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Recent Euler pole parameters and relative velocities of the Nubia–Eurasia and Nubia–South America plates estimated using GPS technique

Allal Saddam Housseyn, Eladj Said, Dekkiche Hicham, Hasni Kamel, Betchim Younes Ahmed

Acta Geophysica

2023

Vol. 71, no. 3

1149--1171

The convergence of the Nubian plate toward Eurasia and the spreading rate between the Nubian and South American plates are currently subjects of scientific debates. In this paper, we improve the estimation of Euler pole parameters and the recent relative velocities of the Nubian plate using Global Positioning System (GPS) velocities. These estimates are based on mathematical models and statistical tests for plate tectonic motion represented on a spherical surface. First, we derive the angular velocity and the precise coordinates of the Euler pole to describe the Nubian plate absolute motion expressed in the ITRF2014 geodetic system. This derivation is obtained by inverting the horizontal velocities of 202 GPS stations well distributed across the Nubian plate. Then, we use the same data to obtain the current relative velocities and parameters of the Euler pole characterizing the Nubia–Eurasia and Nubia–South America relative plate motion. A number of 21 and 29 GPS stations located on tectonically stable domains are used to fix the Eurasian and the South American plates, respectively. The results show Nubia–Eurasia relative velocities ranging from 1 to 7 mm/yr, with a direction of NW to WNW for the northern Nubian plate. The velocity in the southern part of this plate reveals a NNE to N direction. The inversion of these velocities allows the determination of the Euler pole parameters: the coordinates [formula] and the angular velocity [formula]. On the other hand, the estimated relative velocity of Nubia–South America is varying in the range of 15–30 mm/yr, with a NE to ENE direction and rotating around the pole [formula] with an angular velocity [formula]. The obtained research results demonstrate an improved precision compared to the existing studies. Furthermore, the use of the Algerian GPS velocities played a key role in the enhancement of the estimates’ precision, which allows us to better understand and monitor the crustal deformations at the limit of the plates.

Evaluation of the displacements of the permanent GPS stations of Beni Haroun Dam geodetic network (Algeria)

Khelifa Sofane, Dekkiche Hicham, Kahlouche Salem, Boudina Samia

Acta Geophysica

2021

Vol. 69, no. 6

2129--2143

The purpose of this paper is the analysis of the daily coordinate time series of the five permanent GPS (Global Positioning System) stations of the geodetic monitoring network of the Beni-Haroun Dam (Algeria), in order to assess the spectral content of the dam displacements. The coordinate time series analysis was based on the singular spectrum analysis to assess their principal components (trend, seasonal components and noise in phase space), the spectral analysis to identify their noise spectrum (white or colored) and the wavelet thresholding method to determine their noise in frequency space. The results showed that the primary signal present in the analyzed time series is mainly composed of a trend and an annual component. The trend and the annual signal explain more than 95% of the total signal in the three coordinates (x, y, z) for all studied stations. The analyzed time series in the three coordinates (x, y, z) are characterized by a linear drift less than 1 mm/year, their annual amplitudes are in the range of 0.5–2 mm, and the amplitudes of their semiannual, four-monthly and quarterly signals are in the range of 0–0.5 mm. The noise spectrum in the analyzed time series is flicker noise, and the noise level is in the range of 0.2–0.7 mm, 0.3–0.5 mm and 0.5–1.2 mm in, respectively, x-, y- and z-coordinates. The low values of trend and noise level in the analyzed station coordinates indicate that the Beni-Haroun Dam is qualified as stable.