Some of these rifting events were accompanied by volcanic activity; the ground would gradually rise m before abruptly dropping, signalling an impending eruption. Between and , the displacements caused by rifting totalled about 7 m.
When the continental crust stretches beyond its limits, tension cracks begin to appear on the Earth's surface. Magma rises and squeezes through the widening cracks, sometimes to erupt and form volcanoes.
The rising magma, whether or not it erupts, puts more pressure on the crust to produce additional fractures and, ultimately, the rift zone.
East Africa may be the site of the Earth's next major ocean. Plate interactions in the region provide scientists an opportunity to study first hand how the Atlantic may have begun to form about million years ago. Geologists believe that, if spreading continues, the three plates that meet at the edge of the present-day African continent will separate completely, allowing the Indian Ocean to flood the area and making the easternmost corner of Africa the Horn of Africa a large island.
The size of the Earth has not changed significantly during the past million years, and very likely not since shortly after its formation 4. The Earth's unchanging size implies that the crust must be destroyed at about the same rate as it is being created, as Harry Hess surmised.
Such destruction recycling of crust takes place along convergent boundaries where plates are moving toward each other, and sometimes one plate sinks is subducted under another.
The location where sinking of a plate occurs is called a subduction zone. The type of convergence -- called by some a very slow "collision" -- that takes place between plates depends on the kind of lithosphere involved. Convergence can occur between an oceanic and a largely continental plate, or between two largely oceanic plates, or between two largely continental plates. If by magic we could pull a plug and drain the Pacific Ocean, we would see a most amazing sight -- a number of long narrow, curving trenches thousands of kilometers long and 8 to 10 km deep cutting into the ocean floor.
Trenches are the deepest parts of the ocean floor and are created by subduction. Off the coast of South America along the Peru-Chile trench, the oceanic Nazca Plate is pushing into and being subducted under the continental part of the South American Plate. In turn, the overriding South American Plate is being lifted up, creating the towering Andes mountains, the backbone of the continent.
Strong, destructive earthquakes and the rapid uplift of mountain ranges are common in this region. Even though the Nazca Plate as a whole is sinking smoothly and continuously into the trench, the deepest part of the subducting plate breaks into smaller pieces that become locked in place for long periods of time before suddenly moving to generate large earthquakes.
Such earthquakes are often accompanied by uplift of the land by as much as a few meters. On 9 June , a magnitude This earthquake, within the subduction zone between the Nazca Plate and the South American Plate, was one of deepest and largest subduction earthquakes recorded in South America.
Fortunately, even though this powerful earthquake was felt as far away as Minnesota and Toronto, Canada, it caused no major damage because of its great depth. Oceanic-continental convergence also sustains many of the Earth's active volcanoes, such as those in the Andes and the Cascade Range in the Pacific Northwest. Coupled with the evidence for constant Pacific—Antarctic motion since 3. To better characterize the uncertainty in our estimate of Pacific—Nazca motion, we separately inverted the data from the Nazca—Antarctic—Pacific and Nazca—Cocos—Pacific plate circuits to determine independent estimates of Pacific—Nazca plate motion.
The closure-enforced estimates of the Pacific—Nazca spreading rates from these two inversions Fig. Similarly, the Pacific—Nazca directions of motion not shown estimated from these two three-plate circuits differ by only 0. The independent information supplied by closures about these two three-plate circuits is thus consistent and suggests that the closure-enforced MORVEL estimate is more accurate than the best-fitting estimate.
Some caution is however warranted as the Nazca—Pacific—Cocos circuit fails closure Section 6. Solid line shows rates calculated from the best-fitting Nazca—Pacific angular velocity. Dashed red and dashed blue lines show rates calculated from Nazca—Pacific angular velocities that were determined from inversions of all data from the Nazca—Pacific-Cocos and Nazca—Pacific—Antarctic three-plate circuits, respectively. Cocos—Nazca spreading rates a and transform fault azimuths b and rates and directions calculated from the Cocos—Nazca angular velocities specified in the figure legend.
Rates shown by open circles are biased by Galapagos microplate motion and are not used to estimate Cocos—Nazca motion. The data thus require rapid westward migration of the pole from 3. Despite the large change in pole location, the average spreading rate along the plate boundary accelerated by only 1.
