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Earth radial structure large-scale Earth structure Structure of Earth’s interior Vp ,Vs (km/s) a Sea w Con ) −8 km ter (0 tine (20 ntal − 90 t rus 0 crus 0 5 10 15 ic c ean ) Oc (6 km re phe nos e h At transition zone Lith (50 osphe −25 r 0k e m) rm 41 660 Tra nsi km Low tion er m ant le 290 2000 ant le zon e D’’ velocity increase primarily from pressure increase laterally heterogenious (Temp. & composition) core−mantle boundary convecting liquid outter core 4000 Iron−nickle sulphur mixture D’’ m 0k Ou ter cor e m 0k 510 Inn er c 637 m 1k inner core ore 6000 0 5 10 15 ρ (kg/m 3) lithosphere "rigid" asthenosphere "plastic" phase change to high−pressure polymorphs lower mantle depth (km) Up pe m 0k Mohorovicic discontinuity upper mantle t km) laterally heterogenious crust solid anisotropic Structure of Earth’s interior from seismic tomography Solidification of Earth’s inner core and the magnetic field Magnetism geomagnetic field Magnetic anomalies and spreading sea floor Next lecture: Magnetic anomalies Sea floor depth with age (distance) negative g sion. We length gra improved and topog reference than the tr we find th 90-km-thi in the Pac correlation 90–100 M -3000 Pacific plate Depth (m) -4000 -5000 Stein & Stein (1992) -6000 Pacific, this study, a = 90 km Parsons & Sclater (1977) 0 25 50 75 100 Age (Ma) 125 150 175 Crosby, McKenzie, Sclater. Geophys. J. Int. (2006) Figure 8. A comparison between our best-fitting Pacific plate model, and the best-fit models of Parsons & Sclater (1977) and Stein & Stein (1992). Parsons & Sclater (1977) used selected data from the deepest parts of the 4.2 Corr swells an The correl and sedim Fig. 11 an probability DAMTP seminar next week: Geophysical and Environmental Processes Jean-Philippe Avouac: On the effect of fluid injection on seismic and aseismic fault slip Monday January 26, MR5, 1300 -1400 DAMTP: Demonstrations in fluid dynamics Wednesdays Lent term, GKB labs, 1400 -1600