Geology 101 UNC Final Haskin

lapilli (cinders)

"Little stones", they are a type of small pyroclast. The solidified pea-sized to golf ball-sized fragments of glassy lava and scoria, informally called cinders.

Seismic velocity discontinuity

- A boundary in the Earth at which seismic velocity changes abruptly. Experiments suggest that such seismic-velocity discontinuities occur at depths where pressure causes atoms in minerals to rearrange and pack together more tightly.

Characteristics of Convergent Boundaries Zones Seimicity

- Characterized by trenches and mountain ranges - shallow to deep earthquakes - some more than 700 km deep.

Subduction Zones Characterstics:

- a seismic signature called a Wadati-Benioff zone - characteristic seismicity down to ~700 km depth - the potential to create tsunami because of megathrust earthquakes. - documented earthquakes up to magnitude 9.5

Why do subduction zone EQ's have more magnitude than transform boundary EQ's?

Subduction Zones have a greater surface area than Transform Faults. Ex. San Andreas Fault earthquakes can get up to 8.2 magnitude, while the Cascadia subduction zone can have up to 9.0 magnitude!

Which plate boundary do tsunamis occur at?

Subduction zone at convergent ocean-continental boundaries

Where does flux melting happen?

Subduction zones

Focus vs. Epicenter

The focus is the point within the earth where seismic waves originate; it is centered on the part of the fault that has the greatest movement. The epicenter is on the earth's surface directly above the focus.

Liquefaction

The process by which an earthquake's violent movement suddenly turns loose soil into liquid mud

partial melting

The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results.

fractional crystallization

The process by which the crystals formed in a cooling magma are segregated from the remaining liquid at progressively lower temperatures.

magma mixing

The process of altering the composition of a magma through the mixing of material from another magma body

Assimilation

The process of magma contamination in which blocks of wall rock fall into a magma chamber and dissolve.

strike-slip fault

The rocks on either side of the fault slip past each other sideways, with little up or down motion.

Texture definition in geology

The size and arrangement of the grains or crystals in the rock

Basalt, Andesite, Dacite, Rhyolite

Volcanic Rocks

Which ground type has the most ground acceleration: Solid bedrock, Poorly consolidated sediment or soft rock, OR Water-saturated sand and mud?

Water-saturated sand and mud

Are explosive rocks mafic or felsic?

felsic

Vesicular rocks

form at or near the Earth's surface and develop a texture dominated by holes as dissolved gases escape while the magma cooled.

dissolved volatiles

gas and fluids trapped in magma at depth, ex. water, carbon dioxide, sulfur dioxide

Flood basalts are formed by

low viscosity magma **Fissure eruption cracks that just sit and ooze (sometimes for thousands of years), creating stacks of lava flows

Are effusive rocks mafic or felsic?

mafic

Glassy textures indicate fast or slow cooling?

Fast cooling or quenching.

Light rocks are

Felsic

Granite and Ryholite

Felsic Rocks

Silica Composition and Color Felsic Rocks

Felsic rocks are light colored (cream, white, pink) due to Si-, Al-, K-, and Na-rich minerals ex. K-feldspar and Quartz

ultramafic melts

Have an even higher proportion of iron oxide relative to silica

What factors affect seismic risk?

Hazard (the chance the building will shake), vulnerability (likelihood of building collapsing), and value (number of lives potentially affected).

Waves from fastest to slowest and their full names? (L, S, R & P waves)

P, S, R/L P waves- compression body waves S waves- Shear body waves L waves- Love surface waves R waves- Rayleigh surface waves

Degrees of P-wave Shadow Zone?

P-wave Shadow Zone- A band between 103° and 143° from an earthquake epicenter, as measured along the circumference of the Earth

What is an important limitation that must be kept in mind when calculating return periods for earthquakes? How are frequency and on magnitude related to return period?

-Frequency and magnitude are inversely related. So if you have a higher magnitude earthquake, they are going to occur less often therefore the return period is going to be greater -Limitation: return period is an average so not as accurate (an earthquake could come significantly sooner or later than that) → it's a way to compare locations of earthquakes and how often they are going to happen, but shouldn't bet on that data -It's a comparison thing Return period for a Megathrust (M9.0 + at Cascadia and at SZ = 400-600 yrs)

heat transfer melting

-Rising magma carries mantle heat with it. -This raises the T in nearby crustal rock, which then melts.

