Which depth range has the most earthquakes

Emergency Management. Survey Manual. Earthquakes can occur anywhere between the Earth's surface and about kilometers below the surface. For scientific purposes, this earthquake depth range of 0 - km is divided into three zones: shallow, intermediate, and deep.

Shallow earthquakes are between 0 and 70 km deep; intermediate earthquakes, 70 - km deep; and deep earthquakes, - km deep. In general, the term "deep-focus earthquakes" is applied to earthquakes deeper than 70 km.

All earthquakes deeper than 70 km are localized within great slabs of lithosphere that are sinking into the Earth's mantle. The evidence for deep-focus earthquakes was discovered in by H. Turner of Oxford, England. Previously, all earthquakes were considered to have shallow focal depths. The existence of deep-focus earthquakes was confirmed in from studies of the seismograms of several earthquakes, which in turn led to the construction of travel-time curves for intermediate and deep earthquakes.

The distribution of earthquakes in the area of the India-Eurasia plate boundary is shown in Figure This is a continent-continent convergent boundary, and it is generally assumed that although the India Plate continues to move north toward the Asia Plate, there is no actual subduction taking place. There are transform faults on either side of the India Plate in this area.

The entire northern India and southern Asia region is very seismically active. Earthquakes are common in northern India, Nepal, Bhutan, Bangladesh and adjacent parts of China, and throughout Pakistan and Afghanistan.

Many of the earthquakes are related to the transform faults on either side of the India Plate, and most of the others are related to the significant tectonic squeezing caused by the continued convergence of the India and Asia Plates. That squeezing has caused the Asia Plate to be thrust over top of the India Plate, building the Himalayas and the Tibet Plateau to enormous heights.

Most of the earthquakes of Figure The southernmost thrust fault in Figure There is a very significant concentration of both shallow and deep greater than 70 km earthquakes in the northwestern part of Figure This is northern Afghanistan, and at depths of more than 70 km, many of these earthquakes are within the mantle as opposed to the crust. It is interpreted that these deep earthquakes are caused by northwestward subduction of part of the India Plate beneath the Asia Plate in this area.

This map shows the incidence and magnitude of earthquakes in British Columbia over a one-month period in March and April The string of small earthquakes adjacent to Haida Gwaii H. How might these earthquakes be related to that one? Most of the earthquakes around Vancouver Island V. 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. White lines without tick marks are transform faults. The Siberian Craton shaded region is strong 2 billion year old crust. Faults after U. Geological Survey see references.

Base maps inset and rift views with epicentres generated using the U. Visit Latest Earthquakes One reason for the difference in earthquake distribution in continental rift zones is that the rifts are only beginning to form. Earthquakes at Convergent Boundaries Subduction Zones Along convergent plate margins with subduction zones, earthquakes range from shallow to depths of up to km.

White arrows show the directions of plate movement. Circle colours indicate the depths of earthquakes see legend, lower left. Earthquakes become deeper moving north from the subduction zone. Visit Latest Earthquakes Earthquakes occur in subduction zones for a variety of reasons. Not all factors shown here are present in all subduction zones.

Stress from bending, flexing, and stretching may cause ruptures. Changes in the mechanical properties of the mantle may affect how subucting slabs move, contributing additional stresses. The histogram at right shows the global average number of earthquakes at depth, for earthquakes greater than M5.

Modified after Green et al. Continent-Continent Convergence Zones Where continents collide, earthquakes are scattered over a much wider area compared to earthquakes along mid-ocean ridges, transform margins, or subduction zones. Red lines- plate boundaries; red arrows- collision zones; blue arrows- transform zones. Visit Latest Earthquakes The majority of earthquakes in Figure Vuichard Figure 2.

Intraplate Earthquakes Intraplate earthquakes within-plate earthquakes are those that occur away from plate boundaries. The location of the Charlevoix seismic zone is indicated by the star on the map of Canada.

Dots indicate earthquake epicentres. The size of the dots indicates magnitude. White lines indicate fault segments. The dashed circle marks the edge of a crater formed by a meteorite impact million years ago.