Distribution of Earthquakes The most important concentration of earthquakes by far is the Circum-Pacific Belt, which encircles the rim of the Pacific Ocean. Within this belt approximately 80% of the Worlds shallow focus quakes (<60 km), 90% of the intermediate-focus quakes (60-300 km) and essentially 100% of the deep-focus quakes (>300 km) occur. Another major concentration of earthquakes is in the Mediterranean-Himalayan Belt. Careful determination of the locations and depths of focus of earthquakes has revealed the existence of distinct earthquake zones that begin at oceanic trenches and slope landward and downward in to the earth at an angle of about 30-60. Such zones are called Benioff zones (Benioff kua). Seismometers (sismometre): instruments that detect seismic waves Seismographs (sismograf): devices that record motion detected by seismometers Seismograms (sismogram): paper or digital records of seismic wave vibrations

Hypocenter/hiposantr (focus/odak) location of first rupture along fault Epicenter/episantr point on Earths surface above rupture Seismic Waves 1. Body waves (Cisim dalgalar): travel through the earths interior, spreading outward from the focus in all direction. P (primary/birincil) wave: compressional wave in which rock vibrates parallel to the direction of wave propagation. (4-7 km/s) S (secondary/ikincil) wave: rock vibrates perpendicular to the direction of wave propagation. It can travel only through solid materials. (2-5 km/s). 2. Surface waves (Yzey dalgalar): travel on the earths surface away from the epicenter. Rayleigh wave: move forward while individual particles of material move in an elliptical path within a vertical plane oriented in the direction of wave movement. Love wave: individual particles of the material move only back and forth in a horizontal plane perpendicular to the direction of wave travel.

Locating Earthquakes determine distance to epicenter for each station draw circles with center at station and distance to epicenter as the radius Locate epicenter from intersection of the 3 circles Measuring the Strength of an Earthquake Two measures of an earthquakes strength are commonly used: Intensity (iddet), a qualitative assessment of the kinds of damage done by an earthquake. The most common intensity scale is Mercalli Intensity Scale (Mercalli iddet lei), which has values ranging from I to XII. Magnitude (Byklk), quantitative measure of the amount of energy released by an earthquake Richter Magnitude Scale (Richter Byklk lei) Modified Mercalli Intensity Index The Destructive Effects of Earthquakes Shaking and ground rupture Liquefaction (Svlama): transformation of water saturated granular material from solid to a liquid state Fire Tsunami Landslides Regional changes in land elevation