Expose for the dissertation proposal

Anisotropy and deformation beneath the Eastern Alps

Ehsan Qorbani Chegeni

Thesis advisor: Univ.-Prof. Dr. Gotz BokelmannDepartment of Meteorology and Geophysics (IMGW)

University of Vienna

September 2012

Abstract

The Alpine belt is divided into E-trending Eastern Alps and the arc of the Western Alps. At thesurface, the plate tectonic activity is mirrored by the different geological structures in the Eastern andWestern Alps. Even though surface geology of the Alps is relatively well known and several studies,proposing geodynamical hypotheses, have been accomplished the dynamic processes that occur downto the upper mantle are still not clear. This research project is aimed to investigate the mechanismsand the nature of geodynamic processes focusing on the upper mantle beneath the Eastern Alps. Bythe characterization of the seismic anisotropy of upper mantle rocks, the strain field due to geodynamicforces within the Earth’s upper mantle is evaluated. Seismic anisotropy is the velocity variation of theseismic waves with respect to the direction of wave propagation, which is mainly created by crystalalignment of the upper mantles materials. Measuring the anisotropic parameters allows us to map thepresent-day mantle flow direction that brings hints to interpret past geodynamic activities and gaininsights on the geodynamic evolution of the Earth. By using the seismic records of teleseismic earth-quakes, the anisotropic parameters will be measured applying both shear-wave splitting technique andP-wave polarization as complementary methods to cover the imperfections of each fashion. Modelingapproaches will be utilized using synthetic data to find the best possible anisotropic structures fittingthe data. The overall interpretation of the results from two applied methods and modeling approachesis aimed to propose a geodynamic model and deformation patterns for the Eastern Alps.

1 Introduction

Based on seismic observations, our planet is separated into three major zones; cores, mantle, and crust.According to rock rheology and thermal divisions the outer shell of the Earth is defined as the lithosphere.This body, consisting of the rigid upper mantle and crust, is considered to be cold and shows an inflexiblebehavior in response to geodynamic processes during geological time intervals that we know as platetectonic phenomena. Plate tectonics is believed to be a model in which the lithosphere is divided intoa number of rigid plates that move at relative velocities with respect to one another [28]. Below thelithosphere lies the asthenosphere; considered as a soft and hot layer, it constitute the thickest part ofthe upper mantle. The lithospheric blocks slowly creep over the asthenosphere with different velocitiescausing plates motion and consequent deformations mainly at the plate boundaries. Hence, investigatingthe interaction between plate motion and upper mantle flow beneath the lithosphere is a beneficial keyto evaluate the upper mantle’s geodynamics [19, 10]. Consequently, studying the dynamic processes in

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the upper mantle is an important task to evaluate the Earths dynamic evolution. Although the effects ofgeodynamic processes on the lithosphere are observable at the Earths surface as the orogenic processes,faulting, earthquakes, volcanoes, and natural hazards, their mechanisms and nature in the upper mantleare still poorly understood.

The selected region in this study mainly comprises the Eastern Alps (Figure 1). The Alpine belt,according to geomorphological features, orogenic zones and geological structures [23, 22], is divided intoE-trending Eastern Alps and the arc-belt of the Western Alps. Because of the uncertainty and ambiguityof geodynamic mechanisms in the Alps, the understanding and interpretation of tectonics and deformationpatterns are still a matter of some debate. Therefore, the aim of this study is to achieve more detailedinformation on deeper lithosphere and upper mantle structures beneath the Eastern part of the Alps.Furthermore the outputs of this study are valuable to be considered as important inputs to further seismicstudies in the smaller scales with respect to lithosphere scale.One of the best possible ways to understanding the upper mantle structures and dynamic mechanisms isto carry out a study on seismic anisotropy. Seismic anisotropy is known as one of the major characteristicof the lithospheric mantle and it is thought to be the best approaches to image the deformation in theEarth’s interior [10]. It gives many information on its geodynamic history and insights on tectonicprocesses, which drive the shaping of the continents. In principle, seismic anisotropy is defined as thedependence of seismic velocity on the direction of wave propagation. Consequently, the seismic wavestraveling in anisotropic structures move faster in one direction than in the other. One of the mostimportant anisotropy sources in the Earth is the upper mantle anisotropy caused by aligned olivinecrystals in the asthenosphere, i.e. the most ductile and viscous layer in the upper mantle. The cause ofanisotropy is the so-called lattice-preferred-orientation (LPO), generated by the structural alignment ofthe olivine crystals, which constitute the upper most part of mantle. The anisotropic property of thesematerials can be explained as a function of the strain field, which is aligned from the mantle flow pattern.Therefore, the results of anisotropy preferential directions can be translated into observations of natureof geodynamic processes in upper mantle.

