1Rock Deformation: Faults, Folds, and Earthquakes• Why do we care?• Rock deformation- Stress and Strain- Folds- Fractures and Faults1• Generation of an earthquake: Elastic rebound theory• Earthquake Waves• How big was that ‘quake?- Earthquake Intensity- Earthquake Magnitude• Where was it? - Locating EarthquakesGolcuk, Turkey (60 mile east of Istanbul) after the magnitude 7.4 earthquake of August 17, 1999Chapter 18 Understanding Earth2Kobe, Japan after the magnitude 7.2 earthquake of January 16, 1995 Fig. 18.18 Understanding EarthFolded rocks Fig 10.1 Understanding EarthFaulted (broken and shifted) rocks: 3Fig 10.2 Understanding EarthStress and StrainStress: force applied• Compression(squeezing)•Tension (stretching or pulling apart)• Shear (side-by-side)4Strain: change in shape that results from stress• elastic– temporary, material can spring back to original shape• plastic/ductile- includes folding• brittle- includes faulting, and can produce earthquakesStress causes strain.tileThree types of stressand the resulting ductile or brittle strain5Fig 10.6 Understanding EarthBrittle DuctStress and StrainWhy do different types of strain occur?– Amount of strainless: elasticmore: brittle or plastic– Rate of deformation6faster: brittleslower: plastic– Temperaturecolder (shallower): brittlehotter (deeper): plastic– Lithostatic (confining) pressurelower pressure (shallower): brittle higher pressure (deeper): plasticNext: stress and strain demo2Effect of pressure and temperature on the type of straina. nondeformed sample of marbleb. sample compressed under conditions like those in the upper part of the earth’s crustc. sample compressed under conditions like those of the lower part of the earth’s crustFig 10. Understanding Earth7Brittle strain: Joints and FaultsJoints: cracks or fractures along which no movement has occurred.Faults: fractures along which rocks have moved.Types of faults:dd ( i l)8Dip slip - up and down (vertical) movementnormal - related to extensional stressreverse- related to compressional stressthrust- related to compressional stressStrike-slip - side-to-side movementleft lateral or right lateral - related to shear stressOblique - a combination of strike-slip and dip-slipJoints in sedimentary rockOther examples of joints include columnar jointing in lava flows and exfoliation fractures in intrusive igneous rocks.9Geologists often can use the 3-dimensional orientations of joints and faults to learn about the directions of the stresses which created them.Fig 10.20 Understanding EarthDip slipnormal faultreverse fault (or thrust)stretching10(or thrust)Strike-slipright lateralleft lateralsqueezingshearingFault with sideways movement (strike-slip)Close-up of an offset curb along 5th Street in Hollister, California (about 75 km south-southeast of San Jose).11This Dynamic Earth - USGSWhich is type of fault is this?right-lateralorleft-lateralWhat kind of fault is this?12Fault in the Blue Mountains of northeastern Oregon3Fault breccia in basalt - Blue Mountains, OregonWhen faults move, rocks along the fault can be broken into angular pieces of 13gpvarious sizes to create a fault breccia.S. KuehnSlickensides in serpentinite, Sierra foothills along Hwy 70 in CaliforniaWhen faults move they also can produce smooth, grooved surfaces called slickensides. The grooves can be used to determine the direction in which the fault moved.Slickensides - Blue Mountains, OR14This landscape shows evidence of a long history of faulting and folding15SqueezingUSGSNext: basin and range animationMaking an earthquake: Elastic Rebound Theory161. Elastic strain accumulates over time as a result of applied stressFig. 18.1 Understanding Earth172. Eventually the rocks break and released stored energy in an earthquakeFig. 18.1 Understanding EarthNext: elastic rebound animationsEpicenter and focus of an earthquakeThe energy released by an earthquake radiates outward from the focus in the form of earthquake waves (vibrations).Which is 18Fig. 18.3 Understanding Earthtype of fault is this?normal or reverse4During an earthquake, only part of a fault breaks and moves. The portion that breaks is the rupture surface. The rupture also occurs over a short period of time rather than all at once.focus (or hypocenter)– where the rocks first b itb kIn general, the bigger rupture surface and the greater the distance of19begin to breakfrom: http://www.scecdc.scec.org/greater the distance of movement the larger and more damaging is the resulting earthquake.Seismic Waves1. Body WavesP-waves (primary or pressure waves)S-waves (secondary or shear waves)The two kinds of body waves produced by20waves produced by earthquakes. P- and S-waves move through the interior of the earth and thus are both body waves. Sound waves are compressional waves just like P-waves.Fig. 18.7 Understanding EarthInteractive Demo:Pwaves and Swaves21P-waves and S-waves2. Surface WavesSurface waves travel much more slowly than body waves, but surface waves cause most of the shaking that one feels during earthquakes. Shaking due to surface waves also causes most earthquake damage. 22Love waveRaleigh waveA seismograph.Several different types of seismographs are used to record earthquake waves.Fig. 18.5c Understanding Earth23Seismograph recording for an earthquakeThe time of arrival is related to how far away the earthquake was and how fast the waves traveled. The illustration below shows what a recording might look like at a seismograph station located over 5,000 km from the epicenter of a large earthquake.24Modified from: Fig. 18.6 Understanding Earth5How big was that earthquake?Earthquake Intensity and MagnitudeIntensity: • amount of surface shaking• varies with location and distanceMitd25Magnitude: • related to the amount of energy released by the earthquake• Richter magnitude is based on seismic wave amplitude (height) corrected for distance and other factorsMore information:http://pubs.usgs.gov/gip/earthq4/severitygip.htmlhttp://earthquake.usgs.gov/learning/topics/measure.phphttp://earthquake.usgs.gov/learning/topics/mag_vs_int.phpModified Mercalli Intensity ScaleMMI ValueShaking SeveritySummary Damage DescriptionI. . Not felt.II. .. Felt by persons at rest, on upper floors, or favorably placed.III. .. Felt indoors. Hanging objects swing. Vibration like passing of light trucks. May not be recognized as an earthquake.IV. .. Hanging objects swing. Vibration like passing of heavy trucks; or