Annals of Geophysics (INGV, Istituto Nazionale di Geofisica e Vulcanologia)
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Impact of the Crustal Velocity Model on Earthquake Location and Moment Tensor Solution: Case Study on the 2025 Aegean Sea Earthquakes
Full text linkThe densely populated areas in the Eastern Mediterranean are highly vulnerable to a variety of geohazards, including earthquakes, tsunamis, volcanoes and landslides. The Cyclades archipelago region near Santorini in the Aegean Sea lies within a tectonically active belt capable of generating volcanic activity, major destructive earthquakes and subsequent landslides and/or tsunamis. Understanding the properties of plate boundaries, slabs, active faults and the stress field is crucial for identifying the geodynamic factors driving plate deformation and associated geohazards. A dense seismic network is crucial for precisely locating earthquakes and understanding the active tectonics of the area. In recent years, dense seismic networks such as AdriaArray, have been conducted to provide high quality data for imaging crustal and upper mantle structure, as well as analysing seismic activity in the Mediterranean region. This study focuses on the computation of a 1D velocity model in order to improve the earthquake parameters in the region. Taking advantage of recent deployments, dense station coverage, and a comprehensive earthquake catalogue from recent seismic activity in the Cyclades archipelago, Aegean Sea, a new 1D crustal velocity model was developed and compared with existing models in the region. The presented results emphasize the influence of the crustal velocity model on earthquake parameters and moment tensor solutions, with strong potential to enhance forthcoming investigations into source mechanisms, fault kinematics, and seismic velocity structures in the Aegean Sea
A proposed workflow to characterise site conditions and reference potential for Greek AdriaArray stations
Full text linkIn Greece, the 1Y AdriaArray network consists of 31 stations, covering most of the mainland. Although all of them are considered to lie on rock formations, the validity of the reference station assumption has not been verified yet – and neither has it been investigated throughout the rest of the extensive AdriaArray network. In this study, we attempt a systematic compilation of station metadata and site conditions for Greek 1Y stations, coupled with an in‑depth empirical analysis of weak‑ and strong‑motion recordings to estimate site effects. We wish to propose this as a basis for a structured workflow for documenting station and site conditions information across AdriaArray in a consistent and comprehensive way that can be harmonized across all agencies and countries. We have integrated waveform‑derived parameters, focusing on site response and near‑surface properties and parameters based on the analysis of external sources, such as geological maps, topographic maps, etc. Single‑station amplification functions (horizontal‑to‑vertical spectral ratios, HVSR) were estimated from the seismic data, and the site resonance characteristics wereassessed, not only in the conventional way of combining components, but also assessing directional sensitivity. Based on the various criteria investigated, we characterize stations with respect to their potential capacity as reference
AdriaArray temporary deployment in the Po Plain and Sardinia (Italy)
Full text linkWe present the deployment and performance of 17 temporary broadband seismic stations installed in Northern Italy and Sardinia as part of the AdriaArray project. These stations aim to densify the national seismic network, especially in areas with historically sparse coverage such as the Po Plain and Sardinia. We describe here the network design and site selection that follow high‑quality standards developed during previous large‑scale European seismic experiments. Despite challenging environmental and anthropogenic conditions, the stations recorded high‑quality data, enabling both local and teleseismic event detection. We analyze the seismic noise characteristics across the network using probabilistic power spectral densities and observe that stations installed in sedimentary basins typically show higher noise levels at short periods, while stations in rock sites – especially in Sardinia – generally perform better. The use of different sensor types and installation methods also influences noise behavior, particularly in the long‑period components. Despite the diverse conditions, the stations allow for the recording of both local and teleseismic events. The addition of the 4P stations improves the network’s detection threshold by approximately 0.4 magnitude units in Sardinia and 0.2 in the North Italy. The open‑access data from this deployment contribute to AdriaArray’s broader goals of advancing seismic imaging and geodynamic interpretation in the Mediterranean region
