The study of normal fault-generated landforms, such as fault scarps, is commonly performed to investigate fault evolution and the recurrence and magnitude of earthquakes. The Amorgos region (Cyclades, Greece), located in the central part of the Aegean Sea, is structured by ~70km large NE-SW normal faults accommodating the back-arc extension of the Hellenic arc and the Anatolian extrusion. These faults are able to generate large earthquakes such as the Amorgos event (Ms=7.8) on July 09, 1956, followed by a second shock (Ms=7.2) 12 minutes later. This destructive event was the largest Mediterranean earthquake of the 20th century and caused severe damage, especially on Santorini Island. It also triggered a tsunami with reported run-ups reaching locally 30m along the southern coast of Amorgos Island. The submarine Amorgos fault, structuring the island’s southern coast and cumulating a ~2 km high vertical offset, is suggested to be the source of the 1956 main shock and tsunami. However, the accurate position of the 1956 rupture and the magnitude of the slip at surface are unknown, as the fault outcrops at 700m below sea level, as well as the pace at which this fault breaks. Considering that normal faults frequently accommodate the deformation on multiple splays, and within their damage zone, we searched whether the onland faults found within the cumulative scarp of the Amorgos fault ruptured during the 1956 event. We first performed a morphological study of the Chozoviotissa fault segment with satellite imagery, Structure-from-motion modelling, and field observations. We found evidence of recent deformation along this fault, in particular a ~70 cm high fresh ribbon at the base of the fault scarp. To provide chronological constraints, we sampled along-dip the carbonate-rich fault scarp for TCNs (Terrestrial Cosmogenic Nuclides) dating using the chlorine-36 element. This paleoseismic approach provides new insights on the recent slip history of this secondary fault, which is important to better evaluate the activity of the Amorgos fault system and improve the hazard assessment of the archipelago.

The study of normal fault-generated landforms, such as fault scarps, is commonly performed to investigate fault evolution and the recurrence and magnitude of earthquakes. The Amorgos region (Cyclades, Greece), located in the central part of the Aegean Sea, is structured by ~70km large NE-SW normal faults accommodating the back-arc extension of the Hellenic arc and the Anatolian extrusion. These faults are able to generate large earthquakes such as the Amorgos event (Ms=7.8) on July 09, 1956, followed by a second shock (Ms=7.2) 12 minutes later. This destructive event was the largest Mediterranean earthquake of the 20th century and caused severe damage, especially on Santorini Island. It also triggered a tsunami with reported run-ups reaching locally 30m along the southern coast of Amorgos Island. The submarine Amorgos fault, structuring the island’s southern coast and cumulating a ~2 km high vertical offset, is suggested to be the source of the 1956 main shock and tsunami. However, the accurate position of the 1956 rupture and the magnitude of the slip at surface are unknown, as the fault outcrops at 700m below sea level, as well as the pace at which this fault breaks. Considering that normal faults frequently accommodate the deformation on multiple splays, and within their damage zone, we searched whether the onland faults found within the cumulative scarp of the Amorgos fault ruptured during the 1956 event. We first performed a morphological study of the Chozoviotissa fault segment with satellite imagery, Structure-from-motion modelling, and field observations. We found evidence of recent deformation along this fault, in particular a ~70 cm high fresh ribbon at the base of the fault scarp. To provide chronological constraints, we sampled along-dip the carbonate-rich fault scarp for TCNs (Terrestrial Cosmogenic Nuclides) dating using the chlorine-36 element. This paleoseismic approach provides new insights on the recent slip history of this secondary fault, which is important to better evaluate the activity of the Amorgos fault system and improve the hazard assessment of the archipelago.

The Wharton Basin earthquake sequence on April 11, 2012, offshore Sumatra, represents the two largest ( M w > 8.0) strike‐slip earthquakes ever recorded. Ground fault displacements generated a spectrum of acoustic‐gravity waves due to solid Earth–atmosphere coupling. Wave‐like perturbations in Total Electron Content (TEC) were therefore observed in ground‐based Global Positioning System data. The waves arrive about 10 min after each earthquake and their spectral analysis reveals the presence of acoustic resonance frequencies of 3.8 and 4.4 mHz. The acoustic wave speeds of 0.9–1.2 km/s suggest coseismic ground movement as the primary wave generating mechanism instead of seismic Rayleigh waves. Gravity waves with frequencies below 2 mHz traveling with lower speeds of 0.21 km/s are also detected. Ray tracing using a simple numerical model traced the source of observed ionospheric perturbations to within 150 km distance of the epicenters. Large amplitude ionospheric disturbances were found to travel mostly in a north‐south direction, an observation explained by the orientation of Earth’s geomagnetic field.

The largest tsunamis are generated by seafloor uplift resulting from rupture of offshore subduction-zone megathrusts. The rupture of the shallowest part of a megathrust often produces unexpected outsize tsunami relative to their seismic magnitude. These are so called ‘tsunami earthquakes’, which are difficult to identify rapidly using the current tsunami warning systems, even though, they produce some of the deadliest tsunami. We here introduce a new method to evaluate the tsunami risk by measuring ionospheric total electron content (TEC). We examine two M w 7.8 earthquakes (one is a tsunami earthquake and the other is not) generated in 2010 by the Sunda megathrust, offshore Sumatra, to demonstrate for the first time that observations of ionospheric sounding from Global Navigation Satellite System (GNSS) can be used to evaluate the tsunamigenic potential of earthquakes as early as 8 min after the mainshock.

