Analysis of Site Amplification and Nonlinear Response Based on Ground Motion Records at MYGH10 Station in Japan

Strong horizontal ground motions with the peak ground acceleration (PGA) larger than 1400 gal were observed at Yamamoto (MYGH10) station during the February 2021 Mj 7.3 off the east coast of Honshu, Japan, Fukushima earthquake. Firstly, in this paper, we discussed and verified the theoretical assumptions of the “Nakamura” method under weak and strong ground motions. The site amplification factor of the MYGH10 station was estimated using the surface horizontal-vertical spectral ratio (HVSR) and the surface-to-borehole spectral ratio (SBSR), and the corrected HVSRC, respectively. Meanwhile, the reasons for underestimating the site amplification factor when using HVSR were explained. The vertical amplification phenomenon of seismic P-wave in the high-frequency band was analysed under weak and strong ground motions. Secondly, we utilized HVSR, SBSR, and theoretical transfer function (TTF) based on the 1D wave propagation theory to study the nonlinear site response of MYGH10 station under the mainshock of the Fukushima earthquake and the historically weak and strong ground motions, respectively. The changes in frequencies and amplitudes of the spectral ratio curves when nonlinearities were occurring at the site were analysed and compared using the spectra ratio curves of weak ground motion records and TTF as references. Finally, the recovery of the site after strong nonlinearity was also evaluated by comparing the spectral ratio curves of aftershocks records. We found that the most significant amplification factor of the site increased from 7 to more than 10, and the predominant frequency decreased from 10 Hz to 3.8 Hz under the mainshock of the Fukushima earthquake. The predominant frequency returned to the previous value within three days after the mainshock, but the amplification factor did not.

Vulnerability Analysis of Earthquake Hazards in Tasikmalaya City Using Horizontal to Vertical Spectral Ratio (HVSR) Method

Tasikmalaya City is one of the regions in West Java Province that is often hit by earthquakes due to its location near the Indo-Australian Plate subduction zone towards the Eurasian Plate. The surface deposits in this city are alluvium and weakly consolidated step deposits which can cause wave amplification during an earthquake. As a mitigation effort, seismic zoning needs to be carried out to map the areas that will experience heavy damage when an earthquake occurs. This study uses the Horizontal to Vertical Spectral Ratio (HVSR) method which is applied to the microtremor recording data to obtain spatial variations in the predominant frequency and amplification values that can explain the characteristics of the geological layer beneath the surface. Based on the obtained results, the predominant frequency ranging from 0.7 to 9.5 Hz with the lowest frequency distribution in the eastern and northwestern parts, which indicates a thicker sediment layer. Amplification ranging from 1.2 to 12.6 with the distribution of higher values in the eastern, southeastern, and northwestern parts. The inversion of the HVSR curves was carried out to determine the value of shear wave velocity (V s ) in order to obtain a more detailed subsurface geological structure that can be used to determine the level of vulnerability of earthquake hazards. The Neighborhood Algorithm is used to find an optimum model. Based on the results of the inversion process, the V s ranging from 150 - 3054 m/s with lower V s values in the eastern, southeastern, and northwestern parts at depth of about 25 meters. The average value of shear wave velocity at a depth of 30 meters (V s 30) can also be used to determine the type of soil for geotechnical study. From the obtained V s 30data, the types of soil in the research area are classified into moderate soil, hard soil, and rocks.

Numerical Simulations of the Seismic Response of a RC Structure Resting on Liquefiable Soil

The seismic response of buildings resting on liquefiable soil is a complex problem that is still poorly understood despite numerous studies on the topic. This paper attempts to enhance the understanding of this phenomenon by simulating an RC structure resting on liquefiable soil and subjected to seismic shakes. The solid-fluid fully coupled analysis was conducted with OpenSeesPL utilizing 58 earthquake records to simulate a wide range of shaking scenarios. In addition, the effect of the soil density and the thickness of the liquefiable layer were examined. It was noted that the liquefaction-induced settlement of the building increased as peak ground acceleration (PGA) increased, where the percentage increase ranged between 2.5% and 888.0% depending on the soil density, thickness of the liquefiable layer, PGA and the predominant frequency of the seismic shake. However, a scatter of the relationship between the PGA and the liquefaction-induced settlement was also noted due to the effect of the predominant frequency of the seismic shake. In addition, a reduced effect from soil density on the liquefaction-induced settlement was observed, where the settlement changed by up to 55% as the soil density changed from loose to medium, and by 68% as the density changed from loose to dense. Additionally, the results of the lateral displacement of the building did not show a definite trend with the increase in PGA, which could be attributed to the complex interaction between PGA amplification and the predominant frequency of the seismic shake as the liquefiable soil layer thickness changed.

