The research on the rock burst prediction was made on the basis of seismology,rock mechanics and the data from Dongguashan Copper Mine(DCM) ,the deepest metal mine in China.The seismic responses to mining in DCM were ...The research on the rock burst prediction was made on the basis of seismology,rock mechanics and the data from Dongguashan Copper Mine(DCM) ,the deepest metal mine in China.The seismic responses to mining in DCM were investigated through the analyses of the spatio-temporal distribution of hypocenters,apparent stress and displacement of seismic events,and the process of the generation of hazardous seismicity in DCM was studied in the framework of the theory of asperity in the seismic source mechanism.A method of locating areas with hazardous seismicity and a conceptual model of hazardous seismic nucleation in DCM were proposed.A criterion of rockburst prediction was analyzed theoretically in the framework of unstable failure theories,and consequently,the rate of change in the ratio of the seismic stiffness of rock in a seismic nucleation area to that in surrounding area,dS/dt,is defined as an index of the rockburst prediction.The possibility of a rockburst will increase if dS/dt>0,and the possibility of rock burst will decrease if dS/dt<0.The correctness of these methods is demonstrated by analyses of rock failure cases in DCM.展开更多
In the paper, source mechanisms of 33 small-moderate earthquakes occurred in Yunnan are determined by modeling of regional waveforms from Yunnan digital seismic network. The result shows that most earthquakes occurred...In the paper, source mechanisms of 33 small-moderate earthquakes occurred in Yunnan are determined by modeling of regional waveforms from Yunnan digital seismic network. The result shows that most earthquakes occurred within or near the Chuandian rhombic block have strike-slip mechanism. The orientations of maximum compressive stresses obtained from source mechanism are changed from NNW-SSN to NS in the areas from north to south of the block, and tensile stresses are mainly in ENE-WSW or NE-SE. In the eastern Tibetan Plateau, the orientations of maximum compressive stress radiate toward outside from the plateau, and the tensile stress orientations mostly parallel to arc structures. Near 28N the orientations of both maximum compressive stress and tensile stress changed greatly, and the boundary seems to correspond to the southwestern extended line of Longmenshan fault. Outside of the Chuandian rhombic block, the orientations of P and T axes are some different from those within the block. The comparison shows that the source mechanism of small-moderate events presented in the paper is consistence with that of moderate-strong earthquakes determined by Harvard University, which means the source mechanism of small-moderate events can be used to study the tectonic stress field in this region.展开更多
The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs...The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.展开更多
Hot dry rock(HDR) is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management. High-temperature HDR resources were recently detected in deep reg...Hot dry rock(HDR) is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management. High-temperature HDR resources were recently detected in deep regions of the Gonghe Basin on the northeastern edge of the Tibetan Plateau, which led to a significant breakthrough in HDR resource exploration in China. This research analyzes the deep temperature distribution, radiogenic heat production, heat flow, and crustal thermal structure in the Qiaboqia Valley, Guide Plain, and Zhacanggou area of the Gonghe Basin based on geothermal exploration borehole logging data, rock thermophysical properties, and regional geophysical exploration data. The results are applied to discuss the heat accumulation mechanism of the HDR resources in the Gonghe Basin. The findings suggest that a low-velocity layer in the thickened crust of the Tibetan Plateau provides the most important source of constant intracrustal heat for the formation of HDR resources in the Gonghe Basin, whereas crustal thickening redistributes the concentrated layer of radioactive elements, which compensates for the relatively low heat production of the basal granite and serves as an important supplement to the heat of the HDR resources. The negative effect is that the downward curvature of the lithospheric upper mantle caused by crustal thickening leads to a small mantle heat flow component. As a result, the heat flows in the Qiaboqia Valley and Guide Plain of the Gonghe Basin are 106.2 and 77.6 m W/m2, respectively, in which the crust-mantle heat flow ratio of the former is 3.12:1, indicating a notably anomalous intracrustal thermal structure. In contrast, the crust-mantle heat flow ratio in the Guide Plain is 1.84:1, which reflects a typical hot crust-cold mantle thermal structure. The Guide Plain and Zhacanggou area show the same increasing temperature trend with depth, which reflects that their geothermal backgrounds and deep high-temperature environments are similar. These results provide important insight on the heat source mechanism of HDR resource formation in the Tibetan Plateau and useful guidance for future HDR resource exploration projects and target sites selection in similar areas.展开更多