Discuss how tsunami from megathrust earthquakes are created.

-Tsunamis occur when the ground beneath the ocean is displaced (locking and building stress followed by catastrophic release happens every few hundred years) -The thrusting motion of a megathrust earthquake causes large vertical movement on the sea floor and this displaces a large volume of water which travels away from the undersea motion as a tsunami -Tectonic plates pushing against each other in a subduction zone become "stuck" causing a massive build up of pressure-Stress builds up as strain and causes rocks to deform elastically. When accumulated stress becomes greater than friction it results in brittle failure (= rupture along the faults) & elastic energy is released in seismic waves -During subduction: an accretionary wedge builds up, continental plate deforms as a response to the stressWhen plates are locked = stress and deformation When plates release = earthquake and tsunami Not all earthquakes cause tsunamis: most are generated by large, shallow earthquakes at subduction zones One tectonic plate tries to subduct another one, the two plates become stuck together. When the subducting plate finally moves, the overlying plate snaps back uplifting the ocean and causing a tsunami to occur.

How do Megathrusts Earthquakes occur?

-Tsunamis occur when the ground beneath the ocean is displaced (locking and building stress followed by catastrophic release happens every few hundred years) -The thrusting motion of a megathrust earthquake causes large vertical movement on the sea floor and this displaces a large volume of water which travels away from the undersea motion as a tsunami -Tectonic plates pushing against each other in a subduction zone become "stuck" causing a massive build up of pressure-Stress builds up as strain and causes rocks to deform elastically. When accumulated stress becomes greater than friction it results in brittle failure (= rupture along the faults) & elastic energy is released in seismic waves -During subduction: an accretionary wedge builds up, continental plate deforms as a response to the stressWhen plates are locked = stress and deformation When plates release = earthquake and tsunami Not all earthquakes cause tsunamis: most are generated by large, shallow earthquakes at subduction zones One tectonic plate tries to subduct another one, the two plates become stuck together. When the subducting plate finally moves, the overlying plate snaps back uplifting the ocean and causing a tsunami to occur.

Dry vs. Wet Melts

-Variable amounts of dissolved gas occur in a melt -Dry magma: few to no volatiles -Wet magma: up to 15% volatiles

What are the steps that cause an Earthquake?

1) stress builds to cause either sudden formation of a new fault or slip on a pre-existing fault. 2) When the slip takes place, elastically deformed rock on either side of the fault rebounds. 2) This process generates seismic waves. 3) Faults display stick-slip behavior in that stress builds until slip takes place and then builds again.

Igneous activity can occur at 4 geologic settings:

1. hot spots 2. along volcanic arcs boarding ocean trenches 3. along mid-ocean ridges 4. within continental rifts

Mt. St. Helens eruption

1980; Composite volcano; Pelean Eruption; in Washington

Laccolith

A mass of igneous rock, typically lens-shaped, that has been intruded between rock strata causing uplift in the shape of a dome.

Batholith

A mass of rock formed when a large body of magma cools inside the crust

Viscosity of magma

A measure of a material's resistance to flow. - Depends on temperature (hotter is less viscous), volatile content, and silica content (mafic is less viscous)

Moment Magnitude Scale definition and how its better than Richter scale?

A modern scale for measuring the relative size of earthquakes that involves studying the amplitude of waves on a seismograph, along with other parameters. - More accurate than Richter scale because it takes into account the area of slip and the amount of slip on the fault. - Can measure earthquakes with a focus further from the surface than 100km.

Tuff

A pyroclastic igneous rock composed of volcanic ash and fragmented pumice, formed when accumulations of the debris cement together.

large igenous provinces

A region in which huge volumes of lava and/or ash erupted over a relatively short interval of geologic time.

thrust fault

A reverse fault in which the hanging wall slides over to the foot wall; low angle reverse fault.

aphanatic texture

A rock texture in which individual crystals are too small to be identified without the aid of a microscope. In hand specimens, aphanitic rocks appear to be dense and structureless. Fast cooling. Interlocking crystalline texture.

crystalline igneous rock

A rock that consists of minerals that grew when a melt solidified, and eventually interlock like pieces of a jigsaw puzzle example: Granite

Wadati-Benioff zone

A sloping band of seismicity defined by intermediate- and deep-focus earthquakes that occur in the downgoing slab of a convergent plate boundary. Simplified: A seismic pattern distinctive of subduction zones.

