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The power of intuition (Selwyns that is)

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Selwyns career goal #__: What does the asthenosphere have to do with earthquakes, crustal motions, and mantle convection?

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Upper crust Lower crust Upper mantle Upper crust Lower crust Upper mantle Figures courtesy of Liz Hearn

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Time (years) Elastic crust Viscoelastic asthenosphere Viscoelastic upper mantle Steve Cohen Cohen (1992) Far field Near field Horizontal Stress

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Physics says that the lower crust and upper mantle have to relax the coseismic stresses imparted by an earthquake

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A significant correlation is found, in both space and time, between the intraplate (land) and interplate (sea, thrust zone only) earthquakes in Tohoku, NE Japan that has persisted since the times of reliably reported events in AD 1600. The correlation peaks at a land-lead of about 36 yr... Earthquake-pattern inference of rheology Rydelek and Sacks (1990) Paul Rydelek

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Rydelek and Sacks (1990) 7.5-7.9 6.5-6.9 Magnitude 7.0-7.4

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Rydelek and Sacks (1990)

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Post-earthquake mantle relaxation (1896 Riku-U eq.) Rydelek and Sacks (1990)

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Paradigm shift in Earths continental tectonics, from Time-independent crustal deformation, punctuated only by crustal earthquakes and associated localized brittle/plastic deformation, to Time-dependent crustal deformation, involving deep-seated, ductile flow and associated broadscale deformation

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Pollitz, F. F., and I. S. Sacks, Modeling of postseismic relaxation following the Great 1857 Earthquake, southern California, Bull. Seismol. Soc. Am., 82, 454-480, 1992. Pollitz, F. F., and I. S. Sacks, Fault model of the 1891 Nobi earthquake from historic triangulation and leveling, J. Phys. Earth, 42, 1-43, 1994. Pollitz, F. F., and I. S. Sacks, Consequences of stress changes following the 1891 Nobi earthquake, Japan, Bull. Seismol. Soc. Am., 85, 796-807, 1995. Pollitz, F. F., and I. S. Sacks, Viscosity structure beneath northeast Iceland, J. Geophys. Res, 101, 17,771-17,793, 1996. Pollitz, F. F., and I. S. Sacks, The 1995 Kobe, Japan earthquake: A long-delayed aftershock of the offshore 1944 Tonankai and 1946 Nankaido earthquakes, Bull. Seismol. Soc. Am., 87, 1- 10, 1997. Pollitz, F. F., and I. S. Sacks, Stress triggering of the 1999 Hector Mine earthquake by transient deformation following the 1992 Landers earthquake, Bull. Seismol. Soc. Am. 92, 1487-1496, 2002.

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Asthenosphere relaxation must lead to long-range transfer of crustal stress from one fault to another

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Reduced friction 1995 earthquake triggering

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1944/1646 to 1995 postseismic stress change bars

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Pollitz and Sacks (1997)Heinze and Sacks (1979)

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Geodetic inference of rheology

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1999 M7.1 Hector Mine earthquake

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Freed and Burgmann (2004) Post-earthquake (M7.1 1999 Hector Mine eq.) Andy Freed (Purdue Univ.)

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Post-earthquake (M7.5 1959 Hebgen Lake, Idaho, earthquake) Nishimura and Thatcher (2003)

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Post-lake-filling (1935: Lake Mead, Nevada) Kaufmann and Amelung (2000) 200 mm subsidence from 1935-1950

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Gourmelen and Amelung (2005) Post-earthquake (1915-1954; Central Nevada Seismic Zone)

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Post-earthquake (1915-1954; Central Nevada Seismic Zone) Elastic thickness (km)Lower crust viscosity (Pa s) Underlying layer viscosity (Pa s) Gourmelen and Amelung (2005)

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Geologic inference of rheology

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Figures courtesy of Bruce Bills

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Post-lacustrine unloading (Paleolake Lahontan, Nevada)

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2m 4m Adams et al. (1999), Bills et al. (2007) Up to 15m uplift since 15 kyrBP

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Bills et al. (2007) Post-lacustrine unloading (Paleolake Lahontan, Nevada) High-viscosity crust Low-viscosity mantle

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Bills et al. (1994) Post-lacustrine unloading (Paleolake Bonneville, Utah)

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James et al. (2000) Post-glacial rebound

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Modified from Dixon et al. (2004) Jacqueline DixonTim Dixon

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Goes and van der Lee (2002)

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Paradigm shift in Earths continental tectonics, from Time-independent crustal deformation, punctuated only by crustal earthquakes and associated localized brittle/plastic deformation, to Time-dependent crustal deformation, involving deep-seated, ductile flow and associated broadscale deformation

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Rheology of the Lower Crust and Upper Mantle: Evidence from Rock Mechanics, Geodesy and Field Observations, Annu. Rev. Earth Planet. Sci. (2008) Roland BurgmannGeorg Dresen

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American Geophysical Union 2010 Fall Meeting Linking Geodetic Observations to Mechanical Properties of the Lithosphere: New Methods and Models I, II Wayne ThatcherLiz HearnEric HetlandSylvain BarbotYuri Fialko

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SCEC Workshop on Ductile Rheology of the Southern California Lithosphere (May 1-2, 2013) Wayne ThatcherLiz HearnGreg Hirth

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