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As North America collided with Africa to form Pangea during the Alleghanian orogeny, crystalline and sedimentary rocks in the southeastern United States were thrust forelandward along the Appalachian décollement. We examined Ps receiver functions to better constrain the kinematics of this prominent subsurface structure. From Southeastern Suture of the Appalachian Margin Experiment (SESAME) and other EarthScope stations on the Blue Ridge–Piedmont crystalline megathrust, we find large arrivals from a 5–10-km-deep converter. We argue that a strong contrast in dipping anisotropic foliation occurs at the subhorizontal Appalachian décollement, and propose that such a geometry may be typical for décollement structures. Conversion polarity flips can be explained by an east-dipping foliation, but this orientation is at odds with the overlying northeast-trending surface tectonic grain. We suggest that prior to late Alleghanian northwest-directed head-on collision, the Appalachian décollement accommodated early Alleghanian west-vergence, independent of the overlying Blue Ridge–Piedmont structural inheritance. The geophysical expression of dipping anisotropic foliation provides a powerful tool for investigating subsurface kinematics, especially where they are obscured by overlying fabric, to disentangle the tectonic complexities that embody oblique collisional orogens.

Few guidelines have focused on the care delivered after return of spontaneous circulation (ROSC). Post ROSC best practice guidelines lack clarity about important tasks to accomplish in the first hours after ROSC.We conducted a retrospective cohort analysis of adults who had suffered an in hospital cardiac arrest (IHCA) with ROSC over a two-year period to determine the completion rate of critical tasks in the immediate post-ROSC period: ECG within one hour, ABG within one hour, physician documentation within six hours, and surrogate communication within six hours.In the 113 reviewed cases, there was significant variance between completion of all four (19.4%), three (35.3%), two (32.7%), one (20.6%) and none (1.7%) of these critical post ROSC tasks. We observed that 62.8% of IHCA with ROSC had an ECG obtained within one hour of ROSC. The rate of obtaining an ABG within one hour of ROSC was 76.9%. 49.5% of cases had physician documentation of the resuscitation within six hours of ROSC. The rate of documenting surrogate communication within six hours of ROSC was 69.9%.Our study demonstrated that the completion rates of critical tasks in the post ROSC setting were suboptimal within our patient cohort. This provides a baseline for the development of future best practice guidelines and clinical decision-making aids for post ROSC care after IHCA. This can lead to future research in coupling specific care tasks to post ROSC patient outcomes.

Although dormancy is thought to play a key role in the metastasis of breast tumor cells to the brain, our knowledge of the molecular mechanisms regulating disseminated tumor cell (DTC) dormancy in this organ is limited. Here using serial intravital imaging of dormant and metastatic triple-negative breast cancer lines, we identify escape from the single-cell or micrometastatic state as the rate-limiting step towards brain metastasis. We show that every DTC occupies a vascular niche, with quiescent DTCs residing on astrocyte endfeet. At these sites, astrocyte-deposited laminin-211 drives DTC quiescence by inducing the dystroglycan receptor to associate with yes-associated protein, thereby sequestering it from the nucleus and preventing its prometastatic functions. These findings identify a brain-specific mechanism of DTC dormancy and highlight the need for a more thorough understanding of tumor dormancy to develop therapeutic approaches that prevent brain metastasis.

The composition of the crust is one of the most uncertain and controversial components of continental estimates due to (1) limited direct access and (2) inconsistent indirect assessments. Here we show that by combining high-resolution shear velocity (Vs) models with newly measured with newly measured ratio of compressional wave velocity (Vp) and Vs, or Vp/Vs ratio, for the crystalline crust, a 3-D composition (SiO2 wt%) model of the continental crust can be derived with uncertainty estimates. Comparing the model with local xenolith data shows consistency at mid and lower crustal depths. The spatial patterns in bulk SiO2 content correlate with major geological provinces, including the footprints of Cenozoic and Mesozoic mafic volcanism in the western U.S., and offer new insight into the composition and evolution of the continental U.S.

Azimuthal variations in receiver function conversions can image lithospheric structural contrasts and anisotropic fabrics that together compose tectonic grain. We apply this method to data from EarthScope Transportable Array in Alaska and additional stations across the northern Cordillera. The best-resolved quantities are the strike and depth of dipping fabric contrasts or interfaces. We find a strong geographic gradient in such anomalies, with large amplitudes extending inboard from the present-day subduction margin, the Aleutian arc, and an influence of flat-slab subduction of the Yakutat microplate north of the Denali fault. An east–west band across interior Alaska shows low-amplitude crustal anomalies. Anomaly amplitudes correlate with structural intensity (density of aligned geological elements), but are the highest in areas of strong Cenozoic deformation, raising the question of an influence of current stress state. Imaged subsurface strikes show alignment with surface structures. We see concentric strikes around arc volcanoes implying dipping magmatic structures and fabric into the middle crust. Regions with present-day weaker deformation show lower anomaly amplitudes but structurally aligned strikes, suggesting pre-Cenozoic fabrics may have been overprinted or otherwise modified. We observe general coherence of the signal across the brittle-plastic transition. Imaged crustal fabrics are aligned with major faults and shear zones, whereas intrafault blocks show imaged strikes both parallel to and at high angles to major block-bounding faults. High-angle strikes are subparallel to neotectonic deformation, seismicity, fault lineaments, and prominent metallogenic belts, possibly due to overprinting and/or co-evolution with fault-parallel fabrics. We suggest that the underlying tectonic grain in the northern Cordillera is broadly distributed rather than strongly localized. Receiver functions thus reveal key information about the nature and continuity of tectonic fabrics at depth and can provide unique insights into the deformation history and distribution of regional strain in complex orogenic belts.

