Postseismic deformation following the 1991 Racha, Georgia, earthquake

Abstract

[1] The 1991, M s = 7.0 Racha earthquake is the largest ever recorded in the Caucasus Mountains. Approximately three months after this thrust-faulting earthquake, a GPS network was set up to measure postseismic surface deformation. We present an analysis of these data, which indicate accelerated postseismic motions at several nearfield sites. We model this deformation as either afterslip on the rupture surface or viscoelastic relaxation of the lower crust. We find that the postseismic motions are best explained by shallow afterslip on the earthquake rupture plane. The minimum postseismic moment release is estimated at 6.0 Â 10 18 N m, which is over 200 times the moment released by aftershocks in this same period and about 20% of the coseismic moment. We also show that the effective viscosity of the lower crust in the western Greater Caucasus region exceeds 10 18 Pa s.

Izmit earthquake postseismic deformation and dynamics of the North Anatolian Fault Zone

“…Afterslip has been identified following earthquakes in several tectonic settings, including subduction zones [e.g., Heki and Tamura , 1997; Melbourne et al , 2002; Miyazaki and Larson , 2008]; and along thrust‐ and strike‐slip faults within continental crust [e.g., Hsu et al , 2002; Podgorski et al , 2007]. In several cases, afterslip has been modeled as velocity‐strengthening frictional slip [ Perfettini and Avouac , 2004, 2007; Johnson et al , 2006, 2008, and references therein].…”

“…These studies give (A‐B) values of 0.2 to 0.7 MPa, which are consistent with our results, and which likely indicate elevated pore pressures in the fault zone. Other studies, while not explicitly modeling frictional afterslip, show that afterslip occurs near the surface, or within the seismogenic zone between patches of high coseismic slip (where the fault was coseismically loaded, but is not hot enough for significant viscous creep [e.g., Podgorski et al , 2007; Miyazaki and Larson , 2008]). Given the near ubiquity of rapid afterslip following major earthquakes, it would be odd if this were not the cause of the earliest post‐Izmit deformation.…”

Omori‐like decay of postseismic velocities following continental earthquakes

“…Red line shows the best fitting Omori model and black solid lines show the region where 95% of Omori models plot. Data sources: Barbot et al [], Atzori et al [], Reddy et al [], Calais et al [], Hsu et al [], Perfettini and Avouac [], Gourmelen and Amelung [], Hammond et al [], Hetland and Hager [], Bie et al [], Biggs et al [], Freed et al [], Pollitz [], Lammali et al [], Pollitz et al [], Amoruso et al [], Hao et al []; Nishimura and Thatcher []; Reilinger []; Pollitz and Thatcher []; Reilinger [], Dalla Via [], Ergintav et al [], Diao et al [], Ryder et al [], Deng et al [], D'Agostino et al [], Ryder et al [], Vergnolle [], Copley et al [], Floyd et al [], Ryder et al [], Deng et al [], Jouanne et al [], Barbot et al [], Langbein [], Podgorski et al [], Jónsson [], Copley and Reynolds [], Copley [], Riva et al [], Dogan et al [], Feng et al [], Cetin et al [], and Mahsas et al []…”

Estimates of aseismic slip associated with small earthquakes near San Juan Bautista, CA

“…As in Figure 7, circles are for stacked groups, and crosses are for individual earthquakes. Squares, diamonds, and triangles plotted for larger earthquakes show the estimated postseismic to coseismic moment ratios estimated by Savage and Svarc [1997], Segall et al [2000], Bürgmann et al [2001], Jacobs et al [2002], Melbourne et al [2002], Miura et al [2004], Hsu et al [2006], Langbein et al [2006], Pritchard and Simons [2006], Subarya et al [2006], Chlieh et al [2007], Freed [2007], Podgorski et al [2007], Ryder et al [2007], Barbot et al [2008], Furuya and Satyabala [2008], Jónsson [2008], Mahsas et al [2008], Amoruso and Crescentini [2009], Murray-Moraleda and Simpson [2009], Cheloni et al [2010], Johanson and Bürgmann [2010], Ryder et al [2010], Bell et al [2012], Cetin et al [2012], D'Agostino et al [2012, Wen et al [2012], Lin et al [2013], Dogan et al [2014], Gonzalez-Ortega et al [2014], Taira et al [2014], Fattahi et al [2015], and Floyd et al [2016].…”