Preliminary Report on the 2012, May 20Th, Emilia Earthquake
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PRELIMINARY REPORT ON THE 2012, MAY 20TH, EMILIA EARTHQUAKE May 2012, v.1 Luis D. Decanini1 Domenico Liberatore2 Laura Liberatore3 Luigi Sorrentino4 Sapienza University of Rome Department of Structural Engineering and Geotechnics via Antonio Gramsci 53, 00197 Roma Italy Cite as: Decanini LD, Liberatore D, Liberatore L, Sorrentino L 2012. Preliminary Report on the 2012, May 20, Emilia Earthquake, v.1, http://www.eqclearinghouse.org/2012-05-20-italy-it/ [email protected] [email protected] [email protected] [email protected] ABSTRACT This report presents the results of a preliminary survey in the area affected by the May 20, 2012 Emilia, Northern Italy, earthquake. In this report, a reconstruction of the local seismic catalogues is presented, the damage to historical buildings, rural buildings, industrial buildings and reinforced-concrete buildings surveyed on May 21-22 is described, and a short account on soil liquefaction and strong ground motion is given. Keywords: May 20, 2012 Emilia, Northern Italy, earthquake; historical seismic catalogues; historical buildings; rural buildings; industrial buildings; reinforced concrete buildings; soil liquefaction; strong ground motion. 2 TABLE OF CONTENT 1 INTRODUCTION........................................................................................................................................ 4 2 HISTORICAL CATALOUGES .................................................................................................................... 7 3 HISTORICAL BUILDINGS ....................................................................................................................... 10 3.1 Mirabello......................................................................................................................................... 10 3.2 SantAgostino ................................................................................................................................. 11 3.3 Buonacompra (SantAgostino) ....................................................................................................... 13 3.4 Alberone (Cento) ............................................................................................................................ 15 3.5 Massa Finalese .............................................................................................................................. 15 3.6 Finale Emilia................................................................................................................................... 16 3.7 Rivara (San Felice sul Panaro) ...................................................................................................... 19 3.8 San Felice sul Panàro.................................................................................................................... 21 3.9 San Biagio (San Felice sul Panaro) ............................................................................................... 25 3.10 Mirandola........................................................................................................................................ 27 3.11 Mortizzuolo (Mirandola).................................................................................................................. 33 3.12 Casumaro Finalese (Finale Emilia) ................................................................................................ 35 3.13 Not surveyed buildings and preliminary conclusions ..................................................................... 36 4 RURAL BUILDINGS................................................................................................................................. 39 5 INDUSTRIAL BUILDINGS........................................................................................................................ 44 5.1 SantAgostino (industrial area) ....................................................................................................... 44 5.2 San Felice sul Panàro (industrial area).......................................................................................... 49 5.3 Mirandola (industrial area) ............................................................................................................. 50 6 REINFORCED CONCRETE BUILDINGS................................................................................................ 55 6.1 San Felice sul Panaro.................................................................................................................... 55 6.2 Mirandola........................................................................................................................................ 59 6.3 SantAgostino ................................................................................................................................. 64 7 LIQUEFACTIONS..................................................................................................................................... 65 8 STRONG GROUND MOTION.................................................................................................................. 67 Acnowledgements ........................................................................................................................................... 69 References ...................................................................................................................................................... 69 3 1 INTRODUCTION The 2012 Emilia earthquake occurred on May 20 at 02:03:52 UTC (04:03:52 local time). The local magnitude is 5.9, the epicentre has coordinates: 44.89°N, 11.23°E, the ipocentral depth is 6.3 km. The focal mechanism is inverse, with maximum compression along the N-S direction (dip = 46.45, strike = 103.279, rake = 93.87). The municipalities which suffered the highest damage are located in the districts of Modena and Ferrara (INGV 2012). The main shock was preceded by foreshocks, begun on May 18, the strongest of which, with local magnitude 4.1, occurred on May 19 at 23:13:27 UTC. After the main shock, several aftershocks have been occurring. At 23:00 of May 25, more than 500 events took place, two of which with magnitude greater than 5.0 (event of May 25, 02:07:31 UTC, local magnitude 5.1; event of May 20, 13:18:02 UTC, local magnitude 5.1), and 15 with magnitude ranging between 4.0 and 4.9. The map of the aftershocks shows that the epicentres are aligned E from Ferrara, up to a distance of 70 km, approximately along the E-W direction (INGV 2012). A first estimation of the macroseismic intensities was performed on the basis of recorded accelerations and velocities. Because instruments were not present in the epicentral area at the moment of the main shock, the estimation was performed on the basis of attenuation laws and local amplification, the latter depending on soil type. The maximum estimated intensity is VII-VIII degree of the Modified-Mercalli (MM) scale, which corresponds to values slightly greater than VIII degree of the Mercalli-Cancani-Sieberg (MCS) scale (INGV 2012). The maximum horizontal acceleration measured in the epicentral area is 0.26 g, while the maximum vertical acceleration is 0.31 g (§ 8). From historical seismic catalogues, many earthquakes result in the adjacent areas. The area of Ferrara was stricken by an earthquake with magnitude 5.5 in 1570, with maximum intensity VIII degree. In 1987, an earthquake with magnitude 5.4 stroke the area between Bologna and Ferrara. Finally, on July 17, 2011, an earthquake of magnitude 4.7 stroke the area of Reggio Emilia (§ 2). The present seismic zonation specifies, for the epicentral area and return period of 475 years, an expected maximum horizontal acceleration approximately equal to 0.15 g on stiff soil, and to 0.22 g on type C soil. Altogether, based on historical data, the seismicity of the area can be defined as medium- low (DMIT 2008). The residential building stock in the area consists of unreinforced masonry and reinforced-concrete (RC) buildings. The cultural heritage consists of churches, bell towers, towers, palaces and castles. Several industrial plants, mainly of precast concrete, are present in the area, as well as several masonry rural buildings. Damage is particularly serious for cultural heritage, industrial plants and rural buildings. These types of buildings have natural period greater than that of ordinary buildings, suggesting low frequency components in the ground motion. Moreover, some damage modes highlight a strong influence of the vertical component, which is common for a near-fault earthquake with inverse focal mechanism. The casualties of the earthquake are seven, four of which caused by the collapse of the industrial plants of three different sites, one by the falling of rubble, and two because of sudden illness (La Repubblica, May 21, 2012). The injured under treatment in the hospital are 47 (La Repubblica, May 22, 2012). The number of casualties has been limited by the time when the main shock occurred: most people were in dwellings, which were less damaged compared to industrial plants and churches. It is also worth mentioning that in the morning of May 20, First Communion and Confirmation were scheduled in many parish churches, with foreseeable large crowd. Similarly, a main shock during working hours would have caused much more victims in the plants. The National Cabinet declared the state of emergency for 60 days in the districts of Bologna, Modena, Ferrara and Mantua, and decided a first allocation of 50 million