observations from the field and the taboratory show that en echelon fractures withinfracture zones have a foede1 within Ricdel structure’ The tensile fallure mecbanism of en echelonfractures can be described by the p...observations from the field and the taboratory show that en echelon fractures withinfracture zones have a foede1 within Ricdel structure’ The tensile fallure mecbanism of en echelonfractures can be described by the pile-ups of sbear crack-dislocations. A fractal model can be used tosimulate the Riedel within Xiedel geometry, allowing the direct rneasarement of tbe ftactal dimen sions of en echelon fractare systems. The energy dissipation of tbe en ccbe1on fracture system canbe deduced using a fracil damage evo1ution model which exptalns tbe evo1ution process of en eche lon fracture svstems. The fractal nature of the fractures can be used to dcrive an accurate estimateof total energy dissipation.展开更多
The paper deals with the mechanical origin and rules of en echelon folds and their secondary fractures by means of elastic stability theory and nonlinear fracture criterion.Obtains the quantitative relations among en ...The paper deals with the mechanical origin and rules of en echelon folds and their secondary fractures by means of elastic stability theory and nonlinear fracture criterion.Obtains the quantitative relations among en echelon angles of en echelon folds,ratios of boundary stresses and en echelon pitches of shear zone under an action of general boundary forces(tension shear,pure shear or compression shear).As an applied example,the paper researches the displacement field,stress field,distortion energy distribution, state of secondary fractures and energy released by fracturing of en echelon fold structure developed at the east foot of Taihang Mountain.The results of research show that maximum principal (compressive) stresses,maximum shear stresses,high value area of distortion energy are in the nuclear parts of en echelon folds.In these parts compressive fractures were easily developed in approximately parallel with fold axis.So it is verified that the secondary fracture of en echelon folds is a mechanism controlling a strong earthquake.展开更多
The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure a...The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure and prominent unconformities. We employ EBM and 2DMOVE softwares to explore the subsidence history and stratigraphic development history of the basin. We found a rapid subsidence period since 15.5 Ma. Moreover, we calculated the stretching factors of the upper crust and the whole crust in the Huizhou sag. The results show the values are 1.10–1.13 and 1.08–1.31, respectively, indicating faulting in Huizhou sag is relatively small. It is noteworthy that the faults map reveals en echelon distribution at the north and south margins of the basin. We suggest en echelon faults here are caused by the subduction of Proto-South China Sea toward NW Borneo block and cease of the South China Sea. Considering the pronounced unconformities, subsidence rates, fault activities and sediment thickness, the Cenozoic tectonic evolution of the basin can be divided into rifting（49–32 Ma）, post-rifted（32–15.5 Ma） and rapid subsidence（15.5–0 Ma） stages. Our study will shed new light on the tectonics of SE Asia and petroleum exploration in the South China Sea.展开更多
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 struc...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.展开更多
A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sampl...A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ1 and σ2. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may con-tain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models.展开更多
文摘observations from the field and the taboratory show that en echelon fractures withinfracture zones have a foede1 within Ricdel structure’ The tensile fallure mecbanism of en echelonfractures can be described by the pile-ups of sbear crack-dislocations. A fractal model can be used tosimulate the Riedel within Xiedel geometry, allowing the direct rneasarement of tbe ftactal dimen sions of en echelon fractare systems. The energy dissipation of tbe en ccbe1on fracture system canbe deduced using a fracil damage evo1ution model which exptalns tbe evo1ution process of en eche lon fracture svstems. The fractal nature of the fractures can be used to dcrive an accurate estimateof total energy dissipation.
文摘The paper deals with the mechanical origin and rules of en echelon folds and their secondary fractures by means of elastic stability theory and nonlinear fracture criterion.Obtains the quantitative relations among en echelon angles of en echelon folds,ratios of boundary stresses and en echelon pitches of shear zone under an action of general boundary forces(tension shear,pure shear or compression shear).As an applied example,the paper researches the displacement field,stress field,distortion energy distribution, state of secondary fractures and energy released by fracturing of en echelon fold structure developed at the east foot of Taihang Mountain.The results of research show that maximum principal (compressive) stresses,maximum shear stresses,high value area of distortion energy are in the nuclear parts of en echelon folds.In these parts compressive fractures were easily developed in approximately parallel with fold axis.So it is verified that the secondary fracture of en echelon folds is a mechanism controlling a strong earthquake.
基金supported by grants from the Natural Science Foundation of China (Nos. 41272121 , 91028009 , 41302082)the Program of Introducing Talents of Discipline to Universities (No. B14031)
文摘The Huizhou sag is situated on the continental shelf of the northern continental margin of the South China Sea. In this paper we present a grid of reflection seismic and well data to characterize the basin structure and prominent unconformities. We employ EBM and 2DMOVE softwares to explore the subsidence history and stratigraphic development history of the basin. We found a rapid subsidence period since 15.5 Ma. Moreover, we calculated the stretching factors of the upper crust and the whole crust in the Huizhou sag. The results show the values are 1.10–1.13 and 1.08–1.31, respectively, indicating faulting in Huizhou sag is relatively small. It is noteworthy that the faults map reveals en echelon distribution at the north and south margins of the basin. We suggest en echelon faults here are caused by the subduction of Proto-South China Sea toward NW Borneo block and cease of the South China Sea. Considering the pronounced unconformities, subsidence rates, fault activities and sediment thickness, the Cenozoic tectonic evolution of the basin can be divided into rifting（49–32 Ma）, post-rifted（32–15.5 Ma） and rapid subsidence（15.5–0 Ma） stages. Our study will shed new light on the tectonics of SE Asia and petroleum exploration in the South China Sea.
基金Project Study on the Short-term Forecasting Technique of Strong Earthquake (01-04-01) during the Tenth Five-Year Plan from Ministry of Science and Technology of China and Joint Seismological Science Foundation of China (102037).
文摘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.
基金National Natural Science Foundation of China (Grant No. 40072067) and Minister of Science and Technology of China (2004BA601B01).
文摘A preliminary study of b value of rocks with two kinds of structural models has been made on the base of a new acoustic emission recording system. It shows that b value of the sample decreases obviously when the sample with compressive en echelon faults changes into a tensile one after interchange occurs between stress axis σ1 and σ2. A similar experiment is observed when the sample with tensile en echelon faults changes into that with a bend fault after two segments of the en echelon fault linking up. These facts indicate that the variation of b value may con-tain the information of the regional dominant structural model. Therefore, b-value analyses could be a new method for studying regional dominant structural models.
