Earthquakes

Warm-up #37 Mar. 15What is it about earthquakes that make them so devastating?Tell me what you already know about earthquakes.

Warm-up #38Mar.16Each year, more than 30,000 earthquakes occur worldwide that are strong enough to be felt.Only about 75 major earthquakes take place each year and often occur in remote regionsEssential Question: How do we locate an earthquakes epicenter?

EarthquakesUnit 7

General FeaturesVibration of Earth produced by a sudden release of energyAssociated with movements along faultsPlate tectonics theoryEarthquakes can be explained by this theoryThe mechanism for an earthquake was first explained in the early 1900s by H. ReidElastic Rebound TheoryRocks spring back in a process called elastic rebound Vibrations occur as rock elastically returns to its original shapeThe earthquake itself is often preceded by foreshocks and followed by aftershocks

SeismologyWhat do you think this is the study of?Earthquake wavesThe instrument used to record the movements of the earth is called a seismographThe record that is produced is called a seismogram

Earthquakes Produce Different Waves1. Surface Waves: L wavesComplex motionSlowest velocity

2. Body wavesTwo types:Primary & Secondary

Primary Waves (P waves)Push-pull motion: compressional waveTravel through solids, liquids, and gasesGreatest velocity of all earthquakes

Secondary Waves (S waves)Shake motionTravels only through solidsSlower than P waves

Locating an EarthquakeFocus: the place within the Earth where the earthquake waves originateEpicenter: the point on the surface, directly above the focus

ContinuedLocated using the difference in the arrival times b/w P and S wave recordings, which are related to distanceDo you know what it means to triangulate a cell phone call?Its the same ideaIn order to locate an earthquake 3 station recordings are needed

ContinuedA circle equal to the epicenter distance is drawn around each station.The point where the circles intersect is the epicenter.

Warm-up#39Mar.19How long would it take P waves moving at 6.1 km/s to travel 100 km? How long would it take P waves to travel 200 km?S waves move at 4.1 km/s. 100 km? 200 km?What is the time lag between the arrival of P waves and S waves over a distance of 100 km? 200?What you shouldve gottenP waves:100 km = 16.4 s200 km = 32.8 sS waves:100 km = 24.4 s200 km = 48.8 sLag time100 km = 8 s200 km = 16 s

Earthquake IntensityMercalli intensity scaleAssesses damage at a specific locationDepends on:Strength of earthquakeDistance from epicenterNature of surface materialBuilding designMagnitudeConcept introduced by Charles Richter in 1935Measured on the Richter ScaleDepends on the amplitude of the largest wave recordedEach unit of magnitude increase corresponds to a 10-fold increase in amplitude and a 30-fold increase in energyLargest earthquakes are near a magnitude of 8.6Magnitudes below 2.0 are usually not felt

Earthquake DestructionFactors that determine destruction:Magnitude of earthquake Proximity to population

Destruction is caused by:Ground shakingLiquefaction of the groundTsunamisLandslidesFires

Predicting EarthquakesThere is no reliable method for short-range predictionLong-range: we can predict approximate locations based upon previous tectonic activityFrequency

ActivityResearch major earthquake activity along the San Andreas Fault over the past five years. Write a report on your findings.OrResearch a major a earthquake in Earths history and write a report on your findings.Ticket Out the DoorWhat are some differences between Primary (P) and Secondary (S) waves?How do scientists pinpoint the location of an epicenter?Name 3 types of destruction either caused or associated with earthquakes.What is the focus of an earthquake?

Essential QuestionsWhat does an engineer or architect need to think about when design a home in a location prone to earthquakes?What are some ideas you have heard of or researched that have been implemented and successful?Build a house or buildingSimply use the materials available to you and construct a house.Groups of 4 or 5Teamwork is expectedYou will have about 25 30 minutes to build your house.Must be on cardboard.

Warm-up #40Mar.21The deepest well drilled is only 12 km into Earths crust. With limited access, how do we know what Earths interior is like?Earths InteriorMost of what we know about the interior of the Earth comes from the study of P and S waves

CrustThin outer layerVaries in thickness: 5km 70kmTwo types:Continental Crust: lighter granitic rockOceanic Crust: basaltic composition

LithosphereMade up of the crust and uppermost mantle~100km thickCool, rigid, solid

Mohorovicic DiscontinuityThin layer that separates the crust from the mantle

Mantle2885 km thickComposed mostly of igneous rockAsthenosphereUpper mantleLower mantle

AsthenosphereWeak layer below the lithosphere in the upper portion of the mantleTemperatures and pressures reach near melting point conditions for rocks

Lower MantleMore rigid than asthenosphereVery hotRocks still have the ability to flow

Outer CoreBelow mantle2270 km thickMobile liquidDoes not transmit S wavesMainly iron and nickelRelated to Earths magnetic fieldInner Core1216 km radiusSolid Iron and nickel compositionHigh density

Warm-up#41Mar. 22Describe how the three different types of seismic waves move and affect the movement of the material they pass over or throughYou will most likely see this on your testLabel the Earths LayersOn a white sheet of paper, you will draw or construct a cross-section of Earth exposing the different layers.You will need to label the layers and include:How thick Composition1 other factNeeds to be colored