Quiz 2 Flashcards
What do jerky starts and stops in plate motions directly cause?
Major earthquakes
What are some indirect benefits of earthquakes?
- give us uplift in landscape, which allows rivers to have principle sources of water
- if not, land would erode to tide level and diversity in flora and fauna wouldn’t exist
Where do earthquakes occur?
At plate tectonics (ex: San Andreas)
When do rocks break?
When stress is greater than rock strength.
What does energy released during an earthquake cause?
Causes faults to form (“plane of slip”) and can generate frictional heat
What do s the difference in time between the arrival of the P and S waves tell us?
Precise location of earthquake (epicenter)
What did Charles Richter call the total energy released during an earthquake?
Magnitude of the quake
How much more energy is released with each increase in one magnitude?
Logarithmically, by factor of just over 30 times more energy released.
What happens when the period of an earthquake save matches that of a building?
The seismic energy is added to the oscillation of the building, resulting in an increase in the swaying of the building (as long as it is at the natural period).
What does a creep meter measure?
Movement in a specific localized area.
Measures when faults slip (recording amount of motion).
Highly sensitive and covers about 10 meter zone
What changes in water wells in the days preceding an earthquake?
Sudden drop in water levels in wells.
What is the energy source for earthquakes?
Gravity.
What is an earthquake?
A sudden release of energy in earth’s crust or upper mantle, usually caused by movement along fault plans or by volcanic activity and resulting in generation of seismic waves
What are seismic waves?
The waves of energy caused by sudden breaking of rock within the earth or an explosion. They are the energy that travels through the earth and is recorded on seismographs.
What is the earthquake rupture patch?
Starts at he focus (depth)
Distance between focus and epicenter?
How are earthquakes measured (and compared?
- magnitude: The amount of energy released (magnitude is stable, regardless of distance)
- intensity: the effects of ground motion on people and structures (intensity varies depending on closeness to epicenter)
Explain the modified Mercalli scale?
MMI
- Descriptive scale of earthquake effect intensity (at different locations)
- distinguished by use of Roman numerals
- how to find info? Descriptive; based off experiences
- check 2/9/17 packet
Explain the Richter magnitude scale.
A base-10 logarithmic scale, which defines magnitude as the logarithm of the ratio of the amplitude of the seismic waves to an arbitrary, minor amplitude
- based on movement of instrument
- deficient at high energies(big earthquakes)
- Now use the Moment Magnitude Scale
Explain the moment magnitude scale. Equation?
MMS or MvW
Used by seismologists to measure earthquakes in terms of energy released.
think of volcanoes-looking image
moment=
rock rigidity x fault area that slipped x slip distance
What is a foreshock? What is an aftershock?
Foreshock:Smaller earthquakes that occur shortly (usually up to days or weeks or months) before a major earthquake.
Aftershock: occur after major earthquake
(Foreshock)The fault movement that produces the large shock typically leaves areas of relieved stress or strain build up along the fault. (Aftershock) subsequent failures in these areas produce aftershocks
-many will lie along fault plane, but may occur on other nearby faults
Why is an aftershock especially dangerous?
Because the buildings and roads are already weakened.
Landslides and mudslides are also effects.
- ground failure
- liquefaction
- landslides
- tsunamis/seiches?
How is friction important in faulting?
Faulting = fault rupture
Friction along the fault slows, prevents, o from arrests motion
Even motion of lithospheric plates is slowed by friction along their boundary
Rough areas may break off and fault can move
What is stress?
Stress = force/unit area
Pressure or tension exerted on plates
When stress on a fault becomes greater than strength of rock, fault ruptures and moves
Define fault.
A fracture or system of fractures along which movement has occurred parallel to the fracture surface in association with a loss of cohesion
-i.e. Earth’s crust on one side of fracture moved relative to rocks on opposite side
What is a footwall?
Block of rock that lies on the underside of an inclined fault
You would walk on the footwall.
