Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the r...Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. "The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.展开更多
Accurate determination of seismic velocity of the crust is important for understanding regional tectonics and crustal evolution of the Earth. We propose a stepwise joint linearized inversion method using surface wave ...Accurate determination of seismic velocity of the crust is important for understanding regional tectonics and crustal evolution of the Earth. We propose a stepwise joint linearized inversion method using surface wave dispersion, Rayleigh wave ZH ratio (i.e., ellipticity), and receiver function data to better resolve 1D crustal shear wave velocity (Vs) structure. Surface wave dispersion and Rayleigh wave ZH ratio data are more sensitive to absolute variations of shear wave speed at depths, but their sensi- tivity kernels to shear wave speeds are different and complimentary. However, receiver function data are more sensitive to sharp velocity contrast (e.g., due to the existence of crustal interfaces) and Vp/Vs ratios. The stepwise inversion method takes advantages of the complementary sensitivities of each dataset to better constrain the Vs model in the crust. We firstly invert surface wave dispersion and ZH ratio data to obtain a 1D smooth absolute vs model and then incorporate receiver function data in the joint inver- sion to obtain a finer Vs model with better constraints on interface structures. Through synthetic tests, Monte Carlo error analyses, and application to real data, we demonstrate that the proposed joint inversion method can resolve robust crustal Vs structures and with little initial model dependency.展开更多
For sites susceptible to liquefaction induced lateral spreading during a probable earthquake, geotechnical engineers often need to know the undrained residual shear strength of the liquefied soil deposit to estimate l...For sites susceptible to liquefaction induced lateral spreading during a probable earthquake, geotechnical engineers often need to know the undrained residual shear strength of the liquefied soil deposit to estimate lateral spreading displacements, and the forces acting on the piles from the liquefied soils in order to perform post liquefaction stability analyses. The most commonly used methods to estimate the undrained residual shear strength (Su~) of liquefied sand deposits are based on the correlations determined from liquefaction induced flow failures with SPT and CPT data. In this study, 44 lateral spread case histories are analyzed and a new relationship based on only lateral spread case histories is recommended, which estimates the residual shear strength ratio of the liquefiable soil layer from normalized shear wave velocity. The new proposed method is also utilized to estimate the residual lateral displacement of an example bridge problem in an area susceptible to lateral spreading in order to provide insight into how the proposed relationship can be used in geotechnical engineering practice.展开更多
Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5...Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5 and MS4.0 earthquakes on February 8,2016,as well as the epicenter of the Yunlong MS5.0 and Eryuan MS4.6 earthquakes on May 18,2016 through the waveform cross-correlation technique.The wave velocity ratio of the four stations was calculated using the single-station method.At the same time,the b-value and the focal mechanism consistency parameters of the study area were also calculated.The results show that:(1)the wave velocity ratio of each station experienced a process of decline-recovery-fast rise before the two strong earthquakes,and a significant quasi-synchronous rapid rise occurred within 3-12 days before the earthquake;(2)the timing of the rapid rise of the wave velocity ratio of the four stations before the Yunlong MS5.0 and Eryuan MS4.6 earthquakes were related to the epicentral distance.The station which observed the earliest increase in rapid rise is the farthest one from the epicenter,and the station where the rapid rise appeared in the latest is closest to the epicenter;(3)the form of change of the wave velocity ratio before the earthquake was different between stations located at different directions in the epicenter area;(4)the b-value and the focal mechanism consistency parameter which is commonly used to characterize the stress level both showed a downward trend before the two strong earthquakes,and were consistent with the change in the wave velocity ratio.According to the preliminary analysis,the wave velocity ratio obtained by using airgun source can better reflect the change in the stress state of the underground medium.展开更多
In this work,we investigated the influences of salinity,temperature,and hydrostatic pressure on the acoustics of seafloor surficial sediment by theoretically and experimentally analyzing the sound velocity ratio of th...In this work,we investigated the influences of salinity,temperature,and hydrostatic pressure on the acoustics of seafloor surficial sediment by theoretically and experimentally analyzing the sound velocity ratio of the seafloor sediment to the bottom sea-water in typical environmental conditions.Temperature-and pressure-controlled experiments were conducted to examine the charac-teristics of the sound velocity ratio,the results of which agree with the theoretical analysis using the effective density fluid model.Of the three environmental factors considered,the sound velocity ratio was found to be sensitive to temperature and pressure but not to salinity,with the sound velocity ratio decreasing with temperature and hydrostatic pressure.With respect to surficial sediments,pore water plays a key role in the sound velocity ratio of sediment influenced by different environmental factors.The sound velocities of different types of sediments(sandy,silty,and clayey)change similarly with temperature,but change slightly differently with hydro-static pressure.The influence of environmental factors on the sound velocity ratio of seafloor sediment is independent of the detec-tion frequency.The results show that the sound velocity ratio can change up to 0.0008 per℃ when the temperature ranges from 2℃ to 25℃ and up to 0.00064MPa−1 when the seawater depth pressure ranges from 0MPa to 40MPa.展开更多
