Search

We analyze the Basis Pursuit recovery of signals with general perturbations. Previous studies have only considered partially perturbed observations Ax + e. Here, x is a signal which we wish to recover, A is a full-rank matrix with more columns than rows, and e is simple additive noise. Our model also incorporates perturbations E to the matrix A which result in multiplicative noise. This completely perturbed framework extends the prior work of Candes, Romberg and Tao on stable signal recovery from incomplete and inaccurate measurements. Our results show that, under suitable conditions, the stability of the recovered signal is limited by the noise level in the observation. Moreover, this accuracy is within a constant multiple of the best-case reconstruction using the technique of least squares. In the absence of additive noise numerical simulations essentially confirm that this error is a linear function of the relative perturbation.

A stylized compressed sensing radar is proposed in which the time-frequency plane is discretized into an N by N grid. Assuming the number of targets K is small (i.e., K much less than N^2), then we can transmit a sufficiently "incoherent" pulse and employ the techniques of compressed sensing to reconstruct the target scene. A theoretical upper bound on the sparsity K is presented. Numerical simulations verify that even better performance can be achieved in practice. This novel compressed sensing approach offers great potential for better resolution over classical radar.

The 2014 Iquique event was not the earthquake that had been expected to fill the regional seismic gap; given that significant sections of the northern Chile subduction zone have not ruptured in almost 150 years, it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 Iquique sequence. 2014 Iquique earthquake examined Two groups publishing in this issue of Nature analyse the seismic context of the Iquique earthquake that occurred off the coast of northern Chile on 1 April 2014 in a seismic zone that had been quiescent since a significant event in 1877. Gavin Hayes et al. identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region, and conclude that the 2014 Iquique event was not the earthquake that had been anticipated. Given that significant sections of the northern Chile subduction zone have not ruptured in almost 150 years, they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 Iquique sequence. Bernd Schurr et al. show that the April 2014 earthquake broke a central fraction of the 'northern Chile seismic gap', the last major segment of the South American plate boundary that had yet to rupture in the past century. From July 2013 up to the April earthquake they identify three seismic clusters along this part of the plate boundary, each lasting a few weeks, with earthquakes of increasing peak magnitudes. They conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure. The seismic gap theory.sup.1 identifies regions of elevated hazard based on a lack of recent seismicity in comparison with other portions of a fault. It has successfully explained past earthquakes (see, for example, ref. 2) and is useful for qualitatively describing where large earthquakes might occur. A large earthquake had been expected in the subduction zone adjacent to northern Chile.sup.3,4,5,6, which had not ruptured in a megathrust earthquake since a M ~8.8 event in 1877. On 1 April 2014 a M 8.2 earthquake occurred within this seismic gap. Here we present an assessment of the seismotectonics of the March-April 2014 Iquique sequence, including analyses of earthquake relocations, moment tensors, finite fault models, moment deficit calculations and cumulative Coulomb stress transfer. This ensemble of information allows us to place the sequence within the context of regional seismicity and to identify areas of remaining and/or elevated hazard. Our results constrain the size and spatial extent of rupture, and indicate that this was not the earthquake that had been anticipated. Significant sections of the northern Chile subduction zone have not ruptured in almost 150 years, so it is likely that future megathrust earthquakes will occur to the south and potentially to the north of the 2014 Iquique sequence., Author(s): Gavin P. Hayes [sup.1] , Matthew W. Herman [sup.2] , William D. Barnhart [sup.1] , Kevin P. Furlong [sup.2] , Sebástian Riquelme [sup.3] , Harley M. Benz [sup.1] , [...]

