As a consequence of the impacts of climate change, some households and entire communities across the Pacific are making the complex and challenging decision to leave their homelands and relocate to new environments th...As a consequence of the impacts of climate change, some households and entire communities across the Pacific are making the complex and challenging decision to leave their homelands and relocate to new environments that can sustain their livelihoods. This short article charts how the residents of Vunidogoloa village in Fiji relocated in early 2014 to reduce their vulnerability to encroaching sea level and inundation events that regularly devastated the community. As a consequence of the Vunidogoloa relocation, this article also explores how the Fiji Government is planning for similar resettlement transitions, including vulnerability and adaptation assessments to develop a list of potential community relocations and the development of national relocation guidelines. This study draws from key informant interviews(n = 8) with government officials, as well as representatives from intergovernmental and local nongovernmental organizations,who are involved in the relocation issue. Given the speed at which these national, top-down initiatives are being forged and especially in light of the absence of any mention of relocation in Fiji’s 2012 climate change policy, careful and inclusive engagement across all scales and stakeholders,including communities 'earmarked' for relocation, is paramount.展开更多
The widespread variation of focal depths and fault plane solutions observed in the Hindukush region depicts continuous deformation along the Indian-Eurasian collision zone.For period of twelve years i.e.from 2010 to 2...The widespread variation of focal depths and fault plane solutions observed in the Hindukush region depicts continuous deformation along the Indian-Eurasian collision zone.For period of twelve years i.e.from 2010 to 2022,a total of 89 intermediate-depth earthquakes of magnitude(Mw)≥5.5 of the Hindukush Region were considered,relocated using both regional and tele seismic data with 90 per cent confidence limits of less than 20 km.Two distinct seismic activity clusters:First one at a deeper depth and second at a shallower depth having different P-axes were observed that verifies the internal structure and geometry of Hindukush zone as suggested in previous studies.Beneath the Hindukush collision zone,there exists a complex pattern of deformation,arising from a combination of compression,tension,shearing and necking states due to an unusual and a rare case of subduction that is not from oceanic plate.The Hindukush seismic zone extends from 70 to 300 km depth and mostly strikes east-west and then turns northeast.The relocated seismicity by merging data of seismic network close to Hindukush along with international data shows that the Hindukush zone may be divided vertically into upper and lower slabs separated by a gap at about 150 km depth at which strike and dip directions change sharply with significant structural changes.Seismicity rate is higher in the lower part of Hindukush,having large magnitude events in a small volume below 180 km forming complex pattern of source mechanisms.Contrary in upper part seismicity rate is lower and scattered.The Global CMT(Global Centroid-Moment-Tensor Project)source mechanisms of intermediate depth earthquakes have a systematic pattern of reverse faulting with the vertical T-axes,while shallow events do not have such pattern.The vertical T-axes of the intermediate-depth events may be attributed to negative buoyancy caused by subduction of the cold and denser slab.展开更多
The three-dimensional(3D)geometry of a fault is a critical control on earthquake nucleation,dynamic rupture,stress triggering,and related seismic hazards.Therefore,a 3D model of an active fault can significantly impro...The three-dimensional(3D)geometry of a fault is a critical control on earthquake nucleation,dynamic rupture,stress triggering,and related seismic hazards.Therefore,a 3D model of an active fault can significantly improve our understanding of seismogenesis and our ability to evaluate seismic hazards.Utilising the SKUA GoCAD software,we constructed detailed seismic fault models for the 2021 M_(S)6.4 Yangbi earthquake in Yunnan,China,using two sets of relocated earthquake catalogs and focal mechanism solutions following a convenient 3D fault modeling workflow.Our analysis revealed a NW-striking main fault with a high-angle SW dip,accompanied by two branch faults.Interpretation of one dataset revealed a single NNW-striking branch fault SW of the main fault,whereas the other dataset indicated four steep NNE-striking segments with a left-echelon pattern.Additionally,a third ENE-striking short fault was identified NE of the main fault.In combination with the spatial distribution of pre-existing faults,our 3D fault models indicate that the Yangbi earthquake reactivated pre-existing NW-and NE-striking fault directions rather than the surface-exposed Weixi-Qiaohou-Weishan Fault zone.The occurrence of the Yangbi earthquake demonstrates that the reactivation of pre-existing faults away from active fault zones,through either cascade or conjugate rupture modes,can cause unexpected moderate-large earthquakes and severe disasters,necessitating attention in regions like southeast Xizang,which have complex fault systems.展开更多
On December 18,2023,an M_(s)6.2 earthquake jolted Jishishan County in the Linxia Hui Autonomous Prefecture in Northwest China's Gansu Province,causing substantial casualties and building collapses.The earthquake o...On December 18,2023,an M_(s)6.2 earthquake jolted Jishishan County in the Linxia Hui Autonomous Prefecture in Northwest China's Gansu Province,causing substantial casualties and building collapses.The earthquake occurred in the Qilian Block on the northeastern border of the Qinghai-Tibet Plateau,where faults are highly active and the geological structure is complex.In this study,we utilized methods such as relocation,focal mechanism solutions,and earthquake rupture processes to describe seismogenic faults.The results indicated that the majority of aftershocks occurred at a depth of 12 km.The centroid depth of the main shock and the depth of the maximum rupture point during the rupture process were also 12 km.Various geophysical methods exhibited a high degree of consistency in depth exploration.Aftershocks were distributed mainly to the west and north of the main shock and extended in the NNW direction,primarily through unilateral rupture.The main shock was a reverse thrust event with a small dextral strike-slip component.In this study,more regional data,such as previous GPS observations,field geological observations,and the distributions of the primary stress states in the region,were also incorporated.We inferred that the main shock was triggered by the main fault at the northern margin of the Lajishan Fault and that the movement of the main fault also activated some secondary faults.The compressive forces on both sides of the Lajishan Fault Zone led to the uplift of mountain areas,accompanied by some landslides,leading to this catastrophic earthquake event.In this article,the activity relationships among the 2022 M_(s)6.9 Menyuan earthquake,the 2019 M_(s)5.7 Xiahe earthquake,and the Jishishan earthquake under the action of regional stress are also discussed.This study provides additional evidence and new ideas for exploring the seismogenic process of the Lajishan Fault Zone and has implications for future in-depth research on underground activity in this region.展开更多
