Abstract
Faults exhibit a gamut of slip styles from stable sliding and creep events to earthquakes. These slip styles are affected by the fault properties, e.g., weakening or strengthening, and the properties of the loading system. Here, we investigate the poorly understood effect of energy-flux to the fault that should equal or exceed the energy-dissipation-rate along the slipping fault. We explore the relationship between energy-flux and slip style in shear experiments along granite and diorite laboratory faults, during which the faults were subjected to controlled energy-flux, and responded spontaneously to it. The monitored evolution of slip-velocity, shear stress, and slip-distance revealed three slip styles that depend on the applied energy-flux: (1) steady-state slip; (2) spontaneous creep events of small displacement with negligible weakening; and (3) spontaneous, unstable events with slip-velocities up to 0.8 m/s, slip-distances up to 0.5 m, and stress-drops up to 1 MPa, which are comparable to observed values of moderate earthquakes. These slip styles are similar in character to those observed along natural faults. We further propose that the rate of energy flow from crustal blocks can control the slip velocity during earthquakes.
Highlights
Earthquakes are fast slip events driven by the release of elastic energy that was accumulated in crustal blocks[1,2]
The active slip style on a given segment can be attributed to the composition of the gouge zone, environmental conditions[12,13,14,15]
In which the applied slip-velocity is controlled by the experimentalist[12,16,17,18], in the present experiments, we select the intensity of the energy-flux and allow the fault to respond spontaneously. We envision that this loading style may apply to natural fault loading which is controlled by the energy supply rate from the host crustal blocks
Summary
Earthquakes are fast slip events driven by the release of elastic energy that was accumulated in crustal blocks[1,2]. For example, a large strike-slip fault, like the San Andreas fault, for which the interseismic elastic energy is stored within a 50–100 km wide zone[3,10] (Fig. 1A) A large earthquake needs to drain the available elastic energy from the entire energy storage zone (Fig. 1B), and it could take 10–15 s for energy to reach the fault (assuming an energy flow rate equal to the shear wave speed) This finite time could bound the slip-velocity if the frictional dissipation rate exceeds the energy-flux. In which the applied slip-velocity is controlled by the experimentalist[12,16,17,18], in the present experiments, we select the intensity of the energy-flux and allow the fault to respond spontaneously We envision that this loading style may apply to natural fault loading which is controlled by the energy supply rate from the host crustal blocks. The stress-drops and slip-velocities associated with the observed slip events are comparable to other experiments and to earthquake observations
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