scholarly journals Moho and uppermost mantle structure in the greater Alpine area from S-to-P converted waves

2021 ◽  
Author(s):  
Rainer Kind ◽  
Stefan M. Schmid ◽  
Xiaohui Yuan ◽  
Ben Heit ◽  
Thomas Meier ◽  
...  
Keyword(s):  
Pannonian Basin ◽  
P Wave ◽  
Mantle Structure ◽  
Uppermost Mantle ◽  
Waveform Data ◽  
Arrival Times ◽  
Tauern Window ◽  
Lateral Extrusion ◽  
Alpine Area ◽  
Teleseismic Data

Abstract. In the frame of the AlpArray project we analyze teleseismic data from permanent and temporary stations of the greater Alpine region to study seismic discontinuities down to about 140 km depth. We average broadband teleseismic S waveform data to retrieve S-to-P converted signals from below the seismic stations. In order to avoid processing artefacts, no deconvolution or filtering is applied and S arrival times are used as reference. We show a number of north-south and east-west profiles through the greater Alpine area. The Moho signals are always seen very clearly, and also negative velocity gradients below the Moho are visible in a number of profiles. A Moho depression is visible along larger parts of the Alpine chain. It reaches its largest depth of 60 km beneath the Tauern Window. The Moho depression ends however abruptly near about 13° E below the eastern Tauern Window. The Moho depression may represent the mantle trench, where the Eurasian lithosphere is subducted below the Adriatic lithosphere. East of 13° E an important along-strike change occurs; the image of the Moho changes completely. No Moho deepening is found in this easterly region; instead the Moho is updoming along the contact between the European and the Adriatic lithosphere all the way into the Pannonian Basin. An important along strike change was also detected in the upper mantle structure at about 14° E. There, the lateral disappearance of a zone of negative P-wave velocity gradient indicates that the S-dipping European slab laterally terminates east of the Tauern Window in the axial zone of the Alps. The area east of about 13° E is known to have been affected by severe late-stage modifications of the structure of crust and uppermost mantle during the Miocene when the ALCAPA (Alpine, Carpathian, Pannonian) block was subject to E-directed lateral extrusion.

The seismic structure of the lithosphere in the greater Alpine area from S-to-P converted waves

2021 ◽  
Author(s):  
Rainer Kind ◽  
Stefan Schmid ◽  
Xiaohui Yuan ◽  
Ben Heit
Keyword(s):  
Pannonian Basin ◽  
Eastern Alps ◽  
Seismic Structure ◽  
Arrival Times ◽  
Tauern Window ◽  
Lateral Extrusion ◽  
Alpine Area ◽  
Teleseismic Data ◽  
Nappe Emplacement ◽  
Eastern Edge

<p>In the frame of the AlpArray project we analyse teleseismic data from permanent and temporary stations of the greater Alpine region to study seismic discontinuities in the entire lithosphere. We use broadband S-to-P converted signals from below the seismic stations. In order to avoid sidelobes, no deconvolution or filtering is applied and S arrival times are used as reference. We show a number of north-south and east-west profiles through the greater Alpine area. The Moho signals are always seen very clearly, and also negative velocity gradients below the Moho are visible in a number of profiles. The subducting European Moho is visible in the Eastern Alps west of 13.5°E (the eastern edge of the Tauern Window) and reaches there about 60km depth at 47°N. East of about 13.5°E, the image of the Moho changes completely. No south dipping European Moho is found anymore, instead the Moho is shallowing towards the Pannonian Basin. This suggests severe post-nappe emplacement modifications east of about 13.5°E, most probably associated with delamination of the mantle lithosphere within the formerly subducting European slab, i.e. mantle that separated from the crustal parts of the Alpine-West Carpathian orogen during the last ca. 20 Ma when the Pannonian basin formed and the ALCAPA block underwent its E-directed lateral extrusion.</p><p>Ratschbacher, L., Frisch, W., Linzer, H.-G. and Merle, O. (1991) Lateral extrusion in the Eastern Alps, Part 2: Structural analysis. Tectonics, vol.10, No.2, 257-271.</p>

scholarly journals European tectosphere and slabs beneath the greater Alpine area – Interpretation of mantle structure in the Alps-Apennines-Pannonian region from teleseismic V<sub>p</sub> studies

