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A Workshop to Begin Building a Community Rheology Model (CRM) of the Southern California Lithosphere

Conveners: Liz Hearn, Wayne Thatcher, Yuri Fialko, Greg Hirth, Gary Fuis, and Thorsten Becker
Date: September 12, 2015 (09:00-17:00)
Location: Hilton Palm Springs Resort, Palm Springs, CA
Attendance: Contact the conveners if you are interested in attending.
SCEC Award: 15147

OVERVIEW: Constraining the rheology of the lithosphere is important to several SCEC goals. For example, development of a Community Stress Model (CSM) depends on determining forces that drive and resist motion and how these forces are mediated through crust and mantle rheology. On shorter timescales, understanding the structure and rheology of the crust and upper mantle is essential for modeling earthquake-cycle deformation, including post-seismic transients that contribute to the present-day surface deformation rate field and bias fault slip rate estimates. The CRM will enable modelers to tackle scientific questions that require sophisticated representations of lithosphere rheology (i.e., beyond linear elasticity), in an informed, scientifically defensible and reproducible manner. The development of a new CRM will leverage results from several of SCEC’s ongoing community models. In particular, better constraints on the 3D distribution of rock types are needed to constrain rock rheology in both the brittle/elastic and ductile lithosphere. The USR group’s work plan to improve the CVM, CFM and the USR itself will all feed directly into improved constraints on rheology. The SDOT group’s goals of improving understanding of fault loading on timescales of tens to millions of years also depend on an improved understanding rheology.

We propose developing a repository of bulk rock and shear zone rheologies based on composition, temperature and (for power-law flow) assumed strain rate. The foundation of this repository will be three products, two of which will be new for SCEC5. First, we will add to the SCEC USR a 3D representation of subsurface rock type and major lithologic boundaries in the southern California, starting with a crustal layer thickness model, including associated uncertainties. Second, we will continue development of a regional, 3D thermal model. SCEC is currently developing a standard thermal model (the Community Thermal Model, or CTM) that prescribes the lithosphere temperature field beneath southern California with uncertainties. Third, a range of quantitatively prescribed fault slip and bulk rheological rules will be compiled that users may consult and apply at their choosing to incorporate into a particular CRM with follow-on applications. Rock type, temperature and flow laws will be available upon querying the model at geographical coordinates (latitude, longitude and depth). Future versions of the CRM could be united with SDOT geodynamic models to provide stress estimates, which are required as input for power-law flow. The CRM will initially include default strain rates for application of nonlinear viscous flow laws.

WORKSHOP GOALS: The all day workshop will include about 30 invitees and involve both invited presentations by leaders of appropriate CRM sub-disciplines and unstructured group discussion. Its goal will be to bolster scientific buy in to the CRM endeavor; explore particularly challenging issues requiring new work; and make recommendations for research priorities during the final year of SCEC4 (via t!he RFP) and staged, longer term research activities during SCEC5.

PARTICIPANTS: Brad Aagaard (USGS), Thorsten Becker (USC), Whitney Behr (UT Austin), Rachel Bernard (U Texas), Glenn Biasi (UNR), Roland Burgmann (UC Berkeley), Rufus Catchings (USGS), David Chapman (USGS), Fred Chester (TAMU), Judi Chester (TAMU), Mele Deepa (Nanyang Technological University), Yuri Fialko (UC San Diego), Gary Fuis (USGS), Patrick Fulton (UCSC), Jeanne Hardebeck (USGS), Egill Hauksson (Caltech), Liz Hearn (Capstone Geophysics), Greg Hirth (Brown), Bill Holt (SUNY), Nadia Lapusta (Caltech), Laurent Montesi (U Maryland), John Platt (USC), Phil Skemer (Washington U), Wayne Thatcher (USGS), and Terry Tullis (Brown)

SEPTEMBER 12, 2015

Presentation slides may be downloaded by clicking the title of the presentation.
PLEASE NOTE: Files are the author’s property. They may contain unpublished or preliminary information and should only be used while viewing the talk.

08:30-09:00 Workshop Check-In; Continental Breakfast  
09:00-09:20 Overview on CRM goals and ingredients
  • CRM goals and plan per SCEC5 proposal
  • Outcomes from this workshop
  • Structure of today's workshop
Liz Hearn
09:20-09:30 Discussion  
09:30-10:00 Active-source results for southern California; comparison with noise-source Vs modeling (PDF, 6.6MB) Gary Fuis
10:00-10:15 Earthquake-source Vp and Vp/Vs modeling of southern CA; interpretation of top and bottom of seismogenic zone Egill Hauksson
10:15-10:30 Interpretation of Vp/Vs in the shallow crust from active source studies Rufus Catchings
10:30-11:00 Directed Discussion Gary Fuis and All
11:00-11:15 Break  
11:15-11:40 A Road Map to Incorporating Rheology into CRM (PDF, 4.6MB) Greg Hirth
11:40-11:55 The problem (and potential) of using seismic anisotropy to constrain effective viscosity and strain localization in Southern California Phil Skemer
11:55-12:10 Constraints from xenoliths on the rheology of southern California lower crust and lithospheric mantle Whitney Behr
12:10-12:25 Integrating fault zone microstructural observations with rock mechanics data Fred Chester
12:25-13:00 Directed Discussion Greg Hirth and All
13:00-14:00 Lunch  
14:00-14:25 How can the CRM contribute to improved understanding of secular and transient deformation in Southern California and loading of seismogenic faults? (PDF, 7.6MB) Yuri Fialko
14:25-14:40 Role of boundary conditions and mechanical models (PDF, 3.0MB) Thorsten Becker
14:40-14:55 Effects of heterogeneous rheology on deformation, inferred slip rates and inferred stresses Liz Hearn
14:55-15:10 Linear rheologies versus lab-derived flow laws and heterogeneity of lithospheric deformation (PDF, 1.8MB) Roland Bürgmann
15:10-15:30 Directed Discussion Yuri Fialko and All
15:30-15:45 Break  
15:45-17:00 Wrap-Up Session: How to put all the pieces together
  • Perspectives on disciplinary sessions: 5-minute summaries and discussions
  • Next steps: Priorities for SCEC4 2016 RFP; SCEC5 objectives and staged interim goals; discussion
Liz Hearn and Co-PI's
17:00 Adjourn  


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