With the advent of plate tectonics in the last century, our understanding of the geological evolution of the Earth system improved essentially. The internal deformation and evolution of tectonic plates remain however poorly understood. This holds in particular for the Central Mediterranean: The formerly much larger Adriatic plate is recently consumed in tectonically active belts spanning at its western margin from Sicily, over the Apennines to the Alps and at its eastern margin from the Hellenides, Dinarides towards the Alps. High seismicity along these belts indicates ongoing lithospheric deformation. It has been shown that data acquired by dense, regional networks like AlpArray provide crucial information on seismically active faults as well as on the structure and deformation of the lithosphere. The Adriatic Plate and in particular its eastern margin have however not been covered by a homogeneous seismic network yet.

Here we report on the status of AdriaArray – a seismic experiment to cover the Adriatic Plate and its actively deforming margins by a dense broad-band seismic network. Within the AdriaArray region, currently about 990 permanent broad-band stations are operated by more than 40 institutions. Data of 97% of these stations are currently available via EIDA. In addition to the existing stations, 414 temporary stations from 24 mobile pools are deployed in the region achieving a coverage with an average station distance of 50 – 55 km. The experiment is based on intense cooperation between local network operators, mobile pool operators, field teams, ORFEUS, and interested research groups. Altogether, more than 50 institutions are participating in the AdriaArray experiment. We will report on the time schedule, participating institutions, mobile station pools, maps of temporary station distribution with station coverage and main points of the agreed Memorandum of Collaboration. The AdriaArray experiment will lead to a significant improvement of our understanding of the geodynamic causes of plate deformation and associated geohazards.

How to cite: Kolínský, P., Meier, T., and Seismology Group, T. A.: AdriaArray Seismic Network – status in April 2023, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12284, https://doi.org/10.5194/egusphere-egu23-12284, 2023.

We exploit a new template matching based catalogue to study the spatial
and temporal patterns of seismicity in the Eastern and Southern Alps. Data
from the AlpArray Swath-D network from late 2017 to late 2019 were used to
enhance the resolution of the seismic catalogues provided by local
agencies. The template matching method was implemented using our own
GPU-accelerated algorithm to deal with the large data volume. All events
are relocated using waveform-based picking methods.

Based on this result, we study statistical characteristics of the extended
seismicity catalogue, which now has a magnitude of completeness of Mc=0.6
and contains about 7,500 seismic events. We analyse the main spatial and
temporal features of seismicity revealed by this novel dataset. Finally,
we analyse specific event clusters that originated from the template
matching method, and seek to link event interconnectivity to geometrical
properties of the clusters.

How to cite: Hofman, R., Kummerow, J., and Cesca, S. and the AlpArray Working Group: Spatial and Temporal Patterns in Eastern-Alpine Seismicity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12921, https://doi.org/10.5194/egusphere-egu23-12921, 2023.

A strong earthquake, M_L = 6.0 (M_W = 5.7), occurred on 22 April 2022 at 21:07 UTC with an epicentre near Berkovići in Bosnia and Herzegovina, with focal depth of about 20 km. The earthquake was felt throughout Bosnia and Herzegovina, Montenegro, Croatia (especially Dalmatia), but also in Slovenia, Italy (especially the western coast of the Adriatic), Serbia, Albania and North Macedonia. The maximum intensity of the earthquake was rated as VII–VIII EMS in Berkovići and Ljubinje. A young woman in Stolac lost her life from a rock slide caused by the earthquake. In the wider epicentral area the earthquake caused a number of large or small rock falls, many chimneys were damaged, tiles fell from the roofs, plaster fell off, and there were also large cracks in the walls.

