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SCEC Community Rheology Model (CRM) Workshop & Field Trip

Conveners: Laurent Montesi and Elena Miranda
Date: February 27-28, 2023
Location: Kellogg West Conference Center, Pomona, CA
SCEC Award and Report: 22109

SUMMARY: The SCEC Community Rheology Model (CRM) provides a three-dimensional description of the ductile rheology of southern California’s lithosphere, based on constraints from seismic, geologic, and experimental rock deformation studies, and several rounds of community input during workshops such as this one. The September 2020 release comprised two components: a three-dimensional geologic framework model (GFM) of southern California’s crust, and a set of synthetic aggregate ductile flow laws for each GFM rock type. Together with SCEC Community Thermal Model (CTM) temperatures and pressure, this information provides a model for southern California’s ductile rheology. Given strain rate(s), effective viscosity and differential stress may be calculated throughout the region. We anticipate that the CRM will evolve as it is examined by the SCEC community, and all are welcome to participate in the TAG and contribute to future versions.

The CRM research priorities are to:

  1. Generate flow laws and/or guidance for the rheology of ductile shear zones.
  2. Generate flow laws or guidance for addressing transient rheology 
  3. Define a workflow for connecting the results of GF viewer queries to the code RHEOL_GUI (Montesi and Leete, 2018)
  4. Add brittle-plastic rheology (for bulk upper crust, sediments and shear zones) to the CRM 

The February 2023 workshop was held in-person, with the following objectives: 1) Present the latest version of the CRM to the broader community; 2) Discuss the relation between the CRM and other CXM components; 3) Initiate projects aimed at validating, refining, and extending the CRM; and 4) Inspire use of the CRM by the broader community. Session 1 included presentations describing the CRM as it stands and explain how it was built, to stimulate discussion about publications, dissemination, and access to this project. Sessions 2 and 3 were focused on looking ahead. They included round-table discussion and short "idea talks" from each participant. These talks ranged from what is currently missing in the CRM, on information or data they'd like to contribute to the effort, or on ideas for applications that may involve the CRM. By seeding ideas and discusions, we hoped to initiate exiting new projects and collaborations that make the CRM a more useful tool for the broader community.

The workshop was followed by a one-day field trip to local exposures of brittle and ductile shear zones in exhumed deep crustal rocks in Cucamonga Canyon. The southeast corner of the San Gabriel lithotectonic block exposes a thick section of sheared Cretaceous arc rocks that represent some of the deepest exposures of crust in the region (see figure). The close association of the Quaternary faults that bound the San Gabriel lithotectonic block (Cucamonga Fault, San Jacinto) and the Cretaceous ductile shear zone fabrics in the block demonstrates the potential for older rock fabrics to act as stress guides for younger, brittle structures associated with the San Andreas Fault system (Schulte-Pelkum et al., 2020). Including structure of this kind is a major ongoing effort of the CRM Working Group. The field trip will focus on the lower crustal Cucamonga mylonites and middle crustal Black Belt mylonites that comprise the shear zone exposed in the SE San Gabriel Block (Alf, 1948; May & Walker, 1989). The field trip will feature a traverse through the mylonites exposed in Cucamonga Canyon and the location where the mylonites are cut by the Quaternary Cucamonga Fault and its subsidiary brittle deformation (McPhillips & Scharer, 2018; Morton & Matti, 1987). 

Presentation slides may be downloaded by clicking the links following the title. PLEASE NOTE: Files are the author’s property. They may contain unpublished or preliminary information and should only be used while viewing the talk. Only the presentations for which SCEC has received permission to post publicly are included below.


09:00 - 09:30 Breakfast  
09:30 - 09:45 Session 0: Workshop objectives and SCEC update  
09:45 - 12:00 Session 1: Current Status of the CRM  
  - Status of the SCEC Community Models (CXM) (PDF, 4.5MB) Laurent Montesi
  - Community Thermal Model (CTM) Update Wayne Thatcher
  - Perspectives on Lithosphere Rheology through Integration of Experimental Rock Mechanics with - Geological and Geophysical Observations (PDF, 5MB) Greg Hirth
  - Community Rheology Model (CRM) Update (PDF, 3.8MB) Laurent Montesi
  - The Important of Shear Zones for the CRM (PDF, 2.7MB) Elena Miranda
  Discussion: feedback on current product and publication plans  
12:00 - 13:00 Lunch  
13:00 - 15:00 Session 2: Future CRM Development  
  Importance of the rheology of shallow on- and off-fault damage (PDF, 13.1MB) Alexis Ault
  - A "Brittle" Rheology Model? (PDF, 485KB) Nick Beeler
  Integrating the CVM constraints into CTM/CRM (PDF, 3.8MB) William Shinevar
  - Mantle flow distribution beneath the California margin (PDF, 12.9MB) Sylvain Barbot
15:15 - 15:30 Break  
15:30 17:00 Session 3: Using the CRM  
  - Crustal architecture across Southern California and its implications on San Andreas Fault development (PDF, 5.8MB) Bill Holt
  - Can Post-Ridgecrest Deformation Reveal Heterogeneous California Geology? (PDF, 1.6MB) Roland Bürgmann
  - Temperature Variations at the Base of the Seismogenic Zone in Southern California (PDF, 2MB) Laurent Montesi
  - Rheology: View from the field Nikki Seymour
  Discussion: Seed ideas for SCEC and other proposals  
  Session 4: Wrap-up  
17:00 - 17:30 Follow-up Plan, call for volunteers, SCEC request for proposals  
17:30 Adjourn  
18:00 Group Dinner at KWCC  


07:00 - 07:30 Breakfast for participants lodging at KWCC  
08:00 Vehicles depart from KWCC and Pasadena  
09:00 - 17:00 Vehicles arrive at the first field locality at the eastern edge of Cucamonga Canyon. Cucamonga Foothills Preservation Alliance (CFPA) will open gate for the vehicles to access.

The plan was to visit two field localities: (1) the Cucamonga mylonites near the Cucamonga Thrust, and (2) the Black Belt mylonites, further upstream of the Cucamonga mylonites. Due to inclement weather and safety concerns, we were not able to visit the second locality. The field trip leaders (Elena Miranda and Josh Schwartz) provided the group with a lab experience back at KWCC where we examined samples collected from the Black Belt mylonites and continued discussions about the CRM and what was seen on the field trip.

17:00 - 19:30 Group dinner at a local restaurant near Rancho Cucamonga  

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