RHEOL_GUI: A Matlab-based graphical user interface for the interactive investigation of strength profiles

Laurent G. Montesi, & William Leete

Published August 14, 2018, SCEC Contribution #8500, 2018 SCEC Annual Meeting Poster #150 (PDF)

As a contribution to the Community Rheology Model we developed an intuitive tool for the exploration and study of strength profile. Built as a Matlab Graphical User Interface, this tool, called RHEOL_GUI, allows the user to define a stratigraphic column, associate to it a temperature profile, taken for example from the CTM, select for each stratigraphic layer rheologies and assumption on pore fluid pressure and grain size, and compute a strength profile. The tool also allows the user to compute an effective rheology (relation between strain rate and integrated strength) for the lithosphere as a whole, which can used for further modeling.

RHEOL_GUI v1.0 is open source and publicly available under the MIT license at https://github.com/montesi/RHEOL_GUI, doi:10.5281/zenodo.1341844. The package contains a database of rheologies, both brittle and ductile, for several rock types, taken from the literature. Grain size can be specified a priori or allowed to adjust to obey one of several available piezometric relationships to address the possibility of weakening the lithosphere at shear zones through grain size reduction.

As a demonstration, we consider an idealized structure of the Mojave tectonic block, composed of a 30 km thick crust (10 km quartzite and 20 km feldspar) over a 70 km thick lithospheric mantle. Brittle failure obeys Byerlee’s law, with a maximum strength of 300 MPa, and hydrostatic fluid pressure in the crust. Pore fluid pressure is 20% of lithostatic in the mantle. Diffusion and dislocation creep flow laws are taken from Hirth et al. (2001) for quartzite, Rybacki et al. (2006) for feldspar, and Hirth and Kohlstedt (2004) for olivine. Wet or dry rheologies are used in feldspar and wet rheology (fluid-saturated) for the olivine.

Integrated strength (average viscosity) is highly nonlinear, with an effective stress exponent in excess of 10. That is because, although ductile rheologies have n smaller than ~5, at least half of the stress is supported in the brittle regime. This implies that, with regards to long-term tectonics, even a small change of stress can have a dramatic effect on strain rate. Changing grain size can increase strain rate by about two orders of magnitude, but, especially at low strain rate, the largest effect comes from changing the lower crust rheology from dry to wet, implying that details of mineralogy and hydration state are very important for lithospheric strength.

Key Words
rheology, hydration, grain size

Citation
Montesi, L. G., & Leete, W. (2018, 08). RHEOL_GUI: A Matlab-based graphical user interface for the interactive investigation of strength profiles. Poster Presentation at 2018 SCEC Annual Meeting.

Related Projects & Working Groups
SCEC Community Models (CXM)