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doi:10.2204/iodp.proc.343343T.103.2013

Site C0019¹

Expedition 343/343T Scientists²

Introduction

The primary objective of drilling at Integrated Ocean Drilling Program (IODP) Site C0019 was to measure the fault zone physical properties, recover fault zone material, and directly record temperature from the fault zone responsible for a Mw 9.0 earthquake. The shallow distribution of large slip for the Tohoku-oki earthquake provides an unprecedented opportunity to directly access a fault that has recently moved tens of meters. The 2011 Tohoku-oki earthquake and tsunami originated from slip on the megathrust fault surface west of the Japan Trench where the Pacific plate subducts below Honshu Island. The subduction zone is characterized by a relatively rapid convergence rate of ~8 cm/y (e.g., Apel et al., 2006), a high level of seismic activity, and a deep trench.

Site C0019 science objectives, as summarized in the IODP Expedition 343 Scientific Prospectus (Mori et al., 2012), are closely aligned with the overall goals of IODP. In the IODP Initial Science Plan, research concerning solid earth cycles and geodynamics highlights the seismogenic zone initiative, which advocates subduction zone studies that include investigating the behavior of rocks and sediments to better understand the fault zone and integration with studies of earthquake mechanics. Furthermore, Expedition 343 Japan Trench Fast Drilling Project (JFAST) directly addresses Challenge 12 of the IODP Science Plan for 2013–2023: “What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami?” As outlined in the report from the International Continental Scientific Drilling Program (ICDP)/Southern California Earthquake Center (SCEC) international workshop on rapid response drilling (Brodsky et al., 2009), fundamental questions regarding stress, fault-related fluid flow, and the structural and mechanical characteristics of the earthquake rupture zone can be addressed uniquely through rapid response drilling at Site C0019:

1. What was the stress state on the fault that controlled rupture during the earthquake and was the stress completely released?

2. What is the temperature anomaly remaining from the frictional heat produced at the time of the earthquake (which can be used to infer the level of dynamic friction)?

3. How can we identify the fault zone in the core samples?

4. What will detailed analyses of textures and small-scale structures in the fault zone core samples imply about the role of fluids and pressurization during rupture?

Secondary science objectives include carrying out other geological, geochemical, and microbiological observations in accordance with the IODP measurements guidelines (www.iodp.org/program-policies/). As a specific example, there is some evidence that great amounts of hydrogen may be released at the time of large faulting (e.g., Kita et al., 1982). The massive amounts of hydrogen may greatly stimulate microbiological activity; thus, samples of the fault may contain records of biogeochemical and microbiological processes.

¹ Expedition 343/343T Scientists, 2013. Site C0019. In Chester, F.M., Mori, J., Eguchi, N., Toczko, S., and the Expedition 343/343T Scientists, Proc. IODP, 343/343T: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.343343T.103.2013

² Expedition 343/343T Scientists’ addresses.

Publication: 19 July 2013
MS 343343T-103

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