Test 2 - Geology

Earthquakes and Earthquake Hazards Minerals Igneous Rocks

What are Earthquakes?

ground shaking casued by the sudden and rapid movement of one block of rock sliding past another

• Only occurs in lithosphere

What is Elastic Rebound theory and its relation to earthquakes

As the rocks break they “snap back” to their original shape causing vibrations, but now in a new location

• energy has to be built up and stored due to friction, then a fast and sudden release

• Think breaking a stick

What are Faults?

A location where rocks slide past one another along fractures in the crust/lithosphere. Most are locked due to confining pressure

Earthquakes are not random, occuring when and where

At interactions at plate boundaries (divergent. convergent, transform). Most catastrophic earthquakes occur at convergent boundaries or along continental transform.

Events also occur at MOR, continental rifts, and along weak faults with plate interiors. (Non-plate boundary plates)

What is the epicenter of an earthquakes?

The spot on the surface of the earth where motion of eearthquakes is recorded. Directly above the hypocenter/focus

What is the hypocenter/focus of an earthquake?

Deep in the ground, where motion begins for earthquakes. This is where earthqakes originate

What are seismic waves or ripples in relation to earthquakes

Energy waves of stored up energy that radiate from the hypocenter/focus in all directions

What is the difference between foreshocks and aftershocks?

Foreshocks - smaller earthquakes that occur an earthquake; can sometimes predict major earthquakes by days

Aftershocks- smaller earthquakes that occur after and earthquakes; aftershocks often trigger the destruction of already weakened structures; lesser magnitude

Most earthquakes occur at what two types of plate boundaries?

1) Convergent

2) Transform

What is are the relations between earthquakes and convergent plate boundaries?

1) Convergent plate boundaries are associated with thrust faults (a reverse fault with a low angle).

2) In subduction zones, boundaries at convergent plates form a megathrust fault

3) Produce most powerful earthquakes due to compressional stresses

What is a thrust fault?

A reverse fault with a low angle

What is the realtionship between transform plate boundaries and earthquakes?

As transform boundaries slide pass one another, some segments have the fault being stuck and other segments have smaller movement like skips (fault creep) . Thus a large fault has different sections with higher or lower propbablity of an earthquake based on geological history.

What is fault creep?

When plates graudally slide past each other, therefore less strain is accumalting over time, so less energy is stored and it is less likley for an earthquake to occur.

What is the defintion of seismology and the earliest form of this study?

The study of earthquake waves (seismic waves)

• earliest form of this study dates back 2000 years ago to the Chinese, where they would have a small container with a marble that could give direction that the earthquake/seismic wave were coming in

Today, what are used to record earthquakes?

Seismographs (though a little outdated as we are moving to use computers, but the same process is done except with electrial signals instead of a pen)

• Siesmographs were these rotating drums connected to a plate screwed into the earth. A pen would be suspended by a wire and when earthquakes happened, the waves would move the oceans, rocks, and the drums. The drums then would move the pen, creating a seismograms to record earthquakes.

What are seismograms?

A signal produced by seismographs to record earthquakes.

What are the two types of seismic waves

1) Body waves - seismic waves that travel through the earth’s interior/lithosphere

• Primary body waves - compressional waves that travel through all materials (gas, liquids, solid) that push and pull (in direction of motions) Ex. slinkey toy [P interval lag time]

• Secondary body waves - shear waves that can only travel through solid material. They shake at right angles. Ex. A rope moving up and down [S internal lag time]

2) Surface waves - seismic waves that travel just travel below the surface of the earth; lowest velocity; highest amplitude; greatest/majority of damage is this. Energy becomes less and less like ripples

• Rayleigh waves - think ocean waves on a boat. Buildings can withstand this, ground moves up and down [R waves]

• Love waves - ground moves side by side, causes greatest destruction [L waves]

What is triangulation in realtion to earthquakes?

A method to find epicenter, need at least 3 recording centers. To find, measure time from P to S lag time. Travel time graph, distances for each, mark a line. See where the 3 intersect.

What are the different measurements used to describe the size of earthquakes?

1) Intensity scales - observed property damage to estimate the amount of ground shaking

2) Magnitude - use data from seimograpghs to estimate the amount of energy released

We can determine the size of destruction of earthquakes due to what firstly made scale?

