New Research on Earthquakes and Fault Weakening

In today's issue of Nature, Ze've Reches and David A. Lockner present new insights into the mechanics of earthquakes. According to the authors, it isn't all about tectonics. As Reches explains to Nature, "The gradual buildup of stress in a fault as plates collide or slide past each other is necessary. But if nothing else were going on, all the pent-up energy could be released via fault creep, a motion so sluggish it's virtually unnoticeable by human standards, and the temblors that create so much havoc across the globe wouldn't exist."

The paper, Fault weakening and earthquake instability by powder lubrication, explores the role of fault gouge in the weakening -- and strengthening -- of faults during the course of an earthquake. According to the research, depending on the stage of the earthquake, fault gouge may either increase or decrease friction between the plates.

This project is an interesting example of modeling as a research technique. Because it would be virtually impossible to test their hypothesis in an actual earthquake, they created an apparatus in the lab to simulate the friction, speed and movement along fault lines. This allowed them to systematically record how fault gouge contributes to the earthquake process, and identify how gouge essentially acts in the same manner as industrial lubricants.

a, b, Blocks of Sierra White granite after experiment 652. LB, lower block; UB, upper block; SR, sliding ring; EG, gouge ejected. Note adhered gouge coating on the sliding ring (a) and heaps of ejected gouge on the lower block (b). c, Close-up view of a sliding surface showing adhered gouge and gouge layer. d, SEM image with melted-like area in which glass ‘glues’ fine angular grains (test 556). e, Atomic force microscope image of gouge grains of test 670 on glass plate; note the submicrometre grains and agglomerated grains in the lower left corner.

Their research can be found in full for free online here.