“Fast” and “slow” earthquakes are two modes of energy release caused by the slips in a tectonic fault rupture. Fast quakes are swift, powerful, and destructive, while slow ones are drawn-out and relatively mild. However, many of the details of such earthquakes are poorly understood. Now, Professor Ching-Shung Chang of the UMass Amherst Civil and Environmental Engineering Department is providing enlightenment on this subject with his pioneering research as described in a recent issue of the esteemed journal, Proceedings of the National Academy of Sciences (PNAS). One key aspect of the PNAS paper is that Chang’s study has developed an innovative exploration technique, which could ultimately lead to a means of predicting devastating earthquakes before they occur, thus saving many lives. 

According to a release by the School of Science at the University of Tokyo, “Fast earthquakes are violent shakes lasting for a few minutes; slow earthquakes are subdued shakes lasting several days. Understanding slow earthquakes might help forecast fast earthquakes.” 

The trailblazing research conducted by Chang offers insights into the link between the mechanisms of slow and fast earthquakes.

When Chang recently spoke to the UMass Amherst News Office about his PNAS research, he gave this background about his research. “When two tectonic plates push against each other, the stresses gradually build up and then suddenly they have a slip. When the slip happens, it releases a tremendous amount of energy, and that energy will turn into seismic waves and create the shaking of the earth.” 

This is the backstory of Chang’s research, as he explained in his PNAS paper. “Herein, we report on ring-shear experiments with an ultrahigh sampling rate (10 MHz) that illuminate the different physical mechanisms between fast and slow slip events.” 

Chang’s study demonstrates that slip events have extremely brief durations, spanning from dozens to hundreds of milliseconds. He said that, when zooming into each slip event, numerous intriguing sub-events can be observed.

In that context, Chang and his team have developed a new technique that drastically slices the measurement span of a ring-shear experiment for studying earthquakes from the state-of-the-art 0.01 second to one-millionth of a second (or one megahertz). Consequently, the new technique is significantly more adept at revealing detailed events compared to current measurement methods. 

As Chang explained, “So, we can split a second into 1 million divisions and then see what happens [to an earthquake] in that period.”

Chang's groundbreaking research and his innovative exploration technique carry significant implications. Through this advanced approach, he can discern distinct and very revealing dynamic patterns preceding earthquakes. As a result, his work holds the eventual potential to enable the forecasting of earthquake events, predicting whether these events will manifest as fast, intense, violent shakes lasting a few minutes, or slow, subdued, less-destructive shakes persisting over several days. In that way, Chang’s research could lead to saving many lives in many places around the world.

As Chang concluded, “This study may be used to reveal the mechanism of fault slips during fast and slow earthquakes, which explain the potential effect of fast and slow slips on stress redistribution and structural rearrangement in faults.” (December 2023)

Article posted in Research