Moment-tensor statistics of the 1997 Long Valley microearthquake swarm     

A. Stroujkova  P.E. Malin 《Journal of Seismology》2002,6(1):69-85

Abstract. A simple, fast, moment-tensor inversion method using bandpass-filtered P-amplitudes was used to study the moment-tensor statistics of Long Valley caldera microearthquakes. The events were recorded in the summer of 1997, during a swarm in the caldera. The swarm was associated with geodetic extension, uplift, and subsequent moderate earthquake activity. The moment tensor solutions for 1,993 events were calculated using the new method. The majority of the resulting focal mechanisms appear to be explained in terms of double couple mechanisms. Since some events did exhibit considerable deviation from double-couples, the moment data were studied for their statistical significance. The moments of the actual data were compared to the moments of synthetic data with varying degrees of random noise in their spectra. The results of this study suggested that unless data from more than 20 stations are used and the earthquake epicenter is located inside or very close to the network area, moment-tensor inversion does not correctly resolve the non-double-couple components of microearthquakes. Analysis of the inversion residuals shows that the average noise in the P-wave spectra was close to 20%. The fluctuations of the volumetric components of the moment-tensor are in good agreement with those of the synthetic pure double-couples with 20% of added noise. Thus the moment-tensor statistics suggests that little if any volume change is required to explain the observed seismic energy release in the swarm. However, the statistics do show that a significant compensated-linear-vector-dipole component maybe present in the bulk of the seismicity. Given the network used in this study, such a component could not be precisely resolved for individual earthquakes. This possibility deserves further investigation because of its bearing on the nature of fluid-fault-earthquake processes in swarms.  相似文献   

Multiparametric Traveltime Inversion     

Biloti  Ricardo  Santos  Lúcio T.  Tygel  Martin 《Studia Geophysica et Geodaetica》2002,46(2):177-192

In conventional seismic processing, the classical algorithm of Hubral and Krey is routinely applied to extract an initial macrovelocity model that consists of a stack of homogeneous layers bounded by curved interfaces. Input for the algorithm are identified primary reflections together with normal moveout (NMO) velocities, as derived from a previous velocity analysis conducted on common midpoint (CMP) data. This work presents a modified version of the Hubral and Krey algorithm that is designed to extend the original version in two ways, namely (a) it makes an advantageous use of previously obtained common-reflection-surface (CRS) attributes as its input and (b) it also allows for gradient layer velocities in depth. A new strategy to recover interfaces as optimized cubic splines is also proposed. Some synthetic examples are provided to illustrate and explain the implementation of the method.  相似文献   

天山西部中山带积雪变化趋势与气温和降水的关系——以巩乃斯河谷为例   总被引：12，自引：9，他引：12  

张丽旭  魏文寿 《地理科学》2002,22(1):67-71

根据位于巩乃斯河谷的天山积雪雪崩研究站近30年来的年最大雪深、月平均气温、月降水量观测记录，用平均差值法、最小二乘法、自回归滑动平均法检验了天山西部中山带积雪、冷季降水、冷季平均气温的变化趋势，结果表明，天山西部中山带积雪呈增加趋势，近30年来年平均增加1.43%，与青藏高原、南极大陆及格陵兰冰盖表面积雪积累增加相一致。天山西部中山带冷季气温和降水的变化趋势也是增加的，其中冷季降水平年平均增加0．12％，而冷季气温升高了0．8℃，积雪与冷季气温之间存在着弱的负相关关系，而与冷季降水呈显著的正相关关系。积雪的增加主要是因为气候变暖引起的冷季降水的增加对积雪增加的贡献大于由于冷季气温升高而造成积雪减少的贡献的结果。  相似文献   

History and necessity: the evolution of soil conservation technology in a Jamaican farming system     

Rebecca J. Kent 《The Geographical journal》2002,168(1):48-56

The soil conservation campaigns that have been a prominent feature of Jamaican agricultural policy since the 1950s are frequently presented as having failed to ameliorate the problem of soil erosion in hillside agriculture. A case study of a small farming community in the Blue Mountains explores the development of the soil conservation practices currently employed by farmers. The use of trash barriers in carrot farming is described and the origins of this technology and its subsequent adaptation are considered. The study concludes that extension interventions and government policy have influenced the development of current soil conservation practices; practices which have their roots in indigenous techniques. Other factors such as the adaptation of trash barriers to suit local conditions and their importance in soil fertility management also play a role in their widespread use in the study area. The study demonstrates that to understand the process of technical change in farming communities, it is necessary to consider a range of factors, external and internal, technical and social, that have over time influenced farmers' decision making.  相似文献   

A model of the geomagnetic field and its secular variation for epoch 2000 estimated from Ørsted data     

Nils Olsen 《Geophysical Journal International》2002,149(2):454-462

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Data and model uncertainty estimation for linear inversion   总被引：1，自引：0，他引：1  

Kasper van Wijk  John A. Scales  William Navidi  Luis Tenorio 《Geophysical Journal International》2002,149(3):625-632

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Bent-ray traveltime tomography and migration without ray tracing     

P. E. Ecoublet  S. C. Singh  C. H. Chapman  G. M. Jackson 《Geophysical Journal International》2002,149(3):633-645

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Monte-Carlo inversion for a global shear-velocity model of the crust and upper mantle   总被引：15，自引：1，他引：15  

N. M. Shapiro  M. H. Ritzwoller 《Geophysical Journal International》2002,151(1):88-105

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Assessment of crustal velocity models using seismic refraction and reflection tomography   总被引：6，自引：0，他引：6  

Colin A. Zelt  Kalachand Sain  Julia V. Naumenko  Dale S. Sawyer 《Geophysical Journal International》2003,153(3):609-626

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近、现代黄河三角洲地貌形态反演   总被引：5，自引：0，他引：5  

刘庆生  刘高焕  励惠国 《地理与地理信息科学》2003,19(2):93-96

1855年黄河改夺大清河河道后于山东利津县东北入海。至今黄河尾癌河道历经10次大的改道变迁，塑造了近、现代黄河三角洲，形成了7个主要的亚三洲堆积体。该文利用黄河尾癌河道改道资料，近、现代河口流路变迁图，近、现代黄河三角洲体系图以及1985－1986年的水文工程地质钻孔资料，在研究黄河三角洲沉积模式的基础上，对工程地质钻孔数据进行沉积层序分析，将今论古，反推近、现代黄河三角洲沉积地貌，研究结果近似展示了近、现代黄河三角洲二维平面的发育演变和其时其地的地貌形态。  相似文献