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and Society
and Society
Earthquakes & Society7-3
• Key concept: Studying seismic activity can help scientists forecast earthquakes and reduce the damage earthquakes cause.
Earthquake Hazard• Earthquake Hazard is a
measurement of how likely an area is to have a damaging earthquake in the future.
• The hazard level is determined by past seismic activity.
• The more earthquakes occur ,the higher the hazard level
Earthquake Forecasting
• Forecasting when and where earthquakes will happen or how strong they will be is difficult.
• Studying earthquakes, scientists have discovered patterns.
• The patterns allow scientist to make general predictions.
Strength and Frequency
• Stronger earthquakes are much rarer than weaker earthquakes.
• Millions of small earthquakes release the same amount of energy as one large earthquake does.
Gap Hypothesis
• The gap hypothesis is a way to forecast earthquake location, strength, and frequency.
• The gap hypothesis states that sections of active faults that have had relatively few recent earthquakes are likely to be the sites of strong earthquakes in the future.
• The areas along an active fault where relatively few earthquakes have happened are called seismic gaps.
• Stress has a long time to build at seismic gaps.
• When a fault breaks at a seismic gap, the sudden release of stress can cause a large-magnitude earthquake.
Reducing Earthquake Damage• Much of the loss of
human life during earthquakes is caused by buildings that collapse.
• Retrofitting can make older buildings more earthquake-resistant.
• Common ways to retrofit include strengthening structures with steel and fastening the building to its foundation.
Reducing Earthquake Damage
Are You Prepared for an Earthquake?
• You can plan ahead to protect yourself and your property from earthquake damage.
• Safeguard your home by putting heavy objects on low shelves.
• Find places that are safe within each room of your home and outside your home.
• Make a plan to meet with others in a safe place after the earthquake.
• Store water, nonperishable food, a fire extinguisher, flashlight with batteries, radio, medicines, and a first aid kit in a safe place.
Tsunamis
• Earthquakes on the ocean floor can generate tsunamis.
• A tsunami is an extremely long wave that can travel across the ocean at speeds of up to 800 km/h.
• In the open ocean, tsunami waves can seem very small.
• As tsunami waves enter shallow water along a coastline, the energy of the waves is compressed.
• The waves get rapidly taller. By the time they reach shore, waves can be taller than 30 m.
• Tsunamis can cause damage and loss of life by smashing into and washing away anything in their path.
• In 2004, an undersea earthquake of magnitude 9.3 caused a tsunami that killed more than 280,000 people and left 1.25 million people homeless
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Use words below to fill in concept map.
seismometer
earthquakes
body waves
seismic waves
surface waves
S waves
