Chapter 4- Environmental Geology

Foreshocks and Aftershocks

-smaller earthquakes that precede and postdate the mainshock -depend on when the main shock comes -these are really only known after the big earthquake occurs

Bind Faults

-some active faults that do not extend to the surface

What is the standard deviation of 3,4,5?

0.82

S-Waves

-Shear (transverse) or secondary waves -as the wave front passes, material move perpendicular to the direction the wave is moving -produce an up and down motion (sideways shear) -can ONLY pass through solids -have a higher amplitude than P-Waves

Population

-a finite or infinite collection of items under consideration -a sample comes from a hypothetical infinite population possessing constant statistical properties -EX: streamflow

Sample

-a finite set of observations of the random variable

Seismograms

-a graph output by a seismometer -record of the ground motion at a measuring station as a function of time -the unique physical properties of those seismic waves have allowed geologists to decipher a good deal about the Earth's interior

Trendline

-a line drawn through the dots that would show a trend -line is a simple linear regression trendline through a scatterplot

Linear Regression

-a technique to determine the relationship between two random variables

L (Love) Waves

-cause the ground to move side to side as the wave front passes

Strain

-change in shape or location of the rocks due to the applied stress (deformation)

Which is the mean of 1,2,9?

4

What is the median of 2,3,5,6,9,2?

4

Among all stresses, which is the strongest?

Compressive strength

If the deformation was temporary, what kind of behavior is it?

Elastic behavior

When the normal force is increased, the shear stress will decrease

False

There are about 5,000 earthquakes every year in Japan, what is the main reason?

Japan is close to Japan Trench, where the pacific plate is subducting beneath the Eurasian plate

According to the elastic rebound model, earthquakes are caused by energy released when

highly stressed (bent) rocks breaks and abruptly moves

Which of the following describes the stratified sampling method?

pick a spring discharge value from annual maximum discharge series

Surface waves are produced by ____

P and S waves reaching the surface

Compressional seismic body waves are _____

P waves

Among all stresses, which is the weakest?

Shear strength

2011 Tohoku Eathquake

-Japan Trench where pacific plate is subducting underneath the Eurasian plate at about 9 cm/year -the convergence of these two plates means Japan experiences frequent earthquakes (~5000 /year) -March 11 2011 Japan's strongest earthquake with magnitude of 9-9.1 -released energy about 600 times more than the atomic bomb dropped on Hiroshima during WWII -triggered powerful tsunami waves up to 130 ft and travels at up to 435 mph for 6 miles inland -toughest and most difficult crisis for Japan -for than 19,000 killed and $360 billion -tsunami disabled the power supply and cooling system of Fukushima Daiichi reactor as 3 cores were largely melted -one of the most dangerous nuclear accidents since Chernobyl

Types of Sampling

-Random Sampling: the likelihood of selection of each member of the population is equal (pick any streamflow value from a population) -Stratified Population: population is divided into groups, and then a random sampling is used from each individual group (pick a streamflow value from annual maximum series) -Uniform Sampling: data are selected such that the points are uniformly far apart in time or space (pick streamflow values measured on Monday night) -Convenience Sampling: data are collected according to the convenience of experimenter (pick streamflow during summer)

Mohr Failure Envelope

-a mathematical model describing response of brittle materials such as concrete or rubble piles, to shear stress as well as normal stress

Probability

-a measure of how likely an event will occur -EX: flipping coin with head or tails -a number of expressing the ratio of favorable outcome to all possible outcomes

Random Variable

-a quantity used to represent the change of uncertainty (usually written X) -it is a variable whose possible values are numerical outcomes of a random phenomenon

Sample Space

-a set of possible samples that can be selected from a population -EX: instantaneous streamflow, annual maximum streamflow, daily average streamflow

Waves

-a vibration or disturbance in space -can transfer energy without transferring matters -are classified by what they move through (medium) or by how particles move through them (transverse and longitudinal)

Reverse or Thrust Fault

-an upward relative movement of the hanging wall -lithosphere is exercising compressional forces -associated with shortening and thickening of earth's surface -reverse faults create some of the world's highest mountains like Himalaya mountains and Rocky Mountains (collision convergent) -convergent plate boundaries -smaller angle is a thrust fault and larger angle is reverse fault

Deterministic Model

-analysis of geologic process using deterministic processes -physical and hydrological parameters are based on physical relations of the various components -does NOT consider randomness, a given input produces the same output - A leads to B

Fault

-any surface in the brittle lithosphere -there is displacement of one side relative to the other along faults

