Faults and EQ Processes National Meeting Summary Report

Faults and EQ Processes
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• Co-Chair: Chris Marone
• Co-Chair: Ramon Arrowsmith
• Co-Chair: Vince Cronin

Workshops and important research activities

• International collaborations and data sharing
• Earthscope and Earthquake simulator efforts (SCEC)
• (Fault zone) Physics that control the slip variation +/- SAFOD and other FZ drilling efforts and surface exposures. Need Synthesis WORKSHOP Coordinate with SCEC. Need to bring more folks in. Lunar science analogy. (combine with above?)
• Laboratory experiments: slip rate variation and rheology, what do we need to know. Effects of chemistry, fault healing. How to deal with NVT? Spectrum of deformation behaviors along fault zones that we now recognize: fast eqs, creep, tremor. Lots of basic questions about how faults work. New lab capabilities to understand these phenomena? Upper and lower velocity strengthening zones.
• Dynamic rupture simulator physics (SCEC)
• Need to set out the traps where and what tools? (tie with 1 above)
• Look at the lessons of TA to make sure that the best archive of events (catalogs). Joint with ANSS, NRC. Seismic hazard identification in areas not well known. Do this sooner to help inform deployments.

Need good data from these events. Need to make near field observations. Need to set out the traps... Some political issues (Iran, China). Successes: Japan, Taiwan, Italy. What parts of the trap are missing? Strong motion instruments. Just ONE more record!! Big signals, so distribute lots of instruments (even high sample rate GPS receivers 50hz).

Triggering:
Static: Need accurate models for stress transfer. Develop standards for sharing slip models. Static: need stress accumulation rate (from strain accumulation rate) 5-8x variation in strain accumulation (models: Need to densify GPS data and add INSAR; interpolation and how to parameterize the fault zones), earthquake cycle effects, initial stress state is unknown. Dynamic triggering—important for Earthscope; still don’t know how the dynamic triggering occurs for earthquakes, tremor, slow slip, volcanic systems (fluid migration), e.g., Long Valley, frequency and amplitude thresholds.

What happens below onset of QP and what happens with respect to large rupture into the transitional zone? Lots of stress stored down there? Need some new ideas. Geodesy indicates stable sliding similar to that suggested for a-b curve. What happens up and downdip along the subduction interface?

• Lab data on effective stress from Vp and Vs
• Pore pressure, temperature, strain in the near field
• In situ measurements: thickness of shearing zone, Temperature(t), stress (variation in space)
• Lab data: friction, dilatancy, dynamic weakening mechanisms
• Material properties: serpentinite +smectites/chlorite and hydrous clay coatings and pressure solution fabrics (grain scale physics and chemistry) get the most out of the SAFOD samples. Why is shear so localized?

Scientific Targets for EarthScope

1. How does strain accumulate and release at plate boundaries and within the North American plate? Where is slip along a fault aseismic versus seismic? What are the structure and other properties of active fault zones? How do they affect the manner in which faults slip? How can we explain the observed space-time pattern of seismicity? How do earthquakes interact with and triggerone another?

2002 Snowbird report 1965 view of North America— soft gushy plate boundary Rewrite to indicate our understanding of the distributed nature of continental deformation.

2. How do earthquakes start, rupture, and stop? Do all earthquakes start from similar beginnings, or does the nucleation process determine the fi nal size of the earthquake? How do fault properties and rupture dynamics combine to control rupture propagation and extent? What causes the rupture to stop? How are earthquake ruptures on subduction zones different from those on crustal faults? What are the causes of intermediate depth earthquakes (such as the one under Seattle in January 2001), and do they vary with depth?

3. What is the absolute strength of faults and the surrounding lithosphere? Where are plate driving forces carried? Are faults relatively low-strength features? How do faults in different tectonic settings compare?

4. What structural and geological factors give rise to intraplate regions of seismic hazard and seismicity, such as the New Madrid zone?

5. How can we accurately predict earthquake induced ground motions over a wide frequency range? For example, what is the geometry and response of large sedimentary basins? How nonlinear is site response? visservices.sdsc.edu/projects/scec/terashake/

Related ideas from crustal def’m discussion

• Compliant fault zones: how widespread, what are implications for surface deformation models, how extensive are lateral variations in elastic moduli
• Post seismic strain rate changes and time dependent fault healing
• Elastic versus inelastic deformation are gradients controlled by material properties or strength variations.