We present a high-resolution P-wave azimuthally anisotropic velocity model for the upper and middle crust beneath southern California by a novel adjoint-state traveltime tomography technique. Our model reveals significant anisotropy variations between tectonic blocks that clearly reflect both past and current plate boundary deformation. In the shallow crust, seismic anisotropy is mostly controlled by the preferred alignment of microcracks related to the present N-S compressive stress; while at deeper depths (> ∼6 km), seismic anisotropy mainly records paleofabrics formed during the long-lived Farallon subduction and later extension that have not been fully reset by the present transform motion. Interestingly, our model demonstrates distinct fast axes beneath the western Transverse Ranges from its neighboring blocks, probably reflecting the large-scale vertical axis clockwise rotation of the block. In addition, we identify layered structures with distinct anisotropy features beneath the Salton Trough, which could be a result of the current transtension. Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version This study was founded by the National Research Foundation Singapore and the Singapore Ministry of Education under the Research Centers of Excellence Initiative (04MNS001913A620 and 04MNS001953A620). PT was also supported by MOE AcRF Tier-2 (04MNP002073C230) and Tier-1 Grant (04MNP000559C230).

Orthopyroxene is the second most abundant mineral in the upper mantle and, like olivine, can form crystallographic preferred orientations (CPO) during mantle deformation that may influence mantle seismic anisotropy. Here we use a compilation of 21 peridotites in which both olivine and orthopyroxene CPOs are preserved to document the range of orthopyroxene CPO types and to explore their effects on seismic anisotropy of peridotites. In addition to four previously published orthopyroxene CPO types, this study establishes three new CPO types, two of which result in orthopyroxene fast axes aligned parallel to the lineation and the direction of mantle shear/flow. We calculate bulk elastic tensors for each sample from the measured olivine and orthopyroxene CPOs, and use those in turn to calculate Vp and Vs velocities and anisotropy percentages. In order to explore the relative influence of olivine and orthopyroxene on anisotropy, these properties were calculated for a range of possible modal percentages, from 100% olivine to 100% orthopyroxene. While the effect of orthopyroxene CPO appears to be a negligible influence on the orientation of bulk seismic fast axes, the presence of increasing orthopyroxene decreases the anisotropic signal overall. However, at very low olivine modal percentages, olivine and orthopyroxene can be mutually destructive, where the addition of olivine to a mostly orthopyroxene rock can actually decrease anisotropy., Tectonophysics, 814, ISSN:0040-1951, ISSN:1879-3266

BACKGROUND: Evidence is accumulating that coronavirus disease 2019 increases the risk of hospitalization and mechanical ventilation in pregnant patients and for preterm delivery. However, the impact on maternal mortality and whether morbidity is differentially affected by disease severity at delivery and trimester of infection are unknown. OBJECTIVE: This study aimed to describe disease severity and outcomes of severe acute respiratory syndrome coronavirus 2 infections in pregnancy across the Washington State, including pregnancy complications and outcomes, hospitalization, and case fatality. STUDY DESIGN: Pregnant patients with a polymerase chain reaction-confirmed severe acute respiratory syndrome coronavirus 2 infection between March 1, 2020, and June 30, 2020, were identified in a multicenter retrospective cohort study from 35 sites in Washington State. Sites captured 61% of annual state deliveries. Case-fatality rates in pregnancy were compared with coronavirus disease 2019 fatality rates in similarly aged adults in Washington State using rate ratios and rate differences. Maternal and neonatal outcomes were compared by trimester of infection and disease severity at the time of delivery. RESULTS: The principal study findings were as follows: (1) among 240 pregnant patients in Washington State with severe acute respiratory syndrome coronavirus 2 infections, 1 in 11 developed severe or critical disease, 1 in 10 were hospitalized for coronavirus disease 2019, and 1 in 80 died; (2) the coronavirus disease 2019-associated hospitalization rate was 3.5-fold higher than in similarly aged adults in Washington State (10.0% vs 2.8%; rate ratio, 3.5; 95% confidence interval, 2.3-5.3); (3) pregnant patients hospitalized for a respiratory concern were more likely to have a comorbidity or underlying conditions including asthma, hypertension, type 2 diabetes mellitus, autoimmune disease, and class III obesity; (4) 3 maternal deaths (1.3%) were attributed to coronavirus disease 2019 for a maternal mortality rate of 1250 of 100,000 pregnancies (95% confidence interval, 257-3653); (5) the coronavirus disease 2019 case fatality in pregnancy was a significant 13.6-fold (95% confidence interval, 2.7-43.6) higher in pregnant patients than in similarly aged individuals in Washington State with an absolute difference in mortality rate of 1.2% (95% confidence interval, -0.3 to 2.6); and (6) preterm birth was significantly higher among women with severe or critical coronavirus disease 2019 at delivery than for women who had recovered from coronavirus disease 2019 (45.4% severe or critical coronavirus disease 2019 vs 5.2% mild coronavirus disease 2019; P

Plate motions in Southern California have undergone a transition from compressional and extensional regimes to a dominantly strike-slip regime in the Miocene. Strike-slip motion is most easily acco...

TOPIC: Critical Care TYPE: Original Investigations PURPOSE: There are approximately 290,000 in hospital cardiac arrests (IHCA) annually in the United States. Recent evidence suggests that post IHCA outcomes may be more related to post return of spontaneous circulation (ROSC) care than intra cardiac arrest resuscitation. The purpose of this study is to assess the effect of a post ROSC checklist on variability care after IHCA with ROSC. METHODS: We performed a retrospective analysis of inpatient adults with an IHCA with ROSC at Harborview Medical Center (HMC) between 1/1/2018-12/31/2019. Included patients had an ICHA on an acute care or intensive care unit (ICU), were over the age of 18, and not placed on extra corporeal membrane oxygenation. IHCA was defined as cardiopulmonary resuscitation delivered by healthcare personnel. Demographics, clinical variables, and process of care metrics were abstracted from the electronic medical record. We then developed a post ROSC checklist utilizing our retrospective data and expert opinion. The checklist was implemented at HMC in January 2020. We conducted a follow up analysis of post-ROSC care since checklist implementation between 1/1/2020-12/31/2020. Pre and post implementation results were compared. RESULTS: 125 IHCA were included in the pre implementation cohort and 47 were included in the post implementation cohort. The mean age of the pre implementation cohort was 55.1 versus 55.9 post implementation. Women comprised 36.8% in the pre implementation cohort and 37.0% in the post implementation cohort. The rate of obtaining an electrocardiogram within one hour of ROSC was 60.8% prior to checklist implementation, and 76.6% after implementation. The rate of obtaining a formal transthoracic echocardiogram within six hours of ROSC was 32.8% prior to checklist implementation, and 34.0% after implementation. The rate of physician documentation occurring within six hours of ROSC was 47.0% prior to checklist implementation, and 85.1% after implementation. The rate of documented notification of family within six hours of ROSC in 67.2% of cases prior to checklist implementation, and 80.8% after implementation. CONCLUSIONS: The introduction of a post ROSC checklist correlated with an increase in obtaining ECGs and completing documentation tasks after IHCA with ROSC at HMC. This study was limited by the small number patients included as well as being a single site study. Confounding circumstances in code blue management related to COVID-19 must be acknowledged. Further research is needed to assess the durability of these findings, and what impact this may have on post IHCA outcomes. CLINICAL IMPLICATIONS: While there will be differences in the management and evaluation of patients who suffer an IHCA, some interventions such as a timely ECG and documentation should be completed with little variance between patients. The use of a checklist decreased the rate of variance, by providing a cognitive aid to guide clinical decisions in a stressful scenario. The use of a post ROSC checklist has the potential to decrease variance in diagnostic and documentation tasks after IHCA. DISCLOSURES: No relevant relationships by David Carlbom, source=Web Response No relevant relationships by Stephen Ferraro, source=Web Response No relevant relationships by Vince Raikhel, source=Web Response No relevant relationships by Vera Schulte, source=Web Response No relevant relationships by James Town, source=Web Response

Background During the early months of the coronavirus disease of 2019 (COVID-19) pandemic, risks to pregnant women of a severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection were uncertain. Pregnant patients can serve as a model for the success of the clinical and public health response during public health emergencies as they are typically in frequent contact with the medical system. Population-based estimates of SARS-CoV-2 infections in pregnancy are unknown due to incomplete ascertainment of pregnancy status or inclusion of only single centers or hospitalized cases. Whether pregnant women were protected by the public health response or through their interactions with obstetrical providers in the early pandemic is poorly understood. Objective(s) To estimate the SARS-CoV-2 infection rate in pregnancy and examine disparities by race/ethnicity and English-language proficiency in Washington State. Study design Pregnant patients with a polymerase chain reaction (PCR)-confirmed severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection diagnosed between March 1-June 30, 2020 were identified within 35 hospitals/clinic systems capturing 61% of annual deliveries in Washington State. Infection rates in pregnancy were estimated overall and by Washington State Accountable Community of Health (ACH) region and cross-sectionally compared to SARS-CoV-2 infection rates in similarly aged adults in Washington State. Race/ethnicity and language used for medical care among the pregnant patients were compared to recent data from Washington State. Results A total of 240 pregnant patients with SARS-CoV-2 infections were identified during the study period with 70.7% from minority racial and ethnic groups. The principal findings in our study are: 1) The SARS-CoV-2 infection rate in pregnancy was 13.9/1,000 deliveries (95% confidence interval [CI], 8.3-23.2) compared to 7.3/1,000 (95%CI 7.2-7.4) in 20-39 year old adults in Washington State (Rate Ratio [RR] 1.7, 95%CI 1.3-2.3), 2) the SARS-CoV-2 infection rate reduced to 11.3/1000 (95%CI 6.3-20.3) when excluding 45 cases of SARS-CoV-2 detected through asymptomatic screening (RR 1.3, 95%CI 0.96-1.9), 3) the proportion of SARS-CoV-2 cases in pregnancy among most non-white racial/ethnic groups was 2-4 fold higher than the race and ethnicity distribution of women in Washington State who delivered live births in 2018, and 5) the proportion of SARS-CoV-2 infected pregnant patients receiving medical care in a non-English language was higher than estimates of limited English proficiency in Washington State (30.4% versus 7.6%). Conclusions The SARS-CoV-2 infection rate in pregnant people was 70% higher than similarly aged adults in Washington State, which could not be completely explained by universal screening at delivery. Pregnant patients from nearly all racial/ethnic minority groups and patients receiving medical care in a non-English language were overrepresented. Pregnant women were not protected from COVID-19 in the early months of the pandemic with the greatest burden of infections occurring in nearly all racial/ethnic minority groups. This data coupled with a broader recognition that pregnancy is a risk factor for severe illness and maternal mortality strongly suggests that pregnant people should be broadly prioritized for COVID-19 vaccine allocation in the U.S. similar to some states.

