Question

1.What are the zones of the earth’s interior? (Start from the surface and identify the different layers all the way to the center. Include a description of the asthenosphere.

2.What is an earthquake? What causes them?

3.Name and describe the different types of earthquake waves (what material will they travel through; what kind of wave motion is involved).

4.How is the epicenter location determined?

5.When we hear on the news that an earthquake has a magnitude of 7, what does this mean? What scale is being used? How does the scale work? What information is needed for the calculations?

6.Around the world, where do most earthquakes occur? Why in these locations?

7.What are the main factors that determine the amount of building destruction caused by an earthquake?

Answer 1

1. Earth is divided into four difediffe layers genarally:

• Crust: The upper most portion on which we live is crust. It is the thinnest of all layers. The thickness of this layer varies as the thickness of oceanic crust is about 5-10km. Wheras, the crust is much thicker in continental mountainous regions where the thickness ranges from 30-45km.But the thin oceanic crust is denser than the thicker continental crust and hence, the continental crust ''floats" more on the mantle. The crust is further divided into two layers.
  • The Lithosphere: The solid upper crust which is made up of rocks and is the coolest of all layers, and on which we live is the Lithosphere. Its depth extends from 70-100km.
  • The Asthenosphere: This layer of the crust lies just below the lithosphere and extends upto to the upper layer of the mantle. The thickness of this layer is about 700 km. This layer is hot and malleable, and act as a lubricating layer allowing the lithosphere to float over it.
• Mantle: Below the crust lies the largest layer of the earth- the mantle. Mantle accounts for 84% of Earth's volume. It is about 1800 miles thick. The core of mantle is comprised mostly of iron, but as silicate rocks. The temperature of upper mantle rangers from 500-900 degree Celsius which increases to a 4000 degree Celsius in the lower mantle. The mantle act as a plastic as at very high temperature and pressure the rock is deformable at geological time scale.
• The Outer Core: This layer of the earth is 2,300 km thick and extends upto 3,400 km into the earth. The temperature of this layer varies from 4030 degree Celsius to 5730 degree Celsius. Scientists believe that 80% of outer core is comprised of iron, the nickel and other lighter elements. These are present in this core in their liquid form and in less viscosity. This feature of outer core makes it spin faster than the entire earth, and thus, because of this difference in spinning velocity, along with convection and turbulent flow of iron, the Earth's magnetic field is created.
• The inner core: This is the centermost layer of the earth with a radius of 1220 km. The temperature in this layer reaches upto 5400 degree Celsius. It is mainly comprised of iron and nickel but also has heavier elements as gold, silver platinum, palladium and tungsten. Despite of higher temperatures due to intense pressure these metals are in solid form in the inner core.

2. An earthquake is a sudden tremor or shaking that is felt on the surface of the earth due the release of potential energy blocked up in the rocks of the earth. The earthquake occurs due to movement of rocks upon a sudden fracture in them, or due to volcanic eruption or also, due to man-made reasons.

3. The different types of earthquake waves are:

• P waves- These are primary waves that travels from the point of origin of earthquake. These are longitudinal waves and can travel through any medium (solid, liquid, or gas). They are the fastest of all earthquake waves.
• S waves- These are secondary waves, they have higher amplitude but cannot travel in liquid or gas only on solid surface. They travel in transverse form and are destructive.
• Surface waves: These are final waves and occur in two forms: when longitudinal they are called Rayleigh, and when they are transverse are called Love. These seismic waves occurs along the boundary or between the two substance as rock or water. They travel slower than P and S waves but have greatest of the amplitude,and hence, is the most destructive of all.

4. The epicenter location is determined by the records on the seismograph.The seismologists use the difference between the time taken by P and S waves to travel as recorded in the seismograph to calculate the epicenter.