Three-dimensional Crustal Deformation Research Articles

Kilometer-resolution three-dimensional crustal deformation of Tibetan Plateau from InSAR and GNSS

Kilometer-resolution three-dimensional crustal deformation of Tibetan Plateau from InSAR and GNSS

Geodetic constraints on contemporary three-dimensional crustal deformation in the Laji Shan–Jishi Shan tectonic belt

The Laji Shan–Jishi Shan tectonic belt (LJTB), located in the southern part of the northeastern Tibetan Plateau (NETP), is a tectonic window to reveal regional tectonic deformation in the NETP. However, its kinematics in the Holocene remains controversial. We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations. Combined with fault kinematics from geologic observations, we analyze the crustal deformation characteristics along the LJTB. The results show that: (1) The Laji Shan fault (LJF) is inactive, and the northwest-oriented Jishi Shan fault (JSF) exhibits a significant dextral and thrust slip. (2) The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault. (3) With the continuous pushing of the Indian plate, internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

Metamorphic CO2 production in calc-silicate rocks from the eastern Himalaya

The Tibetan Plateau is one of the most geologically dynamic systems and the highest plateau in the world with ongoing three-dimensional crustal deformation. The Plateau is uplifting and deforming horizontally as observed by present-day global navigation satellite system (GNSS) and repeated leveling measurements. Crustal mass is conservative and less dense than the mantle, thus the horizontal shortening must be accompanied by crustal thickening and horizontal extrusion. According to the level of isostatic compensation, the thickening is partitioned into topographic uplift and Moho deepening. Here, we investigate the mass change induced gravity signal observed at or near the crust, and discuss whether this signal could be detected using terrestrial or satellite gravity observations. We set up a model for the Tibetan Plateau crustal thickening and calculate the expected gravity signal. The predictions are then compared with the present-day gravity changes observed by GRACE and with published in situ absolute gravity rates. We conclude that the crustal thickening signal cannot be neglected and that it contributes significantly to the observed signal. Those studies with focus on the mountain glacier and hydrologic mass fluxes should be aware that, if neglected, the crustal signal could introduce a significant bias. The observations give a positive gravity rate over central Tibetan Plateau, unexplained by the hydrologic or cryospheric signals, and a negative rate over the Himalayas and at its foothill, which is attributable to terrestrial hydrologic signals including human depletion of groundwater. Our model shows that the positive gravity rate could be explained by elevation uplift, and a stable or upwelling Moho. The negative gravity change signal is due primarily to the strong elevation-gradient at the foothill of the Himalayas, and to an uplift accompanied by crustal thickening and Moho lowering. The estimated gravity rates can be used when defining the requirements on future gravity missions, as the tectonic signal should be resolved in order to improve its separation from hydrologic and/or cryospheric processes generating a gravity change.

Three-dimensional crustal deformation before and after the Wenchuan earthquake in Guanzhong and adjacent regions

The recent plethora of GPS observations compensates for the 20-year-old lack in vertical displacement data for the Guanzhong region. The 2001–2007 three-dimensional (3D) crustal deformation data suggest regional movement with a horizontal velocity of 3–7mm/a, predominantly from SSE in the west to SE in the east, and vertical inherited movement with velocity of −7mm/a to 4mm/a. After the Wenchuan earthquake, the GPS data suggest that the effect of the earthquake on the regional deformation is greater in the west than the east. The horizontal displacement increased during 2007–2008; however, the reverse was observed in 2008–2009. The vertical displacement in the western part of the region increased in 2008 and has been gradually returning to normal since 2009; however, in the eastern part, the effect of the earthquake remains.

Present three-dimensional crustal deformation in Hainan Island

Abstract: Hainan Island, located at the southeast edge of the Eurasian Plate, is affected by the motion of multiple plates, with its northeast edge mainly dilatating and its western margin presently compressing. By analyzing the GPS rates during 1999 – 2007 in Hainan and its adjacent region, we determined horizontal movement rates of 3. 0–21. 1 mm/a at the west of 104°E, evidently affected by the Indian Plate extrusion. Their directions are SE-SN-SW from east to west and are separated by the main fault. The principal strains have the same characteristics. The stations east of 104°E move mainly in the SEE direction. The eastward rates are 2. 1–8. 5 mm/a and northward rates are 0. 4–2. 7 mm/a. The GPS rates during 2009–2013 show that stations at the edge of the island move SEE relative to the Eurasian Plate, with rates relative to the mean benchmark, indicating that there are small relative movements between stations, whereas QION station, located in the middle, moves in the NW direction at a greater rate. Vertical differential movement is apparent in the northeast zone of the island. Upwelling of mantle plume material possibly influences the local stress. Three-dimensional GPS rates indicate that, at present, inherited crustal movement is dominant in Hainan.

Upper mantle viscosity from continuous GPS baselines in Fennoscandia

Abstract The permanently recording BIFROST (Baseline Inferences for Fennoscandian Rebound Observations, Sea Level and Tectonics) GPS network was set into operation during the early to mid-1990s to monitor the three-dimensional crustal deformation field in Fennoscandia. We have employed 2500 days of BIFROST GPS data to estimate rates of baseline component change (length, transverse and up). Baselines are less sensitive than single-site position estimates to perturbations in satellite orbits and reference frame realizations. Hence, the baseline time series represent a particularly robust data set for model parameter estimation. We use this data set to outline an evaluation scheme for GPS observations of intraplate horizontal movements. Our results show that the data can be used to infer parameters in a model that simulates the glacial isostatic adjustment (GIA) of the region. This process is widely believed to dominate the present-day deformation field, and analysis of the length and transverse components support this view. The data prefer an elastic lithosphere of thickness 120 km and an upper mantle viscosity in the range ( 3 – 10 ) × 1 0 20 Pa s (to 95% confidence). These results are consistent with those obtained in a previous analysis that considered single-site position estimates. This suggests that the problems associated with perturbations in satellite orbits and reference frame realizations have not significantly impacted the analysis of single-site positions from the BIFROST time series. Subtracting the best-fitting GIA model predictions from the observed baseline rates leaves a horizontal residual field of magnitude less than 1 mm year−1.

Space-geodetic constraints on glacial isostatic adjustment in Fennoscandia.

Analysis of Global Positioning System (GPS) data demonstrates that ongoing three-dimensional crustal deformation in Fennoscandia is dominated by glacial isostatic adjustment. Our comparison of these GPS observations with numerical predictions yields an Earth model that satisfies independent geologic constraints and bounds both the average viscosity in the upper mantle (5 x 10(20) to 1 x 10(21) pascal seconds) and the elastic thickness of the lithosphere (90 to 170 kilometers). We combined GPS-derived radial motions with Fennoscandian tide gauge records to estimate a regional sea surface rise of 2.1 +/- 0.3 mm/year. Furthermore, ongoing horizontal tectonic motions greater than approximately 1 mm/year are ruled out on the basis of the GPS-derived three-dimensional crustal velocity field.