Joint inversion of Rayleigh wave phase velocity and ellipticity using USArray: Constraining velocity and density structure in the upper crust

Rayleigh wave ellipticity, or H/V ratio, observed on the surface is particularly sensitive to shallow earth structure. In this study, we jointly invert measurements of Rayleigh wave H/V ratio and phase velocity between 24–100 and 8–100 sec period, respectively, for crust and upper mantle structure beneath more than 1000 USArray stations covering the western United States. Upper crustal structure, in particular, is better constrained by the joint inversion compared to inversions based on phase velocities alone. In addition to imaging Vs structure, we show that the joint inversion can be used to constrain Vp/Vs and density in the upper crust. New images of uppermost crustal structure (<3 km depth) are in excellent agreement with known surface features, with pronounced low Vs, low density, and high Vp/Vs anomalies imaged in the locations of several major sedimentary basins including the Williston, Powder River, Green River, Denver, and San Juan basins. These results demonstrate not only the consistency of broadband H/V ratios and phase velocity measurements, but also that their complementary sensitivities have the potential to resolve density and Vp/Vs variations

3-D crustal structure of the western United States: application of Rayleigh-wave ellipticity extracted from noise cross-correlations

We present a new 3-D seismic model of the western United States crust derived from a joint inversion of Rayleigh-wave phase velocity and ellipticity measurements using periods from 8 to 100 s. Improved constraints on upper-crustal structure result from use of short-period Rayleigh-wave ellipticity, or Rayleigh-wave H/V (horizontal to vertical) amplitude ratios, measurements determined using multicomponent ambient noise cross-correlations. To retain the amplitude ratio information between vertical and horizontal components, for each station, we perform daily noise pre-processing (temporal normalization and spectrum whitening) simultaneously for all three components. For each station pair, amplitude measurements between cross-correlations of different components (radial–radial, radial–vertical, vertical–radial and vertical–vertical) are then used to determine the Rayleigh-wave H/V ratios at the two station locations. We use all EarthScope/USArray Tranportable Array data available between 2007 January and 2011 June to determine the Rayleigh-wave H/V ratios and their uncertainties at all station locations and construct new Rayleigh-wave H/V ratio maps in the western United States between periods of 8 and 24 s. Combined with previous longer period earthquake Rayleigh-wave H/V ratio measurements and Rayleigh-wave phase velocity measurements from both ambient noise and earthquakes, we invert for a new 3-D crustal and upper-mantle model in the western United States. Correlation between the inverted model and known geological features at all depths suggests good resolution in five crustal layers. Use of short-period Rayleigh-wave H/V ratio measurements based on noise cross-correlation enables resolution of distinct near surface features such as the Columbia River Basalt flows, which overlie a thick sedimentary basin

Extracting seismic core phases with array interferometry

Seismic body waves that sample Earth's core are indispensable for studying the most remote regions of the planet. Traditional core phase studies rely on well-defined earthquake signals, which are spatially and temporally limited. We show that, by stacking ambient-noise cross-correlations between USArray seismometers, body wave phases reflected off the outer core (ScS), and twice refracted through the inner core (PKIKP^2) can be clearly extracted. Temporal correlation between the amplitude of these core phases and global seismicity suggests that the signals originate from distant earthquakes and emerge due to array interferometry. Similar results from a seismic array in New Zealand demonstrate that our approach is applicable in other regions and with fewer station pairs. Extraction of core phases by interferometry can significantly improve the spatial sampling of the deep Earth because the technique can be applied anywhere broadband seismic arrays exist

Multiple fluvial processes detected by riverside seismic and infrasound monitoring of a controlled flood in the Grand Canyon

As rivers transport water and sediment across Earth's surface, they radiate elastic and acoustic waves. We use seismic and infrasound observations during a controlled flood experiment (CFE) in the Grand Canyon to show that three types of fluvial processes can be monitored from outside the channel. First, bed-load transport under conditions of evolving bed mobility is identified as the dominant seismic source between 15 and 45 Hz. Two lower-frequency seismic bands also excited by the CFE exhibited greater power increases and are consistent with source processes related to fluid rather than sediment transport. The second fluvial seismic source is inferred to be fluid tractions on the rough riverbed, which drive the maximum seismic power increase at 0.73 Hz, but do not excite infrasound. Waves at the fluid-air interface are suggested as a third source, which generates a common 6–7 Hz peak in seismic and infrasound responses to the CFE

Rare earth element fluorocarbonate minerals from the olympic dam Cu-U-Au-Ag deposit, South Australia