Footwall motions downwards ↙️↘️
What is a hanging wall?
Block of rock that lies above an inclined fault
You would hang your lamp from the hanging wall
Motions upward ↗️↖️
What are the different types of faults?
Dip Slip - Normal & Reverse (or thrust) fault
Strike Slip - Left Lateral or Right Lateral Fault
Oblique Slip Fault
Dip Slips
Move Up & Down
Normal Faults: hanging wall block moves down relative to footwall
- stretched and thins crust
- common along divergent margins and extending intraplate areas
Reverse (or Thrust) Faults: hanging wall block moves up relative to footwall
- shortens and thickens crust
- common along convergent margins and relatively nearby areas
Strike Slips
Move horizontally
Left Lateral Strike-Slip Fault: rocks across the fault from you move to the left
Right Lateral Strike-Slip Fault: rocks across from you move to the right
FOR BOTH:
-blocks of rock move past each other
- conservative (no to little extension or shortening)
- many are transform faults along plate boundaries like San Andreas fault
Oblique Slip
Move horizontally AND up and down
Oblique Slip Fault: hanging wall moved in both strike slip and dip slip directions relative to footwall
What is deformation?
Includes strain and translation along dislocations (e.g. faults)
What is strain?
Any change in shape or volume of a material.
Where is epicenter?
On the ground, above the focus.
Convergent Plate boundaries. What kind of faults? Associated depths?
One plate slides under another
-remember the three types
Continental-continental
Oceanic-continental (ex: Andes Mtns)
Oceanic-oceanic
- faults: reverse (or thrust)
- Associated earthquake depth: Shallow to deep (depending on which type?)
Divergent boundaries. Faults? Associated earthquake depth?
May be intraplate
Faults: normal! and transform
Associated depth: mostly relatively shallow earthquakes
Ex: East African Rift
- early stages of divergent margin - plume and diverging plates - normal faults - shallow earthquakes
Transform boundaries. Depth? Example?
Oceanic type:
Faults: strike-slip (that cut through entire lithosphere)
Ex: Mid-Atlantic Ridge
-right-Lateral strike slip because plate is growing. Ridge is not offset
Continental type:
Faults: strike-slip (that continue through entire lithosphere)
Ex: San Andreas fault
-right-Lateral strike slip
- Associated depth: shallow foci. Commonly powerful
- distribution of earthquakes suggest that where transform fault cuts continental crust a system of parallel faults develops rather than single fracture (like San Andreas)
What is a triple junction?
Located where three tectonic plates come together
Plume: East African Rift
Plates diverging
Cascadia - North America, Juan de Fuca & Gorda, Pacific plates
Can earthquakes occur within a plate?
Yes. Intraplate earthquakes.
Can be larger in magnitude, but are less frequent.
What is the most common type of fault in be Basin and Range province?
Normal faults.
It’s a physiographic province. Characterized by abrupt changes in elevation, alternating between arrow faulted mountain chains and flat arid valleys or basins. (Here, earth is extending).
Stressed have literally pulled apart western part of North American plate, forming basins and ranges
Define earthquake focus and epicenter
Focus: within the earth. Where earthquake is coming from
Epicenter: on ground, above focus
Explain elastic rebound theory.
Energy which is released (which was stored as strain in rock) is converted to seismic waves which radiate from the earthquake focus.
These seismic waves cause ground shaking and can be measured using seismometers.
Strain builds up and then is released during an earthquake. Offset results.
think of the fences moving
What is a P wave and how does it move?
P waves (aka compressional waves)
Deforms rocks through change in volume
Movement: push/pull fashion(compressional motion)
-Consists of alternating pulses of compression and expansion acting in direction in which wave is traveling
Compressive waves that do not produce much damage.
Can move through any type of material (liquids and solids)
Faster (Travel at almost twice the speed of S waves)
Typical speed: 6 km/s
In air, P waves take form of sound waves, so move at speed of sound (330m/s) at sea level
-some people report hearing earthquakes because of object rumbling
What is an S wave and how does it move?
