#6 Faults, Earthquakes, & Seismology

GSC 350Natural Disasters Rocks move past one another due to stresses Gravity Tectonic Regional Elastic vs. Brittle strain Rocks shear along cracks in the Earths crust called Faults Just as tectonic plates, there are different types dependant on the motion of interactionGSC 350Natural Disasters3 Main fault types1) Normal - Block moves down in relation to the other- Forms due to extensionGSC 350Natural Disasters3 Main fault types2) Reverse - Block moves up in relation to the other(thrust) - Forms due to compressionGSC 350Natural Disasters3 Main fault types2) Strike-Slip - Block moves right/left of the other- Right or Left lateralRight Lateral Strike SlipNormalReverse The sudden rupture and release of energy along a fault is called an Earthquake Initiation of rupture point is called the Focus(the surface point is the epicenter) Releaseswaves ofenergyFault planeSurface ruptureGSC 350Natural Disasters Damaging to life and property Can release more energy than any other natural hazard Violently shakes ground Can crumble buildings within seconds Manmade structures respond toground motion Measured in two terms for size Moment Magnitude MW Measured as total energy released Local Magnitude ML- Measured by specific wave periodsGSC 350Natural Disasters Occur along major plate boundaries, or on inter-plate faults It all has to do with the stresses being applied! Different scales used to classify an earthquake-GSC 350Natural Disasters Mercalli Scale- Based on eye-witness accounts and damage Richter Scale- Based on maximum amplitude of waves measured on a specific type ofseismograph (ML)I. Not felt except by a very few under especially favorable conditions.II. Felt only by a few persons at rest, especially on upper floors of buildings.III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. Duration estimated.IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.IX. Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb. Damage great in substantial buildings, with partial collapse. Buildings shifted off foundations.X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations. Rails bent.XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Rails bent greatly.XII. Damage total. Lines of sight and level are distorted. Objects thrown into the air.GSC 350Natural Disasters-Mercalli Intensity Scale-GSC 350Natural Disasters Many types, but we are concerned with two- P-wave (primary wave) occurs first (compressional) Higher average velocity (6-8km/hr) Can move through solid and liquid S-wave (secondary wave) (shear) Lower average velocity (3-5km/hr) Cannot move through liquidSeismic WavesGSC 350Natural Disasters Approach and arrive at a single point, such as a seismograph (the instrument) This returns a seismogram (the output)Seismic WavesP-waveS-waveGSC 350Natural DisastersDetermining Richter Scale(know how to do this)GSC 350Natural DisastersTriangulating the Epicenter(know how to do this)S-P time = 4mS-P time = 7mS-P time = 2mPoint APoint BPoint CABCGSC 350Natural DisastersTriangulating the Epicenter(know how to do this)S-P time = 4mS-P time = 7mS-P time = 2mPoint APoint BPoint C-Distances-Point A- 2600kmPoint B- 5900kmPoint C- 1600kmThese are now plotted on a mapGSC 350Natural Disasters- 400mi fromKuala Lumpur- 400mi fromSingapore- 1100mi fromBangkok Why do we care about the location of an earthquake? Why do we care about the magnitude of an earthquake?GSC 350Natural Disasters For more examples, see your text book.It is explained as seen here Also see Exercise #20 in your exercise book.We will not do this exercise, but it can help youGSC 350Natural Disasters October 17th@ 10:17a 9.4 million people inCalifornia take part Annual earthquake preparedness drill using the big one as a scenario Magnitude 8+ on the Southern San Andreas Public services and government involved Join the Geology Club at the Gallery Lawn North 10:00-10:30!GSC 350Natural DisastersA Canadian video from the 1990s&HistoricalEarthquakes/EarthquakeEffects