Earthquakes – Be Prepared, Not Scared

These Q&A flashcards review definitions, mechanisms, wave types, fault types, earthquake categories, global locations, measurement scales, instruments, safety tips, and notable facts from the earthquake lecture notes.

What is an earthquake?

A sudden shaking of the ground caused by the violent shifting of massive plates beneath Earth’s surface.

Where is the epicenter of an earthquake located?

Directly above the hypocenter (focus) on Earth’s surface.

What is the hypocenter (focus)?

The point within Earth where seismic energy is first released along a fault.

How deep are shallow-focus earthquakes?

0–70 km beneath Earth’s surface.

What are deep-focus earthquakes and how deep can they occur?

Earthquakes with foci 70–700 km deep, often within subducting slabs.

Name two natural causes of earthquakes.

Volcanic eruptions and tectonic plate movements.

Give one man-made cause of earthquakes.

Mining, large construction projects, or explosions.

What is an aftershock?

A lower-magnitude (sometimes higher) quake that follows the main shock, often worsening damage.

Which 2013 Philippine earthquake had a magnitude of 7.2 and where was its epicenter?

The October 15 2013 Bohol earthquake; epicenter near Sagbayan, Bohol.

State the four main parts of a fault.

Fault plane, fault trace, hanging wall, and footwall.

Describe a normal fault.

A steep fault (≈45–90°) where the hanging wall moves downward relative to the footwall due to tension.

Describe a reverse (thrust) fault.

A shallow-dipping (<45°) fault where the hanging wall moves upward over the footwall because of compression.

What characterizes a strike-slip fault?

Horizontal movement where blocks slide past each other parallel to the fault plane.

What are body waves?

Seismic waves that travel through Earth’s interior (P-waves and S-waves).

Which seismic wave is the fastest and what states of matter can it travel through?

P-waves; they travel through solids, liquids, and gases.

Why can S-waves not travel through Earth’s outer core?

Because S-waves (shear waves) require a solid medium and the outer core is liquid.

What are surface waves and why are they destructive?

Waves that move along Earth’s surface with lower velocity but greater amplitudes, causing more damage.

Who are Love waves named after and how do they move the ground?

Augustus E. H. Love; they move the ground horizontally.

What is a Rayleigh wave often called and how does it move?

Ground roll; it moves the ground in an elliptical, rolling motion.

State the most common type of earthquake and its driving mechanism.

Tectonic earthquakes caused by sudden release of stress along faults.

Explain the Elastic Rebound Theory.

Strain accumulates in rocks until stress exceeds strength, causing a sudden rupture and earthquake.

What type of earthquake can serve as a warning of an impending volcanic eruption?

Volcanic earthquake.

Differentiate volcanic-tectonic and long-period volcanic earthquakes.

Volcanic-tectonic occur after volcanic activity; long-period occur after an eruption and involve magma movement.

What is a collapse earthquake?

A small quake resulting from roof failures in mines or underground caverns ("mine bursts").

What causes an explosion earthquake?

Detonation of chemical or nuclear devices.

Name the three major earthquake belts.

Circum-Pacific (Ring of Fire), Alpide Belt, and Mid-Atlantic Ridge.

Which country sits directly atop the Mid-Atlantic Ridge?

Iceland.

Define seismology.

The scientific study of earthquakes and seismic waves.

What instrument records ground vibrations and what are its two main parts?

A seismograph, consisting of a seismometer (sensor) and a recording device.

Who invented the first known seismograph?

Cheng Heng (Zhang Heng) in ancient China.

Who developed the first modern seismograph?

John Milne in the late 19th century.

Differentiate earthquake magnitude and intensity.

Magnitude measures energy released (single value); intensity measures observed effects at a specific location.

What scale did Charles F. Richter develop and what does it measure?

The Richter Scale; it quantifies earthquake magnitude logarithmically using nearby high-frequency data.

Who created the Mercalli Intensity Scale and what does it describe?

Giuseppe Mercalli; it describes perceived shaking and damage using Roman numerals I–XII.

What should you do during an earthquake if you are indoors?

Drop, Cover, and Hold On—get under sturdy furniture, protect head, stay until shaking stops.

If driving when an earthquake strikes, what is the safest action?

Stop the vehicle, stay inside, and avoid bridges, overpasses, and power lines.

Give two preparedness steps to do before an earthquake.

Inspect the house for hazards and prepare an emergency-supply bag.

State two actions you should avoid during shaking.

Do not use elevators and do not run outside unless absolutely necessary.

Why should heavy objects not be stored on high shelves in quake-prone areas?

They can fall during shaking and cause injury.

What common safety phrase summarizes earthquake response?

"Be Prepared, Not Scared."