The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify...The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify the seismogenic fault and better understand the regional tectonic framework,we integrated high-resolution Digital Elevation Models(DEMs)derived from GF-7 stereo satellite and Unmanned Aerial Vehicle(UAV)photogrammetry,relocated aftershock sequences,and conducted detailed field investigations.Our results identify four Late Quaternary thrust faults(F1-1 to F1-4),among which the Zhaomuchuan fault(F1-3),a NE-dipping back-thrust,aligns closely with the main-shock and aftershock distribution and exhibits clear Holocene activity.Seismic relocation reveals a NEdipping seismogenic zone at depths of 5-12 km,consistent with a shallow reverse-faulting mechanism under WSW-ENE oblique compression.Structural analysis and cross-sectional profiles suggest that fault F1-3 propagates into a mid-crustal detachment surface,forming a foreland-vergent thrust-nappe system.Importantly,the rupture of this secondary fault,rather than the locked primary boundary fault F1-1,indicates stress transfer and localization within a critically tapered wedge,consistent with global analogs of back-thrust-dominated earthquakes.These findings underscore the seismotectonic complexity of the LJSFZ and highlight the significant seismic hazard posed by subsidiary structures in compressional settings.展开更多
As a crucial pivot for national strategic development,the university relocation project in Xiong’an New Area undertakes the mission of optimizing capital functions and promoting regional coordinated development.Takin...As a crucial pivot for national strategic development,the university relocation project in Xiong’an New Area undertakes the mission of optimizing capital functions and promoting regional coordinated development.Taking the Xi-ong’an Campus of China University of Geosciences(Beijing)as a case study,this paper explores the collaborative pa-thways between universities and cities in terms of functional complementarity,resource sharing,and ecological symbiosis from the perspective of campus functional layout and spatial optimization.By integrating four core concepts—green ecology,intelligent technology,cultural inheritance,and traffic optimization—it proposes a design strategy of“breaking boundaries and multi-dimensional linkage,”aiming to construct a new spatial paradigm of urban-university integration and provide theoretical support and practical references for the development of higher education and urbanization in Xiong’an New Area.展开更多
The epicenter of the Luxian M_(S)6.0 earthquake on September 16,2021,was located in the southern Sichuan Basin,which is a historically seismically quiescent area.In recent years,the frequency of earthquakes has increa...The epicenter of the Luxian M_(S)6.0 earthquake on September 16,2021,was located in the southern Sichuan Basin,which is a historically seismically quiescent area.In recent years,the frequency of earthquakes has increased with the large-scale exploitation of shale gas.No evident surface fractures or seismic faults were observed after the Luxian earthquake.Based on high-quality data recorded by a dense seismic array composed of 70 portable stations with an average spacing of 2-3 km,a highresolution seismic catalog was constructed for 7 days before and 36 days after the M_(S)6.0 earthquake using LOC-FLOW,an effective workflow of phase picking,phase association,and earthquake location.Based on the new earthquake catalog,four earthquake clusters that occurred within the Yujiasi Syncline during this period were identified.Among them,the M_(S)6.0 main earthquake sequence had a NW-SE trend and inclined towards the SW,with a length of approximately 8 km and width of 5 km.The M_(S)6.0 earthquake sequence only appeared after the mainshock.The other three clusters were located in the northeast direction of the M_(S)6.0 earthquake sequence,all of which were NE-SW trending strips and had no evident direct correlation with the M_(S)6.0 mainshock.The focal depth was concentrated in the range of 2-7 km.Based on the seismic sequence profile and structural background,the M_(S)6.0 seismic structure may be a blind buried fault zone with a NW strike composed of multiple small conjugate faults with NE and SW dip.The fault was not exposed on the surface and was related to the detachment structure in the deep part of the Sichuan Basin.展开更多
Stepping into Donglong Group’s intelligent factory in the Yangtze River Delta,the automated production lines is transforming fluffy down into premium home textiles export to Europe and America.At a pivotal moment of ...Stepping into Donglong Group’s intelligent factory in the Yangtze River Delta,the automated production lines is transforming fluffy down into premium home textiles export to Europe and America.At a pivotal moment of global supply chain restructuring,this homegrown textile and apparel exporter is answering a critical question:How can Chinese textile companies sustain their competitive edge amid tariff barriers and supply chain relocation?展开更多
A new method, named relocation, was proposed to reduce the impact of sensor errors systematically, especially whenavailable data of sensors are abundant. The procedure includes evaluating the reliability of every sens...A new method, named relocation, was proposed to reduce the impact of sensor errors systematically, especially whenavailable data of sensors are abundant. The procedure includes evaluating the reliability of every sensors datum, processing the initiallocation by the credible data, and selecting a set of equations with optimal noise tolerance according to the relative relationshipbetween the initial location and sensors location, then calculating the final location by k-mean voting. The results obtained in thisresearch include comparing traditional location method with the presented method in both simulation and field experiment. In thefield experiment, the location error of relocation method reduced 41.8% compared with traditional location method. The resultssuggested that relocation method can improve the fault-tolerant performance significantly.展开更多
