Susanne Sargeant

Chapter 26 Consequences of long-term volcanic activity for essential services in Montserrat: challenges, adaptations and resilience

Abstract Long-term volcanic activity at Soufrière Hills Volcano (SHV), Montserrat (1995–ongoing) has created challenges for society and the resilience of the essential services (infrastructure) that support it. This paper explores the consequences, adaptations and resilience of essential services through interviews with their staff. We find that quick fixes for essential service reinstatement in the north of Montserrat have prevailed. Yet, the legacy of this approach inhibits functionality through inadequate facilities and the perception of sites as temporary, stalling investment. Emigration resulted in staff shortages, retraining requirements and challenges for the viability of specialist services. Low-impact hazards exacerbate shortcomings in essential services, causing power cuts, corrosion, and temporary closures of schools, clinics and the airport. Adaptations developed over time include changes to roofing materials, the addition of back-up systems, collaborative working and the development of contingency plans. Resilience of essential services has improved through decentralization, adaptations, and via strong community networks and tolerance of disruptions. Barriers to increasing resilience include the expense of some adaptations and the current reluctance to invest in essential services, hindering development. We offer some lessons for policy and practice to guide post-crisis redevelopment, through engagement with the community and by complementing community-level adaptations with investment to address long-term needs.

A Local Magnitude Scale ML for the United Kingdom

We have developed a new local magnitude scale ML for the United Kingdom (UK) to replace the Hutton and Boore (1987) scale developed for southern California, which has been used in the UK until now. The new UK scale is developed from 1482 observations of 85 earthquakes on 50 stations located across the British Isles and Ireland. Most of the observations are from epicentral distances of less than 600 km and only few from greater distances up to 900 km. The distance range of the scale is, therefore, 0–600 km. The amplitude observations were used to invert for the parameters defining distance dependence in the ML scale and station corrections. Synthetic tests showed that the inversion was robust. The new ML scale for the UK is given by ML=logA+0.95logR+0.00183R−1.76, in which A is horizontal‐component ground displacement amplitude in nanometers. The amplitudes are measured on traces that are filtered to simulate the Wood–Anderson seismograph. R is the hypocentral distance (in km). The UK scale is intermediate between scales determined for California and those of other intraplate areas such as Norway or the northeastern United States. The absolute station corrections found are all less than 0.5. The scale derived for the UK helps to reduce the overall variance of the mean magnitude estimates by 30%. Much of this improvement is due to the use of station corrections. Applying the UK scale to the database of recorded earthquakes results in a reduction of magnitude for earthquakes above ML 2 and a slight increase in magnitude for earthquakes below ML 2. The biggest change to the ML computation is likely to be for small earthquakes with few amplitude readings, where the use of station corrections makes a significant difference.

Rotational Earthquake Effects in the United Kingdom

The United Kingdom is an area of low to moderate seismicity, and damaging earthquakes are uncommon. However, even in the limited record of damage from historical British earthquakes, a number of instances can be found of rotational effects on parts of structures, primarily chimneys or the tops of spires. We have assembled all the instances we know of from the United Kingdom record and present them here with illustrations and extracts from the original reports. It is not possible to determine whether these are the effects of true rotational motion or the effects of translatory shaking. Interestingly, this problem was considered in some detail by field investigators as long ago as the 1880s.