Considerations on Different Features of Local Seismic Effect Numerical Simulations: The Case Studied of Castelnuovo Garfagnana

Numerical studies of local seismic effects are commonly carried out by means of 1D and 2D simulations performed in order to evaluate amplification effects in terms of acceleration response spectra and amplification factors. Such approaches can be easily compared with prescriptions from technical provisions as Eurocode 8 that lead design activity whenever a poor soil characterization is available. When suitable investigation campaigns and regional hazard studies are undertaken accurate studies on local seismic effects can be developed. As a matter of fact, soil high heterogeneity and variability, input motion features and geometrical irregularities of soil layer boundaries heavily affect seismic soil response and frequently cause different damages in urban areas. For that reason, although just from deterministic standpoint, spatial variation of amplification effects has been investigated in order to understand how much numerical simulation experiences in amplification previsions can improve simplified approaches suggested by technical codes. In this study Castelnuovo Garfagnana town (Italy) has been studied by means of numerical simulation. Results have been discussed focusing on those aspects which mainly interpret the physical phenomenon that mostly affect seismic local amplification effects

Mechanical characterisation of lacustrine clay by interpreting spatial variability in CPTU measurements

Transportation infrastructure is common in highly populated areas near the major lakes in the Swiss 'Mittelland', where extensive deposits of normally consolidated post glacial clays have formed. Construction on, or in, such soils requires careful consideration during the design process due to their compressibility, low permeability and sensitivity. Achieving a satisfactory engineering characterisation requires a range of field and laboratory tests, which may be evaluated using statistical tools. The Intraclass ratio RI and the modified Bartlett method have been employed for interpreting the variability of the undrained shear strength su from continuous CPTU measurements at the Wauwil site. Finally, comparison between measurements from two cone dimensions, of cross sectional areas of 10 cm2 and 5 cm2, has been undertaken with respect to their capacity of profile detailing based on the normalised cone penetration resistanc

Lessons from April 6, 2009 L'Aquila earthquake to enhance microzoning studies in near-field urban areas

AbstractThis study focuses on two weak points of the present procedure to carry out microzoning study in near-field areas: (1) the Ground Motion Prediction Equations (GMPEs), commonly used in the reference seismic hazard (RSH) assessment; (2) the ambient noise measurements to define the natural frequency of the near surface soils and the bedrock depth. The limitations of these approaches will be discussed throughout the paper based on the worldwide and Italian experiences performed after the 2009 L'Aquila earthquake and then confirmed by the most recent 2012 Emilia Romagna earthquake and the 2016–17 Central Italy seismic sequence. The critical issues faced are (A) the high variability of peak ground acceleration (PGA) values within the first 20–30 km far from the source which are not robustly interpolated by the GMPEs, (B) at the level 1 microzoning activity, the soil seismic response under strong motion shaking is characterized by microtremors' horizontal to vertical spectral ratios (HVSR) according to Nakamura's method. This latter technique is commonly applied not being fully compliant with the rules fixed by European scientists in 2004, after a 3-year project named Site EffectS assessment using AMbient Excitations (SESAME). Hereinafter, some "best practices" from recent Italian and International experiences of seismic hazard estimation and microzonation studies are reported in order to put forward two proposals: (a) to formulate site-specific GMPEs in near-field areas in terms of PGA and (b) to record microtremor measurements following accurately the SESAME advice in order to get robust and repeatable HVSR values and to limit their use to those geological contests that are actually horizontally layered

A numerical approach for liquefaction potential definition

Liquefaction phenomenon in saturated granular soil is not that frequent as amplification cases but can cause heavy damages on buildings and infrastructures whenever is occurs especially within superficial strata. In fact the lack of shear resistance of soil due to liquefaction affects mostly shallow foundations and road surfaces. Up now, several studies have been addressed to overpass the inadequacy of liquefaction safety factor by means of introducing the liquefaction potential. Nevertheless, the difficulty in (1) defining a scale of damage related to liquefaction potential values and (2) collecting field data from damages caused prevalently by liquefaction makes the punctual factor of safety still popular in engineering practice. In this paper a new approach to liquefaction potential estimation is proposed based on finite element dynamic analyses and on the concept of “significant volume” according to possible effects suffered by shallow foundations. One-dimensional simulation of liquefaction occurrence is performed by means of the Pastor-Zienkiewicz constitutive law. Hence the estimation of liquefaction potential is gained as well as the stress influence factor from Westergaard solution is calculated

