Plate Tectonics/ Earthquake Unit

Seismic waves in more depth

During an earthquake, a rapid release of energy along a fault produces seismic waves. Seismic waves travel outward in all directions through rock. Seismic waves transfer energy through the ground and produce the motion that you feel during an earthquake. The energy released is strongest near the epicenter. As seismic waves move away from the epicenter, they decrease in energy and intensity. The farther you are from an earthquake's epicenter, the less the ground moves.

Seismologist

Scientist who studies earthquakes

Surface Wave

Causes particles in the ground to move up and down, similar to ocean waves

Earthquake Risk

Earthquakes occur near tectonic plate boundaries. Converging plate boundaries have the highest risks. Because earthquakes threaten lives, seismologists study the probability that an earthquake might occur in an area by studying past earthquake activities. Governments use these risk assessments to help plan and prepare for future earthquakes.

Seismogram

Graphical illustration of seismic waves

What are volcanoes?

A volcano is a vent (hole) in Earth's crust through which melted rock flows. Molten rock below Earth's surface is called magma.

Ring of Fire

An area of earthquake and volcanic activity that surrounds the Pacific Ocean. When you compare the locations of active volcanoes and plate boundaries you can see that volcanoes are mostly along convergent plate boundaries where plates collide.

Locating Earth's Epicenter

An instrument called a seismometer measures ground motion and is recorded on a seismogram (Graphical illustration of a seismic wave). Seismologists use a method called triangulation to locate the earthquakes epicenter. This method uses speed of seismic waves to determine the distance from the epicenter from three seismometers.

Fault

Break in Earth's lithosphere where one block of rock moves toward, away from, or past another

Properties of Primary wave

Cause rock particles to vibrate in the same direction that waves travel, fastest seismic waves, first to be detected and recorded, travels through solid and liquids

Properties of Secondary wave

Cause rock particles to vibrate perpendicular to the direction that waves travel, slower than p-waves, faster than surface waves, detected and recorded after p-waves, only travel through solids

Properties of Surface wave

Causes rock particles to move in a rolling or elliptical motion in the same direction that waves travel, slowest seismic wave, generally cause the most damage at earth's surface

Earthquake

Causes vibrations in the ground that result from movement along breaks in Earth's lithosphere

What are earthquakes?

Earthquakes are the vibrations in the ground that result from movement along breaks in Earth's lithosphere. These breaks are called faults. The forces that move tectonic plates also push and pull on rocks along the fault. If these forces become large enough, the blocks of rock on either side of the fault can move and cause a destructive earthquake.

More about earthquakes and how they happen

Earthquakes result from the buildup and release of stress along active plate boundaries. Deep Earthquakes result from convergent plate boundaries. Earthquakes that occur along convergent plate boundaries typically release tremendous amounts of energy. They can also be disastrous. Shallow earthquakes are common where plates separate along a divergent plate boundary and result in smaller Earthquakes

pryoclastic flow

Explosive volcanoes can produce fast-moving avalanches of hot gas, ash, and rock called pyroclastic flows that can travel at speeds of more than 100 km/hr and with temperatures greater than 1000°C.

Types of Faults: Normal

Forces pull two blocks of rock apart. The block of rock above the fault moves down relative to the block of rock below the fault. Location: divergent plate boundaries

Types of Faults: Reverse

Forces push two blocks of rock together. The block of rock above the fault moves up relative to the block of rock below the fault. Location: convergent plate boundaries

Shield volcano

Large volcano with gentle slopes of basaltic lava; located along divergent plate boundaries and oceanic hot spots

Composite volcano

Large, steep sided volcano that results from explosive eruptions of andesitic and rhyolitic lavas along convergent plate boundaries

Divergent Boundaries (volcanoes)

Lava erupts along divergent plate boundaries too. As the plates separate, magma rises through the opening in Earth's crust that forms between them. This process commonly occurs at a mid-ocean ridge and forms new oceanic crust.

Viscosity

Liquid's ability to flow

Epicenter

Location directly above the focus of an earthquake

Focus

Location where rocks first move along a fault and seismic waves originate

Magma Chemistry

Magma that forms in different environments have different chemical compositions. Silica is the main component of all magma and determines the viscosity of the magma.

Seismometer

Measures and records ground motion and the distance and direction seismic waves travel

Magma

Molten rock below Earth's surface

Lava

Molten rock that erupts onto Earth's surface

Where do volcanoes form?

Most volcanoes are close to plate boundaries.

Hot Spots

Not all volcanoes form on or near plate boundaries. Volcanoes that are not associated with plate boundaries are called hot spots. Geologists hypothesize that hot spots originate above a rising convection current from deep within Earth's mantle.

Primary wave

P-wave; fastest-moving type of seismic wave; causes particles in the ground to move in a push-pull motion

Types of seismic waves

Primary waves, secondary waves and surface waves

Secondary wave

S-wave; causes particles in the ground to move side to side and up and down at right angles relative to the direction the wave travels

Determining an earthquakes magnitude

Scientists use a scale called a Richter scale to determine the magnitude of an earthquake. The scale begins at 0 and has no upper limit. Each increase of 1 on the scale represents 10x the amount of ground motion recorded on a seismogram. For example, a magnitude 6 will have 10x greater shaking than a magnitude 5. The greatest magnitude ever recorded was a 9.5 in Chile in 1960

Mapping earth's interior

Seismologists (scientists that study Earthquakes) Use the properties of the seismic waves to map the Earth's Interior (What the Earth looks like inside). The seismic waves changes speed and direction depending on the material they travel through. By comparing the measurements and the densities of the Earths materials they have determined the composition of Earth's layers.

How do volcanoes form?

The movement of Earth's tectonic plates causes the formation of volcanoes and the eruptions that result.

Dissolved gasses

The presence of dissolved gasses contribute to how explosive a volcano is. All magma contains dissolved gasses which includes water vapor, carbon dioxide and sulfur dioxide. As the magma moves to the surface bubbles form and gas begins to escape which causes explosive eruptions. Magma with low viscosity is mostly found mid-oceanic volcanos where magma with a high silica content is found on continental plate subduction

Seismic Wave

Travels as vibrations on and in Earth

Types of Faults: Strike Slip

Two blocks of rock slide horizontally past each other in opposite directions. Location: transform plate boundaries

Volcano

Vent in Earth's crust through which molten rock flows

Convergent Boundaries (volcanoes)

Volcanoes can form along convergent plate boundaries. When two plates collide, the denser plate sinks into the mantle. The thermal energy below the surface melts the lower plate and form magma. Magma is less dense than the surrounding mantle and rises through cracks in the crust. Molten rock that erupts onto Earth's surface is called lava.

Rock Deformation

When a force is applied to a body of rock it might bend or break. When a force such as pressure is applied to rock along plate boundaries, the rock can change shape. This is called rock deformation. Eventually the rocks can be deformed so much that they break and move.

Earthquake, Focus and Epicenter

When rocks move along a fault, they release energy that travels as vibrations on and in Earth called seismic waves. These waves originate where rocks first move along the fault, at a location inside Earth called the focus. The epicenter is the location on Earth's surface directly above the earthquake's focus.

Faults

When stress builds in places like a plate boundary, rocks can form faults. A fault is a break in Earth's lithosphere (outer Layer) where a piece of rock moves toward, away from, or past another. When rocks move in any direction along a fault, an earthquake may occur. The direction that rocks move on either side of the fault depends on the forces applied to the fault.

convergent plates

When two plates move towards one another and collide

Divergent plates

move away from each other