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Chapter 10: Earthquakes (Part 1) Class Announcements Papago Park extra credit field trip (worth 20 points). Options: *Mon., April 14: 4-5PM Wed., April 16: 10-11AM or 4-5 PM Thurs., April 17: 10-11AM or 2-3 PM * Added Announcements - Papago Park Fieldtrip Can now sign up at website. Note: Extra trip option added: Mon. April 14, 4-5 PM. See maps and directions. Reminders in class week before trips. - Quiz this Friday Volcanoes (Chap. 9) Earthquakes (Chap. 10) Earth’s Interior (Inter. C) Announcements - Papago Park Fieldtrip Sign up at website. Note: Extra trip option added: Mon. April 14, 4-5 PM. See maps and directions. Reminders in class week before trips. - Quiz this Friday Volcanoes (Chap. 9) Earthquakes (Chap. 10) Earth’s Interior (Inter. C) Student Presentation Coastal Rock Formations Villasinee Kongsomboonvech Today’s Lecture - Introduction to earthquakes What is an Earthquake? Types of faults. Where do Earthquakes occur? Plate tectonic context - Types of earthquake waves Body waves P-waves S-waves Surface waves Rayleigh waves Love waves Today’s Lecture - Introduction to earthquakes Where do Earthquakes occur? Plate tectonic context - Types of earthquake waves Body waves P-waves S-waves Surface waves Rayleigh waves Love waves Definitions Fault - Fracture in the Earth where slip occurs Earthquake - Energy released by slip along a fault Earthquake focus - Location of initial break What is an earthquake? Elastic rebound theory - Describes the origin of earthquakes. - Blocks of rock try to move in opposing directions along a fault. - Friction prevents slippage and stress builds. - Stress is stored in rocks as elastic energy. - When strength of rock exceeded, rock ruptures and slips, releasing the stored elastic energy. Build up of stress. Elastic deformation. Strength of rock exceeded Rock ruptures with slip along fault. Elastic energy released. Fig. 10.01 W. W. Norton Fig. 10.10 W. W. Norton Stress builds up along faults because blocks are locked together by friction along fault plane. Fig. 10.09 W. W. Norton What is an earthquake? fault Definitions Stress - Force applied to a material. Strain - Deformation of a material under stress. Elastic strain - When stress released, material returns to original shape. Ductile (plastic) strain - When stress released, material does not return to original shape. Brittle behavior - Rupture of materials occurs when elastic limit exceeded. Under elastic strain, when stress is released, deformed objects assume their original shape. Fig. 10.08 W. W. Norton Fig. 10.12 W. W. Norton Earthquake! p.276-277b Original artwork by Gary Hincks Elastic energy released travels as a series of spherical waves through the Earth radiating away from the break (focus). Fig. 10.37 W. W. Norton Fig. 10.11 W. W. Norton More definitions: Fault plane: Surface of slippage. Earthquake focus: Point of initial breakage. Epicenter: Site at surface immediately above focus. W. W. Norton Types of Faults Faults With Vertical Slip Normal faults: Block above fault plane has dropped “down”. Fault scarp: cliff produced by vertical slip on fault. Vertical Slip = Normal Faults Up Down Lateral (Strike) Slip Faults Turkey Aug 1999 M 7.4 Fig. 10.05 Fig. 10.06g Photo courtesy of Paul “Kip” OtisDiehl, USMC, 29 Palms, CA Fig. 10.06g Photo courtesy of Paul “Kip” OtisDiehl, USMC, 29 Palms, CA Most earthquakes occur along the margins of tectonic plates Fig. 10.22 W. W. Norton