By 31 October 2022, the DuFAULT project researchers located 6220 aftershocks (39 with M_L≥ 3.0), with as many as 900 located in the first 12 h of the series. The strongest aftershock, M_L = 4.9, occurred on 24 April 2022 at 4:27 UTC with focus at a depth of about 25 km and the epicentre also close to Berkovići. The vast majority of earthquakes have their foci relatively deep for this area, at depths between 15 and 28 km. Most of the epicentres form a compact group slightly elongated parallel to the NW-SE Dinaric strike, however two smaller groups northwest and southeast of the main group stand out with extension perpendicular to the Dinaric strike with somewhat shallower foci. The analysis of the focal mechanism and the hypocentral spatial distribution suggest that the mainshock resulted from the NE-SW directed compression and occurred on a reverse fault, on a moderately NE-dipping plane. Interestingly though, this series is also characterized by earthquakes released by a tension along the NE-SW striking and approximately 45° dipping normal faults, documented in the smaller north-western group.

We will present spatio-temporal analysis of seismicity, resulting focal plane solutions and seismotectonic interpretation.

How to cite: Dasović, I., Herak, D., Herak, M., Latečki, H., Sečanj, M., Tomljenović, B., Cvijić-Amulić, S., Mustać Brčić, M., Belinić Topić, T., and Stipčević, J.: The Berkovići (BA) 22 April 2022 earthquake sequence – seismological and seismotectonic analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13405, https://doi.org/10.5194/egusphere-egu23-13405, 2023.

We used the data from the dense, broadband AlpArray Seismic Network to derive a set of Receiver Function (RF) measurements on the Moho and Lithosphere-Asthenosphere Boundary (LAB) for a broad region encompassing the Western Alps and including the Ivrea Geophysical Body (IGB), a fragment of mantle emplaced in the lower continental crust. Our analysis fills an information gap since, in spite of numerous active and passive seismological investigations on the Alpine orogen, many of the observations focus on the Moho or the deeper part of the mantle, while reliable information on the LAB below the Alps is scarce. Moreover, our findings provide an additional contribution to resolving the debated topic of the existence of continuous or interrupted continental subduction below the Western Alps.

We derive seismic velocity profiles of the crust-uppermost mantle below each of the 50 analyzed stations down to about 250 km depth, through the joint inversion of P and S RFs. We constrain the lateral variations of the Moho and LAB topographies across the colliding plates, and quantify the errors related to our measurements. Our observations allow us to considerably expand the published data of the Moho depth and to add a unique set of new measurements of the LAB (Monna et al., 2022). 

Our results yield a comparable thickness (on average 90–100 km) of the Eurasia and Adria lithospheres, which are colliding below the IGB; Eurasia is not presently subducting below Adria with vertical continuity. These findings suggest that there is a gap between the superficial (continental) European lithosphere and the deep (oceanic) lithosphere, confirming the discontinuous structure imaged by some seismic tomography models.

the AlpArray Working Group: list on http://www.alparray.ethz.ch/home/

Monna, S., Montuori, C., Frugoni, F., Piromallo, C., Vinnik, L., & AlpArray Working Group (2022). Moho and LAB across the Western Alps (Europe) from P and S receiver function analysis. Journal of Geophysical Research: Solid Earth, 127, e2022JB025141. https://doi.org/10.1029/2022JB025141

How to cite: Montuori, C., Monna, S., Frugoni, F., Piromallo, C., Vinnik, L., and Working Group, A.: Moho and LAB below the Western Alps from P and S Receiver Function analysis and joint inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12370, https://doi.org/10.5194/egusphere-egu23-12370, 2023.

Detailed 3D elastic crustal models are of fundamental relevance to many applications in Geosciences, from geodynamic modelling, to simulation of seismic wave propagation and seismic engineering. However, most of the recent models suffer from two main drawbacks: (1) they are often obtained from interpolation of local 1D models; and (2) they cannot be easily updated, without recomputing the entire model (which, as a corollary, implies the availability of the complete data-set of raw seismic data). The first drawback leads to mainly oversmoothed models on the horizontal scale, where vertical boundaries are not considered either in the 1D models and in the interpolated 3D model. The second disadvantage implies that current models are generally "static" and their updates require a research effort which is often not paying back in terms of outputs.

