Exam 3 Flashcards
Geologic time provides a frame of reference for understanding:
Rocks Fossils Geologic structures Landscapes Tectonic events Change
Deep Time
the immense span of geologic time. Human history is miniscule when compared against deep geologic time.
James Hutton (1726–97)
Geologic time. A Scottish physician and farmer, was the first to articulate the Principle of Uniformitarianism. He realized that vast amounts of time were necessary for Earth processes to create rocks. For this discovery, he is called the “Father of Modern Geology
Principle of Uniformitarianism
is paraphrased “The present is the key to the past.” His idea was that the processes we see today are the same as those that operated in the past. Geologic change is slow; large changes require a long time.
Relative dating of geologic materials is
is a qualitative method that was developed hundreds of years ago.
Numerical dating
is a quantitative method that was developed over the last 60 years.
Modern geologists routinely use both ________ & _________ dating methods.
Relative & Numerical
Physical principles: uniformitarianism
States that the processes observed today were the same in the past. Ex= mud cracks. Sir Charles Lyell
Sir Charles Lyell
wrote the textbook Principles of Geology in 1830–33. He established a set of physical principles for deciphering the relative ages of Earth materials to aid in unraveling Earth history. The principles are still in use today.
The Principle of Original Horizontality
states that because sediments settle out of a fluid by gravity, they tend to accumulate horizontally. Sediment accumulation is not favored on a slope. Hence, tilted sedimentary rocks must be deformed.
States that in an undeformed sequence of layered rocks, each bed is older than the one above and younger than the one below. Younger strata are on top; older strata are below.
The Principle of Superposition
The Principle of Lateral Continuity
observes that strata often form in laterally extensive horizontal sheets. Subsequent erosion dissects once-continuous layers.
The Principle of Cross-Cutting Relations
holds that younger features truncate (cut across) older features. Faults, dikes, erosion, etc., must be younger than the material that is faulted, intruded, or eroded. (A volcano cannot intrude rocks that aren’t there yet.)
The Principle of Baked Contacts
observes that an igneous intrusion cooks the invaded country rock. The baked rock must have been there first (it is older). A chill margin is formed within the igneous intrusion at the contact from rapid cooling.
Explains the occurrence of one rock fragment within another. Inclusions are always older than the enclosing material. Weathering rubble must have come from older rock. Fragments (xenoliths) within an igneous intrusion are older.
The Principle of Inclusions
Relative age determination
Folded sediments Intrusions Granite Basalt A fault Xenoliths Inclusions A baked contact
The geologic history must have progressed as follows:
- A sequence of horizontal strata accumulates. Superposition dictates that 1 is the oldest.
- An igneous sill intrudes. Inclusions of 4 and 5 in the sill confirm that it is younger
- Folding, uplift, and erosion take place. Folding occurs after the intrusion because the intrusion is itself folded.
- A granitic pluton intrudes the folded sediments. Xenoliths fall into magma, which bakes the country rock.
- A fault cuts the granitic intrusion and the folded sediments.
- A basalt dike cuts across the block, feeding a volcano. The dike cools; the volcano and the land are eroded.
The Principle of Fossil Succession
describes the predictability of fossil distribution through time. Fossils, which are often preserved in sedimentary rocks, are extremely useful as time markers for relative age dating. This is because specific fossils are only found within a limited, often narrow, time range.
Species evolve, exist for a time, and then disappear forever. The first appearance, range of existence, and final extinction are useful for relative dating. Fossils succeed one another in a known order. Time periods are recognized by their fossil content.
Fossil Succession
The fossil range
describes the first and last appearance of a species. Each fossil has a unique range. Sometimes the ranges of unique organisms overlap.
Index fossils
are diagnostic of a particular geologic time.
An ____________ is a time gap in the rock record, from nondeposition or erosion.
unconformity
The three types of unconformity.
angular unconformity, nonconformity, and disconformity.
