In Italy, rainfall is the primary trigger of landslides that frequently cause fatalities and large economic damage. Using a variety of information sources, we have compiled a catalogue listing 753 rainfall events that have resulted in landslides in Italy. For each event in the catalogue, the exact or approximate location of the landslide and the time or period of initiation of the slope failure is known, together with information on the rainfall duration D, and the rainfall mean intensity I, that have resulted in the slope failure. The catalogue represents the single largest collection of information on rainfall-induced landslides in Italy, and was exploited to determine the minimum rainfall conditions necessary for landslide occurrence in Italy, and in the Abruzzo Region, central Italy. For the purpose, new national rainfall thresholds for Italy and new regional rainfall thresholds for the Abruzzo Region were established, using two independent statistical methods, including a Bayesian inference method and a new Frequentist approach. The two methods proved complementary, with the Bayesian method more suited to analyze small data sets, and the Frequentist method performing better when applied to large data sets. The new regional thresholds for the Abruzzo Region are lower than the new national thresholds for Italy, and lower than the regional thresholds proposed in the literature for the Piedmont and Lombardy Regions in northern Italy, and for the Campania Region in southern Italy. This is important, because it shows that landslides in Italy can be triggered by less severe rainfall conditions than previously recognized. The Frequentist method experimented in this work allows for the definition of multiple minimum rainfall thresholds, each based on a different exceedance probability level. This makes the thresholds suited for the design of probabilistic schemes for the prediction of rainfall-induced landslides. A scheme based on four probabilistic thresholds is proposed. The four thresholds separate five fields, each characterized by different rainfall intensity-duration conditions, and corresponding different probability of possible landslide occurrence. The scheme can be implemented in landslide warning systems that operate on rainfall thresholds, and on precipitation measurements or forecasts.

A seismic sequence in central Italy from August 2016 to January 2017 affected groundwater dynamics in fractured carbonate aquifers. Changes in spring discharge, water-table position, and streamflow were recorded for several months following nine Mw 5.0–6.5 seismic events. Data from 22 measurement sites, located within 100 km of the epicentral zones, were analyzed. The intensity of the induced changes were correlated with seismic magnitude and distance to epicenters. The additional post-seismic discharge from rivers and springs was found to be higher than 9 m³/s, totaling more than 0.1 km³ of groundwater release over 6 months. This huge and unexpected contribution increased streamflow in narrow mountainous valleys to previously unmeasured peak values. Analogously to the L’Aquila 2009 post-earthquake phenomenon, these hydrogeological changes might reflect an increase of bulk hydraulic conductivity at the aquifer scale, which would increase hydraulic heads in the discharge zones and lower them in some recharge areas. The observed changes may also be partly due to other mechanisms, such as shaking and/or squeezing effects related to intense subsidence in the core of the affected area, where effects had maximum extent, or breaching of hydraulic barriers. Une séquence sismique en Italie centrale entre Août 2016 et Janvier 2017 affecte la dynamique des eaux souterraines dans des aquifères carbonatés fracturés. Des changements dans le débit des sources, la position du niveau piézométrique, et l’écoulement ont été enregistrées pour plusieurs mois à la suite des neuf événements sismiques d’intensité 5.0–6.5. Les données de 22 sites de mesures, situés à moins de 100 km des zones des épicentres, ont été analysées. L’intensité des changements induits a été corrélée avec la magnitude sismique et la distance des épicentres. On a constaté que les débits post-sismiques additionnels des rivières et des sources étaient supérieurs à 9 m³/s, totalisant plus de 0.1 km³ de libération d’eaux souterraines sur 6 mois. Cette contribution énorme et inattendue a augmenté les débits des cours d’eau dans les vallées étroites montagneuses jusqu’à des valeurs de pics non mesurées auparavant. De façon analogue au phénomène de l’Aquila 2009 après le séisme, ces changements hydrogéologiques pourraient refléter une augmentation de la conductivité hydraulique apparente à l’échelle de l’aquifère, ce qui augmenterait les charges hydrauliques dans les zones de décharge et les abaisserait dans certaines zones de recharge. Les changements