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Month: January 2013
OVERVIEW OF THE WORKSHOP “SEISMIC RISK IN THE PO PLAIN”
On Nov. 24th 2010, for the anniversary of the 2004 earthquake of Valsabbia and Garda, a workshop on “Seismic risk in the Po Plain” took place at Brescia. The conference was organized by CeSiA (Applied Seismology and Structural Dynamics Research Center), a research center of the University of Brescia, with the cooperation of the Museo Civico di Scienze Naturali of Comune di Brescia, which, moreover, hosted the meeting. The workshop belongs to a cycle which started in 2006 (information on the previous events is available at http://cesia.ing.unibs.it/).
The workshop topic, which respects the aims of CeSiA, is very interesting since the Po Plain includes areas of moderate but complex seismicity; some of these areas have only recently been classified as seismic by the norms. Thus researchers deem necessary both further geologic and seismologic studies and seis- mic risk assessments of an area characterized by an intense urbanization, which in great part occurred in the absence of adequate seismic rules.
After the opening by the President of CeSiA, Claudio Giorgi, by the Director of Museo Civico di Scienze Naturali, Paolo Schirolli, by the alderman for Culture of Comune di Brescia, Andrea Arcai, by the President of Ordine degli Ingegneri della Provincia di Brescia, Marco Belardi, the workshop, attended by about one hundred people (both technicians or professionals and researchers) included two sessions, “Seismic hazard in the Po Plain” and “Seismic Vulnerability in the Po Plain”.
This presentation briefly describes the workshop programme.
QUATERNARY FAULTS AND SEISMIC HAZARD IN THE LAKE GARDA AREA
Evidence of active tectonic shortening in the Lake Garda area (Northern Italy) has been very well described in the geological literature for at least 40 years, mainly due to the extensive research conducted during the siting of nuclear power plants in Lombardia in the 80’s. This area includes in fact the causative faults for some of the largest seismic events ever occurred in Northern Italy, i.e. the two medieval earthquakes of January 3rd, 1117 (Verona, Io = IX-X MCS) and the 25th of December, 1222 (Brescia, Io = IX-X MCS). More recently, two “twin” moderate events occurred at Salò on October 30th, 1901 (Io = VIII MCS) and November 24th, 2004
(Ml =5.4). This is therefore a critical area for understanding the relationship between tectonic structures and earthquake source parameters in the Po Plain. We address this issue through new field data and airphoto interpretation, morphobathymetric investigations in South Lake Garda, and a systematic revision of published data. A new map of Quaternary faults is presented, that shows a good correlation between Quaternary deformations, major regional tectonic structures, and macroseismic information derived from local strong seismic events. Style and rates of activity of the proposed capable faults allow us to infer the typical seismogenic features of the characteristic seismic event for the Lake Garda region, which can be regarded as the controlling earthquake for the seismic hazard of the central part of the Po Plain.
ITHACA PROJECT AND CAPABLE FAULTS IN THE PO PLAIN (NORTHERN ITALY)
The use of the term “capable fault” instead of the more generic “active fault”, is to be preferred when dealing with faults, that, more than being simply active, have the capability to cut or deform the ground surface, generally in association, but not exclusively, with seismic events. Such faults are the most relevant from the societal hazard viewpoint, for the damage they can cause directly or indirectly (e.g., interaction between capable fault and high risk facilities) by offsetting the ground and by shaking (surface ruptures commonly accompany earthquakes above magnitude 6).
Recognition of presence of capable faults and assessment of their potential for surface rupturing is fundamental in the siting process of highly hazardous and strategic structures and, more generally, in land use planning and management of infrastructures, especially during emergencies.
So, being the Italian territory crossed by a large number of potentially capable faults, more than a decade ago the ITHACA (ITaly HAzard from CApable faults) project was initiated, to map and describe all faults recognized or suspected of being capable. The database, that contains more than 1500 faults (with a wide range of variability of the level of reliability of the input data), is managed by the Geological Survey of Italy, department of ISPRA.
In the Po Plain territory, ITHACA displays many of such structures. Despite the modest expected displacement (tens of centimeters at most) for each event along these faults, the high, and still growing, grade of human occupancy of this land makes the risk associated to seismicity and capable faulting a growing factor of anxiety. To begin a process of risk attenuation, specific norms in urban planning are needed to regulate development along capable faults, with special care when dealing with hazardous plants.
