Subduuction Zone Observatory: Faulting and Deformation Jeff Freymueller Geophysical Institute and Dept. of Geology and Geophysics University of Alaska Fairbanks

Along-Strike Variations are Nearly Ubiquitous Freymueller et al. (2008) Q– What controls along-strike and downdip variations in the extent of slip?

Hikurangi Spatial/Temporal Variation McCaffrey et al. (2008, Nature Geosciences)

Estimated Plate Coupling from GPS data Meade and Loveless (2010)

Estimated Plate Coupling from GPS data Meade and Loveless (2010) Slow Slip Events

Estimated Plate Coupling from GPS data Meade and Loveless (2010) Slow Slip Events Afterslip from 1994 quake

Estimated Plate Coupling from GPS data Meade and Loveless (2010) Slow Slip Events Afterslip from 1994 quake

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 Variation Trench relative plate motion

Along-Strike Variations are Nearly Ubiquitous Freymueller et al. (2008) Q– What controls along-strike and downdip variations in the extent of slip?

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?

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)

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.

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.

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.

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)

Upper Plate Slivers are Common Nocquet et al. (2014, ngeo)

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

Questions?