Using surface waves recorded by a large mesh of three-element arrays to detect and locate disparate seismic sources

Author Posting. © The Authors, 2018. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 215 (2018): 942–958, doi:10.1093/gji/ggy316.Surface waves recorded by global arrays have proven useful for locating tectonic earthquakes and in detecting slip events depleted in high frequency, such as glacial quakes. We develop a novel method using an aggregation of small- to continental-scale arrays to detect and locate seismic sources with Rayleigh waves at 20–50 s period. The proposed method is a hybrid approach including first dividing a large aperture aggregate array into Delaunay triangular subarrays for beamforming, and then using the resolved surface wave propagation directions and arrival times from the subarrays as data to formulate an inverse problem to locate the seismic sources and their origin times. The approach harnesses surface wave coherence and maximizes resolution of detections by combining measurements from stations spanning the whole U.S. continent. We tested the method with earthquakes, glacial quakes and landslides. The results show that the method can effectively resolve earthquakes as small as ∼M3 and exotic slip events in Greenland. We find that the resolution of the locations is non-uniform with respect to azimuth, and decays with increasing distance between the source and the array when no calibration events are available. The approach has a few advantages: the method is insensitive to seismic event type, it does not require a velocity model to locate seismic sources, and it is computationally efficient. The method can be adapted to real-time applications and can help in identifying new classes of seismic sources.WF is currently supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution, with funding provided by the Weston Howland Jr. Postdoctoral Scholarship. This work was supported by National Science Foundation grant EAR-1358520 at Scripps Institution of Oceanography, UC San Diego

Relationships between gravity waves observed at Earth's surface and in the stratosphere over the central and eastern United States

Observations of tropospheric gravity waves (GWs) made by the new and extensive USArray Transportable Array (TA) barometric network located east of the Rockies, in the central and eastern United States and of stratospheric (30–40 km above sea level) GWs made by the Atmospheric Infrared Sounder (AIRS) are compared over a 5 year time span from 2010 through 2014. GW detections in the period band from 2 to 6 h made at the Earth's surface during the thunderstorm season from May through August each year exhibit the same broad spatial and temporal patterns as observed at stratospheric altitudes. At both levels, the occurrence frequency of GWs is higher at night than during the day and is highest to the west of the Great Lakes. Statistically significant correlations between the variance of the pressure at the TA, which is a proxy for GWs at ground level, with 8.1 μm brightness temperature measurements from AIRS and rain radar precipitation data, which are both proxies for convective activity, indicate that GWs observed at the TA are related to convective sources. There is little, if any, time lag between the two. Correlations between GWs in the stratosphere and at ground level are weaker, possibly due to the AIRS observational filter effect, but are still statistically significant at nighttime. We conclude that convective activity to the west of the Great Lakes is the dominant source of GWs both at ground level and within the stratosphere

Examination of Douglas-fir clones for differences in susceptibility to damage by cone and seed insects

In 1974 and 1976, Douglas-fir cones from 51 clones and 150 clones, respectively, were collected and determinations were made of the percentage of seed damaged by the cone insects <i>Barbara colfaxiana</i>, <i>Contarinia oregonensis</i>, <i>C. washingtonensis<i/> and <i>Megastigmus spermotrophus</i>. Although statistically significant differences in percentage of damaged seeds were detected among clones, these differences were not great enough to be of practical importance

Observations on a twigminer, Argyresthia pseudotsuga Freeman (Lepidoptera: Yponomeutidae), in Douglas-fir seed orchards

Studies on the twigminer, <i>Argyresthia pseudotsuga</i> Freeman, which kills new growth on twigs of Douglas-fir, showed that adults oviposited from mid-April until May on bud scales or on needles close to the buds. Eggs hatched in mid-May and larvae continued to mine in the new twigs until late fall or early winter. The insects pupated by the end of February in chambers at the bases of the twigs

Damage by two Douglas-fir cone & seed insects: Correlation with cone crop size

Damage by the Douglas-fir cone moth, <i>Barbara colfaxiana</i> (Kearfott), in year N was significantly related to the size of the cone crop the preceding vear (N-1) in the interior of British Columbia but not at the coast. Damage by the Douglas-fir cone gall midge, <i>Contarinia oregonensis</i> Foote, at the coast was also significantly related to cone crop size the preceding year. Fluctuations in cone crop size appear to limit populations of these cone insects