A microseismic monitoring system was installed in an underground room and pillar coal mine in the Eastern United States to analyze the occurrence and characteristics of induced seismicity during the retreat of two pan...A microseismic monitoring system was installed in an underground room and pillar coal mine in the Eastern United States to analyze the occurrence and characteristics of induced seismicity during the retreat of two panels in the mine.This study is the first microseismic monitoring effort at an underground coal mine in nearly 30 years.During the retreat of the first panel,an array of eight uniaxial geophones,installed 10 ft.into the roof,recorded events and their magnitudes.The second panel was monitored using an array of twelve uniaxial geophones and two triaxial geophones,also installed 10 ft.into the roof.Comparing the results of these studies,it has been found that the magnitude of seismic events is minimally affected by immediate roof geology or depth of cover.However,it was observed in both studies that the rate at which seismic events occurred did vary with changing roof geology and depth of cover.Using the seismic data from the second panel retreat,focal mechanism solutions were generated for 50 hand-picked events in order to determine if the failure was in compression,tension,or shear.Results of the focal mechanism solutions show that stress relief resulting in dilational events occurs at significant depths,150-200 m in this case,beneath the active mining face.展开更多
Studies have been made on the source mechanism of acoustic emission produced by pitting corrosion. Methods for identifying pitting corrosion-related AE signals were proposed and the magnitude of surface displacement d...Studies have been made on the source mechanism of acoustic emission produced by pitting corrosion. Methods for identifying pitting corrosion-related AE signals were proposed and the magnitude of surface displacement due to single pitting was estimated. It is concluded that differentiation between background noise and corrosion induced genuine AE signal is possible through using plate wave acoustic emission theory combined with parameter analysis method.展开更多
For the 22-year solar cycle oscillation there is no external time dependent source. A nonlinear oscillation, the solar cycle must be generated internally, and Babcock-Leighton models apply an artificial nonlinear sour...For the 22-year solar cycle oscillation there is no external time dependent source. A nonlinear oscillation, the solar cycle must be generated internally, and Babcock-Leighton models apply an artificial nonlinear source term that can simulate the observations—which leaves open the question of the actual source mechanism for the solar cycle. Addressing this question, we propose to take guidance from the wave mechanism that generates the 2-year Quasi-biennial Oscillation (QBO) in the Earth atmosphere. Upward propagating gravity waves, eastward and westward, deposit momentum to generate the observed zonal wind oscillation. On the Sun, helioseismology has provided a thorough understanding of the acoustic p-waves, which propagate down into the convective envelope guided by the increasing temperature and related propagation velocity. Near the tachocline with low turbulent viscosity, the waves propagating eastward and westward can produce an axisymmetric 22-year oscillation of the zonal flow velocities that can generate the magnetic solar dynamo. Following the Earth model, waves in opposite directions can generate in the Sun wind and magnetic field oscillations in opposite directions, the proposition of a potential solar cycle mechanism.展开更多
Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting fo...Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting for underground mines where the microseismic stations often lack azimuthal coverage.Thus,there is a need for a method to invert fracture mechanisms using waveforms acquired by a sparse microseismic network.Here,we present a novel,multi-scale framework to classify whether a rock crack contracts or dilates based on a single waveform.The framework consists of a deep learning model that is initially trained on 2400000+manually labelled field-scale seismic and microseismic waveforms acquired across 692 stations.Transfer learning is then applied to fine-tune the model on 300000+MT-labelled labscale acoustic emission waveforms from 39 individual experiments instrumented with different sensor layouts,loading,and rock types in training.The optimal model achieves over 86%F-score on unseen waveforms at both the lab-and field-scale.This model outperforms existing empirical methods in classification of rock fracture mechanisms monitored by a sparse microseismic network.This facilitates rapid assessment of,and early warning against,various rock engineering hazard such as induced earthquakes and rock bursts.展开更多
The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Li...The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Lijiang consists of two large ruptures, the time difference and the distance between the two ruptures are about 12 s (by the inversion) and about 26 km respectively. An extensional normal with strike-slip fault in about the north-south direction was formed by the first rupture, the mechanism of the second rupture is to be further studied. The method to inverse mechanisms of two point sources at the same time and the results obtained by directly analyzing P waveform records of the main shock are introduced, some related problems are also discussed. The Wuding earthquakes of October, 1995 and the Lijiang earthquake are considered to be the manifestation of the same dynamic process at different temporal and spatial points and the occurrence order of the two earthquakes is related to the direction of dynamics transmission.展开更多
Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first mot...Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.展开更多
The August 11, 2012 M<sub>w</sub> 6.4 earthquakes in northwestern Iran occurred as a result of oblique strike-slip faulting in the shallow crust of the Eurasia plate, approximately 300 kilometer east of th...The August 11, 2012 M<sub>w</sub> 6.4 earthquakes in northwestern Iran occurred as a result of oblique strike-slip faulting in the shallow crust of the Eurasia plate, approximately 300 kilometer east of the plate boundary between the Eurasia and Arabia plates. The seismotectonics of this region is controlled by the collision of the Arabia and Eurasia plates;at the latitude of the earthquakes, the Arabia plate moves almost due north with respect to the Eurasia plate at a rate of approximately 26 millimeter per year. Over the past forty years, seven earthquakes of M<sub>w</sub> 6 or greater have occurred within 300 kilometer of today’s events. The nearest was a M<sub>w</sub> 6.1 earthquake in February of 1997, approximately 100 kilometer to the east, which caused 1100 fatalities. The studied area encourage the authors to determine the focal mechanism, source time function and sub events’ features which can guide us to reliable judges.展开更多
In unconventional reservoirs, small faults allow the flow ofoil and gas as well as act as obstacles to exploration; for, （1） fracturing facilitates fluid migration, （2） reservoir flooding, and （3） triggering of ...In unconventional reservoirs, small faults allow the flow ofoil and gas as well as act as obstacles to exploration; for, （1） fracturing facilitates fluid migration, （2） reservoir flooding, and （3） triggering of small earthquakes. These small faults are not generally detected because of the low seismic resolution. However, such small faults are very active and release sufficient energy to initiate a large number of microseismic events （MEs） during hydraulic fracturing. In this study, we identified microfractures （MF） from hydraulic fracturing and natural small faults based on microseismicity characteristics, such as the time-space distribution, source mechanism, magnitude, amplitude, and frequency. First, I identified the mechanism of small faults and MF by reservoir stress analysis and calibrated the ME based on the microseismic magnitude. The dynamic characteristics （frequency and amplitude） of MEs triggered by natural faults and MF were analyzed; moreover, the geometry and activity types of natural fault and MF were grouped according to the source mechanism. Finally, the differences among time-space distribution, magnitude, source mechanism, amplitude, and frequency were used to differentiate natural faults and manmade fractures.展开更多
Using the technique of seismic moment tensor inversion, the source mechanisms of 10 earthquakes with Ms5.2that occurred in China from November 1996 to January 1998 were determined rapidly. The determined resultswere s...Using the technique of seismic moment tensor inversion, the source mechanisms of 10 earthquakes with Ms5.2that occurred in China from November 1996 to January 1998 were determined rapidly. The determined resultswere sent as 'Bulletins of Source Mechanism Parameters of Earthquakes' to the Seismic Regime Guards' Office,China Seismological Bureau, and the relevant provincial seismological bureaus. These bulletins have played rolein the fast response to large earthquakes.展开更多
With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better loca...With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of Mw3.4-5.6 earthquakes in the Longmenshan fault （LMSF） zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.展开更多
Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we Studied the char acteristics of 'field precursors' and 'focus precursors' of subsurface fluid and their s...Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we Studied the char acteristics of 'field precursors' and 'focus precursors' of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ② dilatancy emerges and anomalyfocus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③ anomalies spreed continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large scale dilatancy.展开更多
The present investigation is concerned with an axi-symmetric problem in the electromagnetic micropolar thermoelastic half-space whose surface is subjected to the mechanical or thermal source. Laplace and Hankel transf...The present investigation is concerned with an axi-symmetric problem in the electromagnetic micropolar thermoelastic half-space whose surface is subjected to the mechanical or thermal source. Laplace and Hankel transform techniques are used to solve the problem. Various types of sources are taken to illustrate the utility of the approach. Integral transforms are inverted by using a numerical technique to obtain the components of stresses, temperature distribution, and induced electric and magnetic fields. The expressions of these quantities are illustrated graphically to depict the magnetic effect for two different generalized thermoelasticity theories, i.e., Lord and Shulman （L-S theory） and Green and Lindsay （G-L theory）. Some particular interesting cases are also deduced from the present investigation.展开更多
New methanol maser lines at 72 → 63A^-（86.6 GHz） and 72 → 63A^＋（86.9 GHz） together with two candidate methanol maser lines at 72 → 81A-（80.99GHz） and 72→81A^＋（111.29GHz） have been detected in W3（OH）. W...New methanol maser lines at 72 → 63A^-（86.6 GHz） and 72 → 63A^＋（86.9 GHz） together with two candidate methanol maser lines at 72 → 81A-（80.99GHz） and 72→81A^＋（111.29GHz） have been detected in W3（OH）. We use a pumping mechanism, i.e., methanol masers without population inversion, to explain the formation of weak methanol masers of 72 → 81A^＋ and 72→ 81A^-. We explain well why the line-shape of the transition 72 → 81A^＋ is not typical. A similar argument can be applied to the A-type level system 72A^-, 63A^- and 81A^-, as well as to the 72 → 81A^- 80.99 GHz masers.展开更多
The knowledge of crack type and dislocation orientation is helpful for the lifetime prediction of thin plates on aircrafts.The moment-tensor inversion utilizes the Acoustic Emission(AE)signals to detect cracks and the...The knowledge of crack type and dislocation orientation is helpful for the lifetime prediction of thin plates on aircrafts.The moment-tensor inversion utilizes the Acoustic Emission(AE)signals to detect cracks and the source mechanisms can be interpreted by the decomposition of moment tensors.Since the traditional moment-tensor inversion is implemented for the AE sources inside infinite elastic bodies,the inversion needs to be modified for the cracks in thin plates.In this study,the moment tensors of cracks in thin plates are derived and the inversion equation is provided based on the Green's function of second kind.A method of modifying the moment tensors to adapt to the existing decomposition processes and source-type plots is provided.By employing the Finite Element Method(FEM),the wave fields generated by the AE sources are computed.The AE sources continuously changing from pure tensile type(Model I)to shear type(Model II)are achieved in the FE models and the moment tensors are recovered.By the comparison between the reference values and recovered solutions,the source type can be accurately identified in the source-type plot and the applicability of the moment-tensor inversion for cracks in thin plates is confirmed.展开更多
基金Project(2010CB732004) supported by the National Basic Research Program of ChinaProject(50490274) supported by the National Natural Science Foundation of China
文摘The research on the rock burst prediction was made on the basis of seismology,rock mechanics and the data from Dongguashan Copper Mine(DCM) ,the deepest metal mine in China.The seismic responses to mining in DCM were investigated through the analyses of the spatio-temporal distribution of hypocenters,apparent stress and displacement of seismic events,and the process of the generation of hazardous seismicity in DCM was studied in the framework of the theory of asperity in the seismic source mechanism.A method of locating areas with hazardous seismicity and a conceptual model of hazardous seismic nucleation in DCM were proposed.A criterion of rockburst prediction was analyzed theoretically in the framework of unstable failure theories,and consequently,the rate of change in the ratio of the seismic stiffness of rock in a seismic nucleation area to that in surrounding area,dS/dt,is defined as an index of the rockburst prediction.The possibility of a rockburst will increase if dS/dt>0,and the possibility of rock burst will decrease if dS/dt<0.The correctness of these methods is demonstrated by analyses of rock failure cases in DCM.
基金The National Key Basic Research Program under the Project "Mechanism and Prediction of Continental Strong Earthquake"(G1998040700) and Joint Seismological Science Foundation of China (100108).
文摘In the paper, source mechanisms of 33 small-moderate earthquakes occurred in Yunnan are determined by modeling of regional waveforms from Yunnan digital seismic network. The result shows that most earthquakes occurred within or near the Chuandian rhombic block have strike-slip mechanism. The orientations of maximum compressive stresses obtained from source mechanism are changed from NNW-SSN to NS in the areas from north to south of the block, and tensile stresses are mainly in ENE-WSW or NE-SE. In the eastern Tibetan Plateau, the orientations of maximum compressive stress radiate toward outside from the plateau, and the tensile stress orientations mostly parallel to arc structures. Near 28N the orientations of both maximum compressive stress and tensile stress changed greatly, and the boundary seems to correspond to the southwestern extended line of Longmenshan fault. Outside of the Chuandian rhombic block, the orientations of P and T axes are some different from those within the block. The comparison shows that the source mechanism of small-moderate events presented in the paper is consistence with that of moderate-strong earthquakes determined by Harvard University, which means the source mechanism of small-moderate events can be used to study the tectonic stress field in this region.
文摘The Qinghai Gonghe-Guide Basin together with the alternatively distributed mountainous region shows characteristics that the conductive geothermal resource of the basin has high geothermal gradient, the granite occurs in the bottom of borehole for geothermal exploration, and the convective hot springs in the basin-edge uplift fracture are in zonal distribution and with high-temperature geothermal water. There are still some divergences about the heat source mechanism of the basin. In this paper, queries to the view of mantle-derived heat source have been put forward, coming up with geochemical evidences to prove that the radiogenic heat of granite is the heat source within the mantle. Additionally, temperature curve is drawn based on the geothermal boring and geochemical geothermometer has been adopted for an estimation of the temperature and depth of the geothermal reservoir, it has been found that the surrounding mountains belong to the medium-temperature geothermal system while the area within the basin belongs to the high-temperature geothermal system with the temperature of borehole bottom reaching up to 175-180 ℃. In this paper, discussions on the problems existing in the calculation of geothermal gradient and the differences generated by the geothermal system have been carried out.
基金supported by National Key R&D Program of China(Grant No.2018YFB1501803)。
文摘Hot dry rock(HDR) is an important geothermal resource and clean energy source that may play an increasingly important role in future energy management. High-temperature HDR resources were recently detected in deep regions of the Gonghe Basin on the northeastern edge of the Tibetan Plateau, which led to a significant breakthrough in HDR resource exploration in China. This research analyzes the deep temperature distribution, radiogenic heat production, heat flow, and crustal thermal structure in the Qiaboqia Valley, Guide Plain, and Zhacanggou area of the Gonghe Basin based on geothermal exploration borehole logging data, rock thermophysical properties, and regional geophysical exploration data. The results are applied to discuss the heat accumulation mechanism of the HDR resources in the Gonghe Basin. The findings suggest that a low-velocity layer in the thickened crust of the Tibetan Plateau provides the most important source of constant intracrustal heat for the formation of HDR resources in the Gonghe Basin, whereas crustal thickening redistributes the concentrated layer of radioactive elements, which compensates for the relatively low heat production of the basal granite and serves as an important supplement to the heat of the HDR resources. The negative effect is that the downward curvature of the lithospheric upper mantle caused by crustal thickening leads to a small mantle heat flow component. As a result, the heat flows in the Qiaboqia Valley and Guide Plain of the Gonghe Basin are 106.2 and 77.6 m W/m2, respectively, in which the crust-mantle heat flow ratio of the former is 3.12:1, indicating a notably anomalous intracrustal thermal structure. In contrast, the crust-mantle heat flow ratio in the Guide Plain is 1.84:1, which reflects a typical hot crust-cold mantle thermal structure. The Guide Plain and Zhacanggou area show the same increasing temperature trend with depth, which reflects that their geothermal backgrounds and deep high-temperature environments are similar. These results provide important insight on the heat source mechanism of HDR resource formation in the Tibetan Plateau and useful guidance for future HDR resource exploration projects and target sites selection in similar areas.
基金This research is funded by NIOSH capacity-building contract 200-2011-40313 through the OMSHR Ground Control Mining Program Area.
