European-Adriatic plate collision in teleseismic tomography of the Eastern Alps

We present potential scenarios of the European and Adriatic plates&#8217; collision that formed the Alps and the neighbouring mountain belts. Our results are based on teleseismic body-wave data from the AlpArray-EASI complementary experiment (2014-2015, Het&#233;nyi et al., Tectonophysics 2018) and the AlpArray Seismic Network (Het&#233;nyi et al., Surv. Geophys. 2018).&#160; Tomography of seismic velocities in the upper mantle along a ca. 200 km broad and 540 km long north-south transect images steady southward thickening of the lithosphere beneath the Bohemian Massif&#160; and northward dipping East-Alpine lithospheric keel. Thanks to the dense spacing of the AlpArray Seismic Network stations and high-quality data, the high-resolution tomography resolves for the first time two sub-parallel down-going high-velocity heterogeneities beneath the Eastern Alps, instead of a single, thick anomaly. The southern heterogeneity, which we relate to the subducted Adriatic plate, is more distinct than the northern one, which loses its connection with the shallow parts. Moreover, amplitudes and size of this heterogeneity decrease in cross-sections perpendicular to the strike of the Alps when shifting towards the Central Alps. The presented collision scenarios consider the smaller northern heterogeneity as (1) a remnant of a delaminated early phase subduction of the European plate with the reversed polarity relative to that in the Western Alps, (2) a piece of continental and oceanic lithosphere together, or, (3) a fragment of a quite extended lithosphere margin foundering in a preceding phase of the Adriatic subduction.

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Tomography image of double high-velocity heterogeneity beneath the Eastern Alps from the AlpArray data

10.5194/egusphere-egu2020-7728 ◽

2020 ◽

Author(s):

Jaroslava Plomerová ◽

Helena Žlebčíková ◽

György Hetényi ◽

Luděk Vecsey ◽

Vladislav Babuška ◽

...

Keyword(s):

Bohemian Massif ◽

High Velocity ◽

Seismic Anisotropy ◽

Body Wave ◽

Eastern Alps ◽

Quality Data ◽

Seismic Velocities ◽

Adriatic Plate ◽

The Alps ◽

Mountain Belts

Convergence between the European and African plates formed the Alps and the neighbouring mountain belts. We present results based on teleseismic body-wave data from the AlpArray-EASI complementary experiment (2014-2015, Het&#233;nyi et al., Tectonophysics 2018) and the AlpArray Seismic Network (Het&#233;nyi et al., Surv. Geophys. 2018). Tomography of seismic velocities in the upper mantle, as well as seismic anisotropy study along a ca. 200 km broad and 540 km long north-south transect (crossing the Bohemian Massif in the north, the East-Alpine root, and reaching the Adriatic Sea in the south), image the steeply northward dipping East-Alpine root, dominated by the Adriatic plate, steady southward thickening of the lithosphere beneath the Bohemian Massif and distinct regional variations of mantle lithosphere fabrics modelled in 3D. These characteristics imply complex, domain-like architecture of the collisional zone of the European/Adriatic plates beneath the Alps. Thanks to the close spacing of the AlpArray stations and high-quality data, the high-resolution tomography resolved for the first time two neighbouring high-velocity northward-dipping heterogeneities beneath the Eastern Alps, instead of one thick root of the lithosphere. The southern one, which we relate to the Adriatic plate, is more distinct, the northern one is less pronounced, it delaminates at ~100km depth and diminishes in direction toward the Central Alps. It may represent a remnant of an early phase subduction of the European plate with the switched polarity (relative to the polarity in the Western Alps), or a preceding phase of the Adriatic subduction.

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No polarity switch? Continental subduction of European crust below the Eastern Alps imaged by receiver functions

10.5194/egusphere-egu2020-13785 ◽

2020 ◽

Author(s):

Stefan Mroczek ◽

Frederik Tilmann ◽

Xiaohui Yuan ◽

Jan Pleuger ◽

Ben Heit

Keyword(s):

Receiver Function ◽

Eastern Alps ◽

Receiver Functions ◽

Opposite Polarity ◽

Seismic Network ◽

Study Region ◽

Teleseismic Tomography ◽

Minimum Depth ◽

The Alps ◽

Receiver Function Method

In the Eastern Alps, teleseismic tomography suggests that there is a switch from European subduction in the west to Adriatic subduction in the east. The dense SWATH-D seismic network is located in the central-eastern Alps between around 10&#176;E and 14.5&#176;E where a change in the dip direction was suggested to occur (e.g. Lippitsch et al. 2003; Mitterbauer et al. 2011). The receiver function method is particularly sensitive to velocity contrasts and so is suited to imaging the interfaces associated with subduction. New receiver function migrations from SWATH-D stations (supplemented by the AlpArray Seismic Network and the EASI profile) show no evidence for Adriatic subduction in the Eastern Alps. Instead, a southward dipping interface [or pair of interfaces with opposite polarity] which we interpreted as subducting&#160; European lower crust can be traced below the Eastern Alps to a minimum depth of 120 km along the extent of SWATH-D. This suggests that in the Alps the polarity flip in subduction does not occur or is located east of our study region beyond 14.25&#176;E, much further east than tomography suggests.

