SCEC Award Number 19145 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Collaborative Research: What is the Rheology of Rocks within the Geological Framework?
Investigator(s)
Name Organization
Laurent Montesi University of Maryland Michael Oskin University of California, Davis
Other Participants
SCEC Priorities 3b, 1c, 1b SCEC Groups CXM, SDOT, Geodesy
Report Due Date 04/30/2020 Date Report Submitted 11/19/2020
Project Abstract
 This project developed effective rheologies for each of the 19 lithologies that appears in the Geological Framework. Each rheology is obtained by averaging, according to the MPG-e scheme of Huet et al., flow laws derived experimentally for each of the mineral types that define the lithologies. The result are expressed as set of parameters that enter a temperature- and pressure-dependent power-law relationship between stress and strain. Two set of results were provided, one in which the user needs to specify a water fugacity, and the other where default values of fugacity are embedded in the relation. The results were distributed in the CRM 20.9 release. These flow laws are used to generate strength envelopes for each block in the GFM. The strength of the middle crust is quite different between the lithology-derived flow laws and endmember mineral rheologies, which are used in most geodynamical studies. Other mixing schemes show that shear zone fabric can significantly change viscosity of rocks, especially gabbros and metamorphic rocks rich in biotite and feldspar.
Intellectual Merit This project demonstrates the importance of developing rock-specific flow laws rather than relying on end-member mineral flow laws. The depth to brittle-ductile transition in particular can be quite different, and the character of stratification of the strength profile can also be affected significantly by this choice. In this manner the glow laws generated here should be preferred in studies of fault loading and the dynamics of the region.
Broader Impacts The lithology-derived flow laws obtained here have been included in the CRM 20.9 release, available at https://www.scec.org/research/crm/ along with source code and a detailed documentation of the procedure needed to generate flow laws. Thus, the broader community can adopt this set of rheology of follow a similar approach in other regions of interest.
Exemplary Figure Figure 1: Strength profile for the Mojavia block using the CRM rheologies (colors) or a simpler model based on mineral endmembers only (dashed grey lines)
Credit: Montési, 2020.