ALBERT

Beschreibung: De Santis et al. (EPSL 2017) detected that for the first time in Swarm satellite data some magnetic field anomalies associated with the 2015 Nepal M7.8 earthquake, with similar S-shapes for the cumulative number of satellite anomalies and earthquakes, providing an empirical proof on the lithospheric origin of the anomalies. Following the same approach, De Santis et al. (Atmosph. 2019) obtained other promising results for 12 earthquakes in the range M6.1-8.3, in the framework of the ESA funded SAFE (SwArm For Earthquake study) Project. Then, almost five years of Swarm magnetic field and electron density data were analysed with a Superposed Epoch and Space approach finding a robust correlation with major worldwide M5.5+ earthquakes (De Santis et al. Sc.Rep. 2019). The work also confirmed the Rikitake (1987) law, initially proposed for ground data: the larger the magnitude of the impending earthquake, the longer the precursory time of anomaly occurrences. An analogous analysis was also applied in the framework of the ASI funded Limadou-Science Project to the Chinese Seismo-Electromagnetic satellite (CSES) electron density providing similar results (De Santis et al. N.Cim. 2021). Marchetti et al. (Rem.Sens. 2022) confirmed the same result over a longer time series , i.e. 8 years, of Swarm satellite data. Furthermore, we demonstrated in several case studies (e.g. Marchetti et al. JAES 2019, Akhoondzadeh et al. Adv.S.R. 2019; De Santis et al. Fr.E.Sc. 2020) that the integration of CSES and Swarm data with other measurements from ground an atmosphere reveals a chain of processes before many mainshocks.

Beschreibung: Intensity Prediction Equations (IPEs) allow predicting the possible macroseismic intensity values at any site, as a function of epicentral distance and epicentral intensity or magnitude. In Italy, different approaches have been proposed in the last years for developing intensity attenuation models. We evaluated the performance of the five most recent IPEs valid for the Italian area comparing their predictions with intensities documented at Italian localities. We built two different testing datasets using the data contained in the most recent versions of the Italian Parametric Earthquake Catalogue CPTI15 and of the Macroseismic Italian Database DBMI15. Dataset 1 contains 213 earthquakes with instrumental location and magnitude from 1907 to 2020, whereas Dataset 2 includes 357 events that occurred from 1117 to 1978 with the epicentral parameters estimated from macroseismic intensity data. We computed the residuals between documented intensity values and predicted intensities using the IPEs. Analyzing these results as a function of the epicentre-to-site distance, of the values of documented intensities and of the magnitude of each considered earthquake, we observed a systematic underprediction for high intensity values in both datasets for all the considered IPEs. We also investigated the between-event residuals to highlight spatial and temporal patterns. The results did not show any particular spatial trends, but a significant temporal dependence of the results for Dataset 2, with an underestimation of the documented values for all the considered IPEs for earthquakes in the period 1000-1700.

Beschreibung: Integrating macroseismic intensity data recorded through time with those calculated from epicentral parameters with intensity prediction equations (IPEs) is an effective way of investigating the knowledge of the seismic history (i.e., the list of documented effects) of a given site and to estimate its representativeness. For this purpose, we calculated the effects that were not documented at a set of sites in Italy by considering an IPE constrained with intensity values documented at close sites for the same events. We first selected 228 localities according to their geographical distribution and to the number of related documented intensity data contained in the last version of the Italian Macroseismic Database DBMI15 and we then estimated the number of earthquake effects that could be potentially lost. The latter were calculated with a probabilistic approach in order to take into account both the uncertainties related to the assessment of the intensity value at the site and the nature of macroseismic data (ordinal, discrete, and range limited). We finally provided a quantitative estimate of the effects of known past earthquakes that can be considered potentially lost at the 228 sites analyzing the results at both the local (site-by-site) and regional scale. The results showed that at least one effect with intensity greater than or equal to 6 MCS could be potentially lost with a high probability at almost the totality of the investigated sites. Moreover, some geographical dependences and correlations with the intensity levels were identified.