Despite the high number of studies done on the Alps, many questions still remain unanswered inrelation with their geodynamics mechanism and deformation patterns, particularly for the Eastern Alps.One of the most useful investigations to address these questions is the study of seismic anisotropy. Thisresearch project will be carried out for imaging the deformation patterns and mantle flow direction fromthe observed seismic data for the Eastern Alpine orogenic belt. Therefore, the aim of this study is toachieve more detailed information on deeper lithosphere and upper mantle structures beneath this areaof the Alps.

2 State of the Art

The Eastern portion of the Alps is still an unexplored territory in terms of seismic investigations of thelithosphere. The main reason for this was the lack in the past of a good coverage of seismic stationsrecording for long time (i.e. several years). The investigation of the lithosphere is the key to understandthe dynamic processes, which shape the continents, the interaction between the plates at their boundary,and consequently the deformation patterns along and across the lithosphere. In the Alpine region, severalstudies have been performed including geophysical and 3D tomographic models [32, 13, 22, 6, 18]. Inparticular, tomographic images show velocity anomalies linked to suture zones, and subduction. Thetectonic history of the Alps is complex, including besides the two major plates, namely the European andthe Adriatic plate [12, 6, among others], also some small microplates (i.e. Meliata plate and Pannonianfragment), which involvement has driven the complex evolution of the area. The above-cited studiesdid not clarify yet the dynamic of the collision, but brought different hypotheses on the polarity of thesubduction in the Eastern Alps [13, 18], leaving unsolved questions. Moreover, the Eastern Alps evolve

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Figure 1: The Satellite image of Alpine belt. Our study region, the Eastern part of the Alps, includes Austria,Slovenia and the most northern part of Italy. (NASA: http://eoimages.gsfc.nasa.gov/images)

in their easternmost portion towards the Carpathians, thus giving to the belt an asymmetrical shapeelongated towards ENE. A lateral eastward escape was proposed in Meissner [17] to explain the passagebetween the Alps and Pannonian basin, but further investigation into this area is needed to provide morereliable evidence and to prove this hypothesis.

Even though several arguments have been raised regarding the geodynamic processes and deformationmodels in the Alps, very little can be said about the tectonic mechanisms and past-present deformationpatterns, particularly in case of deep lithosphere and upper mantle structures. This problem is especiallysignificant concerning the Eastern Alps geodynamics. In the Western Alps, where denser deployments oftemporary and permanent seismic stations were installed in the past, interesting results came from theanalysis of the core shear wave (SKS) phases. Barruol [1] demonstrated that the fast axis directions showa rotating pattern in accordance with the arc shape in the Western Alpine belt. For the central part of theAlpine chain, the fast anisotropy directions were achieved only for the TRANSALP profile (12° E) [12],showing a NE-ward trend. The results of these two studies for the Western Alps and TRANSALP profileare shown in Figure 2. Although, the above-mentioned studies and some other anisotropic investigationshave been accomplished in the Alps and central Europe (e.g. [5, 30, 20]), the fast axis direction and itsrelation with orogen trends in the Eastern Alps is still unknown. Despite the recent growing interest inanisotropic investigations, no anisotropy study has yet been attempted in the Eastern Alps (Figure 2).Therefore, performing a new anisotropic study in order to facilitate the geodynamic interpretation iscrucial for this area of the Alpine belt.

