T320 Challenges in Tectonics: Beyond Steady State: New Developments in Understanding Strain Localization Processes and the Rheology of the Lithosphere

Wednesday, 25 October 2017
8:00 AM - 12:00 PM
Tahoma 2

LITHOSPHERE AND SHALLOW ASTHENOSPHERE RHEOLOGY FROM OBSERVATIONS OF POST-EARTHQUAKE RELAXATION

Paper number: T320-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Abstract

In tectonically active regions, post-earthquake motions are generally shaped by a combination of continued fault slippage (afterslip) on a timescale of days to months and viscoelastic relaxation of the lower crust and upper mantle on a timescale of days to years. Transient crustal motions have been observed following numerous magnitude >~7 earthquakes in various tectonic settings: continental rift zones (Basin and Range), continental plate boundary zones (San Andreas fault corridor; Alaska; Turkey), back-arc settings (Japan, Chile), ongoing continental collision zones (Arabia; Tibet), and mid-ocean rifting zones (Iceland). When afterslip can be discriminated from viscoelastic relaxation and when temporal coverage of the postseismic measurements is broad (i.e., geodetic surveys of at least several years duration are available), a wide spectrum of relaxation timescales are usually identified. Current temporal resolution and modeling approaches (e.g., Burgers body analog) allow identification of transient (Kelvin) and steady-state (Maxwell) viscosities that are operable in the short-term and long-term, respectively. I compile results from ~30 studies of post-earthquake motions that illuminate current estimates of transient and steady-state viscosity of the lower crust and/or uppermost mantle. Lower crust viscosity estimates range from ~1018 to 1021 Pa s, with most estimates near the upper end except in areas of overthickened crust. Mantle lithosphere and asthenosphere viscosity estimates are particularly abundant and yield a picture of transient viscosity ranging from ~1016 to 1019 Pa s and steady-state viscosity ranging from ~1018 to 1021 Pa s. To first order, both transient and steady-state viscosities are well correlated with regional heat flow, and steady-state viscosities are comparable with temperature and strain-rate dependent rock viscosities from laboratory-based flow laws.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-302324

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