Using pure S wave fitting method, we studied the shear wave velocity structures under the Ordos block and its eastern and southern marginal areas. The results show that the velocity structure beneath Yulin station in ...Using pure S wave fitting method, we studied the shear wave velocity structures under the Ordos block and its eastern and southern marginal areas. The results show that the velocity structure beneath Yulin station in the interior of Ordos block is relatively stable, where no apparent change between high and low velocity layers exists and the shear wave velocity increases steadily with the depth. There is a 12km thick layer at the depth of 25km under this station, with an S wave velocity (V S=3.90km/s) lower than that at the same depth in its eastern and southern areas (V S≥4.00km/s). The crust under the eastern margin of Ordos block is thicker than that of the Yulin station, and the velocity structures alternate between the high and low velocity layers, with more low velocity layers. It has the same characteristic as having a 10km-thick low velocity layer (V S=3.80km/s) in the lower crust but buried at a depth of about 35km. Moreover, we studied the V P/V S ratio under each station in combination with the result of P wave velocity inversion. The results show that, the average velocity ratio of the Yulin station at the interior of Ordos block is only 1.68, with a very low ratio (about 1.60) in the upper crust and a stable ratio of about 1.73 in the mid and lower crust, which indicates the media under this station is homogenous and stable, being in a state of rigidity. But at the stations in the eastern and southern margins of the Ordos block, several layers of high velocity ratio (about 1.80) have been found, in which the average velocity ratio under Kelan and Lishi stations at the eastern margin is systemically higher than that of the general elastical body waves (1.732). This reflects that the crust under the marginal areas is more active relatively, and other materials may exist in these layers. Finally, we discussed the relationship among earthquakes, velocity structures beneath stations and faults.展开更多
The apparent velocity of the incident wave is an important parameter for simulating rotational ground motion with theoretical methods, but it is difficult to estimate effectively when there is only a single record. Th...The apparent velocity of the incident wave is an important parameter for simulating rotational ground motion with theoretical methods, but it is difficult to estimate effectively when there is only a single record. This paper discusses a P-SV ratio method based on elastodynamic theory in a multi-layer isotropic elastic half space. The apparent velocities of four earthquakes in the SMART1 array are calculated with this method. The result is close to a method that uses travel time analysis. Furthermore, the factors that impact the apparent velocity and equivalent incident angle are considered according to records from the Chi-Chi earthquake. There is no obvious relationship between the equivalent incident angle and epicenter distance. However, the equivalent incident angle is obviously dependent on the site conditions.展开更多
Within a short period of 7 months from July 12, 1995 to February 3, 1996, three earthquakes occurred continually to west Menglian in the border area of China Myanmar ( M =7.3), in Wuding county M =6.5 and in L...Within a short period of 7 months from July 12, 1995 to February 3, 1996, three earthquakes occurred continually to west Menglian in the border area of China Myanmar ( M =7.3), in Wuding county M =6.5 and in Lijiang ( M =7.0) in Yunnan area. In this paper, the authors have studied the time space evolution characteristics of wave velocity ratio ( γ ) in observed at 5 single stations and the average value of several stations before the recent strong earthquakes. It is discovered that 5~8 years before the earthquake with M =7, source precursors of long medium term, with high (low) drastic variations of wave velocity ratio, appeared within 120 km from the epicenters, and the source precursors of long medium term entered into medium short term stage when the amplitude of wave velocity ratio suddenly increased (decreased) or times of earthquake increase drastically. Three to five years before M =6 earthquakes, source precursors of long medium term and near field precursors of long medium term, with abrupt velocity change of high values, appeared within 40 and 150 km; however, the indicator is not clear in the period of transition to medium short stage. The anomaly of γ within 150 km from the epicenter reaches as much as 3.0, while the maximum value is 2.36 in the area 250 km away, showing the characteristics that the shorter the distance the bigger the abrupt change. Namely, the anomalous amplitudes of source precursors and near field precursors are 20%~60% bigger than that of far field precursors. The reliability of abrupt variation data of γ and its physical mechanism have also been explored in this paper.展开更多
Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we col...Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.展开更多
Dynamic tracing of space-time evolution pattern of wave velocity ratio before the Lijiang earthquake with M=7.0 occurred on February 3, 1996 in northwestern Yunnan. We compared the Ninglang earthquakes with M=6.7 and ...Dynamic tracing of space-time evolution pattern of wave velocity ratio before the Lijiang earthquake with M=7.0 occurred on February 3, 1996 in northwestern Yunnan. We compared the Ninglang earthquakes with M=6.7 and M=6.4 which occurred on November 7 and December 13. 1976, 90 km away from the Lijiang earthquake. We found that the space-time evolution patterns of velocity that various authors’ studied at different times are very similar.Anomaly areas of wave velocity ratio with high values appeared in the seismogenic areas 5 -7 years before the strong earthquake. Anomalies with low values in large areas appeared 3-4 years before the earthquake. Once again the anomaly areas of wave velocity ratio with high values appear in a lower range 1 ~2 years before. The strong earthquake occurred in the overlapping area of two high value anomaly areas, surrounded by the anomaly areas with low values. The monthly mean values of wave velocity ratio before the two strong earthquakes had maintained low value展开更多