Automated reconstruction of rainfall events responsible for shallow landslides

Over the last 40 years, many contributions have identified empirical rainfall thresholds (e.g. rainfall intensity (I ) vs. rainfall duration (D), cumulated rainfall vs. rainfall duration (ED), cumulated rainfall vs. rainfall intensity (EI)) for the possible initiation of shallow landslides, based on local and global inventories. Although different methods to trace the threshold curves have been proposed and discussed in literature, a systematic study to develop an automated procedure to select the rainfall event responsible for the landslide occurrence has only rarely been addressed. Objective criteria for estimating the rainfall responsible for the landslide occurrence play a prominent role on the threshold values. In this paper, two criteria for the identification of the effective rainfall events are presented. The first criterion is based on the analysis of the time series of rainfall mean intensity values over 1 month preceding the landslide occurrence. The second criterion is based on the analysis of the trend in the time function of the cumulated mean intensity series calculated from the rainfall records measured through rain gauges. The two criteria have been implemented in an automated procedure that is written in the R language. A sample of 100 shallow landslides collected in Italy from 2002 to 2012 was used to calibrate the procedure. The cumulated event rainfall (E) and duration (D) of rainfall events that triggered the documented landslides are calculated through the new procedure and are fitted with power law in the D, E diagram. The results are discussed by comparing the D, E pairs calculated by the automated procedure and the ones by the expert method

Automated reconstruction of rainfall events responsible for shallow landslides

Abstract. Over the last 40 years, many contributions have identified empirical rainfall thresholds (e.g. rainfall intensity (I) vs. rainfall duration (D), cumulated rainfall vs. rainfall duration (ED), cumulated rainfall vs. rainfall intensity (EI)) for the possible initiation of shallow landslides, based on local and global inventories. Although different methods to trace the threshold curves have been proposed and discussed in literature, a systematic study to develop an automated procedure to select the rainfall event responsible for the landslide occurrence has only rarely been addressed. Objective criteria for estimating the rainfall responsible for the landslide occurrence play a prominent role on the threshold values. In this paper, two criteria for the identification of the effective rainfall events are presented. The first criterion is based on the analysis of the time series of rainfall mean intensity values over 1 month preceding the landslide occurrence. The second criterion is based on the analysis of the trend in the time function of the cumulated mean intensity series calculated from the rainfall records measured through rain gauges. The two criteria have been implemented in an automated procedure that is written in the R language. A sample of 100 shallow landslides collected in Italy from 2002 to 2012 was used to calibrate the procedure. The cumulated event rainfall (E) and duration (D) of rainfall events that triggered the documented landslides are calculated through the new procedure and are fitted with power law in the D, E diagram. The results are discussed by comparing the D, E pairs calculated by the automated procedure and the ones by the expert method

Problems Associated With the Assessment of Local Site Effects Through a Multidisciplinary Integrated Study: The Case of Fivizzano’s Town (Italy)

The evaluation of local site effects, by means of ground response analyses, is a very complex and difficult task, which requires a multidisciplinary approach. This is operative philosophy expressed by VEL Project (Valutazione degli Effetti Locali), sponsored by Tuscany Region, to the aim to seismic risk characterization in the main seismic areas (i.e. Garfagnana, Lunigiana, Amiata, Valtiberina and Mugello). One of the most important urban centres, involved in the multidisciplinary activity of the VEL project, is certainly the town of Fivizzano located nearby the city of Massa, which was strongly damaged during the earthquake of September 1920 (the strongest seismic event occurred in Northern Apennines in the latest centuries). Remarkably good macroseismic information is available about the destructive impact yielded at Fivizzano by this earthquake (e.g. number of casualties, level of damage of buildings, etc). The main objective of this paper is to identify the occurrence of possible local site effects in the Fivizzano’s area following the 1920 earthquake and to quantify them by means of one and two-dimensional site response analysis. The input data required for study were obtained through a comprehensive geological survey and a multi disciplinary underground exploration of the area

