Seismic anisotropy in northern and central Gulf of California region, Mexico, from teleseismic receiver functions and new evidence of possible plate capture

Abstract

[1] We present anisotropic models for the shallow lithosphere in the northern and central Gulf of California obtained from receiver function (RF) analysis. This region has undergone intense plate reorganization over the past 25 Ma that led to the transfer of the plate boundary east of the modern Baja California Peninsula posterior to the cease of the subduction of the Farallon plate beneath the North American plate. Our main interest in modeling the seismic anisotropy is to characterize rock fabric inherited from past and recent tectonism and to provide new information for understanding the tectonic processes involved in the evolution of the local plate boundary. We calculate RFs from teleseismic P waves recorded by the Network of Autonomously Recording Seismographs(NARS)-Baja array, and we stack them in 20°wide back azimuthal bins to enhance coherent information. These RFs yield significant transverse energy whose azimuthal variations are not consistent with that expected for a crust with dipping Moho. Therefore we interpret the conspicuous RFs energy of the transverse component as convincing evidence of anisotropy. We present forward models obtained by fitting the radial and transverse RFs with synthetic seismograms calculated with a reflectivity code. Our analysis suggests substantial variations in the structure of the shallow lithosphere along the Baja California Peninsula and the presence of stalled fragments of the extinct Farallon plate beneath its central part. The results at station NE81 in Sonora are interpreted as frozen crustal anisotropy inherited from Miocene Basin and Range extension, consistent with previous observations of the upper mantle anisotropy beneath this station.

Viscous dissipation, slab melting, and post-subduction volcanism in south-central Baja California, Mexico

“…Their analysis of station NE75 is consistent with that of Obrebski and Castro (2008) and points to the existence of a slab beneath this station at a depth of ~30 km (Fig. 3B).…”

“…Recent seismic studies of the shallow mantle underneath the Baja California Peninsula (Wang et al, 2009(Wang et al, , 2013Long, 2010;Zhang et al, 2007Zhang et al, , 2009Obrebski and Castro, 2008;Persaud et al, 2007) cause us to question the formation mechanics of shallow slab gaps and/or slab windows (Dickinson, 1997;Benoit et al, 2002;Calmus et al, 2003Calmus et al, , 2011Ferrari, 2004;Pallares et al, 2008). For example, seismic tomography in the Gulf of California clearly shows that there is no tensional gash beneath southcentral Baja California (Wang et al, 2009(Wang et al, , 2013Zhang et al, 2007Zhang et al, , 2009.…”

“…Even though the Rayleigh-wave tomography offers only a fi rst-order picture of the lithospheric structure of Baja California, the remnants of the slab imaged by Wang et al (2009) and Zhang et al (2007, 2009 have been resolved at much higher resolution by Obrebski and Castro (2008) and Persaud et al (2007). Further information about the anisotropic structure of the lithosphere can be obtained through receiver functions (RFs) analysis, and by forward modeling the anisotropic features observed on radial and transverse ground motion components (Levin and Park, 1998).…”

“…3). This anomaly has been interpreted as a slab remnant still attached to the oceanic plate (Persaud et al, 2007;Obrebski and Castro, 2008;Zhang et al, 2007Zhang et al, , 2009; Wang et al, 2009;Long, 2010).…”

The relationship between upper mantle anisotropic structures beneath California, transpression, and absolute plate motions

“…However, in west southern California the effect of the Big Bend causes the plate margin to be much more diffuse than further north. This contrast south to north, across the Big Bend, extends to Baja California where splitting analyses have obtained similar E-W fast directions to those in southern California [Obrebski et al, 2006;Obrebski and Castro, 2008]. We suggest that the mantle flow models [e.g., Becker et al, 2007aBecker et al, , 2007bSilver and Holt, 2002] are unlikely to have a sudden change across the Big Bend, and that the difference is due to the history of the plate tectonic interactions.…”