2021 ◽  
Author(s):  
Mark Handy ◽  
Stefan Schmid ◽  
Marcel Paffrath ◽  
Wolfgang Friederich ◽  
Keyword(s):  
Pannonian Basin ◽  
Lower Boundary ◽  
Eastern Alps ◽  
P Wave ◽  
Moho Depth ◽  
Abrupt Decrease ◽  
Tauern Window ◽  
Lateral Extrusion ◽  
The Alps ◽  
European Plate

Abstract. Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (180–200 km) European tectosphere. Our approach combines teleseismic P-wave tomography and existing Local Earthquake Tomography (LET) allowing us to image the Alpine slabs and their connections with the overlying orogenic crust at an unprecedented resolution. The images call into question the conventional notion that slabs comprise only seismically fast lithosphere and suggest that the mantle of the downgoing European Plate is heterogeneous, containing both positive and negative Vp anomalies of up to 5–6%. We interpret these as compositional rather than thermal anomalies, inherited from the Variscan and pre-Variscan orogenic cycles. They make up a kinematic entity referred to as tectosphere, which presently dips beneath the Alpine orogenic front. In contrast to the European Plate, the tectosphere of the Adriatic Plate is thinner (100–120 km) and has a lower boundary approximately at the interface between positive and negative Vp anomalies. Horizontal and vertical tomographic slices reveal that beneath the Central and Western Alps, the downgoing European tectospheric slab dips steeply to the S and SE and is only locally still attached to the Alpine crust. However, in the Eastern Alps and Carpathians, the European slab is completely detached from the orogenic crust and dips steeply to the N-NE. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted to represent hot upwelling asthenosphere that was instrumental in accommodating Neogene orogen-parallel lateral extrusion of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the Eastern Alps is likely since its imaged down-dip length (300–500 km) matches estimated Tertiary shortening in the Eastern Alps accommodated by south-dipping subduction of European tectosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as attenuated, largely detached sheets of continental margin and Alpine Tethyan lithosphere that locally reach down to a slab graveyard in the Mantle Transition Zone (MTZ).

Time for a change of paradigm for Alpine subduction?

2021 ◽  
Author(s):  
Mark R. Handy ◽  
Stefan M. Schmid ◽  
Marcel Paffrath ◽  
Wolfgang Friederich
Keyword(s):  
Pannonian Basin ◽  
Lower Boundary ◽  
Eastern Alps ◽  
P Wave ◽  
Moho Depth ◽  
Depth Interval ◽  
Tauern Window ◽  
Adriatic Plate ◽  
Lateral Extrusion ◽  
European Plate