Angular unconformity
James Hutton was the first to recognize the significance of angular unconformities. They represent a huge gulf in geologic time. Horizontal marine sediments are deformed by orogenesis. Then, the mountains are completely removed by erosion. After a renewed marine invasion, a new generation of horizontal sediments are deposited.
Siccar Point, Scotland
Where Hutton deduced the special significance of the angular unconformity. Vertical Ordovician sandstone is overlain by gently dipping Devonian redbeds. The missing time is 50 million years.
A nonconformity
An unconformity where igneous or metamorphic rocks are capped by sedimentary rocks. Crystalline igneous or metamorphic rocks were exposed by erosion. After a renewed marine invasion, sediment was deposited on this eroded surface.
A disconformity
An unconformity within sedimentary layers due to an interruption in sedimentation. Disconformities are often subtle.
The succession of rocks in the Grand Canyon can be divided into ________, based on notable changes in rock type and included fossils.
formations
Describes the sequence of strata. Formations can be traced over long distances. Several formations may be combined as a group.
A stratigraphic column
Lithologic correlation is
based on rock type in a particular region. Several rock columns kilometers apart look slightly different but can be correlated by matching rock types. Geologists can see that some units thicken, some thin, and even pinch out. The overall thinning toward column C suggests that a basin tapered in this direction.
Was the first to note that rock units could be matched across distances. He noted that the same rock types, with the same distinctive fossils, occurred in a similar order in different parts of Great Britain. After years of work, he compiled the first geologic map in 1815.
William “Strata” Smith
Geologic Time Scale Correlation
The composite stratigraphic column was assembled from incomplete sections found in different places across the globe. By correlation, the strata in the different columns can be stacked in a sequence that spans almost all of Earth history.
Geologic Time Scale
The composite geologic column is divided into time blocks that are the equivalent of Earth ‘s calendar
The large time blocks are called ______. They represent hundreds to thousands of Ma
Eons
______ are subdivisions of an eon (65 to hundreds of Ma).
Eras
Periods are subdivisions of an ________
era (2 to 70 Ma)
_______ are subdivisions of a period (0.011 to 22 Ma)
epochs
Life first appeared on Earth ______. Early life consisted of single-celled organisms.
~3.8 Ga
Life evolution can be framed against the _______
geologic column
Around 700 Ma, __________ life evolved.
multicellular
Cambrian explosion
Around 542 Ma marks the first appearance of hard shells. Shells increased fossil preservation. Life diversified rapidly thereafter.
O2 from bacteria built up in the atmosphere by ___.
2 Ga
Many relative ages can be assigned actual numerical dates because of ___________________
radiometric dating or geochronology
radiometric dating
This technique measures certain radioactive isotopes in minerals that decay at a known, fixed rate. Radioactive isotopes act as internal clocks.
Isotopes
are elements that have varying numbers of neutrons. Isotopes of the same element have similar but different mass numbers. Stable isotopes (i.e., Carbon-13 or 13C) never change. Radioactive isotopes (i.e., 14C) spontaneously decay into other elements.
Radioactive decay
progresses along a decay chain, which creates new unstable elements that also decay. The decay proceeds to a stable endpoint
The parent isotope
is the isotope that undergoes radioactive decay
The __________ isotope is the decay product.
daughter
The half-life is
the time it takes for half of an unstable nuclei to decay. The half-life is a unique characteristic of each isotope. As a parent disappears, the daughter “grows in.”
After one half-life, one-half of the original parent remains. After three half-lives, ________ of the original parent remains.
one eighth
The age of a _________ is determined by measuring the ratio of parent to daughter isotopes. The age can be calculated from a knowledge of the ______ half-life. ____________ requires analytical precision.
mineral, parent, and Geochronology
Isotopic dating
dating gives the time a mineral began to preserve all atoms of parent and daughter isotopes, which requires cooling below a “closure temperature.” If rock is reheated, the radiometric clock could be reset.