In this paper,the process of dynamic variation of the wave velocity ratio that occurred at a single station,such as Lancang,Tengchong,and Eryuan stations,8 years before the Lancang-Gengma earthquakes(Ms=7.6 and 7.2),i...In this paper,the process of dynamic variation of the wave velocity ratio that occurred at a single station,such as Lancang,Tengchong,and Eryuan stations,8 years before the Lancang-Gengma earthquakes(Ms=7.6 and 7.2),is studied by applying the synthetic method as a whole.It is found that the moderately strong and strong earthquakes 250 km away that occurred since 1983 may lead to mutation anomalies of the wave velocity ratio in the Lancang region.The mutation amplitude is increased with the approaching time and distance of a large event.The reliability of mutation data for the wave velocity ratio has been demonstrated in many ways.The application of mutation of the wave velocity ratio to earthquake prediction and its physical explanation are discussed.展开更多
The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight ...The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.展开更多
The focal mechanism parameters of small earthquakes are determined by the maximum velocity and displacement amplitude ratio of the direct ^-P- and ^-S-waves recorded by digital stations. The displacement is obtained f...The focal mechanism parameters of small earthquakes are determined by the maximum velocity and displacement amplitude ratio of the direct ^-P- and ^-S-waves recorded by digital stations. The displacement is obtained from the velocity by emulation, and the two results are compared and analyzed. Results of theoretical analysis and practical measurement indicate that the two results of velocity and displacement are consistent, and it is feasible that the maximum displacement amplitude ratio be replaced by the maximum velocity amplitude ratio of the direct ^-P-and ^-S- waves recorded by regional seismic networks when determining focal mechanism solutions of small earthquakes.展开更多
By using the teleseismic receiver function method, this paper analyzes the crustal thickness and Vp/Vs ratios beneath the 4 National seismic stations (KMI, TNC, CD2 and PZH) in the Sichuan-Yunnan area. This study gi...By using the teleseismic receiver function method, this paper analyzes the crustal thickness and Vp/Vs ratios beneath the 4 National seismic stations (KMI, TNC, CD2 and PZH) in the Sichuan-Yunnan area. This study gives the variance of Moho depths and velocity ratios of the 4 stations in different directions. The results show that the Moho depth beneath the Kunming station is around 50km, and the vdocity ratio varies between 1.62 and 1.69. The thickness of crust and the velocity ratio do not change much with the direction. The crust beneath Tengchong station shows clear directivity, being 40.7km thick in the northeast and 49.7km thick in the southeast. The difference of the Vp/Vs values is remarkable between the two directions, reaching 0.2. The Chengdu station also has shallow Moho, about 40km, but is 8km deeper in the northeast and southwest and the vdocity ratio has a change of 0.13 between the two directions. The crust beneath the Panzhihua station is stable. In all directions, the Moho depth is around 60km and the Vp/Vs ratio doesn't change significantly.展开更多
This paper deals with the response features of AR(apparent ratio of seismic wave velocities to the changes of TR(true ratio of wave velocities)in the horizontal layered model by mathematical modeling.The results show ...This paper deals with the response features of AR(apparent ratio of seismic wave velocities to the changes of TR(true ratio of wave velocities)in the horizontal layered model by mathematical modeling.The results show that:(1)the response features of AR are associated with the parameters of the structure and its dynamic changes,and the relative position between the hypocenters and the monitoring networks,showing complicated patterns strongly related to the concrete paths of propagation of seismic waves from the source to the receiver in the observatories of the network;(2)the depth of the seismic source would have important influence on the response features of AR,especially the capacity to carry the anomalous information in the condition of the earth media,being in the anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers;(3)the response features of AR are clearly related to the changes of TR(true ratio of wave velocities)instead of changes of wave velocities themselves,i.e.the response could be small as the changes in TR is small even in the case of large changes in the wave velocities.It is suggested that more attention must be paid to all these features in combination with detailed investigation of the velocity structure of the earth media in the study region and best fitting of precise hypocenter locations when one wants to obtain the reliable precursors from the changes in AR.展开更多
Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using t...Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using the multi-station method in Tianshan,Xinjiang.This paper analyzes the variation of the wave velocity ratio disturbance value to highlight the abnormal,and also back-traces 7 moderate earthquakes at the research area.The results show that:(1)the background value of the wave velocity ratio is almost 1.70,the wave velocity ratio obviously decreases in the middle-eastern part of Tianshan and the region near the Puchang fault;(2)the wave velocity ratio disturbance value is mostly low in the epicenter before four earthquakes of M≥5.0 from 2011 to 2013 in the study area;(3)before 7 moderate strong earthquakes,the earthquake events with low value of the wave velocity ratio account for over 60% of corresponding total events near the epicenters,and the low value of the wave velocity ratio is relatively obvious before moderate earthquakes.展开更多
