Environmental Engineering Chapter 6 Homework Instructors Manual India Deep Waste

Learning Objectives

After reading and studying this chapter, students should

▪ Understand the relationship of earthquakes to faulting

▪ Understand how the magnitude of an earthquake is determined

▪ Know the types of earthquake waves, their properties, and how strong ground motion is

produced

▪ Understand how seismic risk is estimated

Chapter Summary

This extensive chapter on earthquakes covers a diverse array of subjects related to earthquake processes

and earthquake hazard reduction. The chapter begins with a discussion of earthquake measurement and

rating. Several subsequent sections deal with earthquake locations and earthquake processes, in

particular the process of faulting and types of faults, controls on the amount of shaking experienced as a

result of earthquakes, the components of the earthquake cycle, human influences on earthquake

processes, and the direct and indirect effects of earthquakes. The chapter closes with discussions of the

pitfalls and promises of earthquake prediction, and of typical human responses to earthquake hazards.

Chapter Outline

I. Introduction to earthquakes

A. Approximately 1 million earthquakes felt per year

B. Earthquakes can be compared in three ways

2. intensity of shaking

3. resulting impact on people and society

II. Earthquake magnitude

A. Earthquake location

2. Focus

B. Magnitude

2. Richter magnitude

a. great earthquakes

C. Earthquake catastrophes

1. Catastrophic (great) earthquakes

a. devastating events that destroy large cities and kill thousands

III. Earthquake intensity

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Earthquakes and Related Phenomena

Earthquakes

A. Modified Mercalli Scale

B. Shake map

1. shows damage following earthquake

IV. Plate boundary earthquakes

A. Interplate earthquakes

V. Intraplate earthquakes

A. Occur within plates

B. Examples

2. Charleston earthquake of 1886

C. Intraplate earthquakes in the eastern U.S. are generally more damaging and are felt over a larger

VI. Earthquake processes

A. Faulting

1. faulting is analogous to sliding two rough boards past one another

3. slip rate: long-term rate of movement along a fault

5. faults are seismic sources

B. Fault types

1. strike-slip

2. dip-slip

3. buried faults

4. faults and rock folding

C. Fault zones and segments

2. Earthquake segments

D. Active faults

1. active faults: faults active within last 10,000 years

3. inactive faults: not active in last 1.65 million years

4. paleoseismicity: determination of earthquake history along a fault, on basis of geologic record

Chapter 6 – Instructor’s Manual

E. Fault activity

1. Slip rate

2. Recurrance interval

a. May be determined by:

2) slip rate

3. Methods of estimating fault activity

a. investigating landforms

F. Tectonic creep

1. gradual displacement not accompanied by felt earthquakes

3. generally slow and continuous, but may be discontinuous and variable

G. Slow earthquakes

2. a recently recognized Earth process

3. may make significant changes over time

VII. Earthquake shaking

A. Three factors that determine shaking at some location

2. distance from the epicenter

B. Types of seismic waves

1. P-waves

3. surface waves

a. created by seismic waves reaching the Earth’s surface

C. Seismograph

1. seismogram: written or digital record of an earthquake

a. continuous line showing vertical or horizontal motions recorded by a seismograph

D. Frequency of seismic waves

1. frequency: how many waves pass in a given length of time

3. shaking hazards to buildings

1) nearby earthquakes described as “jolting”

2) distant earthquakes described as “rolling”

E. Material amplification

1. different Earth materials respond differently to seismic shaking

Earthquakes

2. examples

F. Directivity

1. amplifies shaking intensity in the direction of fault rupture

G. Ground acceleration during earthquakes

1. strong ground motion can be described as the velocity at which waves travel through rocks or on

surface

2. damage to structures related to two factors

1) measured as a fraction or multiple of gravity

4. buildings must be designed for strong accelerations

H. Supershear

2. Effect

3. Examples

I. Depth of focus

1. varies from few kilometers to almost 700 km

a. deepest earthquakes occur near subduction zones

2. depth of focus strongly influences damage caused by earthquakes

VIII. Earthquake cycle

A. A hypothesis stating that elastic strain drops after an earthquake and reaccumulation of strain

before the next event

2. elastic rebound

a. “snap” of rocks back to original shape as elastic strain is recovered

B. Stages of the earthquake cycle

1. long period of seismic inactivity following a major earthquake and associated aftershocks

