Lecture Outline Wednesday-Monday April 18 23, 2018

Transcription

1 Lecture Outline Wednesday-Monday April 18 23, 2018 Questions? Lecture Final Exam Lecture Section 1 Friday May 4, 8:00-10:00am Lecture Section 2 Friday May 4, 3:10-5:10 pm Final Exam is 70% new material Chapters 13,14,16,15,18,8,Interlude D and 30% Chapters 1-7,9,10 The Final Exam will cover lecture and reading assignments 65 Multiple Choice, Computer Graded Bring Pencil and Photo ID Final Exam Review Session: When? We will talk on Monday or Wednesday Key Points for today Earthquakes What are they, what causes them and where are they likely to occur? Be familiar with earthquake vocabulary: What is the difference between an earthquake epicenter and focus? How are earthquakes located and what is meant by there magnitude? Why do earthquakes affect areas differently? Earthquake related websites Chapter 8 A Violent Pulse: Earthquakes Why should you be concerned with earthquakes? Does the west coast of WA, OR, CA have anything to worry about? Why would they? What are your perceptions of an Earthquake? What will you feel? How might it affect you? What are some of the hazards associated with an earthquake? Earthquakes and Plate Tectonics are linked. Earthquakes occur at all boundary types (modern and ancient), and in some cases within the plates. 95% of energy from earthquakes affect narrow zones along plate edges Some earthquakes are quite deep (subduction zones) What causes earthquakes?

2 Earthquakes are vibrations of the ground created by the accumulating in deformed rocks. Where does that strain energy come from? It is the accumulation of stress energy stored as the rocks are deformed by tectonic pressure. As the rocks are deformed strain energy is stored. When enough stress is applied so that it overcomes the strength of the rock, the rock breaks producing a fault. That sudden release of strain energy moves out in all directions from the break as seismic waves of an earthquake. Earthquakes are generated by all fault types - Normal, Reverse, Thrust, and Strike-slip What is an earthquake? Fault - crack in Earth where slip occurs Earthquake - Earthquake focus (hypocenter) - fault slip location - surface location of focus fault scarp - cliff formed from vertical slip on fault - small earthquakes that follow an initial earthquake in same vicinity foreshock - small earthquakes that sometimes precede a large one by few days Earthquakes occur at all different fault types - Normal, Reverse, Thrust, and Strike-slip Seismic Waves The is transmitted through the rocks in all directions in the form of waves. Seismology is the study of earthquakes and is based on the 2 main types of seismic waves. Body Waves Surface Waves Body Waves Waves ( Waves) waves expand and contact ( ) wave (~6-7 km/sec ; ~4 mi/sec) Waves ( Waves) waves move up/down, side to side (~3.5 km/sec;~2 mi/sec) Waves wave (~2.5 km/sec; 1.5 mi/sec) travel along of the earth side to side up and down

3 Measuring Earthquakes - Device that records seismic wave motion. Seismogram record of shaking Recipe for locating an earthquake s epicenter P-waves(fastest )& S-wave travel at different speeds So you can use this difference to locate earthquakes! 1. Measure time between P and S wave on seismogram 2. Use travel-time graph to get distance to epicenter (need seismograms from at least 3 locations) 3. Draw circle on a map with radius of that distance 4. Three or more circles should intersect at EQ! Measuring Earthquakes scale based on relative destruction and observations by people Delineates 12 intensity levels The scale of 1-10 based on amplitude on seismogram, each number represents x the shaking power x increase in energy released with each number Works best on CA rocks. The Richter scale uses the maximum amplitude to determine the earthquake s magnitude at a standard distance form the earthquake epicenter (100km) depth of fault total amount of slip (movement) on fault The Richter and Moment magnitude produce roughly the same numerical value; the moment magnitude scale is preferred by seismologists. Average Earthquakes per year Magnitude Effects Average/yr <2.5 not felt but 900,000 recorded minor 31, potentially 100 destructive major earthquakes 20 > 8.0 great earthquakes 1 every 5 years Examples of Recent Earthquakes (6.8), WA (2001) Spokane (4.0), WA (2001) (6.8), CA (1994) Loma Prieta (7.1), CA, (1989) (7.2), Japan, (1995)

