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GEGN_468_Exam_2

Earthquake A ground shaking caused by a sudden release of energy within the subsurface. Shearing of the rockmass releases pent up energy.
Explain elastic rebound theory as related to earthquakes :Elastic rebound theory Energy accumulates slowly. Warping starts to occur and the ground slowly deforms. Once the internal strength of the ground is exceeded, there is a sudden release of energy and the ground deforms brittlly.
Focus Start of earthquake at depth along a fault trace
Hypocenter geoscientists best guess at where the focus is
Epicenter Location of focus but brought directly up to the surface. Does not have to lie on a fault trace
Origin time time of initial motion
Travel time time for waves to reach point of observation.
Seismic wave: a propogational disturbance that transmits energy without transmitting mater. (Collision between particles that transmits energy). The velocity of the oscillation is small, but the velocity of the propagating wave disturbance is fast.
Compare and contrast P and S waves Similarities Body waves (fastest groups of waves)
P-waves: Primary waves
P-waves: pressure waves
P-waves (example of waves): sound waves (pool example).
P-waves motion compressing a slinky motion (only displacing in direction of movement (no displacement in yz direction). Compression and expansion in one direction.
P-waves relative speed fastest of all waves. Almost 2x faster than S-waves P-waves materials: solids and liquids
S-waves secondary waves
S-waves shear waves
S-waves (motion): transverse motion (up and down) like moving a slinky up and down.
S-waves (displacement): Displacement perpendicular to motion, but displacement can be vertical or horizontal.
S-waves materials : solids only, since liquids like water donâ€™t have shear strength
NOT A QUESTION BUT I ADDED IT Compare and contrast Rayleigh and Love waves similarities Similarities: Surface waves (slowest groups of waves) These cause the damage in earthquakes
NOT A QUESTION BUT I ADDED IT Compare and contrast Rayleigh and Love waves differences Rayleigh: Similar to ocean waves (including attenuation (effects get muted out) at depth), except these die out because of earth material elasticity while ocean waves die out because of lack of gravity force.
NOT A QUESTION BUT I ADDED IT Love waves (motion): squiggly side to side motion.
Love waves (reason for why they occur): due to a low velocity layer overlying a high velocity layer see velocity note below.
Deterministic produces how many outcomes 1
Love waves (relative speed): Slightly faster than Rayleigh waves
ALSO NOT PART OF THIS QUESTION Velocity note part 1 Material type controls wave velocity. Well cemented, high grain to grain contact, tightly packed materials (hard rocks) tend to have higher velocities. HARDNESS itself does not define velocity
ALSO NOT PART OF THIS QUESTION Velocity note part 2 For example, salt, a soft to medium sedimentary rock, has a relatively high velocity because its structure leads salt particles to be well connected. Energy is allowed to ping off of well connected structures easily, leading to high velocity.
ALSO NOT PART OF THIS QUESTION Velocity note part 3 Poorly cemented, low grain to grain contact, loosely packed materials (loose soils) tend to have lower velocities.
Seismometers: : Instrument that detects seismic waves. How it works: Pen writing on a rotating drum in vertical or horizontal direction.
Seismographs Instrument that records motion
Seismograms The record created by the seismography
Seismometer detects it, seismograph records it, seismogram is the record of it Seismometer detects it, seismograph records it, seismogram is the record of it
Use a travel-time chart to determine the distance of an earthquake epicenter from a seismograph station To do this you need to know either the travel time of the p-waves and s-waves (or the difference in travel time between these waves) at one station. Then the plot can be used and you can go down to the horizontal axis to find distance
Estimate the most likely epicenter location (and the uncertainty associated with the estimation) using a graphical methods based on data from three or more seismograph stations. Need 3 stations for epicenter on surface. Need 4 locations for epicenter at depth. Take the distance from the epicenter to the station and draw circles using radii. The intersection of these circles is the most likely epicenter location.
Compare and contrast the earthquake intensity and magnitude and their respective scales Magnitude is a measurement of the total energy released by an earthquake It is controlled by stiffness, stress-strain relationship, and style of rupture (how brittle or ductile the failure was). There is only one magnitude for one earthquake.
Magnitude scales (general): part 1 Uses seismogram to find: arrival time, amplitude, frequency, and duration.With correction for: distance (from source to receiver), mechanical characteristics of rockmass (stiffness, ability to transmit energy), and characteristics of seismogram.
Magnitude scales (general): part 2 More objective than intensity Logarithmic scale: an 1x increase in M = 10x increase in amplitude from seismogram.
Magnitude scales: Richter scale Based on amplitude of groundshaking recorded by seismograph. See next question for negatives
Magnitude scales: Moment magnitude rigidity*area*displacement Rigidty: shear modulus of rigidity of rockmass Area: area over which rupture occurred Displacement: amount of displacement of ruptured segment Can use 2nd equation to get to moment magnitude mw unitless
Intensity part 1 Intensity is a measurement of the disruptive capacity of an earthquake at a specific site. It is also a measure of the effects of a shock as observed at a specific site. Intensity varies as a function of distance from the epicenter and nature of rock/soil
Intensity part 2 There can be multiple intensity values for one earthquake. Larger, broader spanning earthquake intensities are recorded where rock masses are: Uniform, broadly spanning, unweathered, and unbroken by previous earthquakes and faulting.
