Geology Exam #2 Earthquakes and Minerals

The modified Mercalli intensity scale measures

the amount of destruction caused by an earthquake

An earthquake's Richter magnitude is based on

the amount of ground movement caused by seismic waves

What does the elastic rebound theory describe?

the build-up and release of strain energy during an earthquake

What is true of neutral atoms?

the number of electrons must equal the number of protons

Atomic Number

the number of protons in any atom, fixed

Isotopes of a given element have

the same number of protons but different atomic masses

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

three

Why did Richter develop the Richter Magnitude scale?

to compare the sizes of local earthquakes her in Southern California (Local Magnitude Scale)

Magnitude

total amount of strain energy released by an earthquake

As a rule of thumb aftershocks are typically ____ order(s) of magnitude ____ than the mainshock.

1; lower

What happens if you change the pattern of atoms in a mineral?

You change what the mineral is

What is the difference between a magnitude 8.0 & 1.0?

The length of the fault break

Scientists cannot accurately predict earthquakes

Which of the following statements best describes the current state of earthquake prediction?

As we go deeper in Earth and the pressure grows we encounter minerals with

more compact crystal structures

Minerals

any naturally occurring, inorganic, solid chemical compound, with a more or less fixed chemical composition, is homogeneous in its chemical and physical properties, and has a regular arrangement of its constituent atoms

Isotopes

atoms of the same element that have different number of neutrons

Which of the following measurements collected from seismograph stations gives scientists information regarding the type of faulting that occurred during an earthquake?

the first motion of the P waves

Which of the following substances is not considered a mineral?

coal

Framework Silicates

complex 3-dimensional networks of silica tetrahedra ex. Quartz ex. Feldspar (Plagioclase & Orthoclase) (most common crustal mineral) Si:O Ratio = 1:2

Reverse faults form in response to ______ forces.

compressive

What is the strongest type of bonding found in minerals?

covalent bonding

Strike-slip fault motion

motion along fault is generally in a horizontal (side-to-side) motion

Strike-slip Fault

motion along fault is generally in a horizontal (side-to-side) motion at transform plate boundaries (ex. San Andreas fault)

Dip-slip fault motion

motion along the fault is generally in a vertical term-92 (up-dowterm-1n) direction

Isotopes of an element have different numbers of

neutrons

What is an ion?

any formed atom

Amplitude

Height of the highest wave recorded above baseline in millimeters

Which of the following types of seismic waves arrive at a seismograph first?

P waves

Which of the following correctly lists the order in which seismic waves arrive at a seismograph station?

P waves, S waves, surface waves

Best we can do is long term forecasting based on

Paleoseismic (ancient earthquake) record

What mineral makes up most of the mantle?

Perovskite

_________ is the most common mineral or mineral group in the Earth as a whole.

Perovskite

Hypocenter

Point where fault break starts; Location of an earthquake

Graphite and Diamond are carbon atoms that are considered what?

Polymorphs

What are atoms composed of?

Protons (+), neutrons (neutral), electrons (-)

Which of the following minerals is a framework silicate?

Quartz, orthoclase feldspar, and plagioclase feldspar

Thrust Fault

Reverse fault with a dip-angle less than 45º

Joint

Scientific term for a crack along which no movement has occurred

Foreshock

Smaller earthquakes prior to mainshock

Aftershock

Smaller earthquakes that follow mainshock

Epicenter

Spot on surface directly above hypocenter

Where are electrons located?

Surround the nucleus

right-lateral strike-slip

The San Andreas fault is what type of fault

oxygen and silicon

The two most common elements in Earth's crust are

Which of the following is not a dip-slip fault?

a right-lateral fault

Which of the following types of seismic waves are the slowest?

surface waves

A fault line long-term slip rate of 5 cm/year and slips 2.5 m when it moves. What is the recurrence interval of the fault?

50 years

Fault and how it produces earthquakes

- 2 sides of fault try to move past one another due to tectonics - 2 sides get stuck because of friction - Pressure or strain energy builds along fault and accumulates - That energy is released in the from of Seismic waves

Method to determine the location (Hypocenter)

- Count, in seconds, the time difference between arrival of 1st P & S wave - Multiply by 10 - Gives difference to hypocenter - in km

Modified Mercalli Scale of Intensity

- How much damage caused by an earthquake and how people react. - Rates intensity from I to XII - I = No damage; not felt - XII = Total destruction

Normal Fault

Hanging wall down foot wall up. Generate small to moderate sized earthquakes.....Extend the earths lithosphere at divergent plate boundaries

What are the factors that affect intensity?

- distance away from the epicenter, - depth of the earthquake - population density of the area - local geology of the area - type of building construction in the area - duration of the shaking

What is true of the bonding process?

- through the bonding process atoms gain or lose electrons - minerals form - due to the bonding process there are approx. 4,000 known minerals on planet earth - divide these into just a few groups based on what the Anionic molecule is

What will be the charge of an atom containing eight protons, nine neutrons, and 10 electrons?

-2

Sodium has an atomic number of 11. How many electrons will the sodium ion Na+ have?

10

The ground motion during a Richter magnitude 8 earthquake is ______ times greater than the ground motion during a Richter magnitude 6 earthquake.

100

What is the estimated recurrence interval for a fault line that has a slip rate of 3 cm/year and slips 3 m every time it moves?

100 years

The energy released during a magnitude 8 earthquake is approximately ______ times larger than the energy released during a magnitude 6 earthquake.

1000

In southern California, great earthquakes occur on the San Andreas approximately every ______ years.

150 to 300

Method to determine the magnitude of an earthquake was first developed in ________ by ________?

1930's; Charles Richter

Why did we switch to the Moment Magnitude Scale?

