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1.
Application of 3-D Crustal and Upper Mantle Velocity Model of North America for Location of Regional Seismic Events 总被引：1，自引：0，他引：1
—?Seismic event locations based on regional 1-D velocity-depth sections can have bias errors caused by travel-time variations within different tectonic provinces and due to ray-paths crossing boundaries between tectonic provinces with different crustal and upper mantle velocity structures. Seismic event locations based on 3-D velocity models have the potential to overcome these limitations. This paper summarizes preliminary results for calibration of IMS for North America using 3-D velocity model. A 3-D modeling software was used to compute Source-Station Specific Corrections (SSSCs(3-D)) for Pn travel times utilizing 3-D crustal and upper mantle velocity model for the region. This research was performed within the framework of the United States/Russian Federation Joint Program of Seismic Calibration of the International Monitoring System (IMS) in Northern Eurasia and North America.¶An initial 3-D velocity model for North America was derived by combining and interpolating 1-D velocity-depth sections for different tectonic units. In areas where no information on 1-D velocity-depth sections was available, tectonic regionalization was used to extrapolate or interpolate. A Moho depth map was integrated. This approach combines the information obtained from refraction profiles with information derived from local and regional network data. The initial 3-D velocity model was tested against maps of Pn travel-time residuals for eight calibration explosions; corrections to the 3-D model were made to fit the observed residuals. Our goal was to find a 3-D crustal and upper mantle velocity model capable predicting Pn travel times with an accuracy of 1.0–1.5 seconds (r.m.s.).¶The 3-D velocity model for North America that gave the best fit to the observed travel times, was used to produce maps of SSSCs(3-D) for seismic stations. The computed SSSCs(3-D) vary approximately from +5 seconds to ?5 seconds for the western USA and the Pre-Cambrian platform, respectively. These SSSCs(3-D) along with estimated modeling and measurement errors were used to relocate, using regional data, an independent set of large chemical explosions (with known locations and origin times) detonated within various tectonic provinces of North America. Utilization of the 3-D velocity model through application of the computed SSSCs(3-D) resulted in a substantial improvement in seismic event location accuracy and in a significant decrease of error ellipse area for all events analyzed in comparison both with locations based on the IASPEI91 travel times and locations based on 1-D regional velocity models. 相似文献
2.
利用差异演化（Differential Evolution）非线性全局优化算法,设计了一种反演地壳速度模型和进行地震定位的方法,并给出了反演结果的具体分析.利用有限差分算法计算速度模型的走时场,可以节省大量的计算量,加快计算过程.反演得到的地壳速度模型和地震的震源参数可以直接用于地震层析成像研究,还可以利用地震层析成像得到的三维速度结构对地震重新定位,从而得到较为精确的震源参数.地壳速度模型的反演方法也可以用于三维速度结构的反演. 相似文献
3.
地壳不同深度介质的地震各向异性是研究地壳不同深度范围变形方式的重要依据.鉴于地壳介质的复杂性,如何从远震体波接收函数中提取不同深度的各向异性参数仍是一个有待深入研究的课题.在已有研究的基础上,本文利用广义反射-透射系数矩阵方法计算的合成地震图,研究了复杂地壳分层各向异性介质的接收函数随反方位角(back azimuth)变化及不同层位各向异性参数对接收函数波场的影响,为各向异性介质接收函数的解释提供了新的理论依据.通过引入粒子群优化理论,发展了分层各向异性介质接收函数全局反演算法.数值及观测数据的验证结果表明,在各向同性速度模型确定的前提下,我们的方法能够可靠地提取地壳分层各向异性参数;在反演中引入曲波变换去噪技术,对于正确解析不同层位的各向异性参数具有重要价值. 相似文献
4.
使用阻尼最小二乘法进行震源参数和地壳三维速度结构的走时联合反演．所用资料为Ｓ波和Ｐ波到时差,并用人工地震资料的二维解释结果作为三维速度模型的特定约束条件．为建立初始模型,又利用天然地震构成了准二维剖面．在走时反演基础上,利用遗传算法进行了几个地震事件的波形反演尝试,并对走时反演获得的地壳速度结构模型的局部进行了修正．以３４°～４２°Ｎ,９４°～１１２°Ｅ作为研究区域,在该区域中收集了１９８６年以来大量地震的Ｓ波和Ｐ波到时差资料,７条人工地震二维速度剖面资料和２个数字化地震台的几个地震的三分向记录资料．对这些资料进行了处理,最后得出了０～２５ｋｍ深度不同截面的速度分布,并对所得结果进行了分析． 相似文献
5.
