Studying earthquakes with a flywheel

Seismologists’ understanding of how rock surfaces behave when ground together in earthquake faults has been limited by their ability to conduct experiments that simulate the massive forces generated in a temblor.

For many years, researchers have simply taken two adjoining rock surfaces and placed pressure on them until they broke. This method, however, doesn’t come close to representing the force of large, damaging earthquakes.

Now, seismologists at University of Oklahoma and the U.S. Geological Survey say they have created a device that approximates the force exerted by a Magnitude 8 earthquake. The experiments are detailed this week in the journal Science.

The so-called rotary shear apparatus is similar to a motorized pottery wheel in that it uses large, spinning flywheel to support a disc of rock.

The flywheel is spun at high speed. When it reaches the desired velocity, a fast-acting clutch is used to press the rock disc against a second rock disc immediately above it. The two stone surfaces rub against each other until friction stops and slows the movement.

Lead author Jefferson Chang, a geologist at the University of Oklahoma, said the device allows seismologists to simulate an “earthquake-like slip event.”

In an accompanying paper that also appeared in Science, geologist Toshihiko Shimamoto said the device and experiments would “arouse discussions about whether they are realistic proxies of natural earthquakes.”

monte.morin@latimes.com