Geol 108 exam 2
What is the frequency of earthquakes of different magnitudes, especially 8 or greater
1 annually
At present, an earthquake warning system could provide up to a one minute warning to regions far enough away from the epicentre of an earthquake. Such a warning system is based on the difference between
P and S wave velocities
Forecasting Earthquakes
Paleoseismology Seismic gaps
dip of fault
angle the fault plane makes with the horizontal
Which of the following human activities is known to cause earthquakes?
dam construction
fault plane
surface along which movement occurs
crest
top of the wave
Tsunami Warning System
-Detects, locates, and sends out warnings to locations around the Pacific Ocean -Consists of tide gauges and seismic stations.
steps of the earthquake cycle
1. Long period of inactivity 2.Accumulated elastic strain produces small earthquakes Foreshocks may occur hours or days before a large earthquake 3.Main shock in the form of major earthquake that includes aftershocks: few minutes to a years after
The ground motion from a magnitude 6 earthquake is approximately
10 times as much as ground motion from a magnitude 5 earthquake
Differences in the ground motion for one magnitude increase
10x
where is the most powerful earthquake in human history recorded
1556 in Shaanxi, China Killed 830,000 people - most living in caves excavated in poorly consolidated loess
The speed of a tsunami in 4000 m deep water is
200 m/s
The ________ was the most deadly tsunami disaster in history, responsible for over 230,000 deaths.
2004
Difference in energy for one magnitude increase
32x
Richter scale
A scale that rates an earthquake's magnitude based on the size of its seismic waves.
Mercalli scale
A scale that rates earthquakes according to their intensity and how much damage they cause at a particular place
secondary effects of eq
Aftershocks Liquefaction of ground Regional changes in land elevation Landslides Fire Tsunamis Disease
what is a seismic gap
An area along a fault where there has not been any earthquake activity for a long period of time
strike-slip fault
Dominant displacement is horizontal and parallel to the strike of the fault
2004 Indonesian Tsunami
Killed 230,000 people Result of a Magnitude 9.1 Earthquake Strong Aftershocks 100 ft waves Coastal Communities destroyed Worst Tsunami in recorded history Lessons Learned : Need for Tsunami warning and communication systems Educate people Strengthen disaster preparedness in developing countries
the eruption of which volcano in 1883 caused a tsunami that killed approximately 36,000 people
Krakatoa
trough
Lowest point of a wave
Where do earthquakes occur?
Most natural earthquakes are caused by sudden slippage along a fault zone
Which of the following describes the change in behavior of a tsunami as it enters shallow water?
Slow down and become larger
fault creep
Some faults or parts of faults move continuously without generating earthquakes. This could occur if there is little friction on the fault & tectonic stresses are large enough to move the blocks in opposite directions If creep is occurring on one part of a fault, it is likely causing strain to build on other parts of the fault
hich of the following statements concerning the Indian Ocean tsunami is FALSE?
The tsunami spread across the Indian Ocean in less than an hour
distant tsunami
Travels out to sea and can travel long distances with little loss of energy
local tsunami
Travels towards land very quickly- People have very little time to react
a seismic gap is
a segment along an active fault that has not experienced seismic activity recently.
normal fault
a type of dip slip fault Hanging wall moves down relative to the footwall Accommodate lengthening or extension of the crust Most are small with displacements of a meter or so Larger scale normal faults are associated with structures called fault-block mountains
magnitude
an estimate of the amount of energy released at the source of the earthquake
left lateral strike slip fault
as you face the fault, the opposite side of the fault moves to the left
transform fault
as you face the fault, the opposite side of the fault moves to the left Occur where mid oceanic ridges are offset only occurs between the two segments of the ridge Outside of this area there is no relative movement because blocks are moving in the same direction. These areas are called fracture zones
right lateral strike slip fault
as you face the fault, the opposite side of the fault moves to the right
primary effect of a tsunami
beach erosion
Tsunami
big asss wave
shaking
caused by the sudden and rapid movement of one block of rock sliding past another (a vibration of the earth produced by rapid release of energy) depth of earthquake, deeper eq generate less shaking passage of seismic waves, especially surface waves, near the epicenter of the earthquake are responsible for the most damage Local geologic conditions In general, loose unconsolidated sediment is subject to more intense shaking than solid bedrock Size of the earthquake In general, the larger the earthquake, the more intense is the shaking and the duration of the shaking
earthquakes occur at what kind of tectonic plate boundary
convergent, where the boundaries meet and push against each other
blind faults
do not break the surface-rocks above the fault have behaved in ductile fashion and folded over the tip of the fault
what is a primary cause of tsunamis
earthquakes and landlsides
causes of tsunamis
earthquakes, landslides, volcanic eruptions
how much energy was released by the 1960 chilean earthquake
equivalent to 20,000 hiroshima atomic bombs
An earthquake of magnitude 5 has a shorter return period than an earthquake of magnitude 4
false
On the moment magnitude scale, earthquake magnitude is determined by the intensity of shaking
false
The east coast of Canada is more at risk from tsunamis than the west coast
false
There is a direct correlation between earthquake magnitude and casualties, such that larger earthquakes always result in more deaths
false
Which of the following is a secondary effect of tsunamis?