Rocks in the continental crust are long-lived and have the potential to record a wide span of tectonic history in rock fabric. Mapping rock fabric in situ at depth requires the application of seismic methods. Below depths of microcrack closure seismic anisotropy presumably reflects the shape and crystallographic preferred orientations (CPOs) influenced by deformation processes. Interpretation of seismic observables relevant for anisotropy requires assumptions on the symmetry and orientation of the bulk elastic tensor. We compare commonly made assumptions against a compilation of 95 bulk elastic tensors from laboratory measurements, including electron backscatter diffraction (EBSD) and ultrasound, on crustal rocks. The majority of samples developed fabric at pressures corresponding to mid-lower crustal depths. Tensor symmetry is a function of mineral modal composition, with mica-rich samples trending towards hexagonal symmetry, amphibole-rich samples trending towards an increased orthorhombic symmetry component, and quartz-feldspar-rich samples showing a larger component of lower symmetries. 77% of samples have a best-fit hexagonal tensor with slow-axis symmetry, as opposed to mantle deformation fabric that usually has fast-axis symmetry. The best-fit hexagonal approximation for crustal tensors is not elliptical, but deviates systematically from elliptical symmetry with increasing anisotropy, an observation that affects the magnitude and orientation of anisotropy inferred from receiver function and surface wave observations. We present empirical linear relationships between anisotropy and ellipticity for crustal rocks. The maximum out-of-plane conversion amplitudes in receiver functions scale linearly with degree of anisotropy for non-elliptical symmetry. The elliptical assumption results in a bias of up to 1.4 times true anisotropy.

Strain localization and the development of ductile shear zones in the middle and lower crust play major roles in lithosphere dynamics. Geophysical imaging of ductile shear zones is an issue for ore geology, for the understanding of the lithosphere rheology and of the faults behavior. Indeed, shear zones constitute the ductile roots of the faults of the upper crust; studying these structures can thus help to better understand the behavior of the seismogenic faults (e.g. Sibson, 1977). In the absence of significant seismicity, methods using active source illumination cannot be used to image shear zones. However, by the way of metamorphic and metasomatic reactions, ductile strain localization is accompanied by mineralogical, textural and microstructural changes, that can produce seismic anisotropy. The propagation of teleseismic waves from distant earthquakes is sensitive to this anisotropy, and can be used to image the anisotropic crustal structures through which they propagate. Deep crustal seismic anisotropy has thus the potential to fundamentally advance our understanding of lithospheric structure and deformation processes. Intrinsically anisotropic minerals, the development of preferential crystallographic orientations and layered textures, can produce seismic anisotropy within shear zones (e.g. Mainprice and Nicolas, 1989). However, these intrinsic properties of shear zones change from their margins to their mylonitic cores, that may imply changes in seismic anisotropy. Furthermore, developed shear zones acquire a more complex geometry than these "ideal" tabular strain zones. They form anastomosed networks, with a mylonitic matrix delimiting weakly deformed lenses showing more localized deformation, and in which preexisting textures can be eventually preserved. Thus, there are multiple potential contributions for the shear zones "final" anisotropy. Although many geophysical studies aim to better image crustal anisotropic structures, it is also crucial to study outcropping fossil shear zones, in order to identify and estimate the different contributions to the final anisotropy. This study aims to bring a geological contribution to the understanding of geophysical signals. This approach begins with the study of the simplest case of an "ideal" shear zone, to determine how evolves the seismic anisotropy along a strain gradient. The present study is based on natural samples from eclogitic shear zones developed in the Monte Mucrone metagranodiorite (Sesia zone, Western Alps). We consider homogeneously deformed samples, corresponding to various stages of deformation: undeformed protolith (with potential inherited magmatic textures), orthogneiss, mylonite and ultramylonite. Besides, a composite sample contains a cm-scale shear zone, representing the combination of the different contributions estimated with the homogeneous samples. The seismic anisotropy of both homogeneous and composite samples will be (1) experimentally estimated, by P- and S- waves velocity measurements and (2) modelled using the program MTEX (Mainprice et al., 2011), and a microstructure-sensitive finite element orientation averaging using the ESP toolbox (Vel et al., 2016). The so calculated anisotropies are compared with the petrological features of each sample. The objective is to test the hypothesis that shear zones seismic anisotropy may reflect the lower strained margins of the zones (e.g. Almqvist et al., 2013; Tatham et al., 2008; Schulte-Pelkum and Mahan, 2011).

We extend three-component plane wave beamforming to a more general form and devise a framework, which incorporates velocity heterogeneities of the seismic propagation medium and allows us to estimate accurately sources that do not follow the simple plane wave assumption. This is achieved by utilizing fast marching to track seismic wave fronts for given surface wave phase velocity maps. The resulting matched field processing approach is used to study the surface wave locations of Rayleigh and Love waves at 8 and 16Â s based on data from four seismic arrays in the western United States. By accurately accounting for the path propagation effects, we are able to map microseism surface wave source locations more accurately than conventional plane wave beamforming. In the primary microseisms frequency range, Love waves are dominant over Rayleigh waves and display a directional radiation pattern. In the secondary microseisms range, we find the general source regions for both wave types to be similar, but on smaller scales differences are observed. Love waves are found to originate from a larger area than Rayleigh waves and their energy is equal or slightly weaker than Rayleigh waves. The energy ratios are additionally found to be source location dependent. Potential excitation mechanisms are discussed which favor scattering from Rayleigh-to-Love waves.