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Microseismicity in the Eastern Alps: Preliminary Results From the Swath-D Network

10.5194/egusphere-egu21-9829 ◽

2021 ◽

Author(s):

Rens Hofman ◽

Joern Kummerow ◽

Simone Cesca ◽

Joachim Wassermann ◽

Thomas Plenefisch ◽

...

Keyword(s):

Large Data ◽

Eastern Alps ◽

Detection Methods ◽

Mountain Range ◽

Network Methods ◽

Data Volume ◽

Geophysical Processes ◽

The Alps ◽

Mountain Belts ◽

Surrounding Areas

The AlpArray seismological experiment is an international and interdisciplinary project to advance our understanding of geophysical processes in the greater Alpine region. The heart of the project consists of a large seismological array that covers the mountain range and its surrounding areas. To understand how the Alps and their neighbouring mountain belts evolved through time, we can only study its current structure and processes. The Eastern Alps are of prime interest since they currently demonstrate the highest crustal deformation rates. A key question is how these surface processes are linked to deeper structures. The Swath-D network is an array of temporary seismological stations complementary to the AlpArray network located in the Eastern Alps. This creates a unique opportunity to investigate high resolution seismicity on a local scale.In this study, a combination of waveform-based detection methods was used to find small earthquakes in the large data volume of the Swath-D network. Methods were developed to locate the seismic events using semi-automatic picks, and estimate event magnitudes. We present an overview of the methods and workflow, as well as a preliminary overview of the seismicity in the Eastern Alps.

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Slab Break-offs in the Alpine Subduction Zone

10.5194/se-2019-102 ◽

2019 ◽

Author(s):

Emanuel D. Kästle ◽

Claudio Rosenberg ◽

Lapo Boschi ◽

Nicolas Bellahsen ◽

Thomas Meier ◽

...

Keyword(s):

Deep Structure ◽

Body Wave ◽

Eastern Alps ◽

Central Alps ◽

Slab Geometry ◽

Tomographic Images ◽

Velocity Anomaly ◽

The Alps ◽

Geological Constraints ◽

European Plate

Abstract. After the onset of plate collision in the Alps, at 32–34 Ma, the deep structure of the orogen is inferred to have changed dramatically: European plate break-offs in various places of the Alpine arc, as well as a possible reversal of subduction polarity in the eastern Alps have been proposed. We review body-wave tomographic studies, compare them to our surface-wave-derived model for the uppermost 200 km, and reinterpret them in terms of slab geometries. We infer that the shallow subducting portion of the European plate is likely detached under both the western and eastern (but not the central) Alps. The Alps-Dinarides transition may be explained by a combination of European and Adriatic subduction. This would imply that the deep, high-velocity anomaly (> 200 km depth) mapped by tomographers under the eastern Alps is a detached segment of the European plate. The shallower fast anomaly (100–200 km depth) can be ascribed to European or Adriatic subduction, or both. These findings are compared to previously proposed models for the eastern Alps in terms of slab geometry, but also integrated in a new, alternative geodynamic scenario that best fits both tomographic images and geological constraints.

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The SWATH-D Seismological Network in the Eastern Alps

Seismological Research Letters ◽

10.1785/0220200377 ◽

2021 ◽

Vol 92 (3) ◽

pp. 1592-1609 ◽

Cited By ~ 2

Author(s):

Benjamin Heit ◽

Luigia Cristiano ◽

Christian Haberland ◽

Frederik Tilmann ◽

Damiano Pesaresi ◽

...

