Preliminary Results of Anthropogenic Seismicity Monitoring in the Region of Song Tranh 2 Reservoir,Central Vietnam

Song Tranh 2 hydropower plant and the reservoir containing backed up water are located in the Quang Nam province (Central Vietnam). The region experiences unusual seismic activity related to the reservoir impoundment, with earthquakes of magnitude up to 4.7. In result of cooperation between the Institute of Geophysics, Vietnam Academy of Sciences and Technology and the Institute of Geophysics, Polish Academy of Sciences a seismic network has been built to facilitate seismic monitoring of the Song Tranh 2 area. The network, operating since August 2013, consists of 10 seismic stations. Here we show that the network is sufficient for advanced data processing. The first results of monitoring of the earthquake activity in Song Tranh 2 area in the period between 2012 and 2014, especially the completeness of catalogs, study and comparisons between water level and the seismic activity suggest direct connection between reservoir exploitation and anthropogenic seismicity.     

利用接收函数方法研究蒙古中南部地区地壳结构

2011年8月至2013年7月中国地震局地球物理研究所与蒙古科学院天文与地球物理研究中心在蒙古中南部区域布设了宽频带流动地震台阵,这为开展远东地区深部结构的精细探测提供了有利的数据基础.利用台阵记录的远震地震事件,采用P波接收函数的H-κ叠加分析和共转换点（CCP）叠加方法获得了台站下方的地壳厚度及平均波速比.结果显示研究区的地壳厚度介于39 km至45 km之间.整体上Moho面埋深从西北往东南方向逐渐变浅.在蒙古主线性构造两侧地壳厚度呈现区域性变化特征,东南部地区地壳厚度较薄,约为39 km,而西北部地区地壳较厚,达45 km,为此推测蒙古主构造线可能是地壳的一个陡变带.此外,研究地区地壳的平均波速比值（V_P/V_S）在1.70到1.79之间,均值为1.75,低于全球大陆的平均值1.78,这可能暗示着该区其地壳是缺少铁镁质的.研究还发现测线的西北与东南地区其地壳波速比值较高,推测是古生代铁镁质地壳的残留或是新生代岩浆底侵的反映.     

Microearthquake studies in Egypt carried out by the geological survey of Egypt

Extensive microearthquake studies have been conducted in Egypt as a joint project between scientists from the Egyptian Geological Survey and Mining Authority (EGSMA) and U.S. scientists. At this stage, a great part of the data has been analyzed and two intensively active areas have been located: one in the Abu Dabbab area of the Eastern Desert, the second at the mouth of the Gulf of Suez near Gubal Island (Daggett et al., 1980). Both sites have been reported to be the epicenters of large earthquakes in 1955 and 1969, respectively. A few scattered earthquakes have also been located in the northern part of the Red Sea, some of which lie along its median axis (Daggett et al., 1986) adding to evidence for the medial opening of the northern Red Sea. After the occurrence of an earthquake (M = 5.5) in the Aswan region on 14 November 1981, continuous recording of the many aftershocks was carried out by EGSMA for about seven months from December 1981 to July 1982, when the temporary network was replaced by a network of telemetered seismographs installed and operated by Helwan Institute of Astronomy and Geophysics in cooperation with scientists from Lamont and Doherty Geological Observatory (LDGO). The majority of epicenters are concentrated in the vicinity of G. Marawa about 65 km upstream of Aswan Dam, along the E-W Kalabsha fault. The observed focal mechanism is consistent with a right-lateral strike-slip motion on the Kalabsha fault. Analysis of Aswan microearthquakes has been done by EGSMA in cooperation with scientists from California Division of Mines and Geology (CDMG).     

