The Earth’s tectonic plates are perpetually on the move, but witnessing a slow earthquake as it unfolds is a remarkable feat, previously unachieved. Typically, earthquakes we register result from a rapid rupture or slip between two plates. However, scientists have, for the first time, recorded this elusive phenomenon, providing valuable insights into its mysterious nature.
Slow earthquakes are challenging to detect because they can span days, weeks, or even months without obvious indicators. A groundbreaking effort by researchers at the University of Texas at Austin has successfully captured the dynamics of this event. By focusing on the tsunami-generating fault in Nankai, Japan, they utilized advanced drilling sensors to monitor minuscule movements in the critical offshore zone, where the fault nears the ocean floor.
The first recorded observation occurred in 2015, with a slow-slip earthquake tracing the fault’s path. A second occurrence followed the same trajectory in 2020. As detailed in the Science journal, researchers describe the phenomenon as beginning 30 kilometers inland and migrating seaward at a pace of 1 to 2 kilometers per day, eventually nearing or breaching the trench. These movements coincide with the emergence of tremors and very-low-frequency earthquakes, occurring in a region characterized by high pore fluid pressure and low stress. This provides compelling evidence connecting these conditions to shallow slow earthquakes.
These events reflect decompression movements of the fault and suggest that the deeper fault areas might function like shock absorbers, releasing pressure without sudden jolts. Additionally, both occurrences took place in zones where geological fluid pressure exceeded normal levels, highlighting the significant role of these fluids in slow-slip earthquakes.
This discovery not only advances our understanding of seismic faults but also aids in unraveling the complexities of slow-slip earthquakes, a subject still shrouded in enigma.
