Geology Chapter 5

natural vibration frequency

the frequency at which a building will naturally vibrate when the ground shakes during an earthquake

What happens when the seismic waves travel outward from the rupture point?

the ground vibrates or shakes in the form of an earthquake.

elastic limit

the maximum amount of strain that a rock body can accumulate before either fracturing or undergoing plastic deformation

moment magnitude scale

the modern earthquake magnitude scale that provides a more accurate measure of the amount of ground motion.

Richter magnitude scale

the original earthquake magnitude scale, developed by Charles Richter, used to quantify the amount of ground motion

inertia

the physical tendency of objects at rest to stay at rest, which plays a key role in causing damage during earthquakes when structural foundations are suddenly forced to move

Can Seismologists make reliable short term earthquake predictions?

No, because they are unable to use the precursor data.

What are the two types of body waves ?

P and S

Which body wave travels fastest?

P waves

Which body waves are the least destructive?

P waves

Which body waves travel the slowest?

S waves

How do seismologists make long term predictions?

using statistical probabilities that make use of historical earthquake frequency and magnitude.

earthquake precursors

various physical phenomena that can occur just prior to the release of energy associated with a main earthquake shock

seismic waves

vibrational waves that travel through solid earth materials that are caused by earthquakes, sudden impacts, or explosions.

What causes large earthquakes?

when rocks accumulate greater amounts of strain energy before rupturing.

epicenter

the point on the surface that lies directly above the focus, which is the place where an earthquake originates in the subsurface

focus

the point within a rock body where accumulated strain is suddenly released, causing an earthquake

wave attenuation

the steady decrease in seismic wave energy that occurs as the waves travel away from there point of origin at the focus.

Where do earthquakes occur repeatedly?

In tectonically active areas

What happens to the energy of the seismic wave as it travels?

It decreases

What happens when the deformation exceeds the rock's elastic limit?

It will rupture suddenly, releasing the strain in the form of vibrational waves of energy called seismic waves.

What are some factors that affect the amount of structural damage due to shaking?

Magnitude, wave attenuation, resonance effects in buildings, ground amplification and liquefaction.

What are magnitude scales?

Qualitative measures of the amount of ground motion.

How does the Mercalli intensity scale measure earthquake strength?

Qualitatively through human observation.

Which body waves cause the most damage?

S waves and surface waves

What are some other related hazards to earthquakes?

ground fissures, tsunamis, landslides and fires

earthquake

ground shaking associated with the vibrational wave energy that results when a rock body suddenly fails and releases its accumulated strain

seismographs

instrument that measures the ground motion during an earthquake

ground fissures

large open cracks that form over a wide area of the landscape during an earthquake

What are magnitude scales based on?

measurements taken form a seismograph

primary waves

seismic waves that cause solid particles to vibrate in the same direction the wave is traveling such that the rocks alternately compress and decompress

secondary waves

seismic waves that cause solid particles to vibrate perpendicular to the wave path, which creates a shearing (side-to-side) motion

surface waves

seismic waves that travel along earth's surface. examples include rayleigh and love waves

body waves

seismic waves that travel through earth's interior, which includes primary waves and secondary waves

Where do seismic waves travel from?

The rupture point or focus.

intraplate earthquakes

earthquakes that occur far from a plate boundary or active mountain belt

resonance

A phenomenon that occurs when the natural vibration frequency of a building matches that of the seismic waves, causing the building to shake more violently

How are seismic waves classified?

According to how they force rock particles to vibrate.

Where do most large earthquakes occur?

Along convergent or transform plate boundaries.

What happens to a rock body when placed under force?

It will deform and accumulate strain.

Why do earthquakes occur repeatedly in tectonically active areas?

Because of the cyclic manner in which the strain accumulates and is then released.

Why do most large earthquakes occur along convergent or transform boundaries?

Because rocks are stronger under compressional and shear forces as compared to tension.

Why do the buildings and structural supports commonly fail during an earthquake?

Because they do not have adequate strength against shear force.

What is the single greatest cause of human death and loss of property during an earthquake?

Structural failure of buildings due to ground shaking.

Why do some large earthquakes occur in the interior plates?

Tectonic forces cause strain to accumulate along ancient faults.

Where is the greatest shaking of the surface during an earthquake?

The epicenter, which is directly above the focus.

How can loss of life and property be reduced during and earthquake?

Through seismic engineering controls, early warning systems and better preparedness within the community.

Where do the body waves travel?

Through solid earth.

When do the body waves generate surface waves?

When reaching the land surface.

Can seismologists make reliable long term predictions?

Yes

ground amplification

a phenomenon that occurs when seismic waves encounter weaker materials and begin to slow down, causing an increase in wave amplitude and ground shaking

Mercalli intensity scale

a qualitative means of ranking the intensity of earthquakes based on first-hand human observations, particularly the amount of structural damage.

tsunami

a series of ocean waves that form when energy is suddenly transferred to the water by an earthquake, volcanic eruption, landslide, or asteroid impact.

seismic gap

a tool for predicting the likelihood of an earthquake, based on sections of an active fault where the strain has not been released for an extended period of time

liquefaction

an earthquake phenomenon that occurs when the ground shaking causes sand-rich layers of sediment to behave as fluid

What are some key elements in seismic engineering?

cross-bracing, base isolation, and spiral wrapped support columns.

subduction zone earthquakes

earthquakes which form when an oceanic plate is overridden by another plate. these are some of the most powerful earthquakes on record.

elastic rebound theory

explains how earthquakes originate when a rock body deforms and accumulates strain such that it reaches its elastic limit, at which point the rock suddenly fails and releases its stored energy