volcanic crater

A steep, bowl-shaped depression surrounding a vent. A volcanic crater forms when the walls of a vent collapse inward following an eruption.

normal fault

A type of fault where the hanging wall slides downward; caused by tension in the crust

Reverse Fault

A type of fault where the hanging wall slides upward; caused by compression in the crust

Which volcanic landform is mostly made of small pyroclastic material (~4-32 mm in diameter)? A. cinder cones B. stratovolcanoes (composite cones) C. lava domes D. shield volcanoes

A. cinder cones

What are stratovolcanoes (also called composite cones) made of? Choose all answers that apply. A. intermediate to felsic lava B. pyroclastic material C. magma D. mafic lava

A. intermediate to felsic lava B. pyroclastic material

In the video demonstration, which bottle approximated an EXPLOSIVE eruption? A. the bottle containing soda and wallpaper paste B. the bottle containing only soda

A. the bottle containing soda and wallpaper paste

Factors of Seismic Velocity

A. the rigidity and compressibility of the material B. the composition of the material C. the physical state of the material

The reason behind the video demonstration, which bottle approximated an EXPLOSIVE eruption due which of the following factor(s) discussed in the video demonstration? Choose all answers that apply. A. viscosity B. silica composition C. temperature D. gas content

A. viscosity B. silica composition

Why are tsunamis so destructive?

Affects large areas, momentum of the large water mass waves become a debris-filled, advance AND retreat of subsequent waves, lack of public education

How does Divergent Boundary Seismicity take place?

Along spreading segments, stretching generates normal faults. Earthquakes along mid-ocean ridges take place at depths of less than 10 km, making them shallow-focus earthquakes. Continental rifts are also shallow-focus earthquakes.

How does Transform Boundary Seismicity take place?

Along transform faults, strike-slip displacement occurs. - Shallow-focus earthquakes (less than 30 km deep)

Porphyritic texture

An igneous texture consisting of large crystals embedded in a matrix of much smaller crystals.

Four of the most common igneous rock textures

Aphanitic, phaneritic, porphyritic, and vesicular.

How do recurrence intervals, frequency, and magnitude relate?

As recurrence interval for earthquakes increase, earthquake frequency decreases and earthquake magnitude increase.

Take home message of chapter 5- Eruptive Style

At a volcano, lava rises from a magma chamber and erupts from chimney-like conduits or from crack-like fissures. Geologists distinguish between effusive (lava-dominated) and explosive eruptions. Low-viscosity basaltic lava flows build shield volcanoes. Fountaining basalt spatters tephra to build cones. Successive eruptions of pyroclastic debris and basaltic lava build stratovolcanoes, and some explosive eruptions produce calderas. A large explosive eruption can produce a convective plume of ash that rises to stratospheric heights, as well as devastating pyroclastic flows.

An abundance of volcanic ash is likely associated with which of the following? A. a caldera from an effusive eruption B. a caldera from an explosive eruption

B. a caldera from an explosive eruption

What are the processes involved in a typical volcanic eruption listed in order from beginning to end? A. vesiculation, eruption, magma generation, magma migration B. magma generation, magma migration, vesiculation, eruption C. magma migration, magma generation, vesiculation, eruption D. eruption, magma migration, magma generation, vesiculation

B. magma generation, magma migration, vesiculation, eruption

Which volcanic landforms may be affiliated with intermediate to felsic magmas and lavas? Choose all answers that apply. A. shield volcanoes B. stratovolcanoes (composite cones) C. lava domes D. calderas E. cinder cones

B. stratovolcanoes (composite cones) C. lava domes D. calderas E. cinder cones

Andesitic vs Rhyolitic Lava Flows

Because of its greater viscosity, intermediate-composition (andesitic) lava cannot flow as easily as basaltic lava. Typically, andesitic flows are less than a few kilometers long. Because the lava is so viscous, the surface can solidify as it moves, forming angular chunks that may tumble down in advance of the flow. Rhyolitic lava is the most viscous type of lava because it is the most felsic and the coolest. It tends to accumulate above the vent in a lava dome or in a short and bulbous flow.

Relationship between texture and cooling rate?

Because of the relationship between cooling rate and texture, lava flows, dikes, and sills tend to be composed of fine-grained rock. In contrast, plutons tend to be composed of coarse-grained rock.