Temporal variations of gravity in the Aswan region of Egypt

The Kalabsha region at the northwest side of Lake Aswan has been a subject of seismological and geodetic investigations since 1981, after the 5.5 M earthquake on 14 November. The subsequent seismic activity was related to the effect of water-level oscillations in the Lake. Geodetic measurements provided indications of regional stress and of the local character of vertical movements. As crustal dynamics represents a potential hazard with respect to the size of the lake, other techniques have been applied to the monitoring system. Repeated gravity test measurements were already made in the late 1980s and in 1994, but only in 1997 was a new epoch of long-term investigation initiated. The measured data showed sufficient accuracy of approx. 5 μGal. Already the first difference of the two campaigns of the years 1997 and 2000 showed a few important features. First of all, the temporal non-tidal changes of gravity exceed the level of confidence significantly. The changes were compared with older available geodetic data, and it was concluded, that the gravity changes were not related directly to the vertical movements of the surface. On the contrary, a water loading effect may be expected on the eastern side of the network, especially in the Kalabsha local net. The development of the stress field is considered to be the main source of observed gravity changes. In both the Kalabsha and Seiyal nets the changes differ according to the relative positions of the particular measuring points with respect to the faults.     

Physico‐Chemical and Bacterial Characteristics of Water Quality in Three Villages West of Lake Nasser,Egypt

The present study aims to investigate physico‐chemical and bacterial characteristics of Nasser Lake water and houses drinking water, as well as fish cultures and its wastewater, in three villages west of Lake Nasser, Egypt. Fifteen representative water samples (Nasser Lake, different drinking water, fish cultures, and wastewater sources) were collected from three villages (Garf Hussein, Bashaier, and Kalabsha) in the west of Lake Nasser. Physico‐chemical, total viable counts, and bacterial qualification of water were achieved. The obtained results indicated that the produced water, supposed to be for domestic use in the three villages, contained all the tested organisms. The investigated water samples of the lake and drinking water in the selected three villages are supposed to be chemically safe according to World Health Organization and to Egyptian standards for drinking water. Water pollution index (WPI) was used in this study and the result concluded that for irrigation canals from the lake to the agriculture site, fish cultures (both concrete and earth pond systems), and drainage canal of fish ponds need to be treated before it is discharged to the lake. It is better to reuse it after treatment for agricultural purposes or recycled it to the fish cultures.     

Seismic observations at Lake Emosson,Switzerland

Since 1973 several seismic stations have been brought into operation at Lake Emosson, the last large conventional hydrodam in the Swiss Alps. The reservoir is situated in a seismically active zone which stretches from the Rhone valley in southwestern Switzerland into Haute Savoie, France. The monitoring program was started before the first impounding and continued during four full load cycles. A certain correlation is indicated between water level changes and the occurrence near the reservoir of weak seismic events (M_L<0) with high frequency content. A transient series of 30 tremors occurred in August 1974, during a period of rising water level. Local events of a different type frequently occur during the periods of decreasing water level. Their daily distribution indicates a mechanism which is caused by temperature variations.Contribution No. 131 of the Geophysical Institute, Karlsruhe University. Sonderforschungsbereich Felsmechanik of Karlsruhe University. Contribution No. 299 of the Institute for Geophysics, ETH Zürich.     

Factors affecting seasonal patterns in epilimnion zooplankton community in one of the largest man-made lakes in Africa (Lake Nasser, Egypt)

The objective of the study was to determine which factors regulate zooplankton organisms along Lake Nasser. Temperature, pH, DO, conductivity, turbidity, nutrients, and zooplankton abundance were measured. Twenty-three species of zooplankton were recorded in Lake Nasser included in Copepoda, Cladocera and Rotifera. Copepoda represented the main bulk of the community. The lowest standing stock of zooplankton was noticed during spring due to the highest fish predation during this season associated with the lowest turbidity. Big difference in temperature in Lake Nasser along the year round is considered as a controlling factor related to range of tolerance of species. The oscillation of the lake water level and the different factors affect the standing stock of zooplankton in the lake. Thus, continuous monitoring of Lake Nasser biota should be undertaken to follow the changes in the ecosystem.     

Imaging of convergent zones by seismic acquisition and processing

Abstract The complex crustal geology of convergent zones requires carefully planned seismic experiments for accurate imaging. Situations that require 2-D or 3-D experiments, pre-stack or post-stack processing, and time or depth migration, are discussed. Some of the advanced techniques available for seismic processing are described. Some results of 3-D post-stack depth migration of a 3-D data set on the Barbados margin that were obtained by the University of Texas Institute of Geophysics and reprocessed at the Houston Advanced Research Center illustrate the advantage of three-dimensionality, and the value of advanced processing techniques.     

