Stiffness in faulting and in friction experiments

Analysis shows that the ‘stiffness’ characteristic of large earthquakes is 4 or 5 orders of magnitude less than the ‘stiffness’ characteristic of typical laboratory experiments on rock. Direct application of laboratory experiments to sliding on faults is therefore uncertain. This discrepancy does not necessarily invalidate the suggestion that earthquakes may be large-scale stick-slip sliding, because stick slip is enhanced in machines with low stiffness.