Igneous and metamorphic rocks are best for _____________ study; sedimentary rocks cannot be directly dated.
geochronologic
Annual growth rings (Numerical dating)
from trees or shells are able to be counted to establish dates
Rhythmic layering (Numerical dating)
Annual layers in sediments or ice—can be counted to establish numerical dates.
___________ ages are possible without radioactive isotopes, but they have a very limited range
Numerical
Sediments can be __________ by numerical ages derived from datable materials that crosscut them. This yields age ranges that narrow as data accumulates.
bracketed
Before radiometric dating, age estimates for Earth varied widely. ____________ estimated a 20 Ma age to cool Earth from the temperature of the sun to present.
Lord Kelvin
Uniformitarianism and evolution, however, indicated an Earth that is much older than__________
~100 Ma.
The oldest rocks on Earth’s surface date to 4.03Ga. ________ in ancient sandstones date to 4.4 Ga. The age of Earth is 4.57 Ga, based on correlation with meteorites and moon rocks.
Zircons
Phanerozoic (540)
Cenozoic
Mesozoic
Paleozoic
Mesozoic (251- 65.5)
Cretaceous
Jurassic
Triassic
Paleozoic (542-251)
Permian Carboniferous (Pennsylvania & Mississippi) Devonian Silurian Ordovician Cambrian
_________ reflect geologic processes of uplift, deformation, and metamorphism at work; they are vivid evidence of tectonic activity.
Mountains
__________ processes build mountains up; __________ processes tear them down.
Constructive & destructive
orogenesis
Mountain Building. Applies force to rocks, causing deformation (bending, breaking, shortening, stretching, and shearing).
Mountains occur in
elongate, curvilinear belts
Mountain building involves
uplift, deformation, jointing, faulting, folding, foliation, metamorphism, igneous activity, and sedimentation.
Change in shape via deformation. Caused by force acting on rock
Strain
Undeformed (unstrained) rocks
display horizontal beds and spherical sand grains, with no folds or faults.
Deformed (strained) rocks
show tilted beds, metamorphic alteration, folding, and faulting.
Deformation strain creates _______________
geologic structures
Folds
are bends in layered rock that form by shearing and or by slow plastic flow.
_________ are fractures that have no offset.
Joints
fractures that are offset
faults
A planar metamorphic fabric
Foliation
_________ is a change in location.
Displacement
Rotation
Is a change in spatial orientation.
_________ is a change in shape.
Distortion
Types of strain
Stretching - pulling appart
Shortening - Squeezing together
Shear- sliding past
The two major deformation styles
brittle and ductile
The type of deformation depends on
T and P conditions, deformation rate, and rock composition.
Brittle deformation
Which occurs in the shallower crust, rocks break by fracturing.
Shattering of a porcelain plate is an apt analogy.
________________ occurs at higher P and T conditions, which causes rock to deform by flowing and folding. Flattening a ball of dough is an apt analogy.
Ductile deformation
stress
The force applied across a unit area.
A large force per area results in much deformation.
A small force per area results in scant deformation.
Types of Stress
Compression
Tension
Shear
Pressure
Compression (Stress)
Takes place when an object is squeezed. Deformation shortens and thickens the material.
Horizontal compression drives plate tectonic collision and orogenesis.
Tension (Stress)
Occurs when the ends of an object are pulled apart, which stretches and thins the material.
Horizontal tension drives crustal rifting.
Shear (Stress)
Develops when surfaces slide past one another.
Shear stress neither thickens or thins the crust.
Pressure (Stress)
Occurs when an object feels the same stress on all sides.
A scuba diver is exposed to equal stress on all sides: pressure.
A line formed by the intersection of a horizontal plane with a tilted surface.
