La equivalencia y supresión en la resolución del problema inverso en geoeléctrica: Aplicación en Santa Lucía Cotzumalguapa, Guatemala

Para una correcta interpretación de un sondeo eléctrico vertical (SEV), se deben considerar los principios de supresión y equivalencia, por los que se generan múltiples modelos como consecuencia de la no unicidad de la solución del problema inverso. Debe buscarse entre las soluciones válidas, aquella que armonice más con los SEV contiguos, que tenga un buen significado geológico en función de la información previa del sitio y que se enmarque dentro de la hipótesis planteada en la investigación, tal como se realizó en la localidad de Santa Lucía Cotzumalguapa, Guatemala

GPS-Derived Interseismic Fault Locking along the Jalisco–Colima Segment of the Mexico Subduction zone

Northeastward subduction of the oceanic Rivera and Cocos plates in western Mexico poses a poorly understood seismic hazard to the overlying areas of the North America plate. We estimate the magnitude and distribution of interseismic locking along the northern ∼500 km of the Mexico subduction zone, with a series of elastic half-space inversions that optimize the fits to the velocities of 57 GPS stations in western Mexico. All velocities were corrected for the co-seismic, afterslip and viscoelastic rebound effects of the 1995 Colima–Jalisco and 2003 Tecomán earthquakes. We explore the robustness of interseismic locking estimates to a variety of mantle Maxwell times that are required for the viscoelastic corrections, to the maximum permitted depth for locking of the subduction interface and to the location assigned to the Rivera–Cocos–North America plate triple junction offshore from western Mexico. The best-fitting locking solutions are associated with a maximum locking depth of 40 km, a triple junction location ∼50 km northwest of the Manzanillo Trough and a mantle Maxwell time of 15 yr (viscosity of 2 × 1019 Pa s). Checkerboard tests show that the locking distribution is best resolved at intermediate depths (10–40 km). All of our inversions define a gradual transition from strong locking (i.e. 70–100 per cent) of most (70 per cent) of the Rivera–North America subduction interface to strong but less uniform locking below the Manzanillo Trough, where oceanic lithosphere transitional between the Cocos and Rivera plate subducts, to weak to moderate locking (averaging 55 per cent) of the Michoacán segment of the Cocos–North America interface. Strong locking of the ∼125-km-long trench segment offshore from Puerto Vallarta and other developed coastal areas, where our modelling indicates an average annual elastic slip-rate deficit of ∼20 mm yr−1, implies that ∼1.8 m of unrelieved plate slip has accrued since the segment last ruptured in 1932, sufficient for an M ∼ 8.0 earthquake

Co-Seismic and Post-Seismic deformation for the 1995 Colima–Jalisco and 2003 Tecoman thrust earthquakes, Mexico subduction zone, ́ from modelling of GPS data

We invert ∼25 yr of campaign and continuous Global Positioning System daily positions at 62 sites in southwestern Mexico to estimate co-seismic and post-seismic afterslip solutions for the 1995 Mw = 8.0 Colima–Jalisco and the 2003 Mw = 7.5 Tecomán earthquakes, and the long-term velocity of each GPS site. Estimates of the viscoelastic effects of both earthquakes from a 3-D model with an elastic crust and subducting slab, and linear Maxwell viscoelastic mantle are used to correct the GPS position time-series prior to our time-dependent inversions. The preferred model, which optimizes the fit to data from several years of rapid post-seismic deformation after the larger 1995 earthquake, has a mantle Maxwell time of 15 yr (viscosity of 2 × 1019 Pa s), although upper-mantle viscosities as low as 5 × 1018 Pa s cannot be excluded. Our geodetic slip solutions for both earthquakes agree well with previous estimates derived from seismic data or via static co-seismic offset modelling. The afterslip solutions for both earthquakes suggest that most afterslip coincided with the rupture areas or occurred farther downdip and had cumulative moments similar to or larger than the co-seismic moments. Afterslip thus appears to relieve significant stress along the Rivera plate subduction interface, including the area of the interface between a region of deep non-volcanic tremor and the shallower seismogenic zone. We compare the locations of the seismogenic zone, afterslip and tremor in our study area to those of the neighbouring Guerrero and Oaxaca segments of the Mexico subduction zone. Our newly derived interseismic GPS site velocities, the first for western Mexico that are corrected for the co-seismic and post-seismic effects of the 1995 and 2003 earthquakes, are essential for future estimates of the interseismic subduction interface locking and hence the associated seismic hazard

Large scale observations and strain partitioning analysis in Guatemala from SAR interferometry

The interaction between the Cocos, Caribbean, and North America plates in Central America results in complex deformation mostly accommodated by the sub-parallel Motagua and Polochic left-lateral faults, north-south-trending extensional grabens south of the Motagua Fault, the Middle America subduction zone, and right-lateral faults along the Middle America volcanic arc. Large earthquakes associated with these faults include the destructive 1976 Mw 7.5 earthquake along the Motagua fault and the 2012 Mw 7.5 Champerico subduction thrust earthquake. The most recent GPS-based elastic-kinematic models of the region show that about 80% of the strain accumulation from the North America/Caribbean plates relative motion concentrates on the Motagua fault and 20% across the Polochic fault, with significant internal stretching of the Caribbean plate between Honduras and western Guatemala, a decreasing strike-slip rate from east to west along the volcanic arc, and lateral variations of coupling along the subduction zone. We propose the use of Synthetic Aperture Radar Interferometry (InSAR) to measure slip rates along faults in Guatemala, strain partitioning among them and potential internal deformation within blocks. We analyze Sentinel-1 radar images spanning from 2015 to 2020, from ascending and descending tracks, covering the whole Guatemala region. We use Distributed Scatterers (DS) Interferometry techniques adapted to large Sentinel-1 data sets to better assess and mitigate the various sources of noise. We present the first InSAR-based maps of interseismic velocity for this region, analyze these InSAR results over the whole surface covered by the tracks and along key profiles across main faults for a first comparison with GPS data and the GPS-based block model. The DS results show an overall good agreement with predictions from the GPS-based block model. These InSAR results along with GPS data will be used to refine the block model and estimate the lateral variations of interseismic slip deficit rates along major faults, as well as internal deformation within the western Caribbean plate

GPS constraints on deformation in northern Central America from 1999 to 2017, Part 2: Block rotations and fault slip rates, fault locking and distributed deformation

International audienc