The geological structure is complex in the Hohhot-Baotou area.Several earthquakes with MS≥6.0 have occurred in the area in history.This article selected the Hohhot-Baotou area as the study region and divided it into ...The geological structure is complex in the Hohhot-Baotou area.Several earthquakes with MS≥6.0 have occurred in the area in history.This article selected the Hohhot-Baotou area as the study region and divided it into 2 sub-regions,each with a spatial scope of 3°×2°,according to the spatial distribution of ML≥1.0 earthquakes occurring between January 2001 and April 2010,and the layout of the seismic network in the study region.Average velocity ratios of respective sub-regions were calculated,and comparative analysis was made on their temporal and spatial variations.Results show that there are slight differences between sub-regions in the variation amplitude of average velocity ratio curves over time,which mostly remains between 2.5% to 2.584%.In the Hohhot area,the average velocity ratio is 1.722,significantly lower than the average velocity ratio of 1.733 in the Baotou area.We preliminarily concluded that this was related to the distribution of fault structures and properties of underground media in the Hohhot area.展开更多
The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in v...The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in various isotropic materials such as metals, ceramics and rocks. The characteristic J values of the GMR for E, G, K and l of each material are systematically different and display consistent correlations with the Poisson’s ratio of the nonporous material(v0). For the materials dominated by corner-shaped pores, the fixed point at which the effective Poisson’s ratio(n) remains constant is at v0=0.2, and J(G) > J(E) > J(K) > J(l) and J(G) < J(E) < J(K) < J(l) for materials with v0> 0.2 and v0< 0.2, respectively.J(Vs) > J(Vp) and J(Vs) < J(Vp) for the materials with v0> 0.2 and v0< 0.2, respectively. The effective n increases, decreases and remains unchanged with increasing porosity for the materials with v0< 0.2,v0> 0.2 and v0=0.2, respectively. For natural rocks containing thin-disk-shaped pores parallel to mineral cleavages, grain boundaries and foliation, however, the n fixed point decreases nonlinearly with decreasing pore aspect ratio(a: width/length). With increasing depth or pressure, cracks with smaller a values are progressively closed, making the n fixed point rise and finally reach to the point at v0=0.2.展开更多
The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the w...The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance (CRR)-shear wave velocity (V)-void ratio (e) of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V of soil is raised high enough (i.e., no less than the critical velocity) to resist the given earthquake loading according to the CRR-V relationship, and then this requirement is transferred to the control of target void ratio (i.e., the critical e) according to the V-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.展开更多
The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influ...The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.展开更多
基金National 973 Key Basic Research Development Program (No.2005CB422104)SINOPEC's Scientific and Technological Development Program (No.P05063)
文摘Based on the empirical Gardner equation describing the relationship between density and compressional wave velocity, the converted wave reflection coefficient extrema attributes for AVO analysis are proposed and the relations between the extrema position and amplitude, average velocity ratio across the interface, and shear wave reflection coefficient are derived. The extrema position is a monotonically decreasing function of average velocity ratio, and the extrema amplitude is a function of average velocity ratio and shear wave reflection coefficient. For theoretical models, the average velocity ratio and shear wave reflection coefficient are inverted from the extrema position and amplitude obtained from fitting a power function to converted wave AVO curves. Shear wave reflection coefficient sections have clearer physical meaning than conventional converted wave stacked sections and establish the theoretical foundation for geological structural interpretation and event correlation. "The method of inverting average velocity ratio and shear wave reflection coefficient from the extrema position and amplitude obtained from fitting a power function is applied to real CCP gathers. The inverted average velocity ratios are consistent with those computed from compressional and shear wave well logs.
基金supported by the National Earthquake Science Experiment in Sichuan and Yunnan Provinces of China(#2016 CESE 0201)National Natural Science Foundation of China(#41574034)China National Special Fund for Earthquake Scientific Research in Public Interest(#201508008)
文摘Accurate determination of seismic velocity of the crust is important for understanding regional tectonics and crustal evolution of the Earth. We propose a stepwise joint linearized inversion method using surface wave dispersion, Rayleigh wave ZH ratio (i.e., ellipticity), and receiver function data to better resolve 1D crustal shear wave velocity (Vs) structure. Surface wave dispersion and Rayleigh wave ZH ratio data are more sensitive to absolute variations of shear wave speed at depths, but their sensi- tivity kernels to shear wave speeds are different and complimentary. However, receiver function data are more sensitive to sharp velocity contrast (e.g., due to the existence of crustal interfaces) and Vp/Vs ratios. The stepwise inversion method takes advantages of the complementary sensitivities of each dataset to better constrain the Vs model in the crust. We firstly invert surface wave dispersion and ZH ratio data to obtain a 1D smooth absolute vs model and then incorporate receiver function data in the joint inver- sion to obtain a finer Vs model with better constraints on interface structures. Through synthetic tests, Monte Carlo error analyses, and application to real data, we demonstrate that the proposed joint inversion method can resolve robust crustal Vs structures and with little initial model dependency.
