Fault mechanics and Lithospheric rheology
PAGE UNDER CONSTRUCTION
PAGE UNDER CONSTRUCTION
The rheological structure of the lithosphere is of wide interest, given its role in controlling the lithospheric deformation style, shaping the landscape evolution and affecting stress accumulation and releasing in the crust. Geodynamic and earthquake cycle models require the knowledge of how the strength and rheology vary with depth. On the scale of fault zones, the mechanical properties of faults influence the faulting style (e.g. aseismic creep, earthquake rupture). I use satellite observations of postseismic response of the crust to large earthquakes for investigating rheological structure and fault frictional properties. Areas of interest include continental regions such as the Tibetan Plateau, and subduction zones in South America.
Intermediate depth earthquakes, such as the 2005 Mw 7.8 Tarapaca earthquake within the subducting Nazca plate, represent a different type of event from the megathrust ones in subduction zones. Large intermediate-depth earthquakes induce stresses, which will gradually be relaxed by VER in the adjoining mantle, and produce transient deformation. This provides opportunities for investigation of subduction zone rheology.
Our study of the postseismic deformation following Tarapaca earthquake shows divergent motion of the ground away from the epicentral area. Modelling with consideration of 3D rheological herterogenities suggests existence of stagnant cold mantle nose, and continental asthenospheric viscosity of 4–8 × 10e18 Pa s. Taking a step further, the computed static stress from the Tarapaca earthquake (including co- and post-seismic processes) may load positively on the M 6.7 foreshock before the M 8.2 Iquique earthquake that occurred about nine years after the Tarapaca earthquake.
What is the rheological structure like underneath the Tibetan Plateau? It is one of the key questions relevant to the current deformation on the plateau. Whether the deformation is distributed or localised is strongly linked to the lower crust and/or upper mantle rheology. We study different types of earthquakes within the plateau by constructing postseismic deformation time-series from geodetic observations, and comparing the deformation trend with theoreticall models with different rheological properties. Inversions for afterslip helps constrain fault frictional properties at various depth.
Figures on top show modelled post-seismic line-of-sight displacements due to viscoelastic relaxation at 615 d after the 2008 Mw6.3 Damxung earthquake, using variable viscosities (Pa s) marked as the title of each figure. Bottom figures show the residuals between the cumulative post-seismic deformation at 615 d after the main shock and the modelled deformation due to viscoelastic relaxation in the mid/lower crust. Positive range change represents motion away from the satellite, while negative range change indicates motion towards the satellite.
- Feng, M., Bie, L. & Rietbrock, A., (2018). Probing the rheology of continental faults: Decade of postseismic InSAR time series following the 1997 Manyi (Tibet) earthquake. Geophysical Journal International, 215(1), 600-613. doi: 10.1093/gji/ggy300.
- Bie, L., Ryder, I., Metois, Marianne. (2017). Deep postseismic viscoelastic relaxation excited by an intraslab normal fault earthquake in the Chile subduction zone. Tectonophysics, 712-713, 729–735.
- Ryder, I., Wang, H., Bie, L., & Rietbrock, A. (2014). Geodetic imaging of late postseismic lower crustal flow in Tibet. Earth and Planetary Science Letters,404, 136-143.
- Bie, L., Ryder, I., Nippress, S. E., & Bürgmann, R. (2014). Coseismic and post-seismic activity associated with the 2008 Mw 6.3 Damxung earthquake, Tibet, constrained by InSAR. Geophysical Journal International, 196(2), 788-803.
© 2018 Lidong Bie. All rights reserved. Observing Earth Deformation from Above and Below.