As is shown by Fig. The two independent estimates thus agree to the nearest 1—1. The Pacific—Cocos pole location is well determined due to the abundance of rates and their steep gradient Fig. Similar to the large rms misfit for the fast spreading Pacific—Nazca plate boundary, the 2. Pacific—Cocos spreading rates a and transform fault azimuths b and rates and directions calculated from Pacific—Cocos angular velocities listed in the figure legend.
Map inset depicts tracks of magnetic profiles blue , present plate boundary red and epicentres of shallow earthquakes from to A downward adjustment of 2.
Some of the above misfit may be attributable to active deformation of the lithosphere on one or possibly both sides of the rise axis.
These earthquakes extend southward to Deformation may also occur within the young oceanic lithosphere between the Middle America subduction zone and the rise axis. Some possible causes for these differences are discussed in Section 6. The steep gradient in these rates constrains the best-fitting pole to lie just northeast of the plate boundary Fig. No plate circuit closures influence our estimate of the Pacific—Rivera plate angular velocity, hence the best-fitting and MORVEL estimates are identical.
The two pole locations differ by only 0. Although the spreading rates given by our new angular velocity are 2. Magnetic profiles that cross the rise axis north of The change in the spreading rate gradient at The large uncertainties in the pole location Fig. No circuit closures influence our estimate of the angular velocity for this plate pair, thus the best-fitting and MORVEL estimates are the same. Spreading rates estimated from our new angular velocity Fig.
Applying the same correction to the rates calculated from Wilson's angular velocity reduces the difference to less than 0. Our description of the tectonic implications of these angular velocities is limited in scope and focuses mainly on areas where subduction occurs or the plate boundaries are narrow enough to compare earthquake slip directions from the plate boundary faults with the predicted directions of plate motion.
The India and Australia plates, as well as their intervening diffuse oceanic plate boundary, subduct beneath southeastern Asia along the Java—Sumatra trench Fig. Using velocities measured between and at more than GPS sites in southeastern Asia, Simons et al.
From the velocities of 28 GPS stations within the Sundaland plate interior and additional GPS sites on adjacent plates, they estimate angular velocities for Sundaland relative to its neighboring plates. Velocity arrows are scaled differently by plate boundary for clarity. Uncertainty ellipses are 2-D, 95 per cent. All open red arrows show motions of GPS stations near the Philippine Sea plate boundaries relative to the Philippine Sea plate and are scaled as shown in the legend at the upper left.
Open arrows in the rectangle at the centre of the map include three sites near the intersection of the Ryukyu and Philippine trenches that were used by Zang et al. Right-hand panel: individual and moment-weighted, mean horizontal slip directions for shallow thrust earthquakes from the Izu-Bonin and Mariana trenches and directions calculated from Pacific—Philippine Sea plate angular velocities specified in the legend beneath the figure.
Sixteen of the individual earthquake directions are from table 1 of Seno et al. Earthquake directions are rotated systematically anticlockwise from the predicted directions due to slow to rapid backarc extension along the Bonin extension zone and Mariana backarc spreading centre.
Relative to the interior of the Sundaland plate, all nine stations that are located within several hundred km of the Sumatra trench move northeastward away from the trench at rates of 1.
Their motions are consistent with elastic shortening that should occur inland from a strongly locked subduction interface. We therefore do not use any of these nine velocities to estimate Sundaland plate motion.
We also excluded a tenth station on the island of Java, which is located close enough to the trench to be affected by interseismic and post-seismic effects of plate boundary earthquakes. Station locations are shown in maps and Fig. All velocities are relative to ITRF Panels a and c show the component of the station motion parallel to small circles around the best-fitting poles.
Panels b and d show the radial component of the station motion, which is orthogonal to small circles around the pole. Red arrows show station velocities that are used to estimate the best-fitting angular velocities. Blue arrows indicate stations that Simons et al.
Grey circles show epicentres of — shallow earthquakes. The weighted rms misfits for the north and east velocity components of these 18 stations are 0. The motions of these 18 stations relative to the plate interior shown by the red arrows in Fig. We therefore use these 18 station velocities to define Sundaland plate motion. The 19 Australia plate station velocities have respective north and east velocity component rms misfits of 0.
Our best-fitting Australia plate angular velocity Table 4 gives motions at Australian sites that differ by less than 0. The 18 transformed Sundaland plate station velocities Table S4 were inverted with the other MORVEL data to estimate the best-fitting Australia-Sundaland angular velocity and via circuit closures the angular velocities for the Sundaland plate relative to all the other plates.