&lt;p&gt;The prevailing paradigm of mountain building in the Alps entails subduction of European continental lithosphere some 100km thick beneath the Adriatic plate. Based on recent results of AlpArray, we propose a new model that involves subduction and wholesale detachment of locally much thicker (200-240 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing Local Earthquake Tomography (LET) to image the Alpine slabs and their connections with the overlying orogenic crust at unprecedented resolution. The images call into question the simple notion that slabs comprise only seismically fast lithosphere and suggest that the mantle of the downgoing European plate is compositionally heterogeneous, containing both positive and negative seismic anomalies of up to 5%. We interpret these as compositional rather than thermal anomalies, inherited from the Paleozoic Variscan orogenic cycle and presently dipping beneath the Alpine orogenic front. In contrast to the European Plate, the lithosphere of the Adriatic Plate is thinner (100-120 km) and has a more poorly defined lower boundary approximately at the interface between positive and negative Vp anomalies.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Horizontal and vertical tomographic slices reveal that beneath the Central and Western Alps, the downgoing European Plate dips steeply to the S and SE and is locally detached from the Alpine crust. However, in the Eastern Alps and Carpathians east of the central Tauern Window, the Alpine slab anomaly occupies the 150-400 km depth interval and dips steeply to the N-NE, having completely detached from the &amp;#160;Alpine orogenic crust. This along-strike change coincides with an abrupt eastward decrease in Moho depth (Kind et al., this session), the Moho being underlain by a pronounced negative Vp anomaly reaching eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted to represent hot upwelling asthenosphere that was instrumental in accommodating Neogene orogen-parallel lateral extrusion of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the E.&amp;#160; An Adriatic origin of the northward-dipping, detached slab segment beneath the Eastern Alps is unlikely since its imaged down-dip length (200-300 km) matches estimated Tertiary shortening in the Eastern Alps accommodated by south-dipping subduction of European lithosphere, whereas shortening in the south-vergent eastern Southern Alps is only &amp;#8804; 70 km.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;A slab anomaly beneath the northernmost Dinarides, laterally adjoining the Eastern Alps, is missing. The slab anomaly beneath the northern Apennines, of Adriatic origin und dipping beneath the Tyrrhenian backarc, hangs subvertically and appears to be almost detached from the Apenninic orogenic crust. Except for its westernmost segment where it meets the Alpine slab, this slab is clearly separated from the latter by a broad extent of upwelling asthenosphere located south of the Alpine slabs beneath the Po Plain, i.e., just south of the Alpine subduction zone. Considered as a whole, the slabs beneath the Alpine chain are interpreted as attenuated, largely detached sheets of continental margin and Alpine Tethyan lithosphere that locally reach down to a slab graveyard in the Mantle Transition Zone (MTZ).&lt;/p&gt;

Negative Velocity Gradients in the uppermost Mantle below the larger Alpine Area

2020 ◽  
Author(s):  
Rainer Kind ◽  
Stefan Schmid ◽  
Xiaohui Yuan ◽  
Alparray Working Group
Keyword(s):  
Receiver Function ◽  
Eastern Alps ◽  
Uppermost Mantle ◽  
Seismic Stations ◽  
Arrival Times ◽  
Controlled Source ◽  
Velocity Gradients ◽  
Alpine Area ◽  
Teleseismic Data ◽  
Additional Constraints

&lt;p&gt;In the frame of the Alparray project we analyse teleseismic data from permanent and temporary stations of the greater Alpine area to study the structure of the crust and the uppermost mantle.&amp;#160;We use S-to-p and P-to-s converted waves below the seismic stations which are aligned along the arrival times of the generating P and SV signals. The broadband data used are unfiltered, amplitude normalized and sign corrected. Profiles of migrated data are constructed through the entire Alpine area and compared with results of tomographic, controlled-source and receiver function studies. Thereby we provide additional constraints regarding the ongoing controversies regarding the configuration of the various slabs whose existence was postulated by previous authors within the larger Alpine area including the Western Carpathians. Special attention is given to the possibility of a reversal of subduction polarity in the eastern Alps.&lt;/p&gt;

scholarly journals P-wave first-motion polarity determination of waveform data in western Japan using deep learning

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Shota Hara ◽  
Yukitoshi Fukahata ◽  
Yoshihisa Iio
Keyword(s):  
Training Data ◽  
P Wave ◽  
Data Sets ◽  
Waveform Data ◽  
Arrival Times ◽  
Distribution Maps ◽  
Seismic Waveforms ◽  
Polarity Determination ◽  
Western Japan ◽  
First Motion

