Earthquakes are a dramatic and notable result of tectonic plate movement, causing destruction and death. Slow slip events, on the other hand, occur when tectonic forces are released gradually over days or months, resembling an earthquake in slow motion. While slow slip events may not cause physical destruction, their importance in understanding the earthquake cycle is significant, as they may help in predicting when earthquakes occur. In a recent study published in Geophysical Research Letters, a research group from the Jackson School of Geosciences investigated how rock permeability affects the frequency and intensity of slow slip events.
The research group collected rocks from New Zealand’s North Island, near the Hikurangi Margin, where slow slip events occur regularly. By testing the permeability and elastic properties of these rocks at the University of Texas, the researchers discovered that the pores in the rocks play a crucial role in controlling slow slip events at the subduction zone. A layer of impermeable rock at the top of the descending tectonic plate acts as a seal, trapping fluid in the underlying rock layers. The pressure from accumulated fluid eventually triggers a slow slip event or earthquake, breaking the seal and allowing the rocks to absorb fluids before healing and restarting the cycle.
Laura Wallace, a researcher specializing in slow slip events, highlighted the significance of this study in providing data to understand the time scales over which fault zone permeability changes occur. The research adds data constraints to explain the fault-valve process and fluid cycling at subduction zones, potentially influencing the observed cycles of slow slip events. The ultimate goal of this research is to comprehend the mechanisms behind earthquakes and develop a predictive model, a challenge that scientists have yet to conquer.
Future research will focus on analyzing rock samples from the center of the Hikurangi Margin to identify differences in permeability. Rocks at the northern end of the subduction zone are rich in clays, which can trap, fracture, and channel fluids, possibly explaining the frequent occurrence of slow slip events in that region. By understanding the reasons behind the variation in slow slip events between the northern and southern ends of the Hikurangi Margin, scientists aim to move closer to predicting earthquakes. Graduate students from the Jackson School of Geosciences also contributed to the study, emphasizing the collaborative effort in advancing knowledge of slow slip events and earthquake prediction.
