Earthquakes

What is an Earthquake? A vibration of the Earth’s surface that follows a release of energy in the Earth’s crust

What causes an Earthquake? The Earth’s outer surface is broken up into tectonic plates These plates constantly move away from, towards, or past each other An EQ occurs when the stresses caused by these plate movements are released

EQ Prone Areas? Most of the World’s EQ’s are on the circum-Pacific seismic belt known as the “Ring of Fire” 95% of all EQ’s happen at active plate boundaries

Popular ones? Japan California Philippines Indonesia NZ Alaska Mexico Chile

EQ Terminology The following words will help understand when reading or listening: Focus Epicenter Intensity

Focus The energy released in all directions from EQ’s originate from their source: FOCUS (where they started) The energy released is known as waves that travel quickly through the Earth’s crust As distance from the focus increases, the strength of the waves decreases

Epicenter The Epicenter is the location directly above the Focus of the EQ

Intensity A measure of the effects of the EQ at a particular local Dependent on the following: Strength of EQ (magnitude) Distance from Epicenter Nature of surface materials Building design Many EQ’s occur in oceanic areas or at great focal depths and are either not felt, or their intensities do not reflect their true strength

The Usual Around the world every year this happens: 900,000 - <3.0 Magnitude EQ’s (potentially perceptible) 56,000 - <6.0 Magnitude EQ’s (Destructive) 300 - 6-8 Magnitude EQ’s (Major! Serious Damage) 1.4 - >8.0 Magnitude (Total destruction at epicenter)

Besides the shaking: The biggest reason for EQ’s destruction is usually the shaking of the ground….what else comes with them is sometimes worse! Fires Landslides Liquefaction of ground

Fires When the ground shakes and cracks, gas lines, water lines, electric lines are damaged most of the time (underground usually)

Fires Some times, the most destructive….an easy fix if water is on… San Francisco, 1906: The estimation was 8.3 on the Richter scale, but worse than the shaking itself, the earthquake caused fires that burned out of control for three days. Two thirds of the city burned down, and totally wiped out the downtown business district. Tens of thousands of people lost their homes and fled the city and an estimated 3000 people died.

Landslides Depending on surface material and landscape of what “is being shaken”

Biggest in History… Mt St Helens (Cascade Region) Peru 1970: 66,000 dead

Liquefaction When soil loses strength and stiffness in response to an applied stress, usually an EQ or other sudden change in stress condition, causing it to behave like a liquid.

Ex’s of Liquefaction Alaska 1964 Mexico City 1985 : rests on the ancient lakebed of Lake Texcoco, which is a large basin filled with liquefiable sand and ground water. In the Mexico City earthquake of 1985, the wet sand beneath tall buildings liquefied and most of the 10,000 people who died were in buildings that collapsed as their foundations sank into liquefied sand.

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