This review of Demets 2010 focuses on best-fitting angular velocities and MORVEL, which is an enclosure that sets angular velocities for the geologically current motions of all the 25 tectonic plates, and occupies 97% of the total earth surface. The differences in modern seafloor spreading rates and the old rates are also reviewed. Forty years after the inception of the popular plate tectonic theory, improved satellite coverage has enabled better precision on plate angular velocity. Consequently, it is possible to detect zones of plate deformation, estimating plate motion, and determining limits to the rigid plate approximation. Seafloor spreading rates and fault azimuths are essential in determining the motions of 19 plates, out of the 25 plates, in addition to other major plates (DeMets, Gordon & Argus). Six small plates are not related to the nineteen plates of the earth’s surface. They have no connection to mid-ocean ridges, to which the 19 plates are connected. The six unique plates are linked to MORVEL with GPS Station velocity and azimuthal data.
Naturally, there is no kinematic information exchanged between the geologically determined and the geodetically constrained plates in the global world. Three plate circuits have a vital role in constraining NUVEL-1A and MORVEL angular velocities. MORVEL, for that matter, averages geological motion between all the major plates. The change in plate geometry relative to NUVEL-1A leads to the inclusion of key plates, such as the former African plate that comprises of Nubia, Somalia and Lwande plates. The former Australian plate is also incorporated, and it comprises of The Capricorn, Australia and Macquarie plates. In addition, the geometry change has incorporated the former South America plate, which includes Sur and America plates. MORVEL also includes Amur, Philippine Sea, Sunderland, and Yangtze plates. MORVEL is, therefore, more useful than NUVEL-1A due to its research strengths, especially in gathering geological deformation in both Asia and the Western pacific.
New data reveal significant differences in rates in both the MORVEL and the NUVEL-1A. MORVEL, for example, indicates a slower motion of 0.78-Myr-average across the Nazca-Pacific boundaries, yet NUVEL-1A remains consistent with a slowdown in the eastwards parts of Nazca plate motion since 3.16Ma.Consequently, MORVEL indicates that motions across North America and South America boundaries are twice as fast as provided by NUVEL-1A.
The least square differences of angular velocities obtained from GPS rated with those from NUVEL-1, NUVEL-1A and MORVEL show significant disparities, with up to 50 per cent velocities larger for NUVEL-1A,than for MORVEL ,and 260 per cent velocities for NUVEL-1.The comparison provides resourceful data to support findings that MORVEL accurately describes current plate motions with a clear historical evidence. When using MORVEL, essential differences between plates in the Nazca plate motion including Eurasia and India are reduced. However, they are not eliminated.
MOVEL reveals that since 3.16 Ma, changes have occurred on the plate motions, with a notable negligible difference between use of MOVEL and GPS. The two methods have less than 25 per cent difference in their findings in contrast to huge disparities that arise when NUVEL-1A is used.
Demets 2010 confirms that mid-ocean ridge morphology depends on spreading rate of ridge. The slow mid –ocean segments have great crustal thinning towards transform and non transform offsets; however, fast spreading mid-ocean ridges have smaller crustal thickness. Intermediate and fast slipping transform faults have higher levels of negative gravity anomalies than the adjacent ridge segments.
Works Cited
DeMets, Charles M., Richard G. Gordon, and Donald F. Argus. “Geologically Current Plate Motions.” The Authors (2010): 1-80. Print.