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Midterm 1 Study Guide #2

Midterm 1 Study Guide #2 - OUTLINE FOR MIDTERM I SPRING...

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Unformatted text preview: OUTLINE FOR MIDTERM I SPRING 2008 PROF. SAMMIS Miami 3* Radioactive isotope — an element that breaks down at a constant rate (described by its half life} 0 Half life — the time (in years) that it takes for the mass of 3? Age of the Earth — 4.6 Billion years — how determined — by dating carbonaceous chondrite Meteorites > Age of rocks - 0 — which isotopes and why? Oldest continental rocks — 4 Billion years — where — in the center of continents Oldest oceanic rocks — 200 Million years - where — in ocean basins Power of ten notation — 10*(x), where the X is how many zeros come after the 15' digit. Ages of sun and other planets — 13.6 Billion years? Age of universe — 13.6 Billion years? - honr determined — by taking the current rate the universe is expanding at, 6: reversing the time. V VVV V l gang 2 > What is an earthquake? 0 Fault plane — 0 0 0 0 P 0 5* Leena re 3 9- Fault trace — intersection of the fault plane with the Earth‘s SURFACE. Fault scarp — the uplifted Earth, caused by Hypocenter (focus) — where EQs begin W! a rupture, that spreads thru-out the fault plane Epicenter — the surface projection of the hypocenter Where earthquakes occur 3 types of plate boundary I daemon; = plates move apart (Extension) and have Normal Faults. Found at mid-ocean ridges I W = plates move together (Compression) 8: have ReversefThrust Faults. Found @ trenchfisland-arc structures. The denser crust SUBDUCTS under the less dense crust (Ex: Oceanic crusts sink under 8: thus push up Continental crusts). Wadati-Benioff zone of EQs found here. I transform = shear stresses that make strike-slip faults. Found at fracture zones linking sections of mid-ocean ridges. Plate tectonics — Lithospere — 1001011 thick outermost part of Earth, made up of 12 moving plates, 3: contain both continental and oceanic crusts on its surface. — Aesthenospllere — soft layer of Earth that Lithosphere moves on top of. - Mantle Convection — why’ we have EQs — Hot spots — volcanic activity that doesn't occur at plate boundaries. They don’t move w! the Lithosphere plates. — Continental Collisions — form highest mountains bfc neither content subducts (same densities) — Deep-focus earthquakes — occur 700 km below Earth's surfacehow deep? Wegener’s (“the Father of Plate Tectonics”) evidence for plate tectonics — Continents were all one together (Pangaea) — 300 million year old southern ice sheet - 250 million year old deserts — air flows out of equator and arcs down towards deserts (bio downward moving air traps moisture) — Migration of species from paleontological record — they just walked! Writings — Computer fit of continents at their continental shelves, not shores — Earth's magnetic field Dipole field Inclination i and declination 5 Remnant magnetization. Ferromagnetic minerals — magnetite Fe304 Magnetic domains Curie Temperature Paleomagnetic polar wander curves . How measured? Why_evidence for plate tectonics? Linear magnetic anomalies parallel to the mid-ocean ridges How are they measured? How are they formed? Reversal of magnetic pole Reversal time scales How used to measure spreading rate? Strike and dip Faulting Strike slip - left lateral, right lateral Dip slip — normal, reverse Stress = FHA Normal stress, shear stress Principal stresses: 0' I > 0'; )0; Type of faulting when: 0'; is vertical, 0'; is vertical, 0'; is vertical. Elastic rebound theory of earthquakes H.F. Reid following the 1906 San Francisco earthquake. Geodesy Lecture 5 Fault plane solutions from first motion of P waves. Wave fronts and ray paths Body waves P and S (particle motion relative to ray path) Surface waves. First P motion on a vertical seismometer Up : away from souce, Down = toward source. Pattern of P first motions on a focal sphere for: strike-slip, normal, and reverse faults. Lecture 6 The San Andreas fault. Right lateral strike-slip fault Transform fault linking spreading center beneath the Salton Sea with a spreading center off the Oregon coast. Plate boundary between the Pacific and North American plates. Slip rate = 35 mm/year Leora re 7 M Age 30 million years — before that California coast was a subduction zone like South America today. Sierra Nevada Mountains are granite batholiths that cooled below the now eroded away andesite volcanoes. Coastal ranges are the old trench sediments that popped up when subduction stopped. Big bend north of Los Angeles and compression in the LA basin Volcanoes mostly occur at plate boundaries — exceptions are hot spots. Volcanoes at convergent boundaries are characterized by: Andesite magma — contains a lot of silica SiOz which explains Grey color, explosive eruptions, steep-sided composite (strato) volcanoes. Volcanoes at divergent boundaries (and at hot-spots) are characterized by: Basalt magma — contains minor amounts of SiOz which explains: Black color, quiet eruptions, shallow sloped shield volcanoes. A tsunami is a seismic sea wave usually generated by dip-slip faulting on the ocean floor. It has a very long wavelength (say ZDOkm.) and a very long period (say 15min). Since velocity =frequency times wavelength, the velocity is A W 1%??? , the speed of a jet plane! Amplitude increases as the wave approaches shore since front of wave slows first when it hits shallow water near shore. The back of the wave catches up, shortening the wavelength but increasing the amplitude. This is why ordinary sea waves break when they reach shore. Tsunami early warning system. Characteristics of all waves : Amplitude, wavelength, period, frequency, velocity and relations between them: f: 1/?" (cycles/second) T: M" (seconds/cycle) v=f7L=—; Western US Tectonics: San Andreas Fault Big bend - compression — San Gabriel Mountains and Transverse Ranges. Salton Sea — buried spreading centers and transform faults. Cascadia subduction zone — Cascade Mountains = chain of Andesite volcanoes Basin and Range province = crustal extension behind former subduction zone. Yellowstone hot spot trace. Seismic threat to Les Angeles, San Francisco, Seattle, Salt Lake City. ...
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