Preliminary results, which ground this study, come from the SKS wave analysis of the data recordedat the seismic stations located in Austria. A good agreement with former studies in the overlap area (redbars in Figure 2) is clear. As Figure 2 shows, any information for the Eastern Alps is lacking, and thegoal of this research project is to fill that gap. The importance of the results lies in the observed changein the fast axes pattern between Eastern and Western Alps. It is a prominent feature and its meaningcan be answered by completing the measurement of anisotropic parameters in the area this is what thisresearch project is aimed to.

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4˚ 6˚ 8˚ 10˚ 12˚ 14˚ 16˚ 18˚42˚

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Figure 2: Distribution of fast axis directions from the former studies (e.g. [1, 12]). is demonstrated. The vectorsshow the azimuth of fast direction (φ) and the lengths vector refers to the value of delay time (δt). The redvectors represent preliminary measurements of fast azimuths for the stations of OE network. Note the changingfast directions pattern from west to east around the TRANSALP profile. The location of stations of OE, SL, IV,NI, and SI networks are indicated by different symbols. The lack of any investigation for the eastern part of Alpsis noticeable.

3 Main research questions

According to the aim of this study, the following research questions will be addressed throughout thisresearch project:

1. What is the distribution and dominant fast direction azimuth for the central and Eastern Alps?

2. How does the fast direction pattern change in comparison to previous results in the Western Alps?Do the fast azimuth orientations in the central and Eastern Alps follow the same directions as theWestern arc-belt, or do they show a different pattern? Is there, despite the complex structure, acoherent pattern of seismic anisotropy under the Alps?

3. What is the major anisotropic structure in upper mantle beneath Eastern Alps? Can it be explainedas a single horizontal anisotropic layer, or is there a possibility of more complexity with the existenceof two different anisotropic layers and/or dipping axis anisotropic layer?

4. What causes the observed anisotropic anomalies in the Eastern Alps: The crustal structures or thealigned olivine crystals in the upper mantle? Which depth does the anisotropic layer(s) correspond?

5. How do fast orientation azimuths relate with upper mantle flow in the Eastern Alps?

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6. Can the two suggested subduction mechanisms in the Alps be clarified in relation to the obtainedmantle flow direction in this study?

7. With regard to the observation of both trench-parallel and trench-perpendicular fast orientations inthe subduction zone setting [31], which possible mechanism will be dominant beneath the EasternAlps?

8. What is the relationship between the suggested eastward lateral escaping in the Eastern Alps andmeasured fast azimuths in this study?

4 Methodology

Several developmental seismological methods have been applied to assess anisotropic structures in theupper mantle. The main goal of these approaches is to develop the relationship between mantle flow andpast and present day deformation patterns. The methods that will be used in this study are shear-wavesplitting and P wave polarization. By comparing the results of these two different methods, we will ableto make a reliable conclusion about upper mantle anisotropy and deformation pattern in the EasternAlps.

4.1 Shear wave splitting method

Analysis of displacements due to seismic wave energy is an important part of seismological study. Theseismic displacement is analyzed as a scalar potential and a vector potential corresponding to P wave(primary wave) and S wave (secondary) respectively. In the 3-components seismometers, three orthog-onal components (north-south, east-west, and vertical) record the displacements in three directions.The records of horizontal components are often rotated to source-receiver direction, called the radialcomponent, and the perpendicular direction with respect to radial, called transverse component. Thedisplacement of S wave (shear wave), can be considered as two orthogonal phases, namely SV which is ob-served on the radial component, and SH that is observed on the transverse component. These two phasestravel at the same speed in isotropic medium but they propagate with different velocity in anisotropicmedia. Because of the difference in velocities they arrive at different times at the seismic station. Onetravels faster, is the fast wave and defines the fast polarization. The other has a delay time, is the slowwave, and defines the slow polarization direction. This phenomena caused by anisotropic structures isreferred to as shear-wave splitting.

