Age of Ocean Crust Young at mid-ocean ridges Old at ocean margins (edges) So … where is ocean crust created? And … where is it destroyed? Plate Tectonics I At both areas, there should be earthquakes. Earth’s Ever-Changing Lithosphere Unifying continental drift and seafloor spreading Seismicity the frequency, magnitude, and intensity of earthquakes Earthquakes – produce seismic waves First, a bit of a geological aside … Scientists deduced the interior structure of Earth by using the travel time, arrival location, and refraction of seismic waves P-waves (“primary” – arrive 1st) Quake ! • compressional force • back-and-forth motion Tectonic terminology Next, a bit of a review/clarification … S-waves (“secondary” – arrive 2nd) Continental Crust crust & mantle vs. lithosphere & asthenosphere • shear between layers • up-and-down motion • cannot travel through liquid Tectonic plates are pieces of lithosphere, comprised of the rigid crust and the rigid part of the upper mantle. Tectonic plates float and move on top of the ductile part of the upper mantle called the asthenosphere. Oceanic Crust sea level Lithosphere uppermost Mantle 200 (rigid) 400 • travel through both solids and liquids Oceanic Crust km Asthenosphere = part of upper Mantle 600 800 Mantle (rigid) 1000 Lithosphere rigid outer layer of the Earth that includes the Crust (Continental Crust and Oceanic Crust) and the uppermost Mantle Asthenosphere low strength, ductile part of upper Mantle 700 km Mantle 2900 km Liquid Outer Core 5200 km Solid Inner Core Radius of the Earth = 6370 km 1 Tectonic terminology Another view of the lithosphere / asthenosphere Seismicity around the world Earthquake locations helped lead to Plate Tectonics idea Notice the asthenosphere can deform and flow … whereas the lithosphere maintains its shape. This allows the rigid lithosphere to move atop the weak rock of the asthenosphere. Note difference between Atlantic and Pacific seismicity Note Himalayan-Mediterranean belt HimalayanMediterranean Atlantic Pacific Plate Tectonics Earth’s lithosphere consists of tectonic plates, 7 major plates (most of which contain a major continents plus ocean crust) and 7 minor (or intermediate) plates. major plates: North American, South American, African, Eurasian, Pacific, Australian-Indian, and Antarctic minor plates: Juan de Fuca, Caribbean, Arabian, Cocos, Nazca, Scotia, Philippine Plate boundaries have their faults 3 types of faults (and plate boundaries) normal – result from tension (divergent plate boundaries) reverse – result from compression (convergent plate boundaries) transform – result from sliding (translational plate boundaries) Plates move as coherent units relative to other plates. 2 Plate boundaries – 3 types convergent Divergent spreading ridges (Mid-Atlantic Ridge) divergent Convergent continent-continent collision (Himalayas, Alps) subduction zones translational ocean-ocean (Mariana Trench) ocean-continent (Peru-Chile Trench) Translational (San Andreas Fault) Divergent Convergent Translational 3