Microtremor Research Articles

Analysis of local site conditions through geophysical parameters at a city under earthquake threat: Çanakkale, NW Turkey

Çanakkale is the second province, after Istanbul, that has territories in both Asia and Europe. The city, also known as Dardanelles, is located on the Gallipoli peninsula in the northwest of Turkey, and the Biga peninsula which is an extension of Anatolia at the west. The region is tectonically quite active and it has high earthquake generation potential. The city has experienced a significant earthquake (Mw = 6.8) once again that occurred on May 24, 2014. In addition to these challenges, remarkable part of the city's territory and also potential new settlement areas are located on thick alluvium. Thus, mentioned-above disadvantages clearly increase the importance of this study, which focuses on determining the areas having different earthquake hazard potentials with regard to local site conditions by performing seismic risk assessments, as well as providing a basis for the preparation of settlement suitability maps on different scales that will lead knowledge for zoning plans. To that end, an integrated geophysical and geotechnical study was performed in a detailed manner. Multi-channel analysis of surface waves (MASW) and microtremor (MT) measurements were carried out at properly distributed 110 stations representing the whole survey area. The geotechnical study, planned to contribute geophysical interpretation, involved the drilling of 110 boreholes that are close to geophysical measurement stations. In addition to examining Vs30 variations based on the MASW, the ground dominant vibration period maps were also produced through MT time series analysis. In particular, the mean Vs velocity (Vs30) up to the first 30 m and the ground oscillation period change based on spectral amplitude ratios (HVSR) yielded substantial information that helped generate the seismic microzonation maps and also make the ground classification. These outputs contributed to exhibit the risk zones in the coastal city that has a dense and narrow settlement plan.

OMA of model steel structure retrofitted with CFRP using earthquake simulator

Nowadays, there are a great number of various structures that have been retrofitted by using different FRP Composites. Due to this, more researches need to be conducted to know more the characteristics of these structures, not only that but also a comparison among them before and after the retrofitting is needed. In this research, a model steel structure is tested using a bench-scale earthquake simulator on the shake table, using recorded micro tremor data, in order to get the dynamic behaviors. Beams of the model steel structure are then retrofitted by using CFRP composite, and then tested on the Quanser shake table by using the recorded micro tremor data. At this stage, it is needed to evaluate the dynamic behaviors of the retrofitted model steel structure. Various types of methods of OMA, such as EFDD, SSI, etc. are used to take action in the ambient responses. Having a purpose to learn more about the effects of FRP composite, experimental model analysis of both types (retrofitted and no-retrofitted models) is conducted to evaluate their dynamic behaviors. There is a provision of ambient excitation to the shake table by using recorded micro tremor ambient vibration data on ground level. Furthermore, the Enhanced Frequency Domain decomposition is used through output-only modal identification. At the end of this study, moderate correlation is obtained between mode shapes, periods and damping ratios. The aim of this research is to show and determine the effects of CFRP Composite implementation on structural responses of the model steel structure, in terms of changing its dynamical behaviors. The frequencies for model steel structure and the retrofitted model steel structure are shown to be 34.43% in average difference. Finally, it is shown that, in order to evaluate the period and rigidity of retrofitted structures, OMA might be used.

伝統的木造建築物の微振動計測に基づく構造特性の評価に関する研究

伝統的木造建築物の構造特性を評価する際は、建物の微振動計測データから振動特性を直接推定する手法が有効である。本研究では、解体修理中の重要文化財長福寺本堂に対して常時微動計測と加振実験を行い、固有振動数、振動モード形状、減衰定数等の振動特性を推定、解体過程における構造要素の構成の変化に伴う振動特性の変動を観測した。また、微振動計測から求めた実測値を再現するよう立体フレームモデルを構築し、柱梁接合部や小屋組の寄与する水平構面剛性を対象にパラメータスタディを実施、固有値解析により求めた振動特性と実測値との整合性を検証した。

Story-wise system identification of actual shear building using ambient vibration data and ARX model

A sophisticated story-wise stiffness identification method for a shear building structure is applied to the case where the shear building is subjected to an actual micro-tremor. While the building responses to earthquake ground motions are necessary in the previous method, it is shown that micro-tremors can be used for identification within the same framework. This enhances the extended usability and practicality of the previously proposed identification method. The difficulty arising in the limit manipulation at zero frequency in the previous method is overcome by introducing an ARX model. The weakness of small SN ratios in the low frequency range is avoided by using the ARX model together with filtering and introducing new constraints on the ARX parameters.

Estimation of S-wave Velocity Structures by Using Microtremor Array Measurements for Subsurface Modeling in Jakarta

Jakarta is located on a thick sedimentary layer that potentially has a very high seismic wave amplification. However, the available information concerning the subsurface model and bedrock depth is insufficient for a seismic hazard analysis. In this study, a microtremor array method was applied to estimate the geometry and S-wave velocity of the sedimentary layer. The spatial autocorrelation (SPAC) method was applied to estimate the dispersion curve, while the S-wave velocity was estimated using a genetic algorithm approach. The analysis of the 1D and 2D S-wave velocity profiles shows that along a north-south line, the sedimentary layer is thicker towards the north. It has a positive correlation with a geological cross section derived from a borehole down to a depth of about 300 m. The SPT data from the BMKG site were used to verify the 1D S-wave velocity profile. They show a good agreement. The microtremor analysis reached the engineering bedrock in a range from 359 to 608 m as depicted by a cross section in the north-south direction. The site class was also estimated at each site, based on the average S-wave velocity until 30 m depth. The sites UI to ISTN belong to class D (medium soil), while BMKG and ANCL belong to class E (soft soil).

ESTIMATION OF SUBSURFACE STRUCTURE BASED ON MICROTREMOR OBSERVATIONS AT PADANG, INDONESIA

In this study, we estimated a ground profile in Padang City, Indonesia, using microtremor observations. Indonesian is located on the boundaries of three major tectonic plates, namely the Indian-Australian, Pacific, and Eurasian plates. Consequently, subduction-related major earthquakes occur repeatedly, including, even in the 21st century, such large interplate earthquakes as the 2004 Sumatra earthquake, the 2006 Nias Island earthquake, the 2007 Bengkulu earthquake, and the 2010 Mentawai earthquake. The 2009 Padang earthquake was also one of the most destructive earthquakes in recent times, although it was an intra-plate based earthquake. This earthquake was of magnitude Mw7.6, producing severe tremors and causing extensive damage to buildings and casualties. To prevent loss of human lives and dwellings from a devastating earthquake, we investigated the shaking characteristics of the ground in Padang. Spectral ratios for horizontal and vertical motion, H/V, from single-station microtremor records were used to identify the predominant periods of the ground vibrations. Microtremor array observations were conducted to find the phase velocities of the Rayleigh wave. The ground profile was estimated by means of the dispersion curves obtained using the Spatial Autocorrelatio (SPAC) and Centerless Circular Array (CCA) methods. The Particle Swarm Optimization (PSO) technique was introduced to determine the dispersion curves. By compiling the soil profile model obtained at each site, a three-layered generalized model was proposed. The velocity of the first layer was less than Vs = 300 m/s, the second layer Vs = 300-3000 m/s and the third layer more than Vs = 3,000 m/s. The subsurface structure models constructed provide useful information for 2-D and 3-D simulations of ground motion in Padang.

Measurement of Microtremor by Using a 50m Fabry Perot Interferometer

Measurement of Microtremor by Using a 50m Fabry Perot Interferometer

Micro-tremor and an attempted Application to Exploration of Landslide Aereas

Micro-tremor and an attempted Application to Exploration of Landslide Aereas