PRESENTED IN THE 2011 WORLD CONFERENCE ON CIVIL ENGINEERINIG AND URBAN PLANNING (WCEUP 2011) IN HANGZHOU, CHINA
The accelerations measured in the first event and in the second one, two hours later, were 0,24g (Mw 4,4) and 0,41g (Mw 5,2). The seismic resistant structural code in force, NCSE 02, determines a basic acceleration of 0,12g for the area. The activity of the Alhama-Murcia Fault (FAM), on which the epicentre was located, NE from town centre, at a depth of 2 km and a distance of 10 km. FAM is known since 1979. The amplifying effect of the ground under Lorca, exceeding the previsions of the ground coefficient C established in the code, was one of the causes of the severe damage in built environment.
Fig. 1 Lorca’s earthquake USGS chart (data and map) and IGN map.
According to the report, drafted by the Geological and Mining Institute (IGME) of the Science and Innovation Ministry, a first seismic event (magnitude 4.4 Mw) took place in Lorca, at 15:05 (GMT), followed by a series of minor events (6 tremors, magnitudes around mbLg 2.5) and a second significant shock (5.2 Mw) at 16:47, that lasted 5 seconds.
Up to 130 minor events (between mbLg 0.4 and 3.9 Mw) were registered up until 17th of May. Epicentres were located close at the NE of Lorca (Figure 1), at a distance of about 2 km, coinciding with the Northern part of the Alhama de Murcia Fault (FAM).
The Fault spreads along the NW border of the Guadalentín Valley, from the periphery of Alcantarilla, in Murcia, to the outskirts of Góñar in Almería, a total length of 85 km.
Accelerations reached in the two main events, registered by the stations of the National Net of Accelerographs of ING in Table I and main events in Murcia in the last year in Table II.
Fig. 2 EAE classification table. Rodriguez-Pascua et al. (2011)
Lorca Town Council has implemented a geographical event viewer in its web page, to locate every inspectioned building in the municipality, which has proof to be a very useful tool for stakeholders.
Structural geology techniques were used in the study of the historical building damage included in the IGME Preliminary Field Report.
In the inspection, more than a hundred effects were identified and classified in 33 masonry structural historical buildings, according to what Giner-Robles et al. (2009) and Rodriguez-Pascua et al. (2011) defined as Archaeological Earthquake Effects (EAE), depending on whether they are direct or indirect effects (Fig. 2).
After analyzing the global damage extent, the provisional budget was 50 millions €. Final figure, according to the Framework Plan for the Lorca’s Cultural Heritage Recovery, drafted in July, is 51.287.076,93 €.
Complete restoration is scheduled to be completed in five years. A too long-term period according to the importance of tourism in Lorca’s economy and quite doubtful to comply with, due to the fact that the required funds are not available for the moment. The summary of the restoration cost of the most significant buildings is the following:
Fig. 3 Espolón Tower, before the earthquake
Fig. 4 Damaged tower top, afterwards. SW corner, first plane
Fig. 5 Aerial view of the Church of Santiago, before and after the dome collapse
Fig. 6 Detail of damaged top of the tower, Church of Santiago
|Fig. 9 Inside damage.Convent of the Virgen de Huertas|
Collegiate Church of San Patricio (s.XVIth-XVIIth c.). Renaissance interior, baroque facade, declared Historical-Artistic Ensemble in 1941. Final budget: 2.960.000 €.
Other configurations including short columns, frequent in existing buildings in seismic-prone zones, due to the disposition of staircase landing beams between two floors or variation of columns height with different ground floor levels, are included in first and second place in the same figure.
Different pictures of the collapsed structure in Lorca in Figure 12. Other short column structures did not collapse, Figure 14.
