|SPAIN CROWN PRINCE FELIPE CONSOLES FAMILY MEMBERS OF LAST EARTHQUAKE VICTIMS, MAY 2011|
Recent earthquakes (Mw>5) have spared the Spanish and European major urban centres, but this will not persist indefinitely, examples of their potential severity being the Albolote, Santa Fe and Atarfe earthquakes in Granada Mw 5,1 of 1956, also Assisi 1997 and the Mw 5.8 L'Aquila earthquake of 2009 in Italy, and the most recent Lorca Mw 5.2 earthquake of 2011. In coming years several more cities will be damaged by significant earthquakes. We are most certain of the fate of those cities near plate boundaries, however, mid-continent earthquakes also occur, although less frequently.
1. GREAT FAULTS, SMALL FAULTS AND CODES
|SEISMIC INFORMATION IN THE NCSE 02 CODE|
|THE 1755 LISBON EARTHQUAKE AND TSUNAMI (8,5-8,8)|
|FRONTS OF BUILDINGS, MASONRY, COLLAPSES OF NON STRUCTURAL ELEMENTS, ARE ALWAYS THE SAME KILLERS. WORLDWIDE, EVERYTIME AN EARTHQUAKE STRIKES A CITY, REPORTS ABOUT THE DAMAGE SHOWS THAT THESE CONFIGURATIONS ARE VERY DANGEROUS WITHOUT AN ADEQUATE ANCHORAGE, SOME OTHER SHAPES, IRREGULARITIES, AND DISTANCES AMONG BUILDINGS THAT ARE NOT RECOMMENDED IN SEISMIC PLACES ARE ALWAYS PRESENT, BUT NOBODY PAYS ATTENTION. NON STRUCTURAL QUESTIONS ARE VITAL FOR CITIZENS, URBAN PLANNING WITH SEISMIC CRITERIA AND ALSO AN ADECUATE KNOWLEDGE OF THE GROUND UNDER OUR CITIES, AND OF COURSE, PEOPLE'S BEHAVIOUR, BEFORE, MEANWHILE AND AFTER A SEISMIC EVENT. A MINIMUM SEISMIC CULTURE CORRECTLY TRAINED WILL BE ENOUGH FOR AN IMPLEMENTATION OF AUTOPROTECTION PHILOSOPHY, AND WILL RESULT IN A BENEFIT FOR BOTH THE INDIVIDUAL AND THE COMMUNITY, AND, MOST OF ALL, WILL SAVE MANY OF LIVES ACROSS EUROPE: A NECESSARY LESSON TO BE LEARNT FROM CHILDHOOD.|
It is necessary to inform and instruct architects and city planners on the consequences of their urban planning and architectural decisions, since they (city planners and official entities) should share with structural engineers the great responsibility of mitigating seismic risk and of reaching seismic resilience in Spanish cities. It is essential to convince city officials, urban planners and decision takers of the urgent necessity of revising urban ordinances on seismic places all across our geography. The NCSE 02 map establishes a zonification for the basic acceleration values, the basis to obtain the design seismic acceleration, fundamental data required to design any seismic-resistant structure. The basic acceleration corresponding to Lorca is 0.12g, with Granada and Alicante being the zones with the highest values: over 0.16g.
|NCSE 02 IS ONLY A STRUCTURAL CODE DESIGNED FOR EACH INDIVIDUAL PIECE OF THE SYSTEM: THE BUILDING. BUT THE REAL SCENERY OF THE SEISMIC EVENT IS ALWAYS THE CITY. THE 3D GROUND EFFECT IS NOT CONSIDERED ENOUGH IN NCSE 02, BUT IT IS STILL LESS CONSIDERED IN URBAN ORDINANCES THAT CONTEMPLATE GROUND AS A SURFACE RATHER THAN A VOLUME WITH DISCONTINUITIES, IRREGULARITIES, AND FAILURES. |
The top basic acceleration value in Spain is in the town of Santa Fe in Granada: 0.24g. In spite of this, the latest harmful seismic movements in Spain have been located in the region of Murcia, that suffered five important seisms in the last twelve years: Mula (February, 1999), Bullas (August, 2002) y La Paca (January 29th 2005, magnitude 4.4 Mw, 40 km away from Lorca). And, unfortunately, as with the last two in Lorca (May, 2011), all of them were related to the FAM. The seismic design acceleration obtained by multiplying the basic acceleration by the rest of the parameters included in the NCSE 02 (four coefficients: contribution k = 1.00, ground C =1.61, risk r =1.00 and ground amplification, S =1.27) is 0.15g in Lorca, clearly less than the maximum instrumental basic acceleration registered, 0.41 g.
|SOUTHEASTH IBERIA BIG FAULTS|
|MAP OF THE PALEOSEISMICITY STUDIED IN IBERIA: ONLY THE SOUTHEAST TERRITORY AND CATALUÑA SHOW A FEW STUDIES OF THE LAST MIOCENIC-PLIOCENIC AND QUATERNARY SEISMIC ACTIVITY|
2. THE REALITY OF THE GROUND: A VOLUME, NOT A SURFACE
An example: Lorca is on the axis of the FAM (Alhama de Murcia Fault). Both seismic movements that occurred on May 11th were very superficial (2 km depth): the first (4.5 Mw) two hours before the second (5.2 Mw) was only 3 km NE from town centre. This also explains the high number of minor events registered months after the two main events (more than 300), identified across the segments in which the FAM is divided into. This is a transcendental question because similar configurations may exist not only in the region of Murcia but also in many other regions in Southwest Europe, such as Navarra, the Basque Country, Aragón and Cataluña, in Spain and their counterparts on the North side of Pyrenees: in French Departments, Pyrenées Atlantiques and Orientaux.
|3D GEOLOGICAL STRUCTURE AND MOVING MATERIALS UNDER SOUTHEAST IBERIA|
The year before the earthquakes struck Lorca, the FAM was in an inter-seismic period with no activity at all. Thus, it was quite predictable, with obvious limitations, that something was going to happen; some tectonic experts even announced it, as is the case of Professor Tomás Rodriguez (University of Cartagena). The real unexpected issue was not the earthquake itself but the top basic acceleration that was generated: 0.41g. This was more than 3 times the expected value (0.12g). There is no doubt that among other questions an amplification phenomenon happened. Are the C, k, S coefficients or the other of our capricious inventions, responsible of it? Or certainly we don't have the correct 3D mental-picture of the real nature of the ground under our feet? Is the ground under Lorca smart enough to be "aware" that its coefficients are: k=1, C=1.61, and S=1.27, or does it simply not care?