Present state of geodynamic properties of Kalabsha area, nortwest of Aswan Lake, Egypt

Aswan Lake is the second largest man-made lake in the world. Its filling started 1964 and reached the maximum water level in 1978. An earthquake of magnitude 5.5 took place in 1981 along the most active fault near the lake (Kalabsha fault). This earthquake was follwed by a tremendous number of smaller events that continue till now.Seismicity and the underground water table around the lake are monitored continuously through a radio-telemetered network. A local geodetic network was established around parts of the active faults in the northwestern part of the High Dam Lake, for monitoring vertical and lateral movements. The Kalabsha local geodetic network (the first one) was established around an active part of the Kalabsha fault in 1983. Precise geodetic measurements have benn carried out twice a year since 1984.On the basis of the repeated geodetic measurements, seismicity of the area and geophysical as well as geological data, the present state of the geodynamical properties of the Kalabsha area is studied.Remarkable horizontal movements were detected; they are correlated with the seismicity of the area and are attributed to the differential loading by the lake. The Kalabsha fault is a right-lateral strike-slip motion on an E-W plane. The magnitude of the movements detected along the fault is variable for the different epochs of measurements and is correlated with both seismicity and water loading in the lake.     

Geodetic measurements on the Asal Rift (Djibouti): Twelve years of observations

The resurvey of both a geodetic network and a levelling net was carried out in June 1981, 8 months after the M_s = 7.3 El Asnam earthquake of 10 October 1980. Previous seismological and neotectonic studies indicate that this event results from a north-east-trending overthrust complex fault of about 40-km length, which shows at least three principal segments with slightly different directions.Vertical movements, evaluated by means of a trigonometric levelling method show an uplift of the thrust fault of about 5 m and a depression of the southeastern edge of about 1 m. These movements are progressively attenuated away from the fault trace (see fig. 1). Horizontal movements have been evaluated by a classical first-order triangulation method. (see fig. 2 and table 1).The resulting mean strain tensors, calculated for different triangles of the geodetic network, indicate a shortening of about 2.50 m which is consistent with the SE-NW direction of compression determined from neotectonic evaluations and focal mechanisms (see fig. 3). Dislocation models are used to explain and discuss the observed deformations in the light of the seismological data and the observed ground breakages. Five segments are required to explain both horizontal and vertical deformations. The magnitude of vertical displacement (about 6 m) at the junction between the southwest and the central segments of the fault argues for the breaking of this area during the main shock and for a slip vector of about 8 m, at least in the central segment.In such circumstances where the first field observations show that a strong coseismic movement has taken place, the best methodology to be used seems to be:

• - to resurvey as quickly as possible the widest acceptable zone of the old existing geodetic network, without special attention paid to the precision of these measurements.

• - to set up as soon as possible a small aperture geodetic network of high accuracy in order to monitor the possible postseismic readjustments.

For vertical movements, trigonometric leveling using reciprocal zenith measurements with two high-precision theodolites and EDM appears to be far the best solution. It is much quicker than classical leveling and it can afford the same precision if necessary. In our case, the precision was not critical, so that long ranges (up to 1500 m) between stations were used when necessary.     

新丰江水库库区形变测量与地震活动关系探讨

广东省新丰江水库地区1962年3月19日发生 Ms=6.1的地震.地震前后,库坝区分别布设了水准测量网和三角测量网.形变测量具有精度高、测期密的特点.本文通过对不动点的处理,得出新的形变场并讨论了它的特点;根据各相邻期的三角测量结果计算了各三角形的主应变;依据地震时的应变对一次5.3级的地震的发震断层作了反演.结果表明,地壳水平形变与新丰江水库地区4级以上地震有明显的关系,垂直形变与这些地震无明显关系.      

