results also show that the weakest megathrusts are those that produce very large earthquakes, strongly indicating that large earthquakes do not need strong faults or high stress but only need geological conditions that facilitate the propagation and expansion of seismic rupture. The strength estimates further imply that stress drop in great earthquakes, when compared with the strength of the faults, is neither negligibly small nor nearly 100%. The geological reasons for the weakness of the megathrusts are not yet clear. Pore fluid pressure is generally expected to be rather high, but the presence of weak hydrous minerals in the fault gouge may also play a critical role.
Summary(Plain Language Summary, not published)
To understand the mechanical processes responsible for earthquakes and tsunamis caused by subduction megathrusts, one must understand the strength of these faults. This article provides a brief review of progresses made in understanding the strength of megathrusts over the past twenty years. From studies of force balance in the upper plate and frictional heating along the megathrust, it is known that most of these faults are very weak, represented by an effective friction coefficient of about 0.03, with those that produce great earthquakes being the weakest. The results indicate that great earthquakes do not need strong faults but need geological conditions that facilitate the propagation and expansion of seismic rupture.

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