Mapping the thickness of Quaternary sediments in the Iska alluvial fan (central Slovenia) using microtremor method

Abstract

Resonance frequencies of unconsolidated sediments of the Iška alluvial fan (Ljubljana Moor basin) were derived using microtremor method. Free-field measurements were conducted in a grid with point spacing of approximately 250 m. The sediments frequency-thickness relationship, h = 202.97 f-1.139 , was obtained on the basis of 107 microtremor measurements, six existing boreholes that reached the Pre-Quaternary basement and two seismic reflection profiles. The reliance of the obtained relationship was evaluated with the R 2 coefficient, which shows a very good level of determination. The resonance frequency map reveals the existence of an N-S oriented deeper buried valley (maximum depth 119 m) in the Western part of the alluvial fan. The microtremor HVSR amplitude map does not show any specific spatial distribution pattern, with the exception of a relatively narrow band of low amplitudes located north of Iška vas. This is probably related to an area of severely fractured bedrock along the Mišji Dol fault. Map of the Quaternary sediment thickness and map of the Pre-Quaternary basement topography were constructed on the basis of the established relationship. The basement topography map shows rather steep western slopes of the buried valley down to deepest part, followed by a gradually ascending basement towards the Eastern part of the fan. The comparison of the obtained parameters a and b in frequency-thickness relationship with other sedimentary basins around the world 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 geological areas. The results of this research will find use in constructing more accurate hydrogeological models and for assessment of possible sediments-structure resonance effects in seismic microzonation.

Bedrock Depth Calculation of Çanakkale (Turkey) Basin Using Rayleigh Ellipticity and Microgravity Survey

“…On the other hand, it is imperative to generate the bedrock depth information to obtain a complete ground structure model in basin-type structures and to model information such as possible soil amplification and acceleration distribution. For this purpose, many studies have been carried out to obtain bedrock depth with experimental relations from inversion based on ambient vibration measurements (Delgado et al, 2000a;Hinzen et al, 2004;García-Jerez et al, 2006;D'Amico et al, 2008;Birgören et al, 2009;Özalaybey et al, 2011;Harutoonian et al, 2013;Fairchild et al, 2013;Del Monaco et al, 2013;Mendecki et al, 2014;Kuo et al, 2016;Sant et al, 2017;Molnar et al, 2018;Liang et al, 2018;Moon et al, 2019;Thabet, 2019;Anbazhagan et al, 2019;Rupar and Gosar, 2020;Büyüksaraç et al, 2021;Maghami et al, 2021).…”

Macro-mechnical charakteristics and their control on the strenght of sandstones of western Indo-Burmese Rangers, NE India

“…The area is seismically active and bounded by many geologic and tectonic features (Rakshit and Bezbaruah, 2016;Rakshit et al, 2018;. Construction of a geological map using GIS techniques is useful for understanding aforesaid engineering challenges, including thickness of the near surface sediments (Rupar and Gosar, 2020) around the sample area as shown in Figure 2. These active tectonic features affect the strength of the sandstones in some places by altering the lithostratigraphic positions of silt-clay units.…”