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 Mw = 7.5 Palu earthquake (Sulawesi, Indonesia). With a predominantly strike‐slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake‐induced landslides. In this study we examine the tsunami potential of the co‐seismic deformation. To this end, we present a novel geodetic data set of Global Positioning System and multiple Synthetic Aperture Radar‐derived displacement fields to estimate a 3D co‐seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co‐seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co‐seismic uplift (>2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co‐seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video‐derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co‐seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic data set constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike‐slip faults in transtensional basins. Plain Language Summary: The 28 September Palu earthquake ruptured the Palu‐Koro fault in NW Sulawesi, Indonesia, and was followed by a devastating tsunami in Palu Bay. As the Palu‐Koro fault accommodates mostly horizontal motion, many studies proposed that sub‐marine landslides, rather than the earthquake itself, triggered the tsunami. This study focuses on the contribution of the earthquake to sea floor displacements. We present a unique geodetic data set and estimate a high‐resolution 3D displacement field. The rupture is not a straight feature in the landscape, but rather contains bends. It is near those bends that significant vertical displacements occurred. From the onshore geodetic data we infer another fault bend below Palu Bay. Estimations of fault slip for several scenarios of offshore fault geometries point to a few meters of sea floor uplift. We use these slip models as input for tsunami models, and can qualitatively explain the observations of tsunami runup heights and video‐based tsunami arrival times around Palu Bay. Only at a few locations our models cannot explain tsunami observations, which leaves open the contribution of other possible sources to the tsunami locally. The Palu case underlines the potential importance of fault bends to tsunami generation for similar tectonic settings around the world. Key Points: New Global Positioning System observations as part of a geodetic solution for the full 3D onshore co‐seismic displacements of the 2018 Palu earthquakeBelow Palu Bay we find a strong indication of dip‐slip on a fault bend, agreeing with the notion of Palu Valley being a transtensional basinA large part of the tsunami, both in terms of arrival times and runup heights, can be explained by co‐seismic slip [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic led to an increased need to conduct research and community engagement using digital methods. Unfortunately, the shift away from in-person research activities can make it difficult to engage and recruit participants from under-resourced communities that lack adequate digital infrastructure. At the beginning of the pandemic, our team recognized that imminent lockdowns would significantly disrupt ongoing engagement with low-income housing resident community partners and that we would ultimately bear responsibility if that occurred. This manuscript outlines the development of methods designed to create capacity for virtual engagement with a community advisory board that were subsequently applied to a longitudinal mixed-methods study. We describe how our experience engaging low-income housing residents during the height of the pandemic influenced the approach and offer guidelines useful for engaging under-resourced communities regardless of setting. Of these, a strong commitment to providing technology, unlimited data connectivity, and basic digital literacy training/technical support is most important. While each of these is essential and failure in any one area will reduce overall effectiveness of the effort, providing adequate technical support while maintaining ongoing relationships with community members is the most important and resource-intensive. [ABSTRACT FROM AUTHOR]

The article offers information on initial thrust earthquake and its afterslip enhanced the strike-slip loading within the subducting slab. It mentions that Shumagin Islands region of the Alaska subduction zone was identified as a seismic gap expected to host a future great, moment magnitude earthquake in 1970.

Objectives: Adolescent use of electronic cigarettes has risen dramatically, prompting concerns about the health effects. There is need for brief measures to assess adolescents' perceived threat and efficacy related to e-cigarette use and cessation. A 12-item Likert-type scale was modeled after the Risk Behavior Diagnosis Scale and designed to assess threat (ie, severity and susceptibility of threat) and efficacy (ie, self-efficacy and response efficacy) as they relate to e-cigarette use. Methods: The scale was administered online to a developmental sample of 674 adolescents to examine internal consistency and factor structure. Participants (52.1% female, M age = 14.6) were representative of the surrounding community (60% non-Hispanic white; 27% non-Hispanic black; 8% Hispanic). Results: Factor analysis and Velicer's minimum average partial test revealed 2 factors (as expected), which explained 68% of the variance. Analyses revealed strong internal consistency, with Cronbach's alpha of .93 overall and alphas of .92 and .87 for threat and efficacy subscales, respectively. The measure also exhibited good convergent and discriminant validity with other constructs. Conclusions: The measure demonstrates strong preliminary reliability and validity for a developmental sample of adolescents. [ABSTRACT FROM AUTHOR]

The goal of this paper was to statistically explore the spatiotemporal performance of remotely sensed actual evapotranspiration (ETa) datasets and a remotely sensed ensemble in a region that lacks observed data. The remotely sensed datasets were further compared with ETa results from a physically based hydrologic model (Soil and Water Assessment Tool) to examine the differences and determine the level of agreement between the ETa datasets and the model outputs. ETa datasets were compared on temporal (i.e., monthly and seasonal basis) and spatial (i.e., landuse) scales at both watershed and subbasin levels. The results showed a lack of consistent similarities and differences among the datasets when evaluating the monthly ETa variations; however, the seasonal aggregated data presented more consistent similarities and differences during the spring and summer compared to the fall and winter. Meanwhile, spatial analysis of the datasets showed the MOD16A2 500 m ETa product was the most versatile of the tested datasets, being able to differentiate between landuses during all seasons. Furthermore, the use of an averaging ensemble was able to improve overall ETa performance in the study area. This study showed that the remotely sensed ETa products are not similar throughout the year, but the appropriate application periods for different ETa products were identified. Finally, spatial variabilities of the ETa products are more in tune with landuse and climate characteristics. Research Impact Statement: This study can help policy makers and researchers select the best actual evapotranspiration dataset for different tasks such as monitoring of agricultural lands or tracking deforestation. [ABSTRACT FROM AUTHOR]