By investigating present relocation residential districts for peasants whose houses are removed for the unified planning of rural areas in north Jiangsu Province, as well as residents' feelings about the environme...By investigating present relocation residential districts for peasants whose houses are removed for the unified planning of rural areas in north Jiangsu Province, as well as residents' feelings about the environment of residential district, main architectural structures and energy consumption conditions, the indoor thermal environment, use of main heating and cooling facilities, residents' satisfaction on the acoustical and luminous environment, major space-enclosing structures and calculation of energy-saving designs are analyzed, and suggestions are given for the architectural design of relocation residential districts in the study area. It is stressed that the relationship between energy conservation and architectural layout, orientation, lighting, ventilation, selection of enclosing-structure materials, facade, color and style should be properly handled in the planning, and the focus is to control building orientation and shape coefficient, on the basis of which energy-saving designs of windows, exterior walls and roofs can be done. Energy consumption of present residential buildings is calculated and analyzed to bring forth new ideas to the energy-saving designs for relocation residential districts in north Jiangsu Province, and establish an architectural energy-saving system suitable for climatic and natural conditions of north Jiangsu to instruct the energy-saving designs of relocation residential districts in the study area.展开更多
The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise loc...The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.展开更多
This paper analyses the impact of the poverty alleviation relocation(PAR)program on rural household income and evaluates the heterogeneous income effects of various relocation modes,based on a panel dataset of relocat...This paper analyses the impact of the poverty alleviation relocation(PAR)program on rural household income and evaluates the heterogeneous income effects of various relocation modes,based on a panel dataset of relocated households from 16 counties in eight Chinese provinces.The results show that participation in the PAR increases the income of both rural and urban resettlers.More specifically,it has a significant positive effect on agricultural and wage income for rural and urban resettlers,respectively.Further analyses show that the income increase for rural resettlers was mainly due to agricultural technology training and that the income increase for town resettlers was attributed to medical security.For the village resettlers,policies should focus on strengthening the development of local industries and training of agricultural technologies.For the urban resettlers,non-agricultural employment and public services in the urban resettlement areas should be promoted.展开更多
An earthquake with Ms5.8 occurred on 10 March 2011 in Yingjiang county, western Yunnan, China. This earthquake caused 25 deaths and over 250 injuries. In order to better understand the seismotectonics in the region, w...An earthquake with Ms5.8 occurred on 10 March 2011 in Yingjiang county, western Yunnan, China. This earthquake caused 25 deaths and over 250 injuries. In order to better understand the seismotectonics in the region, we collected the arrival time data from the Yunnan seismic observational bulletins during 1 January to 25 March 2011, and precisely hand-picked the arrival times from high-quality seismograms that were recorded by the temporary seismic stations deployed by our Institute of Crustal Dynamics, China Earthquake Administration. Using these arrival times, we relocated all the earthquakes including the Yingjiang mainshock and its aftershocks using the double-difference relocation algorithm. Our results show that the relocated earthquakes dominantly occurred along the ENE direction and formed an upside-down bow-shaped structure in depth. It is also observed that after the Yingjiang mainshock, some aftershocks extended toward the SSE over about 10 km. These results may indicate that the Yingjiang mainshock ruptured a conjugate fault system consisting of the ENE trending Da Yingjiang fault and a SSE trending blind fault. Such structural features could contribute to severely seismic hazards during the moderate-size Yingjiang earthquake.展开更多
To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were us...To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were used to relocate the earthquake sequence by the tomoDD program, and the focal mechanism solutions and centroid depths of the M_L ≥ 3.5 events in the sequence were determined using the CAP waveform inversion method. Further, the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As). The results indicate:(1) The relocated M_S 7.0 Jiuzhaigou earthquake sequence displays a narrow ～ 38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault, two branches of the East Kunlun Fault Zone. The spatial distribution of the sequence is narrow and deep for the southern segment, and relatively wide and shallow for the northern segment. The initial rupture depth of the mainshock is 12.5 km, the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km. The mainshock epicenter is located in the middle of the aftershock region, showing a bilateral rupture behavior. The centroid depths of 32 M_L ≥ 3.5 events range from 3 to 12 km with a mean of about 7.3 km, consistent with the predominant focal depth of the whole sequence.(2) The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock) is relatively simple, with overall strike of ～150° and dip angle ～75°, but the dip angle and dip-orientation exhibit some variation along the segment. The seismogenic structure on the northern segment is more complicated; several faults, including the Minjiang Fault, may be responsible for the aftershock activities. The overall strike of this section is ～159° and dip angle is ～59°, illustrating a certain clockwise rotation and a smaller dip angle than the southern segment. The differences between the two segments demonstrate variation of the geometric structure along the seismogenic faults.(3) The focal mechanism solutions of 32 M_L ≥ 3.5 events in the earthquake sequence have obvious segmental characteristics. Strike-slip earthquakes are dominant on the southern segment, while 50% of events on the northern segment are thrusting and oblique thrusting earthquakes, revealing significant differences in the kinematic features of the seismogenic faults between the two segments.(4) The strain rosettes for the mainshock and the entire sequence of 31 M_L ≥ 3.5 aftershocks correspond to strike-slip type with NWW-SEE compressional white lobes and NNE-SSW extensional black lobes of nearly similar size. The strain rosette and As value of the entire sequence of 22 M_L ≥ 3.5 events on the southern segment are the same as those of the M_S 7.0 mainshock,indicating that the tectonic deformation here is strike-slip. However, the strain rosette of the entire sequence of 10 M_L ≥ 3.5 events on the northern segment show prominent white compressional lobes and small black extensional lobes, and the related As value is up to 0.52,indicating that the tectonic deformation of this segment is oblique thrusting with a certain strike-slip component. Differences between the two segments all reveal distinctly obvious segmental characteristics of the tectonic deformation of the seismogenic faults for the Jiuzhaigou earthquake sequence.展开更多
