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1.
Stepwise joint inversion of surface wave dispersion,Rayleigh wave ZH ratio,and receiver function data for 1D crustal shear wave velocity structure 
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下载免费PDF全文 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 (v S) structure. Surface wave dispersion and Rayleigh wave ZH ratio data are more sensitive to absolute variations of shear wave speed at depths, but their sensitivity 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 v P/v S ratios. The stepwise inversion method takes advantages of the complementary sensitivities of each dataset to better constrain the v S model in the crust. We firstly invert surface wave dispersion and ZH ratio data to obtain a 1D smooth absolute v S model and then incorporate receiver function data in the joint inversion to obtain a finer v S 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 v S structures and with little initial model dependency. 相似文献
2.
Yinhe Luo Jianghai Xia Jiangping Liu Yixian Xu Qingsheng Liu 《Journal of Applied Geophysics》2008,64(3-4):115-124
Multichannel Analysis of Surface Waves utilizes a multichannel recording system to estimate near-surface shear (S)-wave velocities from high-frequency Rayleigh waves. A pseudo-2D S-wave velocity (vS) section is constructed by aligning 1D models at the midpoint of each receiver spread and using a spatial interpolation scheme. The horizontal resolution of the section is therefore most influenced by the receiver spread length and the source interval. The receiver spread length sets the theoretical lower limit and any vS structure with its lateral dimension smaller than this length will not be properly resolved in the final vS section. A source interval smaller than the spread length will not improve the horizontal resolution because spatial smearing has already been introduced by the receiver spread.In this paper, we first analyze the horizontal resolution of a pair of synthetic traces. Resolution analysis shows that (1) a pair of traces with a smaller receiver spacing achieves higher horizontal resolution of inverted S-wave velocities but results in a larger relative error; (2) the relative error of the phase velocity at a high frequency is smaller than at a low frequency; and (3) a relative error of the inverted S-wave velocity is affected by the signal-to-noise ratio of data. These results provide us with a guideline to balance the trade-off between receiver spacing (horizontal resolution) and accuracy of the inverted S-wave velocity. We then present a scheme to generate a pseudo-2D S-wave velocity section with high horizontal resolution using multichannel records by inverting high-frequency surface-wave dispersion curves calculated through cross-correlation combined with a phase-shift scanning method. This method chooses only a pair of consecutive traces within a shot gather to calculate a dispersion curve. We finally invert surface-wave dispersion curves of synthetic and real-world data. Inversion results of both synthetic and real-world data demonstrate that inverting high-frequency surface-wave dispersion curves – by a pair of traces through cross-correlation with phase-shift scanning method and with the damped least-square method and the singular-value decomposition technique – can feasibly achieve a reliable pseudo-2D S-wave velocity section with relatively high horizontal resolution. 相似文献
3.
Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (QP and QS) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1?10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0?500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 MW4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average vP and vS of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high vP/vS ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain QS and the near surface velocity structure. Our modeling indicates that QS is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (~10), but consistent with QS modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0?50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation. 相似文献
4.
Shanxi Graben is in the middle part of the North China Craton, from south to north. With the teleseismic data recorded by Regional Seismograph Networks and the temporary ZBnet-W Seismic Array around east part of Shanxi Graben, we measured the crustal thickness and vP/vS ratio beneath each station using the H-κ stack of receiver functions. The observed crustal thickness shows obvious lateral variation, increasing gradually from east to west in the Shanxi Graben. Beneath the Shanxi Graben the crust is relatively thicker than both sides of the south and the north. In addition, the vP/vS ratio in the north of study zone is higher than that in the south. The highest vP/vS ratio exists in the crust of the Xinding basin and the Datong basin. Our study also suggests that high velocity ratio might result from the strong activities of the magmation and volcanism. 相似文献
5.