Repeated Geodetic Measurements in the West Bohemia Seismoactive Region: Period 1993 - 1996

The western part of the Bohemian Massif is characterized by repeated occurrences of intraplate earthquake swarms. To study surface deformations of this anomalous region, a network covering about 2000 square kilometres for repeated geodetic measurements was established in 1993 - 1994. The positions of the individual points of the network were carefully picked with respect to local tectonic structure and earthquake foci distribution. GPS and precise levelling measurements were performed 1-2 times a year. The GPS data were processed by Bernese GPS software. No tendency to any displacement - either horizontal or vertical - of geological blocks was derived from the geodetic data for the period 1993 - 96. Only displacements of less than 5 mm/year in average could occur in the whole region in that period; larger displacements would have been revealed by our measurements.     

Deduction of the horizontal gradients of the Hungarian vertical movement velocities by polynomial fitting

Recently, intensive investigations were carried out in Hungary to explore the characteristics of vertical crustal movements. In the first phase (by using repeated geodetic measurements) vertical movement velocities were mapped. In the second phase the aim was to study the movement tendencies in more detail. In the professional literature many mathematical methods are reported. Among these the method of horizontal gradients is applied quite often. In this paper the velocity function of the vertical movements is represented by polynomials and the gradient values are computed from these. To control the values calculated from the velocity functions they were compared to the observed values. The above method was applied to the whole territory of Hungary and also to four zones individually. These zones were determined on the basis of geological information. Besides a short review of the method we present the results: velocity functions, gradients and control data. The gradient vectors are also presented in graphical form.     

Geodesy in Japan

T. Inoh was the first who completed a nation-wide map of Japan, in the beginning of the 19th century. He determined geodetic positions by distance and angle measurements and by astronomical observations. When Japan entered into its modern era, about 100 years ago, the Military Land Survey was established and has conducted geodetic work in Japan ever since until the end of World War II. A German surveying system belonging to Helmert's school was adopted. The Ministry of Education organized later the Geodetic Commission which promoted the geodetic activities in cooperation with the Military Land Survey. Comparison between the first and second nation-wide triangulation results obtained by the Geographical Survey Institute (GSI), the successor of the Military Land Survey, brought out marked horizontal land-deformations associated with a large earthquake. Repetitions of levelling survey also make it clear that vertical land-movements, well consistent with tide-gauge observation data, take place in association with earthquakes. The extensive subsidence in the Northeast Japan may be explained by assuming a sinking lithosphere, as is argued by the theory of plate tectonics. On the other hand, most local movements are closely correlated to pre-, co- and post-seismic land-deformations. The nation-wide gravity survey carried out by the GSI disclosed a complicated gravity distribution in Japan. Ship-borne gravimeters have now been extensively working at sea. One of the recent highlights of gravimetric work is the detection of secular gravity changes which are in accordance with the secular changes of levelling data. A portable absolute-gravity measuring instrument was constructed by the Earthquake Research Institute although it is still in a testing stage. Much advance has been made in the astrogeodetic observation devices since 1950's.     

Relation of surface movements in West Bohemia to earthquake swarms

GPS observations in the Western Bohemia/Vogtland earthquake swarm region revealed indications of horizontal displacements of low amplitude, and no clear long-term trend in 1993–2007. On the other hand, in 1998–2001 there was relatively significant active movement along NNE-SSW oriented line that we called the “Cheb-Kraslice GPS Boundary” (ChKB), identical with an important limitation of earthquake activity. The most impressive were dextral (right-lateral) movements in the 1998–1999 period followed by reverse sinistral (left-lateral) movements in 1999–2000 that correlate with prevailing motion defined by fault plane solutions of the Autumn 2000 earthquake swarm. Before the February 2004 micro-swarm, two points located on opposite sides of the Mariánské Lázně fault showed extension in the order of about 7 mm in the same NNE-SSW direction of ChKB. The new NOKO permanent GPS station in Novy Kostel showed the peak-to-peak vertical changes up to 10 mm before and during the February 2007 micro-swarm. Annual precise levelling campaigns in the local network around Novy Kostel revealed regular vertical displacements during the 1994, 1997 and 2000 earthquake swarms. The points around the Novy Kostel seismological station showed uplift during the active periods, including the micro-swarm February 2004. However, no such indication was observed on levelling points in the period of the February 2007 swarm. Long-term vertical displacements depend on the same direction NNE-SSW (ChKB) as the GPS displacements. Both geodetic techniques have revealed oscillating displacements, GPS horizontal, and levelling vertical, rather than any long-term trends in the study period 1993–2007. The displacements exhibited significant spatial and temporal relation to tectonic activity (earthquake swarms) including their coincidence with the seismologically determined sense of motion along the fault plane during earthquakes.     

