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What is a seismograph?

An instrument that records the movement of the Earth or vibrational energy.

What does a seismogram record?

It records wave amplitude versus time.

What are body waves?

Seismic waves that travel through the Earth’s interior. They include P-waves and S-waves.

What are P-waves?

Primary waves that move by compression, are the fastest, and can travel through all mediums.

What are S-waves?

Secondary waves that move by shear (up and down motion), are slower than P-waves, and only travel through solids.

What are surface waves?

The slowest earthquake waves that cause the most destruction; they shake and/or roll the ground surface.

How do seismic waves help map the Earth's interior?

Body waves pass through all solids in all directions and their velocities change based on the materials they travel through, allowing scientists to map the Earth’s interior.

How do seismic waves behave differently in rigid materials?

Seismic waves travel faster through rigid materials, and they can be reflected, refracted, or diffracted.

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What is the focus (hypocenter) of an earthquake?

The origin of an earthquake, which can be shallow or deep.

What is the epicenter of an earthquake?

The point on the surface directly above the focus.

How are earthquakes located?

By studying the arrival times of body waves and using triangulation.

Where are deep-focus earthquakes most commonly found?

At convergent plate boundaries, such as in the Wadai-Benioff zone or megathrust faults.

What is earthquake intensity?

A qualitative measure of the degree of shaking based on the amount of damage.

What scale is used to measure earthquake intensity?

The Modified Mercalli Intensity Scale.

What is earthquake magnitude?

A measure based on the amplitude of the largest seismic wave, typically measured using the Richter scale.

How does each unit increase in the Richter scale relate to energy release?

Each unit corresponds to a 32-fold energy increase.

What scale estimates large earthquakes more accurately than the Richter scale?

The Moment Magnitude scale.

What factors determine structural damage in an earthquake?

Intensity of the earthquake, duration of vibrations, material upon which the structure rests, and the design of the structure.

What is liquefaction?

A phenomenon where ground water is churned by an earthquake, causing buildings to sink.

What is a tsunami?

A giant ocean wave caused by earthquakes at convergent plate boundaries.

What is mass wasting?

The movement of rock or soil down a slope, often triggered by earthquakes.

Can earthquakes be predicted?

No, earthquakes cannot currently be predicted.

What causes an earthquake?

The rapid release of energy along a fault, producing vibrations of the Earth.

What are faults?

Cracks in bedrock where displacement has occurred.

What is elastic rebound?

The process where rocks "spring back" to their original shape after stress accumulates and is released.

What are foreshocks?

Warning tremors that occur before the main earthquake.

What are aftershocks?

Adjustment tremors that occur after the main earthquake.

What is fault creep?

Slow slippage of rocks along a fault that results in a slower earthquake.

What is the lithosphere?

The rigid outer layer of the Earth, including the crust and upper mantle.

What is the mantle composed of?

Igneous rock peridotite and contains the asthenosphere, which is soft and weak.

What is the outer core?

A molten iron-nickel layer below the mantle that generates Earth’s magnetic field.

What is the inner core?

A solid iron sphere at the center of the Earth.

What is the Mohorovicic discontinuity?

The boundary between the Earth’s crust and the mantle, where seismic waves increase in velocity.

What is the shadow zone?

The absence of S-waves between ~140° to 180° of arc from the earthquake's epicenter, due to the Earth's liquid outer core.

How thick is the oceanic crust?

About 7 km (5 miles) thick.

How thick is the continental crust?

Typically 35–40 km (22–25 miles) thick, but can exceed 70 km (40 miles) in mountainous regions.

What are the main types of rocks in the continental crust?

Felsic rocks in the upper crust and mafic rocks in the lower crust.

What is the density of the mantle?

The upper mantle has a density of ~3.0 g/cm³, and the lower mantle has a higher density (>3.5 g/cm³).

What is the composition of the Earth's outer core?

The outer core is made of molten iron and nickel.