VULNERABILITY ANALYSIS OF RELEVANT AND STRATEGIC BUILDINGS IN SEISMIC ZONE 3 MUNICIPALITIES OF LOMBARDY REGION
The vulnerability analysis is a quick solution for the identification of buildings that, because of the materials characteristics or construction quality or structural scheme, are in critical conditions with respect to their seismic vulnerability, such that either damage or collapse may occur in case of earthquake. The analysis results, carried out on concrete and masonry buildings through the filing of I and II level records /1/ /2/, are based on weighted sums of 11 (12 for concrete) parameters to which the data collectors assign a quality class, taking into account the observed situations during an inspection, the similarities with comparable buildings (with relation to the construction period and the used technology) and the geometrical features, such as the average floor area and the resistant areas. In case of vulnerable buildings, more detailed analysis will be further necessary to define the collapse mechanism and to assess, in case, the necessary rehabilitation works
SEISMIC VULNERABILITY OF THE EMBANKMENTS OF RESERVOIR BASINS FOR FLOOD REDUCTION LOCATED ON THE TRIBUTARY STREAMS OF THE PO RIVER (ITALY)
This paper presents methodology and results of seismic vulnerability analyses performed in flood expansion areas of Parma River, tributary streams of the Po River in Emilia-Romagna (Italy). The proposed methodology included the following steps: collection of the pre-existing information and geologic map; performing of in-situ investigations and geotechnical laboratory tests on the collected soil samples; definition of the geologic-geophysical and geotechnical models; individuation of the expected seismic inputs; analyses of Local Seismic Response; identification of a number of significant sections; analyses of slope stability. The results obtained are discussed in the paper in order to illustrate how the methodology employed enables definition of the seismic vulnerability of the flood expansion area and allows to give indications regarding its future use. The proposed study points out that the flood expansion area has a level of safety adequate for guaranteeing seismic stability taking into account the rules of Italian Ministerial Decrees 14.01.2008 and 24.03.1982. It is therefore possible to consider the area suitable also as a reservoir basin and no intervention is required other than normal monitoring and maintenance.
SEISMIC VULNERABILITY ASSESSMENT: FROM INDIVIDUAL BUILDINGS TO THE URBAN FABRIC AND BEYOND. APPLICATIONS TO THE SALÒ CASE (BRESCIA PROVINCE, ITALY)
In the last years the “disaster” scientific community has increasingly recognized the relevance of vulnerability and related concepts (resilience, coping capacity, adaptation) in managing natural risks. The limitation of structural measures taken with the aim of reducing the hazard severity and/or frequency has come to evidence. Those are still important; yet other measures able to reduce exposure and vulnerability are recognized as increasingly necessary. Seismic engineers have been dealing with physical vulnerability of structures since long time, as clearly nothing can be really done to mitigate earthquakes as phenomena. Not only new constructions were covered by analysis and care, but also the large built stock, including historic heritage.
Seismic engineers have achieved significant advancement in vulnerability assessment. However, several recent events in Italy and elsewhere have dramatically shown that structural resistance is one component of the overall seismic response of complex systems like cities, but not the only one. Urban and spatial planning decisions should embed concerns regarding amplification zones, potential induced effects triggered by an earthquake (like tsunami or land- slides), cascading effects among interconnected systems. This has been done only to a very limited extent until now. Among the reasons is the lack of tools for actually addressing the multiple vulnerability facets that must be looked at for such a comprehensive mitigation effort. In the article, the results of a recently concluded European funded research project (Ensure) are presented; an application of the tool and methodology developed during the project has been carried out on the case of the Salò municipality in the province of Brescia, Northern Italy.
INDUCED SEISMICITY AND RELATED RISK IN ITALY
The seismicity induced by human activities is a subject almost unknown in Italy, with an average of published works on the subject at a fraction of a percentage of what is being published abroad. The first part of this paper discusses the historical reasons for this lack of interest, while the second will examine the implications in terms of seismic risk and possible regulations following the example of other European countries.
STRUCTURAL SETTING OF THE CENTRAL PO PLAIN
The present configuration of the different structural units of central Po Plain is strongly controlled by the tectonic setting that characterized this area since the end of Mesozoic.
The older, mainly extensional structures controlled the evolution of both the Alpine and Apenninic thrust fronts from latest Oligocene to Pleistocene.
The younger reactivations (upper Pleistocene) of these faults are generally located in the outer portions of the Southern Alps and Northern Apennines structural arcs and in the intermediate residual foreland that separates these two thrust-fold belts presently characterized by opposite vergence.