2001年云南地区地震活动概述

1　地震活动概况据昆明区域数字地震台网测定 ,2 0 0 1年 1月至 1 2月云南地区 (2 1°～ 2 9°Ｎ ,97°～ 1 0 6°Ｅ)共发生Ｍ≥ 3 0级地震 1 88次 (不含余震 ) ,其中 3 0～ 3 9级地震 1 49次 ,4 0～ 4 9级地震 2 7次 ,5 0～ 5 9级地　　图 1　 2 0 0 1年云南地区Ｍ≥ 3 0级地震Ｍ -ｔ图震 1 1次 ,6 0级地震 1次。 2 0 0 1年云南省内共发生Ｍ≥ 5 0级地震 7组 9次 ,分别是 3月 1 0澜沧 5 0级地震 ,4月 1 0、1 2日和 6月 8日施甸 5 2、 5 9和 5 3级地震 ,5月 2 4日宁蒗 5 8级地震 ,7月 1 0日楚雄 5 3级地震 ,7月 1 5日江川5 0…     

永胜6.0级地震灾害调查及分析

20 0 1年 1 0月 2 7日 1 3时 3 5分 ,云南省永胜县发生 6.0级地震。据昆明数字地震台网测定 ,截止 2 0 0 1年 1 0月 3 1日 1 9时震区共发生Ｍ≥ 1 0的地震 1 3 6次 ,其中 6 0级 1次 ;4 0～4 9级 1次 ;3 0～ 3 9级 3次 ;2 0～ 2 9级 3 1次 ;1 0～ 1 9级地震 1 0 0次。微观震中位于1 0 0°3 4′Ｅ ,2 6°1 4′Ｎ ,震源深度 1 5ｋｍ ,微观震中位于永胜县涛沅乡东龙潭村附近 ,宏观震中位于微观震中西南约 4ｋｍ ,即涛沅乡下坪村至金江街一带 ,震中烈度Ⅶ度 ,灾区主要涉及丽江地区永胜县、大理州的宾川县、鹤庆县 ;灾区总面积约…     

2000年1月15日云南省姚安县发生5.9、6.5级强震

据云南省地震遥测台网测定 :2 0 0 0年 1月 1 5日 0 6时 0 9分 0 1秒和 0 7时 37分 0 5秒分别在 2 5°34′Ｎ ,1 0 1°0 5′Ｅ ;2 5°35′Ｎ ,1 0 1°0 7′Ｅ ,距姚安县城西北约 1 0ｋｍ处先后发生了 5 9级和 6 5级两次强震 ,震源深度初定为 30ｋｍ。截至 2月 9日共记录到 1级以上地震共 463次 ,其中 1～ 1 9级 2 80次 ,2～ 2 9级 1 56次 ,3～ 3 9级1 6次 ,4～ 4 9级 7次 ,5 9、 6 5级各一次 ,最大余震为 4 7级 ,余震震中高度集中于 7× 8(ｋｍ2 )范围内。现场考察结果显示极震区长轴为Ｎ1 2°Ｅ的椭圆。极震区烈度为ＶＩＩＩ度 ,位于姚安…     

1999年9月14日四川省绵竹清平5.0级地震前区域地震活动

1　空间分布我们采用四川省地震台网目录资料 ,选取发生在北纬 3 0°3 0′～ 3 0°5 0′,东经 1 0 3°5 0′～1 0 5°1 0′德阳及邻区内的地震 ,对 1 970年以来的资料进行了分析。据统计 ,1 970年至 1 999年1 0月 ,该区发生 3 .0级以上地震共 85次 (图1 )。 1 999年 9月 1 4日绵竹清平 5 .0级地震为图 1　德阳地区 M≥ 3.0地震分布图近 3 0年来的最大地震 ,其次是 1 970年 3月 2 2日什邡、绵竹九顶山间 4.9级地震。历史上最大的地震为 1 95 8年 2月 8日绵竹 (微观震中 )6.2级地震 ,宏观震中为北川 ,震害较为严重。2　频次异常从 M-t、 N -…     

