Fault healing promotes high-frequency earthquakes in laboratory experiments and on natural faults

Laboratory experiments and seismological observations show that increased fault healing causes a disproportionately large amount of high-frequency seismic radiation to be produced during fault rupture, which may help to explain recent observations of large megathrust earthquakes. A geological fault can heal, given time and no further disturbance. Here, Gregory McLaskey et al. describe laboratory experiments and seismological observations that show how increased healing causes a disproportionately large amount of high-frequency seismic radiation to be produced during fault rupture. This may help to explain recent observations from large megathrust earthquakes, which indicate that energetic high-frequency seismic radiation originates from locations that are distinct from the geodetically inferred locations of large-amplitude fault slip. Faults strengthen or heal with time in stationary contact1,2, and this healing may be an essential ingredient for the generation of earthquakes1,2,3. In the laboratory, healing is thought to be the result of thermally activated mechanisms that weld together micrometre-sized asperity contacts on the fault surface, but the relationship between laboratory measures of fault healing and the seismically observable properties of earthquakes is at present not well defined. Here we report on laboratory experiments and seismological observations that show how the spectral properties of earthquakes vary as a function of fault healing time. In the laboratory, we find that increased healing causes a disproportionately large amount of high-frequency seismic radiation to be produced during fault rupture. We observe a similar connection between earthquake spectra and recurrence time for repeating earthquake sequences on natural faults. Healing rates depend on pressure, temperature4 and mineralogy1, so the connection between seismicity and healing may help to explain recent observations of large megathrust earthquakes which indicate that energetic, high-frequency seismic radiation originates from locations that are distinct from the geodetically inferred locations of large-amplitude fault slip5,6,7.