The experimental investigation of micro-cracks nucleation in typical tectonics

Li, Shiyu; Teng, Chunyu; Lu, Z.; Xiaohong, Liu; Liu, Qiliang; He, Xinhao

doi:10.1007/s11589-000-0039-2

Cited by 5 publications

(3 citation statements)

References 7 publications

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“…About the creation mechanism for precursors of water level of wells, most scholars believe that it is related to focal process (FENG et al, 1984;HE, 2000;LI et al, 2000;MA et al, 2002) and caused by slow ruptures before large ruptures of fault for strong earthquakes. During the process, focal body would emit seismic wave caused by slow ruptures, whose frequency is very low.…”

Section: Responding Mechanisms For Water Level Of Wells To Precursorsmentioning

confidence: 99%

Analysis on responding ability of well-aquifer system to precursors

Shu-liang

et al. 2006

Acta Seimol. Sin.

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Recording number of precursors from fourteen observation wells in Shanxi, Hebei, Beijing and Jiangsu region is analyzed and percentage of recording number of precursors to total number of earthquakes during the statistic years is presented. The relationship between characteristic parameters of well-aquifer system and responding ability to precursors is analyzed by the expression of amplification factor of well-aquifer system induced by Cooper et al. The results indicate that responding ability of well-aquifer system to precursors is related to inherent period of well aquifer, that is to say, the greater the inherent period is, the stronger the ability of recording precursor is. Responding ability of well-aquifer system to precursors is also related to ratio of transmissivity to square of radius of wells, and the greater the ratio is, the stronger the responding ability is.

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Section: Responding Mechanisms For Water Level Of Wells To Precursorsmentioning

confidence: 99%

Analysis on responding ability of well-aquifer system to precursors

Shu-liang

et al. 2006

Acta Seimol. Sin.

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“…By the experimental techniques of acoustic emission (AE) and surface strain observation, a lot of achievements on the study of deformation and fracture process of samples with en-echelon faults has been obtained (Bomblakis, 1973;LIU, et al, 1986;DU, et al, 1989;ZHANG, FANG, 1989;MA, et al, 1995a, b;LI, et al, 2000). However, there still exist many problems.…”

Section: Introductionmentioning

confidence: 99%

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

Jiang

Zhang

et al. 2002

Acta Seimol. Sin.

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The spatio-temporal characteristics of acoustic emission (AE) during the deformation of rock samples with compressional and extensional en-echelon faults have been studied. The results show that the pre-existing structure can significantly influence the patterns of AE spatial distribution. With increasing of differential stress, AE events firstly cluster around the two ends of pre-existing faults inside the jog and then along the line joining the two ends. The biggish AE events often occur around one end repeatedly. The image of AE clusters indicates the direction and the area of the fracture propagation. The direction of the macroscopic fracture in extensional and compressional jogs is perpendicular and parallel to the direction of axial stress, respectively. The weakening process before the fracturing of jog area is remarkable, and one of the typical precursors for the instability is that the cumulative frequency of AE events increases exponentially. After the fracturing of the jog the frequency and releasing strain energy of AE events decrease gradually. During the friction period, there is no precursory increasing of AE activity before the big stick-slip events. The change of b value in jog shows a typical change of"decreasing tendentiously returning quickly" before the instability. The decrease of b value occurs in the process of stress increasing and sometime goes down to the weakening stage, and the quick increase b values appears in a short time just before the instability. The comparative analysis shows that the difference in b value due to the different structures is larger than b value variation caused by increase of the differential stress. For the same sample, the temporal sequence of AE is strongly affected by the mechanical state, and the high loading velocity corresponds to the high release rate of strain energy and low b value. Due to its lower failure strength, the broken area is sensitive to small changes in differential stress. Therefore, it offers a potential explanation for the phenomena of "precursory window or sensitive point" and "separation of seismic source and precursors". Key words: acoustic emission; rock sample; compressionai en-echelon fault; extensional en-echelon fault; biaxial experiment; differential stress CLC number: P315.8 Document code: A *

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“…ATKINSON (1987) called the zone of microcrack development around the crack tip the process zone. LI et al (2000) used the intensity of penetrating light to study the degree of microcrack development around the tip of a prefabricated crack in a marble sample. In our fracture test of plexiglass samples under biaxial compression we found that shadow areas appeared around the prefabricated crack and at its tips, however the shadow area seemed to be much larger than the plastic area estimated by fracture mechanics.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study of the Process Zone, Nucleation Zone and Plastic Area of Earthquakes by the Shadow Optical Method of Caustics

Xu¹,

Yang²,

Zhao³

et al. 2002

Pure and Applied Geophysics

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On a plexiglass sample, a penetrating crack was prefabricated by laser. The crack is inclined towards the major principal stress r 1 ðr y Þ at an angle of about 30 . Using this sample and by means of shadow optical method of caustics and microcrack location, the process zone, nucleation zone and plastic area of earthquakes were studied experimentally, and the strain variation in the shadow area was monitored. From the result, we comprehend the following. When the stress r y was increased to a certain value, shadow areas were formed around the prefabricated crack and at its tips, with that at the tips being larger. These shadow areas become larger with the increase of load and smaller with unloading. In the shadow area the strain was inhomogeneous: it was very large in some places but very small in others. When the shadow area reached a critical state, microcracks appeared at the tips of the prefabricated crack. Microcracks appeared on one side of the prefabricated crack where the strain and the shadow were both smaller. The zone with concentrated microcracks, or the process zone, was always located at the crack tip; this zone together with a half length of the original crack formed the nucleation zone which fell into the shadow area but was smaller than it. The shadow optical area of caustics bears a certain quantitative relation with the plastic area. Therefore, if an appropriate method is available to obtain the shadow optical area of caustics, it would be possible to detect the area with strong differential deformation change, and hence to determine the zone where strong fracture (an earthquake) would take place.

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The experimental investigation of micro-cracks nucleation in typical tectonics

Cited by 5 publications

References 7 publications

Analysis on responding ability of well-aquifer system to precursors

Analysis on responding ability of well-aquifer system to precursors

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults

Experimental Study of the Process Zone, Nucleation Zone and Plastic Area of Earthquakes by the Shadow Optical Method of Caustics

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