EARTHQUAKES

science of earthquakes

EARTHQUAKE Earthquake = a movement of Earth’s lithosphere that occurs when rocks in the lithosphere suddenly shift, releasing stored energy. The energy released by earthquakes is carried by vibrations called seismic waves.

5:04 pm 3 sec 5 sec 15 sec As a result of the Loma Prieta Earthquake, 62 people died and $6 billion in damage was done. pubs.usgs.gov

TSUNAMI Sometimes earthquakes can cause tsunamis. Tsunami = a series of ocean waves generated by displacements in the sea-floor (earthquake), landslides, or volcanic activity environment

STRESS in the Earth’s Crust Earthquakes happen because of the ways the plate movements affect the lithosphere. The forces of plate movement cause deformation, or changes in the shape or volume of rock.

STRESS Stress = force that squeezes rock together, stretches or pulls them apart, or pushes them in different directions similar to when you are stressed… Think of trying to bend a material… – Chalk…break – Wire…bend

Kit Kat Twizzlers

As tectonic plates move, they cause stress in the crust, which in turn produces faults and folds.

FAULT Fault = a break in a mass of rock along which movement occurs. Ex. San Andreas fault Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range east of the city of San Luis Obispo. (Photograph by Robert E. Wallace, USGS.) geology.com

FOLD Fold = a bend in layers of rock. Rocks tend to fold (rather than break) when they are under high temperature or pressure.

Earthquakes & Seismic Waves The buildup of stress along a fault provides the energy that powers the earthquake. Earthquakes occur because stress forces have exceeded the strength of the rock.

The location beneath the earth’s surface where an earthquake begins is called the focus. The location on the earth’s surface directly above the focus is called the epicenter. Seismic waves move out in all directions from the focus

Physics of Earthquakes Within earth’s crust, forces cause two sides of a fault to move past each other. Sometimes rock may snag and remain locked because of friction. Stress builds up. When rocks are strained beyond limits, they break and slide past each other releasing huge amounts of energy.

As rocks break and move, potential energy is transformed into kinetic energy in the form of waves. Three main types of seismic waves: – P waves – S waves – Surface waves

P waves Longitudinal waves (similar to sound waves) Cause particles in material to vibrate in the direction of the wave’s motion. Compress & expand the ground like accordion. FASTEST. Travel through solid & liquid. ce/terc/content/visualizations/es1002/es1002 page01.cfm

S waves Transverse waves (like light and other electromagnetic radiation) Cause the particles in the materials they pass through to vibrate at right angles to the direction the wave travels. Cannot travel through liquids ce/terc/content/visualizations/es1002/es1002 page01.cfm

Surface Waves Develop when seismic waves reach the earth’s surface. Move more slowly than P waves or S waves. Produce larger ground movements and greater damage. Some are transverse, others are similar to ocean waves.

Measuring Earthquakes Geologists record seismic waves using seismographs. Seismograph can detect and record seismic waves. Earthquake can be located using seismic waves recorded by many different seismographs…triangulation. earthquake.usgs.gov

Richter Scale Developed in 1935 by Charles Richter. Most well-known scale. Based on times and amplitudes of seismic waves. NO LONGER USED by geologists.

Moment Magnitude Scale Gives a measure of the amount of energy released by an earthquake. Each unit increase = 32 times increase in the energy released

Modified Mercalli Scale Developed in 1931 by seismologists Harry Wood and Frank Neumann. Based on observations of ground shaking and damage in area affected by earthquake. Twelve levels, Roman Numerals.

Seismographic Data Most earthquakes are concentrated along plate boundaries, where many faults are found. Can earthquakes happen anywhere else? Some earthquakes occur in the interior of plates.

Earth’s Interior Scientists have analyzed how seismic waves travel through the Earth. Speeds of seismic waves are affected by the temperature, composition, and density of the rocks they pass through. Outer core is liquid because s waves cannot pass through it. ualizations/es1009/es1009page01.cfm