Chapter 8: Earthquakes Flashcards
fault
a fracture plane on which sliding takes place
Earthquake
an episode of ground shaking
seismologist
geoscientists who study earthquakes
seismicity
earthquake activity
seismic waves
the energy released by vibrating rocks caused by an earthquake which travels away from the source in the form of waves
fault displacment
the distance between two ends of the offset marker (at a fault)
fault line/trace
the ground surface exposure of a fault (whether it appears due to erosion of
stress
a push, pull, or shear
elastic behavior
rock bends slightly but doesn’t break
elastic rebound theory
when slip takes place, the once-bent rocks adjacent to the fault rebound and vibrate back and forth until they regain their relaxed shape, thereby relieving the elastic strain.
stick-slip behavior
alternation between stress buildup and earthquake-generating slip events on existing faults
mainshock
the major earthquake
foreshocks
smaller earthquakes that precede the main shock (earthquake)
aftershocks
endured by a region affected by an earthquake in the days to months following, tend to be 10 times smaller than the main shock
focus
the location where seismic waves first begin to be generated, also known as the hypocenter
shallow focus earthquakes
occur in the top 60km of the Earth
intermediate-focus earthquakes
takes place between 60 and 300 km
deep focus earth quakes
occur down to a depth of about 660km
epicenter
the point on the surface of the Earth that lies directly above the focus
categories of seismic waves
- body waves
- surface waves
body waves
pass through the interior of the Earth
- cause material to vibrate in two different ways; compressional and shear
surface waves-
travel along the Earth’s surface; vibrate in two different waves
- up and down, rolling undulations
- side to side, back and forth
compressional waves
body waves that cause particles of material to move back and forth parallel to the direction in which the wave itself moves (squeeze together, then expand)
shear waves
body waves that cause particles of material to move back and forth perpendicular to the direction in which the wave itself moves (up and down)
types of waves all together
P-waves: fastest
S-waves: next fastest (60% of the speed of p-waves)
L-waves: Slow
R-waves: Slow
P-waves
Primary Waves: compressional body waves
S-waves
Secondary Waves: shear body waves
L-waves
Love Waves: surface waves that cause the ground to shimmy back and forth
R-waves
Rayleigh Way: surface waves that cause the ground to undulate up and down
seismometer (also known as seismograph)
measures the ground motion produced by an Earthquake and can be configured in two ways
- vertical motion
- horizontal motion
seismogram
an earthquake record produced by a seismometer
travel time curve
the time delay between P-waves and S-waves, depicted on a graph whose horizontal axis indicates distance from the epicenter and whose vertical axis indicates time.
earthquake intensity
refers to the degree of ground shaking
Modified Mercalli Intensity (MMI) scale
represent intensity at a location by a Roman numeral, intensity greater closer to the epicenter and decreases further away
Earthquake magnitude
represents the amount of energy released from the seismic source, as indicated by the amplitude of ground shaking recorded by a seismometer
richter scale
a logarithmic scale for defining earthquake magnitude
moment magnitude
the most widely used scale to describe Earthquake magnitude; scientist measure the amplitudes of several different seismic waves, determine the dimension of the slipped area on the fault, and estimate the displacement that occurred, also a logarithmic scale
seismic belts/zones
most correspond to plate boundaries, earthquakes here are called plate-boundary earthquakes
intraplate earthquakes
earthquakes that occur away from plate boundaries
