Antonella Paciello

Seismic hazard maps of Italy including site effects

The seismic hazard of Italy was mapped adopting multiple models of seismic sources, recurrence rates and attenuation relationships, and investigating the influence of site effects on assessing the earthquake hazard. This result was achieved by placing all the alternatives in a logic-tree diagram, and performing an uncertainty analysis of the main epistemic variables involved in probabilistic seismic hazard computations. Several ground motion parameters such as peak ground acceleration (PGA), velocity (PGV) and displacement (PGD), spectral accelerations at 0.2 and 1.0 s periods, and site intensities were computed. Maps of PGA and PGV values with a 10% chance of being exceeded in 50 years are shown as an illustration of the seismic hazard of Italy.

High-resolution geological model of the gravitational deformation affecting the western slope of Mt. Epomeo (Ischia)

The recent geological history of Ischia Island is characterized by slope-scale gravitational deformations closely related to volcano-tectonic dynamics of the Mt. Epomeo resurgent caldera. This study focuses on the gravitational deformation that involves alkali-trachytic lava and trachytic ignimbrite flow-units of Mt. Nuovo, located in the western portion of Mt. Epomeo. A preliminary, high-resolution engineering-geological model was obtained through geological, geomorphological and geophysical surveys and reveals a complex morpho-structure with geomorphological evidence of gravitational instability. The complexity of the ongoing slope deformations is confirmed by field geo-structural evidences that led to the identification of a multiple compound mechanism with a main rupture surface which is about 200 m deep. This geometry was better constrained by passive seismic investigations consisting in noise measurements, focused on resonance frequencies of the soil (i.e. based on H/V Nakamura approach). In addition, a close relationship between the outcrop of Mt. Epomeo Green Tuff breccia layers and the distribution of hydrothermal emissions and gas vent can be inferred, as it is related to the higher permeability of the breccia layers with respect to the main Mt. Epomeo Green Tuff flow unit, where the ascent path of deep hydrothermal fluids developed along faults and fracture networks.

Parametric numerical study of observed amplification effects on the colle di roio limestone ridge (Central italy)

Following the seismic microzonation studies of the L’Aquila area, Central Italy, hit by the Mw 6.3 L’Aquila earthquake of 6th April 2009, we observed ground motion amplification at the hilltop of the Colle di Roio limestone ridge. In particular, horizontal-to-vertical spectral ratio amplitude of weak motion waveforms showed average peak level above 5 in the frequency range 4–5 Hz. In order to evaluate the contribution of topography and subsoil heterogeneity on the observed response, we performed 2D numerical simulations of wave propagation through the ridge using a finite difference approach. Different hypothesis of model configuration, consistent with the available geological data, were tested. A homogeneous model was considered to evaluate the effect of surface topography on ground motion amplification, while several heterogeneous models were considered in order to examine the interaction between topography and heterogeneity on the seismic response. Results were analyzed in terms of synthetic horizontal-to-vertical (H/V) spectral ratios and the latter were compared to the observed ones. The results showed that the observed ground motion amplification level cannot be explained only by surface topography effect and that the assumption of an heterogeneous model with complex inner geometry may fairly reproduce the observations.

The Experience of Seismic Microzonation in Lazio Region (Italy) Mountain Municipalities

Within the activities of seismic microzonation promoted and co-funded by Lazio Regional Administration (LRA) and the Department of Civil Protection (DPC), following the issues of the National rule OPCM 3907/2010, seismic microzonation studies were carried out in a set of municipalities, already attributed to the seismic Zone 1 (i.e. with the most severe level of seismic hazard and located in mountain areas). These municipalities show similar geologic and geomorphologic features as they are characterized by a local bedrock constituted of limestone and marly-limestone and fluvial-lacustrine deposits filling intra-mountain alluvial plains. The engineering-geological model of the subsoil as well as the jointing conditions of the outcropping rock masses were defined on the basis of available technical data from public reports, as well as from original geophysical surveys. Different types of microzones (i.e. stable, stable susceptible to seismic amplification and unstable areas) were identified according to the technical rules (ICMS 2008). Nevertheless, the experienced approach highlighted some critical features in the microzonation methodology that encourage future studies devoted to obtain the refinement of the operative procedures.

