Zone Observatory Faulting and Deformation Jeff Freymueller Geophysical Institute and Dept of Geology and Geophysics University of Alaska Fairbanks AlongStrike Variations are Nearly Ubiquitous ID: 259004
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Slide1
Subduuction Zone Observatory:Faulting and Deformation
Jeff Freymueller
Geophysical Institute and Dept. of Geology and Geophysics
University of Alaska FairbanksSlide2
Along-Strike Variations are Nearly Ubiquitous
Freymueller et al. (2008)
Q–
What controls along-strike and downdip variations in the extent of slip?Slide3
Hikurangi Spatial/Temporal Variation
McCaffrey et al. (2008, Nature Geosciences)Slide4
Estimated Plate Couplingfrom GPS data 1995-2000
Meade and Loveless (2010)Slide5
Estimated Plate Couplingfrom GPS data 1995-2000
Meade and Loveless (2010)
Slow Slip EventsSlide6
Estimated Plate Couplingfrom GPS data 1995-2000
Meade and Loveless (2010)
Slow Slip Events
Afterslip from 1994 quakeSlide7
Estimated Plate Couplingfrom GPS data 1995-2000
Meade and Loveless (2010)
Slow Slip Events
Afterslip from 1994 quakeSlide8
Comparison of Locked Zone to SlipColors: Loveless and Meade (2010) interseismic model
Contours: Jack Loveless’ slip model contours
To first order, the rupture area of the earthquake is the same as the interseismic locked zone
Loveless and Meade, 3/14/11Loveless and Meade (2011)Slide9
Along-Strike Variation
Trench
relative
plate
motionSlide10
Along-Strike Variations are Nearly Ubiquitous
Freymueller et al. (2008)
Q–
What controls along-strike and downdip variations in the extent of slip?Slide11
Slip Spectrum I: Seismogenic
Zone Slip Modes
What do we want to know for understanding the slip modes?
Locked or creeping interface? Need better constraints on depth, thickness and properties of plate interface and properties of slab.Are there earthquakes at the updip/
downdip end? What is the slip behavior?Detailed distribution of earthquakes. On interface or not?Structural controls/influences?
Time dependence of above properties?
Outcomes controlled by interface properties or surrounding medium?Slide12
Slip Spectrum II: Slow Slip
Where is there slow slip on a subduction thrust?
Tremor is one marker of slow slip, but there can be slow slip without tremor (why?)
Small migrating earthquakes can be an indication of slow slip?What conditions are necessary for tremor genesis?Dewatering? Chattering of slip?Space/time distribution of tremor?Alaska tremor patchy, are there special locations/conditions?Japan has examples of both patchy and continuousSustained or episodic?
Spectrum of Duration/Size?One >9 (12?) year event now identified (Li et al., S53C-4511)Slide13
Some Complications We Think We Understand (sort of)
Postseismic deformation
Afterslip (on the plate interface)
Viscoelastic relaxation (in mantle wedge)Along-strike variationsExtent of slip deficit varies along strike: why?Slow slip eventsThe locked to creeping transition is dynamicCommon theme: slip along interface varies with time – not just interseismic + coseismic.Slide14
Q– Why are the amounts of afterslip and viscoelastic relaxation so variable?
Earthquake
Afterslip
Viscoelastic Relaxation1960 Chile (M9.5)
??Large, lasted for decades
1964 Alaska (M9.3)
~6 meters (25-30% of coseismic),
decades
Large, lasted for decades
2004
Sumatra-Andaman (M9.2)
Large, lastin
g > several years
Large,
lasting > several years
2005 Sumatra (M8.7)
Large, both updip
and downdip
Clearly present in far-field
data
1995 Antofagasta (M8.1)
Small, gone
within ~3 years
None?
2007
Kurils
(M 8.1)
Ended within 0.5 year
Large, will last ~
decade
1994
Sanriku
(M 7.7)
Equal to coseismic
minimal
We have not been successful in making advance predictions of postseismic deformation following large or great earthquakes.Slide15
Deformation of Upper PlateDeformation of upper plate is complex, and highly varied along the Americas
Broad zones of diffuse deformation
Slip partitioning of oblique subduction and motion of forearc slivers
Back-arc convergence, fold&thrust and basementLinked to subduction, but need to fully measure stress state and strain field.Slide16
Motion of Overriding Plate
SW arc translation
of
4 mm/
yr
Updip limit is poorly constrained by land-based data
But, moment rate deficit is well constrained
Subduction strain
Measured vel.
What is the Arc velocity?
Cross and Freymueller (2008)Slide17
Upper Plate Slivers are Common
Nocquet
et al. (2014,
ngeo)Slide18
Measurement NeedsGeodesy and Deformation
Measurements of long-term and short term steady deformation and transients
Response to loads, earthquakes reveals rheology
SeismologySeismicitySourceStructure (velocity, anisotropy, attenuation)IntegrationSlide19
Questions?