Transcript Chapter 6: Earthquakes

Section 4: Earthquake Safety
1. Earthquake Risk
a. Earthquakes are likely wherever plate movement stores energy in the rock
along faults
b. Geologists can determine earthquake risk by locating where faults are active
and where past earthquakes have occurred
c. In the US, the risk is highest along the west coast of California, Washington,
and Alaska
i. The Pacific plate and North American plate meet in California along the
San Andreas fault
ii. In Washington, earthquakes occur because of the subduction of the
Juan de Fuca plate beneath the North American plate
iii.In Alaska, subduction of the Pacific plate causes many earthquakes
iv.Eastern US has a low risk of earthquakes because it is far from plate
boundaries
1. BUT this region has experienced some of the most powerful quakes
in the nation’s history
2. How Earthquakes Cause Damage
a. Causes of earthquake damage include shaking, liquefaction, aftershocks,
and tsunamis
i. Shaking
1. Can trigger landslides or avalanches
2. Can damage or destroy buildings and bridges, topple utility poles,
and fracture gas and water mains
3. S waves and Surface waves can cause severe damage near the
epicenter, with their side-to-side and up-and-down movement
4. The types of rock and soil determine where and how much the
ground shakes
a. The most violent shaking may occur kilometers from the
epicenter
b.Loose soil shakes more violently than solid rock
ii. Liquefaction
1. Occurs when an earthquake’s violent shaking suddenly turns loose,
soft soil into liquid mud
a. Likely where the soil is full of moisture
b. Can create large cracks in the ground
c. Buildings sink and pull apart
iii. Aftershocks
1. An earthquake that occurs after a larger earthquake in the same area
2. Can cause buildings weakened by an earthquake to collapse
3. May strike hours, day, or even months later
iv. Tsunamis
1. A large wave formed by the water displaced by an earthquake
2. During an earthquake, plate movement causes the ocean floor to
rise slightly, pushing water out of its way
3. Spread out from the epicenter and speed across the ocean
a. As a tsunami approaches shallow water (near land) the wave
grows into a mountain of water
3. Steps to Earthquake Safety
a. The best way to protect yourself is to drop, cover, and hold
i. Indoors
1. Crouch beneath a sturdy table or desk and hold on
2. Stay by inner walls and cover your head and neck
3. Avoid windows, glass, and anything that may fall on you
ii. Outdoors
1. Move to an open area, avoiding vehicles, power lines, trees, and
buildings. Sit down.
iii. Earthquake kit
1. Canned food, water, and first aid supplies should be stored in an
easy to reach area
4. Designing Safer Buildings
a. Most earthquake-related deaths and injuries result from damage to
buildings or other structures
b. New buildings may be made stronger and more flexible
c. Old Buildings may be modified
i. Use metal connectors to strengthen the frame, strap the water heater,
use plywood panels to strengthen walls, remove heavy items from the
walls above beds, place beds away from windows, secure brick chimneys
with metal brackets, and fasten bookshelves and cabinets to walls
d. Protecting Structures
i. Brick buildings and some wood-frame buildings may collapse during an
earthquake if their walls have not been reinforced.
ii. New homes built on soft ground should be anchored to solid rock below
the soil
iii.Bridges and highway overpasses can be built on supports that go to
firmer ground
iv.Base-isolated building: designed to reduce the amount of energy that
reaches the building during an earthquake
1. Rests on shock-absorbing rubber pads or springs
2. During an earthquake, the building moves gently back and forth
without any violent shaking
e. Making Utilities Safer
i. Fires and flooding can be caused if an earthquake breaks gas pipes and
water mains
ii. Flexible joints can be installed to keep them from breaking
iii.Automatic shut-off valves can be installed to cut off gas and water flow