Deformation associated with sliver transport in Costa Rica: seismic and geodetic observations of the July 2016 Bijagua earthquake sequence

SUMMARY Tectonic slivers form in the overriding plate in regions of oblique subduction. The inner boundaries of the sliver are often poorly defined and can consist of well-defined faults, rotating blocks or diffuse fault systems, which pass through or near the volcanic arc. The Guanacaste Volcanic Arc Sliver (GVAS) as defined by Montero et al., is a segment of the Central American Forearc Sliver, whose inner boundary is the ∼87-km-long Haciendas-Chiripa fault system (HCFS), which is located ∼10 km behind the volcanic arc and consists of strike slip faults and pull apart steps. We characterize the current ground motion on this boundary by combining earthquake locations and focal mechanisms of the 2016 Bijagua earthquake sequence, with the surface ground deformation obtained from Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 satellite. The coseismic stack of interferograms show ∼6 cm of displacement towards the line of sight of the satellite between the Caño Negro fault and the Upala fault, indicating uplift or SE horizontal surface displacement. The largest recorded earthquake of the sequence was Mw 5.4, and the observed deformation is one of the smallest earthquakes yet detected by InSAR in the Central American region. Forward and inverse models show the surface deformation can be partially explained by slip on a single fault, but it can be better explained by slip along two faults linked at depth. The best-fitting model consists of 0.33 m of right lateral slip on the Caño Negro fault and 0.35 m of reverse slip on the Upala fault, forming a positive flower structure. As no reverse seismicity was recorded, we infer the slip on the Upala fault occurred aseismically. Observations of the Bijagua earthquake sequence suggests the forearc sliver boundary is a complex and diffuse fault system. There are localized zones of transpression and transtension and areas where there is no surface expression suggesting the fault system is not yet mature. Although aseismic slip is common on subduction interfaces and mature strike-slip faults, this is the first study to document aseismic slip on a continental tectonic sliver boundary fault.

Activity of crustal faults and the Xolapa sliver motion in Guerrero–Oaxaca forearc of Mexico, from seismic data

Oblique convergent margins often host forearc slivers separated by the subduction interface and a trench parallel strike-slip fault system in the overriding plate. Mexican oblique subduction setting led to the formation of a forearc sliver and accomodation of part of the slip at the bounding system of strike-slip faults. The Xolapa sliver is, on average, a $$\sim 105$$ ∼ 105 -km-wide crustal block located along the coast of Guerrero and Oaxaca states of Mexico, and is limited by a $$\sim 650$$ ∼ 650 -km-long La Venta-Chacalapa fault zone. Two types of datasets, local catalog and Global CMT compilation, are used to estimate the motion of the Xolapa sliver using the rigid block model that describes the phenomenon of slip partitioning. According to the results obtained from local and Global CMT catalogs for selected subduction thrust earthquakes, the forearc sliver moves southeastwards with respect to the fixed North America plate at the rate of 10 ± 1 mm/year and 5.6 ± 0.8 mm/year, respectively. These velocities in general agree with the values obtained from long-term GPS observations (5–6 mm/year). The origin of the inconsistency between local and teleseismic estimates is attributed to a difference in the double couple focal mechanism parameters for two types of datasets. Convergence obliquity changes from $$10.42{^\circ }$$ 10.42 ∘ and the rate of 58 mm/year to $$13.29{^\circ }$$ 13.29 ∘ at the rate of 68 mm/year along the Guerrero and Oaxaca coast increasing from northwest to southeast; therefore, the Xolapa sliver is supposed to be stretched. However, the slip vector azimuths of thrust subduction earthquakes tend to approach plate convergence vectors southeastwards along the coast; so, we assume that this may produce the forearc block compression.

Geomorphic analysis of transient landscapes in the Sierra Madre de Chiapas and Maya Mountains (northern Central America): implications for the North American–Caribbean–Cocos plate boundary

We use a geomorphic approach in order to unravel the recent evolution of the diffuse triple junction between the North American, Caribbean, and Cocos plates in northern Central America. We intend to characterize and understand the complex tectonic setting that produced an intricate pattern of landscapes using tectonic geomorphology, as well as available geological and geophysical data. We classify regions with specific relief characteristics and highlight uplifted relict landscapes in northern Central America. We also analyze the drainage network from the Sierra Madre de Chiapas and Maya Mountains in order to extract information about potential vertical displacements. Our results suggest that most of the landscapes of the Sierra Madre de Chiapas and Maya Mountains are in a transient stage. Topographic profiles and morphometric maps highlight elevated relict surfaces that are characterized by a low-amplitude relief. The river longitudinal profiles display upper reaches witnessing these relict landscapes. Lower reaches adjust to new base-level conditions and are characterized by multiple knickpoints. These results backed by published GPS and seismotectonic data allow us to refine and extend existing geodynamic models of the triple junction. Relict landscapes are delimited by faults and thus result from a tectonic control. The topography of the Sierra Madre de Chiapas evolved as the result of (1) the inland migration of deformation related to the coupling between the Chiapas Massif and the Cocos forearc sliver and (2) the compression along the northern tip of the Central American volcanic arc. Although most of the shortening between the Cocos forearc sliver and the North American Plate is accommodated within the Sierra de Chiapas and Sierra de los Cuchumatanes, a small part may be still transmitted to the Maya Mountains and the Belize margin through a "rigid" Petén Basin.