Giuseppe
Emeritus
[Source: Istituto Nazionale di Geofisica e Vulcanologia, Italy, full PDF document: (LINK). Extracts, edited.]
Preliminary Report on the coseismic geological effects related to the May 20, 2012 earthquake in the Emilia Po-Plain
EMERGEO working group - Istituto Nazionale di Geofisica e Vulcanologia - emergeoteam@ingv.it
On May 20, 2012 at 04:03 Italian time, a Mw 5.9 earthquake hit a broad area of the Emilia Po-Plain between the Modena, Ferrara, Rovigo and Mantova provinces. Severe damage occurred mainly in the historical parts of the towns and in the industrial areas. The Emergeo working group was activated to survey the epicentral area in search for coseismic geological effects.
(...)
The media and the internet showed several of these effects that were used as the starting point of our survey. Most of them were located within a polygon enclosed between Mirandola, Camposanto, Bondeno e Sant?Agostino. This is also the area were most of the aftershocks are located.
The field survey is still going on and is involving a dozen of geologists in the field and several others in the lab to gather, organize and interpret the data. This report does not contain details on the surveyed effects but just preliminary information on the investigated areas (Figure 1) and on the type of observed effects.
The most commons among the surveyed effects belong to three types:
In coincidence of some liquefactions and fractures water and gas pipes in the ground were broken.
A first comparison between the geomorphic characteristics of the area and the location of the geological effects described above shows a correlation with the location of paleo-river channels of the Secchia, Panaro and Reno rivers. The main fracture systems seems to be correlated to levees and in particular with the channel named Cavo Napoleonico.
Another common characteristics found in all the investigated areas is the increase of the water table of a few meters that is still not back at the original level.
More images are at: http://www.flickr.com/photos/ingv/.
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Preliminary Report on the coseismic geological effects related to the May 20, 2012 earthquake in the Emilia Po-Plain
EMERGEO working group - Istituto Nazionale di Geofisica e Vulcanologia - emergeoteam@ingv.it
On May 20, 2012 at 04:03 Italian time, a Mw 5.9 earthquake hit a broad area of the Emilia Po-Plain between the Modena, Ferrara, Rovigo and Mantova provinces. Severe damage occurred mainly in the historical parts of the towns and in the industrial areas. The Emergeo working group was activated to survey the epicentral area in search for coseismic geological effects.
(...)
The media and the internet showed several of these effects that were used as the starting point of our survey. Most of them were located within a polygon enclosed between Mirandola, Camposanto, Bondeno e Sant?Agostino. This is also the area were most of the aftershocks are located.
The field survey is still going on and is involving a dozen of geologists in the field and several others in the lab to gather, organize and interpret the data. This report does not contain details on the surveyed effects but just preliminary information on the investigated areas (Figure 1) and on the type of observed effects.
The most commons among the surveyed effects belong to three types:
- 1) Liquefactions related to overpressure in the aquifers hosted in buried sand layers.
- 2) Extentional fractures with opening.
- 3) Liquefactinons related to fractures.
1) Liquefaction is diffused near the towns of San Felice sul Panaro, San Carlo di Sant?Agostino, and Bondeno. It involves mainly fine gray sands but locally brown sands too. Generally sand is ejected through several aligned vents and forms coalescent flat cones. Water wells,10-15 m deep served as artificial vents for liquefied sand and are now completely sand infilled. Manufacts in town likely represented a preferential way for the sands to reach the surface. In some cases obvious localized bulges and subsidence related to the extrusion of sediments are observed (Figure 2).
2) Open fractures with small vertical throws (without a preferential side down) and apparent en-echelon organization are observed mainly in the eastern area and can be traced for some hundreds of meters (Figure 3). Locally, ejected sands occur along the fractures. A trench across one of these fractures has shown the presence of sand along the fracture that did not reach the surface.
3) Fracturing and liquefaction are observed also in the eastern sector between Bondeno, Mirabello, and San Carlo. An important amount of liquefied sand and fine sand was ejected from fractures tens of meters long, frequenly in an apparent en-echelon setting (Figure 4).
(...)2) Open fractures with small vertical throws (without a preferential side down) and apparent en-echelon organization are observed mainly in the eastern area and can be traced for some hundreds of meters (Figure 3). Locally, ejected sands occur along the fractures. A trench across one of these fractures has shown the presence of sand along the fracture that did not reach the surface.
3) Fracturing and liquefaction are observed also in the eastern sector between Bondeno, Mirabello, and San Carlo. An important amount of liquefied sand and fine sand was ejected from fractures tens of meters long, frequenly in an apparent en-echelon setting (Figure 4).
In coincidence of some liquefactions and fractures water and gas pipes in the ground were broken.
A first comparison between the geomorphic characteristics of the area and the location of the geological effects described above shows a correlation with the location of paleo-river channels of the Secchia, Panaro and Reno rivers. The main fracture systems seems to be correlated to levees and in particular with the channel named Cavo Napoleonico.
Another common characteristics found in all the investigated areas is the increase of the water table of a few meters that is still not back at the original level.
More images are at: http://www.flickr.com/photos/ingv/.
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