文摘For sites susceptible to liquefaction induced lateral spreading during a probable earthquake, geotechnical engineers often need to know the undrained residual shear strength of the liquefied soil deposit to estimate lateral spreading displacements, and the forces acting on the piles from the liquefied soils in order to perform post liquefaction stability analyses. The most commonly used methods to estimate the undrained residual shear strength (Su~) of liquefied sand deposits are based on the correlations determined from liquefaction induced flow failures with SPT and CPT data. In this study, 44 lateral spread case histories are analyzed and a new relationship based on only lateral spread case histories is recommended, which estimates the residual shear strength ratio of the liquefiable soil layer from normalized shear wave velocity. The new proposed method is also utilized to estimate the residual lateral displacement of an example bridge problem in an area susceptible to lateral spreading in order to provide insight into how the proposed relationship can be used in geotechnical engineering practice.
基金sponsored by the subproject of Relocation of Earthquakes in Yunnan Area under the project of the Major Seismicity Trend in 2019 of Department of Monitoring and Prediction of CEA,the National Natural Science Foundation of China(41474048,41574059)the Science for Earthquake Resilience of China Earthquake Administration(XH18042Y)
文摘Using the signals excited by the large-volume airgun source at the Binchuan transmitting seismic station from January to June,2016,arrival-time data was acquired at four stations near the epicenter of the Eryuan MS4.5 and MS4.0 earthquakes on February 8,2016,as well as the epicenter of the Yunlong MS5.0 and Eryuan MS4.6 earthquakes on May 18,2016 through the waveform cross-correlation technique.The wave velocity ratio of the four stations was calculated using the single-station method.At the same time,the b-value and the focal mechanism consistency parameters of the study area were also calculated.The results show that:(1)the wave velocity ratio of each station experienced a process of decline-recovery-fast rise before the two strong earthquakes,and a significant quasi-synchronous rapid rise occurred within 3-12 days before the earthquake;(2)the timing of the rapid rise of the wave velocity ratio of the four stations before the Yunlong MS5.0 and Eryuan MS4.6 earthquakes were related to the epicentral distance.The station which observed the earliest increase in rapid rise is the farthest one from the epicenter,and the station where the rapid rise appeared in the latest is closest to the epicenter;(3)the form of change of the wave velocity ratio before the earthquake was different between stations located at different directions in the epicenter area;(4)the b-value and the focal mechanism consistency parameter which is commonly used to characterize the stress level both showed a downward trend before the two strong earthquakes,and were consistent with the change in the wave velocity ratio.According to the preliminary analysis,the wave velocity ratio obtained by using airgun source can better reflect the change in the stress state of the underground medium.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.41676055 and 41776043)the Natural Science Foundation of Guangdong Province(No.2019A1515011055)the Foundation of Qingdao National Laboratory for Marine Science and Te-chnology(No.MGQNLM-KF201805).
文摘In this work,we investigated the influences of salinity,temperature,and hydrostatic pressure on the acoustics of seafloor surficial sediment by theoretically and experimentally analyzing the sound velocity ratio of the seafloor sediment to the bottom sea-water in typical environmental conditions.Temperature-and pressure-controlled experiments were conducted to examine the charac-teristics of the sound velocity ratio,the results of which agree with the theoretical analysis using the effective density fluid model.Of the three environmental factors considered,the sound velocity ratio was found to be sensitive to temperature and pressure but not to salinity,with the sound velocity ratio decreasing with temperature and hydrostatic pressure.With respect to surficial sediments,pore water plays a key role in the sound velocity ratio of sediment influenced by different environmental factors.The sound velocities of different types of sediments(sandy,silty,and clayey)change similarly with temperature,but change slightly differently with hydro-static pressure.The influence of environmental factors on the sound velocity ratio of seafloor sediment is independent of the detec-tion frequency.The results show that the sound velocity ratio can change up to 0.0008 per℃ when the temperature ranges from 2℃ to 25℃ and up to 0.00064MPa−1 when the seawater depth pressure ranges from 0MPa to 40MPa.