We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, includ...We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, including 54 525 seismograms from 1 376 local earthquakes over Ms3.5 between 12 May 2008 and 3 August 2008. The cross-correlation technique used in this paper has greatly improved the relocation precision by giving much more accurate P-wave differential travel-time measurements than those obtained from routinely picked phase onsets. At the same time, we pick P-wave polarity observations of the Wenchuan earthquake series （hereafter referred to as WES） from 1023 stations in China and 59 IRIS （Incorporated Research Institutions of Seismology） stations. Then, employing a newly developed program CHNYTX, we obtain 83 well-determined focal mechanism solutions （hereafter referred to as FMSs）. Based on spatial distribution and FMSs of the WES, we draw following conclusions： （1） The region near the main shock exhibits a buried low-angle northwest-dipping seismic zone with the main shock at its upper end and two conjugated seismic zones dipping southeast with roughly equal dip-angle; （2） The compressional directions of all kinds of FMSs of the WES are subhorizontal, which reflects the dominant stress in this area is eompressional; （3） The principal compressional direction of the regional stress around Wenchuan is roughly perpendicular to the strike of Beichuan-Yingxiu fault, while around Qingchuan it is roughly parallel to the strike of Qingehuan fault. In intermediate part of the Longmenshan area, the principal compressional direction of the stress should be in-between; （4） The possibly existed molten materials in the lower crust of Songpan-Garze terrain have small contribution to the local stress state in Longmenshan area. The listric geometries of the Longmenshan faults most probably resulted from subhorizontal compression along NW-SE direction in history.展开更多
The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and af...The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method.The total length and width of the aftershock sequence are approximately 32 km and 5 km,respectively,and the aftershocks are mainly concentrated at a depth of 7-12 km.The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock,where aftershocks are sparse.The east and west fault structures revealed by aftershock locations differ significantly.The west fault strikes EW and inclines to the south at a 71°-90°angle,whereas the east fault strikes 133°and has a smaller dip angle.Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes.Based on surface traces of faults,the distribution of relocated earthquake sequence and surface ruptures,the mainshock was determined to have occurred at the conjunction of the Tuolaishan(TLS)fault and LLL fault,and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault,respectively.Aftershocks migrate in the early and late stages of the earthquake sequence.In the first 1.5 h after the mainshock,aftershocks expand westward from the mainshock.In the late stage,seismicity on the northeast side of the east fault is higher than that in other regions.The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.展开更多
An Ms 6.4 earthquake occurred in Yangbi,Yunnan,China on May 21,2021,which has obvious foreshock activity and abundant aftershocks.Based on the seismic observation data recorded by the Yunnan Seismic Network three days...An Ms 6.4 earthquake occurred in Yangbi,Yunnan,China on May 21,2021,which has obvious foreshock activity and abundant aftershocks.Based on the seismic observation data recorded by the Yunnan Seismic Network three days before and seven days after the mainshock,a doubledifference location method was used to relocate 2133 earthquakes of the Yangbi sequence.Aftershocks are mostly distributed to the southeast of the mainshock in a unilateral rupture pattern.This sequence exhibits a SE-trending linear alignment with a length of about 25 km,and most of the focal depth is above 12 km.Integrated with the seismic distribution and focal mechanism results,we infer that the strike of the seismogenic fault is about 140°,and dipping to the SW.The fault structure revealed by the seismic sequence is complex,with the NW segment exhibiting a steep dip and relatively simple structure of strike-slip rupture and the SE segment consisting of several branching ruptures.The Yangbi Earthquake is a typical foreshock-mainshock-aftershock sequence,and the mainshock is likely triggered by the largest foreshock.This earthquake occurred in the boundary between high-and lowvelocity anomalous zone,where is susceptible to generate large earthquakes.展开更多
Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monit...Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.展开更多
文摘As a consequence of the impacts of climate change, some households and entire communities across the Pacific are making the complex and challenging decision to leave their homelands and relocate to new environments that can sustain their livelihoods. This short article charts how the residents of Vunidogoloa village in Fiji relocated in early 2014 to reduce their vulnerability to encroaching sea level and inundation events that regularly devastated the community. As a consequence of the Vunidogoloa relocation, this article also explores how the Fiji Government is planning for similar resettlement transitions, including vulnerability and adaptation assessments to develop a list of potential community relocations and the development of national relocation guidelines. This study draws from key informant interviews(n = 8) with government officials, as well as representatives from intergovernmental and local nongovernmental organizations,who are involved in the relocation issue. Given the speed at which these national, top-down initiatives are being forged and especially in light of the absence of any mention of relocation in Fiji’s 2012 climate change policy, careful and inclusive engagement across all scales and stakeholders,including communities 'earmarked' for relocation, is paramount.