文摘A microseismic monitoring system was installed in an underground room and pillar coal mine in the Eastern United States to analyze the occurrence and characteristics of induced seismicity during the retreat of two panels in the mine.This study is the first microseismic monitoring effort at an underground coal mine in nearly 30 years.During the retreat of the first panel,an array of eight uniaxial geophones,installed 10 ft.into the roof,recorded events and their magnitudes.The second panel was monitored using an array of twelve uniaxial geophones and two triaxial geophones,also installed 10 ft.into the roof.Comparing the results of these studies,it has been found that the magnitude of seismic events is minimally affected by immediate roof geology or depth of cover.However,it was observed in both studies that the rate at which seismic events occurred did vary with changing roof geology and depth of cover.Using the seismic data from the second panel retreat,focal mechanism solutions were generated for 50 hand-picked events in order to determine if the failure was in compression,tension,or shear.Results of the focal mechanism solutions show that stress relief resulting in dilational events occurs at significant depths,150-200 m in this case,beneath the active mining face.
基金This work was supported by the National Key Fundamental Research Project of China (G19990650).
文摘Studies have been made on the source mechanism of acoustic emission produced by pitting corrosion. Methods for identifying pitting corrosion-related AE signals were proposed and the magnitude of surface displacement due to single pitting was estimated. It is concluded that differentiation between background noise and corrosion induced genuine AE signal is possible through using plate wave acoustic emission theory combined with parameter analysis method.
文摘For the 22-year solar cycle oscillation there is no external time dependent source. A nonlinear oscillation, the solar cycle must be generated internally, and Babcock-Leighton models apply an artificial nonlinear source term that can simulate the observations—which leaves open the question of the actual source mechanism for the solar cycle. Addressing this question, we propose to take guidance from the wave mechanism that generates the 2-year Quasi-biennial Oscillation (QBO) in the Earth atmosphere. Upward propagating gravity waves, eastward and westward, deposit momentum to generate the observed zonal wind oscillation. On the Sun, helioseismology has provided a thorough understanding of the acoustic p-waves, which propagate down into the convective envelope guided by the increasing temperature and related propagation velocity. Near the tachocline with low turbulent viscosity, the waves propagating eastward and westward can produce an axisymmetric 22-year oscillation of the zonal flow velocities that can generate the magnetic solar dynamo. Following the Earth model, waves in opposite directions can generate in the Sun wind and magnetic field oscillations in opposite directions, the proposition of a potential solar cycle mechanism.
基金supported by Western Research Interdisciplinary Initiative R6259A03.
文摘Rock fracture mechanisms can be inferred from moment tensors(MT)inverted from microseismic events.However,MT can only be inverted for events whose waveforms are acquired across a network of sensors.This is limiting for underground mines where the microseismic stations often lack azimuthal coverage.Thus,there is a need for a method to invert fracture mechanisms using waveforms acquired by a sparse microseismic network.Here,we present a novel,multi-scale framework to classify whether a rock crack contracts or dilates based on a single waveform.The framework consists of a deep learning model that is initially trained on 2400000+manually labelled field-scale seismic and microseismic waveforms acquired across 692 stations.Transfer learning is then applied to fine-tune the model on 300000+MT-labelled labscale acoustic emission waveforms from 39 individual experiments instrumented with different sensor layouts,loading,and rock types in training.The optimal model achieves over 86%F-score on unseen waveforms at both the lab-and field-scale.This model outperforms existing empirical methods in classification of rock fracture mechanisms monitored by a sparse microseismic network.This facilitates rapid assessment of,and early warning against,various rock engineering hazard such as induced earthquakes and rock bursts.
文摘The mechanisms of the February 3, 1996 Lijiang main shock, Yunnan Province, are estimated by using the principle to inverse the mechanisms of two point sources simultaneously. The results are that the main shock of Lijiang consists of two large ruptures, the time difference and the distance between the two ruptures are about 12 s (by the inversion) and about 26 km respectively. An extensional normal with strike-slip fault in about the north-south direction was formed by the first rupture, the mechanism of the second rupture is to be further studied. The method to inverse mechanisms of two point sources at the same time and the results obtained by directly analyzing P waveform records of the main shock are introduced, some related problems are also discussed. The Wuding earthquakes of October, 1995 and the Lijiang earthquake are considered to be the manifestation of the same dynamic process at different temporal and spatial points and the occurrence order of the two earthquakes is related to the direction of dynamics transmission.
