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Measuring stiffness of soils in situ
Published in Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto, Computer Methods and Recent Advances in Geomechanics, 2014
Fusao Oka, Akira Murakami, Ryosuke Uzuoka, Sayuri Kimoto
Microtremor measurements conducted only on a ground surface is very simple, thus widely used method of soil investigation. Horizontal-to-vertical spectral ratios of microtremor (H/V spectral ratio), proposed by Nakamura (1989) give approximate estimation of fundamental frequency of the site. Considering these facts, Mikami (2010) has proposed a method of combining the simple soil investigation (microtremor measurement) and a ground model that was derived as best-simplified model used for the seismic ground response analysis in linear range. This model is based on his finding that site response characteristics of multi-layered ground can be approximately evaluated in the frequency range from zero up to around the first frequency by that of an equivalent homogeneous ground that has the same fundamental frequency. Here, the term "equivalent ground" is used in a sense that the homogeneous ground model has the same fundamental frequency as the original multilayered ground (shear wave velocity is determined as so in the simplified model).
Seismic site amplification and wave energy
Published in Takaji Kokusho, Innovative Earthquake Soil Dynamics, 2017
In order to measure the site amplification, two earthquake observation systems may be available; a horizontal array system at different surface geologies, and a vertical array system consisting of the ground surface and downhole depths of the different geologies in the same place. Besides the earthquake observations, microtremor measurements are often implemented as a convenient and cost-efficient way to roughly evaluate site-specific amplification characteristics, predominant frequencies in particular, in small strain vibrations.
Evaluation of the Local Site Effects and Their Implication to the Seismic Risk of the UNESCO World Heritage Site Old City of Dubrovnik (Croatia)
Published in Journal of Earthquake Engineering, 2023
Davor Stanko, Tvrtko Korbar, Snježana Markušić
Ambient seismic noise measurements or widely known as microtremor measurements are significantly used over the last 30 years as a quick and cheap tool for the estimation of local seismic ground response, fundamental (resonance) site frequency and H/V peak amplitude based on Horizontal-to-Vertical Spectral Ratio (HVSR) method (Nakamura 1989). In the last decade, microtremor measurements have been used for a preliminary site characterization in cases when it is hard or impossible to conduct a geophysical survey or use of invasive and expensive geotechnical borehole, especially sites with land access problem, topographical areas, dense vegetation areas or dense city environment as well historical sites (Del Monaco et al. 2013 D’Amico et al. 2008). Exactly for this reason empirical relations between resonance frequency and bedrock depths have been proposed globally for different local and regional areas (e.g. Seht and Wohlenberg 1999; Tün et al. 2016). Moreover, Luzi et al. (2011) and Stanko and Markušić (2020) presented couples of relationships between resonance frequency, bedrock depth and average shear wave velocity in upper 30 m (Vs30). Shear wave velocity profiles and dynamic shear modulus, are widely used for studying seismic site response and seismic hazard analysis. Fundamental site frequency, bedrock depth and average shear wave velocity in the upper 30 m (Vs30) are important for Eurocode 8 site classification (current and revised one, CEN 2004; Labbé and Paolucci 2022). They are prerequisite input site parameters for the microzonation studies to distinguish local site hazard “diagnosis” of the areas prone to local site effects (Panzera et al. 2019).
Dynamic Characterization of High Plinths of Temples in the Kathmandu Valley Using Microtremors
Published in International Journal of Architectural Heritage, 2022
Chandra Kiran Kawan, Prem Nath Maskey, Gokarna Bahadur Motra
For the determination of the dynamic properties of the high plinths, microtremor instruments were used. Microtremor testing is a non-destructive technique and one of the easiest and cheapest ways to gain an understanding of the main vibration characteristics complex foundation or geotechnical features. Microtremor data provide information on essential features such as natural frequency, amplification, and vibration characteristics of structures at a different frequency. Another benefit of this technique is that it is also feasible without the need for simultaneous measurements, yet results in a faithful representations of the linear elastic behavior of the structures in the frequency domain (Lermo and Chavez-Garcia 1993). This technique provides horizontal to vertical spectral ratios (H/V ratios) and was first applied by Nogoshi and Igarashi (1970, 1971)) and later popularized by Nakamura (1989). This technique has proved to be effective in estimating fundamental periods (Field and Jacob 1993; Mucciarelli and Gallipoli 2004; Ohmachi et al. 1994) as well as relative amplification factors (Konno and Ohmachi 1995; Lermo and Chavez-Garcia 1994). It has also proven to be a reliable technique for identification of the frequency response of artificial structures, such as earthen and concrete dams (Castro et al. 1998, 2000) and civil buildings (Barani et al. 2014; Gallipoli et al. 2004a; Irie and Nakamura 2000). Using the horizontal and vertical component spectral ratio (HVSR), Nakamura (1999) and (2000) also determined the main vibratory frequencies of cultural heritage structures such as the Leaning Tower of Pisa and the Roman Colosseum. Damage enhancement and soil-structure resonance were also studied using microtremors for the Umbria-Marche earthquake (Mucciarelli and Monachesi 1998; Natale and Nunziata 2004), Thessaloniki earthquake (Panou et al. 2005), and Molise earthquake (Gallipoli et al. 2004b).The dynamic characteristics of the remaining of the ancient city of Aptera (Greece) with the aim of identifying the main damage mechanism of structure along with site characterization using HVSR method was done by Moisidi et al. (2004). Using the HVSR method, Gosar (2007) and Gosar and Martinec (2009) studied the soil-structure resonance condition in the Bovec basin and in IIirska Bistrica, respectively. Parajuli et al. (2011) used the HVSR method to determine the fundamental frequency and damping ratio of the two-story masonry building.