Highlights • Deformation in Thailand can be accounted for by interactions at nearby plate boundaries. • The modeled stress field is compatible with the 2014 Mae Lao earthquake. • Most of Southeast Asia remains in the same state of stress after the 2014 event. Abstract Thailand is surrounded by seismically active plate boundary zones and large-offset crustal faults, but there is comparatively little seismic activity within its borders. On 5 May 2014, a moment magnitude (M W) 6.2 earthquake occurred in the Mae Lao district of northern Thailand. To better anticipate future seismic hazards from events like this, we model the state of stress in Thailand and its vicinity using a finite element approach. We identify northern Thailand as a region with significant stress accumulation, consistent with being caused by convergence at the Sumatra-Andaman subduction zone and southward escape of the Himalayan Orogen. The stress field in this region is compatible with the kinematics of the Mae Lao event. Our modeling also shows that the magnitude of the stress field throughout southeast Asia is particularly sensitive to the stage of the earthquake cycle at the Sumatra-Andaman subduction zone, although the Sumatra-Andaman subduction zone produces a smaller effect on the orientations of stresses in the source region of the Mae Lao earthquake. Finally, we find that the stress change effect from the Mae Lao earthquake is geographically limited and the broader region remains in nearly the same state of stress as prior to the event. [ABSTRACT FROM AUTHOR]

The distribution of slip during subduction megathrust earthquakes depends on the slip deficit that accumulates on the plate interface prior to the event. We develop 3‐D finite element models of subduction zones to investigate how locked zones restrict surrounding regions on the plate boundary from sliding. What is new is that we quantify the slip around asperities on the megathrust. The models show plate interface slip increasing from zero at the edge of a locked zone to the relative plate motion over a distance of ~200 km along the megathrust. This area of reduced slip accumulates a seismic moment deficit up to 10 times larger than the moment deficit in the asperity alone. Updip of locked areas, slip at the trench can be reduced by more than 50% of the plate motion. Despite large displacements of the upper plate near the trench, this region moves as a semirigid block. Rupture models of the 2011 Tohoku earthquake, its tsunami characteristics, and geophysical observations near the trench can be interpreted to reflect the consequences of slip deficit accumulated on a low friction interface updip of the seismogenic zone. Neighboring asperities affect plate interface slip in a nonlinear way. Multiple asperities have overlapping pseudo‐coupled regions that may restrict the magnitude of coseismic slip in single‐asperity ruptures. Once an earthquake has a rupture length greater than ~250 km, it may recover the entire accumulated slip deficit. This is consistent with the magnitude of coseismic slip in several recent great megathrust earthquakes. Key Points: Locked asperities on subduction megathrusts cause slip deficit to accumulate in regions that would otherwise slide at the convergence rateUnruptured locked zones restrict the maximum magnitude of slip in earthquakes that rupture adjacent sections of the plate boundaryModeled patterns of interseismic deformation near the trench are compatible with tsunami‐related coseismic observations [ABSTRACT FROM AUTHOR]

We constrain epicentroid locations, magnitudes and depths of moderate-magnitude earthquakes in the 2013-2014 Minab sequence using surface-wave cross-correlations, surface-wave spectra and teleseismic body-wave modelling. We estimate precise relative locations of 54 Mw ≥ 3.8 earthquakes using 48 409 teleseismic, intermediate-period Rayleigh and Love-wave cross-correlation measurements. To reduce significant regional biases in our relative locations, we shift the relative locations to align the Mw 6.2 main-shock centroid to a location derived from an independent InSAR fault model. Our relocations suggest that the events lie along a roughly east-west trend that is consistent with the faulting geometry in the GCMT catalogue. The results support previous studies that suggest the sequence consists of left-lateral strain release, but better defines the main-shock fault length and shows that most of the Mw ≥ 5.0 aftershocks occurred on one or two similarly oriented structures. We also show that aftershock activity migrated westwards along strike, away from the main shock, suggesting that Coulomb stress transfer played a role in the fault failure. We estimate the magnitudes of the relocated events using surface-wave cross-correlation amplitudes and find good agreement with the GCMT moment magnitudes for the larger events and underestimation of small-event size by catalogue MS. In addition to clarifying details of the Minab sequence, the results demonstrate that even in tectonically complex regions, relative relocation using teleseismic surface waves greatly improves the precision of relative earthquake epicentroid locations and can facilitate detailed tectonic analyses of remote earthquake sequences. [ABSTRACT FROM AUTHOR]