Keyword(s):

Eastern Alps ◽

Focal Mechanisms ◽

Seismic Network ◽

Moho Depth ◽

Dense Network ◽

Study Region ◽

The North ◽

Complex Part ◽

Broadband Network ◽

The Alps

Abstract The SWATH-D experiment involved the deployment of a dense temporary broadband seismic network in the Eastern Alps. Its primary purpose was enhanced seismic imaging of the crust and crust–mantle transition, as well as improved constraints on local event locations and focal mechanisms in a complex part of the Alpine orogen. The study region is a key area of the Alps, where European crust in the north is juxtaposed and partially interwoven with Adriatic crust in the south, and a significant jump in the Moho depth was observed by the 2002 TRANSALP north–south profile. Here, a flip in subduction polarity has been suggested to occur. This dense network encompasses 163 stations and complements the larger-scale sparser AlpArray seismic network. The nominal station spacing in SWATH-D is 15 km in a high alpine, yet densely populated and industrialized region. We present here the challenges resulting from operating a large broadband network under these conditions and summarize how we addressed them, including the way we planned, deployed, maintained, and operated the stations in the field. Finally, we present some recommendations based on our experiences.

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Slab Break-offs in the Alpine Subduction Zone

10.5194/se-2019-17 ◽

2019 ◽

Cited By ~ 2

Author(s):

Emanuel D. Kästle ◽

Claudio Rosenberg ◽

Lapo Boschi ◽

Nicolas Bellahsen ◽

Thomas Meier ◽

...

Keyword(s):

Body Wave ◽

Eastern Alps ◽

Central Alps ◽

Slab Geometry ◽

Tomographic Images ◽

Velocity Anomaly ◽

Tectonic Processes ◽

The Alps ◽

Geological Constraints ◽

European Plate

Abstract. After the onset of plate collision in the Alps, tectonic processes are inferred to have changed dramatically in the Alps: European plate break-offs in various places of the Alpine arc, as well as a subduction polarity reversal in the eastern Alps have been proposed. We review body-wave tomographic studies, compare them to our surface-wave-derived model, and interpret them in terms of slab geometries. We infer that the shallow subducting portion of the European plate is likely detached under both the western and eastern (but not the central) Alps. The Alps-Dinarides transition may be explained by a combination of European and Adriatic subduction. This implies that the deep high-velocity anomaly (> 200 km depth) mapped by tomographers under the eastern Alps is a detached segment of the European plate. The shallower fast anomaly (100–200 km depth) can be ascribed to European or Adriatic subduction, or both. These findings are compared to previously proposed models for the eastern Alps in terms of slab geometry, but also integrated in a a new, alternative geodynamic scenario that best fits both tomographic images and geological constraints.

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Filling the Moho gap: High resolution crustal structure of the Eastern Alps

10.5194/egusphere-egu21-11044 ◽

2021 ◽

Author(s):

Stefan Mroczek ◽

Frederik Tilmann ◽

Jan Pleuger ◽

Xiaohui Yuan ◽

Ben Heit ◽

...

Keyword(s):

Receiver Function ◽

Eastern Alps ◽

Seismic Network ◽

Sharp Transition ◽

Low Velocity ◽

Teleseismic Tomography ◽

Conversion Point ◽

Eastern Border ◽

Receiver Function Method ◽

Polarity Switch

The dense SWATH-D seismic network in the Central-Eastern Alps gives an unprecedented window into the collision of the Adriatic and European plates. Previous studies have suggested a Moho gap overlying a subduction polarity switch. This switch, from European subduction in the west to Adriatic subduction in the east, was suggested by teleseismic tomography where low velocity zones in the mantle were interpreted as two slabs with opposite subduction polarity. The TRANSALP profile at 12&#176;E indeed showed a gently southward dipping European Moho truncated by a nearly flat Adriatic Moho in receiver function (RF) images, which clearly indicated southward directed subduction. In contrast, RF images derived from the EASI profile at 13.3&#176;E were interpreted to show Moho topography consistent with underthrusting Adriatic Moho, which would support the hypothesized polarity switch, but the image is actually ambiguous.&#160;We apply the receiver function method to stations in the dense SWATH-D broadband seismic network, covering approximately the area from 45-49&#176;N and 10-15&#176;E, supplemented by the AlpArray Seismic Network and the EASI data. We construct common conversion point stacks in order to pick the Moho conversion and its multiples.&#160; The 15 km average station spacing has allowed us to fill in areas where previously the Moho was too weak to image. In this more comprehensive image, the asymmetry of the Moho in the TRANSALP profile can be traced to continue to at least the longitude of the EASI profile, suggesting continued southward-directed underthrusting of the European crust along the extent of the Eastern Alps, in conflict with the popular polarity switch hypothesis. At the eastern border of our study area we capture a sharp transition from European to extended Pannonian crust. Here the Adriatic Moho retreats and dips below the Pannonian Moho as it continues beneath the Dinarides.

