Frictional Properties of Pelagic Sediments from the Northern Hikurangi Margin: Possible Implication for Fault Slip and Slip Cycles

Edgar Villegas, Rice University
Melodie French, Rice University
Julia Morgan, Rice University

Abstract

The Northern Hikurangi margin hosts multiple modes of fault slip at shallow depths (~6 km), including tsunamigenic earthquakes and slow-slip events (SSEs). The geologic mechanisms and stress conditions responsible for both observed seismic events still remains unknown. The International Discovery Program (IODP) Expedition 375 cored and recovered input sediments from the margin in order to understand how the physical properties that contribute to different slip modes occur during subduction. To determine the frictional strength and evolution of the pelagic sediments that may contribute to slip, long-term slide-hold-slide friction experiments were conducted on input pelagic sediments from site U1520 consisting of a clay-bearing marl (~700-710 mbsf) and clay-poor muddy chalk (~815-825 mbsf). Experiments were conducted in an axisymmetric triaxial sawcut configuration at various effective pressures and temperatures. Frictional strength was measured at an axial displacement rate of 0.1 um/s and holds were performed every 0.5 mm of displacement for durations between 10 and 1,000,000 seconds. Preliminary results show time-dependent strengthening of both marl and chalk at high (70 MPa) and low (21 MPa) effective pressures. Initial shear tests show that marl is weaker (μ ≈ 0.3) than the muddy chalk(μ ≈ 0.6) at low shear displacements (1 mm). However, holds result in permanent time-dependent strengthening, rather than the transient strengthening typical of slide-hold-slide tests or strain-dependent hardening common in friction experiments. Time-dependent strengthening indicates the operation of chemical processes that contribute to fault strength and slip cycles that should be considered in models.

Session

Convergent and transpressional orogens