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Near‐Fault Velocity Spectra From Laboratory Failures and Their Relation to Natural Ground Motion
Author(s) -
Beeler N. M.,
McLaskey Gregory C.,
Lockner David,
Kilgore Brian
Publication year - 2020
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2019jb017638
Subject(s) - overburden pressure , dissipation , spectral line , shearing (physics) , geology , slip (aerodynamics) , dissipative system , seismology , shear (geology) , strong ground motion , fault (geology) , kinetic energy , context (archaeology) , mineralogy , mechanics , geotechnical engineering , physics , petrology , ground motion , classical mechanics , paleontology , astronomy , quantum mechanics , thermodynamics
Abstract We compared near‐fault velocity spectra recorded during laboratory experiments to that of natural earthquakes. We fractured crystalline rock samples at room temperature and intermediate confining pressure (50 MPa). Subsequent slip events were generated on the fracture surfaces under higher confinement (300 MPa). Velocity spectra from rock fracture resemble the inverse frequency (1/ f ) decay of natural earthquake velocity. This spectrum can be attributed to fault creation via seismic fracturing over a wide range of spatial scales. In contrast, subsequent slips on the rough fracture surfaces are depleted in high frequency energy and falloff approximately as 1/ f 2 . The 1/ f 2 spectrum is more consistent with a slider‐block model obeying static‐kinetic friction than a natural earthquake. The depleted high frequency content precludes the rough fault experiments from being directly analogous to natural sources. The suppression of high frequencies may have resulted from two possible factors: (1) the presence of a well‐developed shear zone and coseismic damping of the fault motion by dissipation within it or, in our favored interpretation, (2) a smaller amount of energy dissipated by shearing relative to the total energy release at elevated confining pressure. In context of the latter explanation, a unifying concept that applies to these experiments, earthquakes, ground motion, and models of complex radiated motion is that high frequency radiated energy is relatively enhanced when total energy release is nearly balanced within the source region by dissipative processes. This near‐critical energy release condition can be accessed at low normal stress in laboratory experiments.