The most useful method for constraining upper mantle anisotropy is shear-wave splitting that usesthe splitting of the teleseismic shear waves like SKS/SKKS core phases [26]. Because of the fluid natureof the outer core, there is no shear wave traveling through it. Therefore, the shear wave passing fromthe mantle to the outer core would convert to P phase and would be converted back to shear wave(called SKS) passing to lower mantle. For this reason, during the conversion of the P wave to SKS corephase at the core-mantle-boundary (CMB), SKS phase is entirely polarized in the radial direction (i.e.direction of propagation of the wave). Hence, it is theoretically expected that SKS does not contain anyenergy on the transverse component and the amplitudes of this component should be zero. However,the anisotropic structures in the mantle result as a combination of fast and slow polarization in the tworadial and transverse components [27]; therefore we often observe a significant energy on both radial andtransverse components.

To characterize the nature of anisotropic structures using the shear wave splitting method, two split-ting parameters are defined as: the fast direction azimuth (φ, angle between fast axis and radial direction)and arrival delay time between the fast and slow polarizations (δt). To carry out the measurements ofanisotropic parameters based on shear-wave splitting techniques, the SplitLab package [34] will be used

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as the software. The initial measurements of splitting parameters have been done using the SplitLab forthe stations of Austrian seismological network (OE) (see Figure 2). In addition, as an important part ofthis study, the software development process will be undertaken to improve the abilities of the SplitLabpackage by adding more features.

4.2 P-wave polarization method

The P-wave polarization method will be used as a complementary technique to investigate anisotropicstructures in upper mantle [9]. Some advantages of using the P-wave polarization method include thefollowing: 1) Using teleseismic events (at distances larger than 90°) in the shear-wave splitting method, theSKS core phases have near vertical incidence angles. Therefore the SKS/SKKS phases offer an excellentlateral resolution although their vertical resolution is poor [26], whereas the P waves are affected by uppermantle anisotropy with some lateral offset because their incidence angles are larger than SKS phases [9].2) The azimuthal coverage will be increased using the P wave polarization technique. 3) The P wavepolarization method is able to vertically locate the anisotropy. 4) To identify eventual mis-orientation ofhorizontal components of the seismograph.

The definition of polarization varies in diverse applications. In the seismic anisotropy field, thepolarization of the P wave is defined as the direction of particle motion of P waves [24, 9]. In general, theparticle motion of P wave consists of alternating compression and dilation (extension) which is parallelto the direction of propagation (longitudinal) when propagating through the isotropic medium. Thepropagation direction of the P wave can be defined by two angles: the incidence angle that can becalculated from the normal to the horizontal plane; back azimuth that measured from the station to thesurface projection of seismic source (epicenter) [3]. However, in the heterogeneous and anisotropic mediathe estimated polarization azimuth differs from the direction of source-receiver on the great circle andthe observed incidence angle does not correspond to the predicted one from Earth models as well [3].Therefore, measurement of the polarization direction of P wave allows us to achieve useful informationabout anisotropic structures.

The sensitivity of the P-wave particle motion to anisotropic structures depends on the period of theP phase. At high frequency (i.e. 1 Hz) the P wave particle motion is influenced by the structure of theupper crust, whereas it is affected by the upper mantle structures at longer periods (up to 30 s) [24].Based on the major aim of this study, which is focusing on upper mantle structures, the direction ofparticle motion of the long period P wave will be measured in order to obtain a better understanding onanisotropy in the upper mantle. The following processes will be performed in the P wave polarizationmethod: Selecting teleseismic events with high signal-to-noise ratio; filtering data to obtain long periodP phases; measuring the angles of particle motion; calculation of fast axis direction. Through the particlemotion we can constrain the azimuth direction with respect to radial direction (δθ), and the verticalpolarization (ε), meaning the vertical inclination in the vertical-radial plane [24, 9].

4.3 Modeling

Based on the theory of anisotropy measurement techniques, we start by assessing a single anisotropicmedium with a horizontal symmetric axis to characterize the anisotropic structure from the seismicwaveforms. In this study, to provide a reliable interpretation of the anisotropic structure, the modelingfashion by synthetic data will be utilized. In this process, synthetic waveforms and synthetic anisotropicparameters will be created based on the assumed anisotropic structures to assess the possibility andthe effect of two remarkable features: the presence of two anisotropic layers with different natures andthicknesses, and/or the presence of dipping anisotropic structures. In the case of modeling using theresults of shear-wave splitting method, the splitting parameters (fast axis direction and delay time) forthe two assumed layers are created as a function of polarization angle [25]. The best possible anisotropic

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features are obtained by fitting the variation of measured splitting parameters versus the polarizationangles by the same variation in the synthetic data. In addition, to evaluate the presence of dippingstructures and the effect of sensor misorientation, the modeling process by the results of the P wavepolarization method will be utilized.