Earthquake Resonance

Buildings oscillate at certain frequencies or at their natural periods depending on height, mass, design, construction materials, and contents Resonance causes ground acceleration (up to 4 or 5x), when the period of building approximates the period that the ground that it lies on. Similar to the period of the seismic waves going through the ground. Causes more damage. Ex. Mexico City EQ

Mt. St. Helens and Mt. Vesuvius erupted explosively. What were the characteristics of their magmas and lavas? Choose all answers that apply. A. low viscosity B. high temperature C. high silica composition D. high gas content

C. high silica composition D. high gas content

Large depressions caused by the inward collapse of overlying rock into an evacuated magma chamber

Caldera - can be associated with all types of volcanism.

Volatile and explosive tall, conical, glacier-covered Composed of alternating layers of intermediate to felsic lava and pyroclastic material = moderately steep slopes - Simply: Requires steepness to allow sticky lava to flow down

Composite volcano/ stratovolcanoes

3 Waves to prevent resonance?

Changing building period Changing ground period Factor period of seismic wave

What does viscosity or resistance to flow depend on?

Chemical composition. For silica in lava tends to bond together into large molecules that can't move easily. Therefore, basaltic lava is less viscous than andesitic lava, which in turn is less viscous than rhyolitic lava. As a result, basaltic lava can flow farther than andesitic lava, which can flow farther than rhyolitic lava. Viscosity also depends on temperature—a hotter magma is less viscous than a cooler lava of the same composition, because thermal energy breaks chemical bonds linking molecules.

Built from lapilli

Cinder Cone

A conical hill formed by the accumulation of mafic to intermediate silica content pyroclastic material (cinders 4-32 mm) and lava around a volcanic vent Small (<1500 ft high), steep sided (30-40 degree slopes), easily eroded

Cinder cone (can be independent cones or affiliated with shield volcanoes)

Cinder Cone Volcanos vs. Shield Volcano vs. Stratovolcano

Cinder cone Volcano - flank eruptions - strombolian eruption Shield Volcano - pillow basalt - fire fountain Stratovolcano - pyroclastic flow - lahars - felsic lava

Phaneritic

Coarse-grained, crystals are large enough to be seen w/out a microscope, formed by slow cooling (intrusive) Crystals are forming in the magma, growing into each other. Interlocking crystalline texture.

How do you know you're near the epicenter of an EQ using only seismograms?

Compare several seismograms at different locations for the same earthquake. The location with the least delay between P and S waves is the closest to the epicenter.

How do you find distance from the epicenter?

Compare two seismographs. General rule: The greater the distance between the epicenter and a seismograph station, the longer it takes for earthquake waves to arrive, and the greater the delay between the P-wave and S-wave arrival times (S minus P time)

Causes of heating in the earth?

Compression of mass into a smaller volume, the sinking of iron to form the core, the impact of meteorites, and the decay of radioactive elements.

mafic melts

Contain a relatively high proportion of magnesium and iron oxide compared to silica

4 locations an Earthquake can occur (other than subduction zones)?

Continental Collision (mountains ) Intraplate earthquakes (away from any plate boundaries) Rift valleys (crust pulls apart on continental crust) Continental transform faults

(Geographical Features → Type of Fault) Continental transform → Continental Collisional boundary → Active Rifting→

Continental transform → Strike Slip Faulting Continental Collisional boundary → Reverse faulting (compression from collision) Active Rifting→ Normal Faulting (tension from pulling apart crust)

Intermediate/Deep Earthquakes: What plate boundary?

Convergent boundaries (only oceanic-oceanic and oceanic-continental)

Example of Caldera Volcano

Crater Lake, Oregon Formed after large Vulcanian and Plinian-type eruption phases of a stratavolcano (Mt. Mazama), characterized by a voluminous, felsic, high-volatile eruption Formed North America's deepest lake

Which of the following is associated with EFFUSIVE volcanism? A. rhyolite B. andesite C.dacite D. basalt

D. basalt

List the following volcanoes in order from SMALLEST to LARGEST in terms of height and area. A. cinder cone, shield volcano, stratovolcano B. shield volcano, cinder cone, stratovolcano C. stratovolcano, shield volcano, cinder cone D. cinder cone, stratovolcano, shield volcano

D. cinder cone, stratovolcano, shield volcano

Deep Earthquakes Depth

Deep-focus earthquakes occur down to a depth of about 660 km, Earthquakes don't happen below 660 km.