The knowledge on particle deposition in streams is mainly based on investigations in mountain streams. No data exist from low‐gradient sand‐bed streams that largely differ in the morphological and hydraulic factors proposed to affect deposition. To identify physical control on particle deposition in low‐gradient streams, we assessed deposition of very fine and ultra fine organic particulate matter in 18 sand‐bed stream reaches. We added particles derived from lake sediment and assessed the mean transport distance SP and the deposition velocity vdep. Additionally, reach hydraulics were estimated by injections of a conservative solute tracer (NaCl). Among the low‐gradient streams, particle deposition kinetics were variable but similar to deposition in mountain streams. SP was solely related to the flow velocity. This relation was confirmed when comprising published data on deposition of fine organic particles. An association between particle deposition and transient storage factors was insignificant. We found significance of the transient storage to SP only for repeated measures within a single reach, when flow velocity and benthic conditions were nearly constant. Measured vdep/vfall ratios were much larger than unity in most reaches. Evidence from this relation suggests that the vertical transport of very fine and ultra fine organic particulate matter through the water column was caused mainly by vertical mixing. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
6.
Constraining the crustal structure under the central and western Tian Shan based on teleseismic receiver functions and gravity anomalies 下载免费PDF全文
下载免费PDF全文 The Tian Shan is a vast range that spans several countries in Asia. Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics. In this study, we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region. A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P- to S-wave velocities (vP/vS) for 91 broadband seismic stations in the central and western Tian Shan. Our results revealed significant lateral variations in crustal thickness and vP/vS. A ~45-km-thick crust and an intermediate-high vP/vS (~1.74–1.84) were found in the Kazakh Shield and Tarim Basin, which we interpreted to indicate a mafic crystalline basement and lower crust. The central Tian Shan varied greatly in crustal thickness (40–64 km) and vP/vS ratio (1.65–2.00), which may be due to crustal shortening, mafic underplating, and crustal melting. In contrast, we observed a relatively thin crust (42–50 km) with an intermediate vP/vS ratio (~1.78) in the western Tian Shan. The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric. 相似文献
7.
S-wave velocity structure in Tangshan earthquake region and its adjacent areas from joint inversion of receiver functions and surface wave dispersion* 下载免费PDF全文
下载免费PDF全文 Using the seismic records of 83 temporary and 17 permanent broadband seismic stations deployed in Tangshan earthquake region and its adjacent areas (39°N–41.5°N, 115.5°E–119.5°E), we conducted a nonlinear joint inversion of receiver functions and surface wave dispersion. We obtained some detailed information about the Tangshan earthquake region and its adjacent areas, including sedimentary thickness, Moho depth, and crustal and upper mantle S-wave velocity. Meanwhile, we also obtained the vP/vS structure along two sections across the Tangshan region. The results show that: (1) the Moho depth ranges from 30 km to 38 km, and it becomes shallower from Yanshan uplift area to North China basin; (2) the thickness of sedimentary layer ranges from 0 km to 3 km, and it thickens from Yanshan uplift region to North China basin; (3) the S-wave velocity structure shows that the velocity distribution of the upper crust has obvious correlation with the surface geological structure, while the velocity characteristics of the middle and lower crust are opposite to that of the upper crust. Compared with the upper crust, the heterogeneity of the middle and lower crust is more obvious; (4) the discontinuity of Moho on the two sides of Tangshan fault suggests that Tangshan fault cut the whole crust, and the low vS and high vP/vS beneath the Tangshan earthquake region may reflect the invasion of mantle thermal material through Tangshan fault. 相似文献
8.
The derivation of P and S velocities at the core-mantle boundary (CMB) from long-period diffracted waves by the use of the simple ray-theoretical formulav
CMB=r
c
/p (v
CMB=velocity at the CMB;r
c
=core radius;p=ray parameter) yields apparent velocity values which differ from the true velocities. Using a dominant period of about 20 sec for calculating theoretical seismograms, we found a linear relation between the apparent velocity and the average velocity in a transition zone at the base of the mantle with fixed velocity on top.The ray parameters determined from long-period earthquake data are found to be 4.540±0.035 and 8.427±0.072 sec/deg for Pdiff and Sdiff, respectively. These values yield apparent velocities of 13.378±0.103 for P and 7.207±0.062 km/sec for S waves. By means of the theoretical relation between apparent and average velocity and under the assumption of linear variation of velocity with depth, one can invert the apparent velocities into true CMB velocities of 13.736±0.170 and 7.320±0.124 km/sec. These results imply positive velocity gradients at the base of the mantle and hence no significant departures from adiabaticity and homogeneity.Contribution No. 211 of the Geophysical Institute, University of Karlsruhe. 相似文献
9.
