Campaigns Of GPS Measurements Research Articles

Combined Space–Time Analysis of Geodetic and Geological Surveys for Evaluation of the Reliability of the Position of Points in the Geodynamic Network of the City of Zagreb

This paper describes the long-standing interdisciplinary geodynamic research for the wider Zagreb area, the most seismically active area of the continental part of the Republic of Croatia, extending over an area of around 800 km2. As a result of the research, which is based on geodetic and geological field measurements, a unique interdisciplinary movement model of the surface layers of the Earth’s crust for the project area is created. The analysis of survey data has determined the continuous tectonic activity of the wider Zagreb area. In the past 18 years, a total of 10 GPS measurement campaigns have been conducted. For each campaign, the velocities of geodynamic network points were calculated, and the cumulative velocity rate was determined from all measurement campaigns for the entire period of observations using GAMIT/GLOBK software. Displacements at individual measuring points of the network, throughout research, vary widely and depend on its location within the local geologic structural framework and regional tectonic movements. These displacements in detail represent a measurable insight into the tectonic activity of the area of research. Therefore, in this paper, special attention is given to the analysis and explanation of these variations in the displacements of the individual geodynamic points, even indicating the questionable quality of location selection for some points. In this way, we seek to explain the causes and mechanisms of such displacements. The results presented in this paper represent the preseismic area condition and further can be used in coseismic 2020 earthquake displacement analysis.

The Vertical Pattern of Surface Deformation in Iran, Inferred from the GPS Measurement Campaigns

The Vertical Pattern of Surface Deformation in Iran, Inferred from the GPS Measurement Campaigns

Preliminary crustal deformation model deduced from GPS and earthquakes’ data at Abu-Dabbab area, Eastern Desert, Egypt

A local geodetic network consisting of eleven benchmarks has been established to study the recent crustal deformation in the Abu-Dabbab area. Seven campaigns of GPS measurements have been collected started from October 2008 and ended in March 2012. The collected data were processed using Bernese version 5.0, and the result values were adjusted to get the more accurate positions of the GPS stations. The magnitudes of horizontal displacements are variable from one epoch to another and in the range of 1–3 (±0.2)mm/yr. Due to the differences in rates of the horizontal displacement; the area is divided into two main blocks. The first one, moves to the east direction of about 3mm/yr, while the second block, moves to the SW direction of about 6mm/yr. According to the strain fields that were calculated for the different epochs of measurement, the main force is compression force and is taken the NW–SE to NWW–SEE direction. This force could be because of local and regional tectonic processes affecting on the study area. The maximum values of compression stress are found in the southern central and western part of study area. Estimated accumulation of this strain energy may be considered as an indicator of the possibility of earthquake occurrence.From the seismic tomography study, the 3D Vp and Vp/Vs crustal models indicate high Vp/Vs values forms an elongated anomaly, in the central part of the study area, that extends from a depth of 12km to about 1–2km of depth is obtained. By using this crustal model in relocations all seismicity informed that most of the seismicity strongly tend to occur in a cluster manner exactly above the southern part of the study area. Based on the conducted source mechanism study, it is noticed that shallow earthquakes are associated by a high CLVD ratio (up to 40%). Furthermore, initiation of a high level seismic activity, without a large seismic main shock is observed in the Abu-Dabbab area. The distribution of micro-earthquakes tends to align in an ENE–WSW direction marking a zone of activity verse the Red Sea. The nucleation of the seismic activity beneath the southern part of the Abu-Dabbab crust is more consistent with the obtained crustal deformation result by increasing the crustal movement in the south part than the northern part. Then, based on the obtained results of the above mentioned studies; seismic tomography; source mechanisms, and crustal deformation we conclude that these seismic activities that are associated by crustal deformation are owing to some magma activity beneath the crust of the Abu-Dabbab area.

Comparative deformation analysis for Abu Dabbab area, Egypt

Abu-Dabbab area is characterized by high seismicity and complex tectonic setting, for these facts, a local geodetic network consisting of eleven geodetic benchmarks has been established. The crustal deformation data in this area are collected using the GPS techniques. Five campaigns of GPS measurements have been collected, processed and adjusted to get the more accurate positions of the GPS stations. The horizontal velocity vectors, the dilatational, the maximum shear strains and the principal strain rates were estimated. The magnitude of the movements is distributed inhomogeneous over the area and it varies in average between 3 and 6 mm/yr. The results of the deformation analyses indicate a significant contraction and extension across the southern central part of the study area which is characterized by high seismic activity represented by the clustering shape of the microearthquakes that trending NE-SW direction. The north and north-eastern parts are characterized by small strain rates. This study is an attempt to provide valuable information about the present state of the crustal deformation and its relationship to seismic activity and tectonic setting at Abu-Dabbab area.