4.4 Data

For this study, the recorded seismic waveforms from the three-component seismic stations will be used.The data will be selected from the following networks:

1. Austrian broadband seismological network (OE)

2. Seismic network of republic of Slovenia (SL)

3. Italian seismic network (IV)

4. NE-Italy broadband network (NI)

5. Sudtirol network (SI)

Data from OE and SL networks are available at Orfeus data center (http://www.orfeus-eu.org/) andWebDC-Integrated Seismological Data Portal (http://www.webdc.eu/). Data from SI, NI and IV areprovided directly from ZAMG, OGS and INGV data centers.

5 Expected Outcome

With respect to the described problem statement, the expected outcomes of this thesis will now beoutlined:

• Measurements and analysis of fast axis azimuths from SKS phases splitting in order to find theanisotropy fast directions distribution for the Eastern Alps.

• To find an anisotropic model that describes the fast directions pattern in relation with presence ofsingle or double anisotropic layers in the upper mantle based on the SKS splitting measurements.

• Developing the SplitLab package by adding codes to obtain more abilities to measure the splittingparameters.

• Develop a code for P-wave polarization method to carry out the calculation processes of anisotropicparameters (particle motions angles).

• Calculation and analysis of fast axis azimuths from the polarization of P-waves to obtain the fastdirection pattern in the study region.

• To find an anisotropic model describing the existence of dipping anisotropic structures based onthe obtained distribution of fast azimuths from the P-wave polarization method.

• Create the best anisotropic model combining the obtained anisotropic models from both SKS split-ting and P-wave polarization measurements.

• Interpret the results of both methods in terms of geodynamic processes and mantle flow directionin the asthenosphere.

• Proposing a geodynamic model describing the deformation patterns of lithosphere beneath theEastern Alpine belt using the all results of this study and the related outputs of former investigationsin the Alps.

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6 Timetable

The time plan of this research project is described below by a Gantt chart. Tasks are grouped into sevenphases and each phase is divided into subsections to explain the processes and the objectives.

3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2 3 4 5 6 7 8 9 10 11 12 1 2

Phase A (Collecting and preparing the data)

A1- Austrian seismological network (OE)

A2- Seismic network of Slovenia (SL)

A3- Italian seismic network (IV)

A4- NE-Italy broadband network (NI)

A5- Sudtirol network (SI)

B1-Reading and research on theory and methodology

B2- Being familiar with SplitLab package

B3- Preliminary experience in measurement of splitting parameters

B4- MSP for OE network stations

B5- MSP for SL network stations

B6- MSP for IV, NI, and SI network stations

B7- MSP for all networks using new developed package (D2)

C1- Reading and research on the theory and methodology

C2- Develop a code to measure the anisotropic parameters

C3- MPP for OE network stations

C4- MPP for SL network stations

C5- MPP for IV, NI, and SI network stations

D1- Additional reading into MATLAB graphical user interfaces

D2- Developing the SplitLab package by adding the new codes

E1- Modeling using shear wave splitting results

E2- Modeling using P-wave polarization results

F1- Integrating and interpreting the results of B and C phases

F2- Combination the results of two modeling strategies (E1, E2)

F3- Interpreting the results of F1 and F2

G1- Presenting the anisotropy model from B phase results

G2- Presenting the anisotropy model from C phase results

G3- Create the possible Geodynamic model and final conclusion

G4- Writing the thesis

MSP: Measurement of Splitting Parameters

MPP: Measurement of Particle motion Parameters

2015

Phase G (final outputs and deliverable)

Phase B (Shear wave splitting)

Phase C (P-wave polarization)