Unlike the Australia—Sundaland angular velocity, which is estimated entirely from GPS observations, the motions of the India and Sundaland plates are linked to each other via an extended plate circuit through several seafloor spreading centres in the Indian Ocean Fig. Shen et al. From a joint inversion of 81 Yangtze plate station velocities from Shen et al. We transformed the velocities of 83 Yangtze plate stations from Shen et al. The 83 station velocities are well fit by a single angular velocity Figs 49a and b , with a weighted rms misfit of only 0.
Relative to the plate interior, the station residual motions are apparently random see map in Fig. The new pole predicts rates similar to those found by Simons et al.
The Amur plate, which is located north of a wide deforming region that separates it from the Yangtze plate inset to Fig. Location map, tectonic setting, and GPS station velocities for Amur plate. Map shows Global centroid moment tensor solutions for the period — with centroid depths less than 40 km for locations inland from the Japan and northern Izu-Bonin trenches.
Earthquakes are from to and have magnitudes greater than 3. All velocities on the large map are relative to a fixed Amur plate see legend. Open black arrows J07 show motions predicted by the Amur—Eurasia angular velocity of Jin et al. Red and green focal mechanisms are for normal-faulting and strike-slip earthquakes along the Amur—Eurasia plate boundary and blue lines indicate tension axis orientations for selected normal-faulting earthquakes.
Panels A and B show tangential and radial components of the 20 Amur plate station velocities in ITRF relative to motion calculated from their best-fitting angular velocity red curve and for comparison, the motions of stations from the Yangtze plate blue circles. They also find that recent poles based on GPS station velocities Sella et al. We estimate motion of the Amur plate with the velocities of fourteen survey-mode and six continuous GPS stations map and panels A and B in Fig.
The station velocities are well fit, with north and east weighted rms values of 1. Four of the residual velocities Fig. No other patterns in the residual velocities are apparent.
We link the Amur plate to the global plate circuit using the Australia plate, the same as we used for the Yangtze and Sundaland plates Fig. Doing so ensures that any errors in the Australia plate angular velocity will cancel during the estimation procedure for the angular velocity that specifies the slow motion across the wide deforming zone between the Amur and Yangtze plates.
The new Yangtze—Amur angular velocity Table 3 predicts Yangtze plate motion of 4. The new pole is located north of the plate boundary at Small circles about the new pole red-white dashed lines in Fig. We conclude that the MORVEL Amur—Eurasia angular velocity is consistent with independent observations of deformation along their plate boundary, despite the extended plate circuit that links the two plates.
The consistency between the predicted and observed rates and directions of motion at various locations along the plate boundary implies that the accumulated errors within the circuit that links these two plates are small. More than 90 per cent of the Philippine Sea plate is bordered by active subduction zones Fig. Because much of the plate interior lies beneath water and is thus impractical for geodetic monitoring, estimating its motion has proved challenging.
Prior to the advent of modern GPS measurements, Seno et al. More recent estimates also use velocities for the handful of GPS stations from the plate interior and near its boundaries Sella et al. Although the velocities at these two sites could conceivably be affected by elastic strain associated with subduction along the Ryukyu trench, GPS measurements on islands in the Ryukyu arc indicate that little or no elastic strain accumulates within the arc Nishimura et al.
Even if the nearby subduction interface is fully locked, any elastic shortening at PALA should be only fractions of a millimetres per year, small enough to neglect. Given our concerns about their locations within an active seismic zone, we obtained and processed the original GPS data for these three and two additional campaign sites in the northern Philippines locations and motions indicated by the open red arrows within the rectangle in Fig.
All five sites move relative to the plate interior at rates of Given their locations within an active seismic zone and significant motions relative to the plate interior, we elected not to use these stations to estimate Philippine Sea plate motion.
We also considered whether other GPS sites near the boundaries of the Philippine Sea plate might be located on undeforming areas of the plate. Their motions are consistent with velocities measured at other GPS sites in the Mariana trough Kato et al. In the Izu-Bonin backarc north of the Mariana trench, continuous stations , and also move eastward at rates of 4. Their motions are consistent with marine geophysical evidence for slow extension behind the Izu-Bonin trench Taylor.
None of the GPS sites along the eastern border of the Philippine Sea are therefore suitable for estimating Philippine Sea plate motion.
