Microplasticity effect in low-velocity zone induced by seismic wave

Егоров

2013

J Min Sci

The article studies velocities of P-waves and S-waves in a natural sandstone specimen exposed to axial thrust. The cylindrical core specimen 1 m long and 0.08 m in diameter is composed of different size blocks. Anomalous velocities of the P-waves and S-waves (4-6 kHz) have been revealed by measurements taken in the whole specimen, in its separate blocks and at contacts surfaces between the blocks. The velocities in the whole specimen are much smaller than in its separate blocks. The interblock contacts detain and decelerate the waves. With smaller spacing at the contacts between the blocks, the wave velocities linearly drop to anomalously low vales (hundreds m/s). With higher pressure on the specimen, the wave velocities nonlinearly grow and the time delay reduces. The curve V P / V S -pressure has a peak (1 MPa) that appears for separate blocks and for the whole specimen. The anomalous velocities V P and V S are alleged to appear due to inelastic processes at microcontact surfaces under acoustic wave propagation in the blocky medium.

Section: Resultsmentioning

confidence: 93%

Anomalous P-Wave and S-Wave velocities in a blocky natural sandstone specimen

Егоров

2013

J Min Sci

“…The presence of local inelasticity (in particular, rock microplasticity) offers a reasonable explanation of an unusual increase in wave velocity and decrease in attenuation with increasing amplitude detected in some experiments (Johnston and Toksoz 1980;Mashinskii 2004Mashinskii , 2007aMashinskii , 2008Mashinskii , 2012bZaitsev et al 1999). Microplasticity mechanism does not refute the well-known mechanisms but expands availability of traditional models that show the opposite situation with amplitude dependence of seismic parameters: the wave velocity decreases and the attenuation increases with increasing amplitude (Mavko 1979;Winkler, Nur, and Gladwin 1979;Tutuncu, Podio, and Sharma 1994;Ostrovsky and Johnston 2001).…”

Section: Introductionmentioning

confidence: 79%

“…The laboratory investigations performed on the dry and saturated sandstone under confining pressure showed that attenuation, in comparison with velocity, is more sensitive to the strain-amplitude variations (Mashinskii 2006(Mashinskii , 2007a. This study goes on both the experimental and theoretical plans (Mashinskii 2008(Mashinskii , 2010(Mashinskii , 2012b(Mashinskii , 2014Podladchikov 2008, 2010). Dynamic microplasticity in geologic materials is as yet little studied.…”

Section: Introductionmentioning

confidence: 93%

Dynamic microplasticity manifestation in consolidated sandstone in the acoustical frequency range

Geophysical Prospecting

2016

Self Cite

Microplasticity manifestations caused by acoustical wave in the frequency range of about 4.5 kHz–7.0 kHz are detected in consolidated artificial sandstone. Equipment was tested by means of comparison of data obtained for a standard material (aluminium) and sandstone. Microplasticity manifestations in acoustic records are present in the form of the ladder‐like changes in the amplitude course. The stress plateaus in the acoustic trace interrupt the amplitude course, transform the wavefront, and shift the arrival time along the time axis. Microplasticity contribution to the acoustic record changes with the increase in the strain amplitude value. The combined elastic–microplastic process conditions the wavefront steepness and its duration. Stress plateaus exert influence on the waveform and, accordingly, on pulse frequency response. These results confirm the earlier data obtained for weakly consolidated rock. This contribution to wave propagation physics can be useful in solving applied problems, as, for instance, the reservoir properties prediction by means of wave attenuation in acoustic logging and seismic prospecting.

“…The most probable cause of this phenomenon is microplasticity, as the step-wise discontinuity of the elastic deformation observed in the quasistatic curves of ) (ε σ was the result of the microplasticity [19,21]. This effect of local inelasticity induced in weak-consolidated rocks by a seismic wave is named the seismo-microplasticity phenomenon (SMP) [26,27]. Fig.…”

Section: Results Of the Experimentsmentioning

confidence: 99%

“…The first estimate of the events of the dynamic microplasticity using the high-resolution seismic signal recording was attempted in the work [26]. The microplasticity effect induced by a seismic wave was described in [27]. As like as not, there is another mechanism analogous to the microplasticity.…”

Section: Introductionmentioning

confidence: 99%

Dynamic microplasticity phenomenon in rocks during P-wave propagation

2014

J Min Sci

The article describes local microplastic inelasticity in loam during propagation of P-wave with a frequency of 240-1000 Hz between two shallow wells, one holding piezoelectric radiator and the other containing piezoelectric receiver. The seismic record displays microplasticity phenomenon as the step-wise changes of the signal amplitude with time and the flat sections in the curve from microsecond to dozens microseconds long. These plateaus create short-terms breaks of the process-the time lags that depend on the signal amplitude. As a result, the first arrival time of the wave is changed, and the wave is transformed. It is presumable that microplasticity is conditioned by stress concentration at different defects. The research findings can be used in solving applied problems in mining engineering and seismology.Keywords: Local inelasticity, dynamic microplasticity, time lag and deformations, inelastic seismic parameters, amplitude dependence of wave velocities and attenuation.