Strike
______ is the angle of the tilted surface down from the horizontal. _____ is always perpendicular to strike
Dip, dip
Lake water on a dipping bed of strata defines a _________
strike line
The ________________ features created during rock deformation is easily described using strike and dip.
geometry of planar
Strike and dip are measured using a _________ that has a built-in leveling device.
compass
____________ in rock are described like planar features, except the measurements are bearing (compass direction) and plunge (angle down from the horizontal).
Linear structures
Joints
Are planar rock fractures without any offset that develop from tensile stress in brittle rock.
Systematic joints occur in parallel sets. Joints often control the weathering of the rock in which they occur.
Fractures filled with minerals are called ______.
veins
Groundwater often flows through fractures in the rock where dissolved _____________ .
minerals precipitate
______ are planar fractures that show offset. The amount of offset is called ______________.
Faults & displacement
_______ are abundant in Earth’s crust and occur at all scales.
Faults
On a dipping fault
the blocks are classified as the hanging-wall block above the fault, and the footwall block below the fault.
When you stand in a tunnel excavated along the fault, your head is near the _________ block and your feet rest on the ___________.
hanging-wall & footwall block
Faults are classified by their
geometry (vertical, horizontal, or dipping) and relative motion.
Dip-slip faults (Normal Fault)
are characterized by blocks that move parallel to the dip of the fault.
In strike-slip faults
blocks move parallel to fault plane strike.
_____________ have components of both dip-slip and strike-slip faults.
Oblique-slip faults
Normal Fault
The hanging wall moves down the fault slope.
Dip-slip
Are most common in regions experiencing crustal tension.
They accommodate crustal extension (pulling apart).
The fault below shows displacement and drag folding.
Reverse fault
The hanging wall moves up the fault slope. A thrust fault is a special low-angle type of reverse fault.
Dip-slip
Most common in regions experiencing horizontal compression.
shortening the crust.
Have steeper dips (>35o)
A thrust fault is a special type of __________ with a dip below 35o. Dip-slip
reverse fault
Thrust Faults
Act to shorten and thicken mountain belts.
Can transport sheets of rock hundreds of kilometers and are common features at the leading edge of orogenic deformation.
_______________ are often near vertical, hence, there are no hanging-wall or footwall blocks. These faults are classified by the relative sense of motion of the block on the far side of the fault from the observer.
Strike-slip faults
Left lateral (Strike-slip)
opposite block moves to observer’s left.
Right lateral (Strike-slip)
opposite block moves to observer’s right.
Sudden movements along faults are the dominant cause of __________
earthquakes
The most obvious indication of faulting
Displacement
Brittle faulting generates shattered and crushed rock that creates a ________
breccia
Fault ________ is made of pulverized, powdered rock.
gouge
Slickensides and linear grooves are
slip lineations
________ are visible when faults intersect the surface
Scarps
Fault zones with breccia and gouge may be mineralized by ________. They usually erode preferentially.
fluid flow
Folds
Layered rock may be deformed into complex folds by tectonic compression. Folds occur in a variety of shapes, sizes, and geometries
________________ produce large volumes of folded rock, which may record multiple events of deformation.
Orogenic settings
A hinge
is a line along which curvature is greatest.
Limbs
are the less curved “sides” of a fold.
The axial plane connects
hinges of successive layers.
Anticline
A fold that looks like an arch.The limbs dip out and away from the hinge.
Syncline
A fold that opens upward like a trough. The limbs dip inward and toward the hinge.
Monocline
A fold that looks like carpet draped over a stair step.
Monoclines are generated by blind basement faults that don’t cut to the surface but which still wrinkle the overlying sedimentary cover.
Folds are described by the geometry of the _________.
hinge
A _______________ fold has a horizontal hinge.
nonplunging
A plunging fold has a hinge that is _______.
tilted
Sheep Mountain, Wyoming
A plunging fold that creates a prominent landform.
Erosion-resistant sandstones form the highs; easily eroded shales are the lows
A dome
A fold with the appearance of an overturned bowl. A dome exposes older rocks in the center.
