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Seismology is the study of earthquakes and how the waves emitted from them travel through the earth.

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Introduction

Seismology is the study of earthquakes and how the waves emitted from them travel through the earth. By studying how the waves pass through the earth, seismologists can tell which materials the waves have passed through, and the nature of these materials. This has helped us to build up knowledge of the earth's internal structure and an understanding of how earthquakes happen. To understand why earthquakes happen, we need to understand what is actually happening beneath the earth's surface. Very little is known about inside the earth, because we do not have access to it as the deepest borehole is only a mere 15 kilometers down. Much of what is known comes from studying the way earthquake waves pass through the earth. The earth consists of a number of concentric layers made up of many different rock types, and substances, which stretch from the inner core to the surface crust. There are three main parts which make up the earth, these are; the crust, the mantle and the core. The Core: The center of the earth consists of a molten outer part the outer core and a solid inner part called the inner core. ...read more.

Middle

Types of plate margin: Destructive: Constructive: Collision: Conservative: Colliding plates: When a continental plate meets an oceanic plate, the lighter continental plate moves of the more dense oceanic plate causing a trench to be formed, and over millions of years, mountain ranges are formed. When two continental plates collide, mountain ranges are formed, because neither descends because of the similarity in density. When two oceanic plates collide the slower moving plate is usually sub ducted underneath the faster moving plate. The areas where the oceanic plate descends beneath the continental plate are known as subduction zones. Zones like these have increased temperature and pressure this can cause metamorphism, which is when igneous and sedimentary rocks are changed into new types by recrystallization. Separating plates: When two plates move apart, new crust is created by magma, which comes up from the mantle to fill the gaps. Sometimes continental plates split and continents move apart, causing a rift valley which if flooded will form a sea. The boundaries between separating plates and splitting plates are constructive boundaries because new lithosphere is being formed. Conservative plates: At conservative plate margins the plates slide past each other, there is so much pressure building up until eventually the plate's move with a large jerk causing earthquakes. ...read more.

Conclusion

In some other areas, only P waves are detected. A shadow is cast by the absence of the S waves; this means that the outer core must be liquid. The size of the shadow means that the size of the outer core is about 7000km in diameter. Earthquakes also cause the earth to reverberate for a period of time after the earthquake, the reverberations we can deduce that inside the liquid outer core is a solid inner core about 2400km in diameter. Seismometers: A seismometer consists of a solid base, which should be secured to a rock or the ground. A pen on the base of a heavy mass is suspended above a rotating drum and on which graph paper is attached. As the earth moves in an earthquake, the heavy mass stays still and a jagged trace is drawn on the paper. The different traces produced are analyzed and deductions about the earths structure can be made, the velocities of the waves can be worked out by looking at the time delay between the earthquake and when waves are received. * OCR A Physics separate award * GCSE Physics T.Ducan * OCR a new introduction to Geography (GCSE) * GCSE Geography Revision notes * The Hutchinson Encyclopedia * The internet * Mr. Cocks's vast seismological Knowledge! ...read more.

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