Study On Datum Of Modern Crustal Motion

Due to the confusion of the crustal motion reference datum, for the same plate or crustaldeformation region, the speed and direction of motion or deformation given by differentdocuments are often very different, whose order of magnitude of the difference are much largerthan the measurement error, so an exhaustive study about modern crustal motion reference datumand sorting out the confusion in the use of crustal motion reference datum not only are in urgentneed of geodetic development of the subject, but also are of great significance to promote thedevelopment of related subjects such as earthquakes, geology and geophysics. By using acombination of crustal motion measured data of the newest space observation technology,hotspot data, postglacial crustal rebound model data and other relevant research, this papermakes an exhaustive study of crustal motion reference datum, exploring and putting forward aset of modern crustal motion reference datum which has a clear geophysical significance and iseasy to implement and apply and whose content covers the refinement of global horizontalcrustal motion reference datum, the establishment of vertical crustal motion reference datum anddiscussion on regional crustal motion and so on. The main conclusions and innovation are as thefollowings:1. Summing up the definitions, the present development situations and the existing problemsof modern crustal motion, reference datum, and modern crustal motion reference datumrespectively. This paper elaborates the concepts and relations among reference system, referenceframe and the reference datum, gives the development of International Terrestrial ReferenceFrame (ITRF) series, and introduces the newest ITRF2008frameworks. It points out theproblems existing in the research of modern crustal motion reference datum, including thepresent research situation and existing problems of horizontal datum, vertical datum and theregional datum respectively, and puts forward the importance and necessity to establish theglobal uniform crustal motion datum.2. Using space observation data to build a global plate motion model ITRF2005VEL andITRF2008VEL. Plate motion model is the first step in establishing horizontal crustal motionreference datum. This paper summarizes the plate motion model systematically, includinggeological and geophysical method and space geodetic method, and makes use of the latestITRF2005and ITRF2008data to establish the model of ITRF2005VEL and ITRF2008VELrespectively. Overall the two models and the scale of millions years of geographical modelNNR-NUVEL1A have a better consistency and the two models have a higher model accuracythan the previous ITRF sequences, which are inseparable with the more reasonable distributionof the base stations, and the higher station coordinates and velocity field solver accuracy in the two reference frames. But there exist some differences between them and NNR-NUVEL1A,which is related to the less and the uneven distribution of the corresponding plate’s stations or theinsufficient constraints to plate because of the shortage of observation time. Finally it discussesthe size of the total angular momentum of the tectonic plates, and the result shows that the totalangular momentum of the13plates are not zero, indicating that ITRF2005and ITRF2008framework may not meet the requirements of no-net-rotation, or may be due to the differentchoice of stations that make the plate’s angular momentum be not zero. In fact, the ITRFWorking Group on this question also has no consistent opinions.3. Establishing and refining the global horizontal crustal motion reference datum, puttingforward the method of building the Medial-HotSpot (MHS) Reference Datum and itsconstraining criterion. The horizontal crustal motion reference datum includes two methods, eg.No-net-rotation (NNR) reference datum and Hot-spot (HS) reference datum. Using the latestspace observation data of ITRF2005and ITRF2008, NNR-ITRF2005and NNR-ITRF2008model were established and refined based on the ITRF framework. According to the present platemotion status and relative motions of hotspots, the constraint criterion for MHS ReferenceDatum is put forward, and by using the criterion to constrain the hotspot’s data to achieve theestablishment of the datum, that is, with the geological model NNR-NUVEL1A and geodeticmodel ITRF2005VEL as the foundation, this paper establishes the absolute plate motion modelMHS-NUVEL1A and MHS-ITRF2005VEL based on the Medial-Hotspot reference frame, andcompares and analyzes with other absolute plate motion model based on hotspots.4. Discussing the overall rotation of the lithosphere, and providing a more accuratequantitative estimation about lithosphere’s overall rotation (drift) relative to the lower mantle.The result shows that the overall rotation of the lithosphere based on the reference datum of thehotspots and the overall rotation of the lithosphere calculated by geophysicists based onlithosphere plate force model are basically the same in magnitude and direction, which showsthat MHS Reference Datum may be more consistent with the actual situation. Reference datumbased on the hotspots can be more truly to reflect the actual situation of mantle convection, andthe Geophysicists that study the mantle convection and the motion of the plates prefer to use HSreference datum, but geodetic scientists tend to use NNR reference datum.5. Putting forward and establishing the optimal global vertical crust motion reference datum.This paper discusses the main factors that affect the global vertical motion detailed, includingpost-glacial rebound, ground subsidence, and various tidal changes and so on. After discussingthe necessity of studying vertical datum, this paper puts forward four kinds of schemes toestablish vertical crust motion reference datum, that is SLR vertical motion datum, ICE-5Gmodel datum, the datum that vertical velocity constraint is zero near the equator and crustal isostatic adjustment datum, and makes the corresponding derivation and validation respectively.Comparing those four kinds of vertical datum, the result shows that for SLR vertical motionreference datum, its geophysical significance is clear, and it’s easy to implement and use, whichis the optimal reference datum of the global vertical crustal motion. So it is recommended thatthe vertical datum achieved by SLR technology under the ITRF2008framework is suitable as areference datum of the global vertical crustal motion.6. Putting forward the method of regional horizontal crustal motion reference datum andregional vertical crustal motion reference datum respectively by using the crustal motion inChina as an example, and using the geodetic data to establish the horizontal crustal deformationmodel in China region. For the horizontal crustal motion of the region, the stable main body ofthe plate which the deformation area is attached to can be the reference datum of studying thehorizontal crustal deformation in this region. For the vertical crustal motion of this region, theregional crustal vertical motion data can be imputed unified to the optimal reference datum of theglobal crustal vertical motion, namely SLR vertical motion reference datum to establish avertical crustal motion velocity field of this area, which is consistent with the global crustalvertical motion datum.7. Discussing and using the geodetic data to detect the change trend of the solid earth, andputting forward to attribute the global vertical motion to the established SLR vertical datum. Thispaper systematically discusses the earth’s unsymmetrical phenomenon, and expounds thedoctrine of the earth’s expansion and compression. After a detailed analysis of the status ofglobal change phenomena research, this paper puts forward to unify the global vertical velocityto the optimal global crustal vertical motion reference datum established by this paper, and thenuses the ITRF2008data to study the Earth’s unsymmetrical change phenomenon. The resultshows that the earth radius’s change rate is similar to (-0.1±0.2)mm/a, which shows that theradius of the earth cannot be considered changed in the range of one time mean error.