文摘The widespread variation of focal depths and fault plane solutions observed in the Hindukush region depicts continuous deformation along the Indian-Eurasian collision zone.For period of twelve years i.e.from 2010 to 2022,a total of 89 intermediate-depth earthquakes of magnitude(Mw)≥5.5 of the Hindukush Region were considered,relocated using both regional and tele seismic data with 90 per cent confidence limits of less than 20 km.Two distinct seismic activity clusters:First one at a deeper depth and second at a shallower depth having different P-axes were observed that verifies the internal structure and geometry of Hindukush zone as suggested in previous studies.Beneath the Hindukush collision zone,there exists a complex pattern of deformation,arising from a combination of compression,tension,shearing and necking states due to an unusual and a rare case of subduction that is not from oceanic plate.The Hindukush seismic zone extends from 70 to 300 km depth and mostly strikes east-west and then turns northeast.The relocated seismicity by merging data of seismic network close to Hindukush along with international data shows that the Hindukush zone may be divided vertically into upper and lower slabs separated by a gap at about 150 km depth at which strike and dip directions change sharply with significant structural changes.Seismicity rate is higher in the lower part of Hindukush,having large magnitude events in a small volume below 180 km forming complex pattern of source mechanisms.Contrary in upper part seismicity rate is lower and scattered.The Global CMT(Global Centroid-Moment-Tensor Project)source mechanisms of intermediate depth earthquakes have a systematic pattern of reverse faulting with the vertical T-axes,while shallow events do not have such pattern.The vertical T-axes of the intermediate-depth events may be attributed to negative buoyancy caused by subduction of the cold and denser slab.
基金financial support from the National Key R&D Program of China (No. 2021YFC3000600)National Natural Science Foundation of China (No. 41872206)National Nonprofit Fundamental Research Grant of China, Institute of Geology, China, Earthquake Administration (No. IGCEA2010)
文摘The three-dimensional(3D)geometry of a fault is a critical control on earthquake nucleation,dynamic rupture,stress triggering,and related seismic hazards.Therefore,a 3D model of an active fault can significantly improve our understanding of seismogenesis and our ability to evaluate seismic hazards.Utilising the SKUA GoCAD software,we constructed detailed seismic fault models for the 2021 M_(S)6.4 Yangbi earthquake in Yunnan,China,using two sets of relocated earthquake catalogs and focal mechanism solutions following a convenient 3D fault modeling workflow.Our analysis revealed a NW-striking main fault with a high-angle SW dip,accompanied by two branch faults.Interpretation of one dataset revealed a single NNW-striking branch fault SW of the main fault,whereas the other dataset indicated four steep NNE-striking segments with a left-echelon pattern.Additionally,a third ENE-striking short fault was identified NE of the main fault.In combination with the spatial distribution of pre-existing faults,our 3D fault models indicate that the Yangbi earthquake reactivated pre-existing NW-and NE-striking fault directions rather than the surface-exposed Weixi-Qiaohou-Weishan Fault zone.The occurrence of the Yangbi earthquake demonstrates that the reactivation of pre-existing faults away from active fault zones,through either cascade or conjugate rupture modes,can cause unexpected moderate-large earthquakes and severe disasters,necessitating attention in regions like southeast Xizang,which have complex fault systems.
基金funded by the National Natural Science Foundation of China(Grant No.42304072)。
文摘On December 18,2023,an M_(s)6.2 earthquake jolted Jishishan County in the Linxia Hui Autonomous Prefecture in Northwest China's Gansu Province,causing substantial casualties and building collapses.The earthquake occurred in the Qilian Block on the northeastern border of the Qinghai-Tibet Plateau,where faults are highly active and the geological structure is complex.In this study,we utilized methods such as relocation,focal mechanism solutions,and earthquake rupture processes to describe seismogenic faults.The results indicated that the majority of aftershocks occurred at a depth of 12 km.The centroid depth of the main shock and the depth of the maximum rupture point during the rupture process were also 12 km.Various geophysical methods exhibited a high degree of consistency in depth exploration.Aftershocks were distributed mainly to the west and north of the main shock and extended in the NNW direction,primarily through unilateral rupture.The main shock was a reverse thrust event with a small dextral strike-slip component.In this study,more regional data,such as previous GPS observations,field geological observations,and the distributions of the primary stress states in the region,were also incorporated.We inferred that the main shock was triggered by the main fault at the northern margin of the Lajishan Fault and that the movement of the main fault also activated some secondary faults.The compressive forces on both sides of the Lajishan Fault Zone led to the uplift of mountain areas,accompanied by some landslides,leading to this catastrophic earthquake event.In this article,the activity relationships among the 2022 M_(s)6.9 Menyuan earthquake,the 2019 M_(s)5.7 Xiahe earthquake,and the Jishishan earthquake under the action of regional stress are also discussed.This study provides additional evidence and new ideas for exploring the seismogenic process of the Lajishan Fault Zone and has implications for future in-depth research on underground activity in this region.
基金supported by the National Natural Science Foundation of China(Grant No.42277152,42041006)the Fundamental Research Funds for the Central Universities,Chang'an University(300102262910)+2 种基金supported by the International Science and Technology Cooperation Program of China(202406560140)Shaanxi Province Science and Technology Innovation Team(Ref.2021TD-51)the innovation team of Shaanxi Provincial Tri-Qin Scholars with Geoscience Big Data and Geohazard Prevention(2022)。
文摘The December 18,2023,M_(S)6.2 Jishishan earthquake occurred along the northeastern margin of the Qinghai-Xizang Plateau within the Laji-Jishi Shan Fault Zone(LJSFZ),a complex thrust-dominated tectonic belt.To identify the seismogenic fault and better understand the regional tectonic framework,we integrated high-resolution Digital Elevation Models(DEMs)derived from GF-7 stereo satellite and Unmanned Aerial Vehicle(UAV)photogrammetry,relocated aftershock sequences,and conducted detailed field investigations.Our results identify four Late Quaternary thrust faults(F1-1 to F1-4),among which the Zhaomuchuan fault(F1-3),a NE-dipping back-thrust,aligns closely with the main-shock and aftershock distribution and exhibits clear Holocene activity.Seismic relocation reveals a NEdipping seismogenic zone at depths of 5-12 km,consistent with a shallow reverse-faulting mechanism under WSW-ENE oblique compression.Structural analysis and cross-sectional profiles suggest that fault F1-3 propagates into a mid-crustal detachment surface,forming a foreland-vergent thrust-nappe system.Importantly,the rupture of this secondary fault,rather than the locked primary boundary fault F1-1,indicates stress transfer and localization within a critically tapered wedge,consistent with global analogs of back-thrust-dominated earthquakes.These findings underscore the seismotectonic complexity of the LJSFZ and highlight the significant seismic hazard posed by subsidiary structures in compressional settings.