Observations on a twigminer, Argyresthia pseudotsuga Freeman (Lepidoptera: Yponomeutidae), in Douglas-fir seed orchards

Studies on the twigminer, Argyresthia pseudotsuga Freeman, which kills new growth on twigs of Douglas-fir, showed that adults oviposited from mid-April until May on bud scales or on needles close to the buds. Eggs hatched in mid-May and larvae continued to mine in the new twigs until late fall or early winter. The insects pupated by the end of February in chambers at the bases of the twigs

The academic–vocational divide in three Nordic countries : implications for social class and gender

In this study we examine how the academic–vocational divide is manifested today in Finland, Iceland and Sweden in the division between vocationally (VET) and academicallyoriented programmes at the upper-secondary school level. The paper is based on a critical re-analysis of results from previous studies; in it we investigate the implications of this divide for class and gender inequalities. The theoretical lens used for the synthesis is based on Bernstein´s theory of pedagogic codes. In the re-analysis we draw on previous studies of policy, curriculum and educational praxis as well as official statistics. The main conclusions are that contemporary policy and curriculum trends in all three countries are dominated by a neo-liberal discourse stressing principles such as “market relevance” and employability. This trend strengthens the academic–vocational divide, mainly through an organisation of knowledge in VET that separates it from more general and theoretical elements. This trend also seems to affect VET students’ transitions in terms of reduced access to higher education, particularly in male-dominated programmes. We also identify low expectations for VET students, manifested through choice of textbooks and tasks, organisation of teacher teams and the advice of career counsellors.Peer reviewe

Damage by two Douglas-fir cone & seed insects: Correlation with cone crop size

Damage by the Douglas-fir cone moth, Barbara colfaxiana (Kearfott), in year N was significantly related to the size of the cone crop the preceding vear (N-1) in the interior of British Columbia but not at the coast. Damage by the Douglas-fir cone gall midge, Contarinia oregonensis Foote, at the coast was also significantly related to cone crop size the preceding year. Fluctuations in cone crop size appear to limit populations of these cone insects

EON-ROSE and the Canadian Cordillera Array – Building Bridges to Span Earth System Science in Canada

EON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) is a new initiative for a pan-Canadian research collaboration to holistically examine Earth systems from the ionosphere into the core. The Canadian Cordillera Array (CC Array) is the pilot phase, and will extend across the Cordillera from the Beaufort Sea to the U.S. border. The vision for EON-ROSE is to install a network of telemetered observatories to monitor solid Earth, environmental and atmospheric processes. EON-ROSE is an inclusive, combined effort of Canadian universities, federal, provincial and territorial government agencies, industry, and international collaborators. Brainstorming sessions and several workshops have been held since May 2016. The first station will be installed at Kluane Lake Research Station in southwestern Yukon during the summer of 2018. The purpose of this report is to provide a framework for continued discussion and development.RÉSUMÉEON-ROSE (Earth-System Observing Network - Réseau d’Observation du Système terrestrE) est une nouvelle initiative de collaboration de recherche pancanadienne visant à étudier de manière holistique les systèmes terrestres, depuis l’ionosphère jusqu’au noyau. Le Réseau canadien de la cordillère (CC Array) en est la phase pilote, laquelle couvrira toute la Cordillère, de la mer de Beaufort jusqu’à la frontière étasunienne. L’objectif d’EON-ROSE est d’installer un réseau d’observatoires télémétriques pour suivre en continu les processusterrestres, environnementaux et atmosphériques. EON-ROSE est un effort combiné et inclusif des universités canadiennes, des organismes gouvernementaux fédéraux, provinciaux et territoriaux, de l’industrie et de collaborateurs internationaux. Des séances de remue-méninges et plusieurs ateliers ont été tenus depuis mai 2016. La première station sera installée à la station de recherche du lac Kluane, dans le sud-ouest du Yukon, au cours de l’été 2018. Le but du présent rapport est de fournir un cadre de discussion et de développement continu