No abstract

In the paper "Determination of rock friction constitutive parameters using an iterative least squares inversion method" by Linda A. Reinen and John D. Weeks (Journal of Geophysical Research, 98(B9), 15,937-15,950, 1993), on page 15,938, a line is missing from the last paragraph in the second column. The complete paragraph appears below. Because the values of the model parameters can be several orders of magnitude different (e.g., a = 0.0013, Dc2 = 105.5 [from Reinen et al., 1991, Figure 3a]), the elements in G can also range over several orders of magnitude. In order to reduce errors arising from machine precision, we normalize each variable so that the length (the square root of the sum of the squares of the elements) of each column of G is unity. This procedure nondimensionalizes G and reduces machine rounding errors.

Serpentine is common in many active faults and may be responsible for aseismic creep along segments of these faults. To test this, we have conducted a series of velocity stepping experiments to determine the frictional velocity dependence of serpentinite. We slid initially bare, rough surfaces of antigorite serpentinite at room temperature, with velocities from 0.0032 to 10.0 μm/s (1.0×102 to 3.2×105 mm/yr) and normal stresses from 25 to 125 MPa. We find that the velocity dependence of serpentinite undergoes a transition from velocity weakening at fast loading velocities to velocity strengthening at slow velocities and that this change is accompanied by other changes in the constitutive behavior. These results suggest that serpentinite should not be the site of instability initiation during sliding at plate velocities, but may permit propagation of unstable slip initiated elsewhere.

Room‐temperature experiments on antigorite serpentinite indicate that at least two mechanisms accommodate frictional sliding of the serpentinite: a rate‐weakening, history‐dependent mechanism which dominates at fast slip velocities and a rate‐strengthening mechanism with no apparent history dependence which dominates at slow velocities. We present a two‐mechanism model that successfully describes the two types of behavior observed in the friction experimental data without changing the constitutive parameters over the range of experimental conditions. Multiple mechanisms have been identified in higher‐temperature experiments by previous workers and may be required for proper representation of all rock types at low slip rates and elevated temperatures.