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’

Earthquakes and Related Phenomena chapter 8

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

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

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)

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

where do EQ’s happen?

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

where do EQ’s happen?

fault types strike slip – right lateral – left lateral reverse – hanging wall up normal – footwall up

fault activity use geologic record to determine when was the latest rupture on a fault active faults: movement in the last 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 years

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

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

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

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

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

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

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

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

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/second 2 ) – if an earthquake has 1g ground acceleration, that means the shaking of the ground was increasing at 9.8 meters/second 2 – an earthquake of M7.0 has ~25%g ground acceleration

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

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

effects of earthquakes tsunamis

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

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

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?

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?

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

forecasting methods: radon gas

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

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

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?

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

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