Earthquakes Sudden movement of surface when accumulated strain along opposing sides of a fault is suddenly released. Rock stretches and snaps.

>90% boundaries greatest intensity at subduction zones (also occur at transform boundaries and spreading boundaries) Displacement 1” – 20’ Energy released as seismic waves Vibrations generated by movement Vibrations generated by movement

Waves travel along surface and through earth: Waves travel along surface and through earth: Body waves: move through earth Body waves: move through earth P and S waves P and S waves Surface Waves: move along surface Surface Waves: move along surface

Body Waves P waves: P waves: Primary Primary Fast (3.5 miles per second) Fast (3.5 miles per second) Compression Compression Push-pull Push-pull Travel through liquids and solids Travel through liquids and solids

Body waves S waves: S waves: Secondary Secondary Slower (1.5 miles per second) Slower (1.5 miles per second) Shear waves Shear waves Displace material perpendicular to line of travel Displace material perpendicular to line of travel Do not travel through liquids Do not travel through liquids

Surface Waves Most destructive Most destructive Slower than P or S Slower than P or S

Focus: point of initiation of movement; in crust or upper mantle Focus: point of initiation of movement; in crust or upper mantle Epicenter: point on surface above the focus; geographic center Epicenter: point on surface above the focus; geographic center

Richter scale Instrumental scale showing energy released during quake; based on amplitude of seismic waves Instrumental scale showing energy released during quake; based on amplitude of seismic waves Measured by seismograph Measured by seismograph Logarithmic ; Logarithmic ;

seismograph Pendulum connected to recorder Pendulum connected to recorder

Kobe, Japan 1995 magnitude 7.2

Loma Prieta, California, 1989 magnitude 7.1

Mercalli Scale Based on observed amount of damage to buildings and effects felt by people Based on observed amount of damage to buildings and effects felt by people I - XII I - XII

Moment Magnitude scale Includes amount of movement along fault, geology of substrate, size of failure area Includes amount of movement along fault, geology of substrate, size of failure area

Tsunamis Seismic sea waves Seismic sea waves Caused by earthquake beneath ocean (or submarine volcanoes or landslides) Caused by earthquake beneath ocean (or submarine volcanoes or landslides)

Waves radiate in all directions Waves radiate in all directions Can move across entire ocean Can move across entire ocean 1960 Chile earthquake caused tsunami in Japan 1960 Chile earthquake caused tsunami in Japan Can cross Pacific in < 24 hours Can cross Pacific in < 24 hours Speed and amplitude depend on depth of ocean Speed and amplitude depend on depth of ocean 500 mph in deep ocean; low amplitude crests 500 mph in deep ocean; low amplitude crests mph in shallow ocean, high amplitude mph in shallow ocean, high amplitude

Amplitude increases, wavelength decreases, approaching shore. 213 km 23 km 10.6 km 4000 m 50 m 10 m

Tsunami, Dec. 26, 2004 off western coast of northern Sumatra

275,000 death toll 275,000 death toll Magnitude 9.15 earthquake Magnitude 9.15 earthquake Subduction of Austral-Indian beneath Eurasian plate Subduction of Austral-Indian beneath Eurasian plate 750 miles faultline slipped 50 feet 750 miles faultline slipped 50 feet Slightly altered earth’s rotation Slightly altered earth’s rotation Raised sea level 0.1 mm Raised sea level 0.1 mm

Banda Aceh, Indonesia

Memorial slide show for tsunami victims