3. period of major foreshocks

4. major earthquake

C. Dilatancy-diffusion model

1. Rocks dilate as strength increases

3. Effect of fluid pressure

a. fault-valve mechanism

IX. Earthquakes caused by human activity

A. Several human activities are known to increase or cause earthquake activity

1. Reservoir-induced seismicity: loading of the Earth’s crust and increased water pressure by

2. Deep waste disposal: disposing of liquid waste through disposal (injection) wells

a. Rocky Mountain Arsenal (Denver, CO)

3. Nuclear explosions

a. underground nuclear explosions in Nevada

X. Effects of earthquakes

A. Shaking and ground rupture

2. magnitude of disaster related to intensity

B. Liquefaction

1. transformation of water-saturated sediment from solid to liquid state

C. Landslides

D. Fires

1. dust from landslides can spread spores

3. death of animals and people buried in debris produces potential sanitation problems

F. Regional changes in groundwater and surface water

2. Effects over large areas

3. Vertical deformation

G. Tsunamis

XI. Earthquake risk and earthquake prediction

B. Estimation of seismic risk

1. regional hazard map

a. shows probability of an event or the amount of shaking likely to occur

C. Sources of data for estimates of probability

1. Geology

3. Geodesy

D. Short-term prediction

1. forecasting specifies a relatively short period of time in which an event is likely to occur

2. precursory phenomena

a. pattern and frequency of earthquakes, such as foreshocks

b. preseismic deformation of the ground surface

XII. Toward earthquake prediction

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1. a good deal of information is currently being gathered regarding possible precursory phenomena

2. medium- to long-range forecasting has progressed faster than expected

a. hazard evaluation

b. probabilistic analysis of areas along active faults

XIII. Sequence of earthquakes in Turkey: can one earthquake set up another?

A. East-to-west series of earthquakes on north Anatolian fault during 20th century

1. described as “falling domino scenario”

B. Clusters of earthquakes apparently separated by several hundred years without earthquakes

C. Understanding of earthquake clustering is important in planning for future seismic events

XIV. The response to earthquake hazards

A. Earthquake hazard reduction programs

1. major goals of U.S. program

a. develop an understanding of the earthquake source

b. determine earthquake potential

B. Adjustments to earthquake activity

2. reliable protective measures can be taken

a. structural protection

C. Earthquake warning systems

1. warn of arrival of damaging earthquake waves from event several hundred kilometers away

3. many concerns, including false alarms and liability

D. Perception of earthquake hazard

1. many people suffer mental distress after a major earthquake

a. many families moved away from Los Angeles after major earthquakes

E. Personal and community adjustments: before, during, and after an earthquake

1. community level

2. personal level

Answers to Review Questions and Critical Thinking Questions

Review Questions

2. The Richter magnitude is determined through measurement of the amplitude of waves on

seismograms.

5. Magnitude is the amount of energy released, determined either by seismogram interpretation (Richter)

6. A fault is a fracture along which rocks have moved.

8. In an anticline, the fold is upward, while, in a syncline, the fold is downward.

10. Tectonic creep is the movement, usually relatively constant, of two fault blocks along a fault without

felt earthquakes.

12. P-waves are compressional waves (pushing and pulling rock particles as they move), while S-waves

are shear waves (up and down or side-to-side motion perpendicular to the direction of wave travel).

13. A shake map shows the extent of potential damaging shaking following an earthquake. They are

14. Material amplification is the increase of wave amplitude by unconsolidated sediments.

15. The earthquake cycle is the cycle of elastic strain buildup and release. Following a major

17. Some of the major effects of earthquakes include shaking, liquefaction, landslides, fire, disease,

tsunami, and regional change in land elevation.

19. Precursor phenomena include preseismic deformation, emission of radon gas, seismic gaps, and

anomalous animal behavior.

20. The major goals of earthquake hazard reduction programs are to develop an understanding of the

21. The main adjustments people make are community-level adjustments (building codes, education) and

Critical Thinking Questions

1. The first step in this task should involve basic discussions about the nature of earthquake hazards and

2. A response to this question should include a discussion of both the scientific uncertainties of