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The Soufriere volcano in St Vincent began to erupt on 13 April 1979 after 10 months of mild premonitory activity. A series of strong vertical explosions between 13 and 26 April generated ash falls, pyroclastic flows and mudflows. From about 3 May onwards basaltic–andesite lava has been accumulating in the summit crater.

A review of the history of earthquake observations in Jamaica is presented; there have been several high-intensity earthquakes in the last 300 years. The observed seismicity of the Jamaica region is discussed in the context of what is known of regional tectonics, and possible source regions of earthquakes are identified but a comparison between instrumentally determined seismicity and macroseismicity shows that the instrumental data are of insufficient quantity or quality to permit direct assessment of earthquake risk by conventional techniques. An alternative approach has been adopted; consideration of the macroseismic record suggests that the peak acceleration in rock with 90 per cent probability of not being exceeded in any 50-year period is of order 0.3 g but that there are very significant local variations caused by near-surface geology. Especially this applies to the capital, Kingston, and envelope response spectra are derived for shallow, intermediate and deep thickness of sediments under the city to demonstate the possibility that localized amplification may occur. A current apparent decline in the seismicity of the Jamaica region is noted but it is shown that the decline in the number of earthquakes of engineering interest is not yet statistically significant.

The Soufriere of St. Vincent has been monitored for more than 25 years as part of a regional programme in the Lesser Antilles. In that time the volcano has erupted twice but our studies have shown no discernible change in regional seismicity before either event. However, very small seismic events were observed in the crater during the 1971–1972 eruption and were detected before the start of the 1979 explosive eruption; we believe that they were generated by thermally induced hydraulic fracturing within the lava mass inside the crater lake. We conclude that seismographic monitoring of Lesser Antillean volcanoes can give ambiguous results but that at least one instrument must be placed within 1 km of the vent if the earliest signs of activity are to be detected.

The task of converting analogue recordings of seismic events into digital form for computer input can be rendered faster and more reliable than hand-tracing on a digitizing table by the use of a simple microprocessor-based automatic system. We describe the circuitry and software of a system which takes 4 sec to digitize an event and 40 min to punch a card-deck containing 4096 data points; hand-tracing the same record on a digitizing table takes 8 hr. In addition, the automatic system removes the needs of correcting for duplicate points and axis alignment, and of interpolating to obtain equispaced data points. The system, as described, has been configured at minimal cost for input to an outdated mainframe facility; it demonstrates that microprocessor technology can be used to produce time- and labour-saving gains.

Summary Two-dimensional finite element modelling of subsurface anomalies at shallow depth has been done to obtain the response to incident SH-waves. Vertically incident SH and obliquely incident SH have been examined. Power spectral ratios were studied to determine the effect on the surface seismograms of the position, shape, depth, size and material composition of the anomaly. A number of relationships between the surface response and the anomaly has been identified. These relationships may be used in solving the inverse problem: given the seismic motion of the ground surface, determine the physical properties of the underground structure.

During a 39-day microearthquake survey in the Sulphur Springs geothermal region, St. Lucia, seven local hypocenters were determined. Emergent P onsets and missing S-waves were observed for five of these, and attenuated S-waves recorded for two regional events. These imply the presence of at least two significant fluid bodies beneath the area. Ground noise measurements near natural steam vents suggest a deep source for the steam.

A major earthquake (mb = 6.6; Ms = 7.5, U.S. Geological Survey) occurred in the northern Lesser Antilles on October 8, 1974, causing damage of Modified Mercalli intensity VIII on the island of Antigua and lower intensities on the more distant islands. The damage was confined mainly to larger and older buildings, to a petroleum refinery, and to a deep-water harbor. No earthquake-resistant building code exists in most of the Lesser Antilles, and in the majority of cases examined it was clear that structural damage had occurred because the building concerned could not have met the elementary requirements of a typical code. A few people received minor injuries, but no fatality was reported. The hypocenter of the main shock and many of the aftershocks lay about 30 km above the westward-dipping zone defined by activity over the last decade. The earthquake was tectonic in origin since the epicenter was 50 km from the nearest recent volcano.

The two-island Republic of Trinidad and Tobago in the eastern Caribbean has enjoyed increased physical and industrial development in recent years; however, these islands have been subjected to damaging earthquakes during their history and an up-to-date risk assessment is needed. We examine two approaches to quantifying this problem: (a) the risk estimated probabilistically using recent instrumental data and (b) the hazard inferred from regional tectonic movements. The probabilistic approach indicates that peak ground accelerations with a probability of exceedance of 10 per cent in 50 years could range from 0–23g in Tobago to 0–36g in North-West Trinidad. Tectonic considerations suggest that a maximum-moment earthquake occurring directly under either land mass could generate accelerations as high as 0–6g; the probability of occurrence of such an event is estimated to be about 2 per cent in 50 years for Trinidad and about a tenth this risk for Tobago. This level of hazard would be significant for critical facilities such as LNG plants.

The Soufriere volcano in St. Vincent erupted from October 1971 to March 1972, as 80 x 10(6) m(3) of basaltic andesite lava was quietly extruded inside the mile-wide crater. The eruption was largely subaqueous, taking place in the 180-m-deep crater lake, and resulted in the emergence of a steep-sided island. The mild character of the eruption and the absence of seismic activity stand in direct contrast to the highly explosive character of the eruption of 1902 to 1903.

An earthquake of Mb4.9 caused damage of intensity VI to VII in Liege, Belgium on 8 November 1983. A temporary array of eight seismographs deployed between 10 and 16 November detected seven probable aftershocks, seven mine-related events and seven near events. The aftershocks imply a vertical source plane striking NE-SW and a hypocentral location directly below the area of maximum damage.

Discourse about the L'Aquila trial in Italy has overlooked the many different roles that laws play within risk governance. For volcanic risk governance, laws not only create the duty holders, beneficiaries and the relationships between them (the stakeholders) and the duties and rights (the stakes) but also dictate the acceptable standards of safety and wellbeing (the ultimate rewards). Within any legal regime, certain court cases will attract a high public profile. They can serve a very helpful role by opening the black box of societal risk management so that robust and candid scrutiny of the past can lead to better management of the future. With such cases, the goal of the competent observer is to advance beyond debate about contested factual details of the past (the noise of what happened) and, by process of induction, to identify wider issues of principle and precedent upon which to make reasoned improvements (the signal to guide what should happen differently in the future and why). The generic characteristics of law-based regulatory regimes are identified because they can be treated as 'constants' which do not change, or do so only very slowly over time. Accordingly, these aspects are highly relevant to long-term risk governance. More ephemeral case-specific factual issues often remain contested and, accordingly, receive less attention here. Significant recent court cases, including L'Aquila, are framed by process of deduction within a generalised legal infrastructure in order to identify the root causes of the apparent status quo of risk governance. This forensic approach is vital not only to identify the legal responsibilities of societal risk managers and the managerial risks that they face and their causes but also to consider possible mitigation strategies. We identify the critical issue of managerial risk vulnerability related to 'standard equivocality' which is the absence of commonly recognised standards for hazard communications to risk decision makers. This absence may result from the lack of regulation of relevant practices and practitioners. We offer some recommendations to fuel debate not only within those science groups that reacted to the L'Aquila case but also the scientific community as a whole. Finally, we argue that checklists represent a rational and methodical way to develop acceptable practice standards focussed upon the difficult risk mitigation choices that are made by civil protection authorities and at-risk individuals.

An earthquake swarm that occurred in the vicinity of the island of Tobago (West Indies) during the latter half of 1982 was monitored in the near-field by a five-station seismograph network. The monitoring of the swarm eventually led to the issuing of a potential earthquake hazard alert, 3 days prior to the major energy release (earthquake magnitude mb = 5.2). We discuss the reasons for issuing this alert. In particular, daily monitoring of the changing b value and energy release was used to constrain estimates of future earthquake behavior. The aftershock seismicity showed activity in a direction trending west to WNW. This is in good agreement with the focal mechanism of the main earthquake which showed right-lateral strike-slip motion along an E-W fault plane dipping steeply (71°) to the north. This active fault appears to form part of the previously unrecognized Southern Tobago Fault System for which there is evidence in the geology of the Late Neogene rocks of the island.

