1. An earthquake is the vibration of the Earth produced by the rapid release of energy. Earthquakes occur as rock is deformed it bends and stored elastic energy. Once the rock is strained beyond its breaking point slippage occurs, releasing the stored up energy. The slippage allows the deformed rock to snap back. The Earthquake is caused by the vibrations as the rock elastically returns to its original shape.
2 .Faults, foci, and epicenters, are associated by faults are the large fracture in the Earth in which earthquakes occur along, foci is the place where the earthquake originates, and the epicenter is the location on the surface directly above the focus.
3. Earthquakes occur only in the rigid lithosphere, not in the plastic asthenosphere. This is because of the elastic rebound that occurs in the rigid lithosphere that produces the earthquakes. When strain is applied to the rocks energy is built up and later released with strippage. Then the rock springs back t its original position called elastic rebound which produces the earthquake. Since the asthenosphere is liquid this can not occur.
4. Faults that are experiencing no active creep may be considered "safe." This statement is not true since the areas that are locked segments are building up strain that could result in a major earthquake.
5. The principle of seismograph is the inertia of the suspended mass tends to keep it motionless, while the recording drum, which is anchored to bedrock, vibrates in response to seismic waves. The stationary mass provides a reference point from which to measure the amount of displacement occurring as the seismic wave passes through the ground below.
6. The motion produced by P waves compared with the movement created by S waves is that P waves push and pull rocks in the direction the wave is traveling while S waves shake the particles at right angles to their direction of travel.
7. P waves move through solids, liquids, and gases, where as S waves move only through solids because solids, liquids, and gases resist a change in volume when compressed and will elastically spring back once the force is removed therefore allowing the P waves or compressional waves to travel through S waves change only the shape of the material that transmits them and gases and liquids do not resist shape change, S waves cannot be transmitted through them.
8. The type of seismic wave that causes the greatest destruction to buildings are surface waves.
9. The distance between an earthquake and a seismic station if the first S wave arrives 3 minutes after the first P wave is 1.8 x 10 km.
10. Most strong earthquakes occur in a zone n the globe known as the Benioff zone.
11. Deep-focus earthquakes occur several hundred kilometers below the trenches.
12. Earthquake magnitude differs from earthquake intensity by magnitude is the total amount of energy released during an earthquake at a particular place. Intensity is affected by distance to the epicenter and the nature of the surface materials.
13. For each increase of one on the Richter scale, wave amplitude increases ten times.
14. An earthquake measuring 7 on the Richter scale releases about 30 times more energy than an earthquake with a magnitude of 6.
15. Three factors that affect the amount of distribution caused by seismic vibrations are the intensity and duration of the vibrations, the nature of the material upon which the structure rests and the design of the structure.
16. The factor that contributed most to the extensive damage that occurred in the central portion of Mexico City during the 1985 earthquake was the ancient lake bed of soft sediment that unlined portion of the city and amplified the ground motion.
17. The 1988 Armenian earthquake had a Richter magnitude of 6.9, far less than the magnitude of the great quakes in Alaska in 1964 and San Francisco in 1906. The loss of life was greater in the Armenian event because of poor construction practices. Many of the fallen structures in the region were made of precast concrete slabs that were held together by metal hooks that fell apart the way they were put together.
18. In addition to the destruction created directly by seismic vibrations, three other types of destruction associated with earthquakes are tsunamis, fire, land slide, and ground subsidence.