Transform margins mark slip-sliding plates, such as California's San Andreas fault. The San Andreas fault marks the location where the North America and Pacific plates grind past each other in a horizontal motion. The many tectonic plates shift and interact all the time. Earthquakes, volcanoes and mountains are the result of this process. Nothing can prevent the next major California earthquake from happening.
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Create an earthquake safety plan for you and your loved ones. CEA offers premium discounts for houses and mobilehomes that have been retrofitted. Find about the potential geologic threats to your home in case of a major earthquake. The violent shaking from earthquakes can:.
However, if very small plates are created preferentially at transform faults, then, this discovery becomes more difficult because most transform faults are in oceanic areas and so are less capable of being explored in the detail necessary to find these small plates. In their paper, Bird and Rosenstock emphasize that much detailed field work was necessary to map the faults separating the plates in their model.
Alternatively, there has to be a major investment in GPS stations Meade and Hager to accomplish this task. Maybe very detailed swath mapping and deep towed magnetic field analysis of relevant oceanic areas would be capable of detecting such faults in the deep ocean Harrison ; Tivey et al. On the other hand, it may be that oceanic crust and mantle is much less capable of forming microplates, in which case, attention will have to be given to those places where there are continental transform faults.
One such fault is the Motagua fault, the boundary between the North America and the Caribbean plates that runs through Guatemala.
There is a portion of the boundary between the South America plate and the Scotia plate that runs through the southern end of South America. There are some complex transform faults in SE Asia that could yield information, as well as the Alpine fault in the south island of New Zealand. Stock and Lee have suggested that oceanic plates as they approach ocean-continent subduction zones may sometimes break off microplates. They use as an example the subdivision of the Farallon plate, which is now represented by the Nazca, Cocos, Rivera, Gorda, Juan de Fuca, and Explorer plates.
The Farallon plate is pretty big compared with most of the plates talked about in this paper. Anderson has suggested that the number of plates to be expected could be done by consideration of the ability of plates or bubbles to cover a sphere which he thinks is about Bird has suggested that the seven largest plates have a different arrangement of size as a function of plate number, as can be seen in Fig.
But there does not seem to be any significant break at around the 12th largest plate in any of these figures. The use of space-based geodetic techniques offers up the opportunity of obtaining results not available by using the normal geological and seismological techniques, partly because of the different time constant of the measurements and partly because of different plate coverage.
If this were to happen, then, it should be possible to determine not only present-day rotation vectors but also vector rates-of-change, as has been done already for specific plates Norabuena et al. It would also help in resolving the discrepancies between the two different interpretations of the southern California shear zone Bird and Rosenstock ; Meade and Hager Sizes of plates currently known or proposed vary by a factor of more than 3. They can be divided up into four groups by examination of how the size changes as a function of plate number if the plates are arranged in order of size.
The seven largest plates show a large decrease in plate size from one plate to the next and comprise The next set of 73 plates added to the first number is The third group of 32 plates increases the total to Each break in slope may represent a different underlying cause.
If there were no change in the slope between the seven largest plates and the rest, then, we would be limited to only four more plates before the whole Earth would be covered, but they would have to have very odd shapes.
It should be noted that none of the 31 plates in Hammond et al. At present, they do not greatly impact the agreement between this paper and the results of Koehn et al. One break in slope equivalent to the break between the group of second-largest plates and third-largest plates was identified by Bird as suggesting that more plates were present than the 52 that he had in his catalogue.
Although we have found more plates in the literature, the change in slope is still there. Of these plates, 79 are smaller than the nick point.
This may represent the change from plates that are more permanent from the ones produced during breakup aligned with the major plate boundaries along the lines suggested by Koehn et al. The final change in slope may represent the result of missing plates due to a lack of detailed study.
This could be solved either geologically or by dense space-based geodetic networks. In oceanic areas, it may be much more difficult but attempts could be made by near-bottom observation of topography Spiess et al. There does not seem to be strong evidence that smaller plates are formed preferentially at different types of plate boundaries.
But there is still a possibility that there could be such an effect, which could be more easily determined if we had studies such as those done in the Southern California Shear Zone performed elsewhere. Will small plates be mostly associated with continental transform faults, or with continental AND oceanic transform faults, or some other type of plate boundary, or will they be equally likely to be found on all types of plate boundary?
Will other studies reveal a power law relationship between plate size and number of plates larger than this size, and what is the power law slope? What are the forces that produce small plates, and do they vary according to the original tectonic setting? Article Google Scholar. Anderson DL How many plates? Geology — Geoophys J Int — Bevis M, Cambareri G Computing the area of a spherical polygon of arbitrary shape. Math Geol — Bird P An updated digital model of plate boundaries.
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Download references. Blackett, who got me interested in paleomagnetism and continental drift which led me to plate tectonics. You can also search for this author in PubMed Google Scholar. Correspondence to Christopher G.
Tables S1—S Table S1. Matrix of plates and models. Table S2. List of 23 plates added to the Bird catalogue. Table S3. Table S4. Thirty-one plates from Hammond et al. Table S5.
Plates from Reilinger et al. Table S6. Eleven small plates from Thatcher Table S7. Five plates from Meade and Hager Table S8. Five plates from Wallace et al. The mechanism by which plates move is still a highly controversial subject amongst Earth scientists.
The Geological Society Plate Tectonics. Pioneers of plate tectonics What is a plate? Plate margins Plate tectonics of the UK. Whether that new divide counts as a boundary or not, the Pacific Plate is still the largest of all tectonic plates. It measures 39,, square miles ,, square kilometers in size, and lies hidden beneath the ocean.
There are also many smaller plates throughout the world. While the Earth is estimated to be 4. That means the oldest seafloor is still only about million years old. The oldest ocean rocks are found in the northwestern Pacific Ocean and the eastern Mediterranean Sea.
Fragments of continental crust are much older, with large chunks at least 3. With clues left behind in rocks and fossils, geoscientists can reconstruct the past history of Earth's continents. Most scientists think modern plate tectonics took over from earlier planetary development about 3 billion years ago , based on ancient magmas and minerals preserved in rocks from that period.
However, researchers have found evidence that plate tectonics could have been active for as long as 4 billion years, according to a article in Discover Magazine.
As the continents jostle around the Earth, they occasionally come together to form giant supercontinents or a single landmass. One of the earliest big supercontinents, called Rodinia, assembled about 1 billion years ago. Its breakup is linked to a global glaciation called Snowball Earth. A more recent supercontinent called Pangaea formed about million years ago.
Africa, South America, North America and Europe nestled closely together, leaving a characteristic pattern of fossils and rocks for geologists to decipher once Pangaea broke apart.
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