Caltech engineers have offered substantial experimental evidence for a kind of seismic dispersion presently assumed to be responsible for the magnitude 9.0 earthquake that destroyed the Japanese shore in 2011.
Fault boundaries leading to major quakes
CHRISTIAN MIRANDA/AFP via Getty Images
Fine-grained gravel occurs along fault lines when they grind against one another.
Caltech researchers illustrated in a new report published in the journal Nature on June 1 that tiny gravel, known as rock gouge, initially stops earthquake propagation but later triggers seismic rebirth, resulting in severe ruptures.
According to Vito Rubino, research scientist and principal author of the study, the innovative experimental technique has enabled them to look into the earthquake process up close and identify essential elements of rupture propagation and friction growth in rock gouge, as per ScienceDaily.
As a result of the activation of co-seismic friction weakening processes, fault sections formerly assumed to operate as barriers against dynamic rupture may in fact host earthquakes, according to their results.
Rubino and his co-authors Nadia Lapusta, Lawrence A. Hanson, Jr., Professor of Mechanical Engineering and Geophysics, and Ares Rosakis, Theodore von Kármán Professor of Aeronautics and Mechanical Engineering, demonstrated in the paper that so-called "stable" or "creeping" faults are not immune to major ruptures after all, as previously thought.
Such faults form when tectonic plates slowly glide past one another without causing large earthquakes, such as the San Andreas Fault in central California, which is now creeping.
To create an earthquake simulation, the team first sliced a translucent meter-sized piece of Homalite in two.
Dynamical fracture nucleation can happen in samples as small as tens of centimeters in diameter, whereas rock samples would need tens of meters.
The scientists next delivered massive pressure and shear to both sides of the Homalite, simulating tectonic pressure along a fault line.
Fine-grained quartz powder was used as a stand-in for fault gouge between the pieces.
The scientists then connected the two sections with a short wire fuse, which served as the earthquake's "epicenter."
The majority of earthquakes are caused by movement in small zones along plate borders, as per California Academy.
The majority of seismic activity occurs along plate borders that are divergent, convergent, or transform.
When the plates pass one other, they might get trapped and generate considerable pressure.
Energy is released as seismic waves when the plates ultimately yield and slip, owing to excessive pressure, causing the earth to shake.
When two tectonic plates move from each other, this is known as spreading.
New crust is formed as molten rock from the mantle erupts along the hole.
Such expanding centers, or earthquakes, are usually mild. The Great Rift Valley in Africa, the Red Sea, and the Gulf of Aden were formed by divergence plate motion.
When plates travel towards each other and collide, this is called convergence.
Whenever a continental plate clashes with an oceanic lithosphere, the oceanic plate, which is thinner, denser, and more pliable, sinks beneath the thicker, more rigid continental plate.
Subduction is the term for this.
Subduction creates deep ocean trenches, such as the one off the coast of South America, wherein the rocks of the continent are being pulled down.