Beschreibung: On May 12, 2021 the interplanetary counterpart of the May 9, 2021 coronal mass ejection impacted the Earth’s magnetosphere, giving rise to a strong geomagnetic storm. This work discusses the evolution of the various events linking the solar activity to the Earth’s ionosphere with special focus on the effects observed in the circumterrestrial environment. We investigate the propagation of the interplanetary coronal mass ejection and its interaction with the magnetosphere - ionosphere system in terms of both magnetospheric current systems and particle redistribution, by jointly analysing data from interplanetary, magnetospheric, and low Earth orbiting satellites. The principal magnetospheric current system activated during the different phases of the geomagnetic storm is correctly identified through the direct comparison between geosynchronous orbit observations and model predictions. From the particle point of view, we have found that the primary impact of the storm development is a net and rapid loss of relativistic electrons from the entire outer radiation belt. Our analysis shows no evidence for any short-term recovery to pre-storm levels during the days following the main phase.

Beschreibung: In climate model simulations of future climate change, the Atlantic Meridional Overturning Circulation (AMOC) is projected to decline. However, the impacts of this decline, relative to other changes, remain to be identified. Here we address this problem by analyzing 30 idealized abrupt-4xCO2 climate model simulations. We find that in models with larger AMOC decline, there is a minimum warming in the North Atlantic, a southward displacement of the Inter-tropical Convergence Zone, and a poleward shift of the mid-latitude jet. The changes in the models with smaller AMOC decline are drastically different: there is a relatively larger warming in the North Atlantic, the precipitation response exhibits a wet-get-wetter, dry-get- drier pattern, and there are smaller displacements of the mid-latitude jet. We further investigate the impacts of a weakened AMOC in ad-hoc model experiments using EC-Earth3, a state-of-the-art climate model participating in CMIP6. We compare two model experiments forced with abrupt-4xCO2: one in which the AMOC weakens, and another one in which we artificially force the AMOC to stay at the same strength as in the preindustrial control simulation. With these experiments we are able to further investigate mechanisms of AMOC induced climate change impacts, using a moisture budget framework and assessing daily impacts on weather regimes. Overall, our work indicates that the AMOC is a major source of inter-model uncertainty, and continued observational efforts are needed to constrain the impacts of an AMOC decline in future climate change.

Beschreibung: Time-lapse monitoring of seismic velocity at a volcanic area can provide important information about the dynamics of the volcanic system and its temporal variability. One standard technique to monitor small changes in the medium is ambient noise interferometry. This technique is based on quantifying relative velocity variations (dv/v) by measuring changes in the ambient noise cross-correlation signal phase. In this study, we demonstrate that together with velocity variations, the study of changes in seismic attenuation (Qc) extracted from ambient noise cross-correlation could be relevant for volcano monitoring. The Qc is determined using the lapse-time dependence method (Calvet and Margerin, 2013), in which, Qc is measured as a function of the coda window length for different onsets of the ambient-noise cross-correlation coda. We apply this technique to the 2021 Cumbre Vieja eruption in La Palma (Canary Islands), which started on Sept. 19th and had a significant social and scientific impact. First, we determine a reference Qc model of the Cumbre Vieja volcano using data from Aug. 1st to 31st, 2021. Then, we analyze the spatio-temporal Qc variations during the nineteen days preceding the eruption, and we compare our results with previously obtained dv/v results. We observe an increase of Qc during the pre-eruptive phase, corresponding to a dv/v decrease. We hypothesize that the observed correlated Qc increase and dv/v drop could be explained by the ascent of hydrothermal fluids towards the surface before the eruption.

Beschreibung: In recent years the use of Distributed Acoustic Sensing (DAS) in seismology is gaining extensive usage in different applications. A High-Fidelity DAS system (HDAS) was deployed during the 2021 Tajogaite eruption on Cumbre Volcano (La Palma, Canary Islands), allowing the recording of most of the syn-eruptive and post-eruptive seismicity. The eruption lasted from Sep. 19th until Dec. 13th of 2021. The HDAS was installed on 19th Oct. 2021 and is still operating. The HDAS was installed around 10 km from the eruptive vent and was connected to a submarine fibre optic cable directed toward Tenerife Island. Since then, the HDAS has been recording seismic with a temporal sampling rate of 100 Hz and a spatial sampling rate of 10m for a total length of 30 (first phase) and 50 km using Raman Amplification (last period). The HDAS recorded thousands of local earthquakes as well as regional and teleseismic events. It was revealed to be an excellent tool for volcanic monitoring, allowing a better location of deeper events which location was made difficult by the small aperture of the seismic network of La Palma. The HDAS was also able to record the low-frequency (〈1 Hz) component of the volcanic tremor up to a distance of tens of kilometres from the volcano. We show how, using array-like techniques, it is possible to identify and separate the volcanic tremor signals from the oceanic ambient noise. In this work, we demonstrate the effectiveness of using DAS as a real-time volcano monitoring tool.

