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