4 Why would earthquakes with nearly the same intensities (magnitude) produce such different results? 1. Different type of earth movement is possible with different faults. Earthquakes are associated with, both and as well as other areas. Normal - Divergent earthquakes Strike-slip -Transform earthquakes Reverse - Convergent shallow to deep earthquakes Hotspots shallow earthquakes 2. The ground can amplify the shaking. - Building on is the best - Building on is the worst 3. Depth to the focus 4. of earthquake shaking 5. "Constructive wave interference"or "lensing" Comparing Northridge and Kobe earthquakes there are many similarities, (the exact numbers are not important) Northridge Kobe Magnitude Duration 15 sec 20 sec Depth ~11 miles ~11 miles Estimated Kobe Earthquake damages totaled $95 billion to $147 billion, many times the $15 billion damage inflicted by the 1994 Northridge Earthquake. (the exact numbers are not important) The physical properties are not the only factor that affect how much damage is done to an area by an earthquake. Man plays the largest role. Lecture Outline Friday April 20, 2018 Questions? Key Points for today What are some of the side affects caused by earthquakes? Why do some earthquakes occur within plate interiors? Can earthquakes be predicted? What you can do to reduce your risk from earthquakes? What you can do to prepare and protect yourself during and after an earthquake? Effects of Eathquakes - Unconsolidated sediment becomes water saturated and flows. Seiches - Water sways back and forth over enclosed body of water (lakes, swimming pools).

5 Tsunami - Fast moving. Ground motion displaces sea water above, generates wave. Move at speeds up to 800 km/hr (500 mi/hr), up to 100 ft high. Is there a potential tsunami hazard in Washington? Other possible causes for a Tsunami: - landslides - volcanic island collapse Landslides (Earthquake-induced mass wasting) So do landslides caused by earthquakes only cause property damage? Liquefaction - Unconsolidated sediment becomes water saturated and flows. - can cause mass movements and sinking of structures Ground Shift (Uplift and Subsidence) can be caused by earthquakes Fires are common after earthquakes, broken gas pipelines and broken water mains are contributing factors Earthquakes Within Plates - Possible Causes? Reactivation of faults at old plate boundary Ex. Old faults that have been reactivated by erosion (release of overlying pressure) sediment load (increase in overlying pressure) rainfall human induced Future continental rift zones??????? Human induced earthquakes 1. Example: Hoover dam: 600 earthquakes in 10 years after dam was built. (increased water pressure lubricated faults) 2. Example: Dumping of toxic waste chemical weapons Rocky Mountain Flats, CO So if man can induce earthquakes does this mean man can control or diminish the intensity of an earthquake? What do you think? What would be the consequences? Can earthquakes be predicted? Some animals seem to sense an EQ is coming. World's first successful earthquake prediction: China: Feb 4, Magnitude hours advance warning. - based on animal behavior But then: July 28, 1976: Magnitude ,000 died. No prediction made -- Not too reliable "Recurrence Interval" -

6 There is a relationship between the size of the earthquake and the recurrence interval the between earthquakes, the the probable quake. (energy builds up for longer period of time) Seismic Hazard map for North America - takes into account the intensity of seismic shaking and proximity to active faults. Seismic Risk map for the US - describes the damage that one can expect. It takes into account the seismic hazard but also the population density, building type. So what can we do to reduce the risk from earthquakes? about hazards emergency practices buildings designed to withstand shaking gas lines valves that automatically shutoff redundant water systems to fight fires Earthquake warning and emergency response coordinated by real-time seismic detection devices Lecture Outline Monday April 23, 2018 Video: The Day the Earth Shook (NOVA) This is approximately 35 minute video so I will start as soon as possible so we can have a short discussion afterwards. If more time is needed we will continue the discussion in Wednesday s class. As you view this video please note and answer the following questions. You will be responsible for this material for the Final exam. 1. List the similarities and differences between the Northridge and Kobe earthquakes. Similarities: Differences:

7 2. What are some of the factors which contributed to the higher number of fatalities resulting from the Kobe earthquake? 3. Why did some tall buildings pancake (certain floors collapse)? 4. What are some measures that can be taken to prevent the freeways and some buildings from collapsing? (Build for earthquake protection) 5. What is liquefaction? 7. How are P and S waves used to prevent additional fatalities from train accidents? In what other ways could this same concept be used? 8. Question for thought and discussion. You receive and accept a lucrative job offer, but you will live on the west coast in a high risk seismic area. What are some considerations you should take into account when finding a place to live and precautions you should take at your work place? Home: Work: