Abstract. We use seismic waveform data from the AlpArray Seismic Network and three other temporary seismic networks, to perform receiver function (RF) calculations and time-to-depth migration to update the knowledge of the Moho discontinuity beneath the broader European Alps. In particular, we set up a homogeneous processing scheme to compute RFs using the time-domain iterative deconvolution method and apply consistent quality control to yield 112 205 high-quality RFs. We then perform time-to-depth migration in a newly implemented 3D spherical coordinate system using a European-scale reference P and S wave velocity model. This approach, together with the dense data coverage, provide us with a 3D migrated volume, from which we present migrated profiles that reflect the first-order crustal thickness structure. We create a detailed Moho map by manually picking the discontinuity in a set of orthogonal profiles covering the entire area. We make the RF dataset, the software for the entire processing workflow, as well as the Moho map, openly available; these open-access datasets and results will allow other researchers to build on the current study.
<div class="x_ContentPasted2 x_ContentPasted3"> <p class="x_MsoNormal x_FluidPluginCopy"><span class="x_ContentPasted5">During the last few years, the determination</span><span class="x_ContentPasted5">&#160;of the crust and upper mantle structures in southern Poland is the target of passive seismic experiments such as AniMaLS and PACASE. In this research, the area of Sudetes has been focused on that is located at the margin of the Bohemian Massif. This region represents the NE-most part of the Variscan internides&#160;</span><span class="x_ContentPasted5" lang="EN-GB">between the Elbe Fault in SW and the Odra Fault in NE.</span><span class="x_ContentPasted5" lang="EN-GB">&#160;</span><span class="x_ContentPasted5">The lithosphere of the region is a mosaic of several distinct units/terranes with complex tectonic history ranging from the upper Proterozoic to the Quaternary.</span>&#160;</p> <p class="x_MsoNormal x_FluidPluginCopy"><span class="x_ContentPasted5">To provide information about the crust and upper mantle structure beneath the Sudetes region, Ambient Noise Tomography Analysis has been used. As the input, continuous seismic data acquired during about 2 years (2017 to 2019)&#160;&#160;&#160;have been used. The acquisition involved 41 broadband seismic stations &#8212; 23 temporary stations deployed in the area of Sudetes and Fore-Sudetic block in SW Poland, supplemented with the data from 12 permanent seismic stations, operating in this area in the Czech Republic, Germany, and Poland. Furthermore, data from 6 broadband seismic stations of the Alp Array Seismic Network have been used.</span>&#160;</p> <p class="x_MsoNormal x_FluidPluginCopy"><span class="x_ContentPasted5">Ambient seismic noise methods are now well-established and used in different period bands for different scales. To retrieve the surface wave dispersion curves from the vertical component of recorded noise for a given station pair, the cross-correlation in the frequency domain and stacking of noise records has been done. Then, the spectra from every combination of station pairs are cross-correlated by selecting the longest common time window available between the two stations and the average inter-station dispersion measurements with respect to the periods that have been retrieved. In the next step, the Multiple Filter Analysis technique was applied to analyze the waveforms and obtain the group velocity dispersion curves. In the final step, we are working on surface wave tomography and applying inversion for the shear (or compressional) velocities in the region. Based on the preliminary results, the depth resolution is between 5-50 km and the average shear velocity that is calculated so far is about 2.8 to 4.5 km/s at these depths.&#160;</span></p> <p class="x_Standard x_FluidPluginCopy"><strong>&#160;</strong><strong><span class="x_ContentPasted5">Financial support</span></strong>&#160;</p> <p class="x_MsoNormal x_FluidPluginCopy"><span class="x_ContentPasted6">This presentation is supported by the National Science Centre, Poland, according to the agreements UMO-2019/35/B/ST10/01628 and UMO-2016/23/B/ST10/03204.&#160;</span></p> </div> <div class="x_ContentPasted2 x_ContentPasted3"><strong><span class="x_ContentPasted5">Acknowledgments</span><span class="x_ContentPasted5">&#160;</span></strong></div> <div class="x_ContentPasted2 x_ContentPasted3"> <p class="x_MsoNormal x_FluidPluginCopy"><span class="x_ContentPasted5">"The AniMaLS Working Group comprises: Monika Bociarska, Wojciech Czuba, Marek Grad, Tomasz Janik, Kuan-Yu Ke, Weronika Materkowska, Marcin Polkowski and Monika Wilde-Pi&#243;rko."</span><span class="x_ContentPasted5">&#160;</span></p> <p class="x_Standard x_FluidPluginCopy"><strong>&#160;</strong></p> </div>
<p>The structure of the oceanic crust generated by the ultraslow-spreading mid-ocean Knipovich Ridge still remains relatively uninvestigated compared to the other North Atlantic spreading ridges further south. The complexity of the Knipovich Ridge, with its oblique ultraslow-spreading and segmentation, makes this end-member of Spreading Ridge Systems an important and challenging ridge to investigate. The aim of this work is to better understand the lithospheric structure beneath the rare ultraslow-spreading ridges, using as example the Knipovich Ridge along its spreading direction. Ultraslow spreading ridges are characterized by a low melt supply. At spreading rates below 20 mm/y, conductive cooling effectively reduces the mantle temperature and results in less melt produced at larger depths. The Ocean Bottom Seismometer (OBS) data along a refraction/reflection profile (~280 km) crossing the Knipovich Ridge off the western Barents Sea was acquired by use of RV G.O. Sars on July 24 - August 6, 2019. The project partners are University of Bergen, Institute of Geophysics, Polish Academy of Sciences, and Hokkaido University. The <span>seismic</span> energy was emitted every 200 m by an array of air-guns with total volume of 80 l. To receive and record the seismic waves at the seafloor, ocean bottom seismometers were deployed at 12 positions with about 15-km spacing in 2 deployments. All the stations were recovered and correctly recorded data. <span>S</span><span>eismic energy from airgun shots were obtained up to 50 km from the OBSs. </span>The profile provides information on the seismic crustal structure of the Knipovich Ridge and oceanic and continental crust in the transition zone. This profile is a prolongation of the previously acquired profile AWI-20090200 <span>(</span>Hermann & Jokat 2013) and together allow for the modeling of ~535 km long transect crossing the Knipovich Ridge from the American to the European plate. <span>S</span>eismic record sections were analyzed with 2D trial-and-error forward <span>seismic modeling</span>. This <span>work is</span> supported by the National Science Centre, Poland according to the agreement UMO-2017/25/B/ST10/00488. The cruise was funded by University of Bergen.</p><p>&#160;</p><p>Hermann, T. and Jokat, W., 2013. Crustal structures of the Boreas Basin and the Knipovich Ridge, North Atlantic. Geophys. J. Int., 193, 1399&#8211;1414, doi: 10.1093/gji/ggt048</p><p align="justify">&#160;</p>
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