中蒙弧地区地震活动性及其地球动力学成因研究

应用中国地震局地球物理研究所和蒙古科学院天体和地球物理研究中心合作编制的蒙古国及邻区M≥3.5的地震目录,研究了中蒙弧地区的地震活动性特征.结果表明,与中国大陆的“南北地震带”相对应,研究区地震总体分布大致以107°E为界,呈现西强东弱的特点,7级以上的强震集中于贝加尔湖、萨彦、阿尔泰以及天山地区,107°E以东,除纬度40°线附近（燕山地震带）地震较集中且强度大之外,其它地区地震稀少,强度也低.通过断层的野外调查和本地区震源机制解,进一步研究了该地区地震活动性特征的构造应力场及地球动力学成因.研究区大部份地震都是走滑型断层活动的地震.逆断层活动的地震主要分布于中国的天山地区和中蒙边境一带的阿尔泰山地区,正断层活动的地震主要分布于俄罗斯的贝加尔湖裂谷带,走滑兼倾滑断层活动的地震主要分布在研究区域的西部地区.研究区域内的大部份地区主压应力轴（P）的倾角都小于30°,为水平或近水平的构造应力场,自西向东主压应力轴的走向从近南-北方向逐渐转为北东-南西方向.断层的野外调查、震源机制解和区域构造应力场的方向表明,中蒙弧地区主要来自西南面的印度洋板块向北偏东方向的碰撞挤压,通过青藏高原传递到本区,来自东面太平洋板块的影响已较微弱,这是研究区地震活动西强东弱、8级以上强震都发生在西部的主要原因.     

埃及阿赫米姆古墓遗址浅层地球物理勘查

Ground penetrating radar, electromagnetic terrain conductivity, and electric tomography have proven to be effective tools if they are combined together to investigate archeological sites. We have conducted a geophysical survey at the Akhmim archaeological site, the main objective of our survey is to locate additional buried structures for further excavation. Geophysical data were acquired in the area using the GEM-300 multi-frequency terrain conductivity profiler, the SIR 2000 ground penetrating radar, and the Syscal R2 resistivity meter systems. The results of the integrated interpretation show a number of buried features and a strong linear zone about 1 m wide that coincides with the suspected trend of a buried wall. There appears to be two parallel ridges of strong reflections on either side, indicating two parallel walls extended East-West and a room is identified at the bottom left comer of the site. Moreover, the interpretation results of some selected GPR and dipoledipole resistivity profiles adjacent to the open-air museum suggest the existence of a second statue of Ramses Ⅱ to the right of the previously discovered statue which could still be buried in the sand.     

Deep seismic soundings in southern Spain

Summary In 1974 and 1975 deep seismic sounding experiments were carried out in the area of the Betic Cordillera in southern Spain. A network of crustal seismic profiles was established with shotpoints at sea close to Cádiz, Adra and Cartagena and on land at Alquife near Guadix. The lengths of the profiles range from 50 km near Alquife to 440 km for the main profile between Cádiz and Cartagena parallel to the strike of the Betic Cordillera. The main profile was supplemented by a reversed recording line close to the Mediterranean coast between Adra and Cartagena and another one perpendicular to the main tectonic strike from Adra towards the north. The first interpretation of the data indicates considerable variation in the crustal thickness. A preliminary inversion leads to a three-layered model of the crust. The mean compressional velocity is about 5.1 km/s down to a depth of 4 km. Below this the velocity is 6.13 km/s from 4 to 16 km where it increases to 7.14 km/s. TheP _n-velocity is 8.18 km/s. The crust-mantle boundary is reached at a depth of 27 km near Cartagena and lies 32 km deep near Adra, Underneath the gravity minimum of the Betic Cordillera the crust-mantle boundary is found at a depth of about 36 km. Below the Betic zone a pronounced zone of low velocity with 7.7 km/s seems to exist in the depth range from 40 to 60 km.Contribution No. 4, Grupo de Trabajo de Perfiles Sismicos, Comisión Española del Proyecto Geodinámico, C.S.I.C., Madrid, Spain.Contribution No. 139, Geophysical Institute, University of Karlsruhe, Hertzstrasse 16, D-75 Karlsruhe 21, Germany.Contribution No. 217, Institut de Physique du Globe, Université Paris VI, 4 Place Jussieu, F-75230 Paris Cedex 05, France.Contribution No. 11, Instituto y Observatorio de Marina, San Fernando (Cádiz), Spain.Contribution No. 163, Institute of Geophysics, Swiss Federal Institute of Technology, ETH-Hönggerberg, CH-8093 Zürich, Switzerland.     