利用地震走时数据,采用联合反演方法获取了江苏地区的一维P波速度模型。与仅采用初至波走时的传统天然地震走时获取方法相比,该方法充分利用了大量存在的续至波参与反演,能有效改进中下地壳的反演能力。针对地震震相目录中常存在震相标识错误的问题,采用的自动判别筛选震相方法能最大限度提高数据走时的精度,可以对不同震相进行有效区分。与其他常用一维速度模型相比,本文反演的模型对Pg、Pn震相走时拟合效果最佳,残差最小。当所用走时数据拥有较高定位精度时,该反演方法能为研究区三维速度结构成像和地震定位提供较可靠的一维速度模型。 相似文献
6.
The western part of the Bohemian Massif (West Bohemia/Vogtland region) is characteristic in the relatively frequent recurrence
of intraplate earthquake swarms and in other manifestations of past-to-recent geodynamic activity. In this study we derived
1D anisotropic qP-wave model of the upper crust in the seismogenic West Bohemia/Vogtland region by means of joint inversion
of two independent data sets - travel times from controlled shots and arrival times from local earthquakes extracted from
the WEBNET seismograms. We derived also simple 1-D P-wave and S-wave isotropic models. Reasons for deriving these models were:
(a) only simplified crustal velocity models, homogeneous half-space or 1D isotropic layered models of this region, have been
derived up to now and (b) a significant effective anisotropy of the upper crust in the region which was indicated recently
by S-wave splitting. Both our anisotropic qP-wave and isotropic P-and S-wave velocity models are constrained by four layers
with the constant velocity gradient. Weak anisotropy for P-waves is assumed. The isotropic model is represented by 9 parameters
and the anisotropic one is represented by 24 parameters. A new robust and effective optimization algorithm - isometric algorithm
- was used for the joint inversion. A two-step inversion algorithm was used. During the first step the isotropic P- and S-wave
velocity model was derived. In the second step, it was used as a background model and the parameters of anisotropy were sought.
Our 1D models are adequate for the upper crust in the West Bohemia/Vogtland swarm region up to a depth of 15 km. The qP-wave
velocity model shows 5% anisotropy, the minimum velocity in the horizontal direction corresponds to an azimuth of 170°. The
isotropic model indicates the VP/VS ratio variation with depth. The difference between the hypocentre locations based on the derived isotropic and anisotropic
models was found to be several hundreds of meters. 相似文献
7.
For faster and more robust ray tracing in 1-D velocity models and also due to the lack of reliable 3-D models, most seismological centers use 1-D models for routine earthquake locations. In this study, as solution to the coupled hypocenter-velocity problem, we compute a regional P-wave velocity model for southern Iran that can be used for routine earthquake location and also a reference initial model for 3-D seismic tomography. The inversion process was based on travel time data from local earthquakes paired reports obtained by merging the catalogues of Iranian Seismic Center (IRSC, 6422 events) and by the Broadband Iranian National Seismic Network (BIN, 4333 events) for southern Iran in the period 2006 through July 2017. After cleaning the data set from large individual reading errors and by identifying event reports from both networks belonging to same earthquake (a process called event pairing), we obtained a data set of 1115 well-locatable events with a total number of 24,606 P-wave observations. This data set was used to calculate a regional minimum 1-D model for southern Iran as result of an extensive model search by trial-and-error process including several dozens of inversions. Significantly different from previous models, we find a smoothly increasing P-velocity by depth with velocities of 5.8 km/s at shallow and velocities of 6.4 km/s at deepest crustal levels. For well-locatable events, location uncertainties are estimated in the order of ±?3 km for epicenter and double this uncertainty for hypocentral depth. The use of the minimum 1-D model with appropriate station delays in routine hypocenter location processing will yield a high-quality seismic catalogue with consistent uncertainty estimates across the region and it will also allow detection of outlier observations. Based on the two catalogues by IRSC and BIN and using the minimum 1-D model and station delays for all stations in the region, we established a new combined earthquake catalogue for southern Iran. While the general distribution of the seismicity corresponds well with that of the two individual catalogues by IRSC and BIN, the new catalogue significantly enhances the correlation of seismicity with the regional fault systems within and between the major crustal blocks that as an assembly build this continental region. Furthermore, the unified seismic catalogue and the minimum 1-D model resulting from this study provide important ingredients for seismic hazard studies. 相似文献
8.
收集了1978～2003年位于渤海湾盆地及其邻近地区（大体位于东经112°～122°，北纬34°～44°之间）所记录到的的总计10534个地震或人工爆破事件的Pn、Pg以及P波到时数据，运用GT5准则，从中挑选出相对精确和可信度较高，且具有代表性的的10个地震事件，使用Messy GA算法，分别反演了这10个地震事件所对应的一维地壳P波速度模型.反演的局部地壳模型与已知结果对应较好，基本反映了震中区的地壳速度结构特征.该方法原理简单，计算方便，可用于确定局部和区域的地壳速度模型. 相似文献
9.
