What is Seismology? • Seismology is the study of earthquakes and seismic waves that move through and around the earth • A seismologist is a scientist who studies earthquakes and seismic waves
What Are Seismic Waves? • Seismic waves are the waves of energy caused by the sudden breaking of rock within the earth. • They are the energy that travels through the earth and is recorded on seismographs. • Seismic comes form the Greek word meaning to “SHAKE”
Types of Seismic WavesEarthquakes produce 3 basic kinds of wave motions: • P Waves • S Waves • L Waves
Primary Wavesaka compressional waves • back and forth wave motion • this motion alternates squeezing and stretching the rock through which it passes • can travel through any material- solid rock, magma, ocean water, and air • travel about twice as fast as S waves.
S Wave-Secondary Waves aka Shear Wave • side to side waves • cause particles to move at right angles to the direction the waves are traveling • can travel through solids but not through liquids or gases
L Waves-Surface Waves • When P and S waves reach the surface, they set up a third wave called L waves or surface waves • These waves move like “ripples” on a pond and travel more slowly than P or S waves
Seismographs are instruments that detect and record earthquake waves How Do Seismologists Measure earthquake waves?
Earthquakes are measured according to the RICHTER SCALE. This is based on the size of the largest seismic wave produced by the earthquake. • The damage done by an earthquake is measured according to the MERCALI SCALE.
What Do Seismologists Learn From Seismic Waves? • Seismologists use seismographs to record the amount of time it takes seismic waves to travel through different layers of the Earth. • As the waves travel through different densities, seismologists can deduce the type of material the waves are travelling through. • The results can provide a snapshot of the Earth’s internal structure and help us to locate and understand fault planes and the stresses and strains acting on them.
TRIVIA QUESTIONS • What is the most earthquake prone state in the US? ALASKA- it’s one of the most seismically active regions of the world • Why does California have so many EQ’s and NY does not? CA is on a plate boundary • What states have the least amount of EQ’s? Florida and N. Dakota • Where and when did the largest EQ occur in the 20th Century? 1960 Chilean EQ: Magnitude 9.6 and broke a fault over 1,000 miles long!