Kartiranje debeline kvartarnih sedimentov na območju Iškega vršaja s seizmološko metodo mikrotremorjev

Rupar, Lovro (author), Gosar, Andrej (mentor)

Na območju Iškega vršaja sem s seizmološko metodo mikrotremorjev določil lastne frekvence sedimentov do skalne podlage. Meritve na prostem površju sem izvedel v mreži z okvirno gostoto točk 250 m. Na osnovi 107 meritev mikrotremorjev in podatkov šestih vrtin, ki so dosegle predkvartarno podlago ter dveh refleksijskih seizmičnih profilov sem izpeljal relacijo med debelino sedimentov in njihovo lastno frekvenco. Zanesljivost relacije je bila na podlagi vrednosti R^2 ovrednotena kot zelo dobra. Izdelal sem karto lastnih frekvenc, ki je razkrila obstoj globlje doline (največja globina 119 m) v smeri sever – jug na zahodnem delu Iškega vršaja. Karta amplitud ni pokazala specifične prostorske razporeditve določenih vrednosti, z izjemo ožjega pasu nizkih amplitud, ki se vleče od Iške vasi proti severu, in ki je lahko odraz bolj zdrobljene kamnine v podlagi zaradi prelomne tektonike. Na podlagi dobljene relacije med debelino sedimentov in njihovo lastno frekvenco sem izdelal karto debelin sedimentov in karto nadmorske višine podlage. Primerjava karte debelin sedimentov s podatki vrtin z znano globino do kamninske podlage je pokazala dobro ujemanje. Na karti nadmorskih višin podlage je opazno hitro spuščanje kamninske podlage do dna doline na zahodni strani Iškega vršaja in nato postopno dviganje podlage proti vzhodu. Primerjava parametrov a in b, ki nastopata v relaciji med debelino sedimentov in njihovo lastno frekvenco med različnimi sedimentacijskimi bazeni po svetu in posebej v Evropi je pokazala majhno spremenljivost parametra b in dokaj velik razpon vrednosti parametra a, kar nakazuje da je ta značilen za posamezno območje. Rezultati raziskave bodo uporabni pri izdelavi bolj natančnih hidrogeoloških modelov ter za oceno nevarnosti resonančnih učinkov med sedimenti in objekti pri potresni mikrorajonizaciji.

• Language: Slovenian
• Keywords: metoda mikrotremorjev, Iški vršaj, Ljubljansko barje, lastna frekvenca sedimentov, relacija med debelino in lastno frekvenco sedimentov, kartiranje debeline sedimentov
• Work type: Bachelor thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2019
• PID: 20.500.12556/RUL-110705
• COBISS.SI-ID: 1520222
• Publication date in RUL: 19.09.2019

Secondary language

• Language: English
• Title: Mapping the thickness of Quaternary sediments in the Iška alluvial fan using seismological microtremors method

Abstract

Resonance frequency of unconsolidated sediments on the Iški vršaj area (aluviall fan) were estimated using seismological microtremors method. Free field measurements were conducted in a grid with point density of 250 m. The sediments frequency-thickness relationship was obtained on the basis of 107 microtremor measurements, six existing boreholes that reached the Pre-Quaternary basement and two reflection seismic profiles. The reliancy of the obtained frequency-thickness relationship was evaluated with the R^2 coefficient, which shows a very good level of determination. The resonance frequency map reveals the existence of a deeper burried valley (maximum depth 119 m), with the main axis oriented north-south, in the western part of the Iški vršaj area. The amplitude map does not unveil any specific spatial distribution pattern of amplitudes, with the exception of a relatively narrow band of low amplitudes, north of Iška vas, which could be related to an area of severely fractured rock basement due to the fault tectonics. Map of Quaternary sediment thickness and map of Pre-Quaternary basement elevation were constructed on the basis of the frequency-thickness relationship. The basement depths in existing boreholes agree well with the map of sediment thickness. The Pre-Quaternary basement elevation map displays rather steep western slopes of the buried valley, followed by a gradually ascending basement towards the eastern part of the Iški vršaj. The comparison of the obtained parameters a and b in frequency-thickness relationship with other sedimentary basins around the world and especially in Europe reveals a small variation of b values, and a rather large range of a values, which implies that the parameter a is characteristic for certain areas. The results of this research will find use in establishing more accurate hydrogeological models and for assessment of possible sediments-structure resonance effects in seismic microzonation.

• Keywords: microtremors method, Iški vršaj, Ljubljana Moor, sediments resonance frequency, sediments frequency-thickness relationship, mapping sediment thickness