Download Earthquakes

Earthquakes
What do we know?
What are scientists studying?
What Are Earthquakes?
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Earthquakes are a shaking of the surface of the Earth caused by a sudden
release of energy in the Earth’s crust.
The energy is caused by a buildup and release of tension in Earth’s
tectonic plates.
Most Earthquakes happen along divergent plate boundaries and
transform plate boundaries.
Over 1 million earthquakes occur in a year.
Energy in Earthquakes
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Earthquakes release energy in the form of waves.
P waves, or compression waves, are the fastest and can move through
solids and liquid.
S waves, or shear waves, are slower and can only move through solids.
They move in a rolling motion.
Surface waves are slower and have a lower frequency, but are often the
most destructive. There are two types of surface waves: Love waves and
rayleigh waves.
How do we detect earthquakes?
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When an earthquake happens, P waves and S waves travel through the
Earth. Once the P waves are detected, seismologist are able to detect the
general area where the earthquake had occurred. After the P waves are
detected, seismologist can say exactly where the epicenter is.
P waves and S waves are picked up by seismometers, which are pieces of
equipment that can detect very small movements in the earth.
How do we determine the severity of Earthquakes?
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We are able to detect the severity of
an earthquake through the use of a
seismograph.
The Richter Scale is used to determine
the magnitude and severity of the
Earthquake. The most severe
earthquakes register higher on the
Richter Scale.
Largest Earthquakes in History
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The world’s largest recorded earthquake was a magnitude 9.5 near Valdivia, Chile on May 22,
1960.
International ocean drilling expedition to understand
causes of the Indian Ocean 2004 earthquake and tsunami
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The earthquake struck North Sumatra, Andaman, and the
Nicobar Islands on Dec. 26, 2004, killing 250, 000+ people in 14
countries
The Expedition involved 33 scientists and 2 educators
The Indian Ocean is a site for very large earthquakes that can
cause large tsunamis, this one being caused by a slip on a
subduction zone plate boundary
The ocean drilling will let scientist dig boreholes within the
sediment entering into the subduction zone for the first time
The project will investigate how materials coming into the
system drive shallow earthquake rupture and understand the
hazard potential for this continental margin
Nucleus of Earthquakes
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Many strong earthquakes happen at subduction zones
Earthquakes can cause tsunamis
The main cause for earthquakes are the stresses that occur in the Earth’s interior, when two
tectonic plates pass each other and interlock during this process
Calcareous sediments are the most likely candidates for the first breakage of an earthquake.
Very large quakes first start out as small cracks in the Earth’s crust, and most of the initial
cracks mainly occur in clay-rich sediments.
In the tropical and subtropical area both clayey and calcareous sediment layers are found,
which mechanically weak. Calcareous sediments react poorly to changes in pressure and
temperature by changing their friction. This leads to shallow earthquakes occurring in areas
like Costa Rica.
Further drilling, especially in the framework of the IODP, is required to learn more about the
earthquake processes at depth.
Seismic Strain
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Sections of California have been rising and sinking around the San Andreas fault, building tension
that will be released in a large earthquake
The San Andreas fault is the longest and most dangerous fault in California, and is the result of
the Pacific and North American plates grinding past each other
San Diego county and the Bakersfield area are sinking 2-3 millimeters a year, while Santa Barbara
and San Luis Obispo are rising at the same rate; they will return to “normal” levels in the next big
earthquake
It is a new study by scientists, observing california's changing landscape has not happened until
recently
The time span for a large rupture on the southern San Andreas is on average, every 150 years.
Sometimes the gap can last for more than 300.
The largest earthquake on the San Andreas fault occurred in 1857, and was a magnitude 7.9.
Factors such as changing groundwater levels can affect the land rising and falling
A Small Push to Mt. Everest
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M7.8 Earthquake in Kathmandu, Nepal (April 25, 2015)
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Difficult to get data b/c of poverty and lack of monitoring
stations
Epicenter located west of Kathmandu Valley
Focus was 12-15 km underground
Liquefaction- ground water rises
Mt. Everest moved 3 cm southwest
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Largest aftershock M7.3 (May 12, 2015)
Normal motion is northeast and 0.3 cm taller
The boundary between the India and Eurasia plates
formed the Himalayas and is one of the most seismically
hazardous regions in the world
“Chunks of Earth’s Mantle Are ‘Peeling Off’”
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Background: Southeastern United States has started to feel recent earthquakes, even though
the Southeast is in the middle of a tectonic plate.