observés peuvent aussi être dues en partie à d’autres mécanismes, tels que les effets de secousse et/ou de compression liés à une subsidence intense dans le noyau de la zone affectée, où les effets ont une portée maximale, ou à la rupture des barrières hydrauliques. Una secuencia sísmica en el centro de Italia desde agosto de 2016 a enero de 2017 afectó la dinámica del agua subterránea en los acuíferos de carbonato fracturados. Los cambios en la descarga de los manantiales, la posición de la capa freática y el caudal se registraron durante varios meses luego de nueve eventos sísmicos de Mw 5.0–6.5. Se analizaron datos de 22 sitios de medición, ubicados dentro de los 100 km de las zonas de los epicentros. La intensidad de los cambios inducidos se correlacionó con la magnitud sísmica y la distancia a los epicentros. Se encontró que la descarga postsísmica adicional de ríos y manantiales era superior a 9 m³/s, totalizando más de 0.1 km³ de descarga de agua subterránea durante 6 meses. Esta enorme e inesperada contribución aumentó el flujo de las corrientes en los estrechos valles montañosos a valores máximos previamente no medidos. Análogamente al fenómeno de L’Aquila 2009 después del terremoto, estos cambios hidrogeológicos podrían reflejar un aumento de la conductividad hidráulica global en la escala del acuífero, lo que aumentaría las cargas hidráulicas en las zonas de descarga y las reduciría en algunas áreas de recarga. Los cambios observados también pueden deberse en parte a otros mecanismos, como temblores y/o efectos de compresión relacionados con un hundimiento intenso en el núcleo del área afectada, donde los efectos tuvieron la máxima extensión, o la ruptura de barreras hidráulicas. 2016年8月至2017年1月意大利中部的地震序列影响了断裂碳酸盐含水层的地下水动态。在9次Mw 5.0–6.5地震事件之后的几个月内记录了春季排水量,地下水位和河流的流量的变化。分析了位于震中区100公里范围内的22个测量点的数据。诱发变化的强度与地震的震级和震中距有关。发现河流和泉水的额外震后排水量高于9立方米/秒,超过6个月的地下水排放总量超过0.1立方公里。这个巨大而意想不到的贡献增加了狭窄山谷中的水流量,达到以前未测量的峰值水平。类似于拉奎拉2009年的地震后现象,这些水文地质的变化可能反映出含水层规模的分散水力传导性的增加,这将增加排放区的水头,并在一些补给区域降低它们。观察到的变化还可能部分归因于其他机制,如受影响地区核心的强烈沉降引起的震动和/或挤压效应,其中影响最大,或者破坏水力屏障。 A sequência sísmica no centro da Itália de agosto de 2016 a janeiro de 2017 afetou a dinâmica das águas subterrâneas em aquíferos carbonáticos fraturados. Mudanças na descarga em nascentes, posição do nível freático e nos fluxos foram registrados por vários meses após nove eventos sísmicos com magnitude de 5.0 a 6.5. Dados de 22 locais de medição, localizados a 100 km das zonas de epicentro, foram analisados. A intensidade das mudanças induzidas foi correlacionada com a magnitude e distância dos epicentros. A descarga adicional pós-sísmica dos rios e nascentes foram encontradas acima de 9 m³/s, totalizando mais que 0.1 km³ de água subterrânea liberada em 6 meses. Essa enorme e inesperada contribuição aumentou o fluxo em vales montanhosos estreitos para valores máximos não registrados anteriormente. Analogamente ao fenômeno pós-terremoto de Áquila em 2009, essas mudanças hidrogeológicas podem refletir um aumento da condutividade hidráulica volumétrica na escala do aquífero, que aumentaria o nível potenciométrico nas zonas de descarga e diminuiria em algumas áreas de recarga. As mudanças observadas podem também ser em parte devido a outros mecanismos, como efeito de tremores e/ou compressão relacionados a subsidência intensa no núcleo da área afetada, onde os efeitos atingiram a extensão máxima, ou do rompimento de barreiras hidráulicas.

The interaction between fluids and tectonic structures such as fault systems is a much-discussed issue. Many scientific works are aimed at understanding what the role of fault systems in the displacement of deep fluids is, by investigating the interaction between the upper mantle, the lower crustal portion and the upraising of gasses carried by liquids. Many other scientific works try to explore the interaction between the recharge processes, i.e., precipitation, and the fault zones, aiming to recognize the function of the abovementioned structures and their capability to direct groundwater flow towards preferential drainage areas. Understanding the role of faults in the recharge processes of punctual and linear springs, meant as gaining streams, is a key point in hydrogeology, as it is known that faults can act either as flow barriers or as preferential flow paths. In this work an investigation of a fault system located in the Nera River catchment (Italy), based on geo-structural investigations, tracer tests, geochemical and isotopic recharge modelling, allows to identify the role of the normal fault system before and after the 2016–2017 central Italy seismic sequence (Mmax = 6.5). The outcome was achieved by an integrated approach consisting of a structural geology field work, combined with GIS-based analysis, and of a hydrogeological investigation based on artificial tracer tests and geochemical and isotopic analyses.