AbstractP-wave first-motion polarity is the most useful information in determining the focal mechanisms of earthquakes, particularly for smaller earthquakes. Algorithms have been developed to automatically determine P-wave first-motion polarity, but the performance level of the conventional algorithms remains lower than that of human experts. In this study, we develop a model of the convolutional neural networks (CNNs) to determine the P-wave first-motion polarity of observed seismic waveforms under the condition that P-wave arrival times determined by human experts are known in advance. In training and testing the CNN model, we use about 130 thousand 250 Hz and about 40 thousand 100 Hz waveform data observed in the San-in and the northern Kinki regions, western Japan, where three to four times larger number of waveform data were obtained in the former region than in the latter. First, we train the CNN models using 250 Hz and 100 Hz waveform data, respectively, from both regions. The accuracies of the CNN models are 97.9% for the 250 Hz data and 95.4% for the 100 Hz data. Next, to examine the regional dependence, we divide the waveform data sets according to the observation region, and then we train new CNN models with the data from one region and test them using the data from the other region. We find that the accuracy is generally high ($${ \gtrsim }$$≳ 95%) and the regional dependence is within about 2%. This suggests that there is almost no need to retrain the CNN model by regions. We also find that the accuracy is significantly lower when the number of training data is less than 10 thousand, and that the performance of the CNN models is a few percentage points higher when using 250 Hz data compared to 100 Hz data. Distribution maps, on which polarities determined by human experts and the CNN models are plotted, suggest that the performance of the CNN models is better than that of human experts.

scholarly journals Orogenic lithosphere and slabs in the greater Alpine area – interpretations based on teleseismic P-wave tomography

Solid Earth ◽  
2021 ◽  
Vol 12 (11) ◽  
pp. 2633-2669 ◽  
Author(s):  
Mark R. Handy ◽  
Stefan M. Schmid ◽  
Marcel Paffrath ◽  
Wolfgang Friederich ◽  
Keyword(s):  
Seismic Anisotropy ◽  
Pannonian Basin ◽  
Lower Boundary ◽  
Eastern Alps ◽  
P Wave ◽  
Moho Depth ◽  
Abrupt Decrease ◽  
Lateral Extrusion ◽  
Wave Tomography ◽  
The Alps

Abstract. Based on recent results of AlpArray, we propose a new model of Alpine collision that involves subduction and detachment of thick (∼ 180 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing local earthquake tomography (LET), allowing us to image the Alpine slabs and their connections with the overlying orogenic lithosphere at an unprecedented resolution. The images call into question the conventional notion that downward-moving lithosphere and slabs comprise only seismically fast lithosphere. We propose that the European lithosphere is heterogeneous, locally containing layered positive and negative Vp anomalies of up to 5 %–6 %. We attribute this layered heterogeneity to seismic anisotropy and/or compositional differences inherited from the Variscan and pre-Variscan orogenic cycles rather than to thermal anomalies. The lithosphere–asthenosphere boundary (LAB) of the European Plate therefore lies below the conventionally defined seismological LAB. In contrast, the lithosphere of the Adriatic Plate is thinner and has a lower boundary approximately at the base of strong positive Vp anomalies at 100–120 km. Horizontal and vertical tomographic slices reveal that beneath the central and western Alps, the European slab dips steeply to the south and southeast and is only locally still attached to the Alpine lithosphere. However, in the eastern Alps and Carpathians, this slab is completely detached from the orogenic crust and dips steeply to the north to northeast. This along-strike change in attachment coincides with an abrupt decrease in Moho depth below the Tauern Window, the Moho being underlain by a pronounced negative Vp anomaly that reaches eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted as representing hot upwelling asthenosphere that heated the overlying crust, allowing it to accommodate Neogene orogen-parallel lateral extrusion and thinning of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the east. A European origin of the northward-dipping, detached slab segment beneath the eastern Alps is likely since its down-dip length matches estimated Tertiary shortening in the eastern Alps accommodated by originally south-dipping subduction of European lithosphere. A slab anomaly beneath the Dinarides is of Adriatic origin and dips to the northeast. There is no evidence that this slab dips beneath the Alps. The slab anomaly beneath the Northern Apennines, also of Adriatic origin, hangs subvertically and is detached from the Apenninic orogenic crust and foreland. Except for its northernmost segment where it locally overlies the southern end of the European slab of the Alps, this slab is clearly separated from the latter by a broad zone of low Vp velocities located south of the Alpine slab beneath the Po Basin. Considered as a whole, the slabs of the Alpine chain are interpreted as highly attenuated, largely detached sheets of continental margin and Alpine Tethyan oceanic lithosphere that locally reach down to a slab graveyard in the mantle transition zone (MTZ).

