Repeated large Slow Slip Events at the southcentral Alaska subduction zone

Abstract We identify and study an ongoing Slow Slip Event (SSE) in the southcentral Alaska subduction zone using GPS measurements. This is the second large SSE in this region since modern geodetic measurements became available in 1993. We divide the ongoing SSE into two phases according to their transient displacement time evolution; their slip distributions are similar to each other but slip rates are slightly different. This ongoing SSE occurs downdip of the main asperity that ruptured in the 1964 Alaska earthquake, on the same part of the subduction interface as the earlier 1998–2001 SSE. The average slip rate of this SSE is ∼4–5 cm/yr, with a cumulative moment magnitude of Mw 7.5 ( Mw 7.3 and Mw 7.1 For Phases I and II, respectively) through the end of 2012. The time and space dependence of the GPS displacements suggest that the slip area remained nearly the same during Phase I, while the slip rate increased with time. The SSEs occur on a transitional section of the subduction plate interface between the fully locked updip part and the freely slipping deeper part. During the 1964 earthquake, slip on the region of the SSE was much lower than slip in the updip region. Based on this observation and the repeated SSEs, we conclude that this part of the interface slips repeatedly in SSEs throughout the interseismic period and does not build up a large slip deficit to be released through large slip in earthquakes.

[1]  Jeffrey T. Freymueller,et al.  A viscoelastic and afterslip postseismic deformation model for the 1964 Alaska earthquake , 2009 .

[2]  Jeffrey T. Freymueller,et al.  Seasonal and long-term vertical deformation in the Nepal Himalaya constrained by GPS and GRACE measurements , 2012 .

[3]  S. Miyazaki,et al.  A slow thrust slip event following the two 1996 Hyuganada Earthquakes beneath the Bungo Channel, southwest Japan , 1999 .

[4]  J. Freymueller,et al.  A large slow slip event and the depth of the seismogenic zone in the south central Alaska subduction zone , 2006 .

[5]  Chris Zweck,et al.  Active Deformation Processes in Alaska, Based on 15 Years of GPS Measurements , 2013 .

[6]  Kristine M. Larson,et al.  A large silent earthquake in the Guerrero seismic gap, Mexico , 2003 .

[7]  T. Dixon,et al.  Slow slip events in Costa Rica detected by continuous GPS observations, 2002–2011 , 2012 .

[8]  Time-dependent inversion study of the slow thrust event in the Nankai trough subduction zone , 2001 .

[9]  J. C. Savage.  A dislocation model of strain accumulation and release at a subduction zone , 1983 .

[10]  Kelin Wang,et al.  A Silent Slip Event on the Deeper Cascadia Subduction Interface , 2001, Science.

[11]  J. K. Mitchell,et al.  Coseismic deformation of the 2002 Denali Fault earthquake: Insights from GPS measurements , 2006 .

[12]  J. Freymueller,et al.  Spatial variations in present‐day deformation, Kenai Peninsula, Alaska, and their implications , 2000 .

[13]  M. Wei,et al.  A slow slip event in the south central Alaska Subduction Zone and related seismicity anomaly , 2012 .

[14]  H. Dragert,et al.  Episodic Tremor and Slip on the Cascadia Subduction Zone: The Chatter of Silent Slip , 2003, Science.

[15]  Ian Parsons,et al.  Surface deformation due to shear and tensile faults in a half-space , 1986 .

[16]  J. Freymueller,et al.  Crustal Deformation in Southcentral Alaska: The 1964 Prince William Sound Earthquake Subduction Zone , 2003 .

[17]  S. Miyazaki,et al.  Characteristic silent earthquakes in the eastern part of the Boso peninsula, Central Japan , 2003 .

[18]  J. Freymueller,et al.  Crustal Deformation in the Southcentral Alaska Subduction Zone , 2004 .

[19]  Douglas H. Christensen,et al.  Possible relationship between nonvolcanic tremor and the 1998–2001 slow slip event, south central Alaska , 2009 .

[20]  S. R. Holdahl,et al.  Postseismic crustal uplift near Anchorage, Alaska , 1977 .

[21]  S. Owen,et al.  The angular velocities of the plates and the velocity of Earth's centre from space geodesy , 2010 .

[22]  J. Freymueller,et al.  Seasonal hydrological loading in southern Alaska observed by GPS and GRACE , 2012 .

[23]  T. Dam,et al.  The effect of using inconsistent ocean tidal loading models on GPS coordinate solutions , 2012, Journal of Geodesy.

[24]  David J. Wald,et al.  Slab1.0: A three‐dimensional model of global subduction zone geometries , 2012 .

[25]  Takeshi Sagiya,et al.  A revised dislocation model of interseismic deformation of the Cascadia subduction zone , 2003 .

[26]  S. Matsumura,et al.  A slow slip event in the Tokai area detected by tilt and seismic observation and its possible recurrence , 2005 .

[27]  J. Beavan,et al.  A large slow slip event on the central Hikurangi subduction interface beneath the Manawatu region, North Island, New Zealand , 2006 .