(MODULE 7.1) GEOLOGICAL HAZARDS - EARTHQUAKES Flashcards
waves of energy produced by an earthquake
seismic waves
what are the causes of earthquakes?
1.
2.
3.
- release of energy in faults
- volcanic eruptions
- mineral transformations
the classic explanation of why earthquakes take place.
elastic rebound theory
explain the elastic rebound theory
1.
2.
3.
4.
- tectonic forces act upon a fault over many years
- buildup of energy causes the rock to bend
- built up energy is released, causing the rock to break
- the rocks rebound to a permanently displaced shape
the longer the energy of tectonic forces is stored up, ___.
the more likely that a strong earthquake will occur.
the point within the earth where seismic waves first originate
focus or hypocenter
the point on the earth’s surface directly above the focus
epicenter
types of seismic waves
1.
2.
- body waves
- surface waves
seismic waves that travel through the earth’s interior, spreading outward from the focus in all directions
body waves
seismic waves that travel on earth’s surface away from the epicenter
surface waves
types of body waves
1.
2.
- p wave
- s wave
a compressional or longitudinal wave in which rock vibrates back and forth parallel to the direction of wave propagation
p wave
characteristics of a p wave
1.
2.
3.
- rock vibrates parallel to wave of propagation
- very fast, 4km/s to 7km/s
- first to arrive at a recording station
transverse wave propagated through a shearing motion perpendicular to the direction of wave propagation
s wave
characteristics of an s wave
1.
2.
3.
- travels near the surface and vibrates perpendicular to wave propagation
- slower than p wave, 2km/s to 5km/s
- second to arrive at a recording station
types of surface waves
1.
2.
- love waves
- rayleigh waves
the ground moves side to side in a horizontal plane perpendicular to the direction of wave propagation
love waves
this type of surface wave causes the ground to move in an elliptical path opposite to the direction the wave passes
rayleigh waves
the instrument used to measure seismic waves
seismometer
a recording device that produces a permanent record of earth motion detected by a seismometer
seismograph
a recording device that produces a permanent record of earth motion detected by a seismometer
seismograph
the paper record of earth vibration
seismogram
how is the location of an earthquake determined?
1.
2.
- seismographs record seismic waves. from the seismogram, P and S wave arrival is measured, from which the P-S time interval is determined. the larger the P-S time interval, the farther the earthquake is from the recording station.
- this activity is repeated for at least 3 stations to triangulate the epicenter of the earthquake.
80% of all earthquakes occur in the ___.
15% occur in the ___.
5% occur in the ___.
more than ___ quakes strong enough to be felt are recorded each year.
- circum-pacific belt
- mediterranean-asiatic belt
- 150,000
a measure of an earthquake’s effect on people and buildings
intensity
intensities are expressed as roman numerals ranging from I to XII on the ___.
modified Mercalli scale
this method of measuring the size of an earthquake is done through calculating the amount of energy released by the quake using the ___.
Richter scale
After measuring a specific wave on a seismogram and correcting for the type of seismograph and for the distance from the quake, scientists can assign a number called the ___.
magnitude
the higher the magnitude of an earthquake is, the less frequent it occurs. that is due to the ___.
elastic rebound theory
the trembling and shaking of the land that can cause buildings to vibrate
ground motion
the frequency of shaking differs for different seismic waves.
high body frequency waves shake ___ more, whereas low frequency surface waves shake ___ more.
- low buildings
- high buildings
intensity of shaking also depends on type of subsurface material. ___ amplify shaking more than rocks do.
unconsolidated materials
intensity of shaking also depends on type of subsurface material. ___ amplify shaking more than rocks do.
unconsolidated materials
what are unconsolidated materials?
unconsolidated materials are materials that have not undergone compression to the point of having its moisture squeezed out (aka consolidation)
buildings on soft sediment are __ than buildings on hard rock.
damaged more
a particularly serious problem just after an earthquake because of broken gas and water mains and fallen electrical wires.
fires
can be triggered by the shaking of the ground
landslides
how is a tsunami formed?
when a section of sea floor rises/falls during an earthquake, the water over the moving area is lifted or dropped, forming a fast wave which slows down and builds in height as it approaches a shoreline.
the water will rise for 5 to 10 minutes due to its long wavelength.
this type of ground failure occurs when water-saturated soil/sediment turns from a solid to a liquid due to earthquake shaking.
liquefaction
how does liquefaction work?
the vibration or shaking of loosely packed grains of soil will result to the destabilization of soil, increasing the space between grains.
how can the effects of earthquakes be controlled?
1.
2.
3.
- create earthquake-resistant structures
- pumping fluids into seismic gaps in order to cause smaller earthquakes and prevent large ones
- develop an early warning system
