Earthquakes and Seismic Waves 2-1

What is an Earthquake? Shaking and trembling that results from the movement of rock beneath Earth’s surface Occur when stress along a fault increases so much that the rock breaks Releases an enormous amount of stored energy Most begin in lithosphere

Parts of an earthquake Focus-where earthquake starts beneath the surface Epicenter-point on surface directly above focus

Seismic waves Move like ripples on pond Carry energy from earthquake away from focus, through Earth’s interior, and across the surface Includes P waves, S waves, and surface waves

Types of Seismic Waves

Mercalli Scale Rates level of damage 12 step scale Same earthquake can have different ratings in different locations

Richter Rating of earthquakes magnitude based on size of seismic waves Scale of 10 Measured with seismograph Good for nearby earthquakes **Each point increase in magnitude represents a release of 32x more energy

Moment Magnitude Estimates total energy released Rates earthquakes near and far Looks at: – kinds of seismic waves and how strong they were – how much the fault moved – strength of the rocks that broke What we usually hear on news

Locating Epicenter Measure difference between the arrival of P and S waves The farther away the earthquake, the greater the time difference between the arrival of P and S waves Draw circles from data from at least 3 different seismographs The radius of each circle is the distance from seismograph to epicenter