Upper mantle structure around the Trans-European Suture Zone obtained by teleseismic tomography

Abstract

Abstract. The presented study aims to resolve the upper mantle structure around the Trans-European Suture Zone (TESZ), which is the major tectonic boundary in Europe. The data of 183 temporary and permanent seismic stations operated during the period of the PASsive Seismic Experiment (PASSEQ) 2006-2008 within the study area from Germany to Lithuania was used to compile the data set of manually picked 6008 top-quality arrivals of P waves from teleseismic earthquakes. We used the TELINV nonlinear teleseismic tomography algorithm to perform the inversions. As a result, we obtain a model of P wave velocity variations up to about ±3 % with respect to the IASP91 velocity model in the upper mantle around the TESZ. The higher velocities to the east of the TESZ correspond to the older East European Craton (EEC), while the lower velocities to the west of the TESZ correspond to younger western Europe. We find that the seismic lithosphere-asthenosphere boundary (LAB) is more distinct beneath the Phanerozoic part of Europe than beneath the Precambrian part. To the west of the TESZ beneath the eastern part of the Bohemian Massif, the Sudetes Mountains and the Eger Rift, the negative anomalies are observed from a depth of at least 70 km, while under the Variscides the average depth of the seismic LAB is about 100 km. We do not observe the seismic LAB beneath the EEC, but beneath Lithuania we find the thickest lithosphere of about 300 km or more. Beneath the TESZ, the asthenosphere is at a depth of 150-180 km, which is an intermediate value between that of the EEC and western Europe. The results imply that the seismic LAB in the northern part of the TESZ is in the shape of a ramp dipping to the northeasterly direction. In the southern part of the TESZ, the LAB is shallower, most probably due to younger tectonic settings. In the northern part of the TESZ we do not recognize any clear contact between Phanerozoic and Proterozoic Europe, but further to the south we may refer to a sharp and steep contact on the eastern edge of the TESZ. Moreover, beneath Lithuania at depths of 120-150 km, we observe the lower velocity area following the boundary of the proposed paleosubduction zone.

Upper mantle structure around the Trans-European Suture Zone obtained by teleseismic tomography

“…These data are sparse compared to the study area, and the spatial resolution is questionable; however, the thick seismic lithosphere reported by was also found in the area during other studies. Koulakov et al (2009) observed the positive P wave velocity anomaly beneath the EEC down to at least 300 km, which indicates even thicker lithosphere compared to . Legendre et al (2012) find no indications of a deep cratonic root below about 330 km for the EEC, while Geissler et al (2010) do not observe any clear indications of deep seismic LAB beneath the EEC either.…”

“…Compared to the crust, the structure of the lithosphere and the lithosphere-asthenosphere boundary (LAB) in the TESZ and its surroundings is poorly known. While it was found that the cratonic lithosphere extends much deeper than that of the younger continental regions (e.g., Eaton et al, 2009;Shomali et al, 2006;Gregersen et al, 2010), the studies revealed that the structure of the lithosphere and the LAB differs a lot on both sides of the TESZ (e.g., Zielhuis and Nolet, 1994;Majorowicz et al, 2003;Koulakov et al, 2009;Wilde-Piórko et al, 2010). Regarding different physical properties and geophysical techniques, the LAB has different practical definitions: (1) the seismic LAB defines the transition between the solid outer layer of the Earth, which is characterized by higher seismic velocity values, and its interior, which is characterized by lower seismic velocity values; (2) the thermal LAB defines the transition between the outer layer with dominating conductive heat transfer above the convective mantle that usually coincides with a depth of a constant isotherm of about 1300 • C (McKenzie, 1967); (3) the electrical LAB is a transition between the generally electrically resistive outer layer of the Earth and the conductive layer in the upper mantle.…”

Geophysical and petrological modeling of the lower crust and uppermost mantle in the Variscan and Proterozoic surroundings of the Trans-European Suture Zone in Central Europe

“…The TTZ, at the contact between the East European Craton and West European Platform, is marked by an increased thickness of the crust, forming the "crustal keel", followed to the NE by a steep decrease of the Moho discontinuity depth from 48 km beneath the keel to 37-38 to the SW (Mazur et al, 2015). The TTZ is a major lithospheric structure, which appears to be a deep-seated boundary reaching at least down to a depth of about 200 km (e.g., Zielhuis and Nolet, 1994;Schweitzer, 1995;Wilde-Piórko et al, 2010;Knapmeyer-Endrun et al, 2014;Janutyte et al, 2014Janutyte et al, , 2015Soomro et al, 2016).…”

Reliable workflow for inversion of seismic receiver function and surface wave dispersion data: a “13 BB Star” case study

“…As mentioned above, the R matrix contains full information on the resolution, however reliability of the inversion depends also on adequacy of the starting model or stability of the scheme. To be able to investigate those factors while retaining some insight into the resolution we adopted a checkerboard test known from the seismic tomography (e.g., Janutyte et al 2015) to the 1D problem.…”