The local seismic response of the Fosso di Vallerano valley (Rome, Italy) based on a high-resolution geological model

The main purpose of this study is the analysis of the local seismic response in the Fosso di Vallerano valley, an alluvial basin located in a recently urbanized area of Rome (Italy). A high-resolution geological model was obtained starting from 250 available borehole log stratigraphies and pressiometer in-site tests; the model highlighted a complex and heterogeneous setting of both the local substratum and the alluvial fill. The local seismo-stratigraphy was derived based on several noise measurements as well as one cross-hole test. A preliminary validation of the stratigraphic model was performed by modeling the amplification functions (SSR) derived from weak motions recorded on August 2009 through a temporary velocimetric array. The obtained results show that the recent alluvial deposits have one principal mode of vibration at about 0.8 Hz and different secondary vibrational modes due to the characteristic stratigraphic setting of the alluvia. The seismic bedrock can be located within the Paleo Tiber 4 deposits (Santa Cecilia Formation) by assuming a velocity gradient in these deposits (i.e. corresponding to the Vs increment from about 500 m/s up to 1100 m/s).

Experiment of an innovative nanoseismic monitoring applied to gravity-induced slope instabilities in a karstified rock mass

The Peschiera Springs slope (RI), which hosts the drainage plant of the Romes aqueduct, is affected by a gravitational slope deformation process, that is responsible for a rock-mass lateral spreading, associated to several landforms including sinkholes, subvertical scarps and trenches. An experiment, based on an innovative method of monitoring, was carried out to record microseismic events generated by underground instabilities such as failures and collapses. At this aim a SNS (Seismic Navigation System) array was installed during the year 2013 inside a the tunnel of the drainage plant in order to carry out a continuous monitoring. The nanoseismic monitoring, allowed to record 37 microseismic events. The seismic records were managed by NanoseismicSuite software that allowed to identify and characterize two different typologies of events: 19 underground collapses and 18 underground failures. The locations of these events are in good agreement with the evolutionary geological model of the ongoing gravitational slope deformation, i.e. with the spatial distribution of the main trenches and scarps on the slope.

Analysis of ground motion along a topographic relief: The cerreto di spoleto case-history (Central Italy)

5th ECCOMAS Thematic Conference on Computational Methods in Structural Dynamics and Earthquake Engineering, COMPDYN 2015

Studies of seismic microzonation in Latium region (Italy) by experiencing the application of official guidelines in intra-mountain plains

In 2010, the Latium Regional Administration promoted a systematic study for the seismic microzonation of its Municipalities, according to the official national and regional guidelines. This activity was co-funded by the National Department of Civil Protection (DPC) following the issue of the National rule OPCM 3907/2010. A Working Group including researchers from Latium Regional Administration, ENEA and the Department of Earth Sciences of the ‘Sapienza’ University of Rome performed the studies in some municipalities characterised by the most severe level of seismic hazard. The activity was carried out on the basis of both archive geotechnical data and original geophysical surveys. The whole municipal territory was divided in stable areas, where no further analysis is required, and areas prone to stratigraphic or topographic amplification, as well as to earthquake-induced phenomena such as landslides, sinkholes, liquefaction and seiche. The experienced approach highlighted some critical features in the microzonation methodology that encourage the refinement of the operative procedures.

Seismometric Monitoring of Hypogeous Failures Due to Slope Deformations

Results from a seismometric monitoring of rock mass failures affecting a karstified slope are here presented. The slope, located in Central Apennines (Italy), hosts a drainage plant and is involved in gravity-induced deformations.