Olympic Dam is a world-class breccia-hosted iron-oxide copper-gold-uranium ore deposit located in the Gawler Craton, South Australia. It contains elevated concentrations of rare earth elements (REE) which occur as the REE minerals bastnäsite, synchysite, florencite, monazite, and xenotime. This is the first study to focus on the mineralogy and composition of the most abundant REE mineral at Olympic Dam, bastnäsite, and subordinate synchysite. The sample suite extends across the deposit and represents different sulfide mineralization styles (chalcopyrite-bornite and bornite-chalcocite) and breccias of various types, ranging from those dominated by clasts of granite, dykes, and hematite. The REE-fluorocarbonates (bastnäsite and synchysite) typically occur as fine-grained (<50 m) disseminations in Cu-Fe-sulfides and gangue minerals, and also within breccia matrix. They are also locally concentrated within macroscopic REE-mineral-rich pockets at various locations across the deposit. Such coarse-grained samples formed the primary target of this study. Three general textural groups of bastnäsite are recognized: matrix (further divided into disseminated, fine-grained, and stubby types), irregular (sulfide-associated), and clast replacement. Textures are largely driven by the specific location and prevailing mineral assemblage, with morphology and grain size often controlled by the associated minerals (hematite, sulfides). Major element concentration data reveal limited compositional variation among the REE-fluorocarbonates; all are Ce-dominant. Subtle compositional differences among REE-fluorocarbonates define a spectrum from relatively La-enriched to (Ce + Nd)-enriched phases. Granite-derived hydrothermal fluids were the likely source of F in the REE-fluorocarbonates, as well as some of the CO₂, which may also have been contributed by associated mafic-ultramafic magmatism. However, transport of REE by Cl-ligands is the most likely scenario. Stubby bastnäsite and synchysite may have formed earlier, coincident with hydrothermal alteration of granite releasing Ca from feldspars. Other categories of bastnäsite, notably those co-existing with sulfides, and reaching the top of the IOCG mineralization at Olympic Dam (chalcocite + bornite zone) are relatively younger. Such an interpretation is concordant with subtle changes in the REE patterns for the different categories. The common association of bastnäsite and fluorite throughout the deposit is typical of the hematite breccias and can be deposited from neutral, slightly acidic fluids (sericite stability) at T ≈ 300 °C.Danielle S. Schmandt, Nigel J. Cook, Cristiana L. Ciobanu, Kathy Ehrig, Benjamin P. Wade, Sarah Gilbert and Vadim S. Kamenetsk

Opportunities and challenges for data physicalization

Physical representations of data have existed for thousands of years. Yet it is now that advances in digital fabrication, actuated tangible interfaces, and shape-changing displays are spurring an emerging area of research that we call Data Physicalization. It aims to help people explore, understand, and communicate data using computer-supported physical data representations. We call these representations physicalizations, analogously to visualizations -- their purely visual counterpart. In this article, we go beyond the focused research questions addressed so far by delineating the research area, synthesizing its open challenges and laying out a research agenda

Characterization of rockfalls from seismic signal: insights from laboratory experiments

International audienceThe seismic signals generated by rockfalls can provide information on their dynamics and location. However, the lack of field observations makes it difficult to establish clear relationships between the characteristics of the signal and the source. In this study, scaling laws are derived from analytical impact models to relate the mass and the speed of an individual impactor to the radiated elastic energy and the frequency content of the emitted seismic signal. It appears that the radiated elastic energy and frequencies decrease when the impact is viscoelastic or elasto-plastic compared to the case of an elastic impact. The scaling laws are validated with laboratory experiments of impacts of beads and gravels on smooth thin plates and rough thick blocks. Regardless of the involved materials, the masses and speeds of the impactors are retrieved from seismic measurements within afactor of 3. A quantitative energy budget of the impacts is established. On smooth thin plates, the lost energy is either radiated in elastic waves or dissipated in viscoelasticity when the impactor is large or small with respect to the plate thickness, respectively. In contrast, on rough thick blocks, theelastic energy radiation represents less than 5% of the lost energy. Most of the energy is lost in plastic deformation or rotation modes of the bead owingto surface roughness. Finally, we estimate the elastic energy radiated during field scale rockfalls experiments. This energy is shown to be proportional to the boulder mass, in agreement with the theoretical scaling laws

Designing for emergence and innovation: Redesigning design

We reveal the surprising and counterintuitive truth that the design process, in and of itself, is not always on the forefront of innovation. Design is a necessary but not a sufficient condition for the success of new products and services. We intuitively sense a connection between innovative design and emergence. The nature of design, emergence and innovation to understand their interrelationships and interdependencies is examined. We propose that design must harness the process of emergence; for it is only through the bottom-up and massively iterative unfolding of emergence that new and improved products and services are successfully refined, introduced and diffused into the marketplace. The relationships among design, emergence and innovation are developed. What designers can learn from nature about emergence and evolution that will impact the design process is explored. We examine the roles that design and emergence play in innovation. How innovative organizations can incorporate emergence into their design process is explored. We demarcate the boundary between invention and innovation. We also articulate the similarities and differences of design and emergence. We then develop the following three hypotheses: Hypothesis 1: “An innovative design is an emergent design.” Hypothesis 2: “A homeostatic relationship between design and emergence is a required condition for innovation.”Hypothesis 3: “Since design is a cultural activity and culture is an emergent phenomenon, it follows that design leading to innovation is also an emergent phenomenon” We provide a number of examples of how design and emergence have worked together and led to innovation. Examples include the tool making of early man; the evolutionary chain of the six languages speech, writing, math, science, computing and the Internet; the Gutenberg printing press and techniques of collaborative filtering associated with the Internet. We close by describing the relationship between human and naturally “designed” systems and the notion a key element of a design is its purpose as is the case with a living organism