Coastal Gravity Anomalies from Retracked Geosat/GM Altimetry: Improvement, Limitation and the Role of Airborne Gravity Data   总被引：6，自引：0，他引：6  

Cheinway Hwang  Jinyun Guo  Xiaoli Deng  Hsin-Ying Hsu  Yuting Liu 《Journal of Geodesy》2006,80(4):204-216

We process geophysical and waveform data records of the Geosat/GM (geodetic mission) satellite altimeter mission for waveform retracking and applications. An improved threshold retracker is developed. The performances of the Beta-5, threshold and improved threshold retrackers are assessed over waters around Taiwan. The improved threshold retracker outperforms the other two. The improvement in the accuracy of sea surface height (SSH) is investigated according to marine zone and the distance of waters to the shore. The improvement rate increases closer to the land, with the largest improvement rate of about 20% in waters within 10 km of the shore. Over waters around islands and coasts, there are still retracked SSHs with large errors. Least-squares collocation is used to compute gravity anomalies from the Geosat/GM altimeter data. Use of retracked SSHs improves the accuracy of gravity anomalies by about 11%. Adding airborne gravity data further improves the accuracy, especially in the immediate vicinity of the coasts. Tide model errors over coastal waters remain a problem in altimetry applications, even if the waveforms are properly retracked.  相似文献   

川滇地区速度结构的区域地震波形反演研究   总被引：22，自引：6，他引：22       下载免费PDF全文

吴建平  明跃红  王椿镛 《地球物理学报》2006,49(5):1369-1376

利用云南数字地震台网的区域地震波形资料，对川滇地区的地壳上地幔速度结构进行了初步研究. 结果表明，川滇地区上地幔顶部P波速度较小，约78 km/s，P波速度在上地幔表现为较小的正速度梯度，S波在100～160 km深度范围内表现为弱低速层. 对于较短的观测路径，不同路径的平均P波和S波速度存在明显的横向变化. 与川滇菱形块体内部的速度结构不同，在块体边界附近可以观测到比较明显的上地壳低速层，我们认为它可能与块体边界的断裂带有关；川滇菱形块体内部存在的下地壳低速层，有利于块体向南滑动，而中上地壳没有明显低速结构，可能表明川滇菱形块体向南滑动的解耦深度至少在下地壳. 根据不同路径的反演结果，给出了云南中部地区地壳内部的平均速度结构.  相似文献   

Highland Boundary Fault Zone: Tectonic implications of the Aberfoyle earthquake sequence of 2003     

L. Ottemller  C.W. Thomas 《Tectonophysics》2007,430(1-4):83-95

The Highland Boundary Fault Zone (HBFZ) is one of the major faulted tectonic boundaries in Great Britain. Historically, seismicity has occurred in this zone around the town of Comrie. But an earthquake sequence that occurred in 2003 near the village of Aberfoyle (M_L 1.3–3.2) was the first significant activity to be recorded in the HBFZ since the installation of modern seismograph networks in the 1970s. This study describes detailed analysis of these data. The waveform signals of the events were almost identical and by applying a cross-correlation technique combined with multiple event location, the alignment of the events was found to be WSW–ENE. This alignment matches one of the nodal planes determined by joint focal mechanism analysis. The fault plane dips to the northwest, and shows oblique sinistral strike–slip with normal movement. The orientation of the event alignment matches the direction and orientation of observed features in the HBFZ. Hence, it is concluded that the WSW–ENE striking nodal plane was the causative fault that is associated with the HBFZ. The orientation of maximum compressional stress is rotated from the regional average expected due to the Mid-Atlantic ridge-push force. This rotation is possibly explained by stresses due to postglacial rebound. Smaller events in the sequence were used as empirical Green's functions and deconvolved from the larger events to determine source time functions. The corresponding corner frequencies matched results from spectral fitting, showing that the events were of relatively low stress drop.  相似文献   

Solution of the Inverse Problem of Gravimetry for a Spherical Planetary Body Using the Decomposition of the Interior Potential into a Series of Polyharmonic Functions     

Pohánka  V. 《Studia Geophysica et Geodaetica》1997,41(1):1-14

The interior potential of a spherical planetary body (and the corresponding density distribution) is expressed as the sum of two parts, the first given uniquely by the external gravity field and the surface density and the second depending on an arbitrary function. The first part of the potential (density distribution) is shown to be a 3-harmonic (biharmonic) function, while the second part can be expressed as a series whose i-th term (for i 0) is an (i + 4)-harmonic ((i + 3)-harmonic) function. From this general solution a single solution is then chosen: this is done by imposing certain natural conditions on it, among others that this particular solution is an n-harmonic function for n as small as possible. The paper explains shortly this method of solving the inverse problem of gravimetry; details are presented in Pohánka (1993).  相似文献   

Moment tensor of the 1999 Dead Sea calibration shot: limitations in the isotropic source retrieval without a detailed earth model     