迅速发展并得到广泛应用的空间深地震测深技术通过采用三维数据采集的观测系统,利用三维层析技术,以求获得区域地壳三维分层结构和三维速度分布图像。它与传统的二维宽角反射－折射剖面技术相结合,可以有效地研究区域性地壳结构,特别是壳内深断裂和低速层的空间展布特征。Kanasewich等(1985)给出了利用空间深地震测深资料重建地壳三维界面的方法,我们在其方法的基础之上,进一步提出地壳三维界面和速度分布联合反演的方法。正问题的计算是在Chander(1977)关于三维平界面的快速两点追踪算法上的改进,在获得界面三维反演结果的基础之上,利用剩余走时残差,采用模型不分块反演技术(Tarantola,Nercession 1986)重建地壳三维速度图像。 1998年国家地震局地球物理勘探中心在长白山火山区实施了三维深地震测深观测,目的是研究天池火山的岩浆系统。利用本次实验所获得的780余个PmP波走时数据,采用上述的方法重建了研究区莫霍界面和地壳三维速度分布图像。研究结果表明,本区莫霍界面由北东方向向南逐渐加深,在天池火山口下达最深,并且被一些可能存在的地壳厚度陡变带(或深断裂)所切割。在东西方向莫霍面由西向东缓缓加深,其变化较南北方向缓和。特别值得注意的是,存在着一条近北东方向的莫霍面深度陡变带(或深断裂带)从天池火山口西部穿过,相应位置与马鞍山—三道白河地堑型断裂相一致,该断裂带可能对天山火山喷发时岩浆的运移起到重要作用。深度为15km和25km的P波速度图像表明,在天池火山口下分布着近南北走向明显的低P波速度分布,其南北方向延伸的范围约为80－90公里左右。比较这两个深度上的低P波速度体的分布特点,可以看出这个低P波速度体尺度随深度逐渐变小,但在25km深度处仍清晰可见,这表明该区岩浆自上地幔侵入地壳的“痕迹”,这也意味着,长白山天池火山的岩浆系统极有可能延伸到上地幔或更深一些。 相似文献
10.
天山东北部地震的重新定位和一维地壳速度模型的改善 总被引：1，自引：1，他引：0
We apply three methods to relocate 599 earthquake events that occurred from August 2004 to August 2005 in the northeastern Tianshan Mountains area ( 85°30’ ～ 88°30’E,43°00’ ～ 44°40’ N ) by using travel times recorded by regional seismic network and 10 portable seismic stations deployed around the Urumqi city. By comparing the reliability of different results,we determined a suitable location method,and an improved 1-D crustal velocity model of the study area. The uncertainty of earthquake location is significantly reduced with combined data of seismic network and portable stations. The relocated events are clearly associated with regional tectonics of the northeastern Tianshan Mountains area, and are also in agreement with the existence of active faults imaged by deep seismic reflection profile. The relocated seismicity discovers some potential traces of buried active faults,which need to be validated further. 相似文献
11.
为利用sPn与Pn波的走时差测定震源深度,进一步提高地震震源深度的测定精度,推导多层介质下sPn与Pn波的走时差与震源深度的关系,发现走时差与震中距无关,只与震源深度及区域地壳速度模型有关。震源在同一层中,走时差曲线的斜率不变,而当震源位于不同层中时,sPn-Pn走时差曲线的斜率不同,并呈分段直线的走时差曲线形态。地壳速度结构纵向越不均匀,多层和单层介质下利用sPn-Pn走时差计算的震源深度误差就越大,走时曲线的各分段直线斜率相差越大;探讨地壳中sPn与Pn波传播路径相同但波速不同的单层地壳速度模型,发现单层介质下波速越大,测定的震源深度越大;对于同一地区相同的地壳分层结构,测得的震源深度随着泊松比的增大而减小。基于前人给出的中国五个典型块体多层平均地壳模型,给出sPn-Pn走时差与震源深度计算公式速查表。 相似文献
12.
T. B. Yanovskaya S. V. Medvedev V. S. Gobarenko 《Izvestiya Physics of the Solid Earth》2018,54(2):193-200
In the problems of three-dimensional (3D) travel time seismic tomography where the data are travel times of diving waves and the starting model is a system of plane layers where the velocity is a function of depth alone, the solution turns out to strongly depend on the selection of the starting model. This is due to the fact that in the different starting models, the rays between the same points can intersect different layers, which makes the tomography problem fundamentally nonlinear. This effect is demonstrated by the model example. Based on the same example, it is shown how the starting model should be selected to ensure a solution close to the true velocity distribution. The starting model (the average dependence of the seismic velocity on depth) should be determined by the method of successive iterations at each step of which the horizontal velocity variations in the layers are determined by solving the two-dimensional tomography problem. An example illustrating the application of this technique to the P-wave travel time data in the region of the Black Sea basin is presented. 相似文献
13.