In this study, we build the framework for an evolutionary elastic model of the Central Apennines. The starting data are represented by a huge data-set of local 1D S-wave velocity models (originally obtained from Receiver Function inversion). We invert such data-set following a Bayesian fusion approach, where the full posterior probability distribution (PPD) of the1D models is exploited to build the 3D elastic model (in absence of the full PPD information, estimators like mean posterior and standard deviation can also be used). The 3D distribution of elastic properties (i.e. a model) is represented by a 3D Voronoi tassellation of the study volume, where the number of 3D Voronoi cells and their positions are unknown. A Markov chain Monte Carlo (McMC) algorithm is used to sample the family of Voronoi models which "fit" the data adequately (here the "data" are the PPD of the 1D models). 

Our results are shown on a regular 5x5x5 km grid down to 100 km depth, and they are consistent with previous models in terms of difference in crustal structure between the Tyrrhenian and Adriatic side of the Apennines. The model shows which of the features are coherent between adjacent stations, and which areas are better resolved. Point of strength over previous models is the possibility of identifying  sub-vertical boundaries, that in a complex region of subduction and neo-formed crust are more likely than a horizontally layered structure. More complementary or additional data (in the form, e.g. of tomographic models or 1D models from dispersion curves) can be easily added to this model, to update it, as new data become available. In fact, new "data" can be either added to the full data-set or can be included modifying the PPD of the 3D Voronoi cells.

How to cite: Bianchi, I., Menichelli, I., and Chiarabba, C.: Evolutionary 3D Vs crustal model for Central Apennines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5849, https://doi.org/10.5194/egusphere-egu23-5849, 2023.

The Alpine orogen is a unique geological formation with a highly variable crustal structure. Despite numerous active and passive seismic investigations in the past, constraints on the crustal structure across the whole Alpine domain are still limited. To improve on this, we use waveform data from four past and ongoing large-scale passive experiments in the broader Alpine region: namely the AlpArray Seismic Network (AASN), which also includes many permanent stations in its footprint, the Eastern Alpine Seismic Investigation (EASI), the China-Italy-France Alps seismic transect (CIFALPS-1) and the Pannonian-Carpathian-Alpine Seismic Experiment (PACASE). This results in a composite seismic network of more than 700 broadband seismic stations, providing unprecedented data coverage.  

We apply a systematic processing workflow to these data and calculate Receiver Functions (RF). After applying strict quality control we obtained 107,633 high-quality RF traces, on average of 122 per station. Next, we developed codes to perform time-to-depth migration in a newly implemented 3D spherical coordinate system using a reference P and S wave velocity model. Finally, we compiled a new detailed Moho map by manually picking the depth of the discontinuity. Our Moho depth estimates generally support the results of previous studies in the region and vary from ca. 20 to ca. 55 km depth with the maximum values observed beneath the Alpine orogen. The RF dataset along with the codes and new Moho map are all open-access. 

The high quality and homogeneously calculated RF dataset, along with the new, coherently derived Moho depth map of the Alpine region, can provide helpful information for interdisciplinary imaging and modeling studies investigating the geodynamics of the European Alps orogen and its forelands (e.g., joint inversions with other geophysical and geological datasets). 

How to cite: Michailos, K. and the AlpArray Receiver Function working group: Moho map and receiver functions database beneath the European Alps using data from recent large-scale passive experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13077, https://doi.org/10.5194/egusphere-egu23-13077, 2023.

The Basque-Cantabrian Zone (BCZ) is a large, inverted Mesozoic basin (the Basque-Cantabrian basin or BCB) forming part of the Pyrenean-Cantabrian mountain belt, in the north of Iberian Peninsula. The Mesozoic basin developed in one of the most subsident regions between the European plate and the Iberian sub-plate during the stage of crustal hyperextension linked to the rifting of the Central-North Atlantic and the opening of the Bay of Biscay. The high subsidence rate led to the accumulation of more than 15 km of sediments according to some estimates, and the significant crustal extension caused the exhumation of the mantle in the easternmost sector of the BCB. The Alpine orogeny caused the closure and inversion of the BCB and its incorporation to the Pyrenean-Cantabrian orogen. In this work, we studied the crustal structure of the BCZ resulting from this long and complex tectonic evolution using five years of continuous seismic recordings gathered by a local network of broadband stations, most of them deployed in the framework of projects SISCAN and MISTERIOS. A total of 66 locations were used (not all of them simultaneously), with an average spacing of ~30 km between stations. From this dataset, we extracted the multi-mode phase velocities of surface waves and the ellipticity of Rayleigh waves from cross-correlations of the seismic ambient noise. This allowed us to retrieve the shear-wave velocity structure of the crust, especially at shallow to intermediate depths. To better constrain the deeper crustal structure, we also extracted teleseismic P-wave receiver functions for all suitable events. Each dataset was carefully analyzed before performing a nonlinear, joint inversion using the simulated annealing technique. The result is a set of 1D shear-wave velocity models that represent a compromise between all three datasets. These 1D models were then used in a linear interpolation to build a 3D model of the BCZ. The main feature of the 3D model is a thickened crust of up to 50 km beneath the Cantabrian Mountains. A discontinuous, intracrustal level of high-velocities is identified in the northern part of the model, coherently with previous geological and geophysical observations, suggesting that the thick crustal root would be caused by the indentation of the Cantabrian Margin lower crust into the Iberian crust, as has been already proposed. This new 3D model fills a gap in the knowledge of the study area, whose seismic characterization was primarily based on active source studies, which often only provide estimates of the P-wave velocities along 2D profiles.

How to cite: Olivar-Castaño, A., Pedreira, D., Pulgar, J. A., Pilz, M., Díaz-González, A., and González-Cortina, J. M.: 3D Crustal structure of the Basque-Cantabrian Zone (N Spain) through a nonlinear joint inversion of surface wave phase velocities, teleseismic receiver functions and Rayleigh wave ellipticity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14741, https://doi.org/10.5194/egusphere-egu23-14741, 2023.

In a recent study, a large amount of splitting intensity measurements of the seismic anisotropy for the Central Mediterranean region has been made available, to retrieve an anisotropy tomography (see Baccheschi et al. and Confal et al. posters of session GD7.1). Here we focus on the images obtained for the Alpine region, that strongly benefit of AlpArray and Cifalps1 and 2 data. 
The 3-D distribution of seismic anisotropy, from 70 to 300 km of depth, has been compared with previous SKS shear wave splitting measurements and has been interpreted taking into account remnant and active pieces of slabs. Most of previously defined mantle flows are confirmed, as the asthenospheric toroidal flow around the tip of the slab beneath the Western Alps. Shallower anisotropy pattern show strong relation with main tectonic structures, from the Rhine Graben to the Western Alps arc and so on. However, the no uniqueness of available seismic velocity anomalies mapping keep some part of the interpretation open, as for instance the detectability of proper slab anisotropy. Out of the directional patterns, this splitting intensity tomography gives a map of anisotropy intensity and its variations with depth, with some strong heterogeneities corresponding to regions where previous seismic anisotropy studies described the presence of complex structure, as for the upper mantle beneath the Eastern Alps. All these new information, if integrated with the most recent studies for the Alpine region, may be a relevant support to innovative hypotheses on crust-to-mantle Alpine transition and structure.

How to cite: Pondrelli, S., Confal, J. M., and Baccheschi, P.: New Interpretations of the Deep Structure of the Alps based on 3D Anisotropy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7713, https://doi.org/10.5194/egusphere-egu23-7713, 2023.

The collisional area between the ALCAPA microplate and East European Craton across the Carpathian Orogen, is one of the most intriguing geological areas in Europe.  Here, a variety of tectonic processes are occurring simultaneously, including extensional basins, oceanic subduction, post-collisional volcanism, and active crustal deformation due to the push of the Adria plate or the pull of the actively detaching Vrancea slab, creating it a distinctive tectonic setting.

