GEOL 107 UD (O'Neal)- Exam 3

What do the terms brittle, ductile and elastic properties mean in terms of rock behaviors at faults and plate margins?

-Brittle: material is bent and will not return to its original shape once the stress is removed

-Ductile: material is bent and will not return to its original shape once the stress is removed

-Elastic: deformed materials return to its original shape after the stress is removed

What is the difference between an anticline and a syncline?

-Anticline: upward- arching folds

-Syncline: downward- arching folds

What are thrust, normal, dip-slip, strike-slip, tensional, and compressional faults? Where would you likely find each occurring in terms of plate tectonic settings?

-Thrust: reverse faults with dip angles less than 30° from horizontal (convergent)

-Normal: hanging-wall block has moved down relative to the footwall block due to tensional stress (divergent)

-Dip-slip: movement is parallel (vertical) to the dip of the fault plane (Basin and Range Province)

-Strike- slip: have movement that is predominantly horizontal and parallel to the strike of the fault plane (tectonic)

-Tensional: occurs when two blocks of rock move away from another, creating a normal fault (divergent)

-Compressional: fault motion caused by compressional forces and results in shortening (convergent)

What is a hanging wall and a foot wall? Where will you find them located in different fault/tectonic scenarios?

-Hanging-wall: the rock above the fault zone

-Footwall: the rock below the fault zone

What are the few map symbols you learned in studying faults and folds?— lines with little squares and triangles, and a t-shape symbol. What did they mean?

-Squares indicate where fault creep slippage that has been triggered by an earthquake

-Triangle's/teeth represent a thrust fault

-The T-shaped symbol or a strike and dip represents where layers of rock stack up in tilted bed

What is a strike and how do you determine it? Dip?

-Strike: the compass direction of a line formed by the intersection of a inclined plane with a horizontal line

-Dip: the direction and angle from horizontal in which a plane is oriented

Shear, tensional, and compressive forces, what are they and where do they occur?

-Shear: force that tends to cause deformations of material by slippage along a plane or planes parallel to the imposed stress. Common along transform boundaries

-Tensional: forces pulling in opposite directions, which results in strain that stretches and thins rock. Common along divergent boundaries

-Compressive forces: generate folding and faulting as a consequence of shortening. Common along convergent boundaries

What are geologic cross-sections and what are they used for?

-A vertical slice through a portion of the Earth.

-Used to help understand geological conditions that occur in specific areas of the cross sections

What are P waves and S waves and what do they tell us about the inside of the Earth?

-P-wave: compressional (longitudinal) body wave in which rock vibrates back and forth parallel to the direction of wave propagation. P waves speed up through the inner core. Interior is composed of iron and nickel

-S-waves: shearing (transverse) body wave in which the rock vibrates back and forth perpendicular to the direction of wave propagation. Only pass through solids

What are Rayleigh waves?

Ground moves in an elliptical path opposite the direction of the wave motion; extremely destructive to buildings.

What seismic waves cause the most damage to human infrastructure and why?

S-waves are more dangerous because they have greater amplitude and produce vertical and horizontal motion of the ground and buildings are more vulnerable to horizontal motion

What are the different ways/scales used to measure and earthquake?

-Richter scale: measures magnitude in numerical numbers. Amount of energy released by an earthquake

-Modified Mercalli Scale: Range from 1-12 (I-XII). Measures intensity and damage.

-Moment magnitude scale: more objective measure of energy released by a major earthquake

What is the difference between intensity and magnitude?

-Intensity: A measure of the effects of an earthquake produces (people, structures)

-Magnitude: A measure of the amount of energy released by an earthquake by measuring the amplitude of seismic waves on a seismogram

What are seismometers and seismographs? What do they measure and record?

-Seismometer: used to measure seismic waves

-Seismographs: recording devices used to produce a permanent record of the motion detected by seismometers

What are the epicenter and focus of an earthquake?

-Epicenter: point on Earth's surface directly above the focus

-Focus: (Hypocenter) the point of initial breakage and movement along a fault, where seismic waves originate

What seismic waves travel the fastest? Slowest?

-P-wave: fast

-S-wave: slow (only travel through solids)

-Surface waves: slowest

How many measurement stations are needed to locate the epicenter of an earthquake?

Plotting distances from 3 stations on a map, as circles with radii equaling the distance from the quake locates earthquake epicenter.

What is liquefaction and why does it occur?

Occurs when water saturated soil or sediment sloshes like a liquid during a quake.

What does the term 'elastic rebound' mean?

Earthquakes are a sudden release of strain progressively stored in rock that bends until they finally break and move along a fault.

What are the lithosphere, asthenosphere, and the Mohorovicic discontinuity? What do they represent in terms of plate tectonics and plate motion?

-Lithosphere: crust and upper mantle together. The brittle outer shell of the Earth that makes up the tectonic plates

-Asthenosphere: Beneath the lithosphere, seismic wave speeds abruptly decrease in a plastic low velocity zone. Uppermost layer of solid Earth.

