Mapping the liquefaction hazard at different geographical scales (original) (raw)
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On the 20th and 29th of May 2012, two earthquakes occurred in Emilia-Romagna region (Northern Italy) triggering extensive liquefaction of the subsoil units. The consequences of liquefaction have been observed and reported by several agencies in a widespread area. The most impressive liquefaction manifestations were documented in a zone 3-4 km-long and 1 km-wide, where the villages of Sant'Agostino, San Carlo and Mirabello are located. The existing post-earthquake reports and the availability of geotechnical data provided by in-situ tests consist the basic ingredients for a computation of the liquefaction potential parameters within this zone. In particular, the Liquefaction Potential Index (LPI) and Liquefaction Severity Number (LSN) indexes were evaluated and then correlated by considering liquefaction phenomena either observed on site or not. Thus, the existing classifications of the LPI and LSN were evaluated and compared with the observed liquefaction-induced deformations. The latter was applied and validated for the first time within a liquefiable area using post-earthquake data, after the development by . The outcome of this study shows that a threshold value of LPI around 13 or 14 is better to be taken into account instead of 5 for discriminating sites where liquefaction surface evidences should be expected from the 'non-liquefied' ones. Moreover, from the correlation of the LSN values with the cases of liquefaction-induced ground disruption it is concluded that the proposed threshold value of 10 fits statistically well with our dataset. In addition, a preliminary correlation of LPI and LSN indicates a trend that could be useful in future studies for delineating sites likely to liquefaction. earthquakes ( e.g., Emergeo WG, 2013). Both magnitudes (respectively M w = 6.1 and 6.0; e.g., and focal depths (respectively, 6.3 and 10.2 km; http://iside.rm.ingv.it/) were comparable to the 2011 Christchurch events. Also in this case, several aftershocks up to M w = 5.5 followed. Due to the similar dynamics of the two seismic sequences, as well as the general geological-stratigraphic setting of both epicentral areas characterized by alluvial plains with a flat morphology and a subsoil consisting of recent and poorly consolidated fluvial deposits, the two above mentioned parameters (LPI and LSN) were applied to the Italian case study and correlated the obtained numerical results Engineering Geology 189 (2015) 1-16
An overview of earthquake related liquefaction events in Italy
2010
during the summer pause of Imperial College (London, UK) lectures. Mr Borgomeo have joined the Istituto Nazionale di Geofisica e Vulcanologia (Italian Institute of Geophysics and Volcanology) for an internship under the supervision of Dr. Giuseppe Di Capua
Natural Hazards, 2015
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Technical guidelines for the assessment of earthquake induced liquefaction hazard at urban scale
Bulletin of Earthquake Engineering, 2020
Microzonation for earthquake-induced liquefaction hazard is the subdivision of a territory at a municipal or submunicipal scale in areas characterized by the same probability of liquefaction manifestation for the occurrence of an earthquake of specified intensity. The liquefaction hazard at a site depends on the severity of expected ground shaking as well as on the susceptibility to liquefaction of that site. This in turn depends on geological, geomorphological, hydrogeological and geotechnical predisposing factors. Thus, liquefaction hazard implies the existence of territories characterized by a moderate to high level of intensity of expected ground shaking. Microzonation charts for ground shaking and liquefaction hazard play a key role for the mitigation of seismic risk of an urban centre as they provide a valuable tool for the implementation of prevention strategies and land use planning. The LIQUEFACT project fully addressed the problem of microzoning a territory for earthquake-induced liquefaction hazard in a specific work package. Four municipal testing areas were selected across Europe as peculiar case studies where to construct microzonation charts for earthquake-induced liquefaction hazard. They are located in Emilia-Romagna region (Italy), Lisbon metropolitan area (Portugal), Brežice territory (Slovenia) and Marmara region (Turkey). Their location was identified based on the following criteria: severity of expected seismic hazard, availability of geological and geotechnical data, presence of liquefiable soil deposits, documented cases of liquefaction manifestations occurred in historical earthquakes, representativeness of different geological settings, density of population in selected areas (exposure). This paper illustrates the general procedure developed in LIQUEFACT for the assessment of earthquake-induced liquefaction hazard at urban scale and presents the main achievements of the microzonation studies carried out at the four previously mentioned European testbeds. Since the microzonation studies have been carried out using a shared framework and methodology, this paper has the ambition to serve as technical guidelines for updating the standards and the operational criteria currently used in different countries worldwide to construct seismic microzonation maps of liquefaction hazard.
Liquefaction as a seismic hazard: Scales, examples and analysis
Basics of Computational Geophysics, 2021
Under favorable conditions, apart from the ground shaking earthquakes also trigger hazards like tsunamis, landslides, rockfalls and liquefaction. Liquefaction features are produced in abundance in water saturated sandy soils during an earthquake. Usually an earthquake having a magnitude .M5.5 produces liquefaction features (Ambraseys, 1998). It is a major seismic hazard under favorable conditions especially in urban areas as it results in slope failure, ground subsidence, ground cracking, lateral spreading and sandblows. The liquefied soils lose their bearing capacity which results in slope, bridge and foundation failures. As a result the buildings can be tilted severely, express ways can collapse, roads can get buckled and derailments can also occur.
