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Subduuction - PPT Presentation

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

plate slip deformation slow slip plate slow deformation strike meade loveless interface variations 2010 tremor earthquakes couplingfrom 2000 gps

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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?

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