Beschreibung: 15 new heat flow measurements were obtained during the ALBACORE cruise (R/V Pourquoi Pas ?) in 2021 in the Alboran Sea, the westernmost part of the Mediterranean Sea. Temperature gradients were measured using autonomous thermal probes attached to sediment corers with a length of 6 meters. Thermal conductivity was measured onboard using a needle probe instrument on recovered sediment cores. In previous studies, a large difference in heat flow has been observed between the western and eastern parts of the Alboran Basin, 69 ± 6 mWm〈sup〉-2〈/sup〉 versus 124 ± 8 mWm〈sup〉-2〈/sup〉. Here we focus on the mainly North-South Bokkoya and Al Idrissi active strike-slip fault zones between these two domains. Three heat flow profiles were performed perpendicular to the fault zones that show a marked difference in heat flow values along and between these profiles. The northern profile, 2.5 km long, indicates a homogeneous heat flow with a mean value of 65 mWm〈sup〉-2〈/sup〉. The middle profile shows a heterogeneous heat flow with a mean of 81 mWm〈sup〉-2〈/sup〉 and variations of ± 30 mWm〈sup〉-2〈/sup〉 over a 400 m distance. The southern profile indicates high and heterogeneous heat flow values varying between 155 and 204 mWm〈sup〉-2〈/sup〉 over the 550 m long profile. These local thermal anomalies could be associated with hydrothermal activity along the fault segments. Transport of heat by hydrothermal circulation has been observed in different geological settings. In the Alboran sea basin, some segments of the active fault zones may thus display suitable pathway for hydrothermal circulation.

Beschreibung: During eruptions, volcanoes produce air-pressure waves inaudible for the human ear called infrasound, which are very helpful for detecting early signs of magma at the surface. Compared to violent ash-rich explosions, recording more discreet atmospheric disturbances from effusive eruptions remains a practical challenge. Wind and human activity are other powerful sources of unwanted infrasound noise masking volcanic ones. At Nyiragongo volcano (D.R. Congo), close to a one-million urban area, the drainage of the world’s largest lava lake concomitant with short-duration lava flows on its flank and the renewal of an effusive eruption within its crater a few months later were a series of major volcanic events in 2021, all monitored with infrasound sensors. First, we explore these records for characterizing the temporal and spatial evolution of the flank eruption on May 22, 2021. In a second step, we show evidence of the infrasonic rumbling of a nascent lava lake starting a few months later detected up to the volcano observatory facilities in Goma city center about 17 km from Nyiragongo’s crater. These results show remarkable local recordings of eruptive infrasound from rural and city-based stations and have significant implication for optimizing future monitoring efforts in a harsh field environment.

Beschreibung: 〉The barotropic dispersion relation for Rossby waves is a well-known analytical relation in which the phase speed of Rossby waves can be written as a funtion of the background zonal wind, the background absolute vorticity gradient and the zonal and meridional wavenumbers. To test the ability of such a relation to accurately estimate phase speeds of Rossby waves, ERA5 reanalysis dataset is used with 6-hourly time steps. The meridional wind at 500 hPa is first decomposed into contributions from individual zonal wavenumbers in order to get the phase at each given time. The difference in phase between two consecutive times is then computed to get an estimation of the phase speed for each zonal wavenumber. Such a diagnosed phase speed is then compared to the analytical phase speed deduced from the dispersion relation. The latter phase speed is computed using the zonal averages of the zonal wind and absolute vorticity gradient and by estimating the ratio between the meridional and zonal wavenumbers with the ratio between the variances of the meridional and zonal wind components. A systematic comparison between the diagnosed phase speed and the analytical expression is then made by analysing the climatologies, interannual fluctuations and trends of both quantities. The barotropic dispersion relation is shown to be particularly useful to interpret summertime fluctuations of the phase speed for planetary waves (wavenumbers between 3 and 5).〈/p〉