文摘As a crucial pivot for national strategic development,the university relocation project in Xiong’an New Area undertakes the mission of optimizing capital functions and promoting regional coordinated development.Taking the Xi-ong’an Campus of China University of Geosciences(Beijing)as a case study,this paper explores the collaborative pa-thways between universities and cities in terms of functional complementarity,resource sharing,and ecological symbiosis from the perspective of campus functional layout and spatial optimization.By integrating four core concepts—green ecology,intelligent technology,cultural inheritance,and traffic optimization—it proposes a design strategy of“breaking boundaries and multi-dimensional linkage,”aiming to construct a new spatial paradigm of urban-university integration and provide theoretical support and practical references for the development of higher education and urbanization in Xiong’an New Area.
基金supported by Fundamental Research Funds from the Institute of Geophysics,China Earthquake Administration(Nos.DQJB22B26 and DQJB22B19)the National Key Research and Development Program of China(No.2020YFA0710603-02).
文摘The epicenter of the Luxian M_(S)6.0 earthquake on September 16,2021,was located in the southern Sichuan Basin,which is a historically seismically quiescent area.In recent years,the frequency of earthquakes has increased with the large-scale exploitation of shale gas.No evident surface fractures or seismic faults were observed after the Luxian earthquake.Based on high-quality data recorded by a dense seismic array composed of 70 portable stations with an average spacing of 2-3 km,a highresolution seismic catalog was constructed for 7 days before and 36 days after the M_(S)6.0 earthquake using LOC-FLOW,an effective workflow of phase picking,phase association,and earthquake location.Based on the new earthquake catalog,four earthquake clusters that occurred within the Yujiasi Syncline during this period were identified.Among them,the M_(S)6.0 main earthquake sequence had a NW-SE trend and inclined towards the SW,with a length of approximately 8 km and width of 5 km.The M_(S)6.0 earthquake sequence only appeared after the mainshock.The other three clusters were located in the northeast direction of the M_(S)6.0 earthquake sequence,all of which were NE-SW trending strips and had no evident direct correlation with the M_(S)6.0 mainshock.The focal depth was concentrated in the range of 2-7 km.Based on the seismic sequence profile and structural background,the M_(S)6.0 seismic structure may be a blind buried fault zone with a NW strike composed of multiple small conjugate faults with NE and SW dip.The fault was not exposed on the surface and was related to the detachment structure in the deep part of the Sichuan Basin.
文摘Stepping into Donglong Group’s intelligent factory in the Yangtze River Delta,the automated production lines is transforming fluffy down into premium home textiles export to Europe and America.At a pivotal moment of global supply chain restructuring,this homegrown textile and apparel exporter is answering a critical question:How can Chinese textile companies sustain their competitive edge amid tariff barriers and supply chain relocation?
基金Projects(11472311,41272304,51504288)supported by the National Natural Science Foundation of China
文摘A new method, named relocation, was proposed to reduce the impact of sensor errors systematically, especially whenavailable data of sensors are abundant. The procedure includes evaluating the reliability of every sensors datum, processing the initiallocation by the credible data, and selecting a set of equations with optimal noise tolerance according to the relative relationshipbetween the initial location and sensors location, then calculating the final location by k-mean voting. The results obtained in thisresearch include comparing traditional location method with the presented method in both simulation and field experiment. In thefield experiment, the location error of relocation method reduced 41.8% compared with traditional location method. The resultssuggested that relocation method can improve the fault-tolerant performance significantly.
基金Supported by Talent-Introduction Scientific Research Program of Yancheng Institute of Technology(XKR2011078)~~
文摘By investigating present relocation residential districts for peasants whose houses are removed for the unified planning of rural areas in north Jiangsu Province, as well as residents' feelings about the environment of residential district, main architectural structures and energy consumption conditions, the indoor thermal environment, use of main heating and cooling facilities, residents' satisfaction on the acoustical and luminous environment, major space-enclosing structures and calculation of energy-saving designs are analyzed, and suggestions are given for the architectural design of relocation residential districts in the study area. It is stressed that the relationship between energy conservation and architectural layout, orientation, lighting, ventilation, selection of enclosing-structure materials, facade, color and style should be properly handled in the planning, and the focus is to control building orientation and shape coefficient, on the basis of which energy-saving designs of windows, exterior walls and roofs can be done. Energy consumption of present residential buildings is calculated and analyzed to bring forth new ideas to the energy-saving designs for relocation residential districts in north Jiangsu Province, and establish an architectural energy-saving system suitable for climatic and natural conditions of north Jiangsu to instruct the energy-saving designs of relocation residential districts in the study area.
文摘The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.
基金supported by the National Natural Science Foundation of China(71861147002 and 71761147004)supported by the Fundamental Research Funds for the Central Universitiesthe Research Funds of Renmin University of China(20XHN086)。
文摘This paper analyses the impact of the poverty alleviation relocation(PAR)program on rural household income and evaluates the heterogeneous income effects of various relocation modes,based on a panel dataset of relocated households from 16 counties in eight Chinese provinces.The results show that participation in the PAR increases the income of both rural and urban resettlers.More specifically,it has a significant positive effect on agricultural and wage income for rural and urban resettlers,respectively.Further analyses show that the income increase for rural resettlers was mainly due to agricultural technology training and that the income increase for town resettlers was attributed to medical security.For the village resettlers,policies should focus on strengthening the development of local industries and training of agricultural technologies.For the urban resettlers,non-agricultural employment and public services in the urban resettlement areas should be promoted.
