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Air-to-ground coupled seismic arrivals, resulting from infrasound interacting with the ground surface, can be identified on seismometers co-located with microbarometers. Dense networks of co-located sensors provide detailed spatial information about the infrasonic wavefield, allowing investigation of infrasonic propagation and an assessment of the variability in air-to-ground coupling mechanisms. Signals generated by an explosion at Camp Minden, Louisiana, United States, on 2012 October 16 were recorded across the eastern United States on the USArray Transportable Array. 233 infrasound signals were identified at distances of up to 1566 km from the source, with 105 of these sites, at distances of up to 1147 km from the source, recording above-noise air-to-ground coupled seismic arrivals in the 2–4 Hz passband (chosen to maximise seismic arrival signal-to-noise ratios). The spatially dense infrasound recordings allowed a unique investigation of the azimuthal variation in infrasound amplitudes, showing that stratospheric arrival amplitudes increased by a factor greater than 4 between the edge and centre of the stratospheric propagation duct. Air-to-ground coupling coefficients, calculated as the ratios of temporally coincident peak-to-trough seismic and infrasound time-domain amplitudes, span over two orders of magnitude ([9.0 × 10−8, 5.0 × 10−5] ms−1 Pa−1). Sites exhibiting high coupling coefficients are predominantly located on alluvial sediments that support the generation of air-to-ground coupled Rayleigh waves, resulting in poor coherence between the seismic and infrasonic waveforms. In contrast, sites exhibiting low coupling coefficients are predominantly located on chemically weathered bedrock and only support direct coupling, leading to high coherence between air-to-ground coupled seismic and infrasonic recordings. The Camp Minden explosion observations, and a consideration of expected seismic noise and air-to-ground coupled arrival amplitudes, suggest that co-located pairs of seismometers and microbarometers are likely to record signals from small (tens of tons) explosions at distances of over 1000 km under favourable propagation conditions. Co-located deployments may therefore provide a cost-effective method for augmenting current state-of-the-art infrasound array networks, by providing a higher spatial density of recordings; this may assist in correctly associating recorded signals with, and estimating the location of, source events. [ABSTRACT FROM AUTHOR]

A significant minority of sinkholes that formed in gypsum bedrock in the Delaware Basin region are of human origin. These anthropogenic sinkholes are often associated with improperly cased abandoned oil wells or with solution mining of salt beds in the shallow subsurface. In July 2008, a sinkhole formed abruptly at the site of a brine well in northern Eddy Co., New Mexico. The well operator had been injecting fresh water into underlying salt beds and pumping out the resulting brine for use as oil field drilling fluid. Borehole problems had prevented the operator from conducting required downhole sonar surveys to assess the dimensions of subsurface void space. The resulting sinkhole formed in just a few hours by catastrophic collapse of overlying mudstone and gypsum and in less than 1 month had reached a diameter of 111 m and a depth of 64 m. Fortuitously, a seismometer had been deployed 13 km southeast of the brine well a few months earlier and precursor events were captured on the seismograph record a few hours before the subsurface cavity breached the surface. Four months later, another sinkhole collapse occurred in northern Eddy Co., again associated with a brine well operation. These events prompted the New Mexico Oil Conservation Division to review its regulations regarding brine well operations in the southeastern New Mexico oil fields. A third brine well within the city limits of Carlsbad, N. Mex., has been shut down to forestall possible sinkhole development in this more densely populated area. Electrical resistivity surveys have been conducted adjacent to the Eddy Co. sinkholes to assess the potential for additional subsidence or collapse events in the future. [ABSTRACT FROM AUTHOR]

The article discusses the event of North Korea's nuclear test done on 9 October 2006. According to US Geological Survey the event measured at magnitude of 4.2 and seismographs around the world registered shock waves due to underground nuclear test. The survey says it was not large enough to be caused by conventional explosives nor it can be termed completely successful nuclear test. Responses and comments of nuclear scientists and various organizations on the event are presented.

The article reports that every day, several of California's more than 1000 shifting faults shake some part of the state. This clearinghouse of earthquake data keeps check on the ones that rattle northern California. Sponsored by the University of California, Berkeley, and the U.S. Geological Survey, the site catalogs magnitude, depth, location, and other measurements for earthquakes dating back to 1967. One should check out near-real-time recordings from a network of seismographs scattered around northern and central California.

Reports that a consortium of 90 United States universities is planning a new seismology facility to map North America. Funding for the USArray sought by Incorporated Research Institutions for Seismology (IRIS); Role of the National Science Foundation (NSF); Data which will be obtained by the facility; Use of very broadband, high dynamic range seismometers.