The power of intuition (Selwyn’s that is)

Selwyn’s career goal #__: What does the asthenosphere have to do with earthquakes, crustal

motions, and mantle convection?

Upper crust

Lower crust

Upper mantle

Upper crust

Lower crust

Upper mantle

Figures courtesy of Liz Hearn

Figures courtesy of Liz Hearn

crust

mantle (asthenosphere)

crust

mantle (asthenosphere)

crust

mantle (asthenosphere)

crust

mantle (asthenosphere)

crust

mantle (asthenosphere)

Time (years)

Elastic crust

Viscoelastic asthenosphere

Viscoelastic upper mantle

Steve Cohen

Cohen (1992)

Far field

Near field

Horizontal Stress

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

“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

Rydelek and Sacks (1990)

7.5-7.9

7.5-7.9

6.5-6.9

6.5-6.9

Magnitude

7.0-7.4

7.0-7.4

Rydelek and Sacks (1990)

Post-earthquake mantle relaxation(1896 Riku-U eq.)

Rydelek and Sacks (1990)

Paradigm shift in Earth’s 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

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 historictriangulation 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.

“Asthenosphere relaxation must lead to long-range transfer of crustalstress from one fault to another”

M6.8 Kobe earthquake

Reducedfriction 1995earthquaketriggering

1944/1646 to 1995 postseismic stress change bars

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

Geodetic inference of rheology

1999 M7.1Hector Mine earthquake

Freed and Burgmann (2004)

Post-earthquake (M7.1 1999 Hector Mine eq.)

Andy Freed(Purdue Univ.)

Post-earthquake (M7.5 1959 Hebgen Lake, Idaho, earthquake)

Nishimura and Thatcher (2003)

Post-lake-filling(1935: Lake Mead, Nevada)

Kaufmann and Amelung (2000)

200 mm subsidencefrom 1935-1950

Gourmelen and Amelung (2005)

Post-earthquake(1915-1954; Central Nevada Seismic Zone)

Post-earthquake(1915-1954; Central Nevada Seismic Zone)

Elastic thickness (km) Lower crust viscosity (Pa s)Und

erly

ing

laye

r visc

osity

(Pa

s)

Gourmelen and Amelung (2005)

Geologic inference of rheology

Figures courtesy of Bruce Bills

Post-lacustrine unloading (Paleolake Lahontan, Nevada)

Post-lacustrine unloading (Paleolake Lahontan, Nevada)

2m

4m

Adams et al. (1999),Bills et al. (2007)

Up to 15m upliftsince 15 kyrBP

Bills et al. (2007)

Post-lacustrine unloading (Paleolake Lahontan, Nevada)

High-viscosity crust

Low-viscosity mantle

Bills et al. (1994)

Post-lacustrine unloading (Paleolake Bonneville, Utah)

James et al. (2000)

Post-glacial rebound

Modified from Dixon et al. (2004)

Jacqueline Dixon Tim Dixon

Goes and van der Lee (2002)

Paradigm shift in Earth’s 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

“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

American Geophysical Union 2010 Fall Meeting

Linking Geodetic Observations to Mechanical Properties of the Lithosphere: New Methods and Models I, II

Wayne Thatcher Liz Hearn Eric Hetland Sylvain Barbot Yuri Fialko

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

Wayne Thatcher Liz Hearn Greg Hirth