新疆、青海间发生8.1级巨震

据中国地震台网测定 :2 0 0 1年 1 1月 1 4日 1 7时 2 6分 1 3秒 ,在 3 6 2°Ｎ ,90 9°Ｅ的新疆与青海交界一带发生了Ｍｓ=8 1级巨震 ,震源深度 1 5ｋｍ。该巨震是 1 95 1年 1 1月 1 8日西藏当雄 (3 1 1°Ｎ ,91 4°Ｅ) 8 0级巨震后 5 0年来中国大陆发生的第一次巨震 ,同时也是欧亚带近 5 0年来发生的第一次巨震 ;此次大震后的短时间在其东北部约 40 0ｋｍ的青海格尔木相继发生了 2次 5 0～ 5 7级地震 ;3年前即 1 997年 1 1月在其西部西藏玛尼 (3 5 2°Ｎ ,87 3°Ｅ)发生了 7 5级大震。此次地震发生在东西向东昆仑构造带上 ,该构造…     

2001年7月11日甘肃镜铁山5.4级地震震源机制解刘旭宙

20 0 1年 7月 11日 0 5时 4 1分 3.8秒 ,甘肃省镜铁山发生了ＭＳ5 .4地震 .经甘肃省地震监测台网测定 ,该次地震震中位于 39.2°Ｎ ,98.0°Ｅ ,震源深度 10ｋｍ .作者收集了甘肃及青海地区共 2 6个地震台站的Ｐ波初动资料 ,求出了该次地震的震源机制解 ,见表 1和图1.表 1　 2 0 0 1年镜铁山ＭＳ5 .4地震震源机制解节面参数 Ａ节面Ｂ节面 应力轴参数 Ｐ轴Ｂ轴Ｔ轴倾向 2 2 0° 13 0°方位角 2 65° 2 10° 175°倾角 86° 82°仰角 90° 0° 90°　　 矛盾比 :0 .0 36图 1　 2 0 0 1年 7月 11日甘肃镜铁山　　　 5 .4级地震震源机制解Ｆｉｇ…     

2000年6月6日甘肃景泰5.9级地震震源机制解

20 0 0年 6月 6日 1 8时 59分 ,甘肃省景泰发生了ＭＳ5.9地震 .经甘肃省监测台网测定 ,该次地震震中位于 3 7. 0°Ｎ ,1 0 3 . 9°Ｅ ,震源深度 1 5ｋｍ .作者收集了甘肃及青海地区共 2 5个地震台站的Ｐ波初动符号 ,求出了该次地震的震源机制解 .见表 1和图 1 .矛盾比为 0 .2 8. 表 1　震源参数节面Ａ节面Ｂ节面应力轴Ｐ轴Ｂ轴Ｔ轴倾向 2 72° 1 88°方位角 2 3 5° 1 71° 1 3 4°倾角 82° 56°仰角 1 8° 54° 3 0°图 1　震源机制解Ｆｉｇ. 1　ＴｈｅｆｏｃａｌｍｅｃｈａｎｉｓｍｏｆＪｉｎｇｔａｉ 　　　 ＭＳ5. 9ｅａｒｔｈｑ…     

2000年震情述评

1　全球地震活动概况据我国台网测定 ,2 0 0 0年全球共发生 7级以上强震 2 0次 (表 1 ) ,最高震级为 7 8,即 6月 5日印度尼西亚苏门达腊岛南部、6月 1 8日印度洋和 1 1月 1 6日所罗门群岛共 3次 7 8级地震 (图 1 )。　　表 1　 2 0 0 0年全球 7级以上地震目录序号月日时 分 秒纬度经度　地点震级震源深度0 1 0 1 0 90 0 4 7 0 3 0 1 5 1°Ｓ 1 73 7°Ｗ汤加 7 00 2 0 1 2 82 2 2 1 0 1 94 3 1°Ｎ 1 4 6 7°Ｅ千岛群岛 7 00 3 0 2 2 50 9 4 3 54 0 1 9 0°Ｓ 1 74 5°Ｅ斐济 7 00 4 0 3 2 81 9 0 0 2 1 0 2 2 3°Ｎ 1 4 3 5°…     