J. Sileny  R. Hofstetter 《Tectonophysics》2002,356(1-3)

Records of the November 11, 1999, M_L=3.9 calibration shot observed at three broad-band (BB) stations at a distance range from 35 to 63 km from the epicenter were inverted with a simple 1-D model. Complexity due to the water–solid bedrock interface near the hypocenter effectively masks the explosive mechanism in first-motion polarities. Reverberation in the water and scattering in the crust result in the long duration of the source process if estimated with a simple structure model. Only the part with a significant non-zero isotropic (ISO) component should be considered. We selected this part on the basis of the estimate of error due to inexact modeling of the crust constructed by perturbing the thickness and velocities in individual layers by 5% of their current values. Within this interval, the isotropic process of explosive characteristics is detected. However, if we do not check the significance of the isotropic part in the formally reconstructed source process, then we might miss the information about the explosion and arrive with a spurious nearly double-couple source.  相似文献   

流动台波形的综合分析     

包翠玲  缑兰兰 《高原地震》2005,17(3):35-41

利用波形对比分析与多台到时对比的方法找出了流动台站记录的地震波形常规分析中存在的问题，提高了流动台资料的利用率。  相似文献   

利用地震波形反演研究震源破裂时空过程   总被引：2，自引：0，他引：2       下载免费PDF全文

何玉梅  郑天愉 《地球物理学报》1998,41(2):281-289

本文对近10多年来利用地震波形反演推断震源破裂时空过程这一领域的研究进展作一简单介绍．论述了理论地震图的计算、反演确定震源参数、以及解释反演结果三方面的发展,并对反演结果进行了归纳总结．研究表明,在本文所提到的地震中,多数大地震的震中附近只有相对小的滑动,而在多数中等地震的震中或其附近有较大的滑动．本文认为,在进一步提高反演解答的稳定性和可信程度的基础上,在大地构造背景下研究震源的性质,对一批不同震级、发生在不同构造区的地震进行系统研究是有意义的．  相似文献   

1996年5月3日内蒙古包头西M_S6.4级地震的震源机制研究   总被引：5，自引：3，他引：2       下载免费PDF全文

马淑田  姚振兴 《地球物理学报》1998,41(6):795-803

利用地幔波波形拟合和P波初动符号联合反演的方法,估计了1996年5月3日内蒙古包头西MS6．4级地震的震源机制．得到节面1（40°,70°,－174°）,节面2（308°,84°,－20°）。主压力轴P（-13．95×1017Nm,262°,19°）,主张力轴T（15．66×1017Nm,356°,10°）,中性轴N（B）（1．52×1017Nm,112°,69°）．地震形成左旋走滑兼弱倾滑断裂,断裂面较陡．据ML≥3.0级的余震分布、Ⅷ度区的烈度分布以及宏观震中与微观震中的相对位置推测,节面2可能与实际的地震破裂面相近．据宽频垂直向（BHZ）波形记录中SP与P的到时差估计,震源深度约为21Km．  相似文献   

用宽频带波形资料研究青海西捷6.8级地震的震源过程          下载免费PDF全文

刘振  周蕙兰 《地震地质》1998,20(3):28-224

利用中国数字地震台网（ＣＤＳＮ）的宽频带数字化波形资料进一步研究了１９８８年１１月５日青海省西捷ＭＳ６．８级强震的震源过程。通过波形模拟和基于优化遗传算法的全局反演,对该地震的震源参数和破裂特征进行了分析。初步结果表明,此强震是以一次主破裂为特征的事件,与略带逆掩分量的走滑活动断层有关。根据单向破裂对各台站视震源时间函数的影响的分析,认为破裂可能是沿北西走向的断层面由东南向西北传播  相似文献   

Genetic waveform modeling for the crustal structure in Northeast Japan     

《Journal of Asian Earth Sciences》2014

We propose a genetic algorithm (GA) search procedure for waveform modeling of local crustal earthquakes for optimal one-dimensional (1-D) crustal velocity model. Both waveforms and travel-time data are used for the structure determination. The use of travel times in model evaluation improves the waveform modeling performance in the sense of computation speed and accuracy. We applied this method to broadband waveforms of a local crustal earthquake (M 4.2) in Northeast Japan. P-wave velocities of the crustal model are found to be 4.95 ± 0.30, 5.9 ± 0.02, and 6.51 ± 0.20 km/s for a surface layer, upper crust and lower crust, respectively. The surface layer thickness and the Conrad and Moho depths are found to be 3.01 ± 0.8, 17.77 ± 0.4 and 34.59 ± 1.0 km, respectively. For epicentral distances <200 km, our synthetic waveforms match the observed ones generally well. Early arrivals are mainly observed at stations near the Pacific coast in the forearc area having a thinner crust. In contrast, delayed arrivals appear at stations near the volcanic front and back-arc areas where low-velocity anomalies exist due to the effect of the Pacific slab dehydration and the hot upwelling flows in the mantle wedge. In general, our results agree well with the main tectonic setting of the study area, which confirms the reliability of the proposed approach. Despite a 1-D velocity model is too simple to represent the complex crustal structure, it is still required for the conventional routine analysis of seismology, such as earthquake location and source parameter studies. The current approach is considered as a step toward the genetic full waveform modeling for the 3-D velocity model estimation.  相似文献