 Chapter 5 Section 4

 Liquefaction  Aftershock  Tsunami  Base-isolated Building

 Geologists can determine earthquake risk by locating where faults are active, where past earthquakes have occurred, and where the most damage is caused.  In the Unites States, the risk is highest along the Pacific coast in California, Washington, and Alaska.  The eastern U.S. mostly has a low risk of earthquakes because this region lies far from plate boundaries.

 Using the Mercalli Scale, intensity maps show the ground shaking and damage from an earthquake vary from place to place.  Intensity maps show that most earthquakes happen near fault lines.  Past earthquakes help geologists estimate the risk of future earthquakes.  Geologists study historic earthquake reports, and the rock and soil along faults for evidence of past earthquakes.

 Causes of earthquake damage include shaking, liquefaction, aftershocks, and tsunamis.  The shaking from seismic waves can trigger landslides or avalanches, and can damage or destroy bridges, buildings, utility poles, gas lines, and water mains.  Liquefaction occurs when an earthquake’s violent shaking suddenly turns loose, soft soil into liquid mud.  Aftershocks are earthquakes that occur after a larger earthquake in the same area.  Tsunamis are large waves caused by earthquakes displacing the water in the ocean.

 What areas of the U.S. have the highest earthquake risk? The lowest?  Why do geologists make intensity maps?  What are the four ways earthquakes can cause damage?

 The best way to protect yourself from an earthquake is to drop, cover, and hold.  If you are inside, crouch underneath a sturdy table or desk, or crouch against an inner wall with your head covered.  Avoid windows, mirrors, wall hangings, and furniture that might fall over.  If you are outside, move to an open area such as a playground.  Avoid cars, power lines, trees, and buildings.  To prepare for problems with water and food, have an earthquake kit ready with canned food, water, and first aid supplies. 

 To reduce earthquake damage, new buildings must be made stronger and more flexible.  Older buildings may be modified so as to withstand stronger quakes.  Buildings made of brittle materials such as concrete and brick suffer the most damage in an earthquake.  Buildings made of more flexible materials, such as wood, tend to suffer less damage. 

 A base-isolated building is designed to reduce the amount of energy that reaches the building during an earthquake.  It rests on shock-absorbing rubber pads or springs, which smooth out the bumpy ride to prevent violent shaking.  Flexible joints can be installed in gas and water lines to keep them from breaking. 