3D architecture and complex behavior along the simple central San Andreas fault

Area of Science:

• Geophysics
• Tectonics
• Seismology

Background:

• The central San Andreas Fault (CSAF) has a simple large-scale geometry but complex seismic and aseismic deformation.
• Understanding the fault's fine-scale structure is crucial for predicting earthquake behavior.

Purpose of the Study:

• To investigate fault zone behaviors along the CSAF using geodetic data, seismicity, and microearthquake focal mechanisms.
• To reveal the 3D fine-scale structure and interseismic kinematics of the CSAF.
• To relate fault architecture to future faulting behavior.

Main Methods:

• Analysis of 75,164 earthquakes (M l ≥ 1) from 1984 to 2015.
• Application of an improved focal-mechanism characterization method using relative earthquake radiation patterns.
• Integration of geodetic observations and seismicity data.

Main Results:

• First-order variations in creep rate, creep direction, and stress field are explained by a simple fault coupling model.
• Inferred 3D mechanical properties reveal a weak and poorly coupled fault zone.
• Complex kinematics are unified by understanding distributed slip deficits, stress heterogeneities, and multi-scale ruptures.

Conclusions:

• The CSAF's complex deformation arises from its fine-scale mechanical properties.
• A weak and poorly coupled fault zone facilitates diverse seismic and aseismic behaviors.
• Detailed mapping provides insights into potential future faulting patterns.