A basin
A fold shaped like an upright bowl. A basin exposes younger rocks in the center.
Folds develop in two ways
flexural slip and passive flow
In flexural-slip folds
layers slide past one another, resembling the movement as a deck of cards is bent.
____________ folds form in hot, soft, ductile rock at higher temperatures.
Passive-flow
When generating folds
Horizontal compression causes rocks to buckle.
Shear causes rocks to fold over on themselves.
When layers move over ___________ faults, they fold.
step-shaped
Deep faulting may create a monocline in overlying beds.
monocline
Mountain uplift is driven by
plate tectonic processes at convergent plate boundaries, continental collision zones, and continental rifts.
Curvilinear plate boundaries make ___________ mountain belts.
curvilinear
Causes of mountain building: convergent tectonic boundaries.
Subduction-related volcanic arcs grow on the overriding plate. Accretionary prisms (off-scraped sediment) thicken laterally and grow upward.
Compression shortens and uplifts the overriding plate. A fold-thrust belt develops landward of the orogen.
Causes of mountain building: exotic terranes.
Consist of island fragments of continental crust that had a separate geologic history before being sutured to the overriding plate at a convergent margin.
Northern America has numerous
Causes of mountain building: continental collision.
Continental collision follows ocean-basin closure and complete subduction of oceanic lithosphere. This brings two blocks of continental lithosphere together. Because continental crust is too buoyant to subduct, it shuts down the subduction zone.
The center of the belt consists of high-grade metamorphic rocks. Fold-thrust belts extend outward on either side.
______________ creates a welt of crustal thickening due to thrust faulting and flow folding.
Continental collision
Causes of mountain building: continental rifting.
Normal faulting in continental rifts creates fault-block mountains and basins. Thinning crust results in decompressional melting, which adds volcanic mountains, increases heat flow, and uplifts rocks.
Orogenesis creates igneous and metamorphic rocks.
Regional metamorphic rocks are generated from the intense heat and pressure of compression and burial. Contact metamorphic rocks are created by igneous intrusions.
Intrusive and extrusive igneous rocks are generated from subduction processes.
Orogenesis creates sedimentary rocks.
Orogenesis generates a large amount of sediment that is shed to adjacent regions. The sediments accumulate in basins created by crustal flexure.
Basins preserve evidence of mountains long after they have been erased by erosion.
In some cases, basins preserve evidence of past orogenesis long after the mountains have been erased by erosion.
____________________ make it a simple task to measure rates of horizontal compression and vertical uplift.
Global positioning systems (GPS)
Mountains require elevation changes on Earth’s ________. Mount Everest is 8.85 km above sea level and is made of sediments deposited in marine water.
surface
Mountains reflect a balance between _________ & ________
uplift & erosion.
Mountains are steep and jagged due to high rates of __________.
erosion
When tectonic uplift slows or ceases, or rates of erosion exceed rates of uplift, mountains are reduced in ________
elevation
Eventually, mountains may be eroded back to __________.
Sea level
orogenic collapse
Process which leads to destruction of the mountains.
Ductile rock eventually flows out from beneath high mountains, which then settle downward like soft cheese. The upper brittle crust breaks into faults
There is a limit to mountain heights because the weight of mountains eventually overwhelms the strength of hot _________ in the lower crust
ductile rock
A craton
Continental crust that hasn’t been deformed in 1 Ga.
Has a low-geothermal gradient and are made of cool, strong, and stable continental crust.
There are two cratonic provinces
Shields & Platforms
Shields
Consist of Precambrian igneous and metamorphic rocks
Platforms
The sedimentary cover that is draped over shield rock.
Cratonic platforms consist of sedimentary rocks covering ______________________.
Precambrian basement
Cratons exhibit domes and basins resulting from vertical crustal adjustments due to stresses transmitted from active margins to the ____________.
cratonic interior
Earth shaking is caused by
a rapid release of energy, most of which is due to tectonic forces.
