Research into archaea will not achieve its full potential until systems are in place to carry out genetics and biochemistry in the same species. Haloferax volcanii is widely regarded as the best-equipped organism for archaeal genetics, but the development of tools for the expression and purification of H. volcanii proteins has been neglected. We have developed a series of plasmid vectors and host strains for conditional overexpression of halophilic proteins in H. volcanii. The plasmids feature the tryptophan-inducible p.tnaA promoter and a 6؋His tag for protein purification by metal affinity chromatography. Purification is facilitated by host strains, where pitA is replaced by the ortholog from Natronomonas pharaonis. The latter lacks the histidine-rich linker region found in H. volcanii PitA and does not copurify with His-tagged recombinant proteins. We also deleted the mrr restriction endonuclease gene, thereby allowing direct transformation without the need to passage DNA through an Escherichia coli dam mutant.

We use ambient-noise tomography to improve CVM-H11.9, a community velocity model of southern California. Our new 3-D shear-velocity model with 0:05 x 0:05 lateral and 1 km vertical blocks reveals new structure beneath the San Andreas Fault (SAF), Peninsular Ranges batholith (PRB), southern Sierra Nevada batholith (SNB), and the Salton Trough (ST). We use 4 years of data recorded on 849 broadband stations, vastly more than previous studies and including our own broadband Salton Seismic Imaging Project, a 40 station transect across the ST, as well as other campaign stations in both Mexico and the United States. Mean lower crust and upper mantle wave speeds (3.6 km/s at 20 km, 4.2 km/s at 40 km) are low by global standards. Across the SAF, southeast of San Gorgonio Pass, we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the Moho. Beneath the western PRB and westernmost southern SNB, we observe relatively high shear velocities (!3.8 km/s) in the lower crust that we interpret as the mafic roots of the overlying arc. Relatively high-velocity upper mantle (up to $4.5 km/s) may be part of the intact arc, or possibly a remnant of the Farallon plate. Beneath the ST, we observe zones of low shearvelocity in the lower crust and upper mantle which permit up to $4.5% melt in the lower crust and up to $6% melt in the upper mantle, depending on the assumed composition and pore geometry. Our results preclude the existence of older continental crust beneath the ST and support the creation of new crust beneath the ST.

We present new shear-wave splitting data showing systematic lateral variations in upper-mantle anisotropy across the plate boundary in southernmost California (USA). Beneath the Penin sular Ranges batholith, fast polarization directions parallel the direction of former Farallon subduction, suggestive of a slab remnant. Near the eastern edge of the batholith, across the Elsinore fault, fast polarization directions change rapidly to align with the direction of San Andreas fault shear. We infer that the Elsinore fault penetrates the entire lithosphere and may represent a future localization of the plate boundary that is migrating west from the San Andreas fault. Beneath the Salton Trough and the Chocolate Mountains region, large splitting times, despite a very thin lithosphere, imply vertical melt pockets in the uppermost mantle aligned in the shear direction. Largest splitting times, ~1.2 s, are seen closest to the Sand Hills fault that projects southeast from the San Andreas fault. Further east, in the southern Basin and Range province, fast directions align with North America absolute plate motion. INTRODUCTION Analysis of teleseismic shear-wave splitting is a standard tool for studying upper-mantle anisotropy created by strain-induced lattice-preferred orientation of minerals or by preferentially oriented melt-filled inclusions, and hence also for studying changes in rheology (e.g., Savage, 1999, and references therein). A shear wave passing through an anisotropic medium splits into slow and fast waves with orthogonal polarizations. Two splitting parameters (polarization, j, and delay time, dt) provide a direct estimate of the axis and magnitude of the anisotropy for simple cases and show systematic variations with back-azimuth to the source earthquake in more complex scenarios. Despite Southern California's (USA) complex tectonic history and active plate boundary oriented northwest-southeast (e.g., Dickinson, 2008, 2009; Barak et al., 2015) (Fig. 1A), previous studies of shearwave splitting in Southern California (e.g., Polet and Kanamori, 2002; Kosarian et al., 2011) show a nearly uniform fast axis of anisotropy oriented approximately west-east (Fig. 1C). This has been interpreted as due to inherited North America plate motion (Kosarian et al., 2011), prelate Cenozoic compression (Polet and Kanamori, 2002), or mantle flow around the southern edge of the subducting Gorda slab (Zandt and Humphreys, 2008). The same general west-east pattern continues to the southern tip of Baja California (Mexico), west and east of the Gulf of California rift margins (Long, 2010; Fig. 1A). Recent three-dimensional (3-D) tomographic inversion of shear-wave splitting measurements, despite the previous scarcity of data in southernmost California, has begun to suggest complicated structure, including a northwest fast axis of anisotropy in the Salton Trough (ST) (Monteiller and Chevrot, 2011) where Gulf of California ocean spreading propagates into continental crust along the San Andreas fault (Elders et al., 1972). Here we analyze sh...

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