Intermittent Granular Dynamics at a Seismogenic Plate Boundary

Area of Science:

• Tectonophysics
• Geophysics
• Statistical Mechanics

Background:

• Earthquakes originate from differential motion of tectonic blocks within complex fault networks at plate boundaries.
• Accumulation of elastic strain occurs at slow rates (10^-15 s^-1), released intermittently (>100 yr) as rapid coseismic ruptures.
• Modeling quasistatic tectonic dynamics is challenging due to complexities in fault system behavior and poorly constrained tectonic structure length scales.

Purpose of the Study:

• To analyze interseismic motion fluctuations in Southern California's plate boundary using Global Positioning System (GPS) data.
• To investigate the scaling behavior of tectonic block movements and identify characteristic length scales.
• To explore the applicability of granular media models to plate boundary dynamics.

Main Methods:

• Analysis of Global Positioning System (GPS) observations of interseismic motion in the Southern California plate boundary.
• Statistical analysis of velocity fluctuations to identify heavy-tailed scaling behavior.
• Comparison of observed correlation functions with those typical of granular media.

Main Results:

• Velocity fluctuations in the Southern California plate boundary exhibit heavy-tailed scaling, deviating from Gaussian distributions.
• The correlation function of these fluctuations decays as a stretched exponential, similar to slowly sheared granular media.
• A characteristic tectonic length scale of 91±20 km is predicted, representing the average size of tectonic blocks.

Conclusions:

• The Southern California plate boundary can be modeled as a densely packed granular medium.
• This granular framework explains the observed scaling behavior and predicts a characteristic tectonic block size.
• The model relates earthquake recurrence intervals and slip behaviors to granular dynamics and strain rates.