Active Rifting

Deformation is associated with the impingement on the base of the lithosphere of a mantle plume.

Three factors that control the cooling time of magma?

Depth of intrusion, the size and shape of magma body, the presence of circulating ground water

Shallow earthquakes: What plate boundary?

Divergent, transform, and convergent boundaries

How do seismic alert systems work?

Earthquake advance warning systems detect the nondestructive primary waves (P waves) that travel quickly through the earth's crust, in advance of the destructive secondary waves (S waves). The delay between the arrival of P waves and S waves controls the amount of advance warning that can be given. ----> Help us predict their location (where), magnitude (size) and frequency (how often) in the long term but not in short term

List some less common causes of Earthquakes

Earthquakes can occur due to the intrusion and flow of magma beneath a volcano, to underground nuclear tests, to landslides, or even to meteor impacts. Most earthquakes, though, are a consequence of faulting

Where do intraplate earthquakes occur?

Earthquakes that occur in the interiors of plates and are not associated with plate boundaries, active rifts, or collision zones. - The results of stresses caused by plate motions acting in solid lithosphere.

magmatic earthquakes

Earthquakes that result from the strain that accumulates as rising magma forces its way through crustal rocks.

How are effusive and explosive eruptions different?

Effusive volcanism is when non-viscous (mafic) magma allows the gas bubbles to escape once the magma has risen to a lower pressure. Explosive volcanism is when viscous (felsic) magma traps the gas bubbles and pressure builds, causing an explosion.

Intrusive vs. Extrusive

Extrusive rocks tend to be fine grained because they cool more rapidly than intrusive rocks which tend to be coarse grained.

Hot, low viscosity basaltic lava where volatiles escape easily = lava fountains Formation of spatter cones as blebs of lava collect around a vent or fissure After initial degassing, great volumes of basalt flow out of fissures.

Fissure eruptions

Texture as a proxy for thermal history

For igneous rocks with simple, unidirectional thermal histories, generally the faster the cooling rate the finer-grained the texture

Phaneritic textures

Form intrusively below the surface where the surrounding rocks insulate the magma as it cools, providing an environment where the minerals grow slowly to form a coarse-grained texture.

fragmental igneous rock

Fragments of igneous material that have been stuck together to form a coherent mass.

How is frequency measured?

Frequency = cycles / second (hertz) or 1/Period (Hertz)

Relationship between silica content and proportion of gas?

Generally, lavas with more silica contain a greater proportion of gas.

Can mafic rocks be glassy?

Glassy texture develops more commonly in felsic igneous rocks because the high concentration of silica inhibits the easy growth of crystals. But basaltic and intermediate lavas can form glass if they cool rapidly enough.

Types of textures for igneous rocks

Glassy, aphanitic (dull fine grained), phaneritic (course-grained), Porphyritic

Glassy igenous rocks

Igneous rocks consisting of entirely glass, or tiny crystals surrounded by a glass matrix. - cooled rapidly

Intensity vs magnitude (Earthquake)

Intensity relies on how humans and our infrastructure experience the Earthquake. This depends on magnitude, distance from epicenter, duration of shaking, foundation materials, and building style. It is measured on the Mercalli scale. In contrast, earthquake magnitude is the energy released from the earthquake. It does not depend on distance from the epicenter, but rather the amplitude of the largest ground motion recorded on seismographs and it is measured by the Richter scale.

Diorite and Andesite

Intermediate rocks

Intermediate Earthquakes Depth

Intermediate-focus earthquakes take place between 60 and 300 km

Plutons

Intrusive igneous rock bodies, including batholiths, stocks, sills, and dikes, formed through mountain-building processes and oceanic-oceanic collisions; can be exposed at Earth's surface due to uplift and erosion.

Intrusive vs. Extrusive Igneous Rocks

Intrusive: aka plutonic rocks that form from the crystallization of magma at depth and can produce coarser-grained interlocking textures. Extrusive: aka volcanic rocks form from the crystallization of lava on the surface and produce finer-grained interlocking textures.

Example of Caldera Volcano

Kilauea Hawaii Each collapse dropped caldera floor ~2.5 meters and released the energy to a magnitude 5 earthquake

Biggest amplitude wave?