Magnetic signature of submarine volcanoes in the Phlegrean Fields-Ischia Ridge (North-Western side of the Bay of Naples, Southern Italy)
Full text linkThis paper presents a study of the Phlegrean Fields-Ischia submarine ridge by the analysis and interpretation of
high-resolution aeromagnetic data recently acquired in the Western Procida offshore. The investigated area is located
along the ridge connecting Ischia to the Phlegrean Fields and is characterized by the existence of several
monogenetic volcanoes aligned on a NE-SW system of faults. The high-resolution magnetic data yielded new
information on the area, highlighting particularly the signature of a volcanic body located between Pt. Serra and
the Ruommoli shoal. This structure has not been clearly described before and we named it as the Pt. Serra submarine
volcano. The computation of the analytic signal and horizontal gradient of the data distinctly located this
structure and definined the position of its rims. A 2D modeling and 3D inversion of data provided information
on the volcanos thickness, width and magnetization, disclosing a meaningful igneous body extending down to
several hundred meters b.s.l
Comparative Declustering Approaches for Seismic Data: Insights from Gardner‑Knopoff, Gruenthal, Reasenberg, and Uhrhammer in the Kathmandu Valley
Full text linkDeclustering is a crucial process that filters out dependent events to focus on independent mainshocks, thereby improving the accuracy of seismic hazard analysis. This study analyzes the spatiotemporal features of background seismicity in the Kathmandu Valley, Nepal using four widely applied declustering methods: Gardner and Knopoff, Gruenthal, Uhrhammer, and Reasenberg. A total of 3190 events from 2000 to 2023 that was analyzed using ZMAP software, revealing significant differences in the performance of each method. Statistical tools including the Allan factor, coefficient of variation Morisita index, and the inhomogeneous L-function were employed to assess spatial clustering, and temporal clustering behaviour. The results indicate that clustering persists in all declustered catalogs, with Reasenberg exhibiting the highest residual temporal clustering and Gruenthal the lowest. Spatial clustering analysis using the Morisita index revealed that Uhrhammer retained the strongest clustering, whereas Gruenthal produced the most homogeneous spatial distribution. Furthermore, L-function analysis with Monte Carlo simulations demonstrated that none of the declustered catalogs fully adhered to a homogeneous Poisson process, as all methods yielded p-values of zero. These findings underscore the limitations of current declustering techniques in completely removing clustering effects, emphasizing the need for refined methodologies in seismic hazard analysis. Future research should explore alternative declustering strategies and statistical models to better represent earthquake sequences in tectonically active regions like the Kathmandu Valley
Cellular Nonlinear Network for fluid dynamics: towards geophysical flows modeling
Full text linkThis work proposes an application of Cellular Nonlinear Networks (CNNs) to fluid dynamics, implemented towards the application to geophysical flows. We revisit the CNN paradigm for the solution of Partial Differential Equations with a focus of some main physical properties of geophysical flows. We address numerical aspects of the obtained model, including the treatment of boundary conditions, stability and correctness of the results. This is done by applying our method to canonical testcases and comparing the results with accepted benchmark data and analytical solutions from the literature. The parallelizability of the method is also assessed by means of benchmarking tests on a multi-core processor. We validate the model by simulating classical geophysical flows. The results that we present show the capability of the model to reproduce typical velocity profiles of viscous flows, making it promising for applications that require the simulation of such materials
Stress Transfer and Aftershock Distribution of The Strong Earthquakes in The Thailand‑Laos‑Myanmar Border
