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Określenie struktury skorupy ziemskiej na podstawie sejsmicznej funkcji odbioru

100%

Wilde-Piórko M.

Przegląd Geofizyczny

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2005

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tom Z. 1-2

31-45

EN

During a earthquake some energy is released as seismic waves. Seismograms, recordings of ground velocity deplacement, can be received even for very far earthquakes thanks to present sensitive seismometers. These recordings contain the information about a source, astructure of the earth interior on a ray-path and also about a structure beneath a seismic station. A receiver function is calculated from the seismograms of far events (epicentral distances 30°-90°) recorded by three-component seismic station, mainly by broad-band one. Deconvolving the vertical component of teleseismic P waves (P) from the horizontal one (radial or tangential) we can move out the instrument impulse response, effective source time function and the ray-path effects in the mantle from the seismograms. The receiver function contains only P-to-S converted phases (except the direct P wave) from the seismic discontinuities beneath the station. We can apply to the receiver function the inversion method or forward modelling to investigate the one-dimensional S-wave velocity structure beneath the station. Analysis of the receiver functions of the seismic stations for a passive seismic experiment TOR from Sweden, Denmark and Germany and for permanent stations : Suwałki (SUW) from north-east Poland, Moxa (MOX) from south-east Germany, Pruhonice (PRU) as well as Dobruska/Polom (DPC) and Moravsky Beroun (MORC) from central and north-east Czech shows the big differences of the tectonic structure in these areas. I have applied to calculated receiver functions one-dimensional time-domain linear inversion method (TOR experiment, SUW), three-dimensional trial-and-error forward modelling (MOX) and simultaneous determination of Moho depth and average Poisson's ratio in the crust (PRU, DPC

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Local Seismic Events in the Area of Poland Based on Data from the PASSEQ 2006-2008 Experiment

51%

Polkowski M. , Plesiewicz B. , Wiszniowski J. , Wilde-Piórko M.

Acta Geophysica

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2016

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tom Vol. 64, no. 6

2092--2113

EN

PASSEQ 2006-2008 (Passive Seismic Experiment in TESZ; WildePiórko 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 Gdańsk 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.

3

Frequency analysis of the 2004 Sumatra-Andaman earthquake using spectral seismograms

51%

Wilde-Piórko M. , Duda S. , Grad M.

Acta Geophysica

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2011

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tom Vol. 59, no. 3

483-501

EN

Frequency analysis of the Sumatra-Andaman earthquake of 2004, one of the most significant and best-recorded earthquakes, is based on spectral seismograms obtained from their broadband seismograms. The Sumatra-Andaman earthquake is found to have a wide-range frequency content of P-wave radiation during the rupturing process. On the basis of stacking spectral seismograms we distinguished four time events of the rupturing process of a total length of about 540 s. The frequency, fmax, is the highest for the first event (0.163 Hz in time interval 0-88 s), lowest for the second - which is the strongest (0.075 Hz in time interval 88-204 s). For third and fourth events frequencies are similar (0.089 and 0.082 Hz in time intervals 204-452 and 452-537 s, respectively). The frequency also shows an azimuthal dependence (±0.02 Hz). Azimuths for which the frequency, fmax, has maximum and minimum values are 203-222° and 23-42°, respectively. These observations are discussed in relation to previously published papers on this topic.

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Passive Seismic Experiment "13 BB Star" in the Margin of the East European Craton, Northern Poland

45%

Grad M. , Polkowski M. , Wilde-Piórko M. , Suchcicki J. , Arant T.

Acta Geophysica

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2015

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tom Vol. 63, no. 2

352--373

EN

The lithosphere-asthenosphere boundary (LAB) is investigated recently very effectively, mostly using seismic methods because of their deep penetration and relatively good resolution. The nature of LAB is still debated, particularly under “cold” Precambrian shields and platforms. Passive experiment “13 BB star” is dedicated to study deep structure of the Earth’s interior in the marginal zone of the East European craton in northern Poland. The seismic network consists of 13 broadband stations on the area of ca. 120 km in diameter. The network is located in the area of well-known sedimentary cover and crustal structure. Good records obtained till now, and expected during next 1-year long recording campaign, should yield images of detailed structure of the LAB, „410”, “?520”, and „660” km discontinuities, as well as mantle-core boundary and inner core.

5

Expanding seismic surface waves measurements towards low periods with gravity measurements

32%

Wilde-Piórko M. , Dykowski P. , Polkowski M. , Olszak T. , Grad M. , Kryński J. , Sękowski M. , Krankowski A. , Rajner M.

Geoinformation Issues

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2017

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tom Vol. 9, no. 1(9)

5--13

EN

Seismic events in gravity measurements are considered as disturbances and are usually removed from the records. However, the physical properties of tidal gravimetric instruments allow researchers to record seismic surface waves of very long periods. In the case of a superconducting gravimeter, periods of even up to 400 s can be determined. Simultaneous seismic and gravity records at the same locations allow the study of a wider response for incoming seismic waves by using two quite different instruments. For test purposes 4 seismometer-gravimeter pairs were temporarily deployed in Poland at three locations: Borowa Gora Geodetic-Geophysical Observatory (BG), Jozefoslaw Astro-Geodetic Observatory (JO), and Lamkowko Satellite Observatory (LA). During the test period from December 2016 to May 2017 several large teleseismic events were observed with well-formed surface waves. Group velocity dispersion curves for long surface waves, as well as periods of free oscillations are presented for selected events. The correlation of a broadband seismometer signal with different types of gravimetric sensors signals gives the opportunity to analyse gravimeter noise components, in the instrumental and micro-seismic domains.

PL

Zjawiska sejsmiczne w pomiarach grawimetrycznych są traktowane jako zakłócenia i zwykle ich efekty są usuwane z zapisów grawimetrycznych. Jednakże, grawimetry dzięki swojej konstrukcji umożliwiają rejestrację sejsmicznych fal powierzchniowych o bardzo długich okresach. W przypadku grawimetru nadprzewodnikowego, możliwe jest zaobserwowanie fal powierzchniowych, generowanych przez trzęsienia ziemi, o okresach nawet do 400 s. Przeprowadzenie równoczesnych rejestracji sejsmicznych i grawimetrycznych instrumentami zlokalizowanymi w tym samym miejscu, powinno umożliwić przeanalizowanie szerszego zakresu częstości sygnału sejsmicznego niż w przypadku użycia tylko jednego typu instrumentu. W celu sprawdzenia prawdziwości powyższego stwierdzenia, 4 pary instrumentów: sejsmometrów i grawimetrów zostały zainstalowane w Polsce w trzech lokalizacjach, w Obserwatorium Geodezyjno-Geofizycznym Borowa Góra (BG), Obserwatorium Astronomiczno-Geodezyjnym Józefosław (JO) oraz Obserwatorium Satelitarnym Lamkówko (LA). W czasie projektu pilotażowego, trwającego od grudnia 2016 do maja 2017 roku, zarejestrowano kilka dużych trzęsień ziemi z dobrze wykształconymi falami powierzchniowymi. W pracy zaprezentowano krzywe dyspersji grupowych prędkości fal powierzchniowych, jak również okresy oscylacji swobodnych dla wybranych zjawisk. Korelacja szerokopasmowego sygnału sejsmicznego z sygnałem zarejestrowanym przez różnego typu grawimetry umożliwi analizę szumu grawimetrycznego w zakresie częstości pływowych instrumentów, jak i w zakresie mikrosejsmicznym.