文摘Twenty-two earthquakes (ML=2.2-3.7) in the joint region of Xianshuihe, Longmenshan and An'ninghe faults are studied in this paper. The source mechanism solutions of these events are obtained using P-wave first motion method, and the characteristics of the source stress field and rupture in the joint region are summarized preliminarily with some results of other researchers. Being strongly extruded by the approximately horizontal regional stress with the direction from north-west to south-east and the effect of the complex tectonics in the region, the source stress field has complex and variable characteristics. The earthquakes mainly show normal or strike-slip faults in Yajiang, North-triangle and west of Chengdu-block areas, indicating that the vertical forces have been playing an important role in the source stress fields, while the earthquakes mainly show reverse or strike-slip faults in Baoxing-Tianquan area, with the horizontal components of the principal pressure stress axes identical to the south-west direction to which the shallow mass is moving. We think that the manifold combinations of earthquake faults are the micro-mechanism based upon which the large regional shallow crust mass has been moving continually.
文摘The August 11, 2012 M<sub>w</sub> 6.4 earthquakes in northwestern Iran occurred as a result of oblique strike-slip faulting in the shallow crust of the Eurasia plate, approximately 300 kilometer east of the plate boundary between the Eurasia and Arabia plates. The seismotectonics of this region is controlled by the collision of the Arabia and Eurasia plates;at the latitude of the earthquakes, the Arabia plate moves almost due north with respect to the Eurasia plate at a rate of approximately 26 millimeter per year. Over the past forty years, seven earthquakes of M<sub>w</sub> 6 or greater have occurred within 300 kilometer of today’s events. The nearest was a M<sub>w</sub> 6.1 earthquake in February of 1997, approximately 100 kilometer to the east, which caused 1100 fatalities. The studied area encourage the authors to determine the focal mechanism, source time function and sub events’ features which can guide us to reliable judges.
基金supported by the National Key Research and Development Project of China(No.2016ZX05023-004)
文摘In unconventional reservoirs, small faults allow the flow ofoil and gas as well as act as obstacles to exploration; for, （1） fracturing facilitates fluid migration, （2） reservoir flooding, and （3） triggering of small earthquakes. These small faults are not generally detected because of the low seismic resolution. However, such small faults are very active and release sufficient energy to initiate a large number of microseismic events （MEs） during hydraulic fracturing. In this study, we identified microfractures （MF） from hydraulic fracturing and natural small faults based on microseismicity characteristics, such as the time-space distribution, source mechanism, magnitude, amplitude, and frequency. First, I identified the mechanism of small faults and MF by reservoir stress analysis and calibrated the ME based on the microseismic magnitude. The dynamic characteristics （frequency and amplitude） of MEs triggered by natural faults and MF were analyzed; moreover, the geometry and activity types of natural fault and MF were grouped according to the source mechanism. Finally, the differences among time-space distribution, magnitude, source mechanism, amplitude, and frequency were used to differentiate natural faults and manmade fractures.
文摘Using the technique of seismic moment tensor inversion, the source mechanisms of 10 earthquakes with Ms5.2that occurred in China from November 1996 to January 1998 were determined rapidly. The determined resultswere sent as 'Bulletins of Source Mechanism Parameters of Earthquakes' to the Seismic Regime Guards' Office,China Seismological Bureau, and the relevant provincial seismological bureaus. These bulletins have played rolein the fast response to large earthquakes.
