All over the world, most of the highly populated cities (but also numerous small towns and rural villages) are seriously vulnerable to the effects of natural catastrophes. Natural hazards and catastrophes can be defined as processes, originating in the biosphere, with damaging fall-outs on mankind and the world we live in. The main hazardous catastrophes (varying in magnitude, frequency, duration, extent, onset speed, spatial dispersion and temporal spacing) are: earthquakes, volcano eruptions, landslides, tsunamis, coastal erosions, floods, hurricanes, drought, wild and man-induced fires, etc. It is worth noting that, in absolute terms, the economic costs of disasters have been increasing over the last decades. Furthermore, losses due to earthquakes constitute a significant part of the global losses due to natural hazards, and are those that yearly cause the highest number of casualties. In Europe (EU-27), more than 41 million people (about 8%) live in high seismicity regions; another 64 million (about 13%) live in moderate seismic areas. The total economic loss due to earthquakes during the 20th century is about 40 billion Euro alone in Europe. Between 1980 and 2000, the average yearly death toll because of earthquakes was about 240 casualties in the EU (mainly in Italy) and 950 in Turkey alone. Looking at a larger scale, one can observe that, for example, in 2003 (Bam earthquake, Iran), earthquakes caused 25000 casualties over the 50000 casualties due to catastrophes in general. In 2004, 640 people were killed by an earthquake in Morocco. In 2005 the earthquakes in Kashmir and Indonesia called for around 88000 victims, that represented 95% of the overall fatalities caused by extreme events in the world. Similar trends were registered during the following years, until the earthquake in the Chinese province of Sichuan in 2008 (70000 casualties, 18000 people still missing, 374000 injured, and almost five million people made homeless) (Ref. 1).
Most of the times, in addition to very high loss of human lives, significant loss in Cultural Heritage (CH) assets, in form of movable and immovable objects, is caused by earthquakes. One of the most dramatic events in this respect, is that of Bam. The more than 2000-year old citadel, the world biggest mud brick complex, was destroyed by the 6.3 magnitude earthquake. Subsequently, it was inscribed on the UNESCO list of World Heritage in Danger in 2004. In some other cases, earthquakes may be more ‘respectful’ of human lives. For example, the 1997 earthquake in Umbria-Marche region (Italy, 5.8 on the Richter scale) caused 11 victims and one hundredth injured people (but around 22000 people were left without shelter). However, its effect on CH was enormous: almost 8000 CH assets were damaged (Ref. 4) and the vault of the San Francesco Basilica in Assisi, covered by Giotto’s frescoes, collapsed. As in that case, most of the assets had been retrofitted and strengthened after a previous earthquake (occurred in 1979), post-earthquake survey of damages after the 1997 seismic event allowed the scientific community to understand the drawbacks and limitations of the state-of-the-art technologies and approaches applied at the time. A similar case is that of Bovec (Slovenia, magnitude of 5.2; Ref. 6) in 2004, where a previous earthquake and subsequent reconstruction had occurred only six years earlier (1998), and in Azores (Portugal, magnitude 5.6; Ref. 5) in 1998, where a previous earthquake and subsequent reconstruction has occurred in 1973.
The last, but not less important, catastrophic earthquake that has demonstrated once again the strict correlation among safety of citizens, loss of cultural heritage value, and increased danger caused by wrong interventions is the recent event happened in L’Aquila, Abruzzo (Italy). The mainshock was registered by 57 stations of the Accelerometric National Network on 06/04/2009, 3.32 AM, and had Richter magnitude 5.8. The response spectra were characterized from high acceleration in the low period range, exceeding gravity acceleration by 20% to 60% in the different directions, so that rigid structures were subjected to very high forces. More than 20.000 quakes have been recorded since the mainshock by the INGV station in L’Aquila Castle, extending in NWSE direction, along the Aterno Valley, and consistent with the direction of the principal known active faults of the area. The sequence of historical earthquakes shows that the strongest events occurred on 09/09/1349 (Me 6.5) and on 02/02/1703 (Me 6.7). Similar earthquakes occurred in 1461 (Me 6.4), 1762 (Me 5.9), 1916 (Me 5.2) and 1958 (Me 5.2), all of which caused damage in L’Aquila and surrounding areas (Ref. 2).
The effect of this earthquake were devastating: it caused 300 casualties and around 100.000 evacuated (Ref. 3). The damage to CH buildings was quantified in more than 3.000.000.000,00 € and the inspections revealed that only 23% of CH buildings is fit for habitation (Ref. 7). The Project Coordinator (UNIPD) and the project participant n° 5 (POLIMI) were appointed by the Italian Ministry of Cultural Heritage, in agreement with the Department of Civil Protection, to coordinate the activity on CH buildings, that included the following aspects:
a) inspecting CH buildings and compiling first level form for damage assessment;
b) making first economical assessment of damage and certifying fit for habitation;
c) designing, supervising, coordinating the emergency interventions;
d) coordinating with Art Historians for cataloguing work of arts and for their rescue;
e) coordinating activities on CH with those on ordinary buildings and infrastructures; creating of list of priorities; visits of experts (in this framework, visits for project participant n° 3 ITAM, 4 NTUA, 6 UMINHO, 7 UPC, 8 UBATH and 12 IAA were organized with the DPC), collecting queries of ‘monument’ adoption from Italian and Foreigner Public Bodies and Private Entities, etc.;
f) understanding the effect of the earthquake on CH buildings and, in particular, understanding the effects of past interventions on the behavior shown by CH structures.
Ref.2 - www.ingv.it
Ref.3 - www.protezionecivile.it