We examine the structure of the Denali fault system in the crust and upper mantle using double-difference tomography, P-wave receiver functions, and analysis (spatial distribution and moveout) of fault zone head waves. The three methods have complementary sensitivity; tomography is sensitive to 3D seismic velocity structure but smooths sharp boundaries, receiver functions are sensitive to (quasi) horizontal interfaces, and fault zone head waves are sensitive to (quasi) vertical interfaces. The results indicate that the Mohorovicic discontinuity is vertically offset by 10 to 15 km along the central 600 km of the Denali fault in the imaged region, with the northern side having shallower Moho depths around 30 km. An automated phase picker algorithm is used to identify ~ 1400 events that generate fault zone head waves only at near-fault stations. At shorter hypocentral distances head waves are observed at stations on the northern side of the fault, while longer propagation distances and deeper events produce head waves on the southern side. These results suggest a reversal of the velocity contrast polarity with depth, which we confirm by computing average 1D velocity models separately north and south of the fault. Using teleseismic events with M ≥ 5.1, we obtain 31,400 P receiver functions and apply common-conversion-point stacking. The results are migrated to depth using the derived 3D tomography model. The imaged interfaces agree with the tomography model, showing a Moho offset along the central Denali fault and also the sub-parallel Hines Creek fault, a suture zone boundary 30 km to the north. To the east, this offset follows the Totschunda fault, which ruptured during the M7.9 2002 earthquake, rather than the Denali fault itself. The combined results suggest that the Denali fault zone separates two distinct crustal blocks, and that the Totschunda and Hines Creeks segments are important components of the fault and Cretaceous-aged suture zone structure.

The geometry of faults at seismogenic depths and their continuation into the ductile zone is of interest for a number of applications ranging from earthquake hazard to modes of lithospheric deformation. Teleseismic passive source imaging of faults and shear zones can be useful particularly where faults are not outlined by local seismicity. Passive seismic signatures of faults may arise from abrupt changes in lithology or foliation orientation in the upper crust, and from mylonitic shear zones at greater depths. Faults and shear zones with less than near-vertical dip lend themselves to detection with teleseismic mode-converted waves (receiver functions) provided that they have either a contrast in isotropic shear velocity (V s), or a contrast in orientation or strength of anisotropic compressional velocity (V p). We introduce a detection method for faults and shear zones based on receiver functions. We use synthetic seismograms to demonstrate common features of dipping isotropic interfaces and contrasts in dipping foliation that allows determination of their strike and depth without making further assumptions about the model. We proceed with two applications. We first image a Laramide thrust fault in the western U.S. (the Wind River thrust fault) as a steeply dipping isotropic velocity contrast in the middle crust near the surface trace of the fault; further downdip and across the range, where basin geometry suggests the fault may sole into a subhorizontal shear zone, we identify a candidate shear zone signal from midcrustal depths. The second application is the use of microstructural data from exhumed ductile shear zones in Scotland and in the western Canadian Shield to predict the character of seismic signatures of present-day deep crustal shear zones. Realistic anisotropy in observed shear fabrics generates a signal in receiver functions that is comparable in amplitude to first-order features like the Moho. Observables that can be robustly constrained without significant tradeoffs are foliation strike and the depth of the foliation contrast. We find that an anisotropy of only a few percent in the shear zone is sufficient to generate a strong signal, but that the shear zone width is required to be >2 km for typical frequencies used in receiver function analysis to avoid destructive interference due to the signals from the boundaries of the shear zone.

[1] Rayleigh wave phase velocities across the western arm of the Midcontinent Rift (MCR) and surrounding regions are mapped by ambient noise (8–40 s) and earthquake tomography (25–80 s) applied to data from more than 120 Earthscope/USArray stations across the central U.S. Receiver functions also are computed for those stations using harmonic stripping. Joint Bayesian Monte Carlo inversion is applied to generate 3-D posterior distributions of shear wave speeds (Vsv) in the crust and uppermost mantle to a depth of about 150 km, providing an overview of the seismic structure of the MCR and adjacent structures. Three major structural attributes are identified: (1) There is a high correlation between the long-wavelength gravity field and shallow Vs structure, but the MCR gravity high is obscured by clastic sediments in the shallow crust. This is consistent with an upper crustal origin to the MCR gravity anomaly as well as other anomalies in the region. (2) Thick crust (>47 km) underlies the MCR, but there is a gradient Moho in the northern part of the rift and a sharp Moho in the south. Thickened crust beneath the MCR is evidence for postrifting compression with pure-shear deformation along the entire rift; along-rift differences in lower crustal structure may signify magmatic underplating in the northern rift. (3) Crustal shear wave speeds vary across the Precambrian sutures (e.g., Great Lakes Tectonic Zone, Spirit Lakes Tectonic Zone). This reveals the importance of Precambrian sutures in the subsequent tectonic evolution of the central U.S.

Low‐velocity sedimentary basins introduce error in many standard receiver‐function (RF) analysis techniques including common conversion point (Dueker and Sheehan, 1997) and crustal thickness‐ V P / V S ratio ( H ‐ κ ) stacking (Zhu and Kanamori, 2000). We describe a simple RF analysis method for obtaining accurate crustal thickness below seismic stations located in sedimentary basins. The method extends the methods of Zhu and Kanamori (2000). It employs an iterative two‐layer depth‐ V P / V S stacking approach that first characterizes sediment properties (thickness and V P / V S ) allowing for the accurate interpretation of Moho conversions. Without accounting for sedimentary layers, standard‐RF analysis can mischaracterize crustal thickness based on Ps ‐phase delay by >10 km beneath deep basins. We test the technique with synthetic seismograms and with data from US Array Transportable Array (TA) stations from regions with sediment thicknesses that are well determined through other means. We find sequential H ‐ κ stacking for sediment properties to be a simple technique that can benefit many RF‐analysis studies and can play an important role in crustal seismic studies in areas with thick or variable sediments.

