Advancements in seismometer technology have greatly increased the ability to track minor earthquakes, according to a release from Penn State University. Experts only began to notice the slow quakes about a decade ago.
The advances have also put a wrinkle into traditional concepts of fault line function. So far, researchers say no one has been able to explain the processes that cause the slow, minor earthquakes, which can last minutes, compared to larger, more powerful quakes that last only a few seconds.
There have been explorations into the type of rock involved in the slow quakes and Penn State researchers say clay-rich fault rocks may be of significance. In lab experiments, they found that the clay rocks initially withstood replicated fault shearing but became weaker over the long run and more likely to slip.