Fault Zone

-brittle structure that slip occurs on several faults within a band of definable width

R (Rayleigh) Waves

-cause the ground to move up and down as the wave front passes

Plastic Behavior

-deformation is permanent

Elastic Behavior

-deformation is temporary -it can return to its original size and shape when stress is removed

Geological Models

-deterministic model -stochastic model

Normal Faults

-downward movement of the hanging wall relative to the footwall -these fault are normal because they follow the gravitational pull of the fault plane -lithosphere is exercising tensional forces -associated with extension and thinning of earth's surface -typical divergent boundaries

Finding the Epicenter with Seismometers

-each station time interval between the arrival of the first P waves and the first S wave at that location -the travel-time graph determines each station's distance to the epicenter -We can locate the epicenter of an earthquake with 3 different station recordings -a circle with a radius equal to the distance to the epicenter is drawn around each station and where all 3 circles intersect is the earthquake epicenter

Seismometers (Seimographs)

-earthquake detection and recording instrument -a modern seismometer records the movement of the Earth in relation to a stationary mass on a rotating magnetic tape

Elastic Rebound Theory

-events leading up to, during, and right after earthquake can be explained by this theory -rocks behave elastically like a stretched rubber band -all objects, including rocks, can be deformed elastically up to a certain point before the stress on them overcomes the material's internal strength (friction) -Time 1: rocks of both sides of a fault move with no significant strain -Time 2: the relative motion between blocks on either side causes the deformation and store elastic energy -Time 3: frictional/ cohesional forces holding the rocks together is overcome and there is slippage at the weakest point (the focus) -Time 4: vibrations occur as the deformed rock springs back to its original shape and this is where there is elastic rebound and earthquakes -most earthquakes are produced by the rapid release of stored energy in rocks that have been subjected to stress -the energy can be generated by a sudden dislocation of segments -the energy is released to surroundings as the rocks snap back into their original shape -most large earthquakes are produced by this phenomena along pre-existing faults -the rupture itself may remained buried, invisible underground

Regression

-figuring out how much one thing depends on another things

Tectonic Creep (Fault Creep)

-gradual movement along a fault that is not accompanied by perceptual earthquakes -similar to other earthquakes, slow earthquakes are produced by fault rupture (low friction on the fault) -EX: slow earthquakes along the Cascadia subduction zone -the difference is that the rupture, rather than being nearly instantaneous, can last from days to months

Standard Deviation

-measure of how spread out numbers are 1. find the mean 2. subtract the mean from each score 3. square each deviation 4. add the square divisions and divide the sum by the number of scores

Mechanical Waves

-need medium, requires the particles to vibrate -water waves, sound waves, seismic waves

Strike-Slip Fault

-one along which the displacement is parallel to the strike (horizontal) -transform faults

Dip-Slip Fault

-one in which the displacement is vertical, up or down in the direction of the dip -normal fault -thrust/reverse fault

Histogram

-plot of bars whose height is the number, or fraction, of data falling into one of several intervals of equal width -dividing the number of occurrences with the total number of points will give probability mass function -made by binning data (group)

P-Waves

-primary wave or compressional waves -as the wave front passes, material first compresses then dilates in the direction that the wave is moving -the fastest waves -can pass through solids, liquids, gasses

Probability Distribution

-set of probabilities associated with the values in a random variable's sample space

Ductile Materials

-small region of elastic behavior and a large region of non-elastic behavior before they fracture -gold or aluminum

Brittle Materials

-small to large region of elastic behavior, but only a small region of plastic behavior before they fracture -concrete, glass, bone

1906 San Francisco Earthquake

-stuck northern California coast at 5:12 AM on Wednesday April 18th with magnitude 7.9 -the main shock lasts about 42s and foreshock was 25s -remembered as one of the worst and most deadly earthquakes in history of US -more than 3,000 deaths and 80% of city was destroyed -About 300,000 out of 410,000 population were left homeless -fires that burned out of control afterwards were even more destructive (~80%) -long pressure to change development with insurance

Event

-subset of sample space -EX: daily streamflow > 100 cfs

Dip

-the angle of the plane makes with the horizontal -a measure of the steepness of slope of the plane

Variance

-the average of the squared differences from the mean -standard deviation squared

Refraction

-the bending of a wave as it enters a new medium -caused by a change in the speed of the wave -greater change in speed = more bending of the wave

Compressive Strength

-the capacity of rock to withstand compressive stress (be pushed together) -reduce size or so -strongest among all stresses -unconfined compressive strength test