__________ are common on this planet. They occur every day. There are more than a million detectable _________ per year.
Earthquakes & earthquakes
Most earthquake damage is due to ___________.
ground shaking
Most earthquakes are caused by
Sudden motion along a newly formed crustal fault or existing fault.
Also caused by magma movement, volcanic eruptions, landslides, meteorite impacts, and nuclear deto
The hypocenter (or focus)
The location where fault slip occurs. It is usually on a fault surface.
The land surface directly above the hypocenter. Maps often portray the location of epicenters.
The epicenter
Faults are _________ breaks in the crust
planar
Most faults are ________ (vertical faults are rare).
sloping
The type of fault depends on the ___________ of blocks.
relative motion
Block above the fault
Hanging wall
Block below the fault
Footwall
On a ________ fault, the hanging wall moves down relative to the footwall. It most often results from extension (pull-apart or stretching).
normal
In a __________ fault, the hanging wall moves up relative to the footwall. It usually results from compression (squeezing or shortening).
reverse
The slope (dip) of a reverse fault is ______.
steep
A ________ fault is a special kind of reverse fault that has a lower angle slope (dip). It’s a common fault type in compressional mountain belts.
thrust
The slope (dip) of a thrust fault is ___________ than a reverse fault.
less steep
Along a _________ fault, one block slides laterally past the other block. There is no vertical motion across the fault.
strike-slip
___________ faults tend to be close to vertical. The motion across the fault, however, is not vertical but horizontal.
Strike-slip
_____________ is sometimes evident by offset of fences, roads, streams, etc.
Displacement
Faults are found in many places in the crust and include both ________ & _________.
active & inactive faults
Fault trace
The place that a fault intersects the ground
Displacement at the land surface can create a ________.
fault scarp
True or False: Do all faults reach the surface?
False
blind faults
Faults that don’t reach the surface
_________ occur as the result of fault motion.
Earthquakes
Earthquake energy is created when…
rocks break to form a new fault, or when a preexisting fault is reactivated
Once created, a fault remains a zone of ______________.
crustal weakness
Faults form when tectonic forces add _______ (push, pull, or shear) to rock.
stress
As _______ is added to a rock, it bends slightly without breaking (elastic behavior). Continued _______ causes cracks to develop and grow, eventually progressing to the point of failure. Stored elastic energy is released all at once, creating an _________.
stress, stress & earthquake
When a fault moves, it is quickly _______________ due to bumps along the fault. Eventually, stress will build up again and cause another episode of failure and slip.
slowed by friction
A major earthquake may be preceded by ____________
foreshocks
foreshocks
Smaller tremors indicating crack development in rock.
They may warn of an impending large earthquake.
_____________ usually follow a large earthquake and may occur for weeks or years afterward.
Aftershocks
Larger earthquakes have larger areas of ________
slip.
Displacement is greatest near the __________
hypocenter
_____________ diminishes with distance.
Displacement
________ slip is cumulative.
Fault
___________ can offset rocks by hundreds of kilometers given geologic time.
Faults
Seismic body waves: P-waves
Primary or compressional waves
P-waves travel by
compressing and expanding the material parallel to the wave-travel direction.
P-waves are the __________ seismic waves and they travel through solids, liquids, and gases.
fastest
Seismic body waves: S-waves
Secondary or shear waves
S-waves travel by
moving material back and forth, perpendicular to the wave-travel direction.
S-waves are _______ than P-waves and they travel only through solids, never liquids or gases.
slower
S-waves travel ONLY through _______ NEVER liquids or gases.
solids
Seismic surface waves: L-waves (Love waves)
S-waves that intersect the land surface. They move the ground back and forth like a writhing snake.
_______________ travel along Earth’s exterior.
Surface waves
The slowest and most destructive waves
Surface waves
R-waves (Rayleigh waves)
P-waves that intersect the land surface. They cause the ground to ripple up and down like water.
