KCC - J-DESC

Received
date

Oct. 1, 2023

Repository Core Re-Discovery

Proposal No.

No. 003

Program (ReCoRD)

RevisedNew /New(Above For Official Use Only)

Proposal Form
Basic Information
Title: Understanding the Formation Process and Physical Property
Distribution of the Upper Prism in the Japan Trench
Keywords: Japan Trench, Upper prism, Physical properties, Formation(5 or less) process, Deformation history
Lead Proponent: Nana Kamiya
Affiliation: Kyoto University
Address: C1-1-110 C-cluster, Kyoto Daigaku Katsura, Nishikyo-ku, Kyoto,
615-8540, Japan
Phone: +81 75 383 3403
E-mail: Kamiya.nana.4h@kyoto-u.ac.jp
Permission is granted to post the proposal contents on www.j-desc.org.
☒ Granted.
☐ Not Granted.

Scientific Objectives (250 words or less)
The Japan Trench is an erosional subduction zone, where the shallow part of theplate boundary fault was thought to have neither strain accumulation nor slip
propagation due to the non-asperity nature of the shallow plate boundary. However,the 2011 off the Pacific coast of Tohoku earthquake demonstrated that the shallow
part has the potential to generate a large slip during an earthquake.
IODP Exp. 343 (JFAST), which conducted drilling in the shallow part of the plateboundary at the Japan Trench, found that the plate boundary fault had been developed
in low-friction pelagic claystone and that strain had been accumulated in the frontal
prism of the hanging wall and stress was released during the earthquake. On the otherhand, because of limited sample recovery from the upper prism during the JFAST,
structural development processes and material characteristics of the upper prism
have not been clarified.
1 / 8

The objectives of this project are (1) to elucidate the formation processes of thehanging wall where strain accumulates, and (2) to clarify the temporal and spatialphysical and structural characteristics of the sediments in the hanging wall. These
objectives will contribute to the understanding of the pre-, co-, and post-seismic
processes of a mega-earthquake. To achieve this goal, we plan to construct a gammaray stratigraphy, measure the anisotropy of various physical properties, and perform
microstructural analysis. The structural and physical characteristics obtained in thisproject are comparable with these not only from JFAST but also from JTRACK.

Proposed Target Cores
Leg/Exp.

Site-HoleCoresLeg 56

Site 434-Hole B

1-4, 7-11, 14-20, 24-28, 30, 32-37

Leg 57Site 440-Hole B

1, 3-43, 45-71

Leg 56Site 436

1-42

Leg 57Site 439

14-15, 36, 38

Exp. 343

C0019

1-10, 12-16, 19-21(Only observation and sampling)

Add lines as needed[Note: Only cores in KCC are available.]

Proposed analysis prior to sampling
Analyses by X-ray CT and MSCL at the Kochi Core Center is required prior to thesampling. X-ray CT scans of the cores (AH) will be compared with core structure
description and will be used to estimate continuous density distribution using CTvalues. MSCL (natural gamma ray, gamma ray density, elastic wave velocity, andresistivity) scans of the cores (AH) are important measurements for qualifying thefundamental physical properties of the samples, and also for obtaining more precise
density estimation. Natural gamma rays, in particular, are essential for contrasting thelitho-stratigraphy of the all drilling sites.
[Note: Please describe above any analysis needed prior to sampling. Standard set is Xray CT, split core image (WH and/or AH), microscopic imaging of smear slide
and/or thin section.]

2 / 8

Summary of previous studies of the target cores
DSDP Leg 56, Site 436, is located seaward of the trench and is an important input site
for understanding the structure of the incoming oceanic crust; Site 436 reachedapproximately 0-400 m below the seafloor (mbsf) and drilled cores consist mainly of
Holocene to Eocene mudstones and, at the deepest depth, Cretaceous chert was identified.
Overall, the sediments consist of diatom-rich hemipelagic sediments with volcaniclastics(Langseth et al., 1980). Kameda et al. (2015) conducted mineral analyses of the core samples
from Site 436 and found a smectite concentration of >60 wt% in the uppermost pelagic clay(360 - 366 mbsf), which is contrasted with the plate boundary fault zone at the JFAST site.
Sawai et al. (2014) performed friction experiments using this clay layer and found that theclay layer has low-friction over a wide range of slip velocities. Thus, Site 436 has been used as
an analog for upper prism tips and plate boundary faults.
DSDP Leg 56, Sites 434 and 439, and Leg 57, Site 440 are located landward of thetrench and are important for understanding the deformation structure of the upper prism;
Site 434 is the closest to the trench and penetrated the tip of frontal prism. The main
lithological components are terrigenous silty clay, biogenic silica, and vitric ash, which aresimilar to the Neogene sediments in the surrounding sites. Significant hardening wasobserved at 100 mbsf, and slicken lines are visible on fracture fragments and fracture surfaces(Langseth et al., 1980). Site 440 corresponds to a slope section that is landward of the frontalprism. Samples from this site consist mainly of homogeneous semi-pelagic mudstones withsimilar mineral composition to the landward sites (e.g., Site 439). Several age discontinuities
have been identified in the Miocene and Pliocene sediments, and angular conglomeration wasobserved at depths where the sediments hardened (von Huene et al., 1980). Site 439 is themost landward of the three sites, and its upper section consists mainly of clay minerals such asmontmorillonite, illite, and chlorite, similar to Site 436 (Langseth et al., 1980).

3 / 8

In Legs 56 and 57 of the DSDP, no X-ray CT or natural gamma-ray data were collected,
and the lithology of the sites were not compared with those of other drill sites, thus only asketchy stratigraphic comparison based on age estimations is available. The microstructural
analyses such as magnetic fabric and pore geometry have also not been investigated. By
acquiring these data at both of the input and the upper prism sites, it will be possible tocorrelate the litho-stratigraphy and to discuss the history of structural development.
IODP Exp. 343 (JFAST), C0019 was drilled targeting at a depth of 820 mbsf, which isthe equivalent depth of the plate boundary fault, in the east of the Oshika Peninsula, Miyagi
Prefecture. This site is located at the frontal prism at the south of the drilling sites of DSDP Leg
56. The analyses of drilled cores, logging, and borehole observations revealed differences indeformation structures between the upper and lower part of the fault (Chester et al., 2013;
Kirkpatrick et al., 2014), and the frictional property and permeability of the fault are highly
specific due to clay minerals (Ujiie et al., 2013; Fulton et al., 2013). Furthermore, stressanalysis showed that the accumulated stress was released during the earthquake, suggestingthat strain was accumulated even at the frontal prism (Lin et al., 2013). Despite many
discoveries as described above, because the drilling was conducted at the only one site, thediversity and universality of the constituent lithologies and physicochemical properties of thefaults orthogonal and parallel to the trench remained unclear.

Proponent ListNameAffiliation

Position

Country

Nana Kamiya

Kyoto University

Assistant
Professor

Japan

Physicalproperty

Yohei Hamada

JAMSTEC

Researcher Japan

Logging

Keisuke
Nakamoto*

Hokkaido University

Ph.D.
student

Sedimentology

Hanaya Okuda

JAMSTEC

Researcher Japan

Japan

ExpertiseRockmechanics

4 / 8

Yoshitaka
Kochi University
Professor
Japan
Structure
HashimotoGeology[Note: For proponents who do not have J-DESC memberships, please put an asterisk (*)
AFTER his/her name.]

5 / 8