Fault Lines Can Also Slip Slowly

People usually find out very fast when two locked fault lines slip from each other's grip, as this is when earthquakes are produced. But new data analyzes how fault lines can slip against each other slowly, without triggering these powerful events.

In order to arrive at this conclusion, experts investigated the San Andreas Fault in central California, which is renowned for the earthquake risk it underlies. What the research team learned was that the fault line tended to register periods of accelerated slip.

These took place after earthquakes were produced at other locations around the world. This was also made apparent following the March 11, magnitude 9.0 tremor that devastated Japan.

Geologists found episodes of accelerated slip motion, but they say that the speed at which this process happened was still extremely small by our standards. Instances when this happens are known as creep events, experts say.

Using sensitive seismometers, it's possible for experts to discover such events, as they are accompanied by ground vibrations called tectonic tremors. These are not actual earthquakes because their magnitude is very reduced.

The new study and carried out by experts with the US Geological Survey (USGS) and Georgia Institute of Technology (Georgia Tech), revealed that large tremors, however distant, can cause creep events in the San Andreas fault line system.

Conceivably, this also happens at other locations around the world. This type of connection was not established before, and it paints a new picture of the factors collaborating to determine the overall activities of a fault system.

Details of the new work appear in a paper entitled “Triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes,” which is published in the latest online issue of the top journal Nature Geoscience.

“The researchers also noted that creep events in other locations can sometimes trigger earthquakes,” researchers at the USGS say in a press release.

“While they caution that their study was focused on triggered tremor rather than triggered earthquakes, they suggest that prolonged triggered creep episodes could be relevant for both phenomena,” they add.