文摘Using pure S wave fitting method, we studied the shear wave velocity structures under the Ordos block and its eastern and southern marginal areas. The results show that the velocity structure beneath Yulin station in the interior of Ordos block is relatively stable, where no apparent change between high and low velocity layers exists and the shear wave velocity increases steadily with the depth. There is a 12km thick layer at the depth of 25km under this station, with an S wave velocity (V S=3.90km/s) lower than that at the same depth in its eastern and southern areas (V S≥4.00km/s). The crust under the eastern margin of Ordos block is thicker than that of the Yulin station, and the velocity structures alternate between the high and low velocity layers, with more low velocity layers. It has the same characteristic as having a 10km-thick low velocity layer (V S=3.80km/s) in the lower crust but buried at a depth of about 35km. Moreover, we studied the V P/V S ratio under each station in combination with the result of P wave velocity inversion. The results show that, the average velocity ratio of the Yulin station at the interior of Ordos block is only 1.68, with a very low ratio (about 1.60) in the upper crust and a stable ratio of about 1.73 in the mid and lower crust, which indicates the media under this station is homogenous and stable, being in a state of rigidity. But at the stations in the eastern and southern margins of the Ordos block, several layers of high velocity ratio (about 1.80) have been found, in which the average velocity ratio under Kelan and Lishi stations at the eastern margin is systemically higher than that of the general elastical body waves (1.732). This reflects that the crust under the marginal areas is more active relatively, and other materials may exist in these layers. Finally, we discussed the relationship among earthquakes, velocity structures beneath stations and faults.
基金the National Science Foundation of China Under Grant No.90815026 and 50638010the National Seismic Project Under Grant No.200808074
文摘The apparent velocity of the incident wave is an important parameter for simulating rotational ground motion with theoretical methods, but it is difficult to estimate effectively when there is only a single record. This paper discusses a P-SV ratio method based on elastodynamic theory in a multi-layer isotropic elastic half space. The apparent velocities of four earthquakes in the SMART1 array are calculated with this method. The result is close to a method that uses travel time analysis. Furthermore, the factors that impact the apparent velocity and equivalent incident angle are considered according to records from the Chi-Chi earthquake. There is no obvious relationship between the equivalent incident angle and epicenter distance. However, the equivalent incident angle is obviously dependent on the site conditions.
文摘Within a short period of 7 months from July 12, 1995 to February 3, 1996, three earthquakes occurred continually to west Menglian in the border area of China Myanmar ( M =7.3), in Wuding county M =6.5 and in Lijiang ( M =7.0) in Yunnan area. In this paper, the authors have studied the time space evolution characteristics of wave velocity ratio ( γ ) in observed at 5 single stations and the average value of several stations before the recent strong earthquakes. It is discovered that 5~8 years before the earthquake with M =7, source precursors of long medium term, with high (low) drastic variations of wave velocity ratio, appeared within 120 km from the epicenters, and the source precursors of long medium term entered into medium short term stage when the amplitude of wave velocity ratio suddenly increased (decreased) or times of earthquake increase drastically. Three to five years before M =6 earthquakes, source precursors of long medium term and near field precursors of long medium term, with abrupt velocity change of high values, appeared within 40 and 150 km; however, the indicator is not clear in the period of transition to medium short stage. The anomaly of γ within 150 km from the epicenter reaches as much as 3.0, while the maximum value is 2.36 in the area 250 km away, showing the characteristics that the shorter the distance the bigger the abrupt change. Namely, the anomalous amplitudes of source precursors and near field precursors are 20%~60% bigger than that of far field precursors. The reliability of abrupt variation data of γ and its physical mechanism have also been explored in this paper.
基金supported by Beijing Natural Science Foundation(No.8212041)National Natural Science Foundation of China(Nos.41874063 and U1939203)Shanghai Sheshan National Geophysical Observatory(No.2020K02).
文摘Active faults pose a great threat to urban security.As the largest NW-trend active fault in Beijing area,the Nankou-Sunhe fault plays an important role in earthquake disaster and city construction.In this study,we collect continuous ambient noise data recorded by 43 temporary short-period seismograph between September 21th to October 12th 2019 to investigate the near-surface structure beneath the Nankou-Sunhe fault by using ambient noise tomography(ANT)and horizontal-to-vertical spectral ratio(HVSR)method.From ambient noise processing,fundamental-mode Rayleigh wave signals are clearly observed in the frequency band of 0.4-2.5 Hz.Then direct surface-wave inversion algorithm is applied to calculate the 3D shear-wave velocity model.Our results show that there is a sharp velocity contrast across the Nankou-Sunhe fault,with low velocities down to about 2 km on the hanging wall and high velocity on the footwall of the fault.According to the geological investigation,the low velocities are related to thicker sediments and Jurassic volcanic rock below which are the cap rock of the hydrothermal system.From the HVSR analysis,the HVSR curves of the sites near the fault shows double-peak,one less than 1 Hz and the other centered 7 Hz.After converting frequency to depth by the empirical equation,the results show that the thickness of sediments is thinned from southwest to northeast,which generally agrees well to field survey.Our results provide high-resolution near-surface structure for future study on disaster risk reduction and urban planning.
