| 1. |
- Pan, M., et al.
(författare)
-
An analysis of the Ethiopian Rift Valley GPS campaigns in 1994 and 1999
- 2002
-
Ingår i: Journal of Geodynamics. - 0264-3707 .- 1879-1670. ; 33:3, s. 333-343
-
Tidskriftsartikel (refereegranskat)abstract
- In cooperation with the Geophysical Observatory, Addis Ababa University, the Department of Geodesy and Photogrammetry of the Royal Institute of Technology carried out GPS measurements at three deformation networks in the Ethiopian Rift Valley in 1994 and 1999. For these campaigns the session-to-session repeatabilities were about 5 and 4 mm in the horizontal components and 50 and 10 mm in the vertical components using the IGS precise orbits, respectively. The results show, that the stations of the E3 network in the Rift Valley moved with a magnitude of 2.5 +/- 1.3 mm/a to the SE, and a magnitude of 21.3 +/- 1.4 mm/a to the ENE in the northeast (close to Assab of the Red Sea) relative to the station Addis Ababa on the African plate. The direction of movement is consistent with the local spreading vector of the Red Sea Rift with the N84degreesE slip direction estimated from seismic data. The sites of the E1 network moved by a rate of about 1-2 mm/a to the SE relative also to the station Addis Ababa. Further to the south there is an indication from our GPS data that the stations on the Somalian plate of the E2 network move by a rate of about 2.5 mm/a to the E or SE relative to the African plate. This motion can also be confirmed by geological and geodynamic data.
|
|
| 2. |
- Pan, M., et al.
(författare)
-
Crustal movements in Skane, Sweden, between 1992 and 1998 as observed by GPS
- 2001
-
Ingår i: Journal of Geodynamics. - 0264-3707 .- 1879-1670. ; 31:3, s. 311-322
-
Tidskriftsartikel (refereegranskat)abstract
- We estimate a network of crustal deformations in Skane, southern Sweden, using observations of the Global Positioning System (GPS) from 1992, 1996 and 1998. The network straddles the Tornquist zone, potentially one of the most active fault zones in Sweden. In addition to two stations of the Swedish permanent GPS network (Onsala and Hassleholm), it includes seven GPS sites spaced approximately 80 km apart. The precisions of the relative horizontal components for these stations are described by repeatabilities with approximately 3 mm in the north-south direction and about 2 mm in the east-west direction in the campaigns in the reference frame ITRF96. About 70% of the GPS integer carrier phase ambiguities were resolved for the three campaigns. Three stations south of the Tornquist zone moved with a rate of 5+/-0.2 mm/a toward the SW-SE, and two other stations further to the east with a rate of 2+/-0.2 mm/a toward the SE, relative to station Onsala. The displacements mean that a lateral strike-slip transtensional fault exists within the Tornquist zone, and the relative motion between the two sides along the zone was about 2 mm/a. The old fault is still active, which is consistent with geological results. The station Stavershult closest to Onsala moved NE with about 1.5+/-0.8 mm/a relative to the station Onsala. This may imply a transtensional fault between Stavershult and Onsala. If we assume that Stavershult represents the Baltic shield, Onsala has moved 1.5 mm/a toward the southwest with respect to the Baltic shield, which was confirmed by data of Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) from 1976 to 1997 (Argus, D.F., Peltier, W.R., Watkins, M.M. Glacial isostatic adjustment observed by Very Long Baseline Interferometry and Satellite Laser Ranging geodesy. JGR 1999;104(B12);29077-93).
|
|
| 3. |
- Sjöberg, Lars Erik, et al.
