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How may the study of earthquake waves be used to interpret the earth's internal structure and composition

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Introduction

How may the study of earthquake waves be used to interpret the earth's internal structure and composition? Studying the different waves that are given off in an eathquake can identify the internal composition and structure of the earth. There are three types of wave Primary or 'push' waves (P-waves), Secondary or 'shock' waves (S-waves) and Longitudal or 'long' waves (L-waves). The waves that must be studied to interpret the earth's internal structure and composition are 'Body Waves' Body waves are another name for P or S waves. Earthquakes occur most commonly in seismic zones; these zones are related with oceanic ridges, young fold mountains and island arcs. Earthquake foci are located at depths under the surface up to a maximum of approximately 700km. ...read more.

Middle

As body waves travel into the earth, they enter the Moho, this area of crust is very dense and rigid and so both waves speed up rapidly. At approximately 50km, the waves suffer a slight decrease in velocity, before beginning to increase in velocity again after about 50km. This shows that there must be a zone of less dense rock between these depths. This has been named the Low Velocity Zone (LVZ). After leaving the LVZ, both body waves steadily increase in their velocity as they get deeper and travel through the mantle. This shows that the rock found in the mantle must be both rigid and very dense to accommodate such velocity increases. To be precise, the densities of the upper and lower mantle are 3.3g/cm� and 5.4g/cm� respectively. ...read more.

Conclusion

This evidence gives us the knowledge that the core is of a less rigid, or liquid material as S-waves cannot travel through liquid and P-waves are slowed down by the less rigid rock. It is believed that the core consists of iron with about 7% nickel and 6% sulphur. The low-density sulphur is probably concentrated in the liquid outer core. On the other hand, the high density inner core may contain as much as 40% nickel as the P-waves that reach the inner core are allowed to once again increase in velocity to 11.3km s-1. All this evidence produced by seismic body waves has led geologists to believe that the earth becomes denser with depth but less rigid. The core being the densest zone but the least rigid and the crust being the least dense but the most rigid zone. ...read more.

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