Earthquakes and Society

1. Earthquakes and Society Pgs. 129 - 134

2. Earthquake Hazard • Earthquake hazard measures how prone an area is to experiencing earthquakes in the future. • An area’s level is determined by past and present seismic activity. • Some areas have a higher earthquake-hazard level due to more seismic activity

4. Earthquake Forecasting • It is not easy to predict when and where an earthquake will occur. • However seismologists have discovered some patterns in earthquakes that allow them to make some basic predictions. • For example, the strength of earthquakes is related to how often they occur.

5. Strength and Frequency • On a worldwide scale, the less frequent the earthquake is, the higher in magnitude it is. • There are far more earthquakes occurring that are 2.0 than 7.0 every year. • A minor earthquake of 3.0 may occur 49,000 times a year across the world. • A major earthquake of 7.0 may occur 18 times a year across the world.

6. The Gap Hypothesis • The gap hypothesis states that sections of active faults that have had relatively few earthquakes are likely to be the sites of strong earthquakes in the future. • The areas along a fault where relatively few earthquakes have occurred are called seismic gaps. • The gap hypothesis has helped forecast time, strength and location of the Loma Prieta earthquake in San Francisco. • They predicted a 6.5 magnitude and a 7.1 magnitude earthquake hit.

7. Earthquakes and Buildings • When earthquakes occur the ground moves and if the ground happens to have a building on top of it, it can cause the building to collapse. • Most buildings are not made to withstand earthquakes. • When an earthquake occurs, the earth moves enough to displace the center of gravity of the building and it collapses.

8. Earthquake resistant buildings • Architects and engineers have created several items to help buildings become more earthquake proof. • Mass damper: a weight placed in the roof of a building to counter act any motion of the building during a quake. • Cross-braces: braces placed between floors that counter act pressure that pushes and pulls at the side of a building.

9. Resistant features • Flexible pipes: joints on pipelines that are flexible to allow for movement during a quake. • Base isolators: made of rubber, steel and lead, they act like shock absorbers during an earth quake. • Active Tendon system: based at the bottom of a building it acts like a mass damper and shifts to counteract large weight movement.

10. Earthquake Preparations • Safeguard the house • Place heavy object on lower shelves so they don’t fall. • Have a plan for meeting after an earthquake. • Store nonperishable food and water, flashlight, first-aid kit and fire extinguisher. • When indoors, crouch or lie down under a table in the center of a room. • When outdoors, lie face down (covering your head with hands) away from buildings, power lines, and trees. • If in a vehicle on the road, stop the vehicle, stay inside.

11. After the Quake • After the shaking stops, you and others may be puzzled and confused. • Calm down and get your bearings. • Remove yourself from any immediate danger. • Remember your plan and follow it through. • There may be aftershocks, be ready.