多量程自动选通地震遥测系统

介绍多量程自动选通地震模拟遥测系统的工作原理及使用结果。采用此方案，综合动态范围可扩大到９０－１００ｄＢ，用事件判别触发发射的办法，维持功耗可小于１ｗ。     

Converted-wave seismology in anisotropic media revisited,Part I: Basic theory

We have developed new basic theories for calculating the conversion point and the travel time of the P-SV converted wave (C-wave) in anisotropic, inhomogeneous media. This enables the use of conventional procedures such as semblance analysis, Dix-type model building and Kirchhoff summation, to implement anisotropic processing, and makes anisotropic processing affordable. Here we present these new developments in two parts: basic theory and application to velocity analysis and parameter estimation. This part deals with the basic theory, including both conversion-point calculation and moveout analysis. Existing equations for calculating the PS-wave (C-wave) conversion point in layered media with vertical transverse isotropy (VTI) are strictly limited to offsets about half the reflector depth (an offset-depth ratio, xlz, of 0.5), and those for calculating the C-wave traveltimes are limited to offsets equal to the reflector depth (x/z=l.0). In contrast, the new equations for calculating the conversion-point extend into offsets about three-times the reflector depth (x/z=3.0), those for calculating the C-wave traveltimes extend into offsets twice the reflector depth (x/z=2.0). With the improved accuracy, the equations can help in C-wave data processing and parameter estimation in anisotropic, inhomogeneous media. This work is funded by the Edinburgh Anisotropy Project (EAP) of the British Geological Survey. First author: Xiangyang Li, Mr. Li is currently a professorial research seismologist (Grade 6) and technical director of the Edinburgh Anisotropy Project in the British Geological Survey. He also holds a honorary professorship in multicomponent seismology at the School of Geosciences, University of Edinburgh. He received his BSc(1982) in Geophysics from Changchun Geological Institute, China, an MSc (1984) in applied geophysics from East China Petroleum Institute (now known as the China University of Petroleum), and a PhD (1992) in seismology from the University of Edinburgh. During 1984–1987, he worked as a lecturer with the East China Petroleum Institute. Since 1991, he has been employed by the British Geological Survey. His research interests include seismic anisotropy and multicomponent seismology.     

2-D crustal Poisson’s ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L ₁ are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson’s ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson’s ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson’s ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson’s ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson’s ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson’s ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region. Foundation item: Key Project from China Earthquake Administration and the Project (95-11-02-01) from Ministry of Science and Technology (2001DIA10003). Contribution No. RCEG200401, Geophysical Exploration Center, China Earthquake Administration.     

2-D crustal Poisson's ratio from seismic travel time inversion in Changbaishan Tianchi volcanic region

Based on the inversion method of 2D velocity structure and interface, the crustal velocity structures of P-wave and S-wave along the profile L1 are determined simultaneously with deep seismic sounding data in Changbaishan Tianchi volcanic region, and then its Poisson's ratio is obtained. Calculated results show that this technique overcomes some defects of traditional forward calculation method, and it is also very effective to determine Poisson's ratio distribution of deep seismic sounding profile, especially useful for study on volcanic magma and crustal fault zone. Study result indicates that there is an abnormally high Poisson's ratio body that is about 30 km wide and 12 km high in the low velocity region under Tianchi crater. Its value of Poisson's ratio is 8% higher than that of surrounding medium and it should be the magma chamber formed from melted rock with high temperature. There is a high Poisson's ratio zone ranging from magma chamber to the top of crust, which may be the uprise passage of hot substance. The lower part with high Poisson's ratio, which stretches downward to Moho, is possibly the extrusion way of hot substance from the uppermost mantle. The conclusions above are consistent with the study results of both tomographic determination of 3D crustal structure and magnetotelluric survey in this region.     

Analysis of flood propagation changes in the Kienstock—Bratislava reach of the Danube River/Analyse des changements de propagation des crues dans le tronçon Kienstock—Bratislava du Fleuve Danube

Abstract

In the first part of this study, a flood wave transformation analysis for the largest historical floods in the Danube River reach Kienstock–Bratislava was carried out. For the simulation of the historical (1899 and 1954) flood propagation, the nonlinear river model NLN-Danube (calibrated on the recent river reach conditions) was used. It was shown that the simulated peak discharges were not changed significantly when compared to their historical counterparts. However, the simulated hydrographs exhibit a significant acceleration of the flood wave movement at discharges of between 5000 and 9000 m³ s^-1. In the second part, the travel time-water level relationships between Kienstock and Bratislava were analysed on a dataset of the flood peak water levels for the period 1991–2002. An empirical regression routing scheme for the Danube short-term water level forecast at Bratislava station was derived. This is based on the measured water level at Kienstock gauging station.     

