Preseismic Fault Creep and Elastic Wave Amplitude Precursors Scale With Lab Earthquake Magnitude for the Continuum of Tectonic Failure Modes. Issue 8 (20th April 2020)

• Record Type: Journal Article
• Authors: Shreedharan, Srisharan; Bolton, David Chas; Rivière, Jacques; Marone, Chris
• Is Part Of: Geophysical research letters. Volume 47:Issue 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-04-20
• Subjects: earthquake precursors -- earthquake prediction -- transmissivity -- acoustic signals -- fault creep -- slow slip; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2020GL086986
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Tectonic faults fail in a continuum of modes from slow earthquakes to elastodynamic rupture. Precursory variations in elastic wavespeed and amplitude, interpreted as indicators of imminent failure, have been observed in limited natural settings and lab experiments where they are thought to arise from contact rejuvenation and microcracking within and around the fault zone. However, the physical mechanisms and connections to fault creep are poorly understood. Here we vary loading stiffness during frictional shear to generate a range of slip modes and measure fault zone properties using transmitted elastic waves. We find that elastic wave amplitudes show clear changes before fault failure. The temporal onset of amplitude reduction scales with lab earthquake magnitude and the magnitude of this reduction varies with fault slip. Our data provide clear evidence of precursors to lab earthquakes and suggest that continuous seismic monitoring could be useful for assessing fault state and seismic hazard potential. Plain Language Summary: Earthquakes in nature can occur slowly, over many days, or rapidly within a few seconds or minutes. In a few cases geoscientists have reported, in hindsight, "precursory" changes in seismic velocities, groundwater levels, and elastic wave attenuation that occurred prior to earthquakes. The ability to robustly identify these signals and accurately attribute them to imminent earthquakes could have a profound effect on our hazard preparedness, particularly for coastal communities where tsunamis occur. Here we study lab earthquakes and use acoustic pulses to image the faults. We show that elastic wave amplitude decreases systematically before failure, providing a clear precursor to failure. The magnitude of this lab earthquake precursor is related to the amount of pre‐earthquake fault slip during both slow and fast laboratory earthquakes. Key Points: P ‐wave amplitudes reduce at the onset of preseismic creep for laboratory earthquakes The size and onset of amplitude precursors scale with lab earthquake size and fault slip rate The microphysical mechanisms responsible for amplitude precursors are similar for the spectrum of fault slip modes