We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1° parameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q
P
and Q
S
). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle
n
velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent. 相似文献
14.
Introduction It is well known that the occurrence of moderate and strong earthquakes and the distribution of seismically active belts are most directly related to deep crustal faults. Therefore, studying geometrical spreading and physical state of medium of deep crustal faults has always been a major subject in earthquake science. It is not only of great significance to the understanding of deep structural background and seismogenic mechanism of strong earthquakes, but also of great help to se… 相似文献
15.
Western Yunnan is a region with intensive tectonic activity and serious earthquake risk. It is of significant importance to study three dimensional crustal structure of this region to understand the tectonic setting and disaster mechanism. Densification and digitalization of seismic networks in this region provides an opportunity to study the velocity structure with bulletin data. In this study, we collect P-wave data of 10 403 regional earthquakes recorded by 79 seismic stations from January 2008 to December 2010. In addition to first arrivals data (Pg with epicentral distance less than 200 km and Pn), the Pg (or P) data with epicentral distance more than 200 km are also considered as later direct arrivals in the tomographic inversion. We also compare the quantity and the quality of the seismic data before 2010 and after 2010. The test results show that adding the follow-up Pg phase can effectively improve the inversion ability of crustal imaging, and quantity and the data quality are significantly improved since 2010. The tomographic results show that: (1) The Honghe fault zone, which is the major fault systems in this region, may cut through the entire crust, and the velocity contrasts between two sides at lower crust beneath the Honghe fault are estimated at higher than 10%, while the velocity difference below Nujiang fault zone extends only in the upper crust; (2) Most of the earthquakes in the region occurred at the interface of high-velocity media and low-velocity media, i.e., the areas with high velocity gradient, which has been validated in other areas. 相似文献
16.
17.
地壳三维构造反演和速度层析成像 总被引：5，自引：1，他引：5
本文给出利用空间深地震测深反射资料重建地壳三维构造和速度分布的方法，适用于任意分层并且每层可由若干断块组成的地壳模型。通过采用适当的反演方法获得地壳界面的三维构造，并在此结果基础之上，进一步将剩余走时残差归因于地壳速度的不均匀性，采用东分块的反演方法，重建地壳三维速度分布，数值模拟的结果表明算法是有效的。 相似文献
18.
The inversion of 3-D crustal structure and hypocenter location in the Beijing-Tianjin-Tangshan-Zhangjiakou area by genetic algorithm 总被引：1，自引：0，他引：1
Ｔｈｅｉｎｖｅｒｓｉｏｎｏｆ３┐ＤｃｒｕｓｔａｌｓｔｒｕｃｔｕｒｅａｎｄｈｙｐｏｃｅｎｔｅｒｌｏｃａｔｉｏｎｉｎｔｈｅＢｅｉｊｉｎｇ┐Ｔｉａｎｊｉｎ┐Ｔａｎｇｓｈａｎ┐Ｚｈａｎｇｊｉａｋｏｕａｒｅａｂｙｇｅｎｅｔｉｃａｌｇｏ┐ｒｉｔｈｍＹＯＮＧ－Ｇ... 相似文献
19.
Summary Earthquake investigations in the central United States require a realistic crustal model for accurate location of seismic events, for the determination of earthquake source parameters, and for theoretical ground motion prediction for an assumed earthquake source. A number of crustal models have been proposed which were based on first arrival refraction data obtained from artificial and natural seismic sources.The reflectivity method for generating realistic theoretical seismograms is used together with recently acquired refraction survey data to distinguish among several of the proposed crustal models. The data used in this study preclude a definitive statement about the nature of the lower crust in the region. However, a crust with two or more layers in the upper 20 km immediately below the basement is preferred. The absence of prominent near yertical reflections suggests that the layers may be separated by rapid velocity gradients rather than by sharp discontinuities. 相似文献
20.
In this paper, ray theoretical amplitudes and travel times are calculated in slightly perturbed velocity models using perturbation analysis. Also, test inversions using travel time and amplitude are computed. The pertubation method is tested using a 3-D velocity model for NORSAR having velocity variations up to 8.0 percent. The perturbed amplitudes are found to be in excellent agreement with the calculated ray amplitudes. Velocity inversions based on travel time and amplitude are next investigated. Perturbation analysis using linearized ray equations is efficiently used to compute amplitude derivatives with respect to model parameters. The trial linearized inversions use smaller velocity variations of 1.7 percent to avoid possible effects due to ray shift, even though the perturbation analysis is valid for larger variations. The trial 2-D inversion results show that linearized amplitude inversions are complementary and not redundant to travel time inversions, even in smoothly varying models. 相似文献