scholarly journals Supplementary material to "Moho and uppermost mantle structure in the greater Alpine area from S-to-P converted waves"

2021 ◽  
Author(s):  
Rainer Kind ◽  
Stefan M. Schmid ◽  
Xiaohui Yuan ◽  
Ben Heit ◽  
Thomas Meier ◽  
...  
Keyword(s):  
Mantle Structure ◽  
Uppermost Mantle ◽  
Alpine Area ◽  
Supplementary Material ◽  
Converted Waves

scholarly journals A Teleseismic Study of the 2002 Denali Fault, Alaska, Earthquake and Implications for Rapid Strong-Motion Estimation

2004 ◽  
Vol 20 (3) ◽  
pp. 617-637 ◽  
Author(s):  
Chen Ji ◽  
Don V. Helmberger ◽  
David J. Wald
Keyword(s):  
Moment Tensor ◽  
Strong Motion ◽  
P Wave ◽  
Phase Iii ◽  
Peak Ground Velocity ◽  
Centroid Moment Tensor ◽  
Waveform Data ◽  
Arrival Times ◽  
Denali Fault ◽  
Alaska Earthquake

Slip histories for the 2002 M7.9 Denali fault, Alaska, earthquake are derived rapidly from global teleseismic waveform data. In phases, three models improve matching waveform data and recovery of rupture details. In the first model (Phase I), analogous to an automated solution, a simple fault plane is fixed based on the preliminary Harvard Centroid Moment Tensor mechanism and the epicenter provided by the Preliminary Determination of Epicenters. This model is then updated (Phase II) by implementing a more realistic fault geometry inferred from Digital Elevation Model topography and further (Phase III) by using the calibrated P-wave and SH-wave arrival times derived from modeling of the nearby 2002 M6.7 Nenana Mountain earthquake. These models are used to predict the peak ground velocity and the shaking intensity field in the fault vicinity. The procedure to estimate local strong motion could be automated and used for global real-time earthquake shaking and damage assessment.

scholarly journals A CROSS-CORRELATION TECHNIQUE FOR RELOCATION OF SEISMICITY IN THE WESTERN CORINTH RIFT

2017 ◽  
Vol 43 (4) ◽  
pp. 2015
Author(s):  
V. Kapetanidis ◽  
P. Papadimitriou ◽  
K. Makropoulos
Keyword(s):  
Cross Correlation ◽  
Time Lag ◽  
P Wave ◽  
Double Difference ◽  
Correlation Technique ◽  
S Wave ◽  
Waveform Data ◽  
Arrival Times ◽  
Linkage Algorithm ◽  
Seismogenic Structures

Local seismological networks provide data that allow the location of microearthquakes which otherwise would be dismissed due to low magnitudes and low signal-to-noise ratios of their seismic signals. The Corinth Rift Laboratory (CRL) network, installed in the western Corinth rift, has been providing digital waveform data since 2000. In this work, a semi-automatic picking technique has been applied which exploits the similarity between waveforms of events that have occurred in approximately the same area of an active fault. Similarity is measured by the crosscorrelation maxi-mum of full signals. Events with similar waveforms are grouped in multiplet clusters using the nearest-neighbour linkage algorithm. Manually located events act as masters, while automatically located events of each multiplet cluster act as slaves. By cross-correlating the P-wave or S-wave segments of a master event with the corresponding segments of each of its slave events, after appropriately aligning their offsets, the measured time-lag at the cross-correlation maximum can be subtracted from the arrival-time of the slave event. After the correction of the arrival-times, a double-difference technique is applied to the modified catalogue to further improve the locations of clusters and distinguish the active seismogenic structures in the tectonically complex Western Corinth rift.

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