Final Flashcards
Earthquakes are measured by ___________
seismographs
Earthquakes are compared by ___________
Magnitude
D: Seismic Waves
The energy released from an earthquake
Earthquakes are
The result from the rupture of rocks along a fault
Richter Scale
The original way to measure the magnitude of an Earthquake (no longer)
Earthquakes are measured using
The Moment Magnitude Scale (M)
The Moment Magnitude Scale is determined by:
- the area ruptured along a fault
- the amount of movement along the fault
- the elasticity of the crust at the focus
An M7 earthquake has how much more ground movement than an M6
10 times as much
What is the Modified Mercalli Intensity Scale
It is a qualitative scale for Earthquakes that is based on damage to structures and the effect on people
Where are Earthquakes most common
At or near plate boundaries
Blind faults are
located below the surface
What are faults considered
Seismic sources
What are the 2 types of geologic faults
Strike-slip faults and Dip-slip faults
Strike-slip faults
Displacements are horizontal
Dip-slip faults
Displacements are vertical
What are the three types of Dip-Slip Faults
Reverse Faults, Thrust Faults, Normal Faults
Dip-Slip faults are comprised of what 2 walls
Footwall, (where miners placed their feet)
and
Hanging-wall (where miners placed their lanterns)
Reverse Fault
Hanging wall has moved up relative to the footwall inclined at an angle steeper than 45 degrees
Thrust Fault
Hanging wall has moved up relative to the footwall at an angle less than 45 degrees
Normal Fault
The hanging wall has moved down relative to the footwall
What are the 3 categories of faults
Active, Potentially Active, Inactive
Active Fault
Movement during the past 11,600 years
Potentially Active Fault
Movement during the past 2.6 million years
Inactive Fault
No movements in the past 2.6 million years
Tectonic creep
The slow movement of rock or sediments along a fracture caused by stress
P Waves
Primary (or compressed) waves move fast with a push-pull motion and can travel through solids or liquids
S Waves
Secondary (or shear) waves move more slowly in an up-and-down motion and can only travel through solids
What are the 2 types of Body waves
P waves and S waves
Surface Waves
Seismic waves that form when P and S waves reach Earth’s surface and then move along it
What are responsible for damage near the epicenter of an earthquake
Surface Waves
What are some factors that determine the shaking people experience during an earthquake
- magnitude
- distance to epicenter
- Focal depth (how deep is earthquake?)
- direction of rupture (how was fault aligned?)
- local soil and rock types
local engineering and construction practices
Which type of wave travels faster: P wave or S waves
P waves travel faster and appear first on seismograms
How can we find the distance to the epicenter in an earthquake
Using the difference in the arrival times of the first P and S waves at different locations
What can influence the amount of ground motion
local geology
Where are Earthquakes felt over larger areas
Earthquakes in eastern North America are felt over larger areas than those in western North America
(less rock types and big mountains)
foreshocks
A small to moderate earthquake that occurs shortly before and in the same general area as the mainshock
Mainshock
The largest earthquake in a series of associated earthquakes
Aftershock
A small to moderate earthquake that occurs shortly after and in the same general area as the mainshock
Describe the earthquake cycle
- Inactive period
- Period where strains produce minor earthquakes
- period of foreshocks (not always)
- period of mainshock allowing fault to release built up stress
- Period of aftershocks
What is the formula to calculate how many aftershock there should be after an earthquake
aftershock on given day = (# of aftershocks on the first day after / the given day)
If there were 200 aftershock the next day after an earthquake, how many should you expect on day 7
= 200/7
= 29
Where do most earthquakes occur:
Along plate boundaries:
Pacific Ring of Fire, Himalaya Mountains, Middle East
What are some NA cities that are at high risk for earthquakes
Anchorage, Vancouver, Victoria, Seattle, Portland, San Francisco, Los Angeles, Mexico City
Plate boundary earthquakes
Earthquakes that occur on faults separating lithospheric plates
The 3 types of plate boundary earthquakes
strike-slip earthquakes
thrust earthquakes
normal fault earthquakes
Strike-slip Earthquakes
Occur along transform faults where plates slide horizontally past one another (common in California)
Thrust Earthquake