A new determination of recent vertical movements of the Earth's crust in Poland

A new determination of recent vertical movements of the Earth's crust in Poland is described in this paper. It resulted from the joint adjustment of the network of repeated levelling in 7 countries of Eastern and Central Europe. The author presents the characteristics of the levelling data sets used (measurements made in 1953–1957 and 1974–1979), results of the repeated levelling, the method of determination of the recent crustal movements and of the preparation of the map at a scale of 1:2.500.000 presenting these movements for the area of the whole country. The results of the determination of the Earth's crustal movements are discussed, and causes of the prevailing appearance of sinking movements are suggested. Differences between the values of vertical movements of the Earth's crust obtained during various determinations are presented, as well as the maximum mean error of the difference between new and old determinations. The conformity of these determinations is assessed.     

Recent geodynamics of the faults and paradoxes of the rates of deformation

The results of analyzing the long (20–50 years) time series of geodetic observations carried out in the regions with enhanced seismotectonic activity (Kopet Dag, Kamchatka, and California) are presented. It is established that recent vertical and horizontal displacements in the fault zones estimated by instrumental geodetic observations with increased spatiotemporal resolution indicate that the deformations in the fault zones paradoxically deviate from the movements inherited from the previous geological epochs. The paradoxes of high and low deformation rates in recent geodynamics lie in the reliably established empirical fact that extremely high local deformation rates (up to 10^?5 per annum and higher) exist in the fault zones in the setting of weak regional deformations, whose annual rates are by two to three orders of magnitude lower. Very low annual average rates of relative horizontal deformations, which only measure 3–5 amplitudes of tidal deformations of the solid Earth, are revealed in the seismically active regions of Kopet Dag and Kamchatka as well as in the San Andreas Fault Zone in northern California. The fault-block dilemma arising in the interpretation of the observations of recent fault geodynamics is formulated. Either the role of active element, which forms the present anomalous deformations, is played by a block, while a fault plays the role of the passive element, or the fault zone itself is a source of anomalous movements, while the blocks are passive elements (hosting medium). It is shown that paradoxes of low and high deformation rates vanish if we assume that the recent anomalous geodynamics is formed by parametric excitation of the deformation processes in the fault zones in the conditions of quasi-static loading.     

Recent crustal movement studies in Aswan region, Egypt: introduction

After the November 1981 earthquake in the Aswan area along the Kalabsha fault, Nubian Desert, studies on its origin were initiated in the Helwan Institute of Astronomy and Geophysics [now National Research Institute of Astronomy and Geophysics (NRIAG) in Helwan]. As a first step an array of seismic stations were established in cooperation with the Lamont-Doherty Geological Observatory and the correlation between the number of seismic events and the water level in Lake Nasser was investigated. In order to understand the eartqquake mechanism, additional information on the crustal deformation due to water load was required, and the International Center on Recent Crustal Movements (ICRCM) was invited to consult in the necessary procedures aimed at recent crustal movement studies around part of the western bank of Lake Nasser. The first local network of horizontal and vertical geodetic measurements was established and measured in 1984. Simultaneously, with respect to the extreme meteorological conditions in the desert, additional investigations as refraction studies, stability of bench marks etc. were initiated. The extension of the network and an increase of repeated measurements first brought results during the last few years. The results of these studies will be reported in the following papers in detail as a homogenous block of scientific communication.     

Derivation Of Refractive Index And Temperature Gradients From Optical Scintillometry To Correct Atmospherically Induced Errors For Highly Precise Geodetic Measurements

Refraction effects of optical beams are generally caused by an inhomogeneous propagation medium and are a major source of systematic errors in the precise optical determination of angles and distances in the atmospheric surface layer. In this contribution a method for deriving vertical temperature and refractive index gradients from optical scintillation is presented. Knowledge of these gradients is required for the compensation of atmospherically induced errors for highly precise terrestrial geodetic measurements, like direct transfer and levelling. The advantage of the present optical method is, that temperature and refractive index gradients can be derived as line-averaged values over the propagation path, which is not possible by meteorological point measurements. Field observations have been carried out with a displaced-beam scintillometer over flat terrain and under different atmospheric conditions in order to verify this method. The experiments show, that this method allows to derive accurate correction values for precise terrestrial geodetic measurements.     

The map of vertical crustal movements in Czechoslovakia and its interpretation

In addition to the measurements carried out in the framework of the 1973–1978 international relevellings, further levelling lines have been remeasured on the territory of Czechoslovakia till now. Considering all new relevellings on the region under study, an independent adjustment of annual velocities of vertical movements in whole network was performed. The values of vertical movements were determined relatively to the fundamental benchmark Želešice in the central part of Czechoslovakia, monumented in the bedrock of the southeastern border of the Bohemian Massif. The results are presented in a map of vertical movements and preliminarily interpreted in connection to the geological features of the territory under study.     

Comparison of long-term and short-term uplift rates along an active blind reverse fault zone (Bajo Segura,Se Spain)

The seismic activity of the Guardamar-Torrevieja zone (Eastern Betic Cordillera, SE Spain) can be associated with the Bajo Segura fault zone, an E-W reverse blind fault with secondary NW-SE dextral faults. A high-precision levelling profile 30 kilometers long was set up and levelled in 1997 to monitor the vertical displacement of this active fault zone. This profile runs parallel to an older high-precision levelling line included in the Spanish first order levelling network measured by the Instituto Geográfico Nacional (IGN) in two different campaigns (1934 and 1976). The 1997 line was relevelled in 2003 and 10 new benchmarks were set up, both to increase benchmark density and to restore some of the 1997 benchmarks that had been destroyed. We have used the 1976 IGN and the 2003 measurement to construct a recent vertical movements profile with a significant time difference (27 years). This recent vertical movements profile shows that the vertical movements are very small, nearly equal to the error bars, with a 0.2 mm/year rise in the town of Guardamar, and a 0.2 mm/year subsidence of the southern part of the profile (Punta Prima) respect to the town of Torrevieja. These movements could be related to the activity of the Bajo Segura and the San Miguel faults respectively. Using geological markers we have deduced uplift rates of 0.1 mm/year during the last 3 million years. Therefore, these preliminary results indicate that geodetically (short-term deformation) determined uplift rates are similar to those estimated from geological markers (long term deformation).     

形变测量和道孚地震ht

在四川鲜水河断裂带上的炉霍和道孚两地,分别于1973年和1981年发生了7.9级和6.9级地震,本文根据该断裂带上六处跨地震主破裂面和跨断层短水准、短基线场的多年形变测量资料,分析了断层活动特征与地震孕育和发生的关系,并对运用跨断层形变测最手段与地震预报作了粗浅的探讨.      