S waves are shear waves that arrive second (of body waves)
Typical speed: 3.5 km/s
Movement: side-to-side
-ground moves at right angel to direction of travel of wave through earth
Deform ground perpendicular to travel
Unable to pass through air and liquids (ex: water and magma) (this is how we know earth’s core is molten)
Types of body waves?
P and S waves
Types of surface waves?
Love and Rayleigh
Both named after mathematicians
Surface Waves
Guided by and restricted to the Earth’s surface
Much of the ground shaking that causes damage to structures is from surface waves
Analogous (comparable) to ocean waves because they are restricted to vicinity of a free surface, such as at Earth’s surface, like ocean waves
Travel more slowly than either P or S waves
What is a Love wave and how does it move?
Fastest surface wave
Movement: side-to-side
Confined to surface of crust; produce horizontal motion
Named after: A. E. H. Love
What is a Rayleigh wave and how does it move?
aka: ground roll
Rolls along ground, like waves rolls across lakes or oceans
Movement: up and down, and side-to-side in same direction wave is moving
Most of shaking felt from earthquake is due to Rayleigh wave
Can be much larger than other waves
Named after: John William Strutt, Lord Rayleigh
Within what types of material is ground shaking high and low?
High: on mud (absorbs vibrations, so effect/damage is greater)
Low: bedrock (vibrations just pass through)
How do you locate an earthquake?
As wavefront expands from earthquake, it reaches more distant seismic stations (think of activity)
When earthquake occurs, we mark the times at which the wavefront passes each station
We use the wave arrival times to locate the earthquake
*use distance as the radius of a circle centered on location of seismometer and draw circle –> location of epicenter is at intersection of circles
What are the active and Quaternary Fault classes?
Active: faults that moved in last 10,000 years
-capable of having an earthquake
Quaternary: active faults and potentially active faults that have been recognized at surface and which have evidence of movement during Quaternary time period
- need to be watched, but less of concern
- studied for seismic hazards
What are three types of primary damages from earthquakes?
Strong ground motion:
- results from movement of seismic waves through earth, especially near surface - can completely destroy buildings - loose material/mud shakes a lot, bedrock much less
Surface faulting
- where Fault breaks surface buildings can be split, roads disrupted, and anything that lies on or across fault broken apart.
- even movement of continuous small earthquakes (creep) can result in/contribute to structural damage.
Subsidence/uplift
-large areas may arise or fall due to an earthquake or mountain building process
What are three types of secondary earthquake damage?
Liquefaction: water saturates near surface layer of sand or mud to change rapidly from solid to liquid
Landslides
Tsunamis/Seiches
Explain Liquefaction.
Water-saturates near surface layer of sand or mud to change rapidly from solid to liquid
Three things needed:
1) loose ground
2) water saturated
3) harsh shaking
Ground Failure
General term to reference landslides, liquefaction, Lateral spreads, and any other consequence of shaking that effects stability of ground.
What should you do to protect yourself during an earthquake if you are indoors? Outdoors?
INDOORS:
DROP ground, take COVER by getting under sturdy table or other piece of furniture, and HOLD ON until shaking stops.
- If no table/desk, cover face and head with arms and crouch in an inside corner of building away from windows, bookcases, tall furniture that could fall on you
- move as little as possible
- stay indoors until shaking tops and then exit (then use stairs to exit in case of aftershock, power outages, etc.)
- fire alarms might go off
OUTDOORS:
-find clear spot (away from buildings, power lines, trees, streetlights) and drop to ground. Stay until sharif stops
- if in vehicle, pull over to clear location and stop. Avoid bridges and overpasses and power lines if possible. Stay inside with seatbelt fastened until shaking stops. Then, drive carefully still avoiding ramps and bridges that may have been damaged
- if power line falls on vehicle, don’t get out. Wait for assistance
- if in mountainous area or near unstable slopes or cliffs, be alert for falling rocks and debris. Landslides often triggered.
