 Earthquake Zones • About 95 percent of the major earthquakes occur in a few narrow zones. http://www.iris.edu/seismon/

8.2 Waves and Location seismograph seismogram  Seismographs (seismometer) - instruments that record earthquake waves.  Seismograms - traces of amplified, electronically recorded ground motion made by seismographs. seismograph seismogram

Seismograph/ Seismogram

P = Compressional (Pressure) Types of Waves Earthquake Waves  Body Waves - identified as P or S waves P = Compressional (Pressure)  P-waves: primary waves - Push-pull waves - push (compress) & pull (expand) in the direction that the waves travel - LONGITUDINAL waves - Fastest speed (velocity) of all quake waves - Travel through solids, liquids & gases 1.5 - 8 km/sec

Types of Waves S = Secondary  S-waves: secondary waves 1 - 5 km/sec - Shake particles at right angles to the direction that they travel - TRANSVERSE waves - Travel along Earth’s outer layers - travel only through solids!!!!! - Cause more damage than p-waves 1 - 5 km/sec

Love Waves and Rayleigh waves Types of Waves Love Waves and Rayleigh waves  Surface waves - only move across Earth’s surface - Combination of Earth moving up & down and back & forth - Most destruction due to longer wavelengths

S Wave P Wave Surface Wave Fault line the difference in time between the S and P wave (S-P) tells you how far away the earthquake is

Where is it??? Locating an Earthquake  Earthquake Distance (Triangulation) • Epicenter - located using difference in arrival times between P and S wave recordings.  Earthquake Direction • Travel-time graphs from 3 or more seismographs used to find exact location of the epicenter.  Earthquake Zones • About 95% of major earthquakes occur in a few narrow zones

Locating an Earthquake Explaining Earthquakes