Exploring the Hydraulic Structure of Subduction Faults through Deep-Ocean Drilling
The 2011 Tohoku-Oki earthquake highlighted the unpredictable nature of subduction zones, leading to a significant research endeavor by the IODP in autumn 2024. This expedition aims to analyze the hydraulic structure of the Japan Trench subduction boundary fault to understand fluid dynamics and fault healing, which could impact future seismic risk assessments and preparedness efforts.
The Tohoku-Oki earthquake, which registered a magnitude of 9.0, along with its consequential tsunami, inflicted considerable damage on Japan’s northeastern coastline in 2011. This event was marked by peak tsunami wave heights reaching up to 40 meters, a phenomenon precipitated by significant fault slip of approximately 50 meters along the subduction boundary, leading to substantial seafloor displacement near the trench. These remarkable figures were unexpected in the region, highlighting the current gaps in understanding seismic activity within subduction zones. Researchers propose that following major seismic events, high-pressure fluids may migrate along fault lines, providing lubrication that results in increased fault slip. Direct examination of these subduction boundary faults for their hydraulic properties presents a scientific challenge due to their considerable depth beneath the ocean surface. To address this issue, the International Ocean Discovery Program (IODP) Expedition 405 is scheduled to drill at the Japan Trench subduction boundary fault in autumn 2024, aimed at analyzing the hydraulic condition of the fault several years post the 2011 earthquake. Preliminary analyses suggest that the fault rocks, which suffered damage during the Tohoku earthquake, might have undergone a re-cementation process, effectively impeding fluid movement along the fault zone once again. This potential for fault healing implies the capability to store mechanical energy that could be released in the event of a subsequent earthquake. Gaining comprehensive insights into the role of fluids in the healing processes during the seismic cycle at the Japan Trench is pivotal for improving preparedness for future tsunami-induced earthquakes.
The mechanics of subduction zone earthquakes, including the pivotal role of fault slips and fluid dynamics, are crucial for understanding seismic risk. The 2011 Tohoku-Oki earthquake and tsunami presented a stark reminder of the gaps in current scientific predictions regarding earthquake behavior in subduction zones. Investigating these underwater faults is essential for uncovering the relationship between hydraulic properties and earthquake cycles, as understanding fluid movements can contribute to more accurate forecasting of seismic events and their potential consequences.
In summary, the research facilitated by IODP Expedition 405 seeks to enhance our understanding of subduction zone fault mechanics, particularly in relation to fluid behavior and its influence on fault dynamics following significant seismic events. Understanding these processes will not only provide key insights into fault healing but also temporarily facilitate more effective preparedness measures for future earthquakes and tsunamis in vulnerable regions such as Japan.
Original Source: www.nature.com
