Incorporating teleseismic tomography data into models of upper mantle slab geometry
Earthquake-based models of slab geometry are limited by the distribution of earthquakes within a subducting slab, which is often heterogeneous. The fast seismic velocity signature of slabs in tomography studies is independent of the distribution of earthquakes within the slab, providing a critical constraint on slab geometry when earthquakes are absent. In order to utilize this constraint, researchers typically hand-contour images of subducting slabs in tomography models, leading to a subjective final slab model. With this paper, we present an automated procedure for extracting slab geometry from teleseismic tomography volumes that limits this subjectivity and provides constraints on the structure of aseismic segments of slabs. This procedure is designed as a complement to earthquake-based slab models rather than as a replacement, which can help to broaden the extent of existing subduction zone geometry databases.
Seismicity in the Nazca and Juan de Fuca/Gorda slabs. (A) Map showing earthquakes deeper than 70 km in South America (NEIC ComCat), with colour scaling to depth. The dashed white line shows the cross-section trace for (C). (B) Map showing earthquakes deeper than 30 km in the Cascadia subduction zone (McCrory et al.2012), with colour scaling to depth. In both maps, insets show the global location of the map and solid white lines indicate plate boundaries (Bird 2003). The white corners indicate the regions used for Fig. 3. (C) A cross-section through tomography model SAM4_P_2017 (Portner et al.2017) with earthquakes overlain. The range of %dVp variations in the colour palette is given in the top right-hand corner of the cross-section. Contours are of 0.0, 0.5 and 1.0%dVp. The solid black line is the Slab1.0 model for reference (Hayes et al.2012). The grey area shades out extrapolated and poorly resolved velocity perturbations in the upper 100 km. In all three panels, transparent white ovals indicate notable gaps in slab seismicity. Note in (C) that while the fast velocity anomaly is continuous, the earthquakes are discontinuous, leading to a misrepresentation of slab geometry by the slab model.
Geophysical Journal International, Volume 215, Issue 1, 1 October 2018, Pages 325–332, https://doi.org/10.1093/gji/ggy279