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Capturing, Preserving, and Digitizing Legacy Seismic Data from the Montserrat Volcano Observatory Analog Seismic Network, July 1995–December 2004

Seismological Research Letters ◽

10.1785/0220200012 ◽

2020 ◽

Vol 91 (4) ◽

pp. 2127-2140 ◽

Cited By ~ 1

Author(s):

Glenn Thompson ◽

John A. Power ◽

Jochen Braunmiller ◽

Andrew B. Lockhart ◽

Lloyd Lynch ◽

...

Keyword(s):

Real Time ◽

Seismic Data ◽

Original Data ◽

South Florida ◽

Seismic Network ◽

Quality Data ◽

Spectral Amplitude ◽

Assistance Program ◽

Waveform Data ◽

Amplitude Measurement

Abstract An eruption of the Soufrière Hills Volcano (SHV) on the eastern Caribbean island of Montserrat began on 18 July 1995 and continued until February 2010. Within nine days of the eruption onset, an existing four-station analog seismic network (ASN) was expanded to 10 sites. Telemetered data from this network were recorded, processed, and archived locally using a system developed by scientists from the U.S. Geological Survey (USGS) Volcano Disaster Assistance Program (VDAP). In October 1996, a digital seismic network (DSN) was deployed with the ability to capture larger amplitude signals across a broader frequency range. These two networks operated in parallel until December 2004, with separate telemetry and acquisition systems (analysis systems were merged in March 2001). Although the DSN provided better quality data for research, the ASN featured superior real-time monitoring tools and captured valuable data including the only seismic data from the first 15 months of the eruption. These successes of the ASN have been rather overlooked. This article documents the evolution of the ASN, the VDAP system, the original data captured, and the recovery and conversion of more than 230,000 seismic events from legacy SUDS, Hypo71, and Seislog formats into Seisan database with waveform data in miniSEED format. No digital catalog existed for these events, but students at the University of South Florida have classified two-thirds of the 40,000 events that were captured between July 1995 and October 1996. Locations and magnitudes were recovered for ∼10,000 of these events. Real-time seismic amplitude measurement, seismic spectral amplitude measurement, and tiltmeter data were also captured. The result is that the ASN seismic dataset is now more discoverable, accessible, and reusable, in accordance with FAIR data principles. These efforts could catalyze new research on the 1995–2010 SHV eruption. Furthermore, many observatories have data in these same legacy data formats and might benefit from procedures and codes documented here.

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Non-linear body wave teleseismic tomography along the TOR array

Geophysical Journal International ◽

10.1046/j.1365-246x.2002.01592.x ◽

2002 ◽

Vol 148 (3) ◽

pp. 562-574 ◽

Cited By ~ 52

Author(s):

Z. Hossein Shomali ◽

Roland G. Roberts ◽

Keyword(s):

Body Wave ◽

Teleseismic Tomography ◽

Non Linear ◽

Linear Body

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Neogene kinematics of the Giudicarie Belt and eastern Southern Alpine orogenic front (Northern Italy)

10.5194/se-2021-19 ◽

2021 ◽

Author(s):

Vincent F. Verwater ◽

Eline Le Breton ◽

Mark R. Handy ◽

Vincenzo Picotti ◽

Azam Jozi Najafabadi ◽

...

Keyword(s):

Cross Sections ◽

Eastern Alps ◽

Strike Slip ◽

Fault System ◽

Late Oligocene ◽

Lateral Variation ◽

Tectonic Structures ◽

Tauern Window ◽

Adriatic Plate ◽

Lateral Extrusion

Abstract. Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern Alps. Especially, the offset of the Periadriatic Fault by the Northern Giudicarie Fault marks the initiation of strike-slip faulting and lateral extrusion of the Eastern Alps. Questions remain on the exact role of this fault zone in changes of the Alpine orogen at depth. This necessitates quantitative analysis of the shortening, kinematics and depth of decoupling underneath the Northern Giudicarie Fault and associated fold-and thrust belt in the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local shortening direction reveals that it comprises two kinematic domains with different amounts and partly overlapping ages of shortening. These two domains are delimitated by the NW-SE oriented strike-slip Trento-Cles – Schio-Vicenza fault system, cross-cutting the Southern Alpine orogenic front in the south and merging with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ~18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, the SW kinematic domain experienced a minimum of ~12–22 km shortening, whereas the NE kinematic domain underwent at least ~25–35 km shortening. Together, these domains contributed to an estimated ~53–75 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that (most of) the offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ~15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and was responsible for N-S shortening and eastward escape of deeply exhumed units in the Tauern Window. Finally, the east-west lateral variation of shortening indicates internal deformation and lateral variation in strength of the Adriatic indenter, related to Permian – Mesozoic tectonic structures and paleogeographic domains.

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