2003年5月华北地区ML≥3.0地震动态

根据中国地震局分析预报中心提供的资料 ,2 0 0 3年 5月华北地区 ( 33 0°～ 4 2 0°N ,1 1 1 0°～ 1 2 5 0°E)共发生ML≥ 3 0地震 9次 (见表 1 ) ,其中 2 2日 1 6时 4 8分唐山ML4 1地震是本月最显著的事件。本月地震频次低于上月。参考 1 992年以来的月平均地震频次 ,5月处于中等偏高水平 ,地震活动月能量释放处于中等状态。表 1　 2 0 0 3年 5月华北地区ML≥ 3 0地震序号发　震　时　刻年月日时分秒震中位置φN/°　　　　λE/°震级ML震　中0 12 0 0 3 0 5 0 1T2 3 12 2 2 34 4 115 13 4睢县0 2 2 0 0 3 0 5 0 7T19 34 11…     

2003年6月首都圈地区ML≥2.0地震动态

根据中国地震局分析预报中心提供的资料 ,2 0 0 3年 6月首都圈地区 ( 38 0°～ 4 1 0°N ,1 1 3 0°～ 1 2 0 0°E)共发生ML≥ 2 0地震 1 6次 (见表 1 ) ,其中ML≥ 3 0地震有 4次。 2 1日 2 0时 1 3分唐山ML3 8地震是本月最显著的事件。首都圈本月地震活动频次低于上月 ,处于中等偏高水平。能量释放处于中等水平 ,震中主要在 39 0°～ 4 0 0°N之间成东西方向的带状内分布。表 1　 2 0 0 3年 6月首都圈地区ML≥ 2 0地震序号发　震　时　刻年月日时分秒震中位置φN/°　　　　λE/°震级ML震　中0 12 0 0 3 0 6 0 1T12 30 194…     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.     

Anomalies in the secular variations in the main geomagnetic field in the context of the hierarchic dipole model

The developed dynamic model of the main geomagnetic field (MGF) includes the sources of three levels, which have existed and continuously changed during the 100-year period. The spatial-temporal dynamics of the secular variations in MGF has been considered based on this model. It has been indicated that, at different times, the formation of anomalies (located in similar regions) depended on the total dynamics of different combinations of sources, including a change in the parameters of the dipoles of the secondorder smallness. Anomalies generated by the dynamics of the dipoles of the third-order smallness do not evidently manifest themselves in the total secular variations but are responsible for the specific shapes of isodynamic lines. Based on the stability and continuity of the constructed model, the conclusion is made that long-living turbulent flows of different scales can exist in the liquid core.     

The changes in the electric conductivity of the lithosphere in the source region of the strongest Olyutora earthquake in the Koryak highlands

The results of the magnetotelluric (MT) soundings before and after an earthquake are analyzed. The interpretation is based on the longitudinal and transverse MT curves (along and across the strike of the main tectonic elements, respectively). The MT curves are distorted by the ρ- and coast effect. The distortions due to the coast effect are estimated by the testing three-dimensional (3D) model. It is established that the coast effect distortion at the periods up to 1000 s is small and can be disregarded. The divergence of the longitudinal and transverse MT curves, which points to the presence of the deep faults, is thoroughly studied. The inversion of the MTsounding curves is carried out by the REBOCC program of the numerical two-dimensional modeling. This program implements the procedures of elimination of the ρ-effect and the joint inversion of the longitudinal and transverse MT sounding curves. The obtained geoelectrical cross sections provide an insight into the structure of electrical conductivity of the lithosphere before and after the earthquake. The more intense variations in the electric conductivity are observed in the zone of the deep faults. These variations are related to the changes in the porosity and saturation of the rocks by the highly mineralized fluids.     

Hydrological changes in the Ganges system in Bangladesh in the post-Farakka period

Abstract

The basin area of the Ganges River in Bangladesh is extremely dependent on a regular water supply from upstream to meet requirements for agriculture, fisheries, navigation, salinity control, and domestic and industrial sectors. In 1975, India commissioned a barrage on the Ganges River at Farakka to divert a significant portion of the dry season flow in order to make the Calcutta Port navigable. Statistical analyses of discharge and water level data have been carried out to determine if significant changes have occurred in the hydrology of the Ganges system in Bangladesh in the post-Farakka period. Siltation of the Gorai River (an offtake of the Ganges River) has also been examined using the stage-discharge relationship and regression analysis. The analyses show that the diversion has caused considerable hydrological changes in the Ganges system in Bangladesh. The water supply in the dry season has been reduced substantially, while siltation of the Gorai River has increased significantly.     

The electric field produced in the mantle by the dynamo in the core

A rigorous singular perturbation theory is developed to estimate the electric field E produced in the mantle M by the core dynamo when the electrical conductivity σ in M depends only on radius r, and when |r?_rln σ| ? 1 in most of M. It is assumed that σ has only one local minimum in M, either (a) at the Earth's surface ?V, or (b) at a radius b inside the mantle, or (c) at the core-mantle boundary ?K. In all three cases, the region where σ is no more than e times its minimum value constitutes a thin critical layer; in case (a), the radial electric field E_r ≈ 0 there, while in cases (b) and (c), E_r is very large there. Outside the critical layer, E_r ≈ 0 in all three cases. In no case is the tangential electric field E_S small, nearly toroidal, or nearly calculable from the magnetic vector potential A as ??_tA_S. The defects in Muth's (1979) argument which led him to contrary conclusions are identified. Benton (1979) cited Muth's work to argue that the core-fluid velocity u just below ?K can be estimated from measurements on ?V of the magnetic field B and its time derivative $\text{?}{}_{\mathrm{t}}\text{B}$. A simple model for westward drift is discussed which shows that Benton's conclusion is also wrong.In case (a), it is shown that knowledge of σ in M is unnecessary for estimating E_S on ?K with a relative error |r?_r 1nσ|^?1from measurements of E_S on ?V and knowledge of ?_tB in M (calculable from ?_tB on ?V if σ is small). Then, in case (a), u just below ?K can be estimated as $\text{?}\text{r}\text{×}\text{E}{}_{\mathrm{S}}\text{/B}{}_{\mathrm{r}}$. The method is impractical unless the contribution to E_S on ?V from ocean currents can be removed.The perturbation theory appropriate when σ in M is small is considered briefly; smallness of σ and of |r?_r ln σ|^?1 a independent questions. It is found that as σ → 0, B approaches the vacuum field in M but E does not; the explanation lies in the hydromagnetic approximation, which is certainly valid in M but fails as σ → 0. It is also found that the singular perturbation theory for |r?_r ln σ|^?1 is a useful tool in the perturbation calculations for σ when both σ and |r?_r ln σ|^?1 are small.     

Changes in sediment transport in the Kuye River in the Loess Plateau in China

In this paper, the changes in sediment transport over 51 years from 1955 to 2006 in the Kuye River in the Loess Plateau in China are assessed. Key factors affecting sediment yield and sediment transport, such as precipitation depth, discharge, and human activities are studied. To investigate the changes in sediment yield in this watershed, a trend analysis on sediment concentration, precipitation depth, and discharge is conducted. Precipitation depths at 2 Climate Stations （CSs）, as well as discharge and sediment transport at 3 Gauging Stations （GSs） are used to assess the features of sediment transport in the Kuye River. The rtmoff modulus （defined as the annual average discharge per unit area, L/（s·km^2）） and the sediment transport modulus （defined as the annual suspended sediment transport per unit area, t/（yr km^2）） are introduced in this study to assess the changes in runoff and sediment yield for this watershed. The results show that the highest average monthly discharge during the study period in the Kuye River is 66.23 m^3/s in August with an average monthly sediment concentration of 88.9 kg/m^3. However, the highest average monthly sediment concentration during the study period in the Kuye River is 125.34 kg/m^3 and occurs in July, which has an average discharge of 42.6 m^3/s that is much less than the average monthly discharge in August. It is found that both the runoff modulus and sediment transport modulus at Wenjiachuan GS on the Kuye River has a clear downward trend. During the summer season from July to August, the sediment transport modulus at Wenjiachuan GS is much higher than those at Toudaoguai and Longmen GSs on the Yellow River. The easily erodible loess in the Kuye River watershed and the sparse vegetation are responsible for the extremely high sediment yield from the Kuye River watershed. The analyses of the grain size distribution of suspended load in the Kuye River are presented. The average monthly median grain size of suspended load in the Kuye River is largest in February and then decreases until June. In July, the average monthly median grain size of suspended load approaches another peak and decreases until September. Then, the median grain size of suspended load starts to increase until February of the following year. However, the average monthly median grain size of suspended load in the Yellow River at Toudaoguai and Longmen GSs is the smallest between early summer and late fall The median grain size in the Yellow River starts to increase in November and approaches the largest size in January.     