To explore the lithospheric structure of this collision region, broadband stations operating in the Carpatho-Pannonian area between 2006and 2022 were transformed into virtual sources by cross-correlating simultaneous noise recordings at pairs of stations in the frequency domain and stacking the cross-correlations to obtain one inter-station cross-correlogram per pair (Empirical Green functions). Rayleigh and Love phase velocities, as well as Rayleigh wave attenuation coefficients, were measured and mapped at six discrete periods (5, 10, 15, 25, and 30s) using the latest multiscale seismic imaging algorithms. We used a least-squares inversion approach based on ray theory with adaptive parameterization to map the lateral variations in surface-wave velocity, whereas the attenuation structures were revealed by mapping the frequency-dependent Rayleigh-wave attenuation coefficient.

Our results reveal a strong correlation between geology and tomographic images, suggesting a highly heterogeneous crust. An inverse correlation trend between Rayleigh wave phase velocity and attenuation maps was obtained for all period ranges, revealing a contrast between high attenuation features from the Pannonian Basin, including intra-Carpathian areas, and stable platform regions placed in front of the Carpathians. The shallow crust shear velocity model shows low velocities beneath Neogene and Paleozoic sedimentary basins and volcanic regions and high velocities under collisional fronts. In the middle to lower crust (25–30 km), high shear velocities beneath the Pannonian basin are in agreement with the previous findings.

How to cite: Borleanu, F., Petrescu, L., Magrini, F., and De Siena, L.: Shear wave velocity and attenuation tomography acquired from seismic ambient noise data analysis in a complex collisional area at the edge of the East European Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15098, https://doi.org/10.5194/egusphere-egu23-15098, 2023.

We present here a 3D shear-velocity regional model of the eastern Pyrenees centered at the Cerdanya Basin using seismic ambient noise to image structure of the Iberian and Eurasian uppermost crust. In the context of the SANIMS project, we deployed a network of 24 broadband seismic stations that complement existing permanent stations from the CA, ES and FR networks and previous temporal deployments from the OROGEN project, and aside, a high-density short-period seismic network focused on the study the Cerdanya Basin. For the regional study, we use the broadband dataset to compute symmetric cross-correlations of the seismic noise using the wavelet phase cross-correlation and the time-scale phase weighted stack, then estimate the phase and group velocity of Rayleigh waves between 1.5 – 7 s and 1.5 – 5 s, respectively. Afterwards, we build a 3D S-wave velocity model from path-average velocities in two steps: regionalization and pointwise depth inversion. In the regionalization step, we build velocity maps from the dispersion curves measured using the fast marching method on the forward problem and a hybrid l₁ – l₂ norm criterion on the inversion to enforce robustness to outliers. In the depth inversion step, we apply transdimensional inference to explore for S-wave velocity profiles with an unknown number of layers of constant velocity and the noise variance of the Rayleigh phase and group velocity maps using a least-square misfit function. The best models show a top low-velocity layer 2 – 3 km thick followed by distinct velocity profiles to the North and to the South, corresponding to the expected differences between the Iberian and Eurasian plates. To the South we observe two layers with a boundary at 6 – 7 km depth and velocities of about 3.2 and 3.5 km/s respectively, while to the North velocities are generally lower, increase much less with depth and there is no clear boundary.

How to cite: Ventosa, S., Schimmel, M., Díaz, J., and Ruiz, M.: Imaging the upper crust in the eastern Pyrenees with ambient seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9451, https://doi.org/10.5194/egusphere-egu23-9451, 2023.

The Alpine-Mediterranean region is area of interest for many studies seeking to better understand the geological evolution as well as the present-day mantle and lithosphere structure. However, despite numerous studies, the geological structure of the upper mantle and the geometry of the different subduction zones remain matter of debate.

Here, we use 3D geodynamic models to investigate the impact of the structure and material properties of the upper mantle and lithosphere on the motion of the Alpine-Mediterranean area. The geodynamic simulations are performed by the finite-difference code LaMEM (Kaus et al. (2016)) and a visco-plastic rheology is used to explore the dynamic behaviour of the upper mantle. In particular, we use the recently developed Julia interface to LaMEM to start simulations and read back the results which simplifies postprocessing and comparing the results to observational constraints.