Despite the global threat posed by large‐scale eruptions to communities, to the climate, and to the consequent impacts on the world economy, many active volcanoes still lack of adequate ground‐based instrumentation. Satellite‐based remote sensing has been used to complement volcano monitoring and risk assessment for volcanic ash, but this technique is often limited by weather conditions. In this work, we explore the ionospheric total electron content (TEC) perturbations measured by GNSS to provide additional information and complement conventional monitoring systems. To this end, we measure the GNSS TEC perturbation associated with the acoustic‐gravity waves generated by 22 volcanic explosions. We introduce a new metric—the Ionospheric Volcanic Power Index (IVPI)—to quantify the energy transferred to the ionosphere by volcanic explosions. We evaluate the IVPI against several well‐established metrics from seismic and infrasonic volcano monitoring as well as satellite remote sensing. Our results show that the IVPI successfully correlates with the Volcanic Explosivity Index (VEI) for events larger than VEI 2. Moreover, the IVPI shows strong correlation with both the acoustic source power and the ash plume height, from which depends the style of volcanic activity. Moderate correlation between IVPI and peak ground velocity (PGV) requires further study in order to evaluate the role of different parameters (seismic magnitude, attenuation, style of faulting, crustal structure, etc.). Our results suggest that ionospheric monitoring by GNSS TEC can help to characterize volcanic eruptions, opening new exciting avenues for continuous volcano monitoring and warning systems by remote sensing.

Analogue and numerical simulations have been widely used to describe the mechanisms of bubble and slug ascent during volcanic eruptions as well as their formation and explosion mechanisms. Nevertheless, little is known about the mechanical interaction between the fluid and the surrounding medium. In this work, we report the results from analogue experiments designed to show how deformation of the conduit walls induced by the rising slugs is related to the radiation and propagation of seismic and geodetic signals. For the first time, we investigate the dynamics of bubbles in an elastic conduit unveiling the relationship between slugs and crustal strain accumulation around the conduit. Moreover, we discuss the retroactive effects of the deformed conduit wall on the dynamics of a rising slug, particularly, how the flow is affected, and the eventual implications on the intensity of the eruption. Our results show that the combination of an elastic conduit with a large volume of gas may lead to the development of a new type of slug, here defined as a "super slug," characterized by tapering towards the tail and a much higher ascent velocity and inner pressure compared with ordinary slugs. This newly observed behavior could be linked to vigorous explosive events.

This dataset contains all the outputs obtained during the GNSS data processing aiming to explore the relationship between the power of volcanic explosion and ionospheric TEC perturbation. This dataset also contain the codes used to process the data

(1) Asian School of the Environment, Nanyang Technological University, Singapore (aemadzadeh@ntu.edu.sg), (2) Earth Observatory of Singapore, Nanyang Technological University,Singapore (stepheng001@e.ntu.edu.sg), (3) Earth Observatory of Singapore, Nanyang Technological University,Singapore (fabio001@e.ntu.edu.sg), (4) Earth Observatory of Singapore, Nanyang Technological University,Singapore (btaisne@ntu.edu.sg), (5) Asian School of the Environment, Nanyang Technological University, Singapore

Persistently active volcanoes are characterized by frequent eruptions, in which volatiles dissolved in magma play an important role in controlling the explosivity. Inverting techniques on geodetic data sets have been used to retrieve information about key controlling parameters of these eruptions. However, up to date, several data sets are combined to obtain reliable estimates of the physical parameters using a physical model, hindering the possibility to provide forecasting tools for time and magnitude of eruptions at volcanoes with limited monitoring network. In this work, we propose an approach to extract valuable information out of limited data sets through inverting techniques dealing with limited number of sensors, but high frequency of events. Our method exploits time series of tilt signals recorded by a single station to estimate, by mean of the Bayesian statistics and a physics-based model, the range of the controlling parameters. The method was developed and tested on a synthetic volcanic system before being applied on data from Semeru volcano (Indonesia). Finally, we tested the possibility to forecast explosion magnitude and timing using data recorded by a single tilt station. Results show that data from a limited network or even a single tilt station is sufficient to estimate the controlling parameters. The information obtained is shown to be useful for estimating the time and magnitude of future events, which can enhance the monitoring systems of those volcanoes characterized by frequent, potentially dangerous events.

This study presents a novel approach for the hydrogeological assessment of sedimentary coastal aquifers. Specifically, the methodology is tailored for modeling groundwater flow and nitrates contamination in typical Mediterranean coastal plains with high anthropogenic pressures, as exemplified by the Arborea plain (central western Sardinia, Italy). The study started with development of an updated geological–depositional model based on sequential stratigraphy. Geological and geophysical data, processed in a geographic information system (GIS) environment, supported the definition of a 3D hydrogeological conceptual model and provided a solid basis for the interpretation of groundwater flow directions. The 3D hydrogeological model allowed constraining groundwater circulation, flow paths and distribution of nitrate concentrations in the aquifers. The methodology appears as a valid tool applicable in other coastal areas to determine geological and hydrogeological settings. The definition of a quantitative hydrogeological framework will support the effective management of local water resources.