Modified Mercalli intensity scale

• based of of property damage in a region

• scale of 1-10

• intensity based off of how close you were to the epicenter.

Today, we now use what scale to determine the size of destruction of earthquakes?

In 1935, Richter scale

• Measure the amount of energy release by Charles Richter scale

• 1-10 scale

• calculated by measuring the amplitude of the largest seismic wave (usually S wave) recorded on a seismogram

• logarithmic

• Each unit on the scale means a 10-fold

  difference in wave amplitude and a 32-

  fold difference in energy released. Ex. 1-2 is 30 times, but 1-3 is 30 times 30

Earthqaukes needs to be greater than what on the ritcher scale to feel them

4

The Ritcher scale used what originally to scale, and now what do we use?

Orginal - LM (local magnitude)

Now - Mw (Moment magnitude), which measures total magnitude total enemy released during an earthquake

In conclusion, earthquake size is characterized by what two things

intensity: based on amount of damage; Modified Mercalli Intensity Scale (I-XII)

magnitude: based of amount of energy released; Richter Scale, is logarithmic, each unit on the scale means a 10x fold increase in amplitude on the seismogram which translate to a 32x increase in energy released

The greatest earthquakes occur where?

At the Circum-pacific belt

4 major factors in the amount of destrcution in earthquakes are what?

1) Intensity and duration of the vibrations

2) Construction practices of the region

3) Nature of the material on which the structure rests on

4) Distance from the epicenter

Also with destruction caused by fire, landslides and ground shaking

What is Liquefaction

A phenomenon when lossely packed, waterlogged sediments behave as a fluid during the intense shaking of an earthquake. (Refrence to number 3 of the major factors in the amount of destruction) Ex. Japan apartment buildings

What natural disastres actually cause destructions becasue of an earthquake?

1) Landslides - ground shaking causing loose sediments on a slope to slump

2) Fire damage - can start when gas and electrical lines are destroyed by an earthquake

3) Tsunamis - a series of large ocean waves. Very small on open water, but gathers and gets bigger was we move to the shore. Subduction

What is the defnition of a Mineral?

A mineral is a compound of elements, a compound being something that cannot be physically broken apart(elements that are chemically bound together)

What are the defined characteristics of minerals

1) naturally occuring

2) have orderly crystaline structures (internal repeated structure)

3) solid

4) a definite chemical composition that allows for some variation (Ex. Olivine (MgFe)2 SiO4

What is the defintion of a rock?

A rock is a solid mass (mixture) of minerals

What is the definition of atoms?

Atoms are the smallest particles of matter that cannot be chemicallly split

Atoms are composed of what 3 things

Protons (+1 charge) and Nuetrons (0, neutral charge) surrounded by electrons (-1 charge)

Eletrons interact with other electrons to produce what?

Chemical Bonds

Weight of atoms lie where?

In the nucleus

Electrons exist as what in an atom?

As a cloud of negative charges surrounding the nucleus of protons and neutrons

What are principle shells?

Regions where electrons move about the nucleus

The outermost principle shell contains valance electrons. What are valence electrons?

Electrons on the outmost shell that interact with other atoms to form chemical bonds

What is an atomic number?

The number of protons in the nucleus of an atom that determines the atom’s chemical nature and its name

The first shell of an atom can hold how many electrons

So small, only 2 electrons

The second shell of an atom can hold how many electrons

8

The third shell of an atom can hold how many electrons

8

What does the Octet rule state?

That mother natures wants the most stable shell (by having 8 valance electrons). There are few exceptions to this rule. To get stable, the atom will gain, lose or share electrons under a chemical reaction

What are the 3 types of chemical bonds

1) Ionic Bonds - transfering valence electrons

2) Covalent Bonds - sharing valence electrons

3) Metallic Bonds - sharing valence electrons

What happens in the process of Ionic Bonds

Atoms gain/lose valance (outermost) electrons

What happens in the process of Covalent bonds

• It is the strongest bond

• Atoms share electrons valence (Ex. H2)

What happens in the process of Metallic bonds

• Found only in metallic minerals

• So close together that electrons lsoe thier movement so valence electrons are free to migrate amoung atoms

• Like dominos, energy transfers, not the actual electrons

Metallic bonding gives materials what properties

• Malleable

• Ductile (drawn into thin wires)

Most minerals have a hybrid bond. What does that means

Means that electrons not only share, but transfer as well

What are the 3 different processes that minerals can be made from?

