How deep in the earth do earthquakes occur? many earthquake foci space within a couple of tens the kilometers of the surface. Earthquakes much less than 70 kilometres deep space classified together shallow-focus. Earthquakes with foci 70-300 km deep room classified as intermediate-focus and also those below 300 kilometres are deep-focus (Figure 3.2.1). Shallow-focus earthquakes occur much more often than deeper ones; around 75% of the full energy exit from earthquakes is from shallow-focus ones. Unfortunately, the shallower one earthquake, the more damage it can create at the surface; intermediate and deep-focus earthquakes are seldom destructive. No earthquakes are known to have developed below around 700 km. At greater depths the rocks are very hot and under high push so castle deform through flowing fairly than breaking and faulting.

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Do earthquakes happen everywhere, or just in some parts of the Earth? for this reason far, this course has disputed earthquakes in Japan and also California, and in the Pacific Ocean close to Alaska and near Peru. Friend may likewise recall hearing of earthquakes in Italy, Armenia, Mexico City, China and also even Britain. Number 3.2.1 shows the global distribution of earthquakes.


Figure 3.2.1 worldwide earthquake epicenters for 1980-1996. Shallow-focus earthquakes are white circles, intermediate-focus earthquakes room light red circles and deep-focus earthquakes room deep red circles. Only earthquakes of size 4 and over are included. Data from the British aramuseum.orglogical Survey civilization Seismicity Database, worldwide Seismology and also aramuseum.orgmagnetism Group, Edinburgh. (>means "greater than"; (b) Use figure 3.2.1 and the poster map to recognize which surface features on the Earth show up to have (i) shallow, and (ii) deep earthquakes linked with them.


(a) Earthquakes are not dispersed evenly throughout the Earth"s surface, so it does not seem judicious to explain the pattern simply as a variation indigenous west to east across the map. The truth that earthquakes take place in distinct regions is reflect in the answer given below:

Earthquakes are concentrated in certain regions that the Earth, and also they regularly occur in linear belts or arcs. One belt surrounds the Pacific Ocean, including Japan, Alaska and the western coastline of North, main and south America. Another an ar is from southeastern Europe through the center East and the Himalayan Mountains. Over there are also earthquakes in linear zones in the oceans.

The decision to framework the answer in this way was do after spring at figure 3.2.1. If the question had actually asked you to look at a different map and describe the sports of something different, such together population, you would certainly probably have actually ordered your answer in a different means (possibly continent through continent) so as to give the many logical answer.

(b) In this part, the planning connected looking in ~ two an extremely different maps and also noting their different scales and projections. (Try to acquire into the habit of feather to view if a scale has actually been offered whenever friend look in ~ a map or a diagram, and additionally to put a range on any type of diagrams you develop so that other human being looking at them will recognize what you space depicting.) Comparing figure 3.2.1 with the poster leader to the complying with conclusions around the relationship in between shallow and deep-focus earthquakes and also surface features:

(i) Shallow-focus earthquakes show up to be linked with mid-ocean ridges, with mountain ranges in the internal of the continent of Europe and Asia, and with the mountains and also ocean trenches that surround the Pacific Ocean.

(ii) Deep-focus earthquakes show up to be connected mainly through the mountains and ocean trenches the surround the Pacific ocean (for example, close to the shore of southern America, or the coastline of Japan).

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Earthquakes are mainly confined to certain areas the the Earth, called seismic zones (derived native seismos, the Greek word because that "shaking"). Many of the rest of the earth is relatively free of earthquakes, or in ~ least free of big earthquakes (Figure 3.2.1). However, even the UK has some little earthquakes as explained below.

You will have seen in Exercise3.2.1 that most earthquakes are connected with certain features the the Earth"s solid surface ar - mid-ocean ridges, ocean trenches, and also some hill belts. Us can also see that deeper earthquakes are characteristic of ocean trenches whereas shallower earthquakes are an ext typical that mid-ocean ridges. This relationship between the surface functions of the Earth, and also the movement of block of the planet that causes earthquakes, is among the monitorings of the active Earth that can be defined by the concept of key tectonics. For now, however, we will proceed looking especially at earthquakes.

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