选取2009~2014年发生在云南地区、每个地震均在10个以上台站有记录的7412个地震数据,作走时曲线。同时为提高精度,重点对其中每个地震均在80%以上台站有记录的、ML≥3.0的83个地震数据,再作线性分析、折合走时曲线和区间稳定性分析,结合前人研究成果得到了研究区的初始地壳速度模型。选取2010~2014年云南省内M≥3.0的200次地震,采用Hyposat批处理方法迭代初始速度模型,以及对S波作分层速度拟合,得到云南地区的地壳速度模型,即2015云南模型:v_(P1)=6.01km/s,v_(P2)=6.60km/s,v_(Pn)=7.89km/s,H_1=20km,H_2=21km,v_(S1)=3.52km/s,v_(S2)=3.86km/s,v_(sn)=4.43km/s。基于新模型的地震重定位分析表明,云南地区地震事件大多发生于20km内的上地壳;对2011年3月10日盈江M5.8和2014年8月3日鲁甸M6.5典型地震进行重定位,得出震源深度分别与精定位结果和震中强震台震源距接近,表明新的一维速度模型能更好地反映研究区平均速度结构。 相似文献
10.
The vertical hydraulic conductivity (Kv), elastic (Sske), and inelastic (Sskv) skeletal specific storage of aquitards are three of the most critical parameters in land subsidence investigations. Two new analytic methods are proposed to estimate the three parameters. The first analytic method is based on a new concept of delay time ratio for estimating Kv and Sske of an aquitard subject to long‐term stable, cyclic hydraulic head changes at boundaries. The second analytic method estimates the Sskv of the aquitard subject to linearly declining hydraulic heads at boundaries. Both methods are based on analytical solutions for flow within the aquitard, and they are jointly employed to obtain the three parameter estimates. This joint analytic method is applied to estimate the Kv, Sske, and Sskv of a 34.54‐m thick aquitard for which the deformation progress has been recorded by an extensometer located in Shanghai, China. The estimated results are then calibrated by PEST (Doherty 2005), a parameter estimation code coupled with a one‐dimensional aquitard‐drainage model. The Kv and Sske estimated by the joint analytic method are quite close to those estimated via inverse modeling and performed much better in simulating elastic deformation than the estimates obtained from the stress‐strain diagram method of Ye and Xue (2005). The newly proposed joint analytic method is an effective tool that provides reasonable initial values for calibrating land subsidence models. 相似文献
11.
利用新疆区域地震台网观测到的2009年1月—2014年7月Pn、Sn、Pg和Sg震相数据,综合使用线性拟合、折合走时、PTD定深方法和HypoSAT定位方法确定该地区Pg、Pb和Pn的平均传播速度(v_(Pg),v_(Pb),v_(Pn))、康拉德界面和莫霍面的深度(H_(conr)和H_(moho))范围,以速度和深度步长分别为0.1km/s、1km精度迭代计算样本数据,通过对比分析计算结果与全国地震统一编目和3400模型下样本数据的定位结果后,确定RMS平均值最小的一维速度模型。在新模型中v_(Pg)、v_(Pb)和v_(Pn)分别为6.10km/s、6.70km/s和8.20km/s,H_(conr)和H_(moho)分别为26km、54km。通过检验对比,认为本文获得的新模型优于新疆地区现有的3400模型。 相似文献
12.
A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion.The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV
p
/V
s
in the first 16 km depth. 相似文献
13.
On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake. 相似文献
14.