1)Percipitation from solution , important for sedimentary rocks

2)Crystalization during cooling, important for igneous

3)Deposition due to biological organisim

What is the process of percipitation that forms minerals

Occurs when a solid forms than falls out of solution

Ex. Evaporate deposites and geodes

Ex. Salt Lake forming saltflats

What is the process of crystalliztion that forms minerals

Similar to waterr freezing, liquid to solid

Ex. molten rock (magma) crystalizes as it cools off to freezing point, crystals form to make minerals (which depend on magma compostion)

What is the process of deposition that forms minerals

Based on biological processes. So water dwelling organism take in saltwater (calcium), filter it out, add carbin/oxygen to form a mineral (think the shell of an oyster, clams, coral reefs)

What are the properties of minerals (did in lab)

Metallic vs nonmetallic

Color (though not as important)

Streak

Cleavage

Fracture

Density

Other properties like hardness

Any mineral samples are what

Crystals or crystalline solid

• as well as atomic arrangement that result in basic building blocks —> unit cells

• Ex. repeating colors

Within unit cells, there are what

Repeating elements (compostion of minerals)

• Can be variations, such as ions of similar size can be substituted for one another

• Some have no variations availiable: trace elements can influence color, ex. quartz

What is a polymorph?

Minerals with identical composition but different crystalline structures. Ex. diamond and graphite

There have been about 4-5 thousand minerals named, but only a handful that are common. What are the common minerals called? and list them all

Rock forming minerals

1) O

2) Si

3) Na

4) Mg

5) Fe

6) Al

7) Ca

8) K

What are the 8 most adbundant minerals that make up most of the continental crust

1) Oxygen

2) Silicon

3) Iron

4) Potassium

5) Magnesium

6) Soduim

7) Calcium

8) Almumiun

75% of the earths crust are made from what two most abundant minerals

Silcon and oxygen

Most minerals are seperated into 2 minerals groups based on anions/anionon moelcules

1) Silcate minerals - any material made of oxygen and silcon. most abundant. largest and most common groups. makes up 90% of earths crust

2) Nonsilcate minerals - not as common, but still important economically. Ex. carbonates

Ways to elminate charges to create minerals

1) add cations (positive)

2) link Si-O tetrahedrons to another tetrahedrons (move closer to nuetrons)

3) Combination of both

Most silcate minerals come from crysalization of what

Molten rock

Which silcate mineral is the most common?

Feldspars (50% of the earth’s crust)

Second most common is quartz

Silicate is seperated into what two groups?

Light (non-ferromagnesim)

Dark (ferromagnesian) groups

What arer the two types of light silicates

1) Potassium

2) Plagiclase/sodium calcium

What characteristics are of light silicate minerals

generally light in color

lack of Fe & Mg

consists of quartz. muscovite, caly minerals, and kaolinte

contains varyinf amounts of Al, Ca, K, and Na

What characteristics are of dark silicate minerals

Contain Iron and/or magnesium

henerally dark in color

Common common minerals include olivin, pyroxene, amphiblole, biotite, garnet

What are some characteristics of Non-silicate minerals

They make up 8% of earths crust

Subdivided based on negativily charged ions or complex ion that the members have in common

Soem examples include oxides, carbonate, sulfides

What is the definition of magma

Completly or partially molten rock located within th earth

What is the definition of lava

The penatration of magma on the surface of earth

Magma consits of 3 parts. What parts are those

1) Liquid protion = melt

2) Solid = as magma sloidified, it can form a solid portion of magma

3) Volatiles = dissolved gases, think a drink of Coke or Spirte. Basically dissolved gases in the melt that vaporize at surface pressure. Ex. Water vapor, carbon dioxide, sulfur sioxide

Why is lava missing the volatile portion compared to magma

Because it escapes when the lava erupts onto the surface

Magma goes from what to what

Magma to crysttalline rock

Over 99% of magma is what kind of magma

Silcate magma (rich in siicate/oxygen)

What is the defintion of crystallization?