延庆─怀来地区地壳细结构──利用深地震反射剖面

１９９２年底在延庆－怀来地区实施了深地震反射剖面测量，目的是通过对该区地壳细结构的研究来探讨延庆－怀来盆地形成演化的机制和过程，以及与该区地震活动图像的关系．结果表明，研究区上部地壳总体上呈“透明”性质，厚２５－２６ｋｍ；下部地壳具有强烈的反射性质，厚约１４－１５ｋｍ．壳幔过渡带是由双程走时约２ｓ和厚约５－６ｋｍ的水平反射叠层所组成，莫霍界面具有深度深（约３９－４０ｋｍ）和平坦的特点。     

延庆─怀来地区地壳细结构──利用深地震反射剖面

１９９２年底在延庆－怀来地区实施了深地震反射剖面测量，目的是通过对该区地壳细结构的研究来探讨延庆－怀来盆地形成演化的机制和过程，以及与该区地震活动图像的关系．结果表明，研究区上部地壳总体上呈“透明”性质，厚２５－２６ｋｍ；下部地壳具有强烈的反射性质，厚约１４－１５ｋｍ．壳幔过渡带是由双程走时约２ｓ和厚约５－６ｋｍ的水平反射叠层所组成，莫霍界面具有深度深（约３９－４０ｋｍ）和平坦的特点。     

A statistical model for estimating the accuracy of event location applied to a network of Scandinavian stations

A statistical model for estimating the errors of epicenter location and origin time is proposed and applied to the old Fennoscandian seismic network. An average crustal model (Sellevoll andPomeroy, 1968) and P and S wave residuals as a function of azimuth have been used. The calculations are carried out for different maximum detection ranges. The analysis shows relatively, small (1 km) standard errors of epicenter location of strong earthquakes for central Fennoscandia. The largest errors are found in the southern and eastern parts of Fennoscandia.On leave from Institute of Geophysics, Polish Academy of Sciences, Warsaw, Poland.     

SPICeD: imaging the deep Earth

Michael Kendall and George Helffrich respond to Alan Douglas's paper in the previous issue of Astronomy & Geophysics with a prototype three-component broadband seismic network for the UK.
There are two boundaries in the Earth's deep interior that are as significant in terms of contrast in material properties and dynamics as the lithosphere–atmosphere boundary, where we live. The natures of the core-mantle boundary and the inner-core/outer-core boundary have significant implications for the stability of the Earth's magnetic field, style of convection, moment of inertia and length of day. An array of broadband three-component seismometers (SPICeD) spanning Scotland, England and France has been deployed with the aim of studying these dramatic interfaces within the Earth. A secondary aim of the deployment was to install a working prototype for a permanent three-component broadband seismic network in the UK, as advocated by Alan Douglas in the previous issue of this journal (Douglas 2001).     

