2 Questions1) Where would you expect the higher earthquake insurance rates: Florida or Oregon?2) Briefly explain.3) Did you use inductive or deductive reasoning ?4) explain
3 What is an Earthquake?Vibration of the Earth produced by the rapid release of energy.Energy release due to plate tectonics and failure (fault zones) of the Earth’s crustEnergy radiates as waves in all directions from the focus (source)Epicenter – surface expression of the focus
4 Elastic Rebound Theory Tectonic forces slowly deform the rockAs the rock bends, it stores energyWhen the rock’s resistance to the stress is overcome, the rock slips or breaksSlippage occurs at the weakest point (focus), rock “snaps” back to original positionEnergy released produces the vibrations we know as an earthquake
6 Earthquake Waves - Seismicity Seismic waves – elastic energy released at the focus following the rupture of rockSeismology- study of earthquake (seismic) wavesSeismograph – instrument that records earthquake wavesSeismogram – record of the seismic waves
9 Seismic WavesP-waves and S-waves are body waves, they travel through the Earth’s interior. Surface waves travel along the Earth’s outer layer.
10 P-waves – Primary Waves Compressional wave – push and pull rock in direction of movementCan travel through all materials (solids, liquids, and gases)Fastest moving waveSmallest wave amplitude (lowest energy)
11 S-waves – Secondary Waves Shear wave - Waves shake material at right angles to their direction of movementTRAVEL ONLY THROUGH SOLIDSIntermediate speed – 2nd to arrive as seismic station
12 Surface waves Move up and down, similar to ocean waves Can also move side-to-side.Very damaging wavesTravel the slowest – last to arrive at seismic stationGreatest wave amplitude (highest energy)
14 Locating Earthquakes Need three seismic stations. Use the time difference (tH) in the arrival of the p-waves and the s-waves.Distance (d) extrapolated from a time-distance graph.A circle with a radius of d is drawn around the seismic station.Earthquake occurred somewhere on the circle.The intersection from three stations shows the epicenter location.
15 Locations of Earthquakes By studying 1000s of earthquakes, geologists learned most occur along plate boundaries
16 Earthquake Intensity and Magnitude Mercalli intensity scaleAssesses the damage from an earthquake at a specific locationBased upon human observationCan vary from location to location
17 Earthquake Intensity and Magnitude Richter ScaleDescribes the earthquakes magnitude (energy released)Measures amplitude of largest wave, adjusted for travel timeIs the same from location to locationA 1 digit increase in Richter scale is a 30 fold increase in energy released
18 Is the Earth Entirely Solid? What piece of the Earth is not solid?How do we know this?Seismic wavesDifferent materials transmit waves at different speeds, i.e. p-waves change speed as they move from the crust to the mantle and from the mantle to outer core