Phase D (softwares Developing)

Phase E (Modeling)

2012 2013Task

Phase F (Interpretation)

2014

7 Deliverables

The proposed disseminations of results for this research project can be outlined as follows:1) Publishing the results as papers. According to the arranged work plan, it is expected that the firstpaper will be submitted during the first year including the interpretation and results of SKS phasessplitting using the Austrian network data (referring the research question number.2) Attending the international conferences and meeting such as: PANGEO AUSTRIA (Salzburg, 2012and 2014); American Geophysical Union (AGU) fall meeting (December 2012 and 2013, San Francisco,USA); European Geosciences Union (EGU) General Assembly (Vienna, Austria, April 2013).

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References

[1] G. Barruol, M. Bonnin, H. Pedersen, G.H.R. Bokelmann, and C. Tiberi. Belt-parallel mantle flowbeneath a halted continental collision: The Western Alps. Earth and Planetary Science Letters,302:429–438, 2011. doi:10.1016/j.epsl.2010.12.040.

[2] G. Barruol, P.G. Silver, and A. Vauchez. Seismic anisotropy in the Eastern United States: Deepstructure of a complex continental plate. J. Geophysical Res, 102(B4):8329–8348, 1997.

[3] G.H.R Bokelmann. P wave array polarization analysis and effective anisotropy of the brittle crust.Geophys. J. Int, 120:145–162, 1995. doi:10.1111/j.1365-246X.1995.tb05917.x.

[4] G.H.R Bokelmann. Convection-driven motion of the North American craton: Evidence from P waveanisotropy. Geophys. J. Int, 148(2):278–287, 2002. doi:10.1046/j.1365-246X.2002.01614.x.

[5] P. Bormann, P. Burghardt, T. Makeyeva, and L. Vinnik. Teleseismic shear-wave splitting anddeformation in Central Europe. Phys. Earth Planet. Inter, 78:157–166, 1993.

[6] E. Bruckl, M. Behm, K. Decker, M. Grad, A. Guterch, G.R. Keller, and H. Thybo. Crustal structureand active tectonics in the Eastern Alps. Tectonics, 29, 2010. doi:10.1029/2009TC002491.

[7] L. Buontempo, G.H.R. Bokelmann, G. Barruol, and J. Moralest. Seismic anisotropy beneath South-ern Iberia from SKS splitting. Earth and Planetary Science Lett, 273:237–250, 2008.

[8] S. Chevrot. Multicannel analysis of shear wave splitting. J. Geophysical Res, 105(B9):21579–21590,2000.

[9] F.R. Fontaine, G. Barruol, B.L.N. Kennett, G.H.R. Bokelmann, and D. Reymond. Upper man-tle anisotropy beneath Australia and Tahiti from P wave polarization: Implications for real-timeearthquake location. J Geophysical Res, 114, 2009. doi:10.1029/2008JB005709, 2009.

[10] M. J. Fouch and S. Rondenay. Seismic anisotropy beneath stable continental interiors. Physics ofthe Earth and Planetary Interiors, 158:292–320, 2006.

[11] D. Gubbins. Seismology and plate tectonics. Cambridge University Press, 1990.

[12] J. Kummerow and R. Kind. Shear wave splitting in the Eastern Alps observed at the TRANSALPnetwork. Tectonophysics, 414(1-4):117–125, 2006. doi:10.1016/j.tecto.2005.10.023.

[13] R. Lippitsch, E. Kissling, and J. Ansorge. Upper mantle structure beneath the Alpine orogen fromhigh-resolution tomography. J. Geophys, 108, 2003. doi:10.1029/2002JB002016.

[14] M.D. Long and T.W. Becker. Mantle dynamics and seismic anisotropy. Earth and Planetary Sciencelett, 297:341–354, 2010. doi:10.1016/j.epsl.2010.06.036.

[15] M.D. Long and P.G. Silver. Shear wave splitting and mantle anisotropy: Measurements, interpreta-tions. Surv Geophys, 30:407–461, 2009. doi:10.1007/s10712-009-9075-1.

