Earthquakes Aim: What causes earthquakes?

Stress Stress (stored energy) is created in the crust as the plates move around. Faults are breaks in the rock caused by stress. Stress causes friction (energy) to build along faults. When the energy is released an earthquake occurs.

Folding and Faulting Stress causes rock to fold (bend) and fault (crack)

This orange tree grove has a fault running right through it…how can you tell?

Black dots are earthquake locations…. What do you notice?

Most Earthquakes occur along the plate boundaries where the crust is cracked.

Focus – the place in the crust, along a fault where the earthquake starts Epicenter – on the surface directly above the focus

San Andreas fault in CA

Seismic Waves The energy released from the focus of an earthquake Seismograph a machine to record shaking of the ground

Magnitude (Size) of Earthquakes is measured by: Richter Scale – measures size of earthquake waves Mercalli Scale – describes effects people feel and on buildings, ground

Richter Scale – measures size of earthquake waves Richter Earthquake Effects Less than 3.5 Generally not felt, but recorded Often felt, but rarely causes damage. Under 6.0 At most slight damage to well-designed buildings. Can cause major damage to poorly constructed buildings over small regions Can be destructive in areas up to about 100 kilometers across where people live Major earthquake. Can cause serious damage over larger areas. 8 or greater Great earthquake. Can cause serious damage in areas several hundred kilometers across.

Mercalli Scale – describes effects people feel and on buildings, ground I Most people do not notice, animals may be uneasy, can be detected by a seismograph II Hanging objects sway back and forth III Many people feel the movement, parked cars may rock IV Doors, windows, and shelves may rattle, people indoors can feel movement V Light furniture moves, pictures fall off walls, objects fall from shelves VI Nearly everyone feels movement, light furniture falls over, windows may crack VII Some people fall over, walls may crack VIII Heavy furniture falls over, some walls crumble IX Many people panic, some buildings collapse, dams crack X Railroad lines are bent, most buildings are damaged, roads crack XI Bridges collapse, buried pipes break, most buildings collapse XII All manmade structures are destroyed

Loma Pietra, CA Earthquake 1989 – Estimate the rating on the Richter and Mercalli Scales Bridge Collapse Building Collapse Landslide

A fault after an earthquake…

Uplifted crust along a fault after an earthquake

Three things that happen because of stress in the crust are… Earthquakes Folding of rock Faulting of rock