2004; Suito & Freymueller 2009; Hu & Wang 2012; Kogan etal. 2013). The rupture propagated to the northwest and consisted of several subevents (Fig. (2004) and USGS, and the centroid from the gCMT catalogue (Ekstrm etal. Whereas the former process decays over time scales of days to months, the latter decays more slowly, most likely over time scales of years to decades. 14a). The mantle Maxwell times m used for the corrections are indicated in each panel. The black dashed line marks the time of the 2003 Tecoman earthquake. A comparison of the velocities from models with m = 2.5, 15 and 40yr is shown in Supporting Information Figs S17 and S18. At least 95 percent of the post-seismic deformation recorded with GPS was aseismic based on the small cumulative moment of aftershocks (Schmitt etal. 1). 1998; Fig. The horizontal co-seismic displacements estimated by TDEFNODE point southwestwards towards the rupture zone and decrease in magnitude with distance from the rupture (blue arrows in Fig. S14). B Cosenza-Muralles, C DeMets, B Mrquez-Aza, O Snchez, J Stock, E Cabral-Cano, R McCaffrey, Co-seismic and post-seismic deformation for the 1995 ColimaJalisco and 2003 Tecomn thrust earthquakes, Mexico subduction zone, from modelling of GPS data, Geophysical Journal International, Volume 228, Issue 3, March 2022, Pages 21372173, https://doi.org/10.1093/gji/ggab435. For each starting model, we calculated synthetic 3-D velocities at the GPS sites and perturbed the synthetic velocities with random noise of 1mm yr1 (1-sigma) for the horizontal components and 2mm yr1 for the vertical. Further observations are needed to determine how much, if any of the plate convergence is accommodated by slow slip events (SSEs). The mantle rheology is thus not strongly constrained by our observations, as expected given the many fitting trade-offs that exist between the model parameters. 17 and selected campaign sites in Fig. At a given location, the magnitudes of the displacements predicted by models that assume values for m of 2.5, 15 and 40yr vary by factors of 2 to 5 (Fig. Panels (c) and (d) respectively show the horizontal and vertical site motions predicted by the co-seismic and afterslip solutions from panels (a) and (b) at sites active during the earthquake for panel (c) and sites active between 1995 and 2003 for panel (d). (2010) and GPS-derived solution of Schmitt etal. Due to the sparse GPS site distribution before year 2000 and campaign-dominated nature of the GPS sites during this period, the details of slip during the 1995 earthquake are more poorly resolved than for the 2003 earthquake slip and afterslip (compare Supporting Information Fig. (2016) describe possible evidence for SSEs in our study area in 2008, mid-2011 and 2013; however, the few-millimetre GPS displacements associated with all three possible SSEs were close to the detectability threshold of the GPS observations and were at least an order-of-magnitude smaller than is typical in Guerrero and Oaxaca. Colima at Manzanillo P.S., UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1996, UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1995 03 (March), UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1995 10 (October), UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1997, UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1998, UNAVCO, GPS/GNSS Observations Dataset, Jalisco 1999, UNAVCO, GPS/GNSS Observations Dataset, Jalisco GPS Network - CRIP-Cent. O b. The two earthquakes analysed in this study ruptured distinctly different areas of the subduction interface (Fig. 2007). Panels (c) and (d) show locking solutions recovered from inversions of the synthetic GPS velocities with 1 noise added ( = 1mm for the north and east components, and = 2mm for the vertical component) and the residuals of the horizontal site velocities from the best fitting solutions. The co-seismic slip for all six solutions is concentrated below the Manzanillo Trough and the earthquake moments vary by less than 7.6 per cent relative to an average Mo of 1.98 0.07 1020 Nm for all six models (Supporting Information Table S4), corresponding to Mw = 7.47.5. Modelling of waveforms from local and teleseismic body wave data suggest that this rupture initiated at a depth of 20km and propagated up- and downdip (Yagi etal. (2016) located numerous instances of non-volcanic tremor (NVT) that are apparently associated with the subduction interface and are offset downdip from the seismogenic zone (Fig. We then inverted the corrected GPS position time-series via TDEFNODE while fixing the 1995 co-seismic slip solution to the same preferred estimate as was used to drive the viscoelastic model (Fig. 1.3) and weighted root mean square (wrms) error (eq. Melbourne etal. 2007), in agreement with the seismic results. Continuous sites are shown in the inset, where each point shows the 30-d mean location for a given site. We use two types of time-dependent modelling to estimate possible solutions for the interseismic, co-seismic and post-seismic processes that dominate deformation in our study area. Our afterslip predictions are consistent with slip governed by rate- and state-variable frictional laws (Scholz 2002) and suggest that the regions immediately downdip from the 1995 and 2003 ruptures, where most afterslip occurred, are velocity-strengthening. 