What are some things you can do to prepare for an earthquake?
Learn fire evacuation and earthquake safety plans for all of buildings you occupy regularly
Pick safe places in each room of your home, workplace and/or school. (Under piece of furniture, against interior wall away from things that could break/fall)
Practice DROP, COVER, and HOLD ON in each safe place
Keep flashlight and sturdy shoes by each person’s bed in case earthquake strikes in middle of night
Make sure home is securely anchored to its foundation (not in our control)
Bolt and brace water heaters and gas appliances to wall studs
Bolt bookcases, china cabinets, and all other furniture to wall studs
Hang heavy items away from beds, couches, anywhere people sleep/sit
Brace overhead light fixtures
Install strong latches or bolts on cabinets. Large, heavy items should be closest to floor
Learn to shut off gas valves in home and keep wrench handy for that
Learn your area’s seismic building standards and land use codes before beginning construction
Keep and maintain emergency supplies kit in easy-to-access location
Does Las Vegas have an earthquake hazard?
Yes.
What is a tsunami?
From Japanese “harbor wave”
Series of ocean waves that sends surges of water, sometimes reaching heights of over 100 ft. onto land.
Long high sea wave caused by earthquake, submarine landslide, or other disturbance
What causes a tsunami?
Earthquakes
Landslides
Volcanic eruptions
Meteorite impacts
At what speed do tsunamis travel?
500 miles (805 km) per hour
About as fast jet plane (or a little faster)
How many waves make up a tsunami?
Usually composed of a series of waves, called wave train, so it’s destructive force may be compounded as successive waves reach shore
Why are tsunami waves slower near shore?
Because the ocean bottom is shallower.
In what direction does a tsunami travel from its source?
Waves radiate in all directions
What are three factors that determine how devastating a tsunami will be?
Direct action (primary damage) causes most damage
-depends on wave height, local offshore topography, and orientation of coast relative to orientation of incoming wave
Tides
-tsunami hitting high tide is more dangerous than at low tide
Proximity to causing fault, landslide or volcanic, collapse
-closer spatial association allows greater damage especially because of lack of time to warn citizens.
What causes the local local height of a tsunami go vary from place to place?
Topography of sea floor near coast majorly determines how large those waves become and what places get hit harder than others.
What is runup?
A measurement of the height of the water onshore observed above a reference sea level. VERTICAL measurement.
- Occurs when a crest in the tsunami wave travels onto shore.
- Tsunamis will commonly travel much farther inland than normal waves
What is tsunami inundation?
The result of a tsunami tracking a long distance inland, a HORIZTONAL measurement.
-flooding can occur for up to 300 meters or more covering then area with debris
How does the tsunami warning system work?
Best defense against any tsunami is early warning that allows people to seek higher ground
Maintains a web of seismic equipment and water level gauges to identify tsunamis at sea
Two types:
Tsunami watch: Albert issues to areas outside area. Watch may be upgraded to warning or cancelled depending on severity of tsunami
-area included in watch is based on magnitude of earthquake (earthquakes over M7.0, watch area is 1 hour tsunami travel time outside warning zone. For over M7.5, watch area is 3 hours tsunami travel time outside warning zone)
Tsunami Warning: indicates that tsunami is imminent and that coastal locations in the warned area should prepare for flooding.
- initial warning is typically based on seismic information alone
- earthquakes over M7.0 trigger warning covering coastal regions within 2 hours tsunami travel time from epicenter. When magnitude is greater than 7.5, wanted area is 3 hours tsunami travel time.
- as water level data showing tsunami is recoded, warning will either be cancelled, restricted, expanded incrementally, or expanded in event of major tsunami.
What are three important aspects of mitigation?
1) Evacuation
2) Building Restrictions
- reduce potential property and human damage by restricting building in low-lying areas
3) Education
