Towards understanding relationships between atmospheric pressure variations and long-period horizontal seismic data: a case study

SUMMARY Variations in atmospheric pressure have long been known to introduce noise in long-period (>10 s) seismic records. This noise can overwhelm signals of interest such as normal modes and surface waves. Generally, this noise is most pronounced on the horizontal components where it arises due to tilting of the seismometer in response to changes in atmospheric pressure. Several studies have suggested methodologies for correcting unwanted pressure-induced noise using collocated microbarograph records. However, how applicable these corrections are to varying geologic settings and installation types (e.g. vault versus post-hole) is unclear. Using coefficients obtained by solving for the residuals of these corrections, we can empirically determine the sensitivity of instruments in a specific location to the influences of pressure. To better understand how long-period, pressure-induced noise changes with time and emplacement, we examine horizontal seismic records along with barometric pressure at five different Global Seismographic Network stations, all with multiple broadband seismometers. We also analyse three Streckeisen STS-2 broadband seismometers, which are collocated with a microbarograph, at the Albuquerque Seismological Laboratory. We observe periods of high magnitude-squared-coherence (γ2-coherence; γ2 > 0.8) between the seismic and pressure signals which fluctuate through time, frequency, and even between seismic instruments in the same vault. These observations suggest that these tilt-generated signals are highly sensitive to very local (<10 m) site effects. However, we find that in cases where instruments are not located at a large depth (<100 m), the pressure-induced noise is polarized in a nearly constant direction that is consistent with local topographic features or the geometry of the vault. We also find that borehole instruments at a large depth (>100 m) appear to be unaffected by pressure-loading mechanisms outlined by Sorrells (1971) but possibly by Newtonian attraction. Correlating the induced-noise polarization direction with times of high coherence, we work to identify sensors that are ultimately limited by pressure-induced horizontal noise as well as period bands that can benefit from pressure corrections. We find that while the situation is complex, each sensor appears to have its own unique response to pressure. Our findings suggest that we can determine empirical relationships between pressure and induced tilt on a case by case basis.

Furness’s First Farmers: Evidence of Early Neolithic Settlement and Dairying in Cumbria

In 2015, excavations at Stainton Quarry, Furness, Cumbria, recovered remains that provide a unique insight into Early Neolithic farming in the vicinity. Five pits, a post-hole, and deposits within a tree-throw and three crevices in a limestone outcrop were investigated. The latter deposits yielded potentially the largest assemblage of Carinated Bowl fragments yet recovered in Cumbria. Lipid analysis identified dairy fats within nine of these sherds. This was consistent with previous larger studies but represents the first evidence that dairying was an important component of Early Neolithic subsistence strategies in Cumbria. In addition, two deliberately broken polished stone axes, an Arran pitchstone core, a small number of flint tools and debitage, and a tuff flake were retrieved. The site also produced moderate amounts of charred grain, hazelnut shell, charcoal, and burnt bone. Most of the charred grain came from an Early Neolithic pit and potentially comprises the largest assemblage of such material recovered from Cumbria to date. Radiocarbon dating indicated activity sometime during the 40th–35th centuries cal bc as well as an earlier presence during the 46th–45th centuries. Later activity during the Chalcolithic and the Early Bronze Age was also demonstrated. The dense concentration of material and the fragmentary and abraded nature of the pottery suggested redeposition from an above-ground midden. Furthermore, the data recovered during the investigation has wider implications regarding the nature and use of the surrounding landscape during the Early Neolithic and suggests higher levels of settlement permanence, greater reliance on domesticated resources, and a possible different topographical focus for settlement than currently proposed.

A First-Centurya.d.Burial Plot at Barnwood, Gloucestershire: Excavations in 2013–14

ABSTRACTExcavations at Barnwood, Gloucestershire, revealed several phases of activity dating to thea.d.60s. This included gravel quarrying, with one quarry pit containing a significant assemblage of pottery, metalwork and glass with strong first-century military associations. A large roadside enclosure contained ditches and a post-hole alignment; these were replaced by a square burial plot containing a post-built structure and several pits, which yielded a leadossuariumcontaining cremated human remains and a collection of burnt beans and hobnails. The location of the site raises questions regarding the organisation of the military landscape around Gloucester during the first century. The Supplementary Material available online (https://doi.org/10.1017/S0068113X18000272) contains full specialist reports and catalogues for the excavated artefacts and biological remains.