IMPACT OF HIRDOTHERAPY ON VEGETATIVE DIS-ABILITIES AFTER CORONAVIRUS INFECTION

Вегетативно сосудистые и вегетативнотрофические изменения наблюдались у абсолютного большинства пациентов с ПКВИ с преобладанием частоты эмоциональных нарушений (страха смерти) 100%, генерализованный гипергидроз у 75,9%, наличие гипервентиляционного синдрома 71%, субфебрилитет, наличие вегетососудистых кризов, мигрени, склонности к обморокам 50,6%, боли в икроножных мыщах 48,1%, чувствительность к перемене климатических условий при ПКВИ наличие ухудшения самочувствия при смене погоды у 48,1% пациентов. Дисдинамические и дизритмические расстройства лабильности артериального давления (АД) с тенденцией к повышению и сердечного ритма с тенденцией к тахикардии 46,9% больных с ПКВИ. Под влиянием пятикратной и десятикратной применение грудотерапии обшое количество баллов симптомов вегетативных расстройств после перенесенной КВИ составили 557 баллов и 31 баллов и снизились на 82,4% и 99,1%. Индекс выраженности вегетативных нарушении сизились от 2,23±0,11 условных единиц (уе) на 0,39±0,01 и 0,02±0,001 уе.Результаты нейропсихологического тестирования у больных, принимавших гирудотерапии, показали объективное улучшение у них вегатативных нарушении, средний балл индекс выраженности вегетативных нарушении достоверно снизился после пятикратного и 10 дненого применение на 82,6% и 99,1% (р < 0,001) по сравнению с фоновым показателем.Таким образом, у больных с ПКВИ, принимавших 10 дневный курс гирудотерапии, показали объективное улучшение у них вегатативных функций. Autonomic vascular and autonomictrophic changes were observed in the vast majority of patients with PCVI with a predominant frequency of emotional disturbances (fear of death) 100%, generalized hyperhidrosis in 75.9%, the presence of hyperventilation syndrome 71% , subfebrile, presence of vegetovascular crises, migraine, tendency to fainting 50.6% , calf pain 48.1% , sensitivity to changes in climatic conditions in PCVI presence of worsening of wellbeing at a change of weather in 48.1% patients. Dysdynamic and dysrhythmic disorders of arterial pressure (BP) lability with a tendency to increase and cardiac rhythm with a tendency to tachycardia 46.9% of patients with PKVI. Under the influence of fivefold and tenfold application of chest therapy, the total score of symptoms of autonomic disorders after CPVI was 557 and 31 and decreased by 82.4% and 99.1%, respectively. The index of severity of autonomic disturbances sized up from 2.23±0.11 conventional units (ue) by 0.39±0.01 and 0.02±0.001 ue.The results of neuropsychological testing in the patients who took hirudotherapy showed the objective improvement of vegetative disturbances in them, the average index score of vegetative disturbances expression reliably decreased after 5 and 10 day application by 82,6 % and 99,1 % (p <0,001) in comparison with the background index.Thus, patients with PKVI who underwent hirudotherapy for 10 days showed objective improvement of vegetative functions.

Determination of path attenuation and site characteristics of the North-west Himalayan region and adjoining regions within the Indian Territory using Generalized inversion method

North-west Himalayas and its adjoining regions have been experiencing deadly earthqaukes from time to time and are home for a large portion of population of Indian subcontinent. Knowledge of regional path attenuation and site parameters are prerequisite while attempting seismic hazard studies towards minimizing damages during future earthqaukes for a region. Present work focuses on the determination of path attenuation and site characteristics of earthqaukes recording stations, located in the north-west Himalayas and its adjoining regions, within India. It is done using two- step generalized inversion technique. In the first step of inversion, non-parametric attenuation curves are developed by constraining attenuation to be a smooth decaying function with hypocentral distance. Qs = (105 ± 11)f (0.94 ± 0.08) as S wave quality factor is obtained indicating that the region is seismically active having high degree of heterogeneities in the crustal medium. In the second step of generalized inversion, site amplification curve, at each recording station, is computed as the ratio of site spectral amplitude of horizontal and vertical components. In addition, based on Horizontal to vertical spectral ratio (HVSR) method, predominant frequency of each recording station is calculated. Values of predominant frequencies based on HVSR and generalized inversion are found matching for each of the recording station. Based on obtained predominant frequency, site class of 101 recording stations, which at present are absent, are determined in this work. Determined path attenuation as well as site parameters can be collectively used for developing regional ground motion models and subsequently for seismic hazard studies for the selected region.

