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Slow dynamics in the nonlinear elastic response of Berea sandstone
Author(s) -
Ten Cate James A.,
Shankland Thomas J.
Publication year - 1996
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/96gl02884
Subject(s) - bar (unit) , nonlinear system , resonance (particle physics) , softening , acceleration , amplitude , geology , dynamics (music) , bending , frequency response , modulus , mechanics , materials science , mineralogy , optics , physics , composite material , acoustics , classical mechanics , atomic physics , quantum mechanics , oceanography , electrical engineering , engineering
A typical resonance curve—measured acceleration versus drive frequency—made on a thin bar of rock shows peak bending with a softening (nonlinear) modulus as drive levels are increased. The shapes of these nonlinear resonance curves were found in earlier work to depend somewhat on sweep rate; these “slow dynamics” are now examined and quantified. We have measured slow dynamics in a 0.3 m long, 50 mm diameter bar of Berea sandstone under ambient conditions. Peak strain levels during the experiments ranged from 10 −11 to 10 −5 at driving frequencies near 4 kHz, the fundamental longitudinal resonance frequency of the bar. Slow dynamics begin to manifest themselves at strain amplitudes above 10 −6 at ambient conditions and at the onset of nonlinear peak bending. Strains above this value condition the rock, altering its response for minutes to hours after the drive has been turned off.