基金supported by National Natural Science Foundation of China (Grants No.41374056)the Fundamental Research Funds for the Central Universities (WK2080000053)
文摘With dense seismic arrays and advanced imaging methods, regional three-dimensional （3D） Earth models have become more accurate. It is now increasingly feasible and advantageous to use a 3D Earth model to better locate earthquakes and invert their source mechanisms by fitting synthetics to observed waveforms. In this study, we develop an approach to determine both the earthquake location and source mechanism from waveform information. The observed waveforms are filtered in different frequency bands and separated into windows for the individual phases. Instead of picking the arrival times, the traveltime differences are measured by cross-correlation between synthetic waveforms based on the 3D Earth model and observed waveforms. The earthquake location is determined by minimizing the cross-correlation traveltime differences. We then fix the horizontal location of the earthquake and perform a grid search in depth to determine the source mechanism at each point by fitting the synthetic and observed waveforms. This new method is verified by a synthetic test with noise added to the synthetic waveforms and a realistic station distribution. We apply this method to a series of Mw3.4-5.6 earthquakes in the Longmenshan fault （LMSF） zone, a region with rugged topography between the eastern margin of the Tibetan plateau and the western part of the Sichuan basin. The results show that our solutions result in improved waveform fits compared to the source parameters from the catalogs we used and the location can be better constrained than the amplitude-only approach. Furthermore, the source solutions with realistic topography provide a better fit to the observed waveforms than those without the topography, indicating the need to take the topography into account in regions with rugged topography.
文摘Using finite element technique of the plane-strain problem in solid-liquid two-phase medium, we Studied the char acteristics of 'field precursors' and 'focus precursors' of subsurface fluid and their spatial-temporal evolution in case of dip-slip earthquake. The results show that: ① the change of ground fluid is slow and the anomaly is not prominent in the early period which is of elastic accumulation and non-linear; ② dilatancy emerges and anomalyfocus mainly in the source region in the moderate period which is hardening and of local dilatancy. In the period the focus precursors emerge earlier than the field precursors; ③ anomalies spreed continuously in the source area and new regions with big anomaly emerge out of the source region in the middle-short period which is of large scale dilatancy.
文摘The present investigation is concerned with an axi-symmetric problem in the electromagnetic micropolar thermoelastic half-space whose surface is subjected to the mechanical or thermal source. Laplace and Hankel transform techniques are used to solve the problem. Various types of sources are taken to illustrate the utility of the approach. Integral transforms are inverted by using a numerical technique to obtain the components of stresses, temperature distribution, and induced electric and magnetic fields. The expressions of these quantities are illustrated graphically to depict the magnetic effect for two different generalized thermoelasticity theories, i.e., Lord and Shulman （L-S theory） and Green and Lindsay （G-L theory）. Some particular interesting cases are also deduced from the present investigation.
基金Supported by the National Natural Science Foundation of China.
文摘New methanol maser lines at 72 → 63A^-（86.6 GHz） and 72 → 63A^＋（86.9 GHz） together with two candidate methanol maser lines at 72 → 81A-（80.99GHz） and 72→81A^＋（111.29GHz） have been detected in W3（OH）. We use a pumping mechanism, i.e., methanol masers without population inversion, to explain the formation of weak methanol masers of 72 → 81A^＋ and 72→ 81A^-. We explain well why the line-shape of the transition 72 → 81A^＋ is not typical. A similar argument can be applied to the A-type level system 72A^-, 63A^- and 81A^-, as well as to the 72 → 81A^- 80.99 GHz masers.
基金financial supports provided by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA22000000)National Natural Science Foundation of China(No.41804134)。
文摘The knowledge of crack type and dislocation orientation is helpful for the lifetime prediction of thin plates on aircrafts.The moment-tensor inversion utilizes the Acoustic Emission(AE)signals to detect cracks and the source mechanisms can be interpreted by the decomposition of moment tensors.Since the traditional moment-tensor inversion is implemented for the AE sources inside infinite elastic bodies,the inversion needs to be modified for the cracks in thin plates.In this study,the moment tensors of cracks in thin plates are derived and the inversion equation is provided based on the Green's function of second kind.A method of modifying the moment tensors to adapt to the existing decomposition processes and source-type plots is provided.By employing the Finite Element Method(FEM),the wave fields generated by the AE sources are computed.The AE sources continuously changing from pure tensile type(Model I)to shear type(Model II)are achieved in the FE models and the moment tensors are recovered.By the comparison between the reference values and recovered solutions,the source type can be accurately identified in the source-type plot and the applicability of the moment-tensor inversion for cracks in thin plates is confirmed.