芦山地震强地面运动频谱特征及致灾相关性分析

以芦山地震震中距100km内20个台站的60条原始强震记录为依据,采用零交法计算台站处三方向卓越周期,采用线性加速法计算台站处阻尼比为0.05的三方向反应谱,考察反应谱峰值周期、卓越周期和放大系数在各台站位置处的分布以及在断裂上、下盘的均值。通过研究发现:芦山地震动卓越周期、反应谱峰值周期和放大系数在各台站不同方向上的分量不同;各台站处反应谱的计算表明地震动具有上盘效应以及上盘衰减迅速的特征;地震动卓越周期在芦山地震震中100km的上、下盘上差别不大,其中上盘EW和UD向卓越周期均值略小于下盘,而上盘NS向均值略大于下盘,断裂两盘UD向卓越周期总体小于水平向,断裂两盘三方向卓越周期变化范围为0.013~0.275s;计算得到的放大系数表明80%台站NS向放大系数大于EW向,因此NS向放大系数较大可能是芦山地震诱发崩滑地质灾害的主要因素。     

Hydrological response of an afforested catchment in a Mediterranean humid mountain area: a comparative study with a natural forest

The effects of afforestation on water resources are still controversial. The aim of this paper is to (i) analyse the hydrological response of an afforested area in the Central Pyrenees and (ii) compare the hydrological response of an afforested area with the response observed in a natural undisturbed forest. The Araguás catchment was cultivated until the 1950s, and then afforested with pines in an effort to control the active degradation processes. The hydrological response was variable and complex, because the discharge was generated by a combination of distinct runoff processes. The hydrological response showed that (i) afforestation produced moderate peak discharges, stormflows and recession limbs, and long rising limbs; (ii) no one single variable was able to explain the hydrological response: rainfall volume and intensity did not explain the hydrological response and antecedent rainfall and initial discharge (indicating antecedent moisture conditions) did play an important role; (iii) seasonal differences were observed suggesting different runoff generating processes; and (iv) the effect of forest cover on peak discharges became less important as the size of the hydrological event increased. The stormflow coefficient showed a clear seasonal pattern with an alternation between a wet period, when the catchment was hydrologically responsive, and a dry summer period when the catchment rarely responded to any event, and two transitional periods (wetting and drying). Compared with a natural forest, the afforested area recorded greater flows and peak discharges, faster response times and shorter recession limbs. Afforestation reduces the water yield and the number of floods compared with non‐vegetated areas and abandoned lands. Copyright © 2016 John Wiley & Sons, Ltd.     

Impact of draining hilly lands on runoff and on‐site erosion: a case study from humid Ethiopia

The use of drainage ditches on farmland has an impact on erosion processes both on‐site and off‐site, though their environmental impacts are not unequivocal. Here we study the runoff response and related rill erosion after installing drainage ditches and assess the effects of stone bunds in north Ethiopia. Three different land management systems were studied in 10 cropland catchments around Wanzaye during the rainy season of 2013: (1) the exclusive use of drainage ditches (locally called feses), (2) the exclusive use of stone bunds, and (3) a mixture of both systems. Stone bunds are an effective soil and water conservation technique, making the land more resistant against on‐site erosion, and allowing feses to be installed at a larger angle with the contour. The mean rill volumes for the 10 studied cropland catchments during the rainy season of 2013 was 3.73 ± 4.20 m³ ha^?1 corresponding to a soil loss of 5.72 ± 6.30 ton ha^?1. The establishment of feses causes larger rill volumes (R = 0.59, N = 10), although feses are perceived as the best way to avoid soil erosion when no stone bunds are present. The use of feses increases event‐based runoff coefficients (RCs) on cropland from c. 5% to values up to 39%. Also, a combination of low stone bund density and high feses density results in a higher RC, whereas catchments with a high stone bund density and low feses density have a lower RC. Peak runoff discharges decrease when stone bund density increases, whereas feses density is positively related to the peak runoff discharge. A multiple linear relation in which both feses and stone bund densities are used as explanatory variable, performs best in explaining runoff hydrograph peakedness (R² = 83%). Copyright © 2015 John Wiley & Sons, Ltd.     

基于强震和测震数据对鲁甸6.5级地震发震断层方向的研究

2014年8月3日16时30分,云南省昭通市鲁甸县发生M6.5地震,宏观震中位于鲁甸县龙头山镇(27.1°N,103.3°E),深度约12km。发震断层为NW向包谷垴-小河断裂,是NE向昭通-鲁甸断裂系的NW向次级走滑断层。文中利用鲁甸地震50个强震台站观测记录与135个测震台站观测记录,分别进行峰值加速度计算和S波辐射图案匹配,对此次地震发震断层方向进行讨论。结果表明,"NW向"的断层方向更符合强震、测震仪器观测值,同时与地震灾害现场调查结果一致。