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

Abstract

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 ∼ 105-km-wide crustal block located along the coast of Guerrero and Oaxaca states of Mexico, and is limited by a ∼ 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 • and the rate of 58 mm/year to 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. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

The triple junction of the North America, Cocos, and Caribbean plates. What we know, what we don’t

“…A contradiction arises from the fact that along the CAVA, documented motion, from earthquake focal mechanisms (e.g., Guzmán-Speziale et al, 2005) and GPS (Lyon-Caën et al, 2006;Franco et al, 2012; Álvarez- Ellis et al, 2019;Garnier et al, 2021) is right-lateral, while the northernmost forearc offshore southern Mexico, is flanked by the Tonalá fault, a left-lateral structure (García-Palomares, 1978;Authemayou et al, 2012;Molina-Garza et al, 2015). To complicate matters further, Kazachkina et al (2019;2020) suggest the presence of a Xolapa sliver, located northwest of the Central America forearc, parallel to the Middle America trench, and being displaced to the southeast along the 650-km long Chacalapa fault at a rate of 5.6 to 10 mm/yr (Kazachkina et al, 2019;2020) (Figure 7). The role of these two forearc sliver in the tectonics of the triple junction is still an open question.…”

“…Other strike-slip mechanisms for shallow events (z ≤ 50 km) are found in the gulf of Tehuantepec area, which are probably related to the Isthmus fault (Barrier et al, 1998) (Figure 2). West of 96° W, strikeslip mechanisms for shallow (z ≤ 50 km) earthquakes probably correspond to activity along the Chacalapa (or La Venta-Chacalapa) fault zone (Gaidzik et al, 2016;Kazachkina et al, 2019;2020) (Figure 5).…”

Interplate Slip Rate Variation Between Closely Spaced Earthquakes in Southern Mexico: The 2012 Ometepec and 2018 Pinotepa Nacional Thrust Events

“…3 of 19 component of the subducting slab (Kazachkina et al, 2019(Kazachkina et al, , 2020. Both earthquake swarms and SSEs have been detected at the interface of this fault system in Oaxaca (Fasola et al, 2019).…”

“…Flattening of the slab is likely due to dehydration and rollback that caused a shift in the volcanic arc which lies oblique with an angle of ∼15° with respect to the trench, forming the Trans‐Mexican volcanic belt with very diverse chemical signatures (Ferrari et al., 2012, and references therein; Skinner & Clayton, 2011). Another relevant feature for the regional tectonics consists of a continental left‐lateral 650 km long fault system that extends parallel to the trench that accommodates a significant part of the oblique component of the subducting slab (Kazachkina et al., 2019, 2020). Both earthquake swarms and SSEs have been detected at the interface of this fault system in Oaxaca (Fasola et al., 2019).…”

Active 650-km Long Fault System and Xolapa Sliver in Southern Mexico

“…Analyzing this CMT data subset, the average estimate of V sl ≈ 5.4-6.3 mm/year (see Supplementary Figure A3), which is closer to the V SS values obtained with the GPS. The large dispersion of CMT slip vector angles is apparently related to uncertainties in the CMT catalog, complicated structures of the LVC fault system (Ramírez-Herrera et al, 2018) and the Xolapa sliver, inhomogeneous Co-NA plate interface, variation of the plate coupling (e.g., Kostoglodov and Ponce, 1994), and more complicated than just a simple friction rheology of the fault (Kazachkina et al, 2019). Furthermore, observed dispersion is partially related to the increase of the Co-NA convergence velocity southeastward along the MAT.…”