fire
secondary effects of tsunamis
fires, contaminated water supplies, and disease
primary effects of tsunamis
flooding and erosion
joints
fractures in rock that show no slippage or offset along the fracture. Form as a result of extensional stress acting on brittle rock
primary effects of eq
ground shaking surface rupture
The 1964 Alaska M 9.2 earthquake was far larger than the 1989 Loma Prieta earthquake at M 6.9, yet the Loma Prieta earthquake was far more costly, even when adjusted for inflation. Why?
he population and infrastructure density in Alaska was much lower than in San Francisco.
elastic rebound theory
if slippage along a fault is hindered such that elastic strain energy builds up in the deforming rocks on either side of the fault, when the slippage does occur, the energy released causes an earthquake Prior to an earthquake the rocks adjacent to the fault bend which disappeared after an earthquake suggesting that the energy stored in bending the rocks was suddenly released during the earthquake Friction between the blocks keeps the fault from moving again until enough strain has accumulated to overcome the friction and generate another earthquake
speed of tsunami
in very deep water, a tsunami will travel at high speeds with little loss of energy
correct sequence for the four stages of an earthquake cycle?
inactivity, accumulated strain, foreshock, mainshock
In which ocean are tsunamis most common?
indian
The two tectonic plates involved in the 2004 Indonesian earthquake and tsunami were
indo australia and burma
What factors affects the amount of shaking an area experiences during an earthquake?
intensity
where would be the most prudent place to purchase property, to minimize risk of damage due to earthquakes?
just north of San Francisco, on bedrock
how do you classify earthquakes
magnitude, energy released, richter scale and mercalli scale, size
The run-up of a tsunami is the
maximum horizontal and vertical distances reached by the largest wave
moment magnitude
measures the total energy released during an earthquake» Calculated from the average amount of slip on the fault, the area of the fault surface that slipped, and the strength of the faulted rock» Can also be calculated by modeling data from seismograms
On which tectonic plate is the city of Los Angeles, California located?
north american plate
plate tectonics of tsunamis
occur at subduction zones along oceanic trenches
faults
occur when brittle rocks fracture and there is an offset along the fracture
The most common cause of tsunamis is/are
offshore earthquakes
strike of fault
orientation (trend) of fault plane
In which area are tsunamis most common?
pacific
human interaction and tsunamis
people go to the beach to collect the shells that wash up the waves look cool and they go to watch ignore warnings/don't take the threat seriously
The 2004 Indonesian earthquake
permanently raised and lowered different areas around its epicentre
earthquake hazard risk depends on
population density, construction standards, emergency preparedness
tsunami damage along coastal areas can be minimized with land use practices such as
preservation of vegetation
earthquake cycle
proposes that there is a drop in elastic strain after an earthquake and an accumulation of strain before the next earthquake
earthquake energy
radiates outward from the focus in all directions
what are the strategies used for minimizing tsunami hazard
run-up maps ready-status probablity statys structural control
greatest risk of tsunamis are coastal areas near
subduction zones
Which of the following is a primary effect of an earthquake?
surface rupture
primary effect of an earthquake
surface rupture
Why is the earthquake hazard different in the east coast of the America compared to the west coasts
tectonic plate movements and faults are more prone to earthquakes, west coasts typically sit on those kinds of boundaries
wave height
the distance between a trough and a crest
wavelength
the horizontal distance between crests
Focus of an earthquake
the place within Earth where earthquake waves originate
Epicenter
the point on the Earth's surface directly above the focus of an earthquake located using the difference in arrival times of P and S waves
paleosiesmicity
the study of prehistoric earthquakes through study of the offsets in sedimentary layers near fault zones, it is often possible to determine recurrence intervals of major earthquakes prior to historical records• If it is determined that earthquakes have recurrence intervals of say 1 every 100 years, and there are no records of earthquakes in the last 100 years, then a long-term forecast can be made and efforts can be undertaken to reduce seismic risk
Earthquakes with lateral or side-to-side motion (such as on the San Andreas fault) generally do not produce tsunamis
true
If you live in a house built on unconsolidated sediments, in an earthquake, you can expect to experience a higher Modified Mercalli Intensity than your neighbors whose house is built on bedrock.
true
Local tsunamis can be especially deadly because of reduced warning and reaction times
true
The largest known run-up occurred in a local tsunami in Lituya Bay, Alaska.
true
all tsunamis are caused by displacement
true
if you live in a house built on unconsolidated sediments in an earthquake, you can expect to experience a higher modified intensity than your neighbors who built their house on bedrock
true
reverse/thrust fault
type of dip slip fault Hanging wall block moves up relative to the footwall block Reverse faults have dips greater than 45 degrees and thrust faults have dips less than 45 degrees Accommodate shortening of the crust Strong compressional forces
where is safest place inside during an eq
under a sturdy desk or table
hanging wall
wall above the fault plane
foot wall
wall below the fault plane