• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month
Page
1. 1
1
2. 2
2
3. 3
3
4. 4
4
5. 5
5
6. 6
6
7. 7
7
8. 8
8
9. 9
9

# Seismic waves.

Extracts from this document...

Introduction

Introduction Seismic waves are generated in the earth by the movements of earthquakes or explosions. Depending on the material travelled through, surface and body waves move at unpredictable speeds. Layers of the earth, including the core, mantle, and crust, have been distinguished using seismic wave profiles. Seismic waves from explosions have been used to understand the subsurface structure of the crust and upper mantle and in the exploration for oil and gas deposits. There are several different kinds of seismic waves, and they all move in different ways. The two main types of waves are body waves and surface waves. Body waves can travel through the earth's inner layers, but surface waves can only move along the surface of the planet like ripples on water. Earthquakes radiate seismic energy as both body and surface waves. Types of Wave Body Waves P Waves The first kind of body wave is the P wave or primary wave. This is the fastest kind of seismic wave. The P wave can move through solid rock and fluids, like water or the liquid layers of the earth. It pushes and pulls the rock it moves through just like sound waves push and pull the air. ...read more.

Middle

We also know that the density of the rock that is on the surface is 2800kg/m3. Therefore, there must be denser material further towards the centre of the Earth. We can find out more about the Earth's structure by looking at records of P-waves and S-waves. These conclusions can be made: * Seismic waves cannot be travelling through the earth in straight lines * No S-waves travel to the opposite side of the earth from their origins...something must block them. * P-waves do arrive on the other side of the Earth but not in a ring-shaped shadow zone. Scientists have explained these facts by saying: * Density increases as you go further into the Earth. This changes the speed of the waves and means that they get refracted. * The Earth has a central core and the outer must be liquid because S-waves are blocked and cannot travel through liquid. * The core has a density of 11,000 kg/m3. Patterns in P-wave refraction have shown this. The size of the core was measured in 1914 by Bene Gutenburg using seismic waves tracing. He found its radius to be 3470 km. Inge Lehmann in 1936 studied how seismic waves travelled through the core. ...read more.

Conclusion

Oceanic crust makes up the other 60 percent of the earth's solid surface. Oceanic crust is, in general, thin and dense. It is constantly being made at the bottom of the oceans in places called mid-ocean ridges. Mid-ocean ridges are undersea volcanic mountain chains formed at plate boundaries where there is a build-up of ocean crust. This production of crust does not increase the physical size of the earth, so the material produced at mid-ocean ridges must be recycled, or consumed, somewhere else. Geologists believe it is recycled back into the earth in areas called subduction zones, where one plate sinks underneath another and the crust of the sinking plate melts back down into the earth. Oceanic crust is continually recycled so that its age is generally not greater than 200 million years. Oceanic crust averages between 5 and 10 km thick. It is composed of a top layer of sediment, a middle layer of rock called basalt, and a bottom layer of rock called gabbro. Both basalt and gabbro are dark-coloured volcanic rocks. Conclusion Earthquakes happen when tectonic plates go under, into or alongside each other. P and S waves originate from the earthquake and travel through the Earth. S waves do not travel through liquid and this has helped scientists find out about the Earth's structure. ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Hazardous Environments section.

## Found what you're looking for?

• Start learning 29% faster today
• 150,000+ documents available
• Just £6.99 a month

Not the one? Search for your essay title...
• Join over 1.2 million students every month
• Accelerate your learning by 29%
• Unlimited access from just £6.99 per month

# Related AS and A Level Hazardous Environments essays

1. ## Discuss the degree to which the theory of plate tectonics is supported by seismic ...

5 star(s)

Strike-slip faults, particularly continental transforms can produce major earthquakes up to about magnitude 8 (image 8 shows where earthquakes can occur at various plate margins). Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.

2. ## Volcanic &amp;amp; Seismic events are major factors towards proving that the plate tectonics theory ...

This string of islands, all very similar in composition are neither near a destructive or constructive plate margin and are instead produced through a single hot spot. It is believed that the abnormally hot area of the mantle (the hot spot), produces rising plutons of magma that eventually breaks through

1. ## Plate Tectonics Project.

The text refers to fig 7. Sites West of the Pacific - North America Boundary These involve four sites, two in Mexico, and two in southern California. At the southern tip of the Baja Peninsula is Cabo San Lucas. Here SLR shows a motion which is 52 mm/yr, similar with that predicted by the NUVEL-1 model for Pacific motion.

2. ## The Crust, The Mantle and The Core

As the oceanic plate gets pushed down into the mantle, a vast ocean trench is formed by the drastic lowering of the sea bed. These trenches are by far the deepest areas of the worlds' ocean and are home to some of the planet's most extraordinary wildlife.

1. ## Monserrat - geological uncertanty

Pyroclastic flows are full of lava, hot rocks and gas so they flow like water but a lot faster! It's the pyroclastic flow that most people think about as an "eruption" and it is the pyroclastic flow that produces death and destruction very quickly.

2. ## Earthquake is a shaking of the ground caused by the sudden breaking and shifting ...

For this reason, the ground generally shakes less farther away from the focus. There are two chief kinds of seismic waves: (1) body waves and (2) surface waves. Body waves, the fastest seismic waves, move through the earth. Slower surface waves travel along the surface of the earth.

1. ## Seismology is the study of earthquakes and how the waves emitted from them travel ...

oceanic crust, continental crust is up to 90km thick in areas, whereas oceanic crust at most is 10km thick. The lithosphere overall is between 70 and 125 kilometers thick. The lithosphere s really just a thin skin as the earth's diameter is about 12800km.

2. ## Describe the frequency, origin and distribution ofearthquakes at mid-ocean ridges, ocean basins, subduction zones ...

Divergent boundaries mostly occur on the sea floor and therefore the earthquakes that happen at these boundaries are distributed along the boundary. This means that the distributions of earthquakes at divergent boundaries are at shallow depths, where the crust is been pulled apart.

• Over 160,000 pieces
of student written work
• Annotated by
experienced teachers
• Ideas and feedback to