Plate tectonics how many are there

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. Many of the other studies used locations of faults determined by geological methods, as well as earthquake locations and mechanisms, volcanic activity, and also space-based methods such as GPS observations which have become important over the past decade, especially for the relative motions of small plates, and the locations of their plate boundaries.

Modeling will often accompany GPS data and will frequently allow for elastic strain at plate edges. The authors of all of the other analyses Additional file 1 : Tables S3—S8 state that a plate model, meaning no internal deformation and distances and angles are preserved, is the appropriate model for determining results that they obtained. Elastic deformation is naturally occurring at plate edges, and some authors have shown that this gives a reasonable explanation of those GPS stations close to plate boundaries, the implication being that these elastic displacements will change because of earthquakes which happen at plate edges.

There are situations where deformation is occurring across a broad region. For instance, motion across the Rio Grande Rift appears to be spread out over a width of hundreds of kilometers Berglund et al. No plates are permanent but the time span for plates to remain roughly the same must vary, and it is probable that small plates last for shorter times than large plates.

It also does not mean that all plates are caused by the same phenomena. Morra et al. They also found that the largest six to eight plates in the groups of large plates vary in size. This is measured as the standard deviation of the areas in the plates under consideration, and it varies between 0. Large numbers indicate large variations in size heterogeneous tessellation whereas small values indicate more uniform size distribution homogeneous tessellation.

These results show that plates can change radically over the period of a Wilson cycle. However, what we have done in this paper is to look at a single age 0 Ma , while recognizing that information of some of the very small plates described here and elsewhere will probably not be available for older ages.

The variation in area of these plates is by a factor of over ,—from Mm 2 for the Pacific plate to km 2 for plate 5 of Hammond et al. This huge variation calls for a logarithmic axis when plotting area. However, there is no reason why the plate number should not be plotted on a linear axis at this instant. This is what is shown in Fig. The black line is a line through all of the data. There is a distinct nick point at plate number 80 the Danakil plate, which by chance has the median area.

In this diagram, the plates are ordered in size beginning at the smallest plate. Table 1 gives the number of plates in each study that are smaller in area than the nick point. Plot of plate area logarithmic scale versus plate number from smallest to largest. Equations are given for the two straight lines fitting 35 plates on either side of the nick point. The smallest plate 5 from Hammond et al. Analysis of the data below and above the nick point reveal that the slopes of the points below and above are significantly different.

In Fig. This will be discussed in greater detail during a discussion of the data shown in Fig. Reduced area plotted against plate number smallest to largest for plates numbered from 46 to The reduction emphasizes the statistically significant difference in slope between the smaller data set plates from 46 to 80 in contrast to the larger plates plates from 81 to This suggests that the nick point seen in Fig.

The data for this figure were obtained from some of the data shown in Fig. Z values are the transformed correlation coefficients Fisher , and the Sigma Z values are the standard errors which depend only on the number of data pairs of the Z values. The multiplication factor for X is a slope which is halfway between the slopes of the lines above and below the nick point in Fig.

This results in lines that have positive and negative slopes that are about equally different from zero. The slopes are completely different. I have analyzed the distribution of plate sizes of the plates to compare it with a law proposed by Koehn et al.

They proposed that the number of plates N above a certain size as measured by a linear scale, L km, follows a power law, as follows.

Figure 3 shows the plot of the number of plates larger than a certain value of L km. Being on a log-log scale, this shows the division of plates into those large plates seven of them, in blue falling on a steeply inclined power law curve. This type of plot is the same as the one used by Bird Bird suggested that the sizes of these largest plates were governed in some way by the finite size of the Earth. The equation governing the distribution of these seven largest plates is given by the following equation and is shown by the straight red line at the bottom right of Fig.

Log-log plot of plate number largest to smallest against characteristic plate length square root of area, in km. I have made the assumption that the smaller plates starting at plate 81 are caused by a different process than the larger plates, and the lower graph assumes that these plates are renumbered starting from 1. Straight line fits are given in colored lines with equations in the appropriate colors.

Red is for the seven largest plates. Blue is for the next group of 73 plates. Green is for the smallest group of 79 plates. These 79 plates are renumbered from 1 to The largest 32 of these plates is fit by a straight light blue line.

The light orange equation and line is from the results of Koehn et al. The data are shown by the thin black lines , and for the renumbered set, the individual data are shown by black dots joined by a thin black line. This has a much larger negative slope than do the model studies discussed by Koehn et al. The characteristic length of these seven largest plates varies from to km, i. The large middle section omitting the 75 smallest plates and the seven largest plates has a very good straight line approximation which translates into an equation as follows.

This has a much smaller negative slope the same thing as the fractal dimension than the curve proposed by Koehn et al. It is shown as a straight blue line following the black line joining the points. If the seven largest plates had fallen on this line rather than the steeper line shown in Fig.

This middle section goes from plate 8 to plate These plates have characteristic lengths between km plate 8 and km plate If the largest plates had followed the same power law as to middle section, then plate 7 would have an area equal to 4. The sizes of these largest plates must be controlled by the sizes of the convection currents in the asthenosphere. The third straight line for the smallest plates has a fractal dimension of 0. This line is shown as the green line following the black line connecting the points.

Turcotte has studied fragmentation in three-dimensional situations and comes up with a fractal dimension of about 2. In order to investigate further the arrangement of plate sizes, I supposed that the hypothesis of Koehn et al. I therefore renumbered the 79 smallest plates, those smaller than the nick point in Fig.

This is the black line with individual results as black dots in the lower left side of the figure. Since there is so much curvature in this line, I separated it into two segments, the one with the larger plates has 32 plates, and one having the remainder of the plates has 47 plates. The sizes of the 32 larger plates are well described by a line with an equation given below. This is shown by the straight light blue line that follows the first 32 points.

