test 2

1. test 2 • mean: 75, median: 79 • multiple choice: 42 questions, 2 points each • short answer: 4 questions, 4 points each • 100 total: circled number inside front cover of blue book • answer key to multiple choice is posted on blackboard under ‘test materials’

2. Earthquakes and Related Phenomena chapter 8

3. EQ terms • fault: break (fracture) in a rock • rupture: breaking of rock along a fault • hypocenter (focus): rupture point of rock below surface • epicenter: point on earth surface directly above hypocenter • scarp: topographic (elevation) display of a ruptured fault

4. how to quantify the size of an event? • describes the energy released by an EQ • different types based on different parameters: • Modified Mercalli Scale: based on how much people felt the ground shake • very subjective, but all we have for past events • scale from I to XII • Richter magnitude: based on size (amplitude) of largest seismic wave • easy to measure • scale from 0 to ~9 • moment magnitude: based on amount of energy released by an event • more accurate because takes into account specific factors about the fault (slip area, rigidity of rock, etc.) • scale from 0 to ~10

5. how do we record events? • observations, journals (Mercalli) • seismograms (Richter) • record movement (displacement) of earth in three directions • vertical (up and down) • horizontal (left and right) • transverse (front and back) • known information about specific fault (moment)

6. how to interpret the scales • Richter magnitude (M) is predominantly used • for each 1 step up in M, there are ~1/10 of the number of events from before • for each 1 step up in M, there is an ~10x increase in ground shaking • for each 1 step up in M, there is an ~30x increase in energy release

7. where do EQ’s happen?

8. where do EQ’s happen • plate boundary EQ’s: • transform boundaries (California) • convergent boundaries (Japan) • intraplate EQ’s • seismically active regions not directly linked to plate boundaries (rifts) • New Madrid (Missouri, Tennessee, Arkansas): Reelfoot rift

9. where do EQ’s happen?

10. fault types • strike slip • right lateral • left lateral • reverse • hanging wall up • normal • footwall up

11. fault activity • use geologic record to determine when was the latest rupture on a fault • active faults: movement in the last 10000 years • partially active: movement in the last 1.65 million years • inactive: no evidence of movement within the last 1.65 million years • public policy relationship: US Nuclear Regulatory Commission: “active” faults are movement within the last 50000 years

12. activity measurements • recurrence interval (how often a fault is active) found by: • paleoseismic data: average time between events, according to geologic data • slip rate: average movement (displacement) divided by movement per year • seismicity: averaging time between historical earthquakes

13. seismic waves • actual displacement and shaking of earth is due to seismic waves (energy release when fault ruptures) • seismic waves travel several kilometers per second through the earth • types: • P waves (primary, compressional) • S waves (secondary, shear) • surface waves

14. P waves • faster of seismic waves types • can travel through solids, liquids, and gasses • moves in same direction as wave motion • moves like pushing a slinky together and pulling it apart

15. S waves • slower than P waves • can only travel through solids • moves perpendicular to wave motion • moves like a cracking a whip or a snake along the ground

16. surface waves • slowest seismic wave type • complex vertical and horizontal motion patterns • cause most damage to buildings, etc.

17. how we record EQ’s (again) • each wave type has a characteristic size • by looking at a seismogram that recorded an EQ, we can see when the different wave types arrived

18. how do we know where EQ’s happen? • can analyze multiple seismograms to tell where an EQ’s hypocenter was • we know the time the difference between the amount of times the different wave types took to get to the seismogram • we know how long it takes those wave types to travel a certain distance

19. ground material effects • different earth material respond differently to seismic waves • amplitude: vertical movement of shaking • hard rocks resists shaking, unconsolidated sediments are vulnerable to shaking

20. ground acceleration • ground shaking is recorded as acceleration • how fast the shaking of the ground changes speed (horizontally and vertically) • recorded in comparison to gravity acceleration (9.8 meters/second2) • if an earthquake has 1g ground acceleration, that means the shaking of the ground was increasing at 9.8 meters/second2 • an earthquake of M7.0 has ~25%g ground acceleration

21. EQ cycle • aftershocks (following a large event) • seismic inactivity • strain accumulation • foreshocks • main event

22. effects of EQ’s • shaking and ground rupture • immediate, damage to buildings, loss of life • fires • from gas leaks, electrical lines, etc. • disease • from dust with bacteria or contaminated drinking water

23. effects of earthquakes • tsunamis

24. estimating risk • US Geologic Survey (USGS) produces ‘seismic hazards maps’ for the US and other regions • maps are based on the percentage likelihood that a certain size event will happen in a given timeframe

25. seismic hazard maps • shows a 2% chance that the color percent gravity shaking will be exceeded in the next 50 years • public policy relationship: ability to properly place emergency response facilities and specify building codes

26. forecasting methods • we use ‘forecast’ instead of ‘predict’ because: • forecast includes the percentage chance that an event will happen • predict indicates that the event will happen • public policy relationship: how much of a risk does a possible event need to be before we take action?

27. forecasting methods: foreshocks • foreshocks • M9.0 EQ in Japan occurred on a Friday, on that Wednesday they had experienced a M7.2, and on that Thursday they experienced three M6.0+ • should we have forecasted a major event?

28. forecasting methods: radon gas • radon gas is naturally present in rocks • it is believe that before an EQ, rocks expand and take in water • radon is removed from the rock as the water leaves • the radon gas rises to the top of the atmosphere, and can be seen as a temperature increase

29. forecasting methods: radon gas

30. forecasting methods: seismic gaps • based on the idea that the entire length of a fault should experience similar amount of seismic activity

31. forecasting methods: past EQ’s • develop by Dr. Alan Kafka of BC • EQ’s are more likely to occur where EQ’s have occurred in the past

32. response to EQ hazards • US National EQ Hazard Reduction Program • develop an understanding of the EQ source • determine EQ potential • predict effects of EQ’s • apply research results • what can we do with new information we gather?

33. adjustments to EQ activity • structural protection • stricter building codes • flexible gas and electric lines • EQ warning systems • ability of dangerous materials to shut themselves off • land use planning • putting important structures (schools, hospitals, government offices) away from active areas • putting emergency response facilities close enough to be available to those who will most likely need them

34. Japan • death toll will be over 10000 • tsunami, flooding, fires • nuclear concern • building codes to allow tall buildings to sway but not break • how much should the US help another country?