Maps of recent vertical crustal movements in Romania: Similarities and differences

A new map of recent crustal vertical movements (RCVM) in Romania, on the basis of high-precision geodetical measurements by the repeated levelling method, had become necessary firstly as a consequence of the great seismic event of March 4, 1977 with foci under the Vrancea Region (the most important seismic zone in the country) and secondly because many years had passed since the previous edition.Certainly, there are similitudes and differences between the two editions, and the authors will try to put these into evidence and explain them.The general view of the major geological units of Romania in both maps is the same: the mountain regions being zones of more or less continuous uplift, the plains showing subsidence movements and the plateau regions presenting a relative stability. Some modifications became apparent owing to the improvement of the national geodetical network on which the repeated levelling measurements were performed and following the choice of the Harbour of Constanţa as the fundamental point.     

Recent geophysical investigation at Somma-Vesuvio volcanic complex

Activity at Somma-Vesuvio volcanic area in southern Italy is monitored by seismic stations and periodic geodetic and gravity surveys. The seismic network, which consists at present of four vertical stations and one three-component station, recorded an increase in earthquake activity in 1978 and between November 1988 and March 1989. During the later activity, earthquakes were located in a cluster about 3 km beneath the summit of the volcano. Two tide gauges, two tiltmeters and a recording gravimeter are also operating at Somma-Vesuvio. Yearly levelling surveys are conducted along several closed routes that extend from as much as 6 km from the base of the volcano to the summit area. Survey results reveal no significant ground movement since 1959, except for a slight subsidence around the rim of the summit crater. Gravity changes have been larger than the expected 10 μGal uncertainty of the measurements. The lack of contemporary elevation changes implies that the observed gravity changes are the result of a slight change in density structure. The cone of Somma-Vesuvio has been very stable for the last few decades, showing no indications of a buildup to activity. The lack of surface movement should rule out a magma-supply rate to this volcano at the historic eruptive rate of 0.002 km³/yr.     

The dynamics of the northwestern border of the Carpathians

The border area between the Bohemian Massif and the Carpathians arc is covered by dense networks of repeated levellings as well as horizontal (triangulation, trilateration) measurements. The results were adjusted in separate vertical or horizontal networks respectively. Derived rates of vertical and horizontal movements are presented. The properties of these movements are discussed as a background to the tectonic development of the area under study.     

京、津、唐地区活动断裂带的形变特征

本文主要利用复测水准、基线资料研究本区活动断裂的现代活动性。计算出近20条断裂的垂直运动量及少数断裂的水平运动量。根据断裂活动垂直运动年速率的水平将该区断裂分为两类,第一类1—10毫米,第二类小于1毫米。结合地震、地质资料讨论了本区活动断裂的现代活动特征     

A preliminary report on the frequency characteristics of near-surface layers in the vicinity of the high dam lake

The frequency characteristics of near-surface sediments obtained from small scale S-wave refraction measurements conducted at two sites in the Garf Hussein area, contiguous to the High Dam Lake, South of Aswan, have shown drastic changes in the frequency-selective amplification of horizontal ground motion within a relatively short surface distance. This effect is attributed mainly to such factors as the variation in layer thickness and the presence or absence of soft alluvial deposits.These results indicate that movements initiated deep in the earth's crust may not be faithfully reflected on the ground surface. As geodetic work principally involves monitoring relative horizontal and vertical displacements on the earth's surface with time, geodesists are advised to take the spectral response of the ground into consideration.     

Selecting a method for interpreting GPS measurements of geodynamic movements of a point of the Earth’s surface in the high-frequency range

Different variants for interpreting the data of vertical and horizontal channels of GPS measurements are examined during experimental works. The movements of an observation point are imitated experimentally in the vertical and horizontal directions at a geophysical observatory. The experiments are carried out on a pedestal with original benchmarks in both directions. The movements are imitated in the high-frequency range with different time values of movement from one point to another, which did not exceed 1 h. The errors in imaging movements of measurement points according to the results of interpreting the readings of GPS receivers are shown in relation to the benchmark movements of measurement points in the vertical and horizontal directions. These data are processed in the differential mode using the precise point positioning (PPP) method. The experimental results confirm that there is no potential of imaging vertical movements of the Earth’s surface caused by tidal observations according to GPS receiver data.