All other plausible station groupings give rise to significant misfits to one or more of the station velocities that are assumed to record the motion of the plate interior. The 21 Pacific plate station velocities have respective rms misfits for the north and east velocity components of 0.
The Pacific plate angular velocity Table 4 is strongly constrained due to the large geographic area spanned by these 21 stations Fig. Relative to the Philippine Sea plate, the Pacific plate rotates anticlockwise around a pole near the southern end of their plate boundary Figs 13a and The predicted motion agrees with evidence for slow NW-directed extension across this feature Fujiwara et al.
In contrast, the Pacific-Philippine Sea angular velocity of Zang et al. These large differences reflect the different data and approaches that are used in our two studies. The Philippine Sea plate subducts beneath the eastern boundary of the Yangtze plate along the Ryukyu trench, where slow backarc spreading decouples the forearc from the interior of the Yangtze plate Nishimura et al. The many additional station velocities that we use to estimate Yangtze plate motion therefore only modestly alter the Philippine Sea—Yangtze angular velocity estimate relative to that of Sella et al.
The angular velocity estimated by Sella et al. In contrast, the Amur—Philippine Sea plate angular velocity estimated by Kreemer et al. Jin et al. Our understanding of the tectonic setting of the Nankai Trough thus may evolve as further information about the tectonics of eastern Asia is extracted from future GPS velocity fields for this complexly deforming region. The NUVEL-1 Caribbean plate angular velocities were estimated from a poorly known spreading rate from the mid-Cayman spreading centre, azimuths of the Swan Island and Oriente strike-slip faults, and earthquake slip directions from the Middle America and Lesser Antilles subduction zones.
Subsequent work has shown, however, that almost none of these data unambiguously record Caribbean plate motion. Following DeMets et al. The well-determined azimuths of this fault are consistent with a purely geodetic estimate of Caribbean—North America plate motion DeMets et al.
The misfits are modestly larger than for the other plates with motions determined from GPS velocities, but are unsurprising given that six of the 16 stations are located within km of an active plate boundary fault and 12 stations are survey-mode sites. As measured by their summed data importances, the 16 station velocities and two Swan Islands fault azimuths respectively provide 87 and 13 per cent of the information about Caribbean plate motion.
We refer readers to DeMets et al. Stations from areas of North America that are affected by postglacial rebound are excluded Calais et al. The respective weighted rms misfits for the north and east velocity components are 0.
Calais et al. These are consistent with other recent estimates, which are determined from many of the same data DeMets et al. For example, at a location along the Lesser Antilles trench Fig. Along the Central Range fault of Trinidad Studies of earthquake cycle deformation along the Cascadia subduction zone and Middle America trench, which accommodate subduction of the Juan de Fuca, Rivera and Cocos plates beneath the North America and Caribbean plates, require well-determined angular velocities for the relative motions between these plates.
We therefore estimate an alternative set of angular velocities for these three plates from a shorter, geodetically based plate circuit Fig. The good agreement suggests that motion for this plate pair since 0. At Due to their differing pole locations Fig.
More work is needed to determine which of the two more accurately describes the present motions of these plate pairs. Further discussion of this topic is given in Section 7. The failure of a plate circuit to satisfy closure may be caused by unrecognized plate boundaries, plate deformation, or by a variety of systematic errors.
Our analysis of the MORVEL circuit closures focuses on six three-plate circuits from which kinematic data are available for all three of the intersecting boundaries Fig. Four of these consist of three spreading centres that intersect at a triple junction. These offer strong tests for circuit closure because the motions along all three intersecting plate boundaries are well determined. The other two three-plate circuits, those for Nubia—Eurasia—North America and Arabia—India—Somalia, have spreading rates and fault azimuths along two of the three boundaries that meet at their triple junctions, but have only fault azimuths along the third boundary.
Absent any constraint on the rate of motion for one of the three plate boundaries in these circuits, they offer weaker tests of circuit closure. Our circuit closure analysis excludes all plate circuits that include the Scotia and Sandwich plates, for which the available data are too incomplete or too unreliable to merit a meaningful test of circuit closure.
We determine the magnitude of circuit non-closure using two complementary methods. The first, described by Gordon et al. We examine the effect of outward displacement on circuit non-closure by determining the variation in the misfit and thus the magnitude of non-closure as we change the assumed value for outward displacement Fig.