The plates analyzed for this section were chosen so that the correlation coefficient between the logarithm of plate size abscissa and the logarithm of plate number ordinate , starting at new plate 1, was maximized. In other words, if the total number of plates analyzed was either greater or less than 32, the correlation coefficient was smaller than the number given in Fig. This line is close in fractal dimension to the model results of Koehn et al.

The Koehn et al. The characteristic length of these 32 plates varies from The intercept will change as the number of plates within this size range increases, so it is somewhat of a coincidence that the intercept here is similar to that of Koehn, but the agreement in slope could indicate that the plates in this group are formed by similar forces that formed the experimental results of Koehn et al. The simulations done by Koehn et al. The larger plates need not be considered in this analysis because if they are formed by different causes, then, it is legitimate to consider only those plates that may be formed by the specific forces, whatever they are, producing the very small plates.

The change in slope illustrated by the bottom curve in Fig. Discovery of additional plates with areas between plate 1 and plate 32 on the lower graph in Fig. The conclusion is that the size distribution of this group of plates is very close to the modeling and observational results of Turcotte and Koehn et al.

Analysis of plate size if the blocks from Bird and Rosenstock are substituted by the blocks from Meade and Hager gives similar results although with a somewhat less clear picture than is given in Fig. There is still a kink in the slope of the upper curve between the 79 smallest plates and the larger plates. And replotting the renumbered smaller plates gives a similar slope for the larger group of this smallest set of blocks.

It seems likely that this mode of plate formation may be found when the characteristic length of the plates becomes close to the thickness of the lithosphere. So after the addition of the plates described above, we end up with four sets of plate sizes. The 47 smallest plates have a distinctly different slope from the next set of 32 plates, as illustrated in the lower curve in Fig.

Both of these lowest groups may be biased because of inadequate analysis of very small plates from many other plate boundaries. Also, it has to be remembered that many of the studies of small plates are not complete because the parts of the boundaries of some of the plates are missing, making it impossible to measure their areas and so rendering them not amenable to be added to the plate list. The bulk of the remaining plates fall into the group of 73 plates with a very well-fitting straight line on the log-log plot in Fig.

The largest group of seven plates already identified by Bird has a steeply sloping best fit line. They came to the conclusion that the separation between the seven largest plates South America to Pacific with a steeply descending line showing cumulative area as a function of plate number starting with the largest plate and the smaller set of plates with a smaller negative slope could not be conclusively proved.

Their model was derived from a Pareto distribution. They point out that the number of plates identified becomes smaller the older the plate reconstruction. They used 31 plates for the present and only 10 for the time Ma ago. They plotted the log of cumulative plate area in square kilometers in contrast to the similar plot in Bird and in this paper where the log of cumulative linear plate size is plotted against log of plate number Fig. They showed that this division between the very large plates and the next set of plates is almost certainly permanent for the time period that they considered Ma in contrast to the supposition of Sornette and Pisarenko Depending on exactly which set of data is used, their slope for log plate number versus log cumulative plate area was similar to the slope of the first seven plates of this data set.

Their analysis argued that there was a strong likelihood that the plates could in fact be divided into the seven larger plates and the smaller ones based on data similar to that shown in Fig. It seems likely that the movement of the next set of 73 plates is controlled partly by mantle convection and partly by edge effects caused by the movement of other plates in close proximity.

One of these plates has no rotation vector as yet. The plate size distribution illustrated by Bird is greatly changed by the addition of these other plates which were found mainly using the new technique offered by the relatively inexpensive in contrast to other space-based systems such as VLBI and SLR GPS instruments to measure accurately small relative motions.

Overall, the plate size distribution as illustrated in Figs. If these plates 81st to th in size are thought to be caused by a different phenomenon than the larger plates, then, it is reasonable when plotting the plate sizes starting with the largest as plate 1 to restart the numbering below this kink. This is almost the same as the results from model studies done by Koehn et al.

It consists of both continental crust and oceanic crust. A few hot spots underneath the plate are responsible for active seismic activity, the most famous example of which may be the Yellowstone geyser. The Eurasian Plate has an estimated area of 67,, square kilometers. It is the third-largest of the major tectonic plates. Most of the continents of Europe and Asia are in the Eurasian Plate. Several geological formations can be found on this plate, the most prominent of which is the Himalayan Range.

The Himalayan mountains formed as a result of the collision between the Eurasian Plate and the Indian Plate. The Eurasian Plate is a geologically active plate, with volcanoes and earthquakes occurring in its territory. The African plate is the fourth largest tectonic plate with an estimated area of 61,, square kilometers.

Most of the African continent is on the African Plate. Notably, the Italian island of Sicily is also a part of the African Plate. The Antarctic Plate encompasses the entire continent of Antarctica, as well as the nearby oceans. It is the fifth-largest plate on earth. The Indo-Australian Plate was formed out of a merger of the Australian and Indian plates millions of years ago. When the Eurasian Plate and the Indo-Australian plates collided many many years ago, the Himalayan mountains were formed.

Some are moving toward each other, some are moving apart, and some are grinding past each other. Tectonic plate boundaries are grouped into three main types based on the different movements. The study of plate boundaries and their motion is like figuring out a constantly moving jigsaw puzzle. Subduction zones, or convergent margins, are one of the three types of plate boundaries. At subduction zones, a convergent boundary occurs when two tectonic plates push together.

When an ocean plate and a continental plate collide, the ocean plate slides under the continental plate, and bends downward. A divergent margin occurs when two plates are spreading apart, as at seafloor ridges or continental rift zones such as the East Africa Rift.

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.