Trends in the characteristics of the annual and semiannual variations observed in the radio wave absorption in the lower ionosphere

The continuous increase in concentration of greenhouse gases in the atmosphere is expected to cool higher levels of the atmosphere. There is some direct and indirect experimental evidence of long-term trends in temperature and other parameters in the mesosphere and lower thermosphere (MLT). Here we look for long-term trends in the annual and semiannual variations of the radio wave absorption in the lower ionosphere, which corresponds to the MLT region heights. Data from central and southeastern Europe are used. A consistent tendency to a positive trend in the amplitude of the semiannual wave appears to be observed. The reality of a similar tendency in the amplitude of the annual wave is questionable in the sense that the trend in the amplitude of the annual wave is probably induced by the trend in the yearly average values of absorption. The phases of both the annual and semiannual waves display a forward tendency, i.e. shift to an earlier time in the year. A tentative interpretation of these results in terms of changes of the seasonal variation of temperature and wind at MLT heights does not contradict the trends observed in those parameters.     

Site response in the Qionghai Basin in the Wenchuan earthquake

Amplification effects of soil site response can significantly impact ground motions, and must be considered in the seismic fortification of buildings/structures to prevent or mitigate this potential seismic hazard. Utilizing acceleration time histories from the main shock of the Wenchuan earthquake recorded at four stations (i.e., one on bedrock and three on soil) in the Qionghai Basin, the site responses from three soil sites are studied by using the traditional spectral ratio method. The bedrock site is selected as a reference site. This study found that peak ground accelerations (PGAs) on the soil sites are much larger than on bedrock, with EW, NS and UD components of 3.96–6.58, 6.27–10.98, and 3.17–6.66 times those of the bedrock site, respectively. The amplification effects of the soil sites on ground motions in the frequency range of 0.1 Hz to 10 Hz are significant, depending on the thickness of the soil layer and the frequency content of the site. A significant amplification occurs with high frequency components of ground motion at shallow soil sites, and low and high frequency components of ground motion at intermediate soil sites.     

Variations in the Caspian Sea Level in the Historic Epoch

Reconstruction of variations in the Caspian Sea level is proposed based on the results of investigations of deposits in the Agrakhan sand bar and bays (or former bays) of the eastern sea coast. The history of sedimentation in particular regions is reconstructed by the radiocarbon dating. Generalized data on the age of deposits are used to construct the most likely temporal course of variations in the sea level within the historic epoch.     

浙江省北部及邻区中强地震前地倾斜异常特征及其预测意义

解释并讨论了湖州和宁波台１９９３年以来的地倾斜资料,总结了震前有异常显示的６次地震。发现：①异常在现场记录资料中均有显示,异常形态的识别对预报地震有重要的意义;②能观测到异常全过程的倾斜仪与震中的距离基本符合式ｌｇＤｊ＝０．３０３（ＭＳ＋１．６）给出的监测能力半径,大于这个半径的台有时也能观测到异常,但多为短临异常。如果震前记录到异常的全过程,则利用单台资料可能对地震三要素进行预测。