We investigate the source of the 21st August 2017, Md 4.0 Casamicciola volcano-tectonic earthquake (Ischia Island, Italy), which caused heavy damage on the northern flank of the Mt. Epomeo resurgent block of the Ischia caldera. We adopt a multidisciplinary approach that combines geophysical, geological and coseismic ground deformation data mapped since after the earthquake occurred. Building on a critical review of previous studies, we incorporate new geological field mapping, stratigraphic boreholes, and geophysical surveys to better constrain the seismogenic source of the 2017 Casamicciola earthquake. The results support a model involving the activation of a graben-like fault system, in which the Grande Sentinella Fault acts as an antithetic structure, while the main seismogenic faults correspond to a system of N-dipping normal faults controlling the evolution of the northern flank of Mt. Epomeo. This model implies the involvement of multiple sub-parallel fault segments and provides a physically consistent interpretation of the observed deformation pattern. The proposed solution differs significantly from previously published models and is fully compatible with the geological framework of the area. Our results have profound implications on the seismotectonic modelling and volcano-tectonic earthquakes and for seismic hazard assessment in this crucial region of the Ischia Island.
Identifying the coupling mechanisms that operate in the two directions, upward and downward, between Earth's lower atmosphere and geospace (ionosphere, magnetosphere, and beyond) is currently one of the greatest scientific challenges to be addressed by the atmosphere and space science communities. To meet this challenge, an ISSI Forum on “Physical Links between Weather in Space and Weather in the Lower Atmosphere” was organized in Bern in November 2022. This paper presents a synthesis of the scientific discussions, conclusions and recommendations of this Forum, aimed primarily at the space- and atmospheric-science communities while also identifying implications for operational services, space agencies and other stakeholders. The Forum discussed how the lower atmosphere influences the upper layers through gravity waves, atmospheric tides and planetary waves, thunderstorms, chemical transport and seismic activity, and conversely how solar and space phenomena may affect chemistry, dynamics and climate in the lower atmosphere. It also considered the redistribution of chemical species, momentum and energy within the thermosphere–ionosphere, where forcing from above and below interact. Based on this analysis, the Forum identified observational gaps and needs for new observations, particularly in the lower thermosphere ( 90 to 200 km), as well as modeling needs. Rather than implying that whole-atmosphere models lack all upper-atmosphere electrodynamics, we identify the need to strengthen quantitative coupling between neutral dynamics, ionospheric electrodynamics and magnetospheric forcing, together with systematic model validation and data assimilation. In order to implement its recommendations, the Forum highlighted the need for co-ordinated international efforts to understand the whole atmosphere as a coupled system. It emphasized the importance of developing at the international level a “Great Ionosphere–Thermosphere–Mesosphere (ITM) Observatory”, understood as an interoperable framework linking distributed space- and ground-based assets and models rather than as a single physical observatory. Finally, the Forum emphasized the need for closer collaboration between space scientists, meteorologists and climate scientists, and the importance of upper atmospheric processes for appropriately addressing space sustainability and for understanding possible links between space weather and lower atmospheric climate. The conclusions and recommendations of the Forum motivated the organization of the ISSI Workshop on “Physical Links Between Weather and Climate in Space and the Lower Atmosphere”, held in Bern in January 2024.
The degree-depth relation links the spherical harmonic degree to an operational depth scale for gravity signals. Previous studies have primarily examined the degree-depth relation for the gravity anomaly, the vertical component of the gravitational vector, and the gravity disturbance. However, degree-depth relations for other high-order radial disturbing potential gradients, such as the second- and third-order radial derivatives of the disturbing potential, remain unestablished. This study reviews existing degree-depth relations and their applications in modeling and spectral-scale interpretation of observed gravity signals. degree-depth relations are derived for the components of the second- and third-order radial derivatives of the disturbing potential. Furthermore, the general degree-depth relation for the sth-order ( s ≥ 1 ) radial disturbing potential gradients is established. Numerical results show that, for all degree-depth relations, operational depths decrease as spherical harmonic degrees increase, and vice versa. Results further indicate that distinct degree-depth relations should be applied to the corresponding orders of radial disturbing potential gradients. The derived degree-depth relations offer a self-consistent set of bounds for spectral-filtering choices when working with high-order radial gradients in geodesy, geophysics, and planetary sciences.
The Philippine Sea Plate (PSP) is one of the most important elements of plate tectonics in the western Pacific region. The most conspicuous feature of the PSP is that it is surrounded by subduction zones. Here, we review main geophysical studies in the past two decades on the evolution and general structure of the PSP and its surrounding subduction zones, as well as related seismic and volcanic activities. These studies revealed strong structural heterogeneities in all parts of the PSP and its surrounding subduction zones. Fluids from dehydration reactions of the subducting Pacific and Philippine Sea slabs cause active arc volcanism and affect the generation of large crustal earthquakes, megathrust earthquakes, and intraslab events. Tears and windows are revealed in the subducting Philippine Sea slab, which may be facilitated by subduction of oceanic ridges. There are interactions between the subducting Pacific and Philippine Sea slabs. Significant seismic anisotropy occurs in the mantle above and below the subducting slabs, which reflects mantle flows induced by the plate subductions. These studies shed new light on seismotectonics, volcanism, and geodynamics in the western Pacific and Southeast Asian regions, which are important for both scientific research and reduction of seismic, volcanic, and tsunami hazards.