Intensity Scale: Modified Mercalli scale how much skaing did people feel on a scale
Explain the limitations of the Richter scale (general) The Richter scale was developed in California so it has bias towards near surface earthquakes traveling through unconsolidated sediment
Limitation of Richter scale 1 : Underestimates strong earthquakes M>7. Does not take the duration of shaking into account. (only considers amplitude).
Limitation of Richter scale 2 : Underestimates depth of earthquakes because the resulting surface waves of deep earthquakes tend to be smaller than shallow earthquakes.
Limitation of Richter scale 3 : Underestimates the distance of earthquakes (earthquakes over 600 km away) because it over assumes attenuation of s-waves.
When estimating slope stability, Explain why modeling earthquake loading as a static force leads to a conservative estimate PART 1 When estimating slope stability, the peak ground acceleration (PGA) is used as an input to the back-of the envelope calculation. This results in a conservative estimate because the PGA is the maximum ground acceleration that occurs during the earthquake.
When estimating slope stability, Explain why modeling earthquake loading as a static force leads to a conservative estimate PART 2 but in actuality the majority of the acceleration from the earthquake is smaller than PGA. This solution only treats dynamic loading as a constant force that is equal to the maximum force or acceleration caused by the earthquake.
List the factors that control earthquake induced liquefaction potential 1 Acceleration of earthquake
List the factors that control earthquake induced liquefaction potential 2 Pre-existing connectivity of soil grains before eq acceleration
List the factors that control earthquake induced liquefaction potential 3 Depth to surface (ie amount of confinement)
List the factors that control earthquake induced liquefaction potential 4 Location of groundwater table and saturation of soil
List the factors that control earthquake induced liquefaction potential 5 Looseness of soil
List the factors that control earthquake induced liquefaction potential 6 degree of compaction
List the factors that control earthquake induced liquefaction potential 7 Type of soil
List the factors that control earthquake induced liquefaction potential 8 age of deposit
List the factors that control earthquake induced liquefaction potential 9 costal deposit
Assess the relative earthquake risk of different structures/areas given information on local geology and construction practices . Larger, broader spanning earthquake intensities are recorded where rock masses are: Uniform, broadly spanning, unweathered, and unbroken by previous earthquakes and faulting. Risk = probability*consequence
Describe the general process of earthquake hazard assessment Collect data -> bring the data into your area of interest -> analyzed data and the probability that hazard occurs/affects the area.
Explain the differences between MCE MPE, and MDE: MCE Maximum credible earthquake Largest EQ that may reasonably be expected to occur along a given fault or seismic source under the current tectonic setting Recurrence interval typically ~2,500 yr
Explain the differences between MCE, MPE, and MDE: MPE Maximum possible earthquake The largest EQ a fault is expected to generate within a specific time period of interest (e.g. 30 or 100 years)
Explain the differences between MCE, MPE, and MDE: MDE Maximum design earthquake The EQ selected for design or evaluation of a structure; this EQ would generate the worst-case loading scenario which is expected for the structure.
Given information about seismicity in a given area and a specific design application in that area, suggest and justify a Maximum Design Earthquake for that application To do this consider: the type of structure the degree of safety required at site The return periods for the earthquake
Compare and contrast deterministic and probabilistic analyses in the context of engineering geology problems: deterministic One outcome, based on historical data, and assumes future events are indicative of what will happen in the future.
Compare and contrast deterministic and probabilistic analyses in the context of engineering geology problems: probabilistic Many outcomes "probabilities of excellence", uses intensity or magnitude frequency relationships to produce probability curves for various levels of ground levels of motion.
Describe the different components of risk Probability consequence Spatial impact (SI) Temporal impact (TI) Vulnerability (V) Loss (E)
Explain the conditions under which risk mitigation is appropriate Mitigation is appropriate if: mitigation cost is < the reduction in risk cost (if mitigated). In tunneling example, this occurs where Install support cost is equal to risk cost.
Recall principles of risk acceptability 1 A risk associated with a hazard should not be significant compared to other risks which a person is exposed to in everyday life.
Assess risk (2 techniques) One way to assess the acceptability of risk is to use the frequency vs fatalities plot. Another way is to use the cost vs support class plot.
Recall principles of risk acceptability 2 Risks associated with voluntary actions can be larger than those of involuntary actions
Recall principles of risk acceptability 3 People will often tolerate higher risks than they deem acceptable if they are unable to address/reduce the risk due to financial or other limitations.
Recall principles of risk acceptability 4 Tolerable risks are though to be higher for naturally occurring hazards than engineered hazards
Deterministic evaluation steps ID hazard sources Select controlling sources Shift controlling sources into area Evaluate PGA Find 1 result
Probablisitic evaluation steps ID study area Study reoccurrence rates Apply ground motion-acceleration relationships Develop probabilities of exceedance
Risk Assessment Question 1 What can cause harm?
Risk Assessment Question 2 How often?
Risk Assessment Question 3 What can go wrong, with what severity?
Risk Assessment Question 4 Expected damage?
Risk Assessment Question 5 So what?
Risk Assessment Question 6 What should be done?
Created by: spencersischo19
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