[1] Rayleigh wave phase velocity maps from ambient noise and earthquake data are inverted jointly with receiver functions observed at 828 stations from the USArray Transportable Array west of 100°W longitude for data recorded in the years 2005 through 2010 to produce a 3-D model of shear wave speeds beneath the central and Western US to a depth of 150 km. Eikonal tomography is applied to ambient noise data to produce about 300,000 Rayleigh wave phase speed curves, and Helmholtz tomography is applied to data following 1550 (Ms > 5.0) earthquakes so that Rayleigh wave dispersion maps are constructed from 8 to 80 s period with associated uncertainties across the region. Harmonic stripping generates back-azimuth independent receiver functions with uncertainty estimates for each of the stations. A nonlinear Bayesian Monte Carlo method is used to estimate a distribution of shear wave speed (Vs) models beneath each station by jointly interpreting surface wave dispersion and receiver functions and their uncertainties. The assimilation of receiver functions improves the vertical resolution of the model by reducing the range of estimated Moho depths, improving the determination of the shear velocity jump across Moho, and improving the resolution of the depth of anomalies in the uppermost mantle. A great variety of geological and tectonic features are revealed in the 3-D model that form the basis for future detailed local to regional scale analysis and interpretation.

We demonstrate that observed contrasts of upper crustal structures across large continental strike‐slip faults are sufficient to produce artificial vertical Moho offsets of several kilometers in studies using laterally homogenous models. This can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust. An existing hypothesis that continental strike‐slip faults extend as discrete narrow features through the entire crust rests partly on inferred vertical Moho offsets across the faults based on teleseismic converted wave (receiver function) studies. However, such studies typically do not account for the juxtaposition of different structures across the faults, which can lead to significant (e.g., 10%) contrasts of seismic velocities in the upper crust. Observed profiles of velocity contrasts across faults can bias images of the deep structure to the extent where a large (>5 km) Moho offset can be purely apparent rather than real. Constraining the existence and size of true vertical Moho offsets below continental strike‐slip faults thus require calculations that account for the across‐fault lithology contrasts. Accurate results on the geometry of Moho across faults can have important implications for lithospheric deformation, crustal tomography, strain localization and partitioning in the crust, continental rheology, and geodynamics.

A non-linear Bayesian Monte-Carlo method is presented to estimate a Vsv model beneath stations by jointly interpreting Rayleigh wave dispersion and receiver functions and associated uncertainties. The method is designed for automated application to large arrays of broad-band seismometers. As a testbed for the method, 185 stations from the USArray Transportable Array are used in the IntermountainWest, a region that is geologically diverse and structurally complex. Ambient noise and earthquake tomography are updated by applying eikonal and Helmholtz tomography, respectively, to construct Rayleighwave dispersion maps from 8 to 80 s across the study region with attendant uncertainty estimates.Amethod referred to as ‘harmonic stripping method’ is described and applied as a basis for quality control and to generate backazimuth independent receiver functions for a horizontally layered, isotropic effective medium with uncertainty estimates for each station. A smooth parametrization between (as well as above and below) discontinuities at the base of the sediments and crust suffices to fit most features of both data types jointly across most of the study region. The effect of introducing receiver functions to surface wave dispersion data is quantified through improvements in the posterior marginal distribution of model variables. Assimilation of receiver functions quantitatively improves the accuracy of estimates of Moho depth, improves the determination of the Vsv contrast across Moho, and improves uppermost mantle structure because of the ability to relax a priori constraints. The method presented here is robust and can be applied systematically to construct a 3-D model of the crust and uppermost mantle across the large networks of seismometers that are developing globally, but also provides a framework for further refinements in the method.

SUMMARY Observations of seismic anisotropy in continental crust are of primary importance to understanding deep crustal structure and dynamics. While many crustal minerals are elastically anisotropic, seismic studies commonly assume that only the most anisotropic minerals (e.g. micas) are responsible for the observed anisotropic signal while making the simplifying assumption that potential interaction of multiple mineral phases is insignificant. This study explores the interference effects between mica and quartz on the calculated response of compressional and shear waves in high-strain tectonites (mylonites). Sample texture and mineralogy were evaluated via electron backscatter diffraction and the calculation of seismic response was carried out over a range of mica to quartz ratios. Both natural and synthetic crystallographic orientation data, which mimic quartz and mica orientations under increasing temperature in high, non-coaxial strain settings, were evaluated. Not surprisingly, the results show that adding quartz to micaceous lithologies significantly reduces the magnitude of seismic anisotropy. However, the study also highlights the mutually destructive nature of this relationship and suggests a critical threshold proportion between the two phases across which the symmetry of the end-member induced anisotropies becomes significantly altered, a result that may have significant implications for studies interpreting crustal dynamics from seismic anisotropy.

Stretching of the continental crust can double its surface area, but it is unknown whether similar amounts of extension occur at depth. Seismic results from the central Basin and Range province, western USA, reveal a thick root of lithospheric mantle that has not been extended and indicates that crustal stretching is decoupled from extension at depth. Stretching of the continental crust in the Basin and Range, western USA1, has more than doubled the surface area of the central province2. But it is unknown whether stretching affects the entire column of lithosphere down to the convecting mantle, if deep extension occurs offset to the side, or if deeper layers are entirely decoupled from the upper crust3,4. The central Basin and Range province is unusual, compared with its northern and southern counterparts: extension began later1; volcanism was far less voluminous5; and the unique geochemistry of erupted basalts6,7,8,9,10,11 suggests a long-preserved mantle source. Here we use seismic data and isostatic calculations to map lithospheric thickness in the central Basin and Range. We identify an isolated root of ancient mantle lithosphere that is ∼125 km thick, providing geophysical confirmation of a strong, cold mantle previously inferred from geochemistry6,7,8. We suggest that the root caused the later onset of extension and prevented the eruption of voluminous volcanism at the surface. We infer that the root initially pulled away from the Colorado Plateau along with the crust, but then was left behind intact during extension across Death Valley to the Sierra Nevada. We conclude that the upper crust is now decoupled from and moving relative to the root.