Extreme rainfall events in karst environments: the case study of September 2014 in the Gargano area (southern Italy)

In the first week of September 2014, the Gargano Promontory (Apulia, SE Italy) was hit by an extreme rainfall event that caused several landslides, floods and sinkholes. As a consequence of the floods, two people lost their lives and severe socio-economic damages were reported. The highest peaks of rainfall were recorded between September 3rd and 6th at the Cagnano Varano and San Marco in Lamis rain gauges with a maximum daily rainfall (over 230 mm) that is about 30% the mean annual rainfall. The Gargano Promontory is characterized by complex orographic conditions, with the highest elevation of about 1000 m a.s.l. The geological setting consists of different types of carbonate deposits affected by intensive development of karst processes. The morphological and climatic settings of the area, associated with frequent extreme rainfall events can cause various types of geohazards (e.g., landslides, floods, sinkholes). A further element enhancing the natural predisposition of the area to the occurrence of landslides, floods and sinkholes is an intense human activity, characterized by an inappropriate land use and management. In order to obtain consistent and reliable data on the effects produced by the storm, a systematic collection of information through field observations, a critical analysis of newspaper articles and web-news, and a co-operation with the Regional Civil Protection and local geologists started immediately after the event. The information collected has been organized in a database including the location, the occurrence time and the type of geohazard documented with photographs. The September 2014 extreme rainfall event in the Gargano Promontory was also analyzed to validate the forecasts issued by the Italian national early-warning system for rainfall-induced landslides (SANF), developed by the Research Institute for Geo-Hydrological Protection (IRPI) for the Italian national Department for Civil Protection (DPC). SANF compares rainfall measurements and forecasts with empirical rainfall thresholds for the prediction of landslide occurrence. SANF forecasts were compared to the documented landslides and discussed

Evaluation of liquefaction potential in an intermountain Quaternary lacustrine basin (Fucino basin, central Italy)

In this study, we analyse the susceptibility to liquefaction of the Pozzone site, which is located on the northern side of the Fucino lacustrine basin in central Italy. In 1915, this region was struck by a M 7.0 earthquake, which produced widespread coseismic surface effects that were interpreted to be liquefaction-related. However, the interpretation of these phenomena at the Pozzone site is not straightforward. Furthermore, the site is characterized by an abundance of fine-grained sediments, which are not typically found in liquefiable soils. Therefore, in this study, we perform a number of detailed stratigraphic and geotechnical investigations (including continuous-coring borehole, CPTu, SDMT, SPT, and geotechnical laboratory tests) to better interpret these 1915 phenomena and to evaluate the liquefaction potential of a lacustrine environment dominated by fine-grained sedimentation. The upper 18.5 m of the stratigraphic succession comprises fine-grained sediments, including four strata of coarser sediments formed by interbedded layers of sand, silty sand and sandy silt. These strata, which are interpreted to represent the frontal lobes of an alluvial fan system within a lacustrine succession, are highly susceptible to liquefaction. We also find evidence of paleo-liquefaction, dated between 12.1–10.8 and 9.43–9.13 kyrs ago, occurring at depths of 2.1–2.3 m. These data, along with the aforementioned geotechnical analyses, indicate that this site would indeed be liquefiable in a 1915-like earthquake. Although we found a broad agreement among CPTu, DMT and shear wave velocity ‘‘simplified procedures’’ in detecting the liquefaction potential of the Pozzone soil, our results suggest that the use and comparison of different in situ techniques are highly recommended for reliable estimates of the cyclic liquefaction resistance in lacustrine sites characterized by high content of fine-grained soils. In geologic environments similar to the one analysed in this work, where it is difficult to detect liquefiable layers, one can identify sites that are susceptible to liquefaction only by using detailed stratigraphic reconstructions, in situ characterization, and laboratory analyses. This has implications for basic (Level 1) seismic microzonation mapping, which typically relies on the use of empirical evaluations based on geologic maps and pre-existing sub-surface data (i.e., age and type of deposits, prevailing grain size, with particular attention paid to clean sands, and depth of the water table).Published91-1115T. Sismologia, geofisica e geologia per l'ingegneria sismicaJCR Journa