Determining The Velocities Of The GPS Stations On The African Plate

The development of Global Positioning System have made it possible to obtain a three-dimensional position information accurate to centimeter level with a proper receiver.Thus,GPS applications are now being used in more and more domains,which includes determining the motion of the Earth's tectonic plates.The plate movement can be measured by analyzing the position change and velocities of the GPS stations on this plate.And with the increasing number of observations,improvement of accuracy in satellite based geodetic measurements,data processing software and reference system,the coordinates and velocities of GPS stations can be estimated with a very high accuracy.This thesis chooses African plate,which includes Nubia plate and Somali plate,as the study area,data from 152 stations on and near Africa plate from year 2000 to 2009 are collected.Data processing are performed using Bernese GNSS Software,and then the daily results are combined.After checking the residuals of data processing,49 stations on Africa plate with a time span from 2000 to 2006 are decided to be used for further data analysis.Euler vector and strain rate are thus calculated to indicate the plate motion.The results show a consistent velocity field on African plate,almost every station has a velocity towards northeast direction,with a magnitude of around 20 mm/yr.The Euler vector obtained for African plate is 0.3064±0.0648 deg/Myr,with a latitude of 52.30°N and longitude-84.41 °E,for Nubia plate is 0.2901 ±0.0671 deg/Myr with latitude 52.39°N and longitude-81.96°E,and for Somali plate is 0.3310±0.0959 deg/Myr with latitude 51.54°N and longitude-83.95°E.These results are generally consistent with the published studies.The initial strain rate between stations on Africa plate vary from the order of minus one nanostrain/yr to the order of ten nanostrain/yr,but mostly the strain rate between stations are few nanostrain/yr,which can be indicated as rigid.