Strike

-the compass orientation of the line of intersection of a bed or fault with a horizontal plane

Stochastic Model

-the description and modeling of hydrological phenomena based on probability -statistical analysis of hydrologic/environmental data -A may lead to B (30%) or C (25%) or D (45%)

Amplitude (A)

-the distance from crest or trough from the midpoint

Wavelength

-the distance from crest to crest or trough to trough

Velocity (v)

-the distance traveled by a wave crest in one period -v= wavelength / T

Stress

-the force that results from plate tectonic movement 1. compressive (push together) 2. Tensional (pull apart) 3. Shear (tearing)

Regression Line

-the line that best fits the data in terms of having the smallest overall distance from the line to the points

Rock Strength

-the max stress that a rock can withstand before it fails

Tensile Strength

-the maximum tensile stress (be pulled) it can take before failure -stretched -20-40% of CS

Median

-the middle value, so first we have to sort the list in numerical value (central value) -separates higher and lower bounds -Better to represent central tendency

Strike-Slip Fault

-the movement is parallel to the fault strike (horizontal direction) -lithosphere is experiencing shearing forces -vertical fault plane -Left lateral or right lateral -Most famous is San Andreas Fault -transform plate boundaries

Frequency (f)

-the number of waves that passes as fixed point per sec -F= 1/T

R-Squared

-the percentage of the dependent variable variation that a linear model explains -tells you just how good the trendline fits -the higher the value of r-squared the more successful is the model in explaining Y variation

Resonance

-the phenomenon of increased amplitude that occurs when the frequency of a periodically applied force is equal or close to a natural frequency of another -the two object vibrate at the same frequency -amplitude increase

The Focus (Hypocenter)

-the point of initial breaking or rupturing within the earth

Shear Strength

-the strength of the rock against the failure in shear -20% of CS -dominant model of rock failure -the combination of cohensional (C) and frictional stresses at which the rock type fails

Seismology

-the study of earthquake waves -dates back almost 2,000 years where the earliest seismometer was made by Zhang Heng in 132 AD made from copper, the pendulum in earthquakes

Average (Mean)

-the sum of all values divided by the number of values -sum of samples / number of samples

Epicenter

-the surface location directly above the focus -In most earthquakes, is the point where the greatest damages take place

Period (T)

-the time it takes a wave to travel a distance equal to a wavelength (sec)

Earthquake

-the vibration of earth produced by the rapid release energy in the form of mechanical waves -movements that produce earthquakes are usually associated with faults

Surface Waves

-travel along the surface -R-Waves and L-Waves -slower than body waves -they move along the surface of the earth and have a greater amplitude than body waves so they are DESTRUCTIVE

Electromagnetic Waves

-travel through matter or empty space -radio waves, microwaves, x-rays

Body Waves

-travel within the body of the earth -P-Waves and S-Waves -Difference between P-waves and S-waves depends on the material density, P-Waves are typically faster

Seismic Waves

-when a fault ruptures, rocks break apart suddenly and violently, releasing stored elastic strain energy in the form of seismic waves in all directions

Reflection

-when a wave hits a surface through which it cannot pass, it rebound back -change direction, does not change velocity or frequency

Interference

-when two or more waves combine together -Constructive Interference: two individual same waves will combine to a larger wave -Destructive Interference: Two opposite wave combined to a smaller wave

The Principle of Linear Superposition

-when two or more waves come together, the result is the sum of the individual waves

Normal faults are commonly associated with ____

divergent plate boundaries

To the rocks ____ deformation happens deep beneath the surface where heat and pressure are high

ductile

Which block is located above the fault plane?

hanging wall

Seismic wave is ____

mechanical wave

Which one can be a better representative of the central location of the household income data?

median

Which of the following can describe the regression line best?

regression figures out how much one thing depends on another

For the same data set, higher R-squared values represent _____ difference between the observed data and the fitted values

smaller

Which one is the measure of how spread out the numbers are?

standard deviation

Which of the following models considers the randomness?

stochastic model

In a fault when the displacement is horizontal then the type of fault is called

strike-slip fault

Normal faults are produced when the lithosphere is experience ____ force

tensional

The focus of an earthquake is_____

the primary point of rupture in the earth's crust and origin of the earthquake

We collect all monthly precipitation in 2020 and find that the mean value of monthly precipitation is much greater than the median, which of the following situation is possible?

there are lots of rainy weather days with extremely heavy precipitation in 2020

Sides to Fault

1. Footwall: the block below the fault plane 2. Hanging Wall: the block above the fault plane