基金supported by National Natural Science Foundation of China(Nos.40974201 and 40774044)to J.Lei
文摘An earthquake with Ms5.8 occurred on 10 March 2011 in Yingjiang county, western Yunnan, China. This earthquake caused 25 deaths and over 250 injuries. In order to better understand the seismotectonics in the region, we collected the arrival time data from the Yunnan seismic observational bulletins during 1 January to 25 March 2011, and precisely hand-picked the arrival times from high-quality seismograms that were recorded by the temporary seismic stations deployed by our Institute of Crustal Dynamics, China Earthquake Administration. Using these arrival times, we relocated all the earthquakes including the Yingjiang mainshock and its aftershocks using the double-difference relocation algorithm. Our results show that the relocated earthquakes dominantly occurred along the ENE direction and formed an upside-down bow-shaped structure in depth. It is also observed that after the Yingjiang mainshock, some aftershocks extended toward the SSE over about 10 km. These results may indicate that the Yingjiang mainshock ruptured a conjugate fault system consisting of the ENE trending Da Yingjiang fault and a SSE trending blind fault. Such structural features could contribute to severely seismic hazards during the moderate-size Yingjiang earthquake.
基金supported by National Science Foundation of China(41574047)National Key R&D Program of China(2018YFC150330501)
文摘To reveal the geometry of the seismogenic structure of the Aug. 8, 2017 M_S 7.0 Jiuzhaigou earthquake in northern Sichuan,data from the regional seismic network from the time of the main event to Oct. 31, 2017 were used to relocate the earthquake sequence by the tomoDD program, and the focal mechanism solutions and centroid depths of the M_L ≥ 3.5 events in the sequence were determined using the CAP waveform inversion method. Further, the segmental tectonic deformation characteristics of the seismogenic faults were analyzed preliminarily by using strain rosettes and areal strains(As). The results indicate:(1) The relocated M_S 7.0 Jiuzhaigou earthquake sequence displays a narrow ～ 38 km long NNW-SSE-trending zone between the NW-striking Tazang Fault and the nearly NSstriking Minjiang Fault, two branches of the East Kunlun Fault Zone. The spatial distribution of the sequence is narrow and deep for the southern segment, and relatively wide and shallow for the northern segment. The initial rupture depth of the mainshock is 12.5 km, the dominant depth range of the aftershock sequence is between 0 and 10 km with an average depth of 6.7 km. The mainshock epicenter is located in the middle of the aftershock region, showing a bilateral rupture behavior. The centroid depths of 32 M_L ≥ 3.5 events range from 3 to 12 km with a mean of about 7.3 km, consistent with the predominant focal depth of the whole sequence.(2) The geometric structure of the seismogenic fault on the southern section of the aftershock area(south of the mainshock) is relatively simple, with overall strike of ～150° and dip angle ～75°, but the dip angle and dip-orientation exhibit some variation along the segment. The seismogenic structure on the northern segment is more complicated; several faults, including the Minjiang Fault, may be responsible for the aftershock activities. The overall strike of this section is ～159° and dip angle is ～59°, illustrating a certain clockwise rotation and a smaller dip angle than the southern segment. The differences between the two segments demonstrate variation of the geometric structure along the seismogenic faults.(3) The focal mechanism solutions of 32 M_L ≥ 3.5 events in the earthquake sequence have obvious segmental characteristics. Strike-slip earthquakes are dominant on the southern segment, while 50% of events on the northern segment are thrusting and oblique thrusting earthquakes, revealing significant differences in the kinematic features of the seismogenic faults between the two segments.(4) The strain rosettes for the mainshock and the entire sequence of 31 M_L ≥ 3.5 aftershocks correspond to strike-slip type with NWW-SEE compressional white lobes and NNE-SSW extensional black lobes of nearly similar size. The strain rosette and As value of the entire sequence of 22 M_L ≥ 3.5 events on the southern segment are the same as those of the M_S 7.0 mainshock,indicating that the tectonic deformation here is strike-slip. However, the strain rosette of the entire sequence of 10 M_L ≥ 3.5 events on the northern segment show prominent white compressional lobes and small black extensional lobes, and the related As value is up to 0.52,indicating that the tectonic deformation of this segment is oblique thrusting with a certain strike-slip component. Differences between the two segments all reveal distinctly obvious segmental characteristics of the tectonic deformation of the seismogenic faults for the Jiuzhaigou earthquake sequence.