Recent crustal deformation and seismicity studies at Abu-Dabbab area, Red Sea, Egypt

The Abu-Dabbab area is characterized by high seismicity and complex tectonic setting; for these facts, a local geodetic network consisting of 11 geodetic benchmarks has been established. The crustal deformation data in this area are collected using the GPS techniques. Five campaigns of GPS measurements have been collected, processed, and adjusted to get the more accurate positions of the GPS stations. The horizontal velocity vectors, the dilatational, the maximum shear strains, and the principal strain rates were estimated. The horizontal velocity varies in average between 3 and 6 mm per year across the network. The results of the deformation analysis indicate a significant contraction and extension across the southern central part of the study area which is characterized by high seismic activity represented by the clustering shape of the microearthquakes that trending ENE. The north and northeastern parts are characterized by small strain rates. This study is an attempt to provide valuable information about the present state of the crustal deformation and its relationship to seismic activity and tectonic setting at the Abu-Dabbab area. The present study is the first work demonstrating crustal deformation monitoring at the Abu-Dabbab area. The time interval is relatively short. Actually, these results are preliminary results. So, the continuity of GPS measurements is needed for providing more information about the recent crustal deformation in that area.

Seismicity and kinematic evolution of middle Egypt

Abstract Based on historical and instrumental seismicity as well as recent GPS measurements, the seismicity and kinematic evaluation of middle Egypt is presented. Middle Egypt suffered in historical times by six major earthquakes and the Ramses II temple on the west bank of the Nile in Luxor, was almost destroyed by an ancient event. The temporal distribution of recent earthquakes (1900–1997) is highly scattered with only nine events recorded. Only after the installation of the modern Egyptian national seismograph network (ENSN) the seismic record of middle Egypt increased with a total of 280 earthquakes from 1998 to 2004. Focal mechanism solutions of the largest five events during the ENSN's operation period reveal reverse faulting mechanism with minor strike-slip component on the west bank of the Nile, while a normal faulting mechanism dominate in the eastern side. The orientations of both P- and T-axes are consistent with the Red Sea-Gulf of Suez stress field. Dynamic source parameters of these five events were derived from P-wave spectra as well. Three campaigns of GPS measurements were carried out for the middle Egypt network that established after the first instrumental earthquake on 14 December 1998 in this area. The velocity vectors for each epoch of observations were calculated and deformation analysis was performed. The horizontal velocity varies between 1 and 4 mm/year across the network. The deformation pattern suggests significant contraction across the southeastern sector of the study area while, the northwestern part is characterized by an extension strain rates. High shear strain is observed along the epicenteral area of the Mw = 4.0 June 2003 earthquake possibly reflecting the stress accumulation stage of a seismic cycle.

Kinematic model of the South Icelandic tectonic system

SUMMARY Due to the hot spot‐ridge interaction the tectonical situation in the southern part of Iceland is quite complex. Within this investigation it is shown that the Western Volcanic Zone is, in spite of missing recent volcanic activity, still an active spreading zone. Its annual widening of 8.1 ± 1.0 mm yr −1 represents more than 45 per cent of the spreading of the southern part of Iceland. The full spreading rate of the investigated region amounted to 17.1 ± 3.0 mm yr −1 . These are the results of a constrained linear multiepoch deformation analysis of six GPS measurement campaigns, which have been carried out between 1986 and 1999 in the southwest of Iceland. The presented solution combines the motion information of 79 stations to yield a linear velocity field, which is a snapshot of the medium-term motion. The used GPS measurement campaigns had changing network geometries with a lack of point identities.

Are post-seismic effects of theM= 8.4 Bolnay earthquake (1905 July 23) still influencing GPS velocities in the Mongolia-Baikal area?

SUMMARY GPS measurement campaigns in the Mongolia‐Baikal area show that: (1) the Baikal rift zone is currently opening at 4‐5 mm yr −1 in a NW‐SE direction and (2) the western part of the Amurian‐north China block is moving eastward relative to Eurasia at 5‐7 mm yr −1 . These results are consistent with recent geodetic studies in Asia, and indicate that crustal motions in Mongolia and north China derived from geodetic measurements are significantly faster than those proposed by most deformation models of Asia. Using a numerical model, we test whether post-seismic deformation caused by viscoelastic relaxation in the lower crust following the Tsetserleg‐Bolnay earthquake sequence (Mw = 7.9 and 8.4, 1905 July) can explain this discrepancy. We find that surface velocities at the GPS sites presented here for the 1997‐ 2000 time period can reach 4 mm yr −1 , depending on the earthquake source parameters and the rheology used in the models. Using a model based on our best current knowledge of lithospheric structure and rheology in the Mongolia‐Baikal area, we find that the contribution of post-seismic effects to the GPS velocities presented here is less than 2 mm yr −1 for the Mongolian sites and less than 1 mm yr −1 for the Baikal sites. We therefore conclude that the post-seismic effects of the Mw = 8.4, 1905 Bolnay earthquake cannot explain why the GPS-derived crustal motions in Mongolia and the Baikal rift zone are significantly larger than those proposed by deformation models of Asia. This discrepancy must therefore be sought in processes not accounted for in most of these deformation models, such as the farfield contribution of the Pacific subduction zones and/or the effect of gravitational forces on intracontinental deformation.