_____________ are instruments that record ground motion. A weighted pen on a spring traces movement of the frame. Vertical motion is recorded as up-and-down movement; horizontal motion is recorded as back-and-forth motion.
Seismometers
____________ the data record by a seismometer. It depicts earthquake wave behavior, particularly the arrival times of the different waves, which are used to determine the distance to the epicenter.
Seismogram
Seismic waves arrival sequence.
P-waves are first.
S-waves are second.
Surface waves are last.
Data from three or more stations pinpoints the_______. The distance radius from each station is drawn on a map. Circles around three or more stations will intersect at a point. The point of intersection is the ________.
epicenter, epicenter
_________ and _________ arrival times can be graphed. A travel-time curve plots the increasing delay in arrivals. The time gap yields distance to the epicenter.
P-wave and S-wave
Earthquake size is described two ways:
by the severity of damage observed in the field (intensity) and the amount of ground motion measured on a seismometer (magnitude).
A measurement of size based on the maximum amplitude of seismograph waves.
Magnitude
The severity of damage observed in the field
Intensity
True or False: Are Intensity and magnitude related in an approximate way, even though they are very different measurements?
True
_____________________ is a subjective determination that assigns Roman numerals to differing degrees of damage. Damage intensity decreases with distance from the epicenter.
The Modified Mercalli Intensity scale
Magnitude scales
Richter scale (ML) Moment magnitude scale (MW)
Richter scale (ML)
best for local measurements (near the epicenter).
Moment magnitude scale (MW)
The best measure. Based on characteristics of different seismic waves and the area and displacement of fault slip.
Most accurate.
True or False: Magnitude is related to the energy released
True
True or False: Earthquakes are linked to plate tectonic boundaries.
True
Shallow earthquakes occur at
divergent and transform boundaries
mid-ocean ridges
occur on both plates
Intermediate and deep occur at
convergent boundaries
trace the path of the subducting slab
Large megathrust earthquakes are linked to _________ and are deadly
tsunamis
The __________ slab bends the overriding plate downward. The overriding plate can snap back, creating a huge megathrust earthquake.
subducting , overriding, megathrust
______________ form where the downgoing slab bends and large thrust faults occur at the contact between plates.
Normal faults
__________ plate boundaries have both shallow, intermediate, and deep earthquakes.
Convergent
The Wadati-Benioff zone
where Intermediate and deep earthquakes trace the path of the subducting slab
Earthquakes are rare below 660 km as the mantle becomes too __________.
ductile
______________ cuts through western California where the Pacific plate shears north and the North American plate south. ___________ is a very active strike-slip fault seeing hundreds of earthquakes annually. San Francisco was destroyed in 1906 by a magnitude 7.9. Large earthquakes loom in the future of western California.
The San Andreas Fault, The San Andreas Fault
The San Andreas Fault is what type of fault ?
transform fault.
Large continental transform earthquakes occur in the ____________ and are usually major disasters.
shallow crust
Continental rifts occur where
tension and stretching creates normal faults.
_________ generates shallow earthquakes similar to those at the mid-ocean ridge, except these normal faults impact people.
Rifting
Basin and Range Province (Nevada, Utah, and Arizona) are examples of what?
Continental Rift
Orogenic crustal compression: tectonic collisonal mountain building
Continental lithosphere compresses along thrust faults. Earthquakes can be very large. Orogenic uplift creates landslide hazards.
Intraplate settings: away from tectonic plate boundaries
Around 5% of earthquakes are not near modern plate boundaries In many cases, these quakes occur in places of crustal weakness related to failed rifts or former shear zones.
__________ kill people and destroy cities. Damage can be widespread, horrific, and heartbreaking
Earthquakes
Earthquake waves arrive in a distinct ________ with different motions.
sequence
________ are the first to arrive. They produce a rapid, bucking, up-and-down motion. (Ground moves vertically up and down)
P-waves
_________ arrive next (second). They produce a pronounced back-and-forth motion. This motion is much stronger than that from P-waves. Cause extensive damage.