L/R waves > S waves > P waves

Dangers of Earthquakes

Landslides, liquefaction, fire, disease outbreaks, tsunamis

Bombs (geology)

Larger blobs of soft lava that squirt out of a vent and then solidify becoming streamlined bombs.

Shield volcano characteristics

Largest type of volcano, broad, low, dome-shaped, low viscosity basalt magma (mafic), create pillow basalt rocks underwater

Forms from small amounts of viscous, felsic, low volatile lava extruding after the main eruption above the vent and inside the crater. Often after degassing from Vulcanian/Plinian-style eruptions. - provides a "plug" to the vent

Lava Dome

pillow lava

Lava that cools underwater, taking on a distinctive pillow-like shape as it hardens

Silica Composition and Color Intermediate:

Light and dark

Love waves

Love waves are surface waves that vibrate the ground in the horizontal direction perpendicular to the direction that the waves are traveling. They are formed by the interaction of S waves with Earth's surface and shallow structure and are dispersive waves. Can only travel through solids. Third to arrive.

Volcanic Hazard: Lava Flows

Low viscosity lavas in Hawaiian-type eruptions are greatest lava threat because they can flow quickly and spread laterally. Eruption temperature ~1300 degrees celsius. Travel speed: 10-3000 meters per hour Travel distance: up to 150 kilometers Can be voluminous and difficult to predict travel paths Primary: Cause infrastructure and property damage, disrupt services Secondary: gas in the air

basalt and gabbro

Mafic

Summary Slide

Mafic - Basalt - lower silica % - high temperatures - low viscosity - effusive Felsic - Rhyolite - light colored - low temperature - high viscosity - explosive

Why is mafic melt less viscous than felsic melt?

Mafic melt is less viscous than felsic melt because relatively more silicon-oxygen tetrahedra occur in felsic melt. These tetrahedra link together to make long molecules that can't move past each other easily.

Silica Composition and Color Mafic Rocks:

Mafic rocks are dark-colored (black and green) due to Fe- and Mg-rich minerals ex. Augite and Olivine

example of shield volcano

Mauna Key in Hawaii. - World's tallest mountain

Factors of Moment Magnitude?

Mw = 2/3 log10(Mo) - 10.7 *don't need to know* Mo = (rock shear strength) x (fault rupture area) x (displacement along the fault)

Why do P-waves travel through both liquids and solids?

P-waves- can travel through liquids because liquids are compressible can travel through solids because they are compressional

Generally and Literally: How do you determine the period of a building?

Period = # stories/ 10 (general rule) Period = 1/ Frequency (second)

Periodite, gabbro, diorite, granodiorite, granite

Plutonic rocks

Porphyritic textures

Possess two or more distinct mineral grain sizes, indicating an environmental change as the magma cooled (e.g., cooling slowly and then more rapidly).

Blocks (geology)

Pyroclastic debris from basaltic volcanic vents that are created from fragments of already-solid lava from the walls of the vent.

Why are megathrust earthquakes always M9.0 or greater and can be associated with tsunami?

Return period is high, frequency low due to buildup of stress (this takes a while)The overlying plate deforms (shorterns horizontally and lengthens vertically as strain accumulates. Elastic rebound of the overlying plate at a subduction zone can create tsunami.

Richter vs Moment Magnitude (according to Norton Text)

Richter Magnitude: - Measures earthquakes whose focus lies close to the surface - Measures earthquakes with epicenters close to the seismograph station - Based on wave amplitude - Initial magnitude record Moment Magnitude - Considers amount of slip on the fault - Most accurate representation of an earthquakes size - Takes into account the dimensions of the fault - Official magnitude recorded in books

Pyroclastic rock

Rock made from fragments that were blown out of a volcano during an explosion and were then packed or welded together

How do the velocities of S- waves change throughout the Earths layers?

S-Wave is gaining velocity through the crust, then it slows at the asthenosphere or low velocity zone. It speeds up through the rest of the upper mantle, and lower mantle, then it stops as it hits the outer core, and reappears in the inner core at a lower velocity as a non-primary S-wave but an S-wave that is birthed at the interface from the P wave

Why do S-waves only travel through solids?

S-waves- can travel through solids because solids have shear strength cannot travel through liquids because liquids do not shear

S-waves

Seismic body waves that oscillate perpendicular to the direction their waves are traveling.

