Earthquakes And Earth’s Structure

Earth’s Structure

Origin of the Earth Meteors and Asteroids bombarded the Earth Gravitational compressionGravitational compression Density Stratified planetDensity Stratified planet

Earth’s Interior Core – dense – Iron and Nickel – Inner Core - solid – Outer Core - liquid – Less dense than core – Iron and Magnesium silicates – Mostly solid – Upper mantle is partially molten Mantle – Outermost layer – Very thin and rigid – Continental – granite – Density = 2.8 g/cm 3 – Oceanic – basalt – Density = 3.0 g/cm 3 Crust

Evidence of Internal Structure Granite Density Density – calculate density of Earth – Speculate on probable compositions Basalt Meteorites Meteorites – Use composition and age to determine composition and age of Earth Seismic waves Seismic waves – Travel times and direction give indication of internal structure of Earth

Types of Seismic Waves S waves S waves P waves P waves – Primary waves – Push and pull movement – Travel fastest (~ 6 km/sec) – Travel thru solids and liquids – Secondary waves – Move side-to-side – Slower (~ 4 km/sec) – Travel thru solids only

Seismic Waves Through Earth

What is an Earthquake? The vibration of Earth produced by the rapid release of energy

Elastic Rebound Theory The crust will first bend When the stress exceeds strength of the rock, it will “snap” into a new position In the process of breaking, “seismic waves are released

Parts of an Earthquake Focus Epicenter Energy released radiates in all directions from the focus Energy is in the form of waves – “seismic waves” – Location on surface directly above the focus – place within earth where EQ originate

How Do We Locate an Epicenter? Instruments around the world record EQ Record Earth movements by stationary mass on rotating drum Use seismogram to: – Locate an epicenter – Determine magnitude Seismograph

Seismogram Measure the distance between P- and S-waves –This is the time difference in arrival times Help determine the epicenter

Locating the Epicenter Plot the time difference on y-axis (time interval) Trace plot to blue line to determine distance to epicenter

Locating an Epicenter Triangulation A minimum of 3 seismic stations are needed to determine the epicenter Measure that distance around the seismic station The epicenter may be located anywhere on that line

Determining Magnitude Measure the amplitude of the strongest wave The amplitude is the height on paper Plot distance between p- and s-wave Plot amplitude Connect plots to determine magnitude

You are now a Seismologist!! Virtual Earthquake Introduction: tualEarthquake/VQuakeExecute/htm Virtual Earthquake: