(SEM1Q1, SCI) 2.1 - Intensity and Magnitude of an Earthquake

What happens as seismic waves propagate farther from the focus?

They lose energy.

What are the two general ways to describe an earthquake?

intensity and magnitude

What is intensity?

measure of the amount of earthquake shaking at a given place based on the amount of damage written in Roman numeral

What does PHIVOLCS stand for?

Philippine Institute of Volcanology and Seismology

What is the scale used by PHIVOLCS to measure intensity?

PHIVOLCS Earthquake Intensity Scale (PEIS)

What is the shaking in Intensity I?

scarcely perceptible

What is the shaking in Intensity II?

slightly felt

What is the shaking in Intensity III?

weak

What is the shaking in Intensity IV?

moderately strong

What is the shaking in Intensity V?

strong

What is the shaking in Intensity VI?

very strong

What is the shaking in Intensity VII?

destructive

What is the shaking in Intensity VIII?

very destructive

What is the shaking in Intensity IX?

devastating

What is the shaking in Intensity X?

completely devastating

Starting at which intensity can the earthquake be felt by people indoors?

Intensity II and above

Starting at which intensity is people losing balance in?

Intensity VI and above

Starting at which intensity is old or poorly-built structures damaged?

Intensity VII and above

Starting at which intensity is there landslides?

Intensity VIII and above

What is liquefaction?

strength and stiffness of a soil is reduced; it acts liquid rather than solid

Starting at which intensity does liquefaction occur?

Intensity VIII and above

What is magnitude?

amount of energy released at the source of the earthquake

How can you describe magnitude? (2)

(1) measurement or absolute value of a quantity
(2) represented by a positive real number

What is the Richter Magnitude Scale?

measures magnitude of an earthquake ranging from 0 to 9

What is the Mercalli Intensity Scale?

measures strength of an earthquake upon its impact; used by PHIVOLCS

Who invented the Richter Scale?

Charles Richter

Who invented the Mercalli Scale?

Giuseppe Mercalli

What should you always prepare before an earthquake?

a disaster kit

What should you fasten properly before an earthquake to reduce damages?

cabinets and hanging objects

What should you put from high shelves to low shelves before an earthquake?

heavy, breakable objects

What should you not place your bed near?

glass windows and mirrors

Before a typhoon, what should you secure in a safe place?

important documents

During an earthquake, what should you do?

Duck, Cover, Hold

If you are outside during an earthquake, what should you move away from? (3)

trees, electric post, and buildings that may collapse

If you are indoors during an earthquake, what should you never use?

an elevator

If you live near bodies of water during an earthquake, what should you do?

evacuate to a higher and safer place in case of tsunami

What should you listen to after an earthquake?

news and updates about the epicenter

What two words did the term tsunami derive from?

tsu (harbor), nami (wave)

What is a tsunami?

a series of waves caused by strong earthquakes beneath the seafloor

In a tsunami, what creates large and fast moving waves?

seismic sea waves caused by displacement of huge volumes of sea water

Where does a tsunami result from?

ocean earthquake

What happens to a tsunami when it travels far from the seashore?

amplitude grows; speed slows

Why does not every fault motion under the sea produce tsunamis?

because it only happens when fault moves vertically

How are tsunamis different from tidal waves?

Tsunamis are high, large waves due to strong winds or earthquake. Tidal wave is a shallow water wave due to gravitational attraction of the sun and moon.

How does a tsunami start?

Tectonic upthrust in the form of earthquakes.

What does the energy from underwater earthquakes cause?

train of waves that travel in all directions

When a tsunami is travelling, what continues to grow?

wavelength

As the tsunami approaches the shore, what happens to its wavelength and amplitude?

wavelength decreases, amplitude increases

What does the Richter Magnitude Scale measure?

magnitude of an earthquake's largest jolt of energy

What does the Moment Magnitude Scale measure?

the total energy released by an earthquake