Earthquakes and Earth’s Interior Key Points are Green

What is an earthquake? Earthquake a rapid release of kinetic energy given off in the form of waves. Sensitive instruments around the world record these events

Earthquake faults Fault lines and plate boundaries are the place where these movements normally originate from.

Stored Energy Energy is stored over time in the ground and it gets released once the pressure is greater than the mechanical strength of the rocks can bare. Aftershocks - smaller earthquakes that follow a major earthquake Foreshocks - small earthquakes often preceding a major earthquake by days or, in some cases, by as much as several years.

Seismology: is the study of earth quakes. The study of earthquake waves Dates back almost 2000 years to the Chinese who looked into pots of water to record these movements.

Seismographs: – are instruments that record seismic waves. They work by recording the movement of Earth in relation to a stationary mass on a rotating drum or magnetic tape. Records obtained are called seismograms There are 3 types of seismic waves

Fastest wave which travels only in through solids, liquids, and gases. Push-pull (compression motion). Primary (P) waves

Secondary (S) waves Up down motion at mater moves at right angles to the direction of wave travel. Travels only through solids Slower velocity than P waves But greater intensity and amplitude than P waves

Surface Waves / Rayleigh waves Cause greatest destruction Waves exhibit greatest amplitude and slowest velocity

Focus - the place within Earth where earthquake waves originate Epicenter – location on the surface directly above the focus.

Locating the distance to the epicenter At least Three station recordings are needed to locate an epicenter Each station determines the time interval between the arrival of the first P wave and the first S wave at their location. A travel-time graph is used to determine each station’s distance to the epicenter

Finding Epicenter: A circle with a radius equal to the distance to the epicenter is drawn around each station. The point where at least three circles intersect is the earthquake epicenter.

Two measurements that describe the size of an earthquake are Intensity – a measure of the degree of earthquake shaking at a given locale based on the amount of damage Magnitude – estimates the amount of energy released at the source of the earthquake

Magnitude measurements Richter scale Numerical system used to quantify Earthquake strength. Largest magnitude Earthquake was a 9.5 recorded in Chile in Magnitudes less than 2.0 are not felt by humans Each unit of Richter magnitude increase corresponds to a tenfold increase in wave amplitude and a 32-fold energy increase.

Locating the source of earthquakes Earthquake depths Definite patterns exist Almost all deep-focus earthquakes occur in at convergent boundaries. Many shallow focus occur along the oceanic ridge system or divergent boundaries

Earthquakes of magnitude 5 or greater over a 10 year period