Sorting apples and oranges

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• Sorting apples and oranges
• Shallow and deep slow slip
• Slip with or without regular (small) earthquakes
• Long-term, short-term slip, VLFE, LFE
• Slip with synchronous tremor, interspersed
  tremor, or no tremor
• Strong tremor, weak tremor, or no tremor
• Deep tremor and near-trench tremor
• Tremor on and off the main fault

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Tremor, LFE, VLFE generating patches
Critical size for earthquake rupture
Modified back and forth between Wang (2007) and
Richardson Marone (2008)
Ide et al., 2007
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Nankai (2001-2004)
Cascadia (1997-2007)
Deep and short-duration transient slip with
synchronous occurrence of tremor but not regular
earthquakes
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Cascadia, Kao et al.
Nankai, Shelly et al.
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La Rocca et al., 2009 (Preston slab depth)
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September 2005 Mw 6.76
May 2008
May 2008 Mw 6.73
January 2007 Mw 6.82
McCrory et al. slab contours
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November 2004 Tokai (Eastern Nankai) Hirose
Obara, 2006
Tilt data
Slip patch (Mw 5.9)
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November 2006
GPS and strainmeter data
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November 2006 Small ETS event in central
Vancouver Island Mw 6.2 Wang et al., 2008
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Nankai
Cascadia
Nov. 2006
Jan. 2007
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S. Mexico
Costa Rica
Slab age 24 Ma
Wada and Wang, in prep.
Slab age 13 Ma
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(Shelly et al., 2009)
(Peng et al., submitted)
Being revised, but still around Moho
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California in the wake of the Mendocino triple
junction moving north A dehydrating and
diminishing serpentinized mantle wedge (Kirby,
Wang, and Brocher, submitted)
Water Yield Curve (Stalled-slab model)
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Survival depth of basaltic crust (blue diamonds)
and depth range of intraslab earthquakes (purple)
Modelled basalt-eclogite transformation
(blue) and serpentine stability in subducting
slab (purple)
Thermal Parameter (slab age x descending rate)
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North
After Goldfinger et al. (2003)
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No tremor?
No shallow tremor?
No events?
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• Rugged incoming seafloor
• (seamounts)

Why are megathrust events at Nankai smaller and
more frequent?
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• Rugged incoming seafloor
• (seamounts)
• Severe slab deformation
• enhances its surface relief

Modified from Wang, Wada, Ishikawa (2004)
Why are megathrust events at Nankai smaller and
more frequent?
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Fault strength
Smooth contact
Stress
Stress on locked fault
Distance along strike
Fault strength
Rough contact
Stress
Stress on locked fault
Distance along strike
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Fault strength
Smooth contact
Stress
Stress on locked fault
Distance along strike
Fault strength
Rough contact
Stress
Stress on locked fault
Distance along strike
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Can we identify VLF events at Cascadia?
VLF in Tremor Region
Yes, we can. Said Obara. To be discussed by
Honn Kao (U31B-02)
Ito et al. (2006)
VLF in Accretionary Prism
Ito Obara (2006)
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Cascadia (300 years after earthqauke)
Nankai (60 years after earthqauke)
Present interseismic strain rates are much larger
at Nankai, consistent with predictions of
viscoelastic earthquake cycle models.
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NE Japan