The results of a study concerning the zoning of the area of Montemurro (Potenza) are reported. Aim of this study is the evaluation of litho-stratigraphic, morphostructural, mechanical and physical features of the outcropping formations, as well as the characterization of the seismic response of the diffe-rent sites when struck by a seismic event. In the studied area, a geological survey at scale 1:2.000 was performed. The stratigraphy, the main morphological and structural characteristics were analysed, with special emphasis to the definition of geological and technical features of the built-up area. The evaluation of the frequency response of the various sites having different lithologic features was also attempted. The results of spectral analysis were compared with those obtained throughout the use of theoretical models and they were interpreted in the frame of the geological and structural characteristics of the investigated area. The interpretation of stratigraphic geomechanic and geophysical data allowed the authors to set into evidence the existence of three different zones inside the built-up area. These zones show a different seismic and mechanical behaviour which is also confirmed by the distribution of damage occurred during the November 1980 earthquake. The sector called 1 is located in the northern and north eastern part of the built up area, it is characterized by the existence of arenaceous layers, more or less fractured, and high values of the elastic dynamic moduli. This particular setting allowed to keep the percentage of damage due to the 1980 earthquake at a value less than 5% of the existing buildings. The sector 2 includes the historical part of the village of Montemurro and its western boundaries where the clayey and sandy sediments outcrop. The sediments are not well classified and show values of relative density ranging from medium to high, with relatively high values of the elastic parameters. The spectral analysis of microtremors set into evidence the existence of dominant frequency peaks at quite high values (3.90-4.90) which can be related to the resonance effects of the pleistocene pile of sediments with respect to the bedrock of alternating clays and sands. The percentage of damaged buildings is slightly higher than in the previous sector and reaches values of about 11%. Finally, a third sector showing an higher percentage of damage can be distinguished in the southern and south western part of the considered area. Here, alluvium material, mostly sand and silt outcrop. It is quite well classified and it shows values of relative density ranging from medium to high, while the values of the shear wave velocity and the elastic parameters are relatively low. The dominant frequencies in the spectrum of microtremors reach the higher values in the sistes located on the shallower and thinner levels of loose sediments. This is the sector which has the higher percentage of damaged buil-dings, reaching the value of 24%.
Zonazione geologico-tecnica e sismica del centro abitato di Montemurro
LOMBARDO, Giuseppe;
1989-01-01
Abstract
The results of a study concerning the zoning of the area of Montemurro (Potenza) are reported. Aim of this study is the evaluation of litho-stratigraphic, morphostructural, mechanical and physical features of the outcropping formations, as well as the characterization of the seismic response of the diffe-rent sites when struck by a seismic event. In the studied area, a geological survey at scale 1:2.000 was performed. The stratigraphy, the main morphological and structural characteristics were analysed, with special emphasis to the definition of geological and technical features of the built-up area. The evaluation of the frequency response of the various sites having different lithologic features was also attempted. The results of spectral analysis were compared with those obtained throughout the use of theoretical models and they were interpreted in the frame of the geological and structural characteristics of the investigated area. The interpretation of stratigraphic geomechanic and geophysical data allowed the authors to set into evidence the existence of three different zones inside the built-up area. These zones show a different seismic and mechanical behaviour which is also confirmed by the distribution of damage occurred during the November 1980 earthquake. The sector called 1 is located in the northern and north eastern part of the built up area, it is characterized by the existence of arenaceous layers, more or less fractured, and high values of the elastic dynamic moduli. This particular setting allowed to keep the percentage of damage due to the 1980 earthquake at a value less than 5% of the existing buildings. The sector 2 includes the historical part of the village of Montemurro and its western boundaries where the clayey and sandy sediments outcrop. The sediments are not well classified and show values of relative density ranging from medium to high, with relatively high values of the elastic parameters. The spectral analysis of microtremors set into evidence the existence of dominant frequency peaks at quite high values (3.90-4.90) which can be related to the resonance effects of the pleistocene pile of sediments with respect to the bedrock of alternating clays and sands. The percentage of damaged buildings is slightly higher than in the previous sector and reaches values of about 11%. Finally, a third sector showing an higher percentage of damage can be distinguished in the southern and south western part of the considered area. Here, alluvium material, mostly sand and silt outcrop. It is quite well classified and it shows values of relative density ranging from medium to high, while the values of the shear wave velocity and the elastic parameters are relatively low. The dominant frequencies in the spectrum of microtremors reach the higher values in the sistes located on the shallower and thinner levels of loose sediments. This is the sector which has the higher percentage of damaged buil-dings, reaching the value of 24%.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
