Subduuction Zone Observatory: Faulting and Deformation Jeff
Freymueller Geophysical Institute and Dept. of Geology and
Geophysics University of Alaska Fairbanks
Slide 2
Along-Strike Variations are Nearly Ubiquitous Freymueller et
al. (2008) Q What controls along-strike and downdip variations in
the extent of slip?
Slide 3
Hikurangi Spatial/Temporal Variation McCaffrey et al. (2008,
Nature Geosciences)
Slide 4
Estimated Plate Coupling from GPS data 1995-2000 Meade and
Loveless (2010)
Slide 5
Estimated Plate Coupling from GPS data 1995-2000 Meade and
Loveless (2010) Slow Slip Events
Slide 6
Estimated Plate Coupling from GPS data 1995-2000 Meade and
Loveless (2010) Slow Slip Events Afterslip from 1994 quake
Slide 7
Estimated Plate Coupling from GPS data 1995-2000 Meade and
Loveless (2010) Slow Slip Events Afterslip from 1994 quake
Slide 8
Comparison of Locked Zone to Slip Colors: 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, 3/14/11
Loveless and Meade (2011)
Along-Strike Variations are Nearly Ubiquitous Freymueller et
al. (2008) Q What controls along-strike and downdip variations in
the extent of slip?
Slide 11
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?
Slide 12
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
continuous Sustained or episodic? Spectrum of Duration/Size? One
>9 (12?) year event now identified (Li et al., S53C-4511)
Slide 13
Some Complications We Think We Understand (sort of) Postseismic
deformation Afterslip (on the plate interface) Viscoelastic
relaxation (in mantle wedge) Along-strike variations Extent of slip
deficit varies along strike: why? Slow slip events The locked to
creeping transition is dynamic Common theme: slip along interface
varies with time not just interseismic + coseismic.
Slide 14
Q Why are the amounts of afterslip and viscoelastic relaxation
so variable? EarthquakeAfterslipViscoelastic Relaxation 1960 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, 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
yearsNone? 2007 Kurils (M 8.1)Ended within 0.5 yearLarge, will last
~ decade 1994 Sanriku (M 7.7)Equal to coseismicminimal We have not
been successful in making advance predictions of postseismic
deformation following large or great earthquakes.
Slide 15
Deformation of Upper Plate Deformation 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
basement Linked to subduction, but need to fully measure stress
state and strain field.
Slide 16
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)
Slide 17
Upper Plate Slivers are Common Nocquet et al. (2014, ngeo)
Slide 18
Measurement Needs Geodesy and Deformation Measurements of
long-term and short term steady deformation and transients Response
to loads, earthquakes reveals rheology Seismology Seismicity Source
Structure (velocity, anisotropy, attenuation) Integration