Black dashed line indicates the value Red dashed line similarly indicates the 99 per cent confidence threshold Values are shown only for ridge—ridge—ridge plate circuits since unique velocities of non-closure cannot be determined for ridge—ridge—fault plate circuits.
Three of these additional degrees of freedom represent the additional parameters that are used to estimate three instead of two angular velocities in the best-fitting versus the closure-enforced estimates. The fourth degree of freedom represents the value for outward displacement that is adjusted to explore its effect on the misfit. For the two ridge—ridge—fault plate circuits, no rate data are available from one of the three plate boundaries and hence only a best-fitting pole can be estimated from the data for that boundary.
We also determine a linear rate of non-closure for each of the ridge—ridge—ridge plate circuits to complement the statistical measure of circuit non-closure. We define this as the difference between the motion that is given at the circuit triple junction by any one of the three best-fitting angular velocities and the motion that is predicted from the sum of the remaining two best-fitting angular velocities.
The former gives the plate motion independent of the condition of plate circuit closure whereas the latter predicts motion purely from closure of the plate circuit, thereby providing completely independent estimates of motion. The difference between the two constitutes a useful practical measure of the consistency of the two estimates. Repeated inversions of the rates and azimuths from the Nubia—Antarctic—Sur plate circuit for assumed values of outward displacement between 0 and 3.
The corresponding linear velocity of circuit non-closure at the Bouvet triple junction varies between 2. The few millimetres per year non-closure might be caused by biases in one or more subsets of the kinematic data from this plate circuit. For example, Sempere et al. We explored the effect of using values of outward displacement as large as 5 km, but find that even for such large values, significant circuit non-closure remains.
Differences between the average magnitudes of outward displacement for the three spreading centres in this plate circuit might also contribute to the circuit non-closure, but we did not explore this because of the poorly posed nature of the problem. Better constraints on outward displacement, particularly for ultraslow spreading centres such as the Southwest Indian Ridge, are needed. The effect of non-closure around the Bouvet triple junction on the MORVEL angular velocities is small given that the non-closure is absorbed within this three-plate circuit, mainly as a misfit to data along the American—Antarctic ridge Fig.
The difference between the best-fitting and closure-enforced angular velocities for motion around the Pacific—Antarctic—Nazca plate circuit is statistically insignificant for values of outward displacement equal to or less than 2. For assumed values of outward displacement that are larger than 2. The data thus suggest that outward displacement is unlikely to be larger than 2 km along these three spreading centres. The large misfits and significant non-closure of this three-plate circuit pose a challenge to the rigid plate approximation.
The non-closure is manifested mainly as systematic misfits of the closure-enforced angular velocities to the Pacific—Nazca and Pacific—Cocos spreading rates Figs 44 and 46a.
The non-closure of this plate circuit is insensitive to the assumed value of outward displacement Fig. Below, we address two hypotheses for the cause of the non-closure, namely, a possible diffuse plate boundary within one or possibly both of the Nazca and Cocos plates, or an inconsistency between the spreading rate and transform fault data, possibly due to a change in plate motion within this plate circuit since 0.
We find no evidence that any deforming zone intersects the Pacific—Nazca plate boundary, in accord with the small degree of non-closure for the Nazca—Antarctic—Pacific plate circuit see previous section.
We also find no evidence that a deforming zone intersects the Cocos—Nazca plate boundary. Along the Pacific—Cocos plate boundary, deformation within the Pacific or Cocos plates may occur north of the Orozco transform fault on one or both sides of the rise axis, as described in Section 5.
The circuit non-closure thus also does not appear to be caused solely by deformation of the portion of the Cocos plate north of the Orozco fracture zone. Some of the circuit non-closure may be caused by a hypothesized change in motion within this plate circuit since 0. The rapid westward migration of the Cocos—Nazca pole from 4 Ma to at least 0.
To test whether a change in motion for one or more of the plate pairs might be responsible for the apparent circuit non-closure, we inverted only the spreading rates, which average motion consistently over the past 0. All Pacific-Cocos spreading rates north of For this rates-only inversion, the fits of the closure-enforced and best-fitting angular velocities differ at only the 1 per cent confidence level.
These differences in direction are several times larger than any proposed change for the directions of plate motion for these two plate boundaries since 0. The circuit non-closure is thus not resolved by a rates only inversion, but is instead shifted by an unacceptably large amount to the directional components of motion.