2019
Widespread liquefaction phenomena may also occur in surface alluvial intermediate soils composed of alternations of saturated sandy silts, silts, silty and clayey sands, during earthquakes of moderate magnitude as experienced for the 2012 Emilia Romagna seismic sequence. By the consequence, liquefaction hazard evaluation has been included in the most recent 3rd level microzonation studies promoted by some Regional Governments. The paper presents the results of one of those studies performed for the municipality of Barberino di Mugello that falls within a high seismicity area of Central Italy including typical Appennine intramontane basins where surface alluvial soil layers that overlay fluvio-lacustrine soil deposits can be frequently encountered. With reference to the studied area, the liquefaction potential and the expected settlements of intermediate soil deposits are calculated by using different simplified methods and the corresponding liquefaction hazard maps are presented and...
Soil Dynamics and Earthquake Engineering, 2019
A geophysical conceptual model for sites prone to seismic liquefaction is presented, introducing a geophysical protocol to characterize the liquefaction proneness. Three parameters are used to characterize homogeneous units: v s , a proxy of the geotechnical classes of soils, v p related to the saturation degree and v p /v s ratio, related to the liquefaction geophysical susceptibility. A layer is geophysically susceptible to liquefaction when it meets the following criteria: a) v s < 270 m/s and 1300 < v p < 1800 m/s; b) v p /v s > 5. The model has been tested and validated in the Quistello site, where liquefaction occurred during the 2012 Emilia earthquake. The validation of the proposed geophysical model for liquefaction susceptibility against the geotechnical one, calculated from CPTU, indicates the reliability of the proposed approach. This approach was extended to other sites affected by the 2012 seismic swarm. The study demonstrates that the geophysical susceptibility to liquefaction could be an indicator to support microzonation studies concerning the liquefaction proneness of extended areas.
Geotechnical and Geophysical Tests Following the 2020 Earthquake-Induced Liquefaction Phenomena
2nd Croatian Conference on Earthquake Engineering ‒ 2CroCEE
Earthquakes and related coseismic effects at the surface, such as liquefaction and lateral spreading, can impact humans due to the resulting economic or social disruptions (e.g. slope and foundation failures, flotation of buried structures, etc.). In this respect, the 2020 Petrinja Mw6.4 earthquake (Croatia) provided many examples of liquefaction and lateral spreading, as identified by the post-earthquake field reconnaissance campaigns. The observed liquefaction cases occurred in the alluvial plains of the Kupa, Sava and Glina Rivers or along faults, with ejecta composed of sands and/or gravels of different grain size and mineralogy. The lateral spreading phenomena were observed along river embankments and roads. In this context interest in studying these different features arose, and an international research team from Italy, the United States and Croatia recently performed an intensive geological, geotechnical and geophysical campaign to assess the liquefaction susceptibility at s...
Natural Hazards and Earth System Science, 2013
In this paper we present the geological effects induced by the 2012 Emilia seismic sequence in the Po Plain. Extensive liquefaction phenomena were observed over an area of ∼ 1200 km 2 following the 20 May, M L 5.9 and 29 May, M L 5.8 mainshocks; both occurred on about E-W trending, S dipping blind thrust faults. We collected the coseismic geological evidence through field and aerial surveys, reports from local people and Web-based survey. On the basis of their morphologic and structural characteristics, we grouped the 1362 effects surveyed into three main categories: liquefaction (485), fractures with liquefaction (768), and fractures . We show that the quite uneven distribution of liquefaction effects, which appear concentrated and aligned, is mostly controlled by the presence of paleoriverbeds, out-flow channels and fans of the main rivers crossing the area; these terrains are characterised by the pervasive presence of sandy layers in the uppermost 5 m, a local feature that, along with the presence of a high water table, greatly favours liquefaction. We also find that the maximum distance of observed liquefaction from the earthquake epicentre is ∼ 30 km, in agreement with the regional empirical relations available for the Italian Peninsula. Finally, we observe that the contour of the liquefaction observations has an elongated shape almost coinciding with the aftershock area, the InSAR deformation area, and the I ≥ 6 EMS area. This observation confirms the control of the earthquake source on the liquefaction distribution, and provides useful hints in the characterisation of the seismogenic source responsible for historical and pre-historical liquefactions.
2011
We calculated liquefaction potential index for a grid of sites in the Evansville, Indiana area for two scenario earthquakes-a magnitude 7.7 in the New Madrid seismic zone and a M6.8 in the Wabash Valley seismic zone. For the latter event, peak ground accelerations range from 0.13 gravity to 0.81 gravity, sufficiently high to be of concern for liquefaction. Recently acquired cone-penetrometer test data at 58 sites were used to estimate the factor of safety against liquefaction and liquefaction potential index at each site. To extend the estimation of liquefaction hazard to a grid of sites in the area, the soil columns at these grid sites were divided into three categories, and for each category a sufficient number of conepenetrometer test sites were available to characterize statistically each group's conepenetrometer test tip resistance and sleeve friction. At each grid site, Monte Carlo sampling was used to generate values for these two parameters at 2-meter intervals for depths down to 20 meters or bedrock. The groundwater table at each grid site was likewise sampled from a mean value and group-dependent standard deviation. For each grid site, 25,000 realizations of the soil profile were generated and a probability distribution of liquefaction potential index values was obtained. Maps of liquefaction hazard for each scenario earthquake present (1) Mean liquefaction potential index at each site, and (2) Probabilities that liquefaction potential index values exceed 5 (threshold for expression of surface liquefaction) and 12 (threshold for lateral spreading). Values for the liquefaction potential index are high in the River alluvium group, where the soil profiles are predominantly sand, while values in the Lacustrine terrace group are lower, owing to the predominance of clay. Liquefaction potential index values in the Outwash terrace group are less consistent because the soil profiles contain highly variable sequences of silty sand, clayey sand, and sandy clay, justifying the use of the Monte Carlo procedure to capture the consequences of this complexity.