Transient Creep in Olivine at Shallow Mantle Pressures: Implications for Time‐Dependent Rheology in Post‐Seismic Deformation

• Published in: Geophysical research letters Vol. 51; no. 11
• Main Authors: Ohuchi, Tomohiro, Higo, Yuji, Tsujino, Noriyoshi, Seto, Yusuke, Kakizawa, Sho, Tange, Yoshinori, Miyagawa, Yamato, Kono, Yoshio, Yumoto, Hirokatsu, Koyama, Takahisa, Yamazaki, Hiroshi, Senba, Yasunori, Ohashi, Haruhiko, Inoue, Ichiro, Hayashi, Yujiro, Yabashi, Makina, Irifune, Tetsuo
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.06.2024; Wiley
• Subjects: Burgers rheology; Cadmium; Cadmium telluride; Cadmium tellurides; Crustal deformation; Deformation; Earthquakes; Olivine; post‐seismic deformation; Relaxation time; Rheological properties; Rheology; Seismic activity; Solifluction; Stress relaxation; stress‐relaxation experiments; Time dependence; transient creep; Upper mantle; upper mantle viscosity; Viscosity
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2024GL108356

Transient creep in olivine aggregates has been studied by stress‐relaxation experiments at pressures of 1.7–3.6 GPa and at temperatures of ≤1020 K in a DIA apparatus. Time‐dependent deformation of olivine at small strains (<0.07) was monitored with an ∼1 s of time resolution using a combination of a high‐flux synchrotron X‐ray and a cadmium telluride imaging detector. The observed deformation was found to follow the Burgers creep function with the transient relaxation time ranging from 50 (±20) to 1,880 (±750) s. We show that the Burgers creep for olivine cannot account for the low viscosities in early post‐seismic deformation reported by geodetic observations (<7 × 1017 Pa·s). In contrast, the time‐dependent increase in viscosity observed in late post‐seismic deformation (1018−1020 Pa·s) is explained by the Burgers rheology, suggesting that the combination of the Burgers model and another model is needed for the interpretation of post‐seismic deformation. Plain Language Summary Geodetic observations reveal that the deformation of the crust and upper mantle after a great earthquake continues for decades. Viscosities of the upper mantle estimated from early post‐seismic deformation are often significantly low (1017−1018 Pa·s) and continuously increase to a typical value (∼1020 Pa·s). This characteristic of post‐seismic mantle flow cannot be explained by partial melting (nor water weakening) of upper mantle rocks. Here we performed small‐strain deformation experiments on natural olivine, which is the major mineral in the upper mantle, via a state‐of‐the‐art technology large‐volume deformation apparatus combined with high‐flux synchrotron X‐ray observations. We have successfully shown that the reported time‐dependent crustal deformation, which continues for decades after a great earthquake, is explained by the transient creep of olivine. Key Points In situ deformation experiments on olivine were performed using a high‐flux synchrotron X‐ray and a cadmium telluride imaging detector Transient creep of olivine aggregates follows the Burgers creep function at upper mantle pressures and temperatures Time‐dependent rheology of the shallow mantle observed in the late post‐seismic deformation is explained by the Burgers model