Seismicity pattern in north Sumatra-Great Nicobar region: In search of precursor for the 26 December 2004 earthquake   总被引：1，自引：0，他引：1  

Sujit Dasgupta  Basab Mukhopadhyay  Auditeya Bhattacharya 《Journal of Earth System Science》2007,116(3):215-223

We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990–1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake.  相似文献   

位场向下延拓的波数域广义逆算法   总被引：4，自引：5，他引：4       下载免费PDF全文

陈生昌  肖鹏飞 《地球物理学报》2007,50(6):1816-1822

位场向下延拓是位场数据处理和反演中的重要运算，但是它的不稳定性影响了它在许多处理和反演方法技术中的应用.本文通过把位场向下延拓视为向上延拓的反问题，得到向下延拓的褶积型线性积分方程，再利用Fourier变换矩阵的正交对称特性，并结合矩阵的奇异值分解和广义逆原理，提出了一种稳定的不需要进行求逆运算的位场向下延拓广义逆方法——波数域广义逆算法，解决了位场大深度向下延拓的不稳定性问题.把这种方法用于三维理论模型数据和实际磁场数据的向下延拓获得了理想的结果.  相似文献   

区域开发累积环境影响及其全幕景分析法评价   总被引：3，自引：0，他引：3  

陈剑霄 《地下水》2007,29(2):73-76

在分析区域开发活动及其特点的基础上,论述了区域开发累积环境影响及其累积效应.通过总结常用的累积环境影响评价方法的实质,考察传统幕景分析法评价累积环境影响的工作方法,提出广义的幕景分析法--"全幕景分析法",阐述其用于区域开发累积环境影响分析评价的工作程序与优势."全幕景分析法"可在区域开发累积环境影响评价中起到综合、优化、直观的作用.  相似文献   

Large earthquakes initiate by the acceleration of slips on the downward extensions of seismogenic faults     

Yoshihisa Iio  Yoji KobayashiTakashi Tada 《Earth and Planetary Science Letters》2002,202(2):337-343

In order to examine the relationship between anomalous crustal deformations and subsequent large earthquakes, we compiled and examined data on preseismic anomalous crustal deformations for two earthquakes that occurred in and around the Japanese Islands in recent years. We found that the slip on a downward extension of a seismogenic fault accelerates before the main shock and that the average slip velocity is inversely proportional to the time remaining until the main shock occurs.  相似文献   

Generalized inversion of the Korteweg–de Vries equation     

J. C. Muccino  A. F. Bennett   《Dynamics of Atmospheres and Oceans》2002,35(3)

A generalized inverse is presented for the Korteweg–de Vries (KdV) equation, an initial condition and data from synthetic but realistic solitary internal waves. The synthetic data are statistically consistent with hypothesized levels of error in the KdV equation, initial condition and observing system. The observing system consists of point-wise measurements of the pycnocline displacement, either at fixed locations or from a ship drifting in the soliton current. These synthetic inversions are designed using the environmental conditions and disturbances observed by Pinkel [J. Phys. Oceanogr. 30 (2000) 2906]. The inverse solution is found by minimizing a quadratic cost functional, which yields a weighted least-squares best-fit to the KdV equation, the initial condition and the data. The weight for each squared residual is derived from its hypothesized covariance.The minimal value of the least-squares estimator (or cost function) is the test statistic for the error hypotheses and is shown here to be a reliable indicator of grossly incorrect hypotheses. In particular, it will be shown that even with just a single ship survey, the method does lead to decisive tests of hypotheses concerning the level of error in the model. Also, neglect of ship drift is found to be less deleterious to the inversion than is neglect of error in the KdV dynamics.The inverse is calculated by the iterated, direct representer algorithm [Ocean Model. 3 (2001) 137], which is readily extended to include parameter estimation. Significant skill is found for estimating the linear phase speed.  相似文献   

用解析的垂直正规模展开对大气数值模式进行垂直积分          下载免费PDF全文

刘金达 《大气科学》1993,17(6):651-662

本文提出了一个用大气自由振荡解析的垂直正规模为正交函数系构成一个完备的Hilbert空间,利用广义Fourier展开的概念,在垂直方向进行广义Fourier展开,对大气数值模式进行垂直积分.我们利用两组垂直正规模为正交函数系.第一组是等温大气的垂直正规模;第二组是多元大气的垂直正规模,并用变系数的一维平流方程进行试验积分,将积分结果与差分法、有限元法、Legendre多项式展开的结果进行比较.比较的标准是它们与解析解的均方根误差和相关系数.  相似文献   

地球极表象为直线的再投影法   总被引：1，自引：0，他引：1  

胡景星 《测绘学院学报》1994,(2)

对于地球极表象为直线的投影，本文运用对偶变换和广义轴位变换，得出了它们的几种新款式。  相似文献   

广义权阵及其在平差中的应用     

李广云 《测绘学院学报》1991,(4)

本文提出了协方差阵奇异时广义权阵的概念,给出了适用于设计阵列满秩或降秩、协方差阵奇异或非奇异的所有情况下测量平差的统一准则,并利用这一准则研究了协方差阵奇异时的参数估计问题,证明了其结果和Rao最小二乘统一理论等价。本文利用矩阵的平行加性质,推导了奇异协方差传播时广义权阵的计算公式,最后介绍了广义权阵在系统误差补偿的平差中及变形参数估计中的几个实际应用。  相似文献   

波动方程CT技术在地震数据处理中的应用          下载免费PDF全文

田钢  唱鹤鸣 《地球物理学报》1991,34(2):240-247

本文从畸变的Born近似的微扰技术出发,给出了利用广义Radon变换和Fourier积分算子的理论反演介质间断性的原理.将声学的广义Radon变换与经典Radon变换进行类比,近似地导出了声学广义Radon变换的反演公式. 本文对于反射地震学的情况,提出了一种拟线性化方法,考虑了成象点的一次散射场,从某种程度上减少了Born近似对弱散射的苛求. 利用同一模型的理论记录和物理实验记录的反演计算结果对提出的方法进行了验证,并讨论了进一步提高成象精度的方法.  相似文献   

等幅循环荷载作用下土的动剪模量和阻尼   总被引：3，自引：0，他引：3  

牟崇元  常宝琦等 《华南地震》1991,11(2):13-22

本文根据我国南方8个场址81个试样的动三轴试验资料，对土在等幅循环荷载作用下，其动模量和阻尼与应变幅值的关系进行了分析研究，并与现场测试结果进行对比，分析结果，本文提出一种广义双曲线模型，能更满意地描述各类寺应力应变关系，该模型保持了形式简便，参数物理意义明确等优点，文中还分别对砂土和粘土，给出了模型中参数的统计关系式，这些表达式能明显的映粘性土和非粘性土的特性及其差别。  相似文献