Suspended sediment load estimation and the problem of inadequate data sampling: a fractal view

Suspended sediment load estimation at high resolutions is an extremely difficult task, because: (1) it depends on the availability of high‐resolution water discharge and suspended sediment concentration measurements, which are often not available; (2) any errors in the measurements of these two components could significantly influence the accuracy of suspended sediment load estimation; and (3) direct measurements are very expensive. The purpose of this study is to approach this sampling problem from a new perspective of fractals (or scaling), which could provide important information on the transformation of suspended sediment load data from one scale to another. This is done by investigating the possible presence of fractal behaviour in the daily suspended sediment load data for the Mississippi River basin (at St. Louis, Missouri). The presence of fractal behaviour is investigated using five different methods, ranging from general to specific and from mono‐fractal to multi‐fractal: (1) autocorrelation function; (2) power spectrum; (3) probability distribution function; (4) box dimension; and (5) statistical moment scaling function. The results indicate the presence of multi‐fractal behaviour in the suspended sediment load data, suggesting the possibility of transformation of data from one scale to another using a multi‐dimensional model. Copyright © 2005 John Wiley & Sons, Ltd.     

P-III型分布混合权函数估计法的研究

为克服传统的马秀峰权函数法所存在的缺陷,提出了一种可考虑线性矩法优点的新的权函数估计法即混合权函数法,经过统计试验论证,该法对传统的马秀峰权函数法有较大改进,是一种统计性能较优秀的参数估计方法。     

On the consistency of earthquake moment release and space geodetic strain rates: Europe

In this paper, approximately 100 VLBI/SLR/GPS velocities map European strain rates from <0.09 × 10⁻⁸ to >9.0 × 10⁻⁸ yr⁻¹ with regional uncertainties of 20 to 40 per cent. Kostrov's formula translates these strain-rate values into regional geodetic moment rates M¯˙ _geodetic . Two other moment rates, M¯˙ _seismic , extracted from a 100-year historical catalogue and M¯˙ _plate , taken from plate-tectonic models, contrast the geodetic rates. In Mediterranean Europe, the ratios of M¯˙ _seismic to M¯˙ _geodetic are between 0.50 and 0.71. In Turkey the ratio falls to 0.22. Although aseismic deformation may contribute to the earthquake deficit ( M¯˙ _seismic values less than M¯˙ _geodetic ), the evidence is not compelling because the magnitudes of the observed shortfalls coincide with the random variations expected in a 100-year catalogue. If the lack of aseismic deformation inferred from the 100-year catalogue holds true for longer periods, then much of Europe's strain budget would have to be accommodated by more frequent or larger earthquakes than have been experienced this century to raise the ratios of M¯˙ _seismic to M¯˙ _geodetic to unity. Improved geological fault data bases, longer historical earthquake catalogues, and densification of the continent's space geodetic network will clarify the roles of aseismic deformation versus statistical quiescence.     

A Catalogue of Earthquakes With Moment Magnitude of the Center-Southern Asia Test Area of the Global Seismic Hazard Assessment Program

We compile a regional catalogue of earthquakes with moment magnitude of the Center-Southern Asia test area(20°-35°N,85°-105°E)for the Global Seismic Hazard Assessment Program(GSHAP).There are significant inhomogeneous and uncompleted data,and n uniformity of earthquake magnitudes in this test area because this region is situated on the boundaries of many countries,such as China,India,Nepal,Vietnam,etc.We establish a relationship between Gutenberg surface-wave magnitude and IASPEI surface-wave magnitude,which can be used for conversion of different magnitude scales into moment magnitude for this catalogue.A catalogue of events with Mw≥6.0 of this test area is given at the end of this paper.     

山西断陷带太原-临汾部分的强地震平均复发间隔与未来危险段落研究

1303年山西洪洞M8大地震距今已700年. 为了分析长期地震危险性，本文将山西断陷带太原——临汾部分划分为5个震源段，根据历史地震和GPS观测资料，估算出各段的平均地震矩率与强地震平均复发间隔，进而根据最近30多年的台网地震资料计算获得的b值图象，分析不同段落现今应力积累的相对水平. 主要结果表明:临汾盆地段的平均地震矩率为2.211016~3.031016Nm/a, M7.5地震的平均复发间隔估值为1 560~2 140 a. 灵石——洪洞段M8地震的平均复发间隔估值在4300~5100 a之间, 相当于平均矩率为2.581016~3.101016Nm/a. b值图象显示灵石——洪洞段与临汾盆地段现今处于低或较低的应力水平，可能反映自1303年M8和1695年M7.5大地震破裂后，这两段的断面强度至今仍未恢复. 候马段和介休——汾阳段具有相对较高的应力水平，并结合平均复发间隔估值，判定这两个段落可能是未来强震的潜在危险段.      

地震作用下多层砌块房屋墙体倾覆力矩的计算方法

多层混凝土砌块房屋抗震设计时，仅考虑地震引起的剪力作用和整体房屋的抗倾覆性能是不全面的。为此，提出了多层砌块房屋墙体倾覆力矩的计算与分配方法，通过典型砌块房屋的算例，利用本方法得到的墙体倾覆力矩与有限元结构分析软件SATWE的结果相近，证明了该方法的实用性，为多层砌块房屋抗震分析提供了有效手段。     

Estimating seismic moments and Lg Q using Lg spectra

A multi-event and multi-station inverse method is presented in the paper to simultaneously estimate the seismicmoments (Mo) and source comer frequencies (fc) of several Jiashi (Xinjiang, China) earthquakes, as well as theapparent Lg Q models for the paths from Jiashi to eight seismic stations (WMQ, AAK, TLG MAKZ, KUR, VOS,ZRN and CHK) in Central Asia. The resultant seismic moments correlate well with the Mo values obtained by Harvard University using the centroid moment tensor (CMT) inversion and the surface-wave magnitudes as well. Afterthe correction by a typical value of average radiation coefficient for regional SV waves, the Mo values from Lgspectral inversion are still close to the corresponding values obtained from CMT inversion. The obtained apparentQOLg values (Lg Q at 1 Hz) are consistent with the tectonic features of corresponding propagation paths. The QoLgvalues are 351±87, 349±86 and 300±27 for the paths from Jiashi to AAK, TLG and MAKZ, respectively. They aresmaller than QoLg values for the paths to KUR, VOS, ZRN and CHK, which are 553±72, 569±58, 550±57 and603±65, respectively. These results agree with the condition that the paths to AAK, TLG and MAKZ mainlypropagate through the mountainous Tianshan area where relatively strong seismic activities and large variations oftopography are exhibited, while the paths to KUR, VOS, ZRN and CHK mainly propagate through the stable areaof Kazak platform. The QoLg value for the path to WMQ is 462±56. This is also in agreement with the conditionthat the path to WMQ is basically along the border area between Tianshan Mountain and Tarim Basin, and alongthis path the variations of topography and crustal thickness are moderate in comparison with that along the path toMAKZ.