Fig. 22 NCSE 02 seismic risk map
- Lorca should become an in situ research laboratory for the whole Europe. The earthquake consequences require a much deeper and extensive multidisciplinary analysis, in order to establish the lessons-learnt for seismologists, geologist, engineers, architects and stakeholders. It is too early to have final consistent conclusions, but we are in time to point out a series of striking combined causes. In Spain, we have the first opportunity to apply the content of the NCSE 02 article 1.3.3 after being classified VII, in such an extended area. The content is this: “...after a high intensity seism, an report of every construction located in areas with intensity equal o higher than VII (EMS scale) should be drafted, in order to analyze the consequences of the earthquake on it, as well as to determine the kind of measures to be taken in relationship. The author of the report should be the technical expert responsible for the maintenance, or if there was not one, the proprietor or legal owner of the construction”.
- Actions must be taken in order to raise public awareness. It is essential to raise the awareness of the population in general, specially the building sector, regarding the existence of areas highly vulnerable to earthquakes in Spanish geography. The time has come to determine the preventive actions to be adopted as well as to plan all the procedures to follow in case of high magnitude seism’s striking. These two should be the main objectives to be promoted by the administration, as well as to transmit a clear message: Spain is a country with seismicity capable of killing people, seriously damaging buildings, infrastructures or heritage, or even paralyzing the economic activity of a whole region.
- Urban planning. Tectonic and/or seismic research should be coordinated with micro-zoning and urban planning development, in order to make the location, volume, number and height of buildings and other of their significant characteristics, consistent with the geological and seismic ground information available. Furthermore, urban development of areas with high seismic risk should require the previous elaboration of local maps, including among other natural risks, the seismic risk.
- National Heritage. Spain is the country with the second most important number of National Heritage sites in the world, after Italy and before China. It seems both appropriate and necessary to make an investment in the future of Spain, one of the most important countries in the World regarding cultural tourism and still not developed enough.
- Spanish Heritage (historical, artistic, architectural, landscape, gastronomic and so on) should be promoted to the highest post in the scale of priorities, those regions with the most important cultural or historical richness should be provided with special plans related to seismology and heritage preservation. Possibly, one of the most ambitious tasks to assume in future days may be the reinforcement of churches, palaces, convents and castles, like those now painfully damaged in Lorca, as well as to foresee their behaviour during an earthquake, like the one that shook Lorca, on Wednesday, 11th of May.
- NCSE 02 has proved to be very effective regarding structural elements, but needs to be revised and completed, in reference to: Constructive non-structural elements, such as, parapets, cornices, installations, partitions and other: there is a lot to do regarding their design, location, anchorage, flexibility, etc. It is also obvious the need of reinforcing masonry walls, either made of bricks of or stone in those places where they are traditionally used.
- Local seismotectonic zoning, above all in zones where it is well known that seisms of the L’Aquila or Lorca type could happen in the future.
- New maps are required, as well as new approaches to the response spectrums from waves generated by shallow or superficial faults activity. It is urgent too, to revise the values of the contribution coefficient k after the experience in Lorca.
- Increase on the basic acceleration values of the zones close to active faults, especially in towns in line with the ones already identified with recent activity, and in the future, with those to be discovered.
- Major investigation, study and consideration of all the layers of the ground affected by foundations which may receive seismic waves. The code classification in types I, II, III and IV is too vague and undetermined to prevent structural damage due to geotechnical reasons.
- Real geotechnical effects should be considered, revising the C coefficient associated to the ground. It is not enough to quote the possibility of liquefaction of granular soils, there is a wide range of deflections not considered in NCSE 02, such as collapses, densifications, reactivation of consolidations, etc., either in soil or in rock. Part of the new text to include as an extension of the in force code should have a geotechnical and geomechanical character according to the effects on buildings and infrastructures.
- The appearance of new seismic zones, should also bring about the exigence to adapt, as far as possible, the existing buildings to this new code. The Spanish Technical Building Code (CTE) included two important new concepts: the need to guarantee the safety requirements of structures, not only in the design phase but also during the execution phase, and while the building is being in use. Also, it underlines the requirement of maintaining buildings properly in order to guarantee their performance and behaviour during their useful life. This essential requirement is very important for seismic-resistant structures of existent buildings, that could have been designed complying with former codes. It is absolutely necessary to extend the Technical Buildings Inspection (ITE), already in force in many cities in Spain, to the whole country, with a special emphasis upon those structures in high seism risk areas. That would be the best option to reach our goals.