1970's they realized the Richter scale tends to underestimate the size of big earthquakes

Following a mainshock of magnitude 6 one could expect aftershocks as strong as

5

A fault line has recurrence interval of 100 years and a long-term slip rate of 5 cm/year. How much does the fault slip when it ruptures?

5 m

Alpha Decay

A helium atom is ejected from the nucleus

Dip angle

Angle between Earth's surface, or a plane parallel to Earth's surface, and fault

,the time between the arrival of the P and S waves increases

As the distance to an earthquake increases

Anions

Atoms that gain electrons (become negatively charged)

Cations

Atoms that lose electrons (become positively charged)

Types of Seismic waves

Body waves: - Primary (P) waves - Fastest - Secondary (S) waves - 2nd Fastest Surface waves: (cause most damage) - Love waves (L-waves) - Slowest - Rayleigh Waves

Reverse Fault

Hanging wall up foot wall down. Generate large earthquakes.....Shortens or compress lithosphere at convergent plate boundaries

Elastic Rebound Theory

Build up and release of stress during an earthquake

Who developed the procedure used to measure the size of an earthquake?

Charles Richter

_________ and __________ are examples of polymorphs.

Diamond; graphite

From seismograph recordings we can determine

Earthquake size, location, and fault type

Beta Decay

Electron is ejected out of the neutron changes into a proton

Focus

Entire section of fault that breaks

Fault Scarp

Exposed surface of the fault

_________ is the most common mineral or mineral group in Earth's crust.

Feldspar

Richter Scale conversions

For each magnitude increase of 1.0 on Richter scale, the ground motion increases by 10x For each magnitude increase of 1.0 on Richter scale, the energy increases by aprox. 32x

Where are protons and neutrons located?

In the nucleus

Basic unit of energy for the Moment Magnitude Scale?

Joule (better measure of the total energy released by an earthquake

Mainshock

Largest earthquake in a sequence. Not all mainshocks have foreshocks - We don't know what the mainshock is until after the sequence ends (may be separated by years)

What is Mercalli Intensity controlled by?

Location, opinion, and construction

Moment Magnitude Scale

Moment magnitude measures the size of events in terms of how much energy is released

Can we predict (size, location, time) of earthquakes?

No

Do small earthquakes reduce the probability of a larger one occurring along a fault?

No

Baseline

No seismic activity on a seismograph, no earthquake

Most abundant elements in Earth's crust?

Oxygen 46.6% and Silicon 27.7% and Aluminum 8.1% . They bond to form approx. 95% of all minerals that make-up the crust. These are called SILICATE MINERALS

"Blind" Thrust Fault

Thrust fault that does NOT break through to the Earth's surface

Seismograph

Used to detect and record arrival of different seismic waves. They measure ground motion

Seismographs can tell you what relative to faults?

Which way the fault moves based on the 1st motion of the P-wave - If first motion is up, that is a compressional or towards motion - If first motion is down, that is an extensional (dilation) or away motion

Silicate minerals all have what?

a basic building block called Silica Tetrahedron (1 silicon atom bonded to 4 oxygen atoms)

What is a thrust fault?

a low-angle reverse fault

What type of fault is characterized by the rocks above the fault plane moving downward, relative to the rocks below the fault plane?

a normal fault

Atomic Mass Number

equal to the number of protons plus the number of neutrons in that atom, this varies

Double Chain Silicates

ex. Amphibole Si:O Ratio = 2:5.5

Single Chain Silicates

ex. Pyroxene Si:O Ratio = 1:3

At what point do we assign a series of earthquakes their categories (i.e., mainshock, foreshock, or aftershock)?

following the aftershocks

Solid materials that do not possess an orderly arrangement of atoms are called

glasses

When are atoms only truly stable?

if the number of electrons is equal to one of those of the noble gases

Rocks that form from the solidification of molten rock are called

igneous

How are the elements organized in the periodic table?

in order of increasing number of protons

Island Silicates

individual silica tetrahedra bonded to cations ex. Olivine Si:O Ratio = 1:4

What is the most common type of bonding in minerals?

ionic bonding

What is the term for atoms of the same element that have different numbers of neutrons?

isotopes

The silica tetrahedra readily bonds with cations when available because

it has net negative charge

In order to make a sodium (Na) chlorine (Cl) bond in NaCl,

one electron is transferred from the sodium atom to the chlorine atom.

Chemical substances that have exactly the same chemical formula but different crystal structures are called

polymorphs

Which of the subatomic particles has a positive charge?

proton

The atomic mass of an element is equal to the number of

protons plus neutrons

The average time between large earthquake events along a fault is known as the ______ interval.

recurrence

The difference between a fault and a joint is that

rocks on either side of a fault have moved, whereas rocks on either side of a joint have remained stationary.

The size of an earthquake can be related to fault

rupture area

Energy waves that are released during an earthquake are called

seismic waves

Mica is a common example of a ________ silicate.

sheet

Hanging wall

side above the fault

Footwall

side below the fault

Layer (sheet) Silicates

silicate tetrahedra arranged into infinite 2-dimensional sheets ex. Micas (Biotite & Muscotite) Si:O Ratio = 2:5

The most common rock-forming minerals in the crust are

silicates

Carbon has an atomic number of 6 and an atomic mass of 12. This means that carbon atoms have

six protons and six neutrons

Atom

smallest particle of matter that still retains the characteristics of an atom

What does the symbol Na+ represent?

sodium cation

Mineraloids

substances that have all the properties of a mineral but lack a regular atomic structure

Polymorphs

substances that have the same chemical composition but different structures

What type of seismic wave causes the most building damage?

surface waves

Earthquakes

what you feel during an earthquake are seismic waves as they pass through the Earth. Generated by motion along faults. Any break in the earth's lithosphere (regardless of size) along which movement has occurred. Caused by PLATE TECTONICS