5 research outputs found
Study of Local Seismic Events in Lithuania and Adjacent Areas Using Data from the PASSEQ Experiment
The territory of Lithuania and adjacent areas of the East European Craton have always been considered a region of low seismicity. Two recent earthquakes with magnitudes of more than 5 in the Kaliningrad District (Russian Federation) on 21 September 2004 motivated re-evaluation of the seismic hazard in Lithuania and adjacent territories. A new opportunity to study seismicity in the region is provided by the PASSEQ (Pasive Seismic Experiment) project that aimed to study the lithosphere–asthenosphere structure around the Trans-European Suture Zone. Twenty-six seismic stations of the PASSEQ temporary seismic array were installed in the territory of Lithuania. The stations recorded a number of local and regional seismic events originating from Lithuania and adjacent areas. This data can be used to answer the question of whether there exist seismically active tectonic zones in Lithuania that could be potentially hazardous for critical industrial facilities. Therefore, the aim of this paper is to find any natural tectonic seismic events in Lithuania and to obtain more general view of seismicity in the region. In order to do this, we make a manual review of the continuous data recorded by the PASSEQ seismic stations in Lithuania. From the good quality data, we select and relocate 45 local seismic events using the well-known LocSAT and VELEST location algortithms. In order to discriminate between possible natural events, underwater explosions and on-shore blasts, we analyse spatial distribution of epicenters and temporal distribution of origin times and perform both visual analysis of waveforms and spectral analysis of recordings. We show that the relocated seismic events can be grouped into five clusters (groups) according to their epicenter coordinates and origin and that several seismic events might be of tectonic origin. We also show that several events from the off-shore region in the Baltic Sea (at the coasts of the Kaliningrad District of the Russian Federation) are non-volcanic tremors, although the origin of these tremor-type events is not clear
Local Seismic Events in the Area of Poland Based on Data from the PASSEQ 2006-2008 Experiment
PASSEQ 2006-2008 (Passive Seismic Experiment in TESZ; Wilde-Piórko et al. 2008) was the biggest passive seismic experiment carried out so far in the area of Central Europe (Poland, Germany, the Czech Republic and Lithuania). 196 seismic stations (including 49 broadband seismometers) worked simultaneously for over two years. During the experiment, multiple types of data recorders and seismometers were used, making the analysis more complex and time consuming. The dataset was unified and repaired to start the detection of local seismic events. Two different approaches for detection were applied for stations located in Poland. The first one used standard STA/LTA triggers (Carl Johnson’s STA/LTA algorithm) and grid search to classify and locate the events. The result was manually verified. The second approach used Real Time Recurrent Network (RTRN) detection (Wiszniowski et al. 2014). Both methods gave similar results, showing four previously unknown seismic events located in the Gulf of Gdansk area, situated in the southern Baltic Sea. In this paper we discuss both detection methods with their pros and cons (accuracy, efficiency, manual work required, scalability). We also show details of all detected and previously unknown events in the discussed area
Traces of the crustal units and the upper-mantle structure in the southwestern part of the East European Craton
The presented study is a part of the passive seismic
experiment PASSEQ 2006–2008, which took place around
the Trans-European Suture Zone (TESZ) from May 2006 to
June 2008. The data set of 4195 manually picked arrivals of
teleseismic P waves of 101 earthquakes (EQs) recorded in
the seismic stations deployed to the east of the TESZ was
inverted using the non-linear teleseismic tomography algorithm
TELINV. Two 3-D crustal models were used to estimate
the crustal travel time (TT) corrections. As a result,
we obtain a model of P-wave velocity variations in the upper
mantle beneath the TESZ and the East European Craton
(EEC). In the study area beneath the craton, we observe up
to 3% higher and beneath the TESZ about 2–3% lower seismic
velocities compared to the IASP91 velocity model. We
find the seismic lithosphere–asthenosphere boundary (LAB)
beneath the TESZ at a depth of about 180 km, while we observe
no seismic LAB beneath the EEC. The inversion results
obtained with the real and the synthetic data sets indicate a
ramp shape of the LAB in the northern TESZ, where we observe
values of seismic velocities close to those of the craton
down to about 150 km. The lithosphere thickness in the EEC
increases going from the TESZ to the NE from about 180 km
beneath Poland to 300 km or more beneath Lithuania. Moreover,
in western Lithuania we find an indication of an uppermantle
dome. In our results, the crustal units are not well
resolved. There are no clear indications of the features in the
upper mantle which could be related to the crustal units in the
study area. On the other hand, at a depth of 120–150 km we
indicate a trace of a boundary of proposed palaeosubduction
zone between the East Lithuanian Domain (EL) and theWest
Lithuanian Granulite Domain (WLG). Also, in our results,
we may have identified two anorogenic granitoid plutons
Upper mantle structure around the Trans-European Suture Zone obtained by teleseismic tomography
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