Fault behavior at and near Earth's surface

Johanna Nevitt

Submitted August 15, 2019, SCEC Contribution #9809, 2019 SCEC Annual Meeting Talk on Mon 1330

The question of “What is a fault zone?” in Earth’s shallow crust (<1 km depth) remains open-ended. In addition to expanding our knowledge of fundamental fault processes, answering this question has practical ramifications for hazard models, including the development of Probabilistic Fault Displacement Hazard Analyses in a physics-based framework, and the integration of slip rates into the Uniform California Earthquake Rupture Forecast and the USGS National Seismic Hazard Map.

The knowledge gap surrounding shallow fault processes stems largely from a historic lack of spatially-coherent geodetic data close to active faults, combined with an incomplete mechanical description of the weakly- to un- consolidated materials typically found near Earth’s surface. Recent and ongoing advances in geodetic imaging techniques are allowing us to accurately quantify near-fault deformation with unprecedented spatial resolution, often revealing a zone of distributed shearing (i.e., “off-fault deformation”) that is more complex than originally assumed. By combining near-field geodetic data with geological observations, fault zone drilling, shallow geophysical imaging, laboratory analysis, and mechanical modeling, we are now well-positioned to tackle a number of research questions regarding fault zone structure and behavior in the shallow crust, including:

(1) How do earthquake ruptures reach Earth’s surface? This includes the question of how fault behavior changes as the principal slip surface breaks down to echelon, mixed-mode (i.e., Riedel-type) fractures, along with the enigma of rupture deceleration and arrest in the very shallow crust (<50 m depth).

(2) Is the vertical distribution of fault slip uniform from the shallow crust up to Earth’s surface, or is there a systematic reduction of shallow fault slip?

(3) What is the relationship between compliant damage zones surrounding shallow faults and the distribution of shear deformation at Earth’s surface?

(4) What micro- and meso-scale mechanisms contribute to fault zone deformation and what is the appropriate rheological description?

Answering these questions will require multi-disciplinary collaboration across the earthquake science community and will constitute a big step forward in our understanding of fundamental fault processes and the associated hazards.

Citation
Nevitt, J. (2019, 08). Fault behavior at and near Earth's surface. Oral Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)