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TitlePostseismic geodetic signature of cold forearc mantle in subduction zones
AuthorLuo, H; Wang, KORCID logo
SourceNature Geoscience vol. 14, 2021 p. 104-109,
Alt SeriesNatural Resources Canada, Contribution Series 20200524
PublisherNature Research
Mediapaper; on-line; digital
File formatpdf; html
ProvinceBritish Columbia; Yukon
NTS92; 93; 94; 102; 103; 104; 105; 114; 115
AreaPacific Ocean
Lat/Long WENS 90.0000 -60.0000 65.0000 -60.0000
Subjectstectonics; geophysics; Science and Technology; Nature and Environment; Health and Safety; earthquake studies; subduction zones; earthquakes; plate motions; crustal uplift; deformation; mantle; tectonic setting; satellite geodesy; thermal analyses; rheology; computer simulations; Ring of Fire; 2011 Mw 9 Tohoku-oki Earthquake; 2010 Mw 8.8 Maule Earthquake; 2007 Mw 8.4 Bengkulu Earthquake; 1960 Mw 9.5 Chile Earthquake
Illustrationsschematic cross-sections; diagrams; location maps; charts
ProgramPublic Safety Geoscience Assessing Earthquake Geohazards
Released2021 01 18
AbstractA sharp thermal contrast between the cold forearc and the hot arc and backarc is considered fundamental to a range of subduction zone processes including slab dehydration, arc volcanism, and earthquakes. However, direct observational evidence for the contrast is rather limited; even the most relevant data - heat flow measurements are in question because of large errors. Here we demonstrate that postseismic deformation following large subduction earthquakes yields independent evidence for the contrast. If the thermal contrast is present, it must result in a rheological contrast in the mantle wedge, being elastic in the cold forearc and viscoelastic in the hot arc and backarc. Consequently, seaward postseismic motion is deflected upward at the edge of the cold forearc mantle wedge, causing diagnostic uplift just seaward of volcanic arc. Using numerical models of postseismic deformation following the 2011 Mw 9 Tohoku-oki, 2010 Mw 8.8 Maule, 2007 Mw 8.4 Bengkulu, and 1960 Mw 9.5 Chile earthquakes, together with a global synthesis of postseismic uplift measurements, we show that the presence of the cold forearc mantle is irrespective of the diversity in tectonic settings. Our findings further indicate that the monumental field surveys by G. Plafker 8 years after the 1960 Chile earthquake, provided some of the earliest evidence for viscoelastic postseismic deformation. The link between long-term thermal processes and short-term earthquake cycle deformation established in this study is important to understanding subduction zone dynamics.
Summary(Plain Language Summary, not published)
A sharp geothermal contrast between the area seaward of the volcanic front, called the forearc, and the areas farther landward is of fundamental importance to subduction zone dynamics including its earthquake processes. Thermo-petrologic models predict the forearc mantle wedge to be much colder than the rest of the mantle wedge, but geophysical observational constraints are very limited. In this work, we found strong evidence for the presence of the cold forearc mantle wedge from geodetic observations of crustal motion following large megathrust earthquakes. The presence of the cold mantle wedge affects mantle flow during postseismic deformation. This paper describes this discovery using a combination of global synthesis of relevant observations and modelling postseismic deformation of several large earthquakes.

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