Specifically, we compare the models with recently compiled GPS velocity data (Serpelloni at al. (2022)). As a result of the geological history in the Mediterranean the density and viscosity structure of the upper mantle is rather complex and influenced by various subduction zones, such that geometry, viscosity and density structures are primary parameters of interest in this study.

First results suggest that the Calabria subduction and the Hellenic subduction explain the fastest horizontal velocities in the Mediterranean whereas the horizontal motion in the Alpine area cannot arise from an active subduction zone but rather from large density and viscosity differences caused by the remnants of older subduction zones.

Kaus B J P, Popov A A, Baumann T S, Pusok A E, Bauville A, Fernandez N, and Collignon M (2016): Forward and inverse modelling of lithospheric deformation on geological timescales. Proceedings of NIC Symposium.

Serpelloni E, Cavaliere A, Martelli L, Pintori F, Anderlini L, Borghi A, Randazzo D, Bruni S, Devoti R, Perfetti P and Cacciaguerra S (2022): Surface Velocities and Strain-Rates in the Euro-Mediterranean Region From Massive GPS Data Processing. Front. Earth Sci. 10:907897. doi: 10.3389/feart.2022.907897

How to cite: Schuler, C. and Kaus, B.: Geodynamic inversion to explain the present-day plate motion in the Alpine-Mediterranean area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7881, https://doi.org/10.5194/egusphere-egu23-7881, 2023.

Thermal and compositional anomalies are known to drive changes in the thickness of the mantle transition zone (MTZ), as they modify the P-T conditions under which phase transitions occur. Typically, the phase changes defining the upper and lower boundaries of the MTZ take place at 410 km and 660 km respectively, thus yielding a standard MTZ thickness of 250 km. These phase transitions have opposite Clapeyron slopes, so while a cold temperature anomaly makes the 410 discontinuity shallower and the 660 deeper, a hot anomaly has the contrary effect. In this ongoing study we use P-wave receiver functions to map the MTZ discontinuities below southern Iberia and northwestern Africa and identify anomalous regions that can be linked to regional structures in the mantle. In this area, convergence of the African and Eurasian plates led to the subduction of the ancient Tethys oceanic lithosphere, from which a remnant slab is stalled below the Gibraltar arc, introducing thermal and chemical heterogeneities that alter the MTZ.

Roughly 33000 receiver functions were obtained from 501 seismic stations, from both permanent and temporary deployments, including four seismic profiles with high density of stations (interstation distances from 2 to 10 km). We constructed a grid of N-S and W-E sections with a spacing of 0.25x0.25 degrees by depth-migrating and projecting the receiver functions with a phase-weighted common conversion point stacking method. An algorithm for the automatic detection of the MTZ discontinuities was then used, and the results allowed us to obtain preliminary 2D and 3D maps containing the depth, width and number of peaks of the pulses attributed to the 410 and 660 discontinuities. Overall, the MTZ reaches its maximum thickness under the Alboran basin (290 km), but the region with anomalous thickness extends well into southeastern Iberia. This feature is attributable to a cold temperature anomaly and matches the position where tomographic studies locate the stalled Tethys slab. Two small areas in the Gulf of Cadiz also stand out for displaying a MTZ thickness of 290 km, coinciding with a region where the 410 discontinuity splits in two pulses. On the contrary, the MTZ is generally thinner than usual towards the south and west of the Alboran basin, especially in sections of the Rif and the Strait of Gibraltar where it can reach 205 km. Our results show, though, that while changes in the 410 discontinuity can be correlated with the tectonic configuration of the region and known anomalies in the mantle such as the Tethys slab, the 660 displays a much more unpredictable pattern.

How to cite: Parera-Portell, J. A., Mancilla, F. D. L., and Morales, J.: Mapping the mantle transition zone beneath the Ibero-Maghrebian region with P-wave receiver functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11792, https://doi.org/10.5194/egusphere-egu23-11792, 2023.