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- Title
Spatial Patterns in Frictional Behavior of Sediments Along the Kumano Transect in the Nankai Trough.
- Authors
Okuda, Hanaya; Ikari, Matt J.; Roesner, Alexander; Stanislowski, Katja; Hüpers, Andre; Yamaguchi, Asuka; Kopf, Achim J.
- Abstract
Fault slip activity at subduction zones is governed by sediment frictional properties, which in turn are affected by diagenetic processes. To study the spatial patterns in frictional properties across the Nankai Trough, SW Japan, and their relations to fault slip activity, we used sediment samples (10%–59% clay mineral content) along the Kumano transect covering a large spatial range from the inputs via the outer prism to the inner prism, including the deepest sample ever recovered to date. We performed laboratory friction experiments under in situ effective normal stresses and seawater‐saturated conditions. Our results generally demonstrate that the friction coefficient inversely correlates with the clay mineral content. However, the outer prism sediments show higher friction coefficients than sediments from the other locations for a comparable clay mineral content. All samples show velocity‐weakening behavior at low velocities, but the outer prism and the deep inner prism sediments show velocity strengthening at higher velocities. Based on the experimental results combined with a Coulomb wedge model, we propose that the lowest friction coefficient on the décollement occurs beneath the trenchward portion of the outer prism, whereas the minimum friction coefficient of the prism sediment occurs in the landward portion of the outer prism. In addition, the calculated critical nucleation length for slip instability suggests that the décollement beneath the outer prism area is more frictionally unstable than it is beneath the inner prism. This inference is consistent with the spatial distribution of very‐low‐frequency earthquakes and slow slip events along the shallow Nankai Trough. Plain Language Summary: Subduction zones host the largest earthquakes on earth, and such earthquakes cause severe damage to regions nearby. Therefore, how and where an earthquake is triggered are the most important questions for the future mitigation of seismic hazards. An important factor controlling seismicity is the frictional behavior of the subduction zone fault. In this study, we study the Nankai subduction zone, SW Japan, which hosts both fast and slow earthquakes. Conducting laboratory friction experiments, we examine the spatial patterns in frictional properties of sub‐seafloor sediments sampled by ocean drilling. Experimental results indicate that the friction coefficients of sediments vary with the position in the subduction system, which may reflect diagenetic processes or tectonic history. Combined with the topographical information, we estimate the friction coefficient of the plate boundary fault (décollement) and propose that the friction coefficient increases landward. Our results can provide useful information on the location of future fault slip activities at the Nankai Trough. Key Points: Friction measurements and Coulomb wedge modeling indicate that the décollement and prism strengths vary spatiallyNucleation length for slip instability suggests the décollement is more unstable beneath the outer prism than the inner prismOur results explain the spatial distribution of slip events at the shallow Nankai Trough
- Subjects
NANKAI Trough; SEDIMENTS; SUBDUCTION zones; EARTHQUAKES; NUCLEATION
- Publication
Journal of Geophysical Research. Solid Earth, 2021, Vol 126, Issue 11, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2021JB022546