Geodetic slip solutions for the Mw = 7.4 Champerico (Guatemala) earthquake of 2012 November 7 and its postseismic deformation

Abstract

As the first large subduction thrust earthquake off the coast of western Guatemala in the past several decades, the 2012 November 7 M w = 7.4 earthquake offers the first opportunity to study coseismic and postseismic behaviour along a segment of the Middle America trench where frictional coupling makes a transition from weak coupling off the coast of El Salvador to strong coupling in southern Mexico. We use measurements at 19 continuous GPS sites in Guatemala, El Salvador and Mexico to estimate the coseismic slip and postseismic deformation of the November 2012 Champerico (Guatemala) earthquake. An inversion of the coseismic offsets, which range up to ∼47 mm at the surface near the epicentre, indicates that up to ∼2 m of coseismic slip occurred on a ∼30 × 30 km rupture area between ∼10 and 30 km depth, which is near the global CMT centroid. The geodetic moment of 13 × 10 19 N m and corresponding magnitude of 7.4 both agree well with independent seismological estimates. Transient postseismic deformation that was recorded at 11 GPS sites is attributable to a combination of fault afterslip and viscoelastic flow in the lower crust and/or mantle. Modelling of the viscoelastic deformation suggests that it constituted no more than ∼30 per cent of the short-term postseismic deformation. GPS observations that extend six months after the earthquake are well fit by a model in which most afterslip occurred at the same depth or directly downdip from the rupture zone and released energy equivalent to no more than ∼20 per cent of the coseismic moment. An independent seismological slip solution that features more highly concentrated coseismic slip than our own fits the GPS offsets well if its slip centroid is translated ∼50 km to the west to a position close to our slip centroid. The geodetic and seismologic slip solutions thus suggest bounds of 2-7 m for the peak slip along a region of the interface no larger than 30 × 30 km.

GPS constraints on deformation in northern Central America from 1999 to 2017, Part 1 – Time-dependent modelling of large regional earthquakes and their post-seismic effects

“…9(b). The estimated geodetic moment, 1.45 × 10 20 N m, is close to the 1.3 × 10 20 N m moment estimated by Ellis et al (2015) and 1.33-1.5 × 10 20 N m seismological estimates (Ekström et al 2012;Ye et al 2013). The coseismic offsets recorded in the position time-series of nearby continuous GPS stations are well fit by the new TDEFNODE model (Supporting Information Fig.…”

“…Slip of 0.5-1.2 m was concentrated at depths of 10-30 km, close to the global CMT earthquake centroid (white star in Fig. 9a) and in good agreement with the Ellis et al (2015) slip solution shown in Fig. 9(b).…”

“…The 2012 Champerico earthquake ruptured the Middle America trench offshore from southern Guatemala, where locking transitions from strong near Chiapas to weak offshore El Salvador (Lyon-Caen et al 2006;Correa-Mora et al 2009;LaFemina et al 2009;Franco et al 2012). Inversions by Ellis et al (2015) of coseismic offsets and afterslip amplitudes at 19 continuous GPS sites in Guatemala, El Salvador, and southern Mexico indicate that coseismic slip of up to 2 m was concentrated in a relatively compact region above 30 km depth, immediately updip from the afterslip. Their coseismic slip estimate agrees well with an independent solution from an inversion of regional and teleseismic P waves (Ye et al 2013).…”

“…Fault node spacings are ≈20 km along-strike and 10-km down-dip. From a standard checkerboard test, Ellis et al (2015) find that inversions of synthetic data created from slip patches at various depths off the coast of Guatemala near the Champerico earthquake recover the starting models relatively well at depths of 10 km to 60 km (details are given in the Ellis et al (2015) supplementary materials). Checkerboard tests using the sparser GPS network configuration from El Salvador, Nicaragua, and Honduras that existed during the 2012 El Salvador earthquake (Supporting Information Fig.…”

“…1). Using a static-deformation approximation and subsets of the data used herein, previous authors have estimated geodetic coseismic slip solutions for each of these earthquakes (Graham et al 2012;Ellis et al 2015;Geirsson et al 2015) and afterslip solutions for two of the three earthquakes (Ellis et al 2015;Geirsson et al 2015). Here, we simultaneously invert all available GPS data from the region to jointly estimate coseismic and afterslip solutions for all three earthquakes, thereby assuring that their summed elastic effects correctly describe the evolving space-time pattern of GPS station positions in northern Central America between 1999 and the present.…”