Enhancement of long period components of recorded and synthetic ground motions using InSAR

Tall buildings and flexible structures require a better characterization of long period ground motion spectra than the one provided by current seismic building codes. Motivated by that, a methodology is proposed and tested to improve recorded and synthetic ground motions which are consistent with the observed co-seismic displacement field obtained from interferometric synthetic aperture radar (InSAR) analysis of image data for the Tocopilla 2007 earthquake (M_w=7.7) in Northern Chile. A methodology is proposed to correct the observed motions such that, after double integration, they are coherent with the local value of the residual displacement. Synthetic records are generated by using a stochastic finite-fault model coupled with a long period pulse to capture the long period fling effect.It is observed that the proposed co-seismic correction yields records with more accurate long-period spectral components as compared with regular correction schemes such as acausal filtering. These signals provide an estimate for the velocity and displacement spectra, which are essential for tall-building design. Furthermore, hints are provided as to the shape of long-period spectra for seismic zones prone to large co-seismic displacements such as the Nazca-South American zone.     

Characterization of ground motions using recurrence plots

The current analysis of earthquakes is typically based on linear mathematical models that may fail to describe and forecast particular behaviors, because in many cases the data complexity may induce a highly non linear behavior. In this paper the implementation of an alternative method for seismic time series analysis is presented. The RPs (Recurrence Plots) enables recognition and treatment of measured accelerations. An RP obtained from seismic data allows a more efficient interpretation of the ground motions and this explanation contributes to characterize materials and responses. The nonlinear attributes from RPs analysis can be used as filters to reveal patterns or be combined to predict a seismic property. Automated seismic data characterization, based on nonlinear seismic attributes, could rewrite the rules of earthquake phenomena interpretation. The objective of this work is to establish a new methodology for practical application of nonlinear dynamics in seismic pattern/attributes recognition, an evolving and challenging engineering field.     

Introducing new design spectra derived from Italian recorded ground motions 1972 to 2017

The shape of design spectra, traditionally based on regions characterized by constant displacement, constant velocity, and constant acceleration, has been discussed from a conceptual point of view by Calvi (2018). In the same study, a formulation for the definition of the design spectra relying on four parameters was proposed. Predictive models are proposed herein to calculate these four parameters, conditional on magnitude and distance. These models were developed using a large number of recorded ground motions in Italy, and they allow defining combined spectral acceleration versus spectral displacement plots. Such design spectra are shown to reasonably interpolate the experimental data, resulting in acceleration and displacement demand that approximate the response spectra resulting from +1σ results obtained from recorded ground motions. While it is recognized that numerous additional parameter should be considered (eg, focal depth and fault distance, site amplification), it is also concluded that this approach to define the seismic demand is promising toward a rationalization of seismic design. A thorough application of the approach developed and preliminary tested in this work may result in a re‐visitation of seismic design approaches and, ultimately, in a more efficient use of the available resources.     

Ground motion prediction equation considering combined dataset of recorded and simulated ground motions

Himalayan region is one of the most active seismic regions in the world and many researchers have highlighted the possibility of great seismic event in the near future due to seismic gap. Seismic hazard analysis and microzonation of highly populated places in the region are mandatory in a regional scale. Region specific Ground Motion Predictive Equation (GMPE) is an important input in the seismic hazard analysis for macro- and micro-zonation studies. Few GMPEs developed in India are based on the recorded data and are applicable for a particular range of magnitudes and distances. This paper focuses on the development of a new GMPE for the Himalayan region considering both the recorded and simulated earthquakes of moment magnitude 5.3–8.7. The Finite Fault simulation model has been used for the ground motion simulation considering region specific seismotectonic parameters from the past earthquakes and source models. Simulated acceleration time histories and response spectra are compared with available records. In the absence of a large number of recorded data, simulations have been performed at unavailable locations by adopting Apparent Stations concept. Earthquakes recorded up to 2007 have been used for the development of new GMPE and earthquakes records after 2007 are used to validate new GMPE. Proposed GMPE matched very well with recorded data and also with other highly ranked GMPEs developed elsewhere and applicable for the region. Comparison of response spectra also have shown good agreement with recorded earthquake data. Quantitative analysis of residuals for the proposed GMPE and region specific GMPEs to predict Nepal–India 2011 earthquake of Mw of 5.7 records values shows that the proposed GMPE predicts Peak ground acceleration and spectral acceleration for entire distance and period range with lower percent residual when compared to exiting region specific GMPEs.     

M computed from strong motion accelerograms recorded in Yugoslavia

It is shown that the new definition¹ of strong motion local magnitude M leads to stable estimates of magnitudes for earthquakes in Yugoslavia, with epicentral distances R <100 km and for 2.5 < M < 6.5. Tables with magnitudes computed using this new procedure are presented for all earthquakes contributing to the strong motion accelerogram files in EQINFOS for Yugoslavia.² The similarity of our findings with the analogous analyses for California suggests new possibilities for relative calibration between various local magnitude scales, which are used in southeastern Europe, and M_L in California.     

Evaluation of ground motion selection and modification procedures using synthetic ground motions

This study presents a novel approach for evaluating ground motion selection and modification (GMSM) procedures in the context of probabilistic seismic demand analysis. In essence, synthetic ground motions are employed to derive the benchmark seismic demand hazard curve (SDHC), for any structure and response quantity of interest, and to establish the causal relationship between a GMSM procedure and the bias in its resulting estimate of the SDHC. An example is presented to illustrate how GMSM procedures may be evaluated using synthetic motions. To demonstrate the robustness of the proposed approach, two significantly different stochastic models for simulating ground motions are considered. By quantifying the bias in any estimate of the SDHC, the proposed approach enables the analyst to rank GMSM procedures in their ability to accurately estimate the SDHC, examine the sufficiency of intensity measures employed in ground motion selection, and assess the significance of the conditioning intensity measure in probabilistic seismic demand analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of pulse-like ground motions using artificial neural network

For more than 20 years, the concept of near-fault pulse-like ground motion has been a topic of great interest due to its distinct characteristics, particularly due to directivity or fling effects, which are hugely influenced by the rupture mechanism. These unexpected characteristics, along with their effective frequency, energy rate, and damage indices, create a near-fault, pulse-like ground motion capable of causing severe damage to structures. One of the most common approaches for identifying ...     

