Lithologic control of frictional strength variations in subduction zone sediment inputs

Abstract

At convergent margins, marine sediments deposited seaward of the subduction zone forearc on the incoming plate (the "subduction inputs") represent the initial condition for geomechanical processes during subduction. The frictional strength of these sediments is a key parameter governing deformation during subduction, which is controlled to first order by lithologic composition. We combine here the results of laboratory friction experiments and quantification of mineral assemblage for scientific drilling samples recovered from three particularly well-studied subduction zones: the Nankai Trough (southwestern Japan), the Japan Trench (northeastern Japan), and Costa Rica. In the Japan Trench, frictionally weak smectite-rich pelagic clay contrasts sharply with stronger, more siliceous hemipelagic material. This strength contrast dictates the stratigraphic position of initial plate boundary formation and influences slip behavior of the shallow megathrust. In the Costa Rica subduction zone, relatively weak clay-rich hemipelagic sediment overlies frictionally strong pelagic nannofossil oozes and chalks, which could be a factor for the development of features such as a small amount of offscraping near the toe and subduction erosion where ooze or chalk dominates. In the Nankai Trough, however, a wide range of frictional strength values is observed that does not correlate with clay mineral content. In this case, mechanical behavior at Nankai is likely influenced by other factors related to diagenesis or fluid overpressuring.

Observations of Laboratory and Natural Slow Slip Events: Hikurangi Subduction Zone, New Zealand

“…Prior to these expeditions, scientific drilling in this region was limited to the sedimentary sequence on the subducting Pacific plate (~400 km east of the Hikurangi Trough) that was drilled during ODP Leg 181, at Site 1124 (Carter et al, ). Although the goals of Expedition 181 did not focus on plate‐boundary fault behavior, the incoming sediments at subduction zones are expected to be similar to those which constitute the shallow megathrust fault and are thus a valuable resource for investigating the mechanical behavior of the shallow plate boundary (e.g., Hüpers et al, ; Ikari et al, ; Underwood, ). The sample we use is a mixture of three core samples (20X‐5, 21X‐5, and 22X‐5) from Site 1124, which span a recovery depth from ~195 to 215 meters below seafloor (mbsf); this is the same sample used in a recent friction study by Rabinowitz et al ().…”

Frictional Strengths of Subduction Thrust Rocks in the Region of Shallow Slow Earthquakes

“…Observations of slow slip phenomena are more abundant from the downdip limit of the seismogenic zone where land-based seismic and geodetic networks have better resolution, but advanced processing methods and increasing ocean-bottom instrumentation has revealed similar events at the updip limit (Figure 1; e.g., Obana & Kodaira, 2009;Saffer & Wallace, 2015;Araki et al, 2017;Mcguire et al, 2018;Nakano et al, 2018). The predominant slip behavior at a given depth (i.e., earthquakes, slow slip, fault creep) is controlled by the frictional properties of subducting materials (Ikari et al, 2018;Saffer & Marone, 2003;Scholz, 1998), particularly in the shallow portion of subduction zones where dislocationand diffusion-creep are unlikely to occur due to low temperatures (Kohlstedt et al, 1995). Understanding the frictional properties of units typical of shallow subduction zones is therefore important for understanding the complex slip behavior of these environments.…”

Slow Slip Events Following the 2002 Mw 7.1 Hualien Offshore Earthquake Afterslip

“…Coulomb 3.3 uses the same dislocation equation (Okada 1992) to calculate the shear and normal stresses on the fault and then the Coulomb stresses. The friction coe cients in shallow subduction zones mainly range from 0.2 to 0.4 from drilling sites in Nankai Trough, Japan Trench, and Costa Rica (e.g., Ikari et al 2018;Namiki et al 2014). In the seismogenic zone, the friction coe cients are usually less than a peak value of 0.35 ± 0.04 along a subducting oceanic plate interface (Kaneki and Hirono 2019).…”