While the tectonic plates on Earth are constantly moving, it is very difficult to observe a slow earthquake in real time. In fact, the earthquakes that are recorded are those resulting from a sudden break or slip between two distinct plates. However, scientists have managed to record this type of phenomenon for the first time ever.
It is important to note that this type of event is still poorly understood by science. What’s more, it is quite difficult to record. A slow earthquake can take days, weeks, or months to occur, without any apparent signals.
A team from the University of Texas at Austin achieved this feat by recording the propagation of the earthquake when tectonic pressure was released along the tsunami-generating fault in Nankai, Japan. To achieve this, the researchers used drilling sensors capable of detecting the slightest movements, placed in the critical area offshore. This is where the fault is closest to the seabed.
As a result, the first observation took place in 2015, when a slow-slip earthquake ran along the tail of the fault. Subsequently, in 2020, a second earthquake occurred, following the same trajectory. In the journal Science, researchers explain the following: “Slip initiates ~30 kilometers landward of the trench; migrates seaward at 1 to 2 kilometers per day to within a few kilometers of, and possibly breaching, the trench; and coincides with the onset and migration of tremor and/or very-low-frequency earthquakes. The SSE source region lies in a zone of high pore fluid pressure and low stress, which provides clear observational evidence linking these factors to shallow slow earthquakes.“
These two events correspond to decompression movements of the fault. But that’s not all, as researchers also point out that this discovery suggests that this deep part of the fault acts more like a shock absorber, relieving pressure without generating sudden tremors. Furthermore, they occurred in areas where geological fluid pressure was higher than normal, indicating that these fluids play a major role in slow earthquakes. Thus, this discovery could help researchers better understand the functioning of seismic faults and slow-slip earthquakes, which are still poorly understood.
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