Nuclear disarmament versus peace in the twenty‐first century*

In his analysis of the continuing necessity for Britain to retain its nuclear capability, the author argues that the purpose of the British nuclear deterrent is what it has always been—‘to minimize the prospect of the United Kingdom being attacked by mass destruction weapons’. His discussion ranges from the ethical paradox surrounding the possession of nuclear weapons, the central problem of their predictability, the problem of new threat and, in his view, the Utopian non‐proliferation obligations. The possession of the deterrent may be unpleasant, he concludes, but it is necessary, its purpose lying‘not in its actual use but in its nature as the ultimate “stalemate weapon”.’     

THE EFFECTIVE DURATION OF EARTHQUAKE STRONG MOTION

The duration of strong ground shaking during earthquakes can play an important role in the response of foundation materials and structures, particularly when strength or stiffness degradation is encountered. A thorough seismic hazard assessment should therefore include an estimation of the expected duration of strong motion, which first requires criteria to define the part of an accelerogram considered to represent the duration of strong ground motion. Some 30 different definitions of strong motion duration are reviewed and classified into generic groups. Problems that arise with the use of these definitions for duration are highlighted. A new definition of duration is presented using a previously unexplored option which identifies the part of the record where the main energy is contained and constrains this strong shaking phase by absolute criteria. This new definition is shown to give consistently meaningful durations for strong earthquake accelerograms from an engineering viewpoint. The correlations between the new definition of duration and magnitude, soil conditions and distance are explored as a first step towards the development of predictive equations.     

THE RAW MATERIALS OF EARLY GLASS PRODUCTION

This paper discusses raw materials used in ancient glasses. Following a consideration of some archaeological reasons for studying glass, the discussion concentrates on the evidence provided by chemical analysis of the glass, and focuses on glass from later prehistoric Western Europe. Consideration of the major, minor and trace components of the glass leads to a conclusion that prehistoric glass artisans were able closely to control the addition of small quantities of colorants, opacifiers and clarifiers to the glass melt. Some possible ways of introducing such small quantities of these substances are suggested. A related implication is that glass production in prehistoric Europe was a mainly specialist industry, being part of a 'high-status'socio-economic sphere. When interpreting technical analyses a full consideration of the socio-economic niche occupied by the glass industry is urged.     

IS THERE A NEAR-FIELD FOR SMALL-TO-MODERATE MAGNITUDE EARTHQUAKES?

The major hazard posed by earthquakes is often thought to be due to moderate to large magnitude events. However, there have been many cases where earthquakes of moderate and even small magnitude have caused very significant destruction when they have coincided with population centres. Even though the area of intense ground shaking caused by such events is generally small, the epicentral motions can be severe enough to cause damage even in well-engineered structures. Two issues are addressed here, the first being the identification of the minimum earthquake magnitude likely to cause damage to engineered structures and the limits of the near-field for small-to-moderate magnitude earthquakes. The second issue addressed is whether features of near-field ground motions such as directivity, which can significantly enhance the destructive potential, occur in small-to-moderate magnitude events. The accelerograms from the 1986 San Salvador (El Salvador) earthquake indicate that it may be unconservative to assume that near-field directivity effects only need to be considered for earthquakes of moment magnitude M 6.5 and greater.