India-Eurasian collision vs. ocean-continent collision＊

Introduction Major tectonic activities occur in collisions zones between plates or intra-plate continental blocks. Therefore, it is significant to investigate collision processes. We know that orogenic and seismic belts in plate margins are closely relate…     

汶川地震断裂带科学深钻WFSD-3附近上地壳S波分裂特征

为配合汶川地震断裂带科学钻探工程(WFSD),中国地震局地球物理研究所在四川省绵竹市天池乡和灌县—安县断裂附近分别架设了15套微震仪器和17个短周期地震台.基于WFSD-3附近的微震、短周期和区域台网的固定台站记录的近震数据,通过横波窗内S波分裂计算,得到其上地壳各向异性参数,即快波偏振方向和慢波的时间延迟,并分析了研究区的上地壳各向异性特征.结果显示,研究区大部分区域的快波偏振方向为NE向,与龙门山断裂带走向一致,但在研究区微震台阵布设小区域内,快波偏振方向表现出东西分区特征,东部为NE向,西部为NW向.上地壳各向异性主要是受到岩层中随应力分布排列的微裂隙和岩石或矿物结构的影响,研究区内快波偏振方向主要表现为NE方向,与断裂走向一致,反映了研究区上地壳各向异性主要受控于结构控制的各向异性,局部区域的快波偏振方向为NW向,与区域最大主压应力方向一致,说明区域应力场对研究区上地壳各向异性也有影响.通过分析微震台阵的归一化时间延迟随时间的变化情况可以反映区域应力场的变化情况.微震台阵的慢S波时间延迟在2012、2013年较为离散,在2014年有收敛的趋势,反映了强震后区域应力场逐渐稳定的趋势.     

蒙古中部地区SKS分裂研究的初步结果

为了进行蒙古中部地区的深部构造观测与模型研究, 中国地震局地球物理研究所和蒙古科学院天文与地球物理研究中心合作, 在该地区架设了60台宽频带流动地震台. 这些台站分布在被额尔齐斯—中蒙古—额尔古纳断裂隔断的加里东、 海西两个构造域. 本文选取了2011年8月—2012年7月部分台站记录的震中距在85°—135°且M_W≥5.0的远震事件, 通过SplitLab软件来进行SKS分析. 使用最小能量法、 旋转相关法和最小特征值法进行处理, 取得了蒙古中部地区各向异性的初步结果. 结果显示: 快慢波延时在0.8—2.0 s之间. 西北部区域靠近杭爱山脉与肯特山脉的区域构造走向均为ENE--WSW方向, 而快波方向大多为N40°W, 与区域构造走向近似垂直.根据HS3-NUVEL-1A板块模型计算的该地区板块绝对运动方向与快波偏振方向呈顺时针约15°夹角. 然而, 有个别台站表现出了两种模式的快波分裂, 其中一种与当地ENE--WSW向的断裂方向近似一致.      

Long- and middle-term behaviour of the tilt and strain variations in the decade following the 1976 friuli earthquake in NE Italy

Tilt and strainmeter data collected in the Friuli seismic area between 1977 and 1985 have been analyzed to study the stress-strain field and/or the elastic parameter variations in the area after the strong 1976 seismic event.We concentrated on three different frequency bands, respectively linked with the tidal waves, the seasonal effect and the secular one. The results from the first two bands point at an increase of the local rigidity modulus.Relevant stresses induced by the seasonal groundwater level variations have been found, thus supporting the hypothesis that they can act as triggering effects. The secular trend reveals significant tectonic stress modifications. It appears that the post-seismic tectonic stresses faded during 1981–1983, and were followed by a new loading phase.On leave from the Institute of Geodesy and Geophysics of the Chinese Academy of Sciences. Ph. D. student at the Institute of Geodesy and Geophysics, Trieste University.     

Electrical investigation in the Chaîne des Puys (France)

Numerous geologists have studied the structure of the Chaîne des Puys, our knowledge of which has recently been enlarged by geophysical research. Some of the hypotheses concerning its structure at average depth had to be checked, and so in 1975 the National Institute for Astronomy and Geophysics (I.N.A.G.) provided the necessary support for such work.An anomaly of the electrical conductivity was clearly apparent, both from the magnetotelluric method in a wide range of frequencies as well as from more classical methods (electrical sounding) or from newer methods such as differential magnetic sounding.It has been proved that the structure, which is believed to be responsible for this anomaly of conductivity, is quite different from other inferred structures which result from the interpretation of magnetic data only. However, although the coexistence of these different structural elements is not impossible, heat-flow measurements and geochemical studies do not support the assumption of an active magma chamber (a few kilometres deep).