(författare)
-
Glacial rebound near Vatnajokull, Iceland, studied by GPS campaigns in 1992 and 1996
- 2000
-
Ingår i: Journal of Geodynamics. - 0264-3707 .- 1879-1670. ; 29:2-Jan, s. 63-70
-
Tidskriftsartikel (refereegranskat)abstract
- Since about 1920 the Vatnajokull ice cap in Iceland has experienced a significant retreat, corresponding to a volume reduction of more than 180 km(3). With two GPS campaigns in 1992 and 1996 along the southern border of the glacier preliminary results reveal land uplift rates of 1-6 mm/yr, after a one-parameter (bias) fit with recent earth rheology models. The best fit model suggests that the lithosphere in the area is about 30 km thick and the viscosity of the asthenosphere 5 x 10(18) Pa s. The rms fit of uplift rate at all GPS sites is +/-1.4 mm/yr. As the GPS data alone cannot provide the absolute uplift rates, the one-parameter fit to the theoretical modelling implies that the absolute rates were estimated by the matching of the GPS data and model. The resulting uplift rate at station Hofn (1 mm/yr) is not consistent with two independent sources, and we therefore conclude that further GPS epoch and permanent GPS site data are needed to confirm the present geodynamic processes near Vatnajokull.
|
|
| 4. |
- Sun, W. K., et al.
(författare)
-
Permanent components of the crust, geoid and ocean depth tides
- 2001
-
Ingår i: Journal of Geodynamics. - 0264-3707 .- 1879-1670. ; 31:3, s. 323-339
-
Tidskriftsartikel (refereegranskat)abstract
- The tidal deformation caused by the luni-solar potential includes not only a periodic part, but also a time-independent part, called the permanent tide. How to deal with the tidal correction in gravimetric observations, especially the treatment of the permanent tide, has been discussed for a long time, since some practical and physical problems exist anyhow. A resolution adopted by IAG (1983) was that the permanent tidal attraction of the Moon and the Sun should be eliminated, but the permanent tidal deformation of the Earth be maintained. This is called zero gravity, and the geoid associated with it is the zero geoid. As to the crust deformation, Poutanen et al. (Poutanen, M., Vermeer, M., Makinen, J., 1996. The permanent tide in GPS positioning. Journal of Geodesy 70, 499-504.) suggested that co-ordinates should be reduced to the zero crust, i.e. the crust that includes the effect of the permanent tide. This research shows that horizontal components of the permanent earth tides, which are not considered in recent studies, are also important in GPS positioning and geoid determination. Since the tide-generating potential can be expanded into harmonics and divided into two parts (geodetic coefficients and the group of harmonic waves), the permanent earth tides can be easily obtained by multiplying the amplitude of the zero-frequency wavelength by the corresponding geoid geodetic coefficient. Formulas for both elastic and fluid cases are presented. Numerical results for the elastic case show that he vertical permanent crust (zero crust), geoid and ocean depth tides reach -12.0, -5.8 and 6.1 cm at the poles, and 5.9, 2.9 and -3.0 cm at the equator, respectively. The horizontal permanent crust, geoid and ocean depth tide components reach as much as 2.5, 8.7 and 6.3 cm, respectively. According to the solution of IAG (1983), the permanent vertical components are kept in GPS positioning and geoid computation. Thus, it is natural to include the horizontal components correspondingly.
|
|
| 5. |
- Corti, G, et al.
(författare)
-
Centrifuge models simulating magma emplacement during oblique rifting
- 2001
-
Ingår i: JOURNAL OF GEODYNAMICS. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0264-3707. ; 31:5, s. 557-576
-
Tidskriftsartikel (refereegranskat)abstract
- A series of centrifuge analogue experiments have been performed to model the mechanics of continental oblique extension (in the range of 0 degrees to 60 degrees) in the presence of underplated magma at the base of the continental crust. The experiments re
|
|
| 6. |
- Pan, M, et al.
(författare)
-
Crustal movements in Skane, Sweden, between 1992 and 1998 as observed by GPS
- 2001
-
Ingår i: JOURNAL OF GEODYNAMICS. - 0264-3707. ; 31:3, s. 311-322
-
Tidskriftsartikel (refereegranskat)abstract
- We estimate a network of crustal deformations in Skane, southern Sweden, using observations of the Global Positioning System (GPS) from 1992, 1996 and 1998. The network straddles the Tornquist zone, potentially one of the most active fault zones in Sweden
|
|
