Strain budget of the Ecuador–Colombia subduction zone: A stochastic view

The 2016 Pedernales earthquake (M_W=7.8) ruptured a portion of the Colombia–Ecuador subduction interface where several large historical earthquakes have been documented since the great 1906 earthquake (M=8.6). Considering all significant ruptures that occurred in the region, it has been suggested that the cumulative moment generated co-seismically along this part of the subduction over the last century exceeds the moment deficit accumulated inter-seismically since 1906. Such an excess challenges simple models with earthquakes resetting the elastic strain accumulated inter-seismically in locked asperities. These inferences are however associated with large uncertainties that are generally unknown. The impact of spatial smoothing constraints on co-seismic and inter-seismic models also prevents any robust assessment of the strain budget. We propose a Bayesian kinematic slip model of the 2016 Pedernales earthquake using the most comprehensive dataset to date including InSAR and GPS offsets, tsunami waveforms, and kinematic records from high-rate GPS and strong-motions. In addition, we use inter-seismic geodetic velocities to produce a probabilistic inter-seismic coupling model of the subduction interface. Our stochastic co-seismic and inter-seismic solutions include the ensemble of all plausible models consistent with our prior information and that fit the observations within uncertainties. The analysis of these model ensembles indicates that an excess of co-seismic moment during the 1906–2016 period is likely in Central Ecuador only if we assume that 1942 and 2016 earthquakes are colocated. If this assumption is relaxed, we show that this conclusion no longer holds given uncertainties in co- and inter-seismic processes. The comparison of 1942 and 2016 teleseismic records reveals large uncertainties in the location of the 1942 event, hampering our ability to draw strong conclusions on the unbalanced moment budget in the region. Our results also show a heterogeneous coupling of the subduction interface that coincides with two slip asperities in our co-seismic model for the 2016 Pedernales earthquake and with the location of historical ruptures in 1958, 1979 and 1998. The spatial variability in coupling and complexity in earthquake history suggest strong heterogeneities in frictional properties of the subduction megathrust.

[1]  K. Sieh,et al.  Irregular Recurrence of Large Earthquakes Along the San Andreas Fault: Evidence from Trees , 1988, Science.

[2]  J. Avouac,et al.  From Geodetic Imaging of Seismic and Aseismic Fault Slip to Dynamic Modeling of the Seismic Cycle , 2015 .

[3]  Sarah E. Minson,et al.  The 2011 Magnitude 9.0 Tohoku-Oki Earthquake: Mosaicking the Megathrust from Seconds to Centuries , 2011, Science.

[4]  Marie-Pierre Doin,et al.  Shallow creep on the Haiyuan Fault (Gansu, China) revealed by SAR Interferometry , 2012 .

[5]  Hai Cheng,et al.  Earthquake Supercycles Inferred from Sea-Level Changes Recorded in the Corals of West Sumatra , 2008, Science.

[6]  K. Koketsu,et al.  A very long-term transient event preceding the 2011 Tohoku earthquake , 2015, Nature Communications.

[7]  C. Mendoza,et al.  Seismicity associated with the great Colombia-Ecuador earthquakes of 1942, 1958, and 1979: Implications for barrier models of earthquake rupture , 1984 .

[8]  F. Masson,et al.  Aseismic slip and seismogenic coupling in the Marmara Sea: What can we learn from onland geodesy? , 2017 .

[9]  J. Avouac,et al.  Stress transfer and strain rate variations during the seismic cycle , 2004 .

[10]  K. Heki,et al.  Accelerated Pacific Plate Subduction Following Interplate Thrust Earthquakes at the Japan Trench , 2013 .

[11]  H. Mora-Páez,et al.  Space Geodesy Infrastructure in Colombia for Geodynamics Research , 2018 .

[12]  H. Kanamori.  Mechanism of tsunami earthquakes , 1972 .

[13]  Robert B. Herrmann,et al.  Computer Programs in Seismology: An Evolving Tool for Instruction and Research , 2013 .

[14]  F. Hernán,et al.  Aseismic Deformation in Subduction Megathrusts: Central Andes and North-East Japan , 2013 .

[15]  P. Charvis,et al.  Seismological study of the central Ecuadorian margin: Evidence of upper plate deformation , 2011 .

[16]  P. Segall,et al.  A decadal‐scale deformation transient prior to the 2011 Mw 9.0 Tohoku‐oki earthquake , 2014 .

[17]  T. V. McEvilly.  Seismicity of the earth and associated phenomena , 1967 .

[18]  Masayuki Kikuchi,et al.  Inversion of complex body waves , 1982 .

[19]  C. Beauval,et al.  Motion of continental slivers and creeping subduction in the Northern Andes , 2014 .

[20]  Rowena B. Lohman,et al.  Some thoughts on the use of InSAR data to constrain models of surface deformation: Noise structure and data downsampling , 2005 .