The cooling of magma

What are the two steps to crystallization

1) Silcon and oxygen atoms link together first to form oxygen-silicate tetrahedra

2) As heat loss continues, the tetrahedra join with each other (polymenzation) and other ions to form crystal nuclei

Igneous rocks are subdivided into 2 types. What are those 2 types

1) Intrusive (Plutonic) - magma that crystallizes within the earth; basically you tend to see large crystals

2) Extrusive (Volcanic) - the solidification of lava on surface of earth; basically they cool so fast that they tend to have very small crystals

What is a magma chamber

an area in the earth where magma sits until possible eruption onto the surface

Igneous rocks are mostly made up of what type of minerals

Of both light and dark silicate mineral

What does the word ferromagnesium mean when one says light ferromagnesium silcate minerals

Basically silicate minerals that are rich iron and magnesium

What does the word nonferromagnesium mean when one says dark nonfeeromagensium silicate minerals

Basically silicate minerals that have very little to non iron and magnesium.

What are the 4 broad groups of Igenous rock’s by mineral compostition

1) Felsic - granite, rhyolite

2) Intermediate- diorite, andesite

3) Mafic - gabbro, basalt

4) Ultramafic - peridotite, komatiite

Describe the felsic igneous rock group, its composition, how it forms and the most common in the group if applicable

Aka the granite composition, since granite is the most common in this group

• major constituent of continental crust

• forms mostly due to melting of continenetal crust

• has about 10% of dark silicate

• most rich in nonferrmagneium

Describe the intermediate igneous rock group, its composition, how it forms and the most common in the group if applicable

aka the Andesitic compostiion, since andesetitic is the most common

• 25% or more dark silicate minerals

• associated with volcanic activity at convergent plate boundaries

Describe the mafic igneous rock group, its composition, how it forms and the most common in the group if applicable

aka the Baslatic compostion, since basalt is the most common

• Comprises the ocean floor and many volcanic islands (think hawaii)

• Forms mostly at divergent plate boundaries, hotspots

• 45% dark slilcate and calcium rich feldspar

Describe the ultramafic igneous rock group, its composition, how it forms and the most common in the group if applicable

• composed of almost entirely of ferromagneium, rich in it

• rare composition, mostly olvine and pyroxene

What is the defintion of viscosity

resistance to flow

Crystal rocks have a range of what kind of content, and about how much

Silica content, 40%-75%

What are the names of the two magmas formed when silica content is iinfluence

1) Granitic magmas - high viscousity, go through polymerization more (like in chains togother, so more resistance to flow); high silica content, erupt at lower temperature

2) Basaltic magmas - lower silca content, more fluid so lesser viscosity

What is the definition of polymerization

any process in which relatively small molecules combine chemically to produce a very large chainlike or network molecule

Ex. linking of Si-O tetrahedrons in silicate minerals

The overall apperance of an igneous rock is based on what

on the size of mineral grains (so whether or not it is intrusive or etrusive)

What is the big factor that influences igneous rock texture and size

The rate of cooling

• Intrusive rocks → cool very slow →has fewer but larger crystals

• Extrusive rocks →cool very fast →has more but smaller crystals

What are the 3 types of igneous texture

1) Aphanietic, aka extrusive or volcanic rock - finely grained texture becasue has rapid cooling. cant see grain

2) Phanerititic, aka intrusive or plutonic rock - coarse grained texture becuase has slow cooling. Large visible crystals

3) Porphyritic, aka has both coarse AND fine texture. Large crystals embeddded in a matrix of small crystals. Possible due to 2 step cooling, where a rock was in the earth, got erupted suddenly due to a circumstance, then the rest of it cooled on the surface.

Igneous rocks that are porphyritic in texture are called what kind of rocks

Porphyry

• Note: you use the word porphyry as a surname to the rock name. Ex. granite porphyry, andesite porphyry, etc

4 other special texture catorgories that igneous rocks can have

1) Vesicular texture - rock contains holes/voids left by gas bubble in the lava

2) Glassy texture - rapid cooling, no crystals form cause it cools super super super fast

3) Fragmental or Pyroclaustle texture - forms from the consolidation of individuals fragments ejected during explosive eruptions, forming rocks called Tuffs

4) Pegmatite texture - heehe JRWI. exceptionally coarse grained. Typically tens of cm HUGE

What is the importance of texture for igneous rocks

Texture tells us when they crystalize

Remember: Igneous rocks classification based on what

Mineral compostion (mineralogy, which can influence color of rock)

Texture

How does magma form

Due to a change in temperature as you go into the earth (aka the Geothermal gradient)

Temperatures in the earths crust increase by how much

25*C per kilometer in the lithosphere