The Himalayan Nepal - Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadband seismometers throughout eastern Nepal and southern Tibet in 2001- 2002. The main goals of the project were to better understand the mountain building processes of this region through studies of seismicity and Earth structure determined from local and teleseismic earthquakes. The seismic deployment was in collaboration with the National Seismological Centre, Department of Mines and Geology, Nepal, and the Institute of Geology and Geophysics of the Chinese Academy of Sciences. Our new subsurface images from HIMNT teleseismic receiver functions and local earthquake tomography show evidence of the basal decollement of the Himalaya (Main Himalayan Thrust, MHT) and an increase in Moho depth from - 45 km beneath Nepal to -75 km beneath Tibet. We find strong seismic anisotropy above the decollement, likely developed in response to shear on the MHT. The shear may be taken up as slip in great earthquakes at shallower depths. Many local earthquakes were recorded during the deployment, and the large contrast in crustal thickness and velocity structure over a small lateral distance makes the use of a 3D velocity model important to determine accurate hypocentres. Large north-south variations are found in P and S wave velocity structure across the array. High Pn velocities are found beneath southern Tibet. Seismicity shows strong alignment of shallow (15-25 km depth) events beneath the region of highest relief along the Himalayan Front, and a cluster of upper mantle earthquakes beneath southern Tibet (70-90 km depth). Weak-mantle models do not expect the upper mantle earthquakes. Focal mechanisms of these upper mantle earthquakes beneath southern Tibet are mostly strike-slip, markedly different from the norm al faulting mechanisms observed for earthquakes in the mid and upper crust beneath Tibet. This change in the orientation of the major horizontal compression axis from vertical in the upper crust to horizontal in the upper mantle suggests a transition from deformation driven by body forces in the crust to plate boundary forces in the upper mantle. Several lines of evidence point to a decoupling zone in the Tibetan mid or lower crust, which may be related to the presence of a previously suggested flow channel in the Tibetan mid crust.

Im folgenden Kapitel werden Forschungsstromungen beschrieben, die zur Entwicklung eines grundlegenden Verstandnisses der Interaktions- und Verkauferforschung beitragen. Insofern werden der Interaktionskompetenz ahnlich gelagerte Phanomene auf ihren aktuellen Stand der Forschung sowie auf Einflussfaktoren und Erfolgsgrosen analysiert. Durch diese Erkenntnisse wird es moglich sein, das Phanomen Interaktionskompetenz genauer zu verstehen und von bereits existierenden Konzepten abzugrenzen.

Bezug nehmend auf die Ergebnisse der durchgefuhrten Literaturanalyse wurde eine erste Arbeitsdefinition der Interaktionskompetenz entwickelt. Im Folgenden soll diese Definition anhand einer qualitativen Untersuchung weiter spezifiziert werden, um ein Messinstrument der Interaktionskompetenz zu konzipieren. In diesem Kapitel werden zuerst die Zielsetzungen der qualitativen Forschung erortert und von denen der quantitativen Forschung abgegrenzt (Kapitel 5.1). Anschliesend wird der Prozess der Erhebung der qualitativen Daten dargestellt (Kapitel 5.2), worauf aufbauend die Auswertung und die Sicherung der Gute aufgezeigt werden (Kapitel 5.3).

Nachdem zuvor das Konstrukt Interaktionskompetenz operationalisiert wurde, werden in diesem Abschnitt mogliche Einflussgrosen identifiziert und wird ein Modell entwickelt, durch welches sich die Auspragung der Interaktionskompetenz erklaren lasst. Wie die Experteninterviews gezeigt haben, wirken personliche Faktoren und unternehmensbezogene Voraussetzungen auf das Mas der Interaktionskompetenz.

We show that SKS splitting in the westernmost United States (polarization of the fastest shear waves and splitting times, including their back-azimuthal dependence) can be explained by a geodynamic model that includes a continuum-mechanics description of plate motions and underlying asthenospheric circulation. Models that include a counterflow at depths of ∼300 km are preferred, which may indicate a far-field effect of the Farallon slab anomaly sinking underneath the central continental United States. This finding is broadly consistent with earlier suggestions, and we demonstrate that a mechanically coupled system, though with a strong viscosity contrast with depth, is consistent with the data. We explore the depth dependence of predicted anisotropy by means of computing seismogram synthetics and comparing synthetic splits with observations. Some patterns in the data, including null observations, are matched well. Linked models of geodynamic flow and mineral alignment in the mantle provide a means to test the relationship between strain and the saturation of texturing. Lower fabric saturation strains than for global models are preferred by the data, which may reflect the relatively active tectonic setting and thin asthenosphere of the study region. In general, our results show that seismic anisotropy, when interpreted jointly with mineral physics theories, may be used to quantitatively constrain the spatial character of flow, and the degree of force coupling, at depth.

