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Crustal rheology of southern Tibet constrained from lake-induced viscoelastic deformation

Henriquet, Maxime and Avouac, Jean-Philippe and Bills, Bruce G. (2019) Crustal rheology of southern Tibet constrained from lake-induced viscoelastic deformation. Earth and Planetary Science Letters, 506 . pp. 308-322. ISSN 0012-821X. http://resolver.caltech.edu/CaltechAUTHORS:20181120-100648209

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Abstract

We probe the rheology of the Tibetan lithosphere using the rebound that accompanied climate-driven lake level variations. At the modern decadal time scale, we used deformation around Siling Tso measured from InSAR. At the millennial time scale, we use Holocenepaleoshorelines around Siling Tso and Zhari Nam Tso. We use chronological constraints from the literature and Digital Elevation Models to constrain their ages and geometry. We observe a small post-highstand subsidence of the area near the center of mass of the paleolake-load and a low-amplitude short-wavelength outer bulge. In the context of a model consisting of an elastic lid over a viscous channel with a rigid base, these observations preclude the existence of a thick low viscosity channel and require a thin elastic lid. Based on Monte Carlo inversion, we constrain the range of possible equivalent elastic thickness of the lid (<5 km), the viscosity (2×10^(18)–10^(20) Pa.s) and thickness of the crustal channel (<10–20 km). By contrast, the modern data requires a stiffer lid with equivalent elastic thickness >20 km and a >20 km thick channel with lower crustal viscosity (<5×10^(18) Pa.s). The different rheologies inferred at these different time-scales could be explained by a Burgers body rheology of the middle and lower crust, with a short-term viscosity of 10^(18) Pa.s and long-term viscosity of 10^(20) Pa.s, or even better by vertical variations of viscosity. To illustrate the latter claim, we show that the observations at the decadal and Holocene time scales can be reconciled by assuming a low viscosity zone (10^(18) Pa.s) at mid-crustal depth (between ∼10 and 30 km depth) embedded in a higher viscosity crust (>10^(20) Pa.s). In both cases, the interferences in space of the deformation signals induced by the lakes geometry, and in time through the viscoelastic response to the lake level variations results in limited distortion of the paleo-shorelines. While the elastic lid in the upper crust needs in any case to be thin (<10 km), the low amplitude distortion requires significant viscoelastic support from the lower crust and upper mantle; this explains the relatively high effective elastic thickness (>20 km) inferred in some previous studies of Holocene paleoshorelines. In the longer term, the effective elastic thickness of the lithosphere must drop asymptotically to the value of the elastic lid in the upper crust (<10 km); this explains the low effective elastic thickness derived from gravity studies.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2018.11.014DOIArticle
https://doi.org/10.1016/j.epsl.2018.12.017DOIErratum
Additional Information:© 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Received 16 April 2018, Revised 2 November 2018, Accepted 5 November 2018, Available online 20 November 2018. This study was partially supported by NSF award EAR-1821853. We thank Marie-Pierre Doin for providing the data used for the analysis of the ground deformation driven by modern water level variations of Siling Tso. We also thank one anonymous reviewer and Philip England for insightful comments that considerably help improve this contribution.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-1821853
Subject Keywords:viscosity; elastic thickness; paleoshorelines; Tibet
Record Number:CaltechAUTHORS:20181120-100648209
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20181120-100648209
Official Citation:Maxime Henriquet, Jean-Philippe Avouac, Bruce G. Bills, Crustal rheology of southern Tibet constrained from lake-induced viscoelastic deformation, Earth and Planetary Science Letters, Volume 506, 2019, Pages 308-322, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2018.11.014. (http://www.sciencedirect.com/science/article/pii/S0012821X18306654)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:91067
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Nov 2018 18:23
Last Modified:21 Dec 2018 17:34

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