Comparison between crustal density and velocity variations in southern California

We predict gravity from a three-dimensional V_p model of the upper crust and compare it to the observed isostatic residual gravity field. In general this comparison shows that the isostatic residual gravity field reflects the density variations in the upper to middle crust. Both data sets show similar density variations for the upper crust in areas such as the Peninsular Ranges and the Los Angeles basin. Both show similar variations across major faults, such as the San Andreas and Garlock faults in the Mojave Desert. The difference between the two data sets in regions such as the Salton Trough, the Eastern California Shear Zone, and the eastern Ventura basin (where depth to Moho is <30 km), however, suggests high-density middle to lower crust beneath these regions. Hence the joint interpretation of these data sets improves the depth constraints of crustal density variations

Ground magnetic studies along a regional seismic-reflection profile across Bare Mountain, Crater Flat and Yucca Mountain, Nevada

Ground magnetic data were collected along a 26-km-long regional seismic-reflection profile in southwest Nevada that starts in the Amargosa Desert, crosses Bare Mountain, Crater Flat and Yucca Mountain, and ends in Midway Valley. Parallel ground magnetic profiles were also collected about 100 m to either side of the western half of the seismic-reflection line. The magnetic data indicate that the eastern half of Crater Flat is characterized by closely-spaced faulting (1--2 km) in contrast to the western half of Crater Flat. Modeling of the data indicates that the Topopah Spring Tuff is offset about 250 m on the Solitario Canyon fault and about 50 m on the Ghost Dance fault. These estimates of fault offset are consistent with seismic-reflection data and geologic mapping. A broad magnetic high of about 500--600 nT is centered over Crater Flat. Modeling of the magnetic data indicates that the source of this high is not thickening and doming of the Bullfrog Tuff, but more likely lies below the Bullfrog Tuff. Possible source lithologies for this magnetic high include altered argillite of the Eleana Formation, Cretaceous or Tertiary intrusions, and mafic sills

Gravity and magnetic investigations of the Ghost Dance and Solitario Canyon faults, Yucca Mountain, Nevada

Ground magnetic and gravity data collected along traverses across the Ghost Dance and Solitario Canyon faults on the eastern and western flanks, respectively, of Yucca Mountain in southwest Nevada are interpreted. These data were collected as part of an effort to evaluate faulting in the vicinity of a potential nuclear waste repository at Yucca Mountain. Gravity and magnetic data and models along traverses across the Ghost Dance and Solitario Canyon faults show prominent anomalies associated with known faults and reveal a number of possible concealed faults beneath the eastern flank of Yucca Mountain. The central part of the eastern flank of Yucca Mountain is characterized by several small amplitude anomalies that probably reflect small scale faulting

Organic residue analysis of Egyptian votive mummies and their research potential

YesVast numbers of votive mummies were produced in Egypt during the Late Pharaonic, Ptolemaic, and Roman periods. Although millions remain in situ, many were removed and have ultimately entered museum collections around the world. There they have often languished as uncomfortable reminders of antiquarian practices with little information available to enhance their value as artefacts worthy of conservation or display. A multi-disciplinary research project, based at the University of Manchester, is currently redressing these issues. One recent aspect of this work has been the characterization of natural products employed in the mummification of votive bundles. Using gas chromatography–mass spectrometry and the well-established biomarker approach, analysis of 24 samples from 17 mummy bundles has demonstrated the presence of oils/fats, natural waxes, petroleum products, resinous exudates, and essential oils. These results confirm the range of organic materials employed in embalming and augment our understanding of the treatment of votives. In this first systematic initiative of its kind, initial findings point to possible trends in body treatment practices in relation to chronology, geography, and changes in ideology which will be investigated as the study progresses. Detailed knowledge of the substances used on individual bundles has also served to enhance their value as display items and aid in their conservation.RCB is supported by a PhD studentship from the Art and Humanities Research Council (43019R00209). L.M. and S.A.W. are supported by a Leverhulme Trust Research Project Award (RPG-2013-143)

Upper Crustal Structure from the Santa Monica Mountains to the Sierra Nevada, Southern California: Tomographic Results from the Los Angeles Regional Seismic Experiment, Phase II (LARSE II)

In 1999, the U.S. Geological Survey and the Southern California Earthquake Center (SCEC) collected refraction and low-fold reflection data along a 150-km-long corridor extending from the Santa Monica Mountains northward to the Sierra Nevada. This profile was part of the second phase of the Los Angeles Region Seismic Experiment (LARSE II). Chief imaging targets included sedimentary basins beneath the San Fernando and Santa Clarita Valleys and the deep structure of major faults along the transect, including causative faults for the 1971 M 6.7 San Fernando and 1994 M 6.7 Northridge earthquakes, the San Gabriel Fault, and the San Andreas Fault. Tomographic modeling of first arrivals using the methods of Hole (1992) and Lutter et al. (1999) produces velocity models that are similar to each other and are well resolved to depths of 5-7.5 km. These models, together with oil-test well data and independent forward modeling of LARSE II refraction data, suggest that regions of relatively low velocity and high velocity gradient in the San Fernando Valley and the northern Santa Clarita Valley (north of the San Gabriel Fault) correspond to Cenozoic sedimentary basin fill and reach maximum depths along the profile of ∼4.3 km and >3 km, respectively. The Antelope Valley, within the western Mojave Desert, is also underlain by low-velocity, high-gradient sedimentary fill to an interpreted maximum depth of ∼2.4 km. Below depths of ∼2 km, velocities of basement rocks in the Santa Monica Mountains and the central Transverse Ranges vary between 5.5 and 6.0 km/sec, but in the Mojave Desert, basement rocks vary in velocity between 5.25 and 6.25 km/sec. The San Andreas Fault separates differing velocity structures of the central Transverse Ranges and Mojave Desert. A weak low-velocity zone is centered approximately on the north-dipping aftershock zone of the 1971 San Fernando earthquake and possibly along the deep projection of the San Gabriel Fault. Modeling of gravity data, using densities inferred from the velocity model, indicates that different velocity-density relationships hold for both sedimentary and basement rocks as one crosses the San Andreas Fault. The LARSE II velocity model can now be used to improve the SCEC Community Velocity Model, which is used to calculate seismic amplitudes for large scenario earthquakes