fs01.epsPS document27KExpanded view of a portion of experiment p2393 (see Figure 1c) showing shear stress (solid line) and small AE precursors (circles) as a function of time during stick-slip events. The AE precursors are plotted according to their relative strain amplitude, which varies from 3x10-9 – 5x10-8. Note that precursory AEs begin late in the stick-slip cycle and the rate of occurrence increases as stress increases to failure. The AE amplitude increases as time-to-failure approaches zero as well. Stress drop and recurrence interval are noted. Here the shear stress signal is left unsmoothed to show the electro-magnetic spikes. Spurious spikes are eliminated in Fig. 2b (inset) to illustrate only the stress drop behavior.
fs02.epsPS document5640KCumulative number of micro-slip events in each successive group of precursors preceding a slip event for (a) the entire experiment p2393 and (b) for a portion of the experiment. (c) All data for the full experiment shown in (a) plotted on the same figure, with each characteristic slip event set to time = 0.
fs03.epsPS document18KBlock motion with the AE, friction, and thickness as a function of time for experiment p2393. (a) The block displacement is shown by the thick dark curve, the friction is shown as the thin line, and the AE are shown as open circles. (b) Thickness of the gouge layers (thick solid line, with scale). At the time of a stick-slip event, the central block shown in Fig. 1 stops abruptly. The frictional force builds rapidly (region I) via the driving RAM, and continues to force the system linearly with time via the stiff spring. The central block then begins to slip ‘silently and slowly’ (region II), followed eventually by precursor AE activity (region III) with associated stress drops. During the entire sequence, the displacement of the forcing RAM is linear in time.
fs04.epsPS document4036KOverview of experiment p2394. (a) Experimental protocol showing applied normal load versus time. (b) Friction versus time. (c) Recorded AE of the stick slip events versus time.
fs05.epsPS document595KRelative probability of AE event occurrence plotted versus magnitude (log-log scale), for all AE in experiment p2394. The AE from characteristic events, the stick-slips, are labeled. The slope of the precursor AE is denoted by the thin, dotted line.
fs06.epsPS document906KTime characteristics of slip as a function of the applied normal load for experiment p2394. (a) Time to slip of the first AE in each successive sequence. (b) Time to slip of the last AE in each successive sequence.
fs07.epsPS document1194KAE preceding slip for individual normal loads in experiment p2394. (a) through (f) show the results for 3-8 MPa, respectively. The data at 2 MPa did not contain a sufficient number of stick-slip events to obtain a clear signal. The upgoing and downgoing applied normal loads (at a given load level) are combined in this figure. The slope of the exponential increase in AE activity (linear in log-log space) is noted for loads greater than 3 MPa.
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