—?We present results from a large-scale study of surface-wave group velocity dispersion across the Middle East, North Africa, southern Eurasia and the Mediterranean. Our database for the region is populated with seismic data from regional events recorded at permanent and portable broadband, three-component digital stations. We have measured the group velocity using a multiple narrow-band filter on deconvolved displacement data. Overall, we have examined more than 13,500 seismograms and made good quality dispersion measurements for 6817 Rayleigh- and 3806 Love-wave paths. We use a conjugate gradient method to perform a group-velocity tomography. Our current results include both Love- and Rayleigh-wave inversions across the region for periods from 10 to 60 seconds. Our findings indicate that short-period structure is sensitive to slow velocities associated with large sedimentary features such as the Mediterranean Sea and Persian Gulf. We find our long-period Rayleigh-wave inversion is sensitive to crustal thickness, such as fast velocities under the oceans and slow along the relatively thick Zagros Mts. and Turkish-Iranian Plateau. We also find slow upper mantle velocities along known rift systems. Accurate group velocity maps can be used to construct phase-matched filters along any given path. The filters can improve weak surface wave signals by compressing the dispersed signal. The signals can then be used to calculate regionally determined M S measurements, which we hope can be used to extend the threshold of m b :M S discriminants down to lower magnitude levels. Other applications include using the group velocities in the creation of a suitable background model for forming station calibration maps, and using the group velocities to model the velocity structure of the crust and upper mantle. 相似文献
15.
Velocity and density contrasts across the Moho interface of Guangdong province in south China constrained by receiver functions* 下载免费PDF全文
下载免费PDF全文 The P receiver function includes P-to-SV converted phases and multiple reverberations of the discontinuities in the crust and mantle. The time of these phases is related to the crustal thickness and vP/vS ratio, and the amplitude of these phases is mainly controlled by the velocity and density contrast of interfaces. By using H-κ stacking method, this work estimated the crustal thickness and vP/vS ratio beneath the stations in the Guangdong province of South China. The velocity and density contrast (δβ-δρ) scanning stacking algorithm of the receiver function is applied to constrain the velocity and density contrast of the Moho in Guangdong province. This work analyzed the results of the crustal thickness, vP/vS ratio, and the velocity and density contrasts of Moho. The results indicate that the velocity contrast is higher beneath Yangjiang area in western Guangdong province and Nanao area in eastern Guangdong, which has a strong correlation with the distribution of geothermal springs in local areas and the characteristics of high heat flow. The velocity contrast of Moho has also a good correlation with the vP/vS ratio and the crustal thickness, which indicates that there is a strong material composition contrasts of the Moho in the study area. Velocity and density contrasts of Moho in some local area (such as western Guangdong) are somewhat consistent with the seismic activities. 相似文献
16.
采用GAMIT/GLOBK软件对云南境内及邻区近400个GNSS测点1999～2018年的观测数据进行解算,在各个测点时间序列和速度场的基础上,采用克里金插值方法分时段估计该区域在1999～2004年、2004～2007年、2009～2013年、2013～2015年、2015～2018年共计5个时间区域应变率场;根据区域地壳面应变率和最大剪应变率的空间变化以及相应时段之后3年内的MS≥5. 0地震事件分布特征,分析发现:绝大部分震例发生在面应变高梯度带的张压转换区和最大剪应变高值区,可见研究区各个观测时段GNSS应变率场对后期1～3年内的中强震发生区域有一定的指示意义;以2014年盈江6. 1级、鲁甸6. 5级和景谷6. 6级地震为样本,建立监视块体获取应变时间序列,分析发现:地震前三个月左右均出现震中附近短期应变趋势改变、快速增强、转折的现象,这些形变异常变化或许反映了发震区应力-应变积累在接近临界破裂状态时的非线性调整,为地震短临预测尤其是时间要素的判断提供参考。 相似文献
17.
