Italy-Indonesia cooperation: A system for the seismological monitoring of Mt. Marapi (Sumatra)

Several risks impend on the environment, on public and private properties, on strategic and priceless infrastructures in any inhabited area of our planet. They are generated by different sources, both natural and anthropogenic, and have different relevance depending on the synergy between the generated events and on the peculiar interaction with the region where they break out. The evaluation of risks related to different sources is generally done through independent analyses, adopting disparate procedures and time-space resolutions. In most of cases, only qualitative estimates of the risk level are available. Such a strategy of risks evaluation has some evident major drawbacks: 1) it is difficult, if not impossible, to compare risks of different origins; 2) the implicit assumption of independence of the risk sources leads to neglect possible interactions among threats and/or ‘cascade’ effects. In practice, this means that a potential ‘multi-risk’ index could be higher than the simple aggregation of single risk indexes calculated considering each source as independent from the others. A joint analysis and quantification of all the anthropogenic and natural risks which can affect a territory (multi-risk approach) is a basic factor for the development of a sustainable environment and land use planning as well as for a competent emergency management before and during catastrophic events (Durham, 2003). Multi-risk evaluation is a relatively new field, until now developed only partially by experts with different backgrounds (engineering, statistics, seismology, toxicology etc.). Among the few works on this field we quote the UNDRO study (1977), the KATANOS report (1995), Granger et al. (1999), Van Westen et al. (2002), Ferrier and Haque (2003), Grunthal et al. (2006), Blong (2003). However the problem of interaction among different threats is not approached, even in these cases. Objective difficulties in the quantification of risk and thus of multi-risk exist. The first is that scientists of various disciplines do not use a common terminology. In some cases scientists dealing with different types of environmental risks assign different definitions even to the same term. Other difficulties are mostly due to different practices (qualitative and quantitative) and spatial and temporal resolutions that make hard the comparison among different risks. In this document, we propose a new quantitative procedure for multi-risk assessment that makes easier the comparison among different threats and accounts for possible triggering effects. We consider only the major threats typical for Southern Europe, which were the objectives of the EC FP6 NaRaS (Natural Risk Assessment) Project. Forest fires, snow avalanches, wind storms, heat waves are not specifically considered, although the general methodology we propone can be applied to evaluate risk related to these adverse events. In this part of the document, a clarification of the used terminology and a homogenization of the concepts used by the scientists and practitioners in the different risks areas are proposed. This effort does not aim at providing ‘the solution’ of the lack of homogeneity in terminology, but just at being a useful reference to clarify the meaning of the terms used here. At the end of part 1, we report the principles and rationales that stand behind our procedure for multi-risk assessment. In part 2, a short description of the most advanced procedures generally adopted to estimate individually natural and anthropogenic risks representing major threats for Southern Europe is provided. In part 3, we tackle directly the problem of multi-risk assessment applying innovative procedures and protocols to the case study of a town close to Naples (Casalnuovo). The multi-risk problem is split in two distinct phases: in a first phase, the whole set of risks is homogenized to facilitate their comparison ranking; in the second phase, we explore in detail possible “triggering” effects, showing how they can increase significantly the risk in a specific site. We want to underline that the logical sequence of the multi-risk procedure is contained in Parts 1 and 3, which are self-consistent. Part 2 contains several details on the actual way to compute different parameters. Anyway it can be omitted by readers who are interested only in the logical process we have followed.

Italy and Indonesia started a cooperation project in 2005-2006 to cover issues for the mitigation of volcanic risk. In this project, the west area of Sumatra was identified as the area for intervention. In particular, the Marapi volcano was considered. This volcano has shown frequent eruptive activity over recent decades, with the last eruption occurring in 2004. Although its activity is of moderate intensity, it creates a civil protection problem, because since 1980 it has resulted in several injuries and a number of deaths among the tourists who visit the summit crater area. To monitor the activity of Marapi volcano as part of this project, a broadband seismic network has been implemented that consists of four stations based on Guralp GMG 40T sensors with period of 60 s and on GAIA2 data-loggers, which are produced at the INGV. The instrumentation was brought from Italy and was installed by a working group comprising Italians and Indonesians. In addition to the instrumentation in the field, it was necessary to set up a monitoring centre in the Bukittinggi Observatory, which is near the north-western slopes of the Marapi volcano. This is equipped with computers for data acquisition, analysis and archiving. The system for seismological monitoring that has been realized atMarapi volcano is an important tool in the prevention of the risk associated with this volcano, and it is providing a rich dataset that will be of great use for the characterization of the seismicity of the Marapi volcanic structure and the surrounding area. A preliminary analysis of the data recorded during the period 19/10/2006 - 24/11/2008 evidences that the volcano shows VT and LP seismicity. In August 2007 were also recorded signals probably attributable to small explosive activity in the summit area.