The "Ceppo Lombardo Formation" (Riva, 1957) is the name of a collection of Quaternary clastic conglomeratic units outcropping and sub-outcropping in the Po Plain, North to the city of Milan (Italy). Due to the shallow depth and the areal extension of this formation, the geophysical characterization assume a great importance for geotechnical engineering, territory use and local seismic hazard studies. The geophysical characterization of such clastic units shows several and not negligible issues, starting from its great areal extension to the great variability in the cementation and alteration parameters. The main geological, geophysical and geotechnical information about this formation, derive from a great amount of data and studies available from local administration and professional studies, these datasets were not ever integrated to have a more robust geotechnical knowledge. With the aim of a more consistent characterization, we gathered and analysed all available data from geophysical and geological datasets, result of the studies of the stratigraphies of wells and geophysical soundings. Additional geophysical surveys were conducted, using the single station passive seismic (HVSR) technique; one single site investigation and two 10-km-long perpendicular transects. New and old geophysical data were integrated with the information from geognostic tests (e.g. core drilling and cutting from well drilling) for an efficient validation, then a statistics study was performed. We present the geophysical methods, the statistical analysis results of Vs parameter and several depth maps of its distribution in all study area. The main final results show that Ceppo Lombardo Formation offers a well detectable impedance contrast where it overlies other units with poor geotechnical characteristics. The formation has also been classified as overconsolidated soil (Vs < 500 m s-1) with the exception of the Brembo unit that has Vs values of a seismic bedrock (Vs > 800 m s-1). Additionally, the great variability output of the HVSR tests, expressed as periods, indicates that the top surface has irregular geometry with variable impedance contrasts up to about 30 m depth.
Geophysical characterization of Ceppo Lombardo Formation (Po Plain NE of Milan, Italy): new data from passive seismic surveys
De Franco R;Caielli G
2021
Abstract
The "Ceppo Lombardo Formation" (Riva, 1957) is the name of a collection of Quaternary clastic conglomeratic units outcropping and sub-outcropping in the Po Plain, North to the city of Milan (Italy). Due to the shallow depth and the areal extension of this formation, the geophysical characterization assume a great importance for geotechnical engineering, territory use and local seismic hazard studies. The geophysical characterization of such clastic units shows several and not negligible issues, starting from its great areal extension to the great variability in the cementation and alteration parameters. The main geological, geophysical and geotechnical information about this formation, derive from a great amount of data and studies available from local administration and professional studies, these datasets were not ever integrated to have a more robust geotechnical knowledge. With the aim of a more consistent characterization, we gathered and analysed all available data from geophysical and geological datasets, result of the studies of the stratigraphies of wells and geophysical soundings. Additional geophysical surveys were conducted, using the single station passive seismic (HVSR) technique; one single site investigation and two 10-km-long perpendicular transects. New and old geophysical data were integrated with the information from geognostic tests (e.g. core drilling and cutting from well drilling) for an efficient validation, then a statistics study was performed. We present the geophysical methods, the statistical analysis results of Vs parameter and several depth maps of its distribution in all study area. The main final results show that Ceppo Lombardo Formation offers a well detectable impedance contrast where it overlies other units with poor geotechnical characteristics. The formation has also been classified as overconsolidated soil (Vs < 500 m s-1) with the exception of the Brembo unit that has Vs values of a seismic bedrock (Vs > 800 m s-1). Additionally, the great variability output of the HVSR tests, expressed as periods, indicates that the top surface has irregular geometry with variable impedance contrasts up to about 30 m depth.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