基金This project was sponsored by China Seismological Bureau (95-04-04).
文摘Dynamic tracing of space-time evolution pattern of wave velocity ratio before the Lijiang earthquake with M=7.0 occurred on February 3, 1996 in northwestern Yunnan. We compared the Ninglang earthquakes with M=6.7 and M=6.4 which occurred on November 7 and December 13. 1976, 90 km away from the Lijiang earthquake. We found that the space-time evolution patterns of velocity that various authors’ studied at different times are very similar.Anomaly areas of wave velocity ratio with high values appeared in the seismogenic areas 5 -7 years before the strong earthquake. Anomalies with low values in large areas appeared 3-4 years before the earthquake. Once again the anomaly areas of wave velocity ratio with high values appear in a lower range 1 ~2 years before. The strong earthquake occurred in the overlapping area of two high value anomaly areas, surrounded by the anomaly areas with low values. The monthly mean values of wave velocity ratio before the two strong earthquakes had maintained low value
文摘In this paper,the process of dynamic variation of the wave velocity ratio that occurred at a single station,such as Lancang,Tengchong,and Eryuan stations,8 years before the Lancang-Gengma earthquakes(Ms=7.6 and 7.2),is studied by applying the synthetic method as a whole.It is found that the moderately strong and strong earthquakes 250 km away that occurred since 1983 may lead to mutation anomalies of the wave velocity ratio in the Lancang region.The mutation amplitude is increased with the approaching time and distance of a large event.The reliability of mutation data for the wave velocity ratio has been demonstrated in many ways.The application of mutation of the wave velocity ratio to earthquake prediction and its physical explanation are discussed.
基金Project supported by the National Natural Science Foundation of china
文摘The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.
基金the"Strong Earthquake Monitoring and Prediction Research"for the 11th"Five-Year Plan"under the grant No.2006BA(01B02-01-01)subspecial subject of 2006BAC01 B02-01-01the State Key Basic Research Development Programme (2004CB418404),China
文摘The focal mechanism parameters of small earthquakes are determined by the maximum velocity and displacement amplitude ratio of the direct ^-P- and ^-S-waves recorded by digital stations. The displacement is obtained from the velocity by emulation, and the two results are compared and analyzed. Results of theoretical analysis and practical measurement indicate that the two results of velocity and displacement are consistent, and it is feasible that the maximum displacement amplitude ratio be replaced by the maximum velocity amplitude ratio of the direct ^-P-and ^-S- waves recorded by regional seismic networks when determining focal mechanism solutions of small earthquakes.
文摘By using the teleseismic receiver function method, this paper analyzes the crustal thickness and Vp/Vs ratios beneath the 4 National seismic stations (KMI, TNC, CD2 and PZH) in the Sichuan-Yunnan area. This study gives the variance of Moho depths and velocity ratios of the 4 stations in different directions. The results show that the Moho depth beneath the Kunming station is around 50km, and the vdocity ratio varies between 1.62 and 1.69. The thickness of crust and the velocity ratio do not change much with the direction. The crust beneath Tengchong station shows clear directivity, being 40.7km thick in the northeast and 49.7km thick in the southeast. The difference of the Vp/Vs values is remarkable between the two directions, reaching 0.2. The Chengdu station also has shallow Moho, about 40km, but is 8km deeper in the northeast and southwest and the vdocity ratio has a change of 0.13 between the two directions. The crust beneath the Panzhihua station is stable. In all directions, the Moho depth is around 60km and the Vp/Vs ratio doesn't change significantly.
文摘This paper deals with the response features of AR(apparent ratio of seismic wave velocities to the changes of TR(true ratio of wave velocities)in the horizontal layered model by mathematical modeling.The results show that:(1)the response features of AR are associated with the parameters of the structure and its dynamic changes,and the relative position between the hypocenters and the monitoring networks,showing complicated patterns strongly related to the concrete paths of propagation of seismic waves from the source to the receiver in the observatories of the network;(2)the depth of the seismic source would have important influence on the response features of AR,especially the capacity to carry the anomalous information in the condition of the earth media,being in the anomalous state would be greater for those earthquakes which occur inside the anomalous layers than those underneath the anomalous layers;(3)the response features of AR are clearly related to the changes of TR(true ratio of wave velocities)instead of changes of wave velocities themselves,i.e.the response could be small as the changes in TR is small even in the case of large changes in the wave velocities.It is suggested that more attention must be paid to all these features in combination with detailed investigation of the velocity structure of the earth media in the study region and best fitting of precise hypocenter locations when one wants to obtain the reliable precursors from the changes in AR.