Unrest at the Greek volcanic island of Santorini in 2011–2012 was a cause for unease for some governments, concerned about risks to their nationals on this popular holiday island if an eruption took place. In support of urgent response planning undertaken by the UK government, we developed a rapid evaluation of different eruption scenario probabilities, using the Bayesian Belief Network (BBN) formulation for combining multiple strands of scientific and observational evidence. Here we present three alternative BBN models that were devised in early 2012 for assessing the situation: (1) a basic static net for evaluating probabilities at any one moment in time, utilising just four key unrest indicators; (2) a compound time-stepping net, extending the basic net to update probabilities through time as the indicators changed; and (3) a more comprehensive net, with multiple lines of other data and observations incorporated, reflecting diversity of modern multi-parameter monitoring techniques. A key conclusion is that, even with just three or four basic indicators, it is not feasible, or defensible, to attempt to judge mentally the implications of signs of unrest – a structured probabilistic procedure using Bayes’ Rule is a rational approach for enumerating evidential strengths reliably. In the Santorini case, the unrest, and official anxiety, diminished quite quickly and our approach was not progressed to the point where detailed consideration was given to BBN parameters, analysis of data uncertainty or the elicitation of expert judgements for quantifying uncertainties to be used in the BBN. Had this been done, the resulting scenario probabilities could have been adopted to determine likelihoods of volcanic hazards and risks caused by possible eruptive activity, as identified in a concurrent assessment of the scale and intensities of potential volcanic impacts (Jenkins et. al., Assessment of ash and gas hazard for future eruptions at Santorini Volcano, Greece. forthcoming). Ideally, such hazard and risk assessments should be elaborated in detail and critiqued well before crisis-level unrest develops – not initiated and implemented within a few hours just when a situation looks ominous. In particular, careful analysis of all information is required to determine and represent parameter uncertainties comprehensively and dependably.

Much uncertainty surrounds transmission of transmissible spongiform encephalopathies (TSEs) through blood and blood derived products. A first expert elicitation with 14 experts was conducted in March 2008, and a second re-elicitation involving 11 experts was held a year later in March 2009. Both expert groups were calibrated using a series of seed questions for which values are known, and then were asked to provide their individual judgements on a set of seven target questions for which values are not known or have not been determined through conventional research. Questions dealing with uncertainty of TSE prevalence, genotype effects, susceptibility, and infectivity were answered by the experts. Elicitation can be used to obtain quantitative values for parameters affecting prion uncertainty gaps. We show that the method is amenable to re-elicitation over time allowing refinement of expert opinion as new knowledge becomes available for improved risk assessments where data gaps continue to exist. Copyright © 2012 Inderscience Enterprises Ltd.

THE Soufriere Volcano in the north of St Vincent last erupted in 1902–03 (refs. 1, 2). This eruption was extremely violent: an estimated 1.4 km3 of pyroclast flow and fall was emitted, devastating the northern third of the island and killing 1,565 people. After this eruption, a lake was re-established in the summit crater, and since 1910 the lake water seems to have remained constant in level to within a few metres and in temperature to within a few degrees. The presence of fumaroles on the lake bottom is postulated to account for the fact that the lake temperature, which was measured regularly from 1946–1952, remained at about 4° C above the expected from the ambient air temperature3. Apart from this and since the occurrence between November 1945 and February 1946 of a swarm of local earthquakes4, several tens of which were felt around the flanks of the volcano, the Soufriere remained dormant until October 1971.

The uncertainties associated with tephra thickness measurements are calculated and implications for volume estimates are presented. Statistical methods are used to analyse the large dataset of Walker and Croasdale J Geol Soc 127:17-55, 1971 of the Fogo A plinian deposit, Sao Miguel, Azores. Dirichlet tessellation demonstrates that Walker and Croasdale’s measurements are highly clustered spatially and the area represented by a single measurement ranges between 0.5 and 10 km2. K-means cluster analysis shows that lower thickness uncertainties are associated with closely spaced measurements. Re-examination and analysis of Fogo A fall deposits show thickness uncertainties are about 9% for measured thickness while uncertainty associated with natural variance ranges, between 10 and 40%, with an average error of 30%. Correlations between measurement uncertainties and natural variance are complex and depend on a unit’s thickness, position within a succession and distance from source. Normative error increases as tephra thickness decreases. The degree to which thickness measurement error impacts on volume uncertainty depends on the number of measurements within a given dataset and their associated uncertainty. The uncertainty in volume associated with thickness uncertainty calculated herein for Fogo A is 1.3%, equivalent to a volume of 0.02 km3. However uncertainties associated with smaller datasets can be much larger; for example typically exceeding 10% for less than 20 data points.