The L’Aquila 2009 earthquake: an application of the European Macroseismic Scale to the damage survey

Abstract

In April 2009 the Abruzzo region in Central Italy was hit by a strong earthquake (Ml 5.8, Mw 6.3) with epicentre near the town of L’Aquila. In the following days some members of the QUEST team, the expert working group for macroseismic surveys, began a detailed inspection of the most damaged areas with the aim to apply the European Macroseismic Scale (EMS, Grünthal, 1998) for estimating the intensities. A field form, tested during many other campaigns, was used as a common base for collecting data (Fig. 1).

Fig. 1 – Field form used during survey with percentage of damage observed in Onna.

At the end of the survey, that lasted for two months, about 100 localities were visited. In the investigation, attention has been devoted to establish building typology, grade of damage and percentage of damaged buildings, that is all the basic information for evaluating diagnostics of the EMS. A preliminary analysis of collected data has shown that the application of the EMS allows to better discriminate the effects mainly for higher intensity values. On the other hand, for intensity representing the damage threshold, the MCS scale tends to saturate, skipping from grade V to VI. One of the reasons is that EMS takes into account the building vulnerability, so that damage effects can be partitioned into different classes. The examples of Onna, Coppito and L’Aquila are hereinafter briefly discussed, and EMS intensities compared with estimations obtained by using MCS scales. Onna was almost completely destroyed (Fig. 1). The MCS scale reports at grade IX, destruction and heavy damage in about half of buildings, while at grade X the destruction of about ¾ of the buildings. The intensity evaluated by Galli and Camassi (2009) is IX-X MCS. In the EMS perspective, Onna is a village with 477 buildings, of which ca. 300 have vulnerability class A, 150 class B and 30 are C/D types (Fig. 2).

Fig. 2 – Onna, different building vulnerability classes: a) type A; b) type C; c) type D building. The type A house is destroyed, the type C is slight damaged, the type D is undamaged.

The collected data do not match all the diagnostics expected for a given degree (Fig. 1). In the field we observed 20% of buildings with vulnerability class B suffering damage of grade 5 while buildings with vulnerability classes C and D are scarcely involved (10%), that is they suffer less damage than expected at intensity IX. However, the overall percentage of damage fits the best with intensity IX, discarding the occasional extreme cases. At Coppito the MCS intensity is VI-VII (Galli and Camassi, 2009) since damage was moderate and not diffuse. By using the EMS approach, we observed two buildings with vulnerability class A suffering damage of grade 4 (some collapse of roofs), and many buildings with damage of grade 3. Buildings with vulnerability class B had damage of grade 2, a few of grade 3 (partial collapse of chimneys and fall of tiles). A building of type C with a big antenna onto the roof, suffered the partial collapse (Fig. 3). Few buildings with vulnerability class C or D showed damage of 2 grade. The overall observed effects are consistent with intensity VII EMS. The case of L’Aquila is quite complex to analyse. The town has been ‘divided’ in different but homogeneous sectors for two reasons: i) different geotechnical conditions in contiguous quarters and ii) different building typologies occurring in the historical centre - mainly ancient buildings of vulnerability class A and B - with respect to the new districts (edifices with prevailingly vulnerability classes C and D).

Fig. 3. Coppito. Different damage in buildings of vulnerability class C.

As a consequence, the level of damage was quite different throughout the town. In the NW sector of the city, the new quarters of Cansantessa and Pettino (Fig. 4), the buildings of vulnerability class C and D suffered damage of grade 2 and 3. Just one among the few buildings of class A - it is located along the main street - the roof collapsed. Estimated EMS intensity is VII-VIII.

Fig. 4. a) Cansantessa and b) Pettino. Different damage of grade 3 in buildings of vulnerability class C and D.

In the southeastern suburbs of L’Aquila, Torretta and Gignano suffered less damage on the whole (Fig. 5). Few buildings of vulnerability class C and D suffered damage of grade 2. Few buildings of vulnerability class B suffered damage of grade 3. Estimated EMS intensity is VII. Regarding the historical centre of l’Aquila, many buildings of vulnerability class A suffered damage of grade 4, some damage of grade 5. Many buildings of vulnerability class B suffered damage of grade 3, few damage of grade 4.

Fig. 5. a) Gignano; b) Torretta. Different damage of grade 2 in buildings of vulnerability class C and D and damage of grade 3 in one building of type B.

The very few constructions of classes C and D were slightly damaged. We observed only a few partial collapses in the Casa dello studente, in other two C buildings located near it and in buildings in via Campo di Fossa. We estimated the intensity VIII-IX EMS, because much of the observed damage is of intensity VIII but some diagnostics are of intensity IX. The lack of buildings with classes C and D does not allow to discriminate. This preliminary evaluation for L’Aquila downtown, has been confirmed after the detailed analysis performed by Tertulliani et al. (2009). Acknowledgements. We are grateful to the other QUEST members who contributed with useful information.