Tracking Tsunamigenic Slip Across the Japan Trench (JTRACK)1
1 Kodaira, S., Conin, M., Fulton, P., Kirkpatrick, J., Regalla, C., Ujiie, K., Okutsu, N., Maeda, L., Toczko, S., and Eguchi, N., 2023. Expedition 405 Scientific Prospectus: Tracking Tsunamigenic Slip Across the Japan Trench (JTRACK). International Ocean Discovery Program. https://doi.org/
The 11 March 2011 M 9.0 Tohoku-oki earthquake was one of the largest earthquakes ever recorded and was accompanied by a devastating tsunami. Slip during the earthquake was exceptionally large at shallow depth on the plate boundary fault, which was one of the primary factors that contributed to the extreme tsunami amplitudes that inundated the coast of Japan. International Ocean Discovery Program Expedition 405 aims to investigate the conditions and processes that facilitated the extremely shallow slip on the subduction interface in the 2011 Tohoku-oki earthquake. Proposed work includes coring and logging operations at two sites in a transect across the trench. The first site, located within the overriding plate, will access the fault zone in the region of large shallow slip, targeting the plate boundary décollement, overlying frontal prism, and subducted units cut by the décollement. The second site, located on the Pacific plate, will access the undisturbed sedimentary and volcanic inputs to the subduction zone. A borehole observatory will be installed into the décollement and surrounding rocks to provide measurements of the temperature in and around the fault over the following several years. Sampling, geophysical logs, and the observatory temperature time series will document the compositional, structural, mechanical, and frictional properties of the rocks in the décollement and adjacent country rock, as well as the hydrogeologic structure and pore fluid pressure of the fault zone and frontal prism—key properties that influence the effective stress to facilitate earthquake slip and potential for large slip. Results from Expedition 405 will address fundamental questions about earthquake slip on subduction zones that may directly inform earthquake and tsunami hazard assessments around the world.
The magnitude 9.0 earthquake that occurred off the coast of northeast Japan on 11 March 2011 was one of the largest ever recorded and caused a devastating tsunami. The earthquake happened because two tectonic plates meet and are pushing past one another in a subduction zone under the ocean offshore Japan. During the earthquake, there was a lot of slip at a shallow depth along the subduction fault where the two tectonic plates meet. This shallow slip played a major role in generating the large tsunami waves that inundated the Japanese coast. The International Ocean Discovery Program Expedition 405 aims to investigate the conditions and processes that led to this shallow fault slip during the 2011 earthquake by collecting samples of the materials that are in and around the shallow fault and by installing sensors to monitor temperature and subseafloor fluids. These data will provide critical information about the composition, structure, mechanics, and fluids within the subduction fault and surrounding rocks that will help us understand the conditions that allow large shallow slip to occur. The findings from Expedition 405 will address fundamental questions about how earthquakes occur in subduction zones and can provide valuable insights for assessing earthquake and tsunami risks worldwide.