S-Wave Velocities of the Lithosphere–Asthenosphere System in the Caribbean Region

Abstract

An overview of the S-wave velocity (Vs) structural model of the Caribbean with a resolution of 2° 9 2° is presented. New tomographic maps of Rayleigh wave group velocity disper- sion at periods ranging from 10 to 40 s were obtained as a result of the frequency time analysis of seismic signals of more than 400 ray-paths in the region. For each cell of 2° 9 2°, group velocity dispersion curves were determined and extended to 150 s by adding data from a larger scale tomographic study (VDOVIN et al., Geo- phys. J. Int 136:324–340, 1999). Using, as independent a priori information, the available geological and geophysical data of the region, each dispersion curve has been inverted by the ‘‘hedgehog’’ non-linear procedure (VALYUS, Determining seismic profiles from a set of observations (in Russian), Vychislitielnaya Seismologiya 4, 3–14. English translation: Computational Seismology (V.I. Keylis- Borok, ed.) 4:114–118, 1968), in order to compute a set of Vs versus depth models up to 300 km of depth. Because of the non- uniqueness of the solutions for each cell, a local smoothness optimization has been applied to the whole region in order to choose a three-dimensional model of Vs, satisfying this way the Occam’s razor concept. Several known and some new main fea- tures of the Caribbean lithosphere and asthenosphere are shown on these models such as: the west directed subduction zone of the eastern Caribbean region with a clear mantle wedge between the Caribbean lithosphere and the subducted slab; the complex and asymmetric behavior of the crustal and lithospheric thickness in the Cayman ridge; the predominant oceanic crust in the region; the presence of continental type crust in Central America, and the South and North America plates; as well as the fact that the bottom of the upper asthenosphere gets shallower going from west to east

Lithospheric structure below seismic stations in Cuba from the joint inversion of Rayleigh surface waves dispersion and receiver functions

“… The stations are within cells, whose models are defined with adequate resolution, located in the region studied by surface wave tomography (Gonzalez et al 2011). These cellular models are the solutions of the non‐linear inversion of dispersion curves. In each cell, each model differs from the others by at least ±Δ P i for one of the free parameters P i (thickness, V s ), where Δ P i is consistent with the resolving power of the dispersion data, as described by Panza (1981). They allow to minimize the drawbacks intrinsic in the linearization of a non‐linear inverse problem. …”

“… Final results obtained with the four stability tests performed at station MOA. The starting thickness of the layers in the initial models (15 in total) is determined by Gonzalez et al (2011), using in the inversion the ‘incremental step' (IS), calculated on the base of the resolving power of dispersion data. The initial layering has been refined considering sublayers with thickness equal to the corresponding IS divided by 1 (a), 1.25 (b), 1.5 (c) and 2 (d), respectively.…”

“… Location of seismic stations of the National Seismological Service of Cuba (modified from Moreno 2003) and USGS used in this study. Triangles represent the seismic stations used in this study; the dashed line represents the ‘axial fault'; the dotted line represents the ‘Cauto‐Nipe fault'; barbed lines represent plate boundaries (modified from Gonzalez et al 2011). …”

“…Van Der Hilst 1990;Montagner & Kennett 1996) and, more recently, by using the surface wave dispersion analysis (e.g. Vdovin et al 1999;Gonzalez et al 2007Gonzalez et al , 2011. Moreno 2003) and USGS used in this study.…”

Caveats on tomographic images

“…Only in a few cases have formal uncertainties in tomographic results been published (e.g. Panza et al ., ; Brandmayr et al ., ; Corchete and Chourak, , ; Raykova and Panza, ; Gonzales et al ., ). If uncertainties were published routinely, many seismic anomalies interpreted geologically, widely used in undergraduate teaching, and relied upon to support geochemical and geodynamic models, would be recognized as noise or artefacts (Shapiro and Ritzwoller, ).…”