Among livestock systems, grazing is likely to be most impacted by climate change because of its dependency to feed quality and availability. In order to reduce the impact of climate change on grazing livestock systems, adaptation measures should be implemented. The goal of this study is to identify the best pasture composition for a representative grazing dairy farm in Michigan in order to reduce the impacts of climate change on production. In order to achieve the goal of this study, three objectives were sought: (1) identify the best pasture composition, (2) assess economic and resource use impacts of pasture compositions under future climate scenarios, and (3) evaluate the resiliency of pasture compositions. A representative farm was developed based on a livestock practices survey and incorporated into the Integrated Farm System Model (IFSM). For the pasture compositions, four cool-season grass species and two legumes were evaluated under both current and future climate scenarios. The effectiveness of adaptation measures based on economic and resource use criteria was evaluated. Overall, the pasture composition with 50% perennial ryegrass (Lolium multiflorum) and 50% red clover (Trifolium pratense) was identified as the best. In addition, the increase in precipitation and temperature of the most intensive climate scenario could significantly improve farm net return per cow (Bos taurus) and whole farm profit while no significant impact was observed on resource use criteria. Finally, the overall sensitivity assessment showed that the most resilient pasture composition under future climate scenarios was ryegrass with red clover and the least resilient was orchardgrass (Dactylis glomerata) with white clover (Trifolium repens). [ABSTRACT FROM AUTHOR]

In April 2017, a sequence of earthquakes offshore Valparaíso, Chile, raised concerns of a potential megathrust earthquake in the near future. The largest event in the 2017 sequence was a M6.9 on 24 April, seemingly colocated with the last great-sized earthquake in the region-a M8.0 in March 1985. The history of large earthquakes in this region shows significant variation in rupture size and extent, typically highlighted by a juxtaposition of large ruptures interspersed with smaller magnitude sequences. We show that the 2017 sequence ruptured an area between the two main slip patches during the 1985 earthquake, rerupturing a patch that had previously slipped during the October 1973 M6.5 earthquake sequence. A significant gap in historic ruptures exists directly to the south of the 2017 sequence, with large enough moment deficit to host a great-sized earthquake in the near future, if it is locked. [ABSTRACT FROM AUTHOR]

In the context of changing climate, this study assessed the effects of global warming on water resources in Tanzania for the mid- 21st century. Climate projections from six global circulation models under the most extreme emission scenario (RCP 8.5) were used as inputs to the soil and water assessment tool (SWAT) to examine the effects. The results were analyzed both at spatial (country-level, watershed-level, and subbasin-level) and temporal (annual and seasonal) scales concerning potential and actual evapotranspiration, surface runoff, water yield, and soil moisture. At the country level, the results showed a 0.8-27.4% increase in annual precipitation, which led to a general increase in evapotranspiration (-2.2-7.3%), surface runoff (12.6-94.1%), water yield (7.5-73.4%), and soil moisture (2.9-20.7%). Watershed-level analysis showed 2.4-31.5%, -2.6-6.8%, 18.4-159.7%, and 3.2-22.8% changes in average precipitation, evapotranspiration, surface runoff, and soil moisture, respectively. While no distinct spatial trend was identified for evapotranspiration and surface runoff, soil moisture was projected to increase in the majority of the areas during both the wet and dry seasons. Probability analysis at the subbasin level showed that less than 15% of the area, during the wet season, experienced decline in precipitation, soil moisture, potential and actual evapotranspiration, surface runoff and water yield, while less than 86% of the country experienced decline during the dry season. Overall, the climate change was found to create a more favorable condition for agricultural production during the wet season by increasing the supply of water, but in the dry season, less favorable conditions were projected. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) is defined as a branch of fluid mechanics that solves fluid flow problems using numerical algorithms and methods. Using CFD to model water and contaminants transport in rivers, lakes, and coastal areas can significantly improve our understanding to manage these hydrodynamic systems. In this paper, 111 studies have been reviewed on different aspects of CFD application in ecohydrology that include: flow simulation and pressure distribution, sediment transport, hyporheic zone, fish habitat and temperature distribution. In general, three-dimensional models are reported to be more capable than two-dimensional models to predict flow features and have been used more recently due to their ability to capture secondary flow. Two-dimensional models with secondary flow correction terms are acceptable and are being used as well. Discretization techniques and turbulence closures are also reported with comparisons. In general, majority of the studies were focused on flow and sediment transport; however, our knowledge about temperature distributions in near-bed regions and pool-riffle structures is limited and can be the subject of future studies. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems are impacted by climate change. However, the level of impacts, especially on macroinvertebrates, are not well known, which is the goal of this study. Here, three biotic indices were used. The Saginaw River Basin, the largest watershed in Michigan was selected for this study. Since no know modeling package exists to evaluate the impacts of climate change on these biotic indices, a coupled modeling approach was proposed. First, the Soil and Water Assessment Tool (SWAT) was setup to estimate streamflow and water quality for all stream segments. Next, the results from the SWAT model in combination with long-term biological monitoring data were used to develop biotic indices predictive models using a two-phase approach. An assemblage of 42 climate scenarios (2040-2060) were obtained from the National Aeronautics and Space Administration, which are biased corrected and statistically downscaled. The dataset provides two extreme Representative Concentration Pathways (RCPs) to account for best (RCP 4.5) and worst (RCP 8.5) case scenarios. The climate data were incorporated in SWAT and biotic indices predictive models to understand stream health conditions in the watershed. Results showed that the majority of streams have a probability of declining in values of biotic indices while streams that currently have excellent conditions are the most vulnerable streams to the climate change. This modeling approach provides a new mean to link more strongly biota indicators with flow regime indicators, which is of prime interest for the implementation of ecohydrology principles. [ABSTRACT FROM AUTHOR]

