Chapter 11: Earthquake

Earthquake

rapid release of energy shakes earth

Hypocenter

origin/source of earthquake

Energy is in the form of

waves

Energy travels away from the hypocenter as

seismic waves

How does energy travel?

Away from center as seismic waves

Energy Reduced Theory

explains how energy builds up and is released in earth’s crust

In elastic rebound theory: as force is applied to a fault

fault becomes locked in place

In elastic rebound theory: continued stress leads to what in rocks?

built up strain

When a fault slips…

it releases seismic energy

After releasing seismic waves from slipping, the fault is…

displaced

What rate does the rupture surface travel?

2-3 km/sec

Small-scale, minor earthquakes that take place before the big main earthquake?

foreshock

Small tremors that happen after the big main earthquake takes place

aftershocks

Seismic waves

energy released from fault slippage

Seismic waves cause

violent shaking, earthquakes

Instrument that records movement of ground relative to stationary mass

seismograph

3 components of ground motion that seismographs measure

up-down, north-south, east-west

P-waves

travels the fastest; arrives first

S-waves

comes after P-waves

Surface waves

slowest; arrive last

Primary (P) waves travel through sold rock with avg. velocity of

5 km/sec

P waves can travel through

solids, liquids, gas

P waves can push or pull particles of…

matter in the direction of their travel path

Secondary(S) Waves travel through solid rock at what speed?

Half the speed of p waves

Secondary waves are also called _________ because they push material at ________ to their path of travel

shear waves; right angles

S waves can travel through solids but not…

liquids or gases

Surface waves are confined to

surface of the earth

Some surface waves are similar to

ocean waves

Surface waves role in earthquakes

do the most damage

The time intervals between the first arrival of P-waves and S-waves can determine…

how far away the epicenter is to a station

Measures the strength of ground shaking and damage at a specific location

intensity

Measures the total energy released at the source of the earthquake using seismographs

magnitude

2 measurements used for earthquakes

intensity; magnitude

What kind of numbers does the Mercalli Intensity Scale use?

roman numerals

Range in Mercalli Intensity Scale

I - shaking; XII - catastrophic

True/false: Mercalli Scale has no mathematical basis and is an arbitrary ranking scale based on observed effects

true

Buildings resting on ___________ experience more damage than buildings resting on ____________

unconsolidated soil; solid bedrock

Soil type and bedrock affect

destructiveness of earthquake

Why did Loma Prieta earthquake in Marina District, San Francisco cause so much damage (VII)?

buildings sat on a landfill

When loosely packed, water-soaked sandy or silty soil temporarily loses its strength and acts like a thick liquid or quicksand

liquefication

When seismic waves from an earthquake pass through bodies of water like lakes, rivers, reservoirs

seiche

Who devised a procedure to measure the size of an earthquake based on ground motion rather than amount of destruction?

Charles Richter

How is the Richter Magnitude determined?

measuring the max amplitude of P-wave or S-wave

A magnitude 1 difference on the Richter Scale = factor of __ difference in the amplitude of ground motion

10

How much a fault slips, area of fault break, and strength of rock are all things that affect

moment magnitude

Log₁₀E = A + (B x M)

moment magnitude formula

The energy released by an earthquake increases by a factor of __ for each unit on the ____________

32; Richter Scale

Occur along all plate boundaries

shallow earthquakes

Restricted to convergent plate boundaries

intermediate and deep earthquakes

Occur in subduction zones

intermediate and deep earthquakes

The strongest earthquakes mostly occur along

convergent plate boundaries

The first motion of P-Waves arriving at seismograph stations is used to determine… (2 things)

fault plane orientation; slip direction

The first P-wave motions on a stereonet may be a…

push or pull

Black quadrants:

White quadrants:

Plate movement type:

push; pull; transform

Tsunamis are also called

seismic sea waves

Volcanic eruptions; undersea landslides; vertical displacement of faults along the ocean floor can all…

trigger a tsunami

What happens to the height of tsunami waves when they approach the coast?

Become taller; more destructive

In deep ocean water, tsunami waves are almost

undetectable

The Great Tsunami of 2004 affected which countries?

Indonesia, Thailand, Sri Lanka

The Great Tsunami of 2004 was triggered by ________ and killed _____ people

magnitude 9 earthquake off Sumatra; 230k

Are reliable short-range predictions for earthquakes currently possible?

No

Long-range forecasts give the probability of a certain magnitude earthquake occurring on a time scale of…

30-100+ years

Animals behaving strangely and tilting of the earth and other ground deformations are examples of…

short range earthquake predictions

The opening of micro-fractures in bedrock prior to the main earthquake changes the…

physical properties of rock

What physical properties in rocks change from foreshocks.

conductivity of electric current; p wave velocity

The study of past seismic activity to predict future earthquakes

paleoseismology

Segments along a fault where no major earthquakes have occurred recently, while surrounding areas have slipped

seismic gaps

How do seismic gaps predict an earthquake?

strain build ups until a fault segment slips

Example of an active earthquake zone

San Andreas

San Andreas Fault Displacements:

Displacement occurs along discrete segments ________ long

100-200 km long

Slow and gradual fault displacement is called:

fault creep

San Andreas Fault Displacements:

Some segments regularly ____ and produce small earthquakes; other segments store _________ for _______ before rupturing in great earthquakes.

slip; elastic energy; hundreds of years

When two rough surfaces try to move past each other, get stuck due to friction, build up stress, and then suddenly break free in a fast, violent burst

stick slip motion

San Andreas Fault Displacements:

Great earthquakes should occur every…

50-200 years

San Andreas Fault: Most likely source of next major earthquake

southernmost section