Earthquake Measurement Scales & Related Vocabulary

Vocabulary flashcards summarizing the key instruments, scales, categories, and energy/frequency concepts related to measuring earthquakes.

Seismometer

An instrument with a sensitive needle that records seismic waves produced by earthquakes.

Richter Scale

A logarithmic scale that calculates earthquake magnitude from seismometer data to express the energy released.

Modified Mercalli Scale

A twelve-level, linear intensity scale (I–XII) that rates an earthquake by observed effects and damage.

Magnitude (Earthquake)

Numerical value expressing the size/energy of an earthquake, determined from the Richter Scale.

Intensity (Earthquake)

Qualitative measure of an earthquake’s effects on people, structures, and the Earth’s surface, expressed by the Mercalli Scale.

Logarithmic Scale

Scale in which each whole-number step represents ~32 times more energy; used by the Richter Scale.

Linear Scale

Scale with uniform step sizes; the Modified Mercalli Scale increases evenly from I to XII.

Great Earthquake

Approx. magnitude 9; near total destruction and massive loss of life.

Major Earthquake

Approx. magnitude 8; severe economic impact and large loss of life.

Strong Earthquake

Approx. magnitude 7; causes significant damage (e.g., Kobe 1995, Northridge 1994).

Moderate Earthquake

Approx. magnitude 6; capable of notable property damage.

Light Earthquake

Approx. magnitude 5; some property damage, often felt by most people.

Minor Earthquake

Approx. magnitude 4; felt by humans with little to no damage.

Instrumental Intensity (Mercalli I)

Shaking detected only by sensitive instruments; not felt by people.

Very Feeble Intensity (Mercalli II)

Noticed only by people at rest; swinging objects may move slightly.

Slight Intensity (Mercalli III)

Felt indoors by people at rest; vibration like passing of a truck.

Moderate Intensity (Mercalli IV)

Generally perceptible to people in motion; loose objects disturbed.

Rather Strong Intensity (Mercalli V)

Felt by all; dishes break, bells ring, pendulum clocks stop.

Strong Intensity (Mercalli VI)

Felt by everyone; some people frightened, slight structural damage.

Very Strong Intensity (Mercalli VII)

Noticed by people in autos; damage to poorly built structures.

Destructive Intensity (Mercalli VIII)

Chimneys fall; heavy furniture overturned; substantial damage.

Ruinous Intensity (Mercalli IX)

Great damage to substantial buildings; ground cracks, pipes break.

Disastrous Intensity (Mercalli X)

Many buildings destroyed; widespread infrastructure failure.

Very Disastrous Intensity (Mercalli XI)

Few structures remain standing; extensive landscape deformation.

Catastrophic Intensity (Mercalli XII)

Total destruction of man-made structures and major ground changes.

TNT Equivalent (Earthquake Energy)

Comparison of seismic energy to explosive energy—for example, magnitude 9 ≈ 20 trillion kg of TNT.

Earthquake Frequency

Relationship showing that smaller-magnitude quakes occur far more often than larger ones.