Which plates cause earthquakes

The rocks pulled down under the continent begin to melt. Sometimes the molten rock rises to the surface, through the continent, forming a line of volcanoes. Another form of convergent boundary is a collision where two continental plates meet head-on.

Since neither plate is stronger than the other, they crumple and are pushed up. This can lead to the formation of huge, high mountain ranges such as the Himalayas. When two tectonic plates slide past each other, the place where they meet is a transform or lateral fault. The San Andreas Fault is one of the best examples of lateral plate motion. This material is also available as a free iBooks textbook and iTunes U course.

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More info. Donate Join Tickets. The most spectacular example of this is the Himalayas. The space created can also fill with new crustal material sourced from molten magma that forms below. Divergent boundaries can form within continents but will eventually open up and become ocean basins. On land Divergent boundaries within continents initially produce rifts, which produce rift valleys. Under the sea The most active divergent plate boundaries are between oceanic plates and are often called mid-oceanic ridges.

The relative motion of the plates is horizontal. They can occur underwater or on land, and crust is neither destroyed nor created. Because of friction, the plates cannot simply glide past each other. Rather, stress builds up in both plates and when it exceeds the threshold of the rocks, the energy is released — causing earthquakes. Privacy Statement Disclaimer and Copyright. Staff Search. Earthquakes Earthquakes at a Plate Boundary. Where continents collide, earthquakes are scattered over a much wider area compared to earthquakes along mid-ocean ridges, transform margins, or subduction zones.

An example is where the Indian plate collides with the Eurasian plate Figure At one time, India was a separate continent, and ocean crust separated India from the Eurasian plate.

For a time, a subduction zone existed where ocean lithosphere from the Indian plate subducted beneath the Eurasian plate. But when the two land masses finally met, they became locked together and the subduction zone was closed off. Today the Indian plate is still pushing against the Eurasian plate in the regions indicated by the red arrows in Figure The collision is accommodated by transform boundaries along the Indian plate. Regions of overall transform motion are indicated in Figure The majority of earthquakes in Figure Deeper earthquakes may be caused by continued northwestward subduction of part of the Indian plate beneath the Eurasian plate in this area.

Even though the area is no longer a subduction zone, the subducted slab still remains, and is subject to stresses that can trigger earthquakes. Some of the earthquakes in Figure That squeezing has caused the Eurasian plate to be thrust over the Indian plate, building the Himalayas and the Tibet Plateau to enormous heights. Most of the earthquakes of Figure The southernmost thrust fault in Figure Intraplate earthquakes within-plate earthquakes are those that occur away from plate boundaries.

Some intraplate earthquakes are related to human activities. When humans trigger earthquakes it is referred to as induced seismicity.

In Saskatchewan there have been 20 earthquakes since all less than magnitude 4 , and the majority occurred near potash mines. Excavation changes the stress in surrounding rocks, so earthquakes may occur in the rocks above excavated parts of the mine.

In Alberta, induced seismicity is triggered by hydraulic fracturing operations when water pressure increases along existing faults, causing them to slip. Intraplate earthquakes not related to human activities often occur along ancient rift zones.

Coincidentally, the rocks of the Charlevoix Seismic Zone are also fragmented because of a meteorite impact the crater margin is indicated by the blue circle in Figure While the Charlevoix zone is far from any boundary of the North American plate, tectonic forces acting on plate boundaries are still transmitted to the interior of the continent, contributing to the stress that causes the faults along the rift zone to rupture.

Intraplate earthquakes can be large earthquakes. The Charlevoix seismic zone has had five earthquakes of magnitudes between 6 and 7 since The New Madrid seismic zone in the Mississippi River Valley had a series of four earthquakes with magnitudes between 7 and 8 in the winter of The population of the region was sparse at the time, but today there are major cities in the New Madrid seismic zone, including Memphis, Tennessee, and St. Louis, Missouri. Buck, W. Modes of faulting at mid-ocean ridges.

Nature , Coastal and Marine Geology Program, U. Geological Survey n. Visit website. DeMets, C. Geologically current plate motions. Geophysical Journal International , Skip to content Bands of earthquakes trace out plate boundaries coloured dots, Figure Figure Bands of earthquakes mark tectonic plates. Narrow bands with shallow earthquakes marked in red indicate transform boundaries or mid-ocean ridge divergent boundaries. Wider bands with earthquakes at a range of depths are subduction zones.

Wide bands of scattered earthquakes mark continent-continent convergent margins e. Plate and ocean basin labels added. Click the image for terms of use. Earthquakes at Divergent and Transform Plate Boundaries Earthquakes along divergent and transform plate margins are shallow usually less than 30 km deep because below those depths, rock is too hot and weak to avoid being permanently deformed by the stresses in those settings. Plate boundaries are marked in red. Arrows show the direction of plate motion.

Left: Rapidly spreading Pacific-Antarctic ridge with earthquakes concentrated along transform faults. Right: Slowly spreading Southwest Indian Ridge, with earthquakes along both spreading segments and transform faults. Base maps with epicentres generated using the U. Geological Survey Latest Earthquakes website. White lines show some of the faults in the region.

White lines with tick marks are normal faults related to spreading. Arrows show the direction of spreading.