Full text linkThis study analyzed the stress transfer and the aftershock distribution in the Thailand-Laos-Myanmar border. The fault parameters of the three strong earthquakes with M ≥ 6.0 that occurred during 2010-2022 in the Thailand-Laos-Myanmar border were used to calculate the Coulomb stress change with the numerical modeling techniques resolved on the receiver fault with i) focal mechanism similar to the mainshock, ii) strike-slip, iii) thrust, and iv) normal faulting, respectively. The earthquake events were declustered spatially and temporally to identify the aftershocks in the area. Then, the stress transfer and aftershock distribution were analyzed to investigate the relationship. The results indicated that the type of receiver fault was the important factor that influenced the pattern of stress transfer on the Thailand-Laos-Myanmar border. The M6.1 earthquake in 2014 in Thailand generated most aftershocks in the areas of increased stress with stress change levels of more than 0.8 bar. The M6.9 earthquake in 2011 in Myanmar caused the stress to transfer into Thailand with increased stress levels smaller than 0.3 bar, and there was no aftershock generated in this area of Thailand. Meanwhile, the M6.2 earthquake in 2019 in Laos induced stress transferred into Thailand with levels of increased stress up to 0.8 bar, and there was one aftershock generated around this area of Thailand. The results are likely to be the characteristic of stress transfer and aftershock distribution, especially with increased stress levels above 0.8 bar, which can be used to identify the areas of aftershocks after the strong earthquake occurred in the Thailand-Laos-Myanmar border
A single-station spectral model of the monthly median foF2 over Chongqing, China
Full text linkHourly values of the critical frequency of the ionospheric F region, foF2, obtained at Chongqing ionospheric observatory
(geographic 29.50N, 106.40E), China, during the interval of 1977 to 1997 (solar cycle 21 and 22) have
been used to investigate the dependence of the monthly median foF2 on solar activity and geomagnetic activity,
and to construct single-station model (SSM) using Fourier expansion. The results of the present analysis show
that there is a significant nonlinear relationship between monthly median foF2 and sunspot number R especially
at daytime in each month and nighttime in summer. Furthermore, introducing geomagnetic index Ap further
improves the description of variation of monthly median foF2, and the standard deviations decrease also dependently
on time and month. Thus the complex influence of solar activity and geomagnetic activity may be approximately
expressed by a general multiple nonlinear function at Chongqing station, China. The basic aim of this
paper is to show that considering the nonlinear influence both of solar activity and geomagnetic activity improves
the monthly median model. The SSM is in good agreement with observations, with standard deviation
0.65MHz, while IRI model has a lower accuracy with standard deviation 0.96MHz
Ionospheric error analysis in gps measurements
Full text linkThe results of an experiment aimed at evaluating the effects of the ionosphere on GPS positioning applications are presented in this paper. Specifically, the study, based upon a differential approach, was conducted utilizing GPS measurements acquired by various receivers located at increasing inter-distances. The experimental research was developed upon the basis of two groups of baselines: the first group is comprised of "short" baselines (less than 10 km); the second group is characterized by greater distances (up to 90 km). The obtained results were compared either upon the basis of the geometric characteristics, for six different baseline lengths, using 24 hours of data, or upon temporal variations, by examining two periods of varying intensity in ionospheric activity respectively coinciding with the maximum of the 23 solar cycle and in conditions of low ionospheric activity. The analysis revealed variations in terms of inter-distance as well as different performances primarily owing to temporal modifications in the state of the ionosphere
Characterizing Seismic Response and Ground Motion Topographic Effects: A Local-Scale Study for Geotechnical Applications
No full textThis study focuses on enhancing our understanding of sites dominated by both soil properties and complex topographic conditions by analyzing ground motion records collected by the Pereira Ground motion network. We implemented various techniques to investigate the site effects, including empirical site classes and their relative amplification. Additionally, the fragility index (Kg) was estimated using earthquake and microtremor data, enabling a comparison between the two approaches. Furthermore, we identified how the topographic conditions of the terrain modified the seismic response at station sites. This research aims to comprehensively understand site effects during seismic events by combining site classification, fragility assessment, and topographic analysis. The findings from this study have the potential to contribute to the development of effective strategies for seismic response zonation and assessment, building design, and seismic risk assessment from a site characterization perspective