-Mohorovicic discontinuity: the boundary surface between the Earth's crust and mantle. Marks the change in seismic wave velocity from the crust to the uppermost mantle

What is isostasy and what are some of the different ways it was discussed in class with regards to the lithosphere, ice sheets, and mountains?

-Isostasy: Equilibrium of adjacent block of brittle curst "floating" on upper mantle.

-Is the rising and settling of a portion of the Earth's lithosphere that occurs when weight is removed.

-Is also the process by with the lithosphere is pressed under the weight of an ice sheet.

-The thickness and velocity determine how high mountains rise above the surface on continents.

What is the curie point. How does it relate to magnetic materials in rock?

-Curie point: temperature at which certain magnetic materials undergo a sharp change in their magnetic properties.

-Recorded by magnetic materials in igneous rocks as they cool below their curie point

How do we use magnetic alignment of minerals in rocks to understand plate movements over time? (especially sea floor rocks and paleogeography of supercontinents)

-Paleomagnetism is the study of ancient magnetic fields in rocks. It allows for reconstruction of plate motions over time.

-Magnetic signatures of rocks allows the knowledge to record dates of the rocks and map the position of the field at the time of their formation.

Why does earth have an electromagnetic field? Are the magnetic poles stationary?

-The Earth has an electromagnetic field to protect the planet from cosmic radiation and from charged particles emitted by the sun.

-They are not stationary, they move under the influence of currents in the Earth's core as well as electric currents in the ionosphere and radiation belts at the Earth's magnetosphere.

What are Benioff seismic zones and what processes/settings do we associate with them?

-Benioff zones is an area within the Earth's crust where earthquakes frequently occur.

-Nearly all intermediate and deep focus earthquakes occur here.

-Benioff zone earthquakes foci begin at wrenches and dip landward under continents or island arcs.

-Ocean-ocean plate convergence

-Ocean-continent plate convergence

Do you know the parts of the sea floor: abyssal plain, submarine canyon, continental shelf, rise, trench? Can you relate their size/presence to different tectonic settings?

-Abyssal plain: extremely flat regions beyond the base of the continental rise. It is the flattest feature on Earth with a slope of <0.01°. 10,000-20,000 ft below surface

-Submarine Canyon: V-shaped valleys that run across continental shelves and down continental slopes. They deliver sediment to the abyssal fan on deep sea floor. Extends nearly 30 miles

-Continental shelf: gently (0.1°) seaward-sloping shallow submarine platform at the edges of continents. Typically covered in young sediment.

-Continental rise: gently seaward-sloping (0.5°) wedges of sediments extending from base of continental slope to deep sea floor. Sediment deposited by turbidity and contour currents

-Oceanic trench: a narrow, deep trough parallel to the edge of a continental or an island arc. Deepest part of the ocean

What is continental drift vs. the term plate tectonics?

-Continental Drift: Hypothesis proposed in the early 20th century by Alfred Wegener to explain the "fit of continents," matching rock types and fossils across ocean basins. Drifting of continents on the ocean bed.

-Plate tectonics: describes the features and movement of Earth's surface in the present and in the past

What is the nature of rock formation and plate movement at mid ocean ridges?

As plates separate at mid-ocean ridges along divergent plate boundaries, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt.

What role did heat convection play in Hess's mechanism of sea floor spreading? Do we think it is more complicated today and how so?

-Harry Hess proposed the concept that the seafloor is moving like a conveyor belt away from the crust of the mid-oceanic ridge until it disappears by plunging beneath a continent or island arc.

-His driving force was deep mantle convection, which is the circulation pattern driven by rising of hot material (hot mantle rock) and/or sinking of cold material (oceanic crust)

What are Pangea, Laurasia, and Gondwanaland?

-Pangaea: Supercontinent proposed by Wegener

-Laurasia: Northern supercontinent containing North America and Asia (excluding India)

-Gondwanaland: Southern supercontinent containing South America, Africa, India, Antartica and Australia

How fast is new oceanic crust made and how fast do sea-floor plates move?

-The speed of new oceanic crust formation varies from ridge to ridge. Some fast-spreading ridges produce up to 6in of new crust per year. Slower ridges creep along just 2in per year

-The typical rate of plate motion is 1-10cm per year

What is a hot spot. Where are the few most notable ones we discussed?

-Hot spots form from large mantle plumes spreading out and tearing apart the overlying plate

-Examples include: Hawaii, Yellowstone and Iceland

What tectonic settings have big, new mountains and which ones have the old, eroded ones?

-Mountains form where two continental plates collide. Higher mountain ranges tend to be geologically younger

-Ancient mountain belts have eroded nearly flat to form stables cores (cratons) of the continents

What is a craton?

An old and stable part of the continental lithosphere, which consists of the crust and uppermost mantle