基金supported by the Wenchuan Fault Scientific Drilling Program(WFSD),the Key Projects in the National Science and Technology Pillar Program during the Eleventh Five-year Plan Period under grant No. 2008BAC38B02-4the National Natural Science Foundation of China under grant No. 40821062
文摘We relocate the spatial distribution of its aftershocks. The relocation database is obtained the devastating 12 May 2008 Wenchuan earthquake and from 89 stations deployed by the China Earthquake Administration, including 54 525 seismograms from 1 376 local earthquakes over Ms3.5 between 12 May 2008 and 3 August 2008. The cross-correlation technique used in this paper has greatly improved the relocation precision by giving much more accurate P-wave differential travel-time measurements than those obtained from routinely picked phase onsets. At the same time, we pick P-wave polarity observations of the Wenchuan earthquake series （hereafter referred to as WES） from 1023 stations in China and 59 IRIS （Incorporated Research Institutions of Seismology） stations. Then, employing a newly developed program CHNYTX, we obtain 83 well-determined focal mechanism solutions （hereafter referred to as FMSs）. Based on spatial distribution and FMSs of the WES, we draw following conclusions： （1） The region near the main shock exhibits a buried low-angle northwest-dipping seismic zone with the main shock at its upper end and two conjugated seismic zones dipping southeast with roughly equal dip-angle; （2） The compressional directions of all kinds of FMSs of the WES are subhorizontal, which reflects the dominant stress in this area is eompressional; （3） The principal compressional direction of the regional stress around Wenchuan is roughly perpendicular to the strike of Beichuan-Yingxiu fault, while around Qingchuan it is roughly parallel to the strike of Qingehuan fault. In intermediate part of the Longmenshan area, the principal compressional direction of the stress should be in-between; （4） The possibly existed molten materials in the lower crust of Songpan-Garze terrain have small contribution to the local stress state in Longmenshan area. The listric geometries of the Longmenshan faults most probably resulted from subhorizontal compression along NW-SE direction in history.
基金jointly funded by the National Key Research and Development Program of China (No. 2021YFC3000702)the Special Fund of the Institute of Geophysics, China Earthquake Administration (No. DQJB21Z05)the National Natural Science Foundation of China (No. 41804062)
文摘The 2022 Menyuan M_(S)6.9 earthquake,which occurred on January 8,is the most destructive earthquake to occur near the Lenglongling(LLL)fault since the 2016 Menyuan M_(S)6.4 earthquake.We relocated the mainshock and aftershocks with phase arrival time observations for three days after the mainshock from the Qinghai Seismic Network using the double-difference method.The total length and width of the aftershock sequence are approximately 32 km and 5 km,respectively,and the aftershocks are mainly concentrated at a depth of 7-12 km.The relocated sequence can be divided into 18 km west and 13 km east segments with a boundary approximately 5 km east of the mainshock,where aftershocks are sparse.The east and west fault structures revealed by aftershock locations differ significantly.The west fault strikes EW and inclines to the south at a 71°-90°angle,whereas the east fault strikes 133°and has a smaller dip angle.Elastic strain accumulates at conjunctions of faults with different slip rates where it is prone to large earthquakes.Based on surface traces of faults,the distribution of relocated earthquake sequence and surface ruptures,the mainshock was determined to have occurred at the conjunction of the Tuolaishan(TLS)fault and LLL fault,and the west and east segments of the aftershock sequence were on the TLS fault and LLL fault,respectively.Aftershocks migrate in the early and late stages of the earthquake sequence.In the first 1.5 h after the mainshock,aftershocks expand westward from the mainshock.In the late stage,seismicity on the northeast side of the east fault is higher than that in other regions.The migration rate of the west segment of the aftershock sequence is approximately 4.5 km/decade and the afterslip may exist in the source region.
基金financially supported by National Science Foundation of China(No.41774067)the National Key R&D Program of China(No.2018YFC1503400)+1 种基金the Special Fund of the Institute of GeophysicsChina Earthquake Administration(No.DQJB20X07)。
文摘An Ms 6.4 earthquake occurred in Yangbi,Yunnan,China on May 21,2021,which has obvious foreshock activity and abundant aftershocks.Based on the seismic observation data recorded by the Yunnan Seismic Network three days before and seven days after the mainshock,a doubledifference location method was used to relocate 2133 earthquakes of the Yangbi sequence.Aftershocks are mostly distributed to the southeast of the mainshock in a unilateral rupture pattern.This sequence exhibits a SE-trending linear alignment with a length of about 25 km,and most of the focal depth is above 12 km.Integrated with the seismic distribution and focal mechanism results,we infer that the strike of the seismogenic fault is about 140°,and dipping to the SW.The fault structure revealed by the seismic sequence is complex,with the NW segment exhibiting a steep dip and relatively simple structure of strike-slip rupture and the SE segment consisting of several branching ruptures.The Yangbi Earthquake is a typical foreshock-mainshock-aftershock sequence,and the mainshock is likely triggered by the largest foreshock.This earthquake occurred in the boundary between high-and lowvelocity anomalous zone,where is susceptible to generate large earthquakes.
基金supported by the National Natural Science Foundation of China(No.41074074)
文摘Because surface-based monitoring of hydraulic fracturing is not restricted by borehole geometry or the difficulties in maintaining subsurface equipment, it is becoming an increasingly common part of microseismic monitoring. The ability to determine an accurate velocity model for the monitored area directly affects the accuracy of microseismic event locations. However, velocity model calibration for location with surface instruments is difficult for several reasons： well log measurements are often inaccurate or incomplete, yielding intractable models; ori- gin times of perforation shots are not always accurate; and the non-uniqueness of velocity models obtained by inver- sion becomes especially problematic when only perforation shots are used. In this paper, we propose a new approach to overcome these limitations. We establish an initial velocity model from well logging data, and then use the root mean square （RMS） error of double-difference arrival times as a proxy measure for the misfit between the well log velocity model and the true velocity structure of the medium. Double-difference RMS errors are reduced by using a very fast simulated annealing for model perturbance, and a sample set of double-difference RMS errors is then selec- ted to determine an empirical threshold. This threshold value is set near the minimum RMS of the selected samples, and an appropriate number of travel times within the threshold range are chosen. The corresponding velocity models are then used to relocate the perforation-shot. We use the velocity model with the smallest relative location errors as the basis for microseismic location. Numerical analysis with exact input velocity models shows that although large differences exist between the calculated and true velocity models, perforation shots can still be located to their actual positions with the proposed technique; the location inaccuracy of the perforation is 〈2 m. Further tests on field data demonstrate the validity of this technique.