[16] M.D. Long and R.D. van der Hilst. Shear wave splitting from local events beneath the Ryukyu arc:Trench-parallel anisotropy in the mantle wedge. Phys Earth and Planetary Interior, 155:300–312,2006. doi:10.1016/j.pepi.2006.01.003.

[17] R. Meissner, W.D. Mooney, and I. Artemieva. Seismic anisotropy and mantle creep in young orogens.Geophys. J. Int, 149:1–14, 2002.

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[18] U. Mitterbauer, M. Behm, E. Bruckl, R. Lippitsch, A. Guterch, G.R. Keller, E. Koslovskaya,E. Rumpfhuber, and F. Sumanovac. Shape and origin of the East-Alpine slab constrained by theALPASS teleseismic model. Tectonophysics, 510(1):195–206, 2011. doi:10.1016/j.tecto.2011.07.001.

[19] J.P. Montagner. Where can seismic anisotropy be detected in the earths mantle? in boundary layers.Geophys, 151:223–256, 1998.

[20] J. Plomerova, L. Vecsey, and V. Babuska. Mapping seismic anisotropy of the lithosheric mantlebeneath the Northern and Eastern Bohemian Massif (Central Europe). Tectonophysics, 564-565:38–53, 2012. doi:10.1016/j.tecto.2011.08.011.

[21] S. Salimbeni, S. Pondrelli, S. Danesi, and A. Morelli. Seismic anisotropy of the Victoria land region,Antarctica. Geophys. J. Int, 182(B4):421–432, 2010. doi:10.1111/j.1365-246X.2010.04624.x.

[22] S.M. Schmid, B. Fugenschuh, E. Kissling, and R. Schuster. Tectonic map and overall architectureof the Alpine orogen. Eclogae geol. Helv, 97:93–117, 2004. doi:10.1007/s00015-004-1113-x.

[23] S.M. Schmid, O.A. Pfiffner, and G. Schreurs. Rifting and collision in the Penninic zone of EasternSwitzerland. in: Pfiffner a.o. et al. (eds.): Deep structure of the Swiss Alps: Results from NRP 20.pages 160–185, 1997.

[24] V. Schulte-Pelkum, G. Masters, and P.M. Shearer. Upper mantle anisotropy from long-period Ppolarization. J Geophys Res, 106:21917–21937, 2001.

[25] P. Silver and M.K. Savage. The interpretation of shear-wave splitting parameters in the presence oftwo anisotropic layers. Geophys. J. Int, 119:949–963, 1994.

[26] P.G. Silver and W.W. Chan. Shear wave splitting and subcontinental mantle deformation. J GeophysRes, 96(B10):16429–16454, 1991.

[27] S. Stein and M. Wysession. An Introduction to seismology, earthquakes, and earth structure. Black-well, 2003.

[28] D.L. Turcotte and G. Schubert. Geodynamics. Cambridge University Press, 2002.

[29] A. Udias. Principle of seismology. Cambridge University Press, 1999.

[30] L. Vinnik, V. Krishna, R. Kind, P. Bormann, and K. Stammler. Shear wave splitting in the recordsof the German Regional Seismic Network. Geophys. Res. Lett, 21(6):457–460, 1994.

[31] D.A. Wiens and G.P. Smith. Seismological constraints on structure and flow patterns within themantle wedge. in: Eiler, j.m. (ed.), inside the subduction factory. Am. Geophys. Union, Geophys.Monogr. Ser, 138, 2003.

[32] TRANSALP working group. First deep seismic reflection images of the Eastern Alps re-veal gaint crustal wedges and transcrustal ramps. Geophys. Res. Lett, 29(10):92–1–92–4, 2002.doi:10.1029/2002GL014911.

[33] A. Wustefeld and G. Bokelmann. Null detection in shear-wave splitting measurements. Bull. Seism.Soc. Am, 97(4):1204–1211, 2007. doi:10.1785/0120060190.

[34] A. Wustefeld, G. Bokelmann, C. Zaroli, and G. Barruol. SplitLab: A shear-wave splitting environ-ment in Matlab. Computers and Geosciences, 34:515–528, 2008.

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