Landslides and Avalanches

Shaking causes material on steep slopes to fail and frequently accompany earthquakes in uplands

Shallow Earthquakes Depth

Shallow-focus earthquakes occur in the top 60 km of the Earth

Volcanic Landforms with Height and Slope

Shield volcanoes (28,000 ft 5-10 degrees) Stratovolcanoes/Composite Volcanoes (8000 ft 10-25 degrees) Volcanic domes (2000 ft steep slope) Cinder cone volcanoes (1500 ft 30-40 degrees) Calderas (Diameter: 1.45 miles)

Why do igneous rocks have silicate?

Silicate rich mantle and crust melts to create igneous rocks.

Dike vs Sill

Sill: Follow bedding, concordant Dike: Cuts across bedding; discordant

Why could a Mw6.5 earthquake with a focus of 6 km depth be more damaging than a Mw8.0 earthquake with a focus at 500 km depth?

Since the focus is closer to the surface, more damage will be felt by people.

Lava flows interlayered with tephra

Stratovolcano

How an Earthquake occurs (duplicate question)

Stress builds -> new fault or slip on pre-existing fault -> elastically deformed rock on either sides of the fault rebounds→ seismic waves are generated→ faults have stick-slip behavior The focus or hypocenter is the point within the Earth where the slip begins The epicenter is the point on the Earth's surface vertically above the focus.

Rayleigh waves

Surface waves that travel in a backward-rotating, elliptical motion, causing both vertical and horizontal ground movement. Can travel through solid, liquid, and gas. Fourth to arrive. Dangerous.

Do taller buildings have higher or lower freq and periods than shorter buildings?

Taller building: low frequency (num of cycles), higher period (time of cycle)

What contributes to volcanic landforms?

Temperature, silica content, viscosity, volatiles -> eruptive style -> landforms

How do the velocities of P- waves change throughout Earths layers?

The P wave is gaining velocity through the crust, then it slows at the asthenosphere or low velocity zone. It speeds up through the upper mantle, lower mantle, and the slowing down dramatically at the outer core and regaining velocity at the inner core but staying at a constant velocity all the way through

Richter Magnitude Scale

The Richter scale defines earthquakes on the basis of the largest ground motion recorded or greatest amplitude of S-waves on a seismogram.

Displacement (geology)

The amount of slip on a fault

What's the name of the layer where BOTH P- and S-waves SLOW DOWN?

The asthensosphere. Low Velocity Zone- The asthenosphere in the upper mantle where seismic waves travel more slowly, probably because rock has partially melted (or deformed plastically) and seismic waves move slower in liquid.

Geotherm

The change Earth's in temperature with depth.

Source Rock Melting

The composition of a melt reflects the composition of the solid from which it was derived.

P-waves

The fastest velocity seismic waves where compression and dilation of particles is in the same direction the wave is traveling.

fractional crystallization

The continuous process of removing mafic minerals from the magma results in a chamber enriched in magnesium and iron at its base, but with an overall much more intermediate magma throughout.

lava tube

The empty space left when a lava tunnel drains; this happens when the surface of a lava flow solidifies while the inner part of the flow continues to stream downslope.

Stress (geology)

The intangible force applied to Earths materials

What composes the mantle?

The mantle is composed of the solid rock called peridotite.

Why do waves travel faster through the mantle than the crust?

The mantle, made of peridotite, is denser than the crust, composed of granite. Thus, waves will travel faster through peridotite.

What is a recurrence interval? Limitations? Formula?

The number of years between Earthquakes of the same magnitude - Can't predict next EQ, only probability (1/RI) RI = (time span of data) / (cases of magnitude M)

Magma chamber

The pocket beneath a volcano where magma collects. They hold a "mush" consisting of solid, but hot, crystals mixed with melt. Very high magma pressures can develop in a magma chamber, and these pressures can push magma into underground cracks, sometimes all the way to the surface.

Elastic Rebound Theory

The theory that continuing stress along a fault results in a buildup of elastic energy in the rocks, which is abruptly released when an earthquake occurs. Another definition: How rocks deform slowly through time and "bounce" back to their near original shape when stresses are released.

How do the velocities of seismic waves change as they get farther from the focus of the earthquake?

The velocities of seismic waves traveling from earthquake foci generally increase with depth, occasionally making abrupt jumps termed seismic-velocity discontinuities.