Research: Berk Biryol, a seismologist, and colleagues took 3D images of the uppermost part of
the mantle, which revealed that the tectonic plate was uneven.
Findings: Over time, as new material was added to the plate and pieces were pulled apart,
areas of higher density formed; gravity pulled down the denser areas into the mantle and the
chunks broke off to sink into the gooey asthenosphere, a layer of warm, viscous fluid in the
mantle; chunks peeled off the bottom of the plate and lighter material moved up to fill the
space, cooling into a thinner section.
Long term: Biryol doesn’t believe that the Southeast will need any earthquake kits yet because
geological processes occur over long periods of times and nothing will change dramatically
overnight.
Characterizing Faults and Earthquakes
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Alaska has more large earthquakes than the rest of the united states.
Scientists first need to know where the faults are and how they behave in order to understand
the risk that different areas of the US face.
The trans-Alaska pipeline transports about 17% of the nation’s crude oil.
Fault systems can create very large earthquakes (San Andreas Fault)
Where the oceanic tectonic plate is diving under the continental plate, hazards can come from:
earthquakes occurring within the shallow continental crust, earthquakes within the subducting
oceanic slab, and tsunamis from local and distant sources.
Southern California has over 300 faults capable of producing 6 earthquakes
Motion between the North American plate, the Pacific plate, and the remnant of the Juan de
Fuca plate off the coast of the Pacific Northwest, is causing deformation throughout western
North America.
Ground Motion
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Pacific and American plates get stuck, don’t move for thousands of years,
building up stress.
Steady background motions of the Earth’s crust occur as a result of
tectonic plates moving.
Hayward, Calaveras, San Andreas faults not stuck, consistent fault creep.
Fault creep- steady motion along a fault line.
Faults generally creep at lower depths because heat lessens friction.
Some earthquakes occur without shaking, called slow earthquakes.
Earthquakes of magnitude 5 and greater create permanent damage to
the ground.
Man-Made Earthquake Hotspots Revealed: OK
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Man-made activities related to oil and gas production are
creating shaky conditions in a region of the central and
eastern U.S.
7 million people live and work in areas at risk of
human-induced seismicity
CEUS earthquakes are often products of wastewater
disposal (used in fracking), according to USGS
“In the past five years, the USGS has documented high
shaking and damage in the areas of these six states…”
States that are at risk: Oklahoma, Kansas,Texas, Colorado,
New Mexico, and Arkansas
USGS Did You Feel It? Website recorded almost 1,500 locals
reporting strong shaking and/or damage
Earthquakes have increased in the central United States by
an average of 294 per year.
Man Made Earthquakes: Part Two
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USGS has also discovered an overall 21 areas within the US with increased rates of
“human-induced seismicity”, such as 24 3.0+ earthquakes between 1973 and 2008
In Oklahoma, researchers found a 10-12% risk of strong earthquakes that could register a 6 or
greater on the Richter Scale.
Number of earthquakes in central US has increased from 24 earthquakes a year to 318 with a
magnitude of 3.0 or higher.
Earthquakes caused by humans are likely to cause smaller events at shallower depths.
Seismology in the City
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Of the non-invasive techniques scientists use to obtain Vs30 and DEEPER S-wave velocity,
the spatial autocorrelation, or SPAC, method is especially well suited for working in urban
areas with high levels of ambient noise.
Noise is anything that shows up on a seismic instrument (air conditioners, animals, electric
equipment)
The amount of shaking the earthquake causes is registered as its “earthquake hazard”
Scientists use a “thumping method” to test out the unnecessary noise
Scientist can study area by using four stakes in the ground
Both earthquakes and “thumps” are used by scientists to study characteristics and properties
of the earth, to determine what the shaking would be like in different areas from future nearby
earthquakes could cause shaking, and the amount of shaking it could cause, it is called
“earthquake hazard”
Better Understanding Fault Movement
after an earthquake, fault moves to adjust to it movement during the earthquake
-sometimes the afterslip hits harder than the initial earthquake
Post earthquake fault movement (afterslip) usually concentrates in loosely packed sediment.
Geological information can give a guide to the likely extent of future earthquakes, and
also for planning earthquake response.
20 GPS sensors have been set up to observe post earthquake events observing the earth for
four weeks after the earthquake occurred
-scientist still wonder if we can use geology as a proxy for fault behavior
-The South Napa earthquake was the first big earthquake to be digitally imaged by the
Sentinel-1A