1. Despite the geometric similarities of the Guerrero and Oaxaca subduction interfaces, SSEs beneath Guerrero have larger magnitudes (M7.5) than those beneath Oaxaca (M6.57), and the SSEs are shallower, possibly intruding the seismogenic zone and releasing a portion of the accumulated shallow elastic strain (Kostoglodov etal. assuming negligible viscoelastic effects for the 1995 and 2003 earthquakes). 1998; Wang 2007). Table S2: Co-seismic displacements from the 1995 ColimaJalisco earthquake at GPS sites active during the earthquake. This result, and the reversal of vertical motions with respect to the co-seismic direction, strongly indicate that the fault afterslip was focused downdip of the co-seismic rupture (compare Figs14a andb). (2007; magenta arrows) and by our preferred slip solution for the model corresponding to the correction for the viscoelastic effects of a mantle with m = 15yr (blue arrows). It is movement during an earthquake that adds to built up tectonic stress. Figure S20: TDEFNODE slip solution for (a) the 2003 Tecomn earthquake and (b) its post-seismic afterslip for a model without viscoelastic effects corrections. An educated guess b. Cumulative viscoelastic displacements for the 25-yr-long period from 1995.77 to 2020.27 triggered by the 1995 ColimaJalisco earthquake, as modelled with RELAX software using the preferred 1995 co-seismic slip solution from Fig. 14c and Supporting Information Table S8), particularly at inland locations. 2006; Hu & Wang 2012; Wang etal. Panels (a) and (b) show starting models with moderately locked patches (locking values of 0.5) and their predicted (synthetic) horizontal GPS velocities. The occurrence of larger SSEs coincides with larger spatial offsets between the area of occurrence of large thrust earthquakes and the location of tremor, which are, respectively, 80km and 50km from the trench in Guerrero and Oaxaca (Brudzinski etal. Although Lin etal. If the frictional properties of subduction interfaces differ significantly in areas where post-seismic afterslip and interseismic SSEs occur, as suggested by Malservisi etal. 2020) and Nankai, Japan (Sherrill & Johnson 2021). 2017). 9a). Freed A.M., Brgmann R., Calais E., Freymueller J.. 14d). 2). S11 shows the modelled displacements at selected sites. For example, during the years immediately after the 1995 Mw = 8.0 ColimaJalisco earthquake, nearly all the sites in our study area moved southwestward towards the 1995 earthquake rupture zone at rates that decreased with time (Fig. Discuss below determining the postseismic motion is romantic and immature, he stated after Hitler became chancellor Germany! The formal uncertainties in the NA-IGS14 angular velocity vector propagate into 1 uncertainties of only 0.03mm yr1 in the north and east components of the velocity for the North America plate relative to IGS14 at the centre of our study area, too small to affect any of the results or interpretations that follow. 1997) and 2003 (Yagi etal. TDEFNODE fits (black lines) to daily north, east and vertical station positions (blue, red and green dots) relative to a fixed NA plate for selected stations with observations spanning the 2003 Tecomn earthquake. Our geodetically derived co-seismic moment, 1.84 1020 Nm (Mw = 7.4), is close to seismologic estimates of Mo = 2.0 1020 Nm (Ekstrm etal. At present, the motions at sites in western Mexico are a superposition of steady interseismic strain accumulation due to frictional locking of the Mexico subduction interface and transient surface deformations from post-seismic afterslip and viscoelastic rebound triggered by the 1995 and 2003 earthquakes. We imposed a shear modulus = 40 GPa and a Poissons ratio = 0.25 for the whole domain. GPS station displacements are modelled in TDEFNODE as, $$\begin{equation*} Based on results from static modelling of the newly estimated interseismic motions (CM21-II), we adopt a best viscosity of 1.9 1019 Pas (m = 15yr). Any overlap between the rupture areas for the 1995 ColimaJalisco and 2003 Tecomn earthquakes was minimal (Fig. For example, the seismic potency estimated in the latter study, P0 = 2.5 1010 m3, where the potency P0 is defined as the estimated seismic moment normalized by the shear modulus (Ben-Menahmen & Singh 1981), differs by only 3 per cent from P0 = 2.43 1010 m3 for this study. Dashed lines show the slab contours every 20km. (2). Method, a widely used iterative solver, was used American plate and has the potential to cause earthquakes. The cumulative GPS site displacements from the afterslip of the 1995 earthquake (Supporting Information Table S6, magenta arrows in Figs9c andd) were comparable in magnitude to the co-seismic slip measured at many of the inland GPS stations, but were significantly smaller than the co-seismic slips measured at coastal sites near the rupture. 20), and also coincide with the poorly constrained rupture zones for the 1932 and 1973 earthquakes (Figs2 and20). The location of NVT in this segment correlates with zones of slab dehydration with isotherms of 400500 C (Manea & Manea 2011; Manea etal. 2 is shown in blue. Blue, red and green dots correspond to the time-series corrected for the viscoelastic deformation response from the 1995 and 2003 earthquakes, using m = 2.5, 15 and 40yr, respectively. 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