EARTHQUAKES

EQ facts  Largest EQ recorded in the US 9.2  Largest in world 9.5  Average rate of motion across the San Andreas Fault is 2 in./yr. (3 million years L.A. will be next to S.F.)  500,000 detectable EQ each year.  More damage is caused indirectly from the EQ, not the EQ itself.

EQ facts cont.  10,000 EQ’s will develop in southern Cali this year. Most will not be felt.  Powerful EQ’s rocked the midwest in the early 1800’s. New madrid fault had a magnitude of over 8 and caused church bells to ring in Boston Mass.  Deadliest in China 1557, killing 830,000 people.

WHAT ARE EQ’S  Vibrations of the earth’s crust.  Movement of plates along faults  Fault-crack in rock where movement occurs  Elastic Rebound Theory – Rocks of both sides of the fault are in constant movement. When these rocks lock up stress is increased. When this lock is broken an EQ occurs.

TYPES OF FAULTS  Normal fault – hanging wall moves down the footwall.  Reverse fault – hanging wall moves up the footwall  Strike-slipe fault – rock on either side slide past each other.

SIESMOGRAPH/GRAM  Seismograph – instrument used to detect earthquakes.  Seismogram – Recorded waves of an earthquake.

TYPES OF WAVES  P waves (primary) Compressional waves. Very fast. First to be seen on a seismogram.  S waves (secondary) Side to side. Can only travel through solids.  L waves (Long) Slowest moving. Very destructive. Rolling waves.

Magnitude  Richter Scale – Scale used to measure the magnitude of an earthquake. Measured by the release of energy of an earthquake.  Each increase of one whole number is 31.7 times more powerful.  Mercali Scale – Scale used to measure the amount of damage an EQ causes. Roman numerals.

Location  Determine the difference between the S-P lag time.  Plot the distance for 3 stations. Where your points meet is where your EQ’s epicenter is.