EarthquakesWhat do we know?

What are scientists studying?

What Are Earthquakes?● 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● 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?● 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?● 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● 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● 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● 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

● 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 ● M7.8 Earthquake in Kathmandu, Nepal (April 25, 2015)

○ Largest aftershock M7.3 (May 12, 2015)

● 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

○ 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’”★ 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● 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● 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● 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● 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● 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 Movementafter 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