Statistical methods are available which predict the maximum response of simple oscillators given the peak acceleration (Ap), peak velocity (Vp) or peak displacement (Dp) of seismic ground motions. An alternative parameter, namely an ordinate (or ordinates) of the Fourier amplitude spectrum of ground motion acceleration, FS(f), may in fact be a preferred predictor of peak response, especially in a frequency range close to f. Other statistical methods (attenuation laws) use distance R and other parameters such as magnitude (M), Modified Mercalli epicentral Intensity (Io) and Modified Mercalli site Intensity (MMI or Is) to predict spectral velocity (Sv(f)), etc. In using such approaches, it is most desirable to know the total uncertainty in the predicted peak response of the system given the starting parameter values. An extensive strong motion data set is used to study these questions, The most direct prediction models are found to be preferable (have lower prediction dispersion) but data may not be available in all regions to permit their use. 相似文献
18.
从新疆乌鲁木齐市2004—2015年得到的841个钻孔中选择深度达30 m以下且钻孔资料记录完整的有效钻孔123个,通过计算5~30 m范围内不同深度的等效剪切波速,分别利用线性拟合、二次拟合和三次拟合对各深度vS（d）及其vS30进行拟合。通过对比发现,三个方程的拟合误差都随深度的增加而减少,且三次拟合方程的误差始终小于同深度的线性拟合和二次拟合方程,因此推荐使用三次拟合方程来估计新疆乌鲁木齐市钻孔的vS30值。同时将此结果和Boore的结果进行比较后发现,不同深度处的等效剪切波速vS（d）和vS30具有地域差异性;Boore得到的结果在钻孔深度小于20 m时明显高估vS30值,拟合曲线偏离实际数据点较远,所以本文拟合结果更适用于新疆乌鲁木齐市。综合比较可知,三次拟合得到的研究结果可以为新疆乌鲁木齐市钻孔深度不足30 m的地区求解vS30值提供参考。最后,利用新疆克拉玛依市2004—2015年钻孔资料检验三个拟合公式对克拉玛依市的适用性,发现深度越接近30 m,误差越小;线性模型和二次模型相对来说比较可靠,平均误差接近于0,并且对深度大于10 m的钻孔有高估现象;三次模型相对来说误差比较大,并且几乎在所有深度都有低估现象。 相似文献
19.
使用基于机器学习构建的贵州西部多流域水库区地震目录和震相报告,采用波速比一致性约束的双差层析成像方法联合反演得到了该地区的地震位置和三维vp、vs、vp/vs结构。结果显示,研究区内的地壳速度结构具有明显的不均匀性,不同大地构造变形分区展现出不同的速度结构特征。在10km以上深度,横穿黔西中部NW向的威宁构造变形区显示出显著的低速异常条带,揭示了威宁—水城深大断裂带的影响深度和范围。受库区岩性和流体渗透的影响,0km深度的速度结构显示普遍的低波速和高波速比特征,包括夹岩、平寨、光照和马马崖水库区域。重定位后,地震的空间分布勾勒出大量隐伏断层的几何展布特征,结合三维速度结构,推测该区域的地震活动与水库周围的断层活化有关。 相似文献
20.
The Yangbi MS6.4 earthquake occurred on May 21, 2021 in western Yunnan, China, where moderate earthquakes strike frequently. It exhibited a typical “foreshock-mainshock-aftershock” sequence and did not occur on a pre-existing active fault. The seismogenic environment and mechanism of this earthquake have aroused considerable research attention. In this study, we obtain the three-dimensional vP, vS and vP/vS images using the vP/vS consistency-constrained double-difference tomography method, which improves the accuracy of vP/vS models. We focus on characteristics of vP/vS images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi MS6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-vP/vS anomalies are revealed at different depths around the northern segment of the Red River fault. vS and vP/vS images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature. (2) The source region of the Yangbi MS6.4 earthquake is located in a low-vP/vS zone implying high medium strength. High-vP/vS anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts, which are unfavorable for stress accumulation and triggering large earthquakes. Such conditions have also prevented the earthquake sequence from extending northwestward. (3) With the southeastward extrusion of materials from the Tibetan Plateau, fluid migration was blocked by the low-vP/vS body in the source region. The high-vP/vS anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer, and preparing the largest foreshock in the transition zone of high to low vP/vS. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the MS6.4 earthquake occurrence. 相似文献