[21]  M. Ruiz,et al.  Monitoring the Earthquake Cycle in the Northern Andes from the Ecuadorian cGPS Network , 2018 .

[22]  T. Heaton.  Evidence for and implications of self-healing pulses of slip in earthquake rupture , 1990 .

[23]  P. Charvis,et al.  Distribution of discrete seismic asperities and aseismic slip along the Ecuadorian megathrust , 2014 .

[24]  F. N. Teferle,et al.  Complementary slip distributions of the August 4, 2003 Mw 7.6 and November 17, 2013 Mw 7.8 South Scotia Ridge earthquakes , 2014 .

[25]  J. Beck,et al.  Accounting for prediction uncertainty when inferring subsurface fault slip , 2014 .

[26]  M. Moreno,et al.  The super‐interseismic phase of the megathrust earthquake cycle in Chile , 2017 .

[27]  H. Kanamori,et al.  VARIABLE RUPTURE MODE OF THE SUBDUCTION ZONE ALONG THE ECUADOR-COLOMBIA COAST , 1982 .

[28]  M. Vallée,et al.  Ten year recurrence time between two major earthquakes affecting the same fault segment , 2014 .

[29]  Aurore Laurendeau,et al.  Supercycle at the Ecuadorian subduction zone revealed after the 2016 Pedernales earthquake , 2017 .

[30]  Martin Jakobsson,et al.  A new digital bathymetric model of the world's oceans , 2015 .

[31]  François Renard,et al.  The Burst‐Like Behavior of Aseismic Slip on a Rough Fault: The Creeping Section of the Haiyuan Fault, China , 2015 .

[32]  T. Lay.  The surge of great earthquakes from 2004 to 2014 , 2015 .

[33]  Hiroyuki Kumagai,et al.  Depth‐dependent rupture mode along the Ecuador‐Colombia subduction zone , 2017 .

[34]  M. Régnier,et al.  Intense interface seismicity triggered by a shallow slow slip event in the Central Ecuador subduction zone , 2013 .

[35]  Caijun Xu,et al.  Rupture process of the 2016 Mw 7.8 Ecuador earthquake from joint inversion of InSAR data and teleseismic P waveforms , 2018 .

[36]  Nadia Lapusta,et al.  Towards inferring earthquake patterns from geodetic observations of interseismic coupling , 2010 .

[37]  Takashi Nakata,et al.  Time‐predictable recurrence model for large earthquakes , 1980 .

[38]  D. P. Schwartz,et al.  Fault behavior and characteristic earthquakes: Examples from the Wasatch and San Andreas Fault Zones , 1984 .

[39]  B. Gutenberg,et al.  Seismicity of the Earth and associated phenomena , 1950, MAUSAM.

[40]  S. Beck,et al.  Historical 1942 Ecuador and 1942 Peru subduction earthquakes and earthquake cycles along Colombia-Ecuador and Peru subduction segments , 1996 .

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

[42]  Piyush Agram,et al.  Aseismic slip and seismogenic coupling along the central San Andreas Fault , 2015 .

[43]  P. Charvis,et al.  Deep structures of the Ecuador convergent margin and the Carnegie Ridge, possible consequence on great earthquakes recurrence interval , 2004 .

[44]  Raul Madariaga,et al.  Complexity of seismicity due to highly rate‐dependent friction , 1996 .

[45]  M. Ruiz,et al.  Seismic, Volcanic, and Geodetic Networks in Ecuador: Building Capacity for Monitoring and Research , 2018 .

[46]  P. Charvis,et al.  Subducted oceanic relief locks the shallow megathrust in central Ecuador , 2017 .

[47]  D. Melgar,et al.  Systematic Observations of the Slip Pulse Properties of Large Earthquake Ruptures , 2017 .

[48]  J. Avouac,et al.  The 16 April 2016, MW 7.8 (MS 7.5) Ecuador earthquake: A quasi-repeat of the 1942 MS 7.5 earthquake and partial re-rupture of the 1906 MS 8.6 Colombia–Ecuador earthquake , 2016 .

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

[50]  Hiroo Kanamori,et al.  Uncertainty estimations for seismic source inversions , 2011 .

[51]  Yangmao Wen,et al.  Coseismic Slip in the 2016 Mw 7.8 Ecuador Earthquake Imaged from Sentinel-1A Radar Interferometry , 2017 .

[52]  J. Loveless.  Super‐interseismic periods: Redefining earthquake recurrence , 2017 .

[53]  L. Ruff,et al.  The rupture process of the Great 1979 Colombia Earthquake: Evidence for the asperity model , 1984 .

[54]  Keiiti Aki,et al.  Discrete wave-number representation of seismic-source wave fields , 1977, Bulletin of the Seismological Society of America.

[55]  James L. Beck,et al.  Bayesian inversion for finite fault earthquake source models I—theory and algorithm , 2013 .