New seismic images reveal the geometry of the Indian plate as it passes beneath the Himalayan plateau. Several important subsurface features of vanished India are revealed, including a shear zone above the base of the Indian crust beneath the Himalaya, and conversion of the deep Indian crust into denser rock. The rocks of the Indian subcontinent are last seen south of the Ganges before they plunge beneath the Himalaya and the Tibetan plateau. They are next glimpsed in seismic reflection profiles deep beneath southern Tibet1, yet the surface seen there has been modified by processes within the Himalaya that have consumed parts of the upper Indian crust and converted them into Himalayan rocks2,3. The geometry of the partly dismantled Indian plate as it passes through the Himalayan process zone has hitherto eluded imaging. Here we report seismic images both of the decollement at the base of the Himalaya and of the Moho (the boundary between crust and mantle) at the base of the Indian crust. A significant finding is that strong seismic anisotropy develops above the decollement in response to shear processes that are taken up as slip in great earthquakes at shallower depths. North of the Himalaya, the lower Indian crust is characterized by a high-velocity region consistent with the formation of eclogite, a high-density material whose presence affects the dynamics of the Tibetan plateau.

Upper-mantle seismic anisotropy has been observed using a variety of methods, including S and SKS splitting, P and P n traveltimes, P polarization anomalies and P to S conversions, and surface waves. Care must be taken when comparing the results from different methods because of bias introduced by depth sensitivity, frequency dependence, and simplifying assumptions concerning the form of anisotropy. We examine the differences and show that some apparent contradictions cited in previous studies can be reconciled using simple models. We perform forward modelling on a suite of anisotropic media, progressing from simple elastic symmetries to tensors obtained from laboratory measurements and numerical strain models. The results provide a systematic overview of the effect of a given anisotropy class and geometry on seismic observables. We simulate the full complement of body wave measurements-SKS and S splitting, P n traveltimes, teleseismic P traveltimes and teleseismic P particle motion (P p o l )-to show any apparent differences between the phases. We also investigate depth and frequency sensitivity using reflectivity modelling in layered anisotropic media. Our principal findings are as follows. (1) No models, including low-order symmetries and multiple layers, exhibit a mean fast shear wave splitting direction nearly orthogonal to a consistent fast direction determined from P observables. For P delays, the azimuthal cos(2θ) variation is representative of the fast direction of anisotropy (rather than cos(1θ), which has led to a certain amount of confusion in the literature). (2) P times average linearly over the raypath; SKS weights toward the upper part of the model; and P p o l and P n are even more sensitive to shallow anisotropy. Conclusive evidence in the literature for a disagreement between fast directions from SKS, on one hand, and P n and P p o l , on the other hand, can be explained by layering. (3) The azimuthal dependence of SKS splitting results does not necessarily indicate layered or laterally heterogeneous anisotropy. The azimuthal dependence of SKS splitting is not observed for hexagonal symmetry with horizontal fast or slow axes, but has to be taken into consideration for dipping hexagonal and any orthorhombic and lower symmetry media. Teleseismic S shows a much stronger azimuthal dependence than SKS and SKKS. This makes procedures that stack splitting results over a wide range of incidence angles or azimuths questionable.

We measure the plane wavefront incidence azimuth for teleseismic P at large-aperture (∼50 km) broadband arrays. The incidence azimuth is determined by crosscorrelation of the P arrivals on the vertical component seismograms filtered in successive frequency bands. The periods considered range from 10 to 35 sec. At the Anza array in southern California, the plane wave direction is deflected from the great circle azimuth of the event by up to 20°. In addition, we find a surprisingly strong frequency dependence of the same magnitude and a striking antisymmetric pattern of the deflection as a function of backazimuth, whereas the curvature of the wavefront is small. Similar characteristics are found at the Grafenberg array in Germany and the NORSAR array in Norway, however, with much weaker amplitudes of ∼5°. We ascribe the behavior at Anza to structure in the lower crust and uppermost mantle beneath the array, given that the observations are only a function of source backazimuth and not of source depth and source mechanism, that the wavelengths under consideration range from 50 to 270 km, and that the sign of the deviation is opposite to that predicted from shallow crustal structure and Moho topography. We are able to reproduce the magnitude and frequency dependence of the wavefront deflection using finite difference numerical modeling of plane wave propagation through simple 2D structures.

We introduce a method to infer upper mantle azimuthal anisotropy from the polarization, i.e., the direction of particle motion, of teleseismic long-period P onsets. The horizontal polarization of the initial P particle motion can deviate by >10° from the great circle azimuth from station to source despite a high degree of linearity of motion. Recent global isotropic three-dimensional mantle models predict effects that are an order of magnitude smaller than our observations. Stations within regional distances of each other show consistent azimuthal deviation patterns, while the deviations seem to be independent of source depth and near-source structure. We demonstrate that despite this receiver-side spatial coherence, our polarization data cannot be fit by a large-scale joint inversion for whole mantle structure. However, they can be reproduced by azimuthal anisotropy in the upper mantle and crust. Modeling with an anisotropic reflectivity code provides bounds on the magnitude and depth range of the anisotropy manifested in our data. Our method senses anisotropy within one wavelength (250 km) under the receiver. We compare our inferred fast directions of anisotropy to those obtained from Pn travel times and SKS splitting. The results of the comparison are consistent with azimuthal anisotropy situated in the uppermost mantle, with SKS results deviating from Pn and Ppol in some regions with probable additional deeper anisotropy. Generally, our fast directions are consistent with anisotropic alignment due to lithospheric deformation in tectonically active regions and to absolute plate motion in shield areas. Our data provide valuable additional constraints in regions where discrepancies between results from different methods exist since the effect we observe is local rather than cumulative as in the case of travel time anisotropy and shear wave splitting. Additionally, our measurements allow us to identify stations with incorrectly oriented horizontal components.