基金funded by the Earthquake Science Fund of Xinjiang (201404)Seismic Tracing Oriented Task of China Earthquake Administration(2015010122)
文摘Based on the seismic observation report data provided by the Xinjiang Digital Seismic Network from 2009 to 2014,we calculate the wave velocity ratio and its background value for medium and small earthquakes by using the multi-station method in Tianshan,Xinjiang.This paper analyzes the variation of the wave velocity ratio disturbance value to highlight the abnormal,and also back-traces 7 moderate earthquakes at the research area.The results show that:(1)the background value of the wave velocity ratio is almost 1.70,the wave velocity ratio obviously decreases in the middle-eastern part of Tianshan and the region near the Puchang fault;(2)the wave velocity ratio disturbance value is mostly low in the epicenter before four earthquakes of M≥5.0 from 2011 to 2013 in the study area;(3)before 7 moderate strong earthquakes,the earthquake events with low value of the wave velocity ratio account for over 60% of corresponding total events near the epicenters,and the low value of the wave velocity ratio is relatively obvious before moderate earthquakes.
基金sponsored by the Earthquare Science and Technology Spark Plan(Project No.XH12010Y)
文摘The geological structure is complex in the Hohhot-Baotou area.Several earthquakes with MS≥6.0 have occurred in the area in history.This article selected the Hohhot-Baotou area as the study region and divided it into 2 sub-regions,each with a spatial scope of 3°×2°,according to the spatial distribution of ML≥1.0 earthquakes occurring between January 2001 and April 2010,and the layout of the seismic network in the study region.Average velocity ratios of respective sub-regions were calculated,and comparative analysis was made on their temporal and spatial variations.Results show that there are slight differences between sub-regions in the variation amplitude of average velocity ratio curves over time,which mostly remains between 2.5% to 2.584%.In the Hohhot area,the average velocity ratio is 1.722,significantly lower than the average velocity ratio of 1.733 in the Baotou area.We preliminarily concluded that this was related to the distribution of fault structures and properties of underground media in the Hohhot area.
文摘The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in various isotropic materials such as metals, ceramics and rocks. The characteristic J values of the GMR for E, G, K and l of each material are systematically different and display consistent correlations with the Poisson’s ratio of the nonporous material(v0). For the materials dominated by corner-shaped pores, the fixed point at which the effective Poisson’s ratio(n) remains constant is at v0=0.2, and J(G) > J(E) > J(K) > J(l) and J(G) < J(E) < J(K) < J(l) for materials with v0> 0.2 and v0< 0.2, respectively.J(Vs) > J(Vp) and J(Vs) < J(Vp) for the materials with v0> 0.2 and v0< 0.2, respectively. The effective n increases, decreases and remains unchanged with increasing porosity for the materials with v0< 0.2,v0> 0.2 and v0=0.2, respectively. For natural rocks containing thin-disk-shaped pores parallel to mineral cleavages, grain boundaries and foliation, however, the n fixed point decreases nonlinearly with decreasing pore aspect ratio(a: width/length). With increasing depth or pressure, cracks with smaller a values are progressively closed, making the n fixed point rise and finally reach to the point at v0=0.2.
基金National Natural Science Foundation of China under Grant No.51578501 and No.51127005the Foundation for the Author of National Excellent Doctoral Dissertation of P R China under Grant No.201160+3 种基金the Zhejiang Provincial Natural Science Foundation of China under Grant No.LR15E080001the National Basic Research Program of China(973 Project)under Grant No.2014CB047005the Fundamental Research Funds for the Central Universities under Grant No.2014FZA4016Zhejiang University K.P.Chao’s High Technology Development Foundation(2014)
文摘The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance (CRR)-shear wave velocity (V)-void ratio (e) of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre- and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target V of soil is raised high enough (i.e., no less than the critical velocity) to resist the given earthquake loading according to the CRR-V relationship, and then this requirement is transferred to the control of target void ratio (i.e., the critical e) according to the V-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed V-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.
基金supported by the National Natural Science Foundation of China (Grants No.50879019,50909036,and 50879020)the Research Fund for the Doctoral Program of Higher Education (Grants No.200802940001 and 200802941028)+3 种基金the Fundamental Research Funds for the Central Universities (Grants No.2010B02214,2009B08014,and 2010B14214)the Natural Science Foundation of Hohai University(Grant No. 2008426411)the Jiangsu "333" Program for High Level Talents (Grant No. 2017-B08038)the National Undergraduate Innovation Training Plan (Grant No.G20101106)
文摘The velocity dip phenomenon may occur in a part of or in the whole flow field of open channel flows due to the secondary flow effect. Based on rectangular flume experiments and the laser Doppler velocimetry, the influence of the distance to the sidewall and the aspect ratio on the velocity dip is investigated. Through application of statistical methods to the experimental results, it is proposed that the flow field may be divided into two regions, the relatively strong sidewall region and the relatively weak sidewall region. In the former region, the distance to the sidewall greatly affects the location of maximum velocity, and, in the latter region, both the distance to the sidewall and the aspect ratio influence the location of the maximum velocity.