Analysis of accelerograms recorded in the source zone of the 1995 Neftegorsk earthquake and computation of synthetic accelerograms

The strongest Neftegorsk earthquake, which occurred in 1995 in the northern part of the Sakhalin Island, was studied by the Epicentral Seismological Expedition, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences. The performed observations yielded the unique accelerograms of strong aftershocks, which were then applied as a basis for detailed analyses. The recorded accelerations were in satisfactory compliance with the current ground motion relations. The design spectra developed on the basis of analyzed records were proposed as an example. The synthetic accelerograms were calculated using the records of the strongest aftershocks for two modal earthquakes by the empirical Green’s function technique. This technique can be recommended for practical application as the most physically substantiated method taking into account all regional features.     

The imaginary counterpart of recorded motions

In this paper it is shown that any recorded motion has an imaginary counterpart. Starting from the harmonic input motion where the sine function is the imaginary counterpart of the cosine function, it is shown that all time histories exist in pairs. The imaginary counterpart of records is not needed when the response of a system is described by a real-parameter constitutive model. However, it is shown that when complex-parameter models are used, the imaginary counterpart of records has equal importance as the real-valued record and in this case the input motion should be strictly complex valued. The procedure to construct the imaginary counterpart of any piecewise continuous record is developed. A constructed complex-valued earthquake time history is used as input motion to a system described by a Kelvin model with complex damping constant. The validity of the procedure is demonstrated by comparing the response of the complex-damping Kelvin model against the results obtained from a mathematically equivalent real-valued formulation.     

Soil-structure interaction effects on strong motion accelerograms recorded on instrument shelters

The distortions of earthquake ground motions recorded in small instrument shelters as a result of soil-structure interaction effects are investigated by means of a theoretical parametric study. A total of 12 foundation geometries varying in basal radius, embedment depth and extension above the ground surface and a number of soil profiles including uniform and layered soil models were considered. The results obtained show significant amplification and deamplification of the free-field ground motion for sufficiently soft soils (β<200 m/sec) and sufficiently high frequencies (f>20 Hz).     

利用高频GPS技术进行强震地面运动监测的研究进展

回顾了高频(1 Hz) GPS在地学应用中的研究进展和主要的数据处理方法,全面比较了高频GPS与地震仪的工作原理与性能,认为高频GPS可为后者进行有效的补充;分析了高频GPS应用于监测短周期强震地面运动的技术优势,以及在处理方法和实际的地学应用中存在的不足;通过对高频GPS的应用领域与发展前景的研究,对我国开展高频GPS数据的处理方法与地学应用研究提出了自己的观点和看法.     

The synthesis of strong ground motion accelerograms from existing records

The paper discusses the synthesis of acceleration time histories primarily for use in structural response estimation. A proposed model for the acceleration time history is based on the summation of dispersive wave modes over the range of frequencies of typical interest to structural response. The values of the modal amplitudes and the travel times (or group velocities) are, for cases examined here, extracted from a target earthquake (or an ensemble of them). The synthetic accelerograms are constructed from these parameters with the inclusion of a probabilistic definition of those or other characteristics of the strong ground shaking and, in particular, the modal phase angle. The probability distributions of the peak acceleration and the integral of the square acceleration of the synthetic records are examined along with comparisons of the pseudo spectral velocity (PSV) response.     

Estimating site-specific strong earthquake motions

The Campus Earthquake Program (CEP) of the University of California (UC) started in March 1996, and involved a partnership among seven campuses of the UC—Berkeley, Davis, Los Angeles, Riverside, San Diego, Santa Barbara, Santa Cruz—and the Lawrence Livermore National Laboratory (LLNL). The aim of the CEP was to provide University campuses with site-specific assessments of their earthquake strong motion exposure, to complement estimates they obtain from consultants according to the state-of-the-practice (SOP), i.e. Building Codes (UBC 97, IBC 2000), and Probabilistic Seismic Hazard Analysis (PSHA). The Building Codes are highly simplified tools, while the more sophisticated PSHA is still somewhat generic in its approach because it usually draws from many earthquakes not necessarily related to the faults threatening the site under study.Between 1996 and 2001, the site-specific studies focused on three campuses: Riverside, San Diego, and Santa Barbara. Each campus selected 1–3 sites to demonstrate the methods and procedures used by the CEP: Rivera Library and Parking Lots (PL) 13 and 16 at UCR, Thornton Hospital, the Cancer Center, and PL 601 at UCSD, and Engineering I building at UCSB. The project provided an estimate of strong ground motions at each selected site, for selected earthquake scenarios. These estimates were obtained by using an integrated geological, seismological, geophysical, and geotechnical approach, that brings together the capabilities of campus and laboratory personnel. Most of the site-specific results are also applicable to risk evaluation of other sites on the respective campuses.The CEP studies have provided a critical assessment of whether existing campus seismic design bases are appropriate. Generally speaking, the current assumptions are not acknowledging the severity of the majority of expected motions. Eventually, both the results from the SOP and from the CEP should be analyzed, to arrive at decisions concerning