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本科毕业设计（论文）

外文翻译

REGAT: A permanent GPS

network in Algeria,

configuration and first results

Author：Abdel Karim Yelles-Chaouche,Kamel Lammali,Amar Bellik,Amina Bougrine,Abdel Hakim Mahsas,Wahab Bacha,Toufik Terki,Othmane Meliani,

Fares Ouzzani,Yacine Lakehal,Ahcene Ait Amir,Kamel Khellaf,Sid Ahmed Khentar,Abdelkader Chouiref,Abdelhamid Bendekan,Eric Calais

Nationality：Algeria,France

Source：Heliyon 5 (2019) e01435.

Abstract

The REGAT (“REseau Geacute;odeacute;sique de lrsquo;ATlas”) geodetic network is composed of 53 continuously–recording GPS stations distributed in the Algerian Atlas. It spans the whole width of the Algerian coast and reaches 300 km inland, with inter-sites distance of about 100 km. One additional site is located in Tamanrasset in the southernmost part of the country. The network, whose oldest stations started operating in 2007, encompasses the main active tectonic features of the most seismically active segment of the Nubia-Eurasia plate boundary in the Western Mediterranean. Here we describe the network configuration, the data collection and analysis strategy, as well as some preliminary results on horizontal GPS velocities. A detailed analysis of the velocity field in terms of plate boundary kinematics is the topic of a separate publication. The REGAT network fills an important gap in our knowledge of present-day plate boundary deformation in the Western Mediterranean. It will soon be enhanced by an additional 100 sites in order to improve deformation monitoring with a higher spatial resolution for a better assessment of the regional seismic hazard.

Keywords: Atmospheric science, Geology, Geophysics, Geoscience, Natural hazards

1. Introduction

The past decade has seen a rapid growth in the number of continuously–recording Global Positioning System (GPS) sites around the globe for applications to mapping and navigation, reference frame determination,and deformation monitoring for geodynamics.The distribution of continuous GPS (cGPS) stations remains however uneven amongst countries and continents. Africa, except for a few countries such as South Africa (Figure 2), remains poorly covered in spite of international efforts such as the “AFrican REference Frame” (AFREF) sub-commission of the International Association of Geodesy (e.g., Saria et al., 2013). As a result, the determination of the present-day kinematics of the Nubian plate and of its internal deformation still need

significant improvement. In addition, the paucity of cGPS measurements in northern Africa is still preventing us to accurately resolve the present day kinematics of plate boundary deformation in the Mediterranean where three major tectonic plates – Nubia, Eurasia and Arabia – interact (Nocquet and Calais, 2004; Serpelloni et al.,2007; Nocquet, 2012).

In this paper, we present efforts performed in Algeria over the past decade to increase GPS monitoring in the northern, most tectonically active, part of the country thanks to a 54–site network of continuously–recording GPS stations, the REGAT (“REseau Geacute;odeacute;sique de lrsquo;ATlas”) geodetic network. This network fills a hole in the description of kinematics of the Nubia – Eurasia plate boundary in the Mediterrean

and complements existing networks elsewhere in the Mediterranean, for instance RING in Italy (Avallone et al., 2010) and NOANET in Greece (Chousianitis et al., 2015). Along the Algerin segment of the plate boundary, kinematic models all show a counter-clockwise rotation of Nubia with respect to Eurasia, resulting in a NW-SE convergence oblique to the direction of the plate boundary, with a rate increasing from 2–4 mm/yr in Gibraltar to 3–8 mm/yr in the Sicily Strait (Nocquet, 2012). REGAT will help understand how this motion is partitioned on the various

active tectonic structures in Algeria, on land and offshore (e.g. Domzig et al., 2006; Meghraoui and Pondrelli, 2012).

2. Background

2.1. Motivation for the REGAT network

The country of Algeria occupies a wide segment of the Nubia-Eurasia plate

boundary (Figure 1) along which the oblique convergence between the two plates is accommodated by active faults and folds in the Algerian Atlas (e.g., Meghraoui and Pondrelli, 2012) and offshore (e.g., Yelles et al., 2009), both accompanied by significant seismicity (e.g., Yelles-Chaouche et al., 2017). The 1980 El Asnam

Figure 1. Active tectonic setting of the Western Mediterranean. White circles show earthquakes with magnitude greater than 4.5 (NEIC database, earthquakes.usgs.gov). Black arrows at the bottom of the figure show model velocities for the Nubia plate with respect to Eurasia Calais et al. (2003). Red arrows are selected GPS velocities from a regional compilation by Nocquet (2012).

earthquake (Ouyed et al., 1981) triggered the first geodetic measurements for tectonic purposes in Algeria. Ruegg et al. (1982) quantified the associated co–seismic vertical displacement using terrestrial geodetic techniques. Soon after, the Algerian institution in charge of seismic hazard determination, the Centre de Recherche en Astronomie, Astrophysique et Geacute;ophysique (CRAAG) densified the initial network

and regularly remeasured it from 1986 to 1994 in order to monitor post-seismic deformation (Dimitrov et al., 1987; Bezzeghoud et al., 1995; Lammali et al., 1997).

The first GPS network for crustal deformation monitoring was installed and measured by the CRAAG around the Thenia fault in the Boumerdes–Zemmouri area in 2002. GPS data were collected during two c

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