Exploring Hydraulic Structures of Subduction Faults Through Deep-Ocean Drilling

This article discusses the IODP Expedition 405’s drilling of the Japan Trench subduction fault to investigate its hydraulic state post the 2011 Tohoku earthquake. Preliminary findings suggest fault healing may limit fluid flow and store mechanical energy, enhancing the risk of future seismic events. This research aims to bridge gaps in understanding subduction zone mechanisms and improve disaster preparedness.

In the aftermath of the 2011 Tohoku-Oki earthquake (Mw 9.0) and its devastating tsunami, which affected the northeastern coast of Japan, scientists have undertaken significant explorations to better understand the mechanics behind subduction zone earthquakes. The tsunami, which reached a maximum height of 40 meters, was exacerbated by an unprecedented slip of up to 50 meters along the subduction boundary that caused considerable seafloor displacement. These events have highlighted substantial gaps in our comprehension of the processes governing subduction zones, particularly the role of high-pressure fluids in facilitating fault movement. To deepen this understanding, the International Ocean Discovery Program (IODP) Expedition 405, scheduled for autumn 2024, engaged in drilling the Japan Trench subduction boundary fault. This endeavor aimed to gather critical data regarding the hydraulic state of the fault several years post the 2011 earthquake. Preliminary findings from this expedition suggest that the fault rocks, previously damaged during the quake, may have re-cemented, resulting in restricted fluid flow along the fault line. This phenomenon of fault healing could potentially store significant mechanical energy, which might accumulate until it is released in a subsequent earthquake. These insights are poised to enhance our understanding of the impact of fluids on fault healing through seismic cycles at the Japan Trench, ultimately aiming to improve preparedness for future tsunami and earthquake events.

The Tohoku-Oki earthquake serves as a stark reminder of the potential for catastrophic seismic events in subduction zones, where one tectonic plate is forced beneath another. The resulting tsunami and fault slip were greater than previously anticipated, stressing the need for further investigation into the hydraulic properties of these faults. Recent hypotheses posit that fluid dynamics may influence fault behavior, particularly during major earthquakes. Accessing these deeply submerged faults is logistically challenging, yet insights gleaned from the IODP’s exploration efforts are crucial in understanding the mechanics underlying these geological phenomena.

The ongoing research into the hydraulic properties of the Japan Trench’s subduction boundary faults is vital for advancing our comprehension of earthquake mechanics. Initial findings from the IODP expedition indicate potential fault healing, which may contribute to increased seismic risks in the future. By uncovering the intricate relationships between fluid dynamics and fault behavior, researchers aspire to bolster tsunami and earthquake preparedness, mitigating risks associated with these natural disasters.

Original Source: www.nature.com