(Ground moves back and forth)
S-waves
___________ are delayed traveling along the exterior. ___________ follow quickly behind the S-waves. They cause the ground to writhe like a snake. (undulate the ground laterally)
Surface waves, L-waves
_________ are the last to arrive. The land surface undulates like ripples across a pond. These waves usually last longer than the other kinds. ________ cause extensive damage. (Ground surface moves in a wave-like motions)
R-waves, R-waves
True or False: Severity of shaking and damage depends on the magnitude (energy) of the earthquake, the distance from the hypocenter, and the intensity and duration of the vibrations.
True
_________ transmits seismic waves quickly = less damage.
Bedrock
________ reflect and refract waves = amplified damage.
Sediments
During an earthquake building floors _______ and bridges/ roadways
pancake , topple
(Earthquakes) Worst thing to make building out of…
bricks. ex= masonry
_________ frequently accompany earthquakes in places with topographic relief
Landslides
Unstable slopes often bear evidence of ancient _______________.
slope failures
__________ causes material on steep slopes to fail.
shaking
Earthquake hazards: liquefaction
Seismic waves liquefy water-filled sediments by increasing the pressure of water in pores. This reduces friction, sediment flows as a slurry, and land founders and cracks. Sand becomes “quicksand” and clay becomes “quickclay.”
____________ causes soil to lose strength. Land, and the structures on it, will slump and flow.
Liquefaction
Earthquake hazards: fire
common result of earthquakes. Shaking topples stoves, candles, and power lines, and breaks gas mains. Important infrastructure may be destroyed (water, sewer, electricity, roads
___________ are often powerless to combat fire with no road access, no water, and too many hot spots. Fire may greatly magnify the destruction and toll in human lives.
Firefighters
Earthquake hazards: tsunamis
Tsunami means harbor wave in Japanese. Tsunamis result from displacement of the sea floor by an earthquake, submarine landslide, or volcanic explosion that displaces the entire volume of overlying water.
Destructive tsunamis occur
frequently, about one per year.
__________________ creates a giant mound (or trough) on the sea surface. This feature may cover an enormous area (up to a 10,000 mi2). The feature collapses and creates waves that race rapidly away.
Sea-floor displacement
___________ race at jetliner speed across the open ocean and may be almost imperceptible due to low wave height (amplitude) and long wavelength (frequency).
Tsunamis
Earthquakes CAN be predicted in
the long term (tens to thousands of years)
Earthquakes CANNOT be predicted in
the short term (hours and weeks).
Hazards can be mapped to
assess risk and develop building codes, implement land-use planning, and disaster response.
Earthquake devastation fuels disease outbreaks.
Food, water, and medicines are scarce. Basic sanitation capabilities are nonexistent. Hospitals are damaged or destroyed. Health professionals are overwhelmed. There are likely to be decaying corpses.
Tsunami detectors
are placed on the deep sea floor. Sense pressure increases from changes in sea thickness. Prediction/detection can save thousands of lives.
Indian Ocean tsunami
The tsunami killed close to a quarter of a million people. Many people explored the shore that was exposed when the water drained away (a clear indication of an impending tsunami).
Wind waves
Influence the upper ~100 m.
Have wavelengths of several tens to hundreds of meters.
Wave height and wavelength related to wind speed.
Wave velocity maximum several tens of km per hour.
Waves break in shallow water and expend all stored energy.
Tsunami waves
Influence the entire water depth.
Have wavelengths of several tens to hundreds of kilometers.
Wave height and wavelength unrelated to wind speed.
Wave velocity maximum several hundreds of km per hour.
Water arrives as a raised plateau that pours onto the land with no dissipation.
When they approach land and the water becomes shallower, friction slows the base of the sheet of water and the tsunami thickens, growing to 10–15 m or more.
Tsunami
