Need help with number 1, 2, 6, 8, 9, 12, 13, 16, 17, 20 . assignment due today.

Question

Need help with number 1, 2, 6, 8, 9, 12, 13, 16, 17, 20 . assignment due today. please help me

Key Terms aftershock asthenosphere body wave Richter scale mantle Modified Mercalli Intensity fault creep focus foreshock inner core intensity liquefaction lithosphere lower mantle secondary (S) wave Mohoroviëie discontinuity seismogram seismology seismic sea wave (ts seismograph surface wave GEODe: Earths GEODe: Earth Science (Moho) earthquake elastic rebound moment magnitude outer core inforcing key concepts epicenter fault primary (P) wave Forces within Review Questions 1: What is an earthquake? Under what circumstances do 9.Which type of seismic wave causes the greatest destnuc earthquakes occur? tion to buildings? 2. How are faults, foci, and epicenters related? 3. Who was first to explain the actual mechanism by which 10. Most strong earthquakes occur in a zone on the globe known as the earthquakes are generated? 4. Explain what is meant by elastic rebound. 5. Faults that are experiencing no active creep may be con- 11. In 1988 an earthquake in Armenia caused approximately 25,000 deaths. A year later an earthquake in the Bay Area of California, having the same Richter magnitude of 69 had only 62 deaths. Suggest a reason for the greater los of life in the Armenian event. sidered safe. Rebut or defend this statement. 6. Describe the principle of a seismograph. 7. Using Figure 10B, determine the distance between an 12: An earthquake measuring 7 on the Richter scale releass earthquake and a seismic station if the first S wave ar- rives 3 minutes after the first P wave. about a magnitude of 6. times more energy than an earthquake with 8. List the major differences between P and S waves. 13. List three reasons why the moment magnitude scale gained wide acceptance among seismologists.

Explanation / Answer

1. An earthquake is an major demonstration of the power of the tectonic forces caused by endogenetic thermal conditions of the interior of the earth.

Earthquakes are caused mainly due to disequilibrium in any part of the crust of the earth. A number of causes have been assigned to cause isostatic imbalance in the earth's crust such as

i. volcanic eruptions

ii. faulting and folding

iii. upwarping and downwarping

iv. gaseous expansion and contraction inside the earth and

v. Plate movements.

2. the vertical and horizontal movements caused by endogenetic forces result in the formation of faults and folds which in turn cause isostatic disequilibrium in the crustal rocks which ultimately causes earthquakes of varying magnitudes depending on the nature and magnitude of dislocation of rock blocks caused by folding and faulting. In fact, sudden dislocation of rock bodies caused by both tensile and compressive forces trigger immediate earth tremors due to sudden displacement of rock blocks. The place of the occurence of an earthquake is called focus and the place which experiences the seismic event first is called epicenter, which is always perpendicular to the focus and located on the earth's surface.

6. Seismograph is an instrument which records the seismic waves generated by the occurrence of earthquake. It calculates the location and magnitude of an earthquake.

Principle : The basic principle on which seismograph works is to understand the up-down motion of a seismometer (a ground-motion detection sensor) by visualizing a weight hanging on a spring.

8. P-wave : this is also called primary waves or longitudinal or compressional waves, are analogous to sound waves wherein particles move both to and fro in the line of propagation of the ray. This koves in fastest speed through solid materials.

S-wave : This is called secondary waves or transverse or distortional waves. These are analogous to light waves in which particles move at right angles to the rays. This wave can not pass through liquid material and the speed is less than the P-wave.

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