Brittle Failure

The way a rock breaks to form faults

Pyroclastic debris from Andesitic and Rhyolitic Eruptions

These lavas are more viscous than basalt and richer and gas. They tend to be explosive and eject lots of pyroclastic debris, such as ash, pumice lapilli, accretionary lapilli,

S-wave Shadow Zone

Those areas more than 103 degrees from an earthquake focus where no S-waves are recorded. - According to text: 103 degrees - 180 degrees

True or False: An increase in one magnitude in number represents a 10 fold increase in the amplitude of shaking at a reference distance (Intensity), and a 32 fold increase in energy release from the source (Moment Magnitude)

True- Remember the moment magnitude scale values are converted to a logarithmic scale so it mimics the Richter scale. Mw = 2/3 log10(Mo) - 10.7 Mo = (rock shear strength) * (fault rupture area) * (displacement along the fault)

magma mixing

Two chemically distinct magmas may produce a composition quite different from either original magma

What are the different types of earthquakes common in the Pacific Northwest? Which ones are likely to cause more ground shaking (refer to the next question for a hint)?

Types: subduction, deep, and crustal. Crustal Earthquakes cause more ground shaking, because the focus is closer to the surface.

Komatite and periodite

Ultramafic

Do waves refract away from or towards denser/more rigid material?

Waves bend towards slower or less dense material. This is why P-waves refract or bend inwards towards the liquid core.

vesicles in geology

When lava freezes, the bubbles are trapped in the rock and become holes called vesicles. In high-viscosity magma, gas has trouble escaping because bubbles can't push through the stick lava.

Volcanic Debris Flows and Lahars

When volcanoes are covered with snow/ice, or are drenched with rain, water can mix with debris to form a volcanic debris flow that moves downslope like a sheet of wet concrete. When ash-rich debris becomes very wet, it turns into a muddy, rapidly flowing slurry called a lahar.

Discuss secondary hazards/disasters/problems that can happen as a result of a moderate to large magnitude earthquake and what can be done to mitigate or prevent them.

You have the primary disaster → then other things that come from thatEx.) San Francisco Fire: there was a fire but no water to put it out Ex.) Disease in Haiti: cholera outbreak → disease took off as a result of damaged infrastructure and no food

Mineral definition

a naturally occurring, inorganic solid that has a fixed crystalline structure and a definite chemical composition formed by geologic processes.

xenolith

a piece of rock within an igneous rock that is not derived from the original magma but has been introduced from elsewhere, especially the surrounding country rock.

Fault scarp

a small step on the ground surface where one side of a fault has moved vertically with respect to the other

pyroclastic debris

ash, lapilli, blocks, bombs

Tephra

bits of rock or solidified lava dropped from the air during an explosive volcanic eruption; ranges in size from volcanic ash to volcanic bombs and blocks

Pyroclastic Debris from Basaltic Eruptions

blocks, bombs, and cinder-like lapilli

Why does magma rise?

buoyancy and magma pressure

EQ Hazard

ground shaking. landslides. liquefaction.

An aphanitic texture

is a fine-grained texture where the mineral crystals have cooled relatively rapidly at or near the surface of the Earth. Typically, the mineral composition of rocks with aphanitic textures cannot be identified by the unaided eye.

Igenous rocks form from

magma, created by the melting of pre-existing rock, crystallizing in the crust OR when it reachest the surface through fractures and extrudes as lava.

What are the 5 factors of the Mercalli Intensity Scale?

magnitude, distance from epicenter, duration of shaking, foundation materials, and building style

decompression melting

melting that occurs as rock ascends due to a drop in confining pressure

Kilauea, Hawaii

most active volcano in the world - shield volcano - East Rift Zone - also causes Earthquake

volcanic cone

mountain that forms as a result of volcanic activity

Stoping by magmas occurs when ____________.

pieces of surrounding country rock are broken off and assimilated

Melt that is explosively ejected in a volcanic eruption is called

pyroclastic debris

Volcanic glass

rock that forms when lava cools to quickly to form crystals. Obsidian and pumic

EQ Vulnerability

soft stories, unreinforced masonry, vertical irregularity

Magma contamination/assimilation

the process in which flowing magma incorporates components of the country rock through which it passes

flux melting

the transformation of hot solid to liquid that occurs when a volatile material injects into the solid

Volcanic Gas

water vapor, carbon dioxide, sulfur, and nitrogen