Analysis of H/V Ratio Curve to Estimate Seismic Hazard Vulnerability in Lombok Island, West Nusa Tenggara, Indonesia

In 2018, Lombok Island was hit by a series of destructive earthquakes. According to Indonesian Meteo- rological, Climatological, and Geophysical Agency data, about 1,973 felt earthquakes (M > 3) which shaken Lombok were recorded during August 2018 with three earthquakes with the largest magnitude of 6.9 Mw, 6.8 Mw, and 6.2 Mw. National Board for Disaster Management reported about 555 deaths, 1,833 people injured, and 186,010 houses damaged as a result of Lombok earthquake on August 5th, 2018. A number of seismometers were placed on Lombok Island from August 3rd, 2018 to October 19th, 2018 to monitor the aftershock events. There are 17 stations that record seismicity in Lombok consisting of 10 broadband sensors and 7 short period sensors. In this study, we used the Horizontal-to-Vertical Spectral Ratio (HVSR) method to analyze the risk of earthquake in the Lombok region. The basic concept of this method is to do a comparison between the horizontal component spectrum and the vertical component spectrum of a wave, where theoretically the particle movement of the horizontal component is greater than the particle movement of the vertical component on soft ground, whereas on the hard ground both components (horizontal and vertical) will be similar. H/V curve obtained from earthquake record- ings (Earthquake Horizontal-to-Vertical Ratio/EHVR) and H/V curve obtained from microtremor recordings (Microtremor Horizontal-to-Vertical Ratio/MHVR) shows good agreement and high correlation. Empirical correction of EMR (Earthquake-to-Microtremor Ratio) managed to decrease the difference of estimation of predominant frequency and amplification factor between EHVR and MHVR. Predominant frequency, amplification, and seismic vulnerability map agree with the geological condition of Lombok Island, where high value of amplification and seismic vulnerability was found on soft and thick ground. This study conclude that the maximum ground acceleration and the construction of the building should also considered when one wants to investigate the effect of an earthquake to the damage occurred, beside the site effects.

Horizontal-to-Vertical Spectral Ratio (HVSR) IRIS Station Toolbox

The horizontal-to-vertical spectral ratio (HVSR) for seismic ambient noise is a popular method that can be used to estimate the predominant frequency at a given site. In this article, we introduce the Incorporated Research Institutions for Seismology (IRIS) Data Management Center’s (DMC’s) openly available HVSR station toolbox. These tools offer a variety of ways to compute the spectral ratio by providing different averaging routines. The options range from the simple average of spectral ratios to the ratio of spectral averages. Computations take advantage of the available power spectral density estimates of ambient noise for the seismic stations, and they can be used to estimate the predominant frequency of the many three-component seismic stations available from the IRIS DMC. Furthermore, to facilitate the identification of the peaks in HVSR profiles for the assessment of the predominant frequency of station sites, the toolbox can also process the results of HVSR analysis to detect and rank HVSR peaks. To highlight the toolbox capabilities, three different examples of possible use of this toolbox for routine site-effect analysis are discussed: (1) site effects related to thawing in Arctic regions, (2) ground-motion amplification in urban area, and (3) estimation of station VS30.

Modeling of Seismic Motion Time Histories with Time-Variable Predominant Frequencies

Seismic motions occurring at sites with soft soils and located hundreds of kilometers away from the earthquake focus can be long-lasting and show changes in the frequency spectrum. Although these motions are characterized by low values of peak ground accelerations, they can lead to resonance vibration of buildings and structures. An especially dangerous situation occurs when the seismic load frequencies decrease simultaneously with the natural frequencies of the structure that is damaged during the earthquake. For designing buildings and structures, and for carrying out probabilistic assessment of seismic risk taking into account the changes in time of the seismic load spectrum, an ensemble of seismic motion time histories is required. The article presents a method for modeling unsteady random processes with a variable predominant frequency in the Simulink software system environment.