Occur on faults that separate converging plates (also called subduction earthquakes)
The strongest types; can produce tsunamis (common in BC)
Normal fault earthquakes
Occur on faults associated with divergent plate boundaries
(common along Mid-Atlantic Ridge)
Intraplate Earthquakes
An earthquake on a fault in the interior of a continent, far from a plate boundary
(typically smaller than plate boundary earthquakes)
Primary effects of earthquakes
Ground shaking, surface ruptures
Secondary effects of earthquakes
liquefaction, land-level change, landslides, fire, tsunamis
Liquefaction
The transformation of water-saturated sediment from solid to liquid
Natural service functions of earthquakes
- Faults provide pathways for the downward flow of surface water
- Can channel groundwater to surface discharge points (springs)
- New material resources can be found
- Scenic landscapes can develop in fault zones over time
What is the main reason earthquakes cause such death and destruction
They occur with little to no warning
What are the safest location during an earthquake
Under desks and tables
Where are most volcanoes located
Near plate boundaries
2/3 of volcanoes are found where
On the “Ring of Fire” surrounding the Pacific ocean
Magma
Found within the crust and upper mantle
Lava
found flowing from an erupting volcano
what is the relationship between lava and magma
lava is essentially magma on the earths surface
What are the most abundant elements in magma
Silicon and oxygen
What are the types of volcanic rocks from least silica present to most
Basalt
Andesite
Dacite
Rhyolite
What else is contained in magma
small amounts of gases (water vapour, CO2)
Describe Magma with high silica content
Cooler, more viscous, more gases
Describe Magma with low silica content
Hotter less viscous, fewer gases
What influences a more explosive volcanic eruption
Volcanoes with higher silica magma
Which 2 types of magma produce volcanoes that tend to flow
Basalt
Andesite
Which 2 types of magma produce volcanoes that tend to explode
Dacite
Rhyolite
What are volcanoes classified based upon
Shape
Appearance
Style of eruption
What are the 4 types of volcanoes
Shield
Composite
Volcanic Dome
Cinder Cone
Shield Volcanoes
Largest volcanoes on earth
Shaped as broad arcs
Associated with Basaltic Magma
Flows
Common in Hawaii, Iceland
Tephra
Fragmented material blown out during an eruption
Compacted together are referred to as pyroclastic rock
Composite Volcanoes
More dangerous and explosive eruptions
Less common than shield
Common along the west coast from Alaska to Northern California
Volcanic Domes
Steep-sided mounts that form around vents
Contain highly viscous rhyolite magma
Cinder Cone Volcanoes
Relatively small volcanoes composed of small pieces of tephra
Found in Mexico
Ice-Contact Volcanoes
Erupt beneath or against Glaciers
When the lava contacts glaciers it quickly cools to form pyroclastic rock
Found in Iceland and BC
Geyser
Groundwater that boils underwater and periodically produces a release of steam or water
here are Geysers most common
About half of all geysers on earth reside in Yellowstone
About how many volcanoes erupt each year
50-60 volcanoes
What is an effect volcanoes have
Powerful eruptions can impact global climate
Lava flows
occur when magma flows out of a central crater
Pahoehoe Lava
Low viscosity (a few km per hour), high temperature. When hardened, it has a smooth texture
Aa Lava
High viscosity (a few meters per day), lower temperature. When hardened, it has a blocky texture
Lateral Blasts
An eruption directed away from a volcano where materials are blown parallel to the surface
Ash Fall hazards
- destroys vegetation
- contaminates surface water
- health hazards to people and animals
- causes aircraft engine failure
Pyroclastic flows
Avalanches of ash, gas, and rock that travel down the slopes of a volcano during an explosive eruption
Largest cause of death involving volcanoes
Natural Service functions of volcanoes
- Internal heat from volcanoes can produce renewable geothermal energy
- Volcanic soils can be good for agriculture
- Volcanic landscapes attract tourism and recreation
Eruptions can create new land (Hawaii, Iceland)
What are ways to minimize the volcanic hazard
1 Monitor seismic activity ((shallow earthquakes usually precede)
2. Thermal and Hydrologic monitoring
3. Land surface monitoring
4. Monitoring volcanic gas emissions
5. Understanding local geologic history
What are technological hazrads
They have a wide and varied interpretation
Can vary from a single toxic chemical accident to an entire industry (e.g. nuclear energy)