Compressive imaging (CI) is a subset of computational photography where a scene is captured via a series of optical, transform-based modulations before being recorded at the detector. However, unlike previous transform imagers, compressive sensors take advantage of the inherent sparsity in the image and use specialized algorithms to reconstruct a high-resolution image with far lower than 100% of the total measurements. Initial CI systems exploited the properties of random matrices used in other areas of compressive sensing (CS); however, in the case of imaging, there are immense benefits to be derived by designing measurement matrices that optimize specific objectives and enable novel capabilities. In this article, we survey recent results on measurement matrix designs that provide the ability of real-time previews, signature-selective imaging, and reconstruction-free inference. [ABSTRACT FROM PUBLISHER]

Sustainability and the health of freshwater ecosystems are vital to insure their safe and continued use. This study introduces a new approach to improve stream health to a desirable condition at the lowest cost by optimizing the best management practice (BMP) implementation plan. Several hydrological models including the Soil and Water Assessment Tool (SWAT) and Hydrologic Index Tool were integrated and the results were used to develop a stream health model. SWAT model was calibrated and validated against daily streamflow data from nine US geological gauging stations for a 10-year-period while the stream health model was calibrated and validated against 193 biological monitoring sites operated by the Michigan Department of Natural Resources. The stream health model was guided by a genetic algorithm to design the watershed-scale management strategies that included five BMPs. Out of 182 BMP implementation scenarios, eight unique scenarios resulted in an overall excellent stream health for the Honeyoey Creek-Pine Creek Watershed in Michigan. In addition, no tillage was the most selected BMP in three of the eight implementation scenarios. The BMP implementation costs for these eight scenarios ranged from 4.28 to 6.41 million dollars. Therefore, the integration of genetic algorithm techniques in stream health modeling resulted in a savings of over 2 million dollars. In addition, the implementation of the lowest costing scenario resulted in a 52% improvement and 36% reduction in stream health scores, with respect to stream length, compared to current conditions. The technique introduced here can be successfully adapted in different regions to identify the optimal solution from both environmental and economic points of view. [ABSTRACT FROM AUTHOR]

The article discusses 3 student center projects to explore how various physical and social contexts inform the role of student centers in shaping student life and campus identity. It cites the common themes that have emerged from the projects such as a new academic typology, diversity and inclusiveness and connecting beyond the building. It notes that methodologies applied by the project team including a series of "eco-charrettes" that focused on environmental initiatives and innovation.

The focus of this review is to discuss the current uses and developments of macroinvertebrate and fish indicators in riverine ecosystems. Macroinvertebrates and fish are commonly used indicators of stream heath, due to their ability to represent degradation occurring at the local or regional scales, respectively. A total of 78 macroinvertebrate and fish indices were reviewed, and the frequently used macroinvertebrate and fish indices are discussed in detail in the context of aquatic ecosystem health evaluation. This review also discusses several types of common components, or metrics, used in the creation of indices. Following this, the review will focus on the different methods used for macroinvertebrate and fish collection, in both wadeable and non-wadeable aquatic ecosystems. With the basics of macroinvertebrate and fish indices discussed, emphasis will be placed on the application of indices and the different regions for which they are developed. The final section will provide a summary of the benefits and limitations of macroinvertebrate and fish indices. In general, the majority of studies have been performed in wadeable streams; therefore, our knowledge about these indices in non-wadeable streams is limited, which should be the subject of future research. [ABSTRACT FROM AUTHOR]