We experimented with other subsets of the rates and transform azimuths from these three plate boundaries, but found none that reduce the circuit non-closure to insignificant levels without systematically misfitting either the rates or directions along one or more of the three plate boundaries.
The best-fitting and closure-enforced angular velocities for the Capricorn—Somalia—Antarctic plate circuit do not differ significantly Fig. The linear velocity of non-closure at the Rodrigues triple junction is only 1.
The low level of circuit non-closure is partly an outcome of our systematic search for a Capricorn plate geometry that minimizes non-closure of this plate circuit Section 5.
Both of the three-plate circuits that include one plate boundary without rates are consistent with closure Fig. Along the Nubia—Eurasia plate boundary, the three Gloria fault azimuths are fit well when inverted with the many spreading rates and azimuths from the Eurasia—North America and Nubia—North America plate boundaries Fig. The data from this plate circuit are therefore consistent with strike-slip motion along the well-mapped Gloria fault.
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.
Geochem Geophys Geosyst Geol Soc Am Bull 95 — Google Scholar. Geophys Res Lett — Chase CG The N plate problem of plate tectonics.
Geoophys J Roy Astron Soc — Sci Lett — Geophys J Int — Fisher RA Statistical methods for research workers, Thirteenthth edn. Oliver and Boyd, Edinburgh, p J Geophys Res — Forsyth D, Uyeda S On the relative importance of the driving forces of plate motion.
Geophys J Roy Astron Soc — J Geophys Res Harrison CGA Marine magnetic anomalies—the origin of the stripes. Ann Rev Earth Planet Sci — Tectonics — Jennings CW Fault activity map of California and adjacent areas with location and ages of recent volcanic eruptions, Calif. Data Map Ser. Phys Earth Planet Int — Nature — Tectonophysics — J Geophys Res B Gondwana Research — Le Pichon X Sea-floor spreading and continental drift.
Rev Geophys — Geol Geof — Bull Seismol Soc Am — Madiera J, Ribeiro A Geodynamic models for the Azores triple junction: a contribution from tectonics. Morgan WJ Rises, trenches, great faults, and crustal blocks. Morgan WJ Plate motions and deep mantle convection. Earth Planet Sci Lett — J Geophys Res B4. J Geophys R Sornette D, Pisarenko V Fractal plate tectonics. Geophys Res Lett Mar Geol — Thatcher W Microplate versus continuum descriptions of active tectonic deformation.
Thatcher W Microplate model for the present-day deformation of Tibet. Thatcher W How the continents deform: the evidence from tectonic geodesy.
Annual Rev Earth Planet Sci — Turcotte DL Fractals and chaos in geology and geophysics. 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. Table S9. Seventeen plates from Meade and Hager Table S List of 32 smallish plates and their geological settings.
DOCX 51 kb. Reprints and Permissions. Harrison, C. The present-day number of tectonic plates. Earth Planet Sp 68, 37 Download citation. Received : 27 August Accepted : 05 February Published : 02 March Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative.
Skip to main content. If the plates there continue to diverge, millions of years from now eastern Africa will split from the continent to form a new landmass. A mid-ocean ridge would then mark the boundary between the plates. The San Andreas Fault in California is an example of a transform boundary, where two plates grind past each other along what are called strike-slip faults.
These boundaries don't produce spectacular features like mountains or oceans, but the halting motion often triggers large earthquakes, such as the one that devastated San Francisco. All rights reserved. They move at a rate of one to two inches three to five centimeters per year. Convergent Boundaries Where plates serving landmasses collide, the crust crumples and buckles into mountain ranges. Divergent Boundaries At divergent boundaries in the oceans, magma from deep in the Earth's mantle rises toward the surface and pushes apart two or more plates.
Share Tweet Email. Why it's so hard to treat pain in infants. This wild African cat has adapted to life in a big city. Animals Wild Cities This wild African cat has adapted to life in a big city Caracals have learned to hunt around the urban edges of Cape Town, though the predator faces many threats, such as getting hit by cars.
India bets its energy future on solar—in ways both small and big. Environment Planet Possible India bets its energy future on solar—in ways both small and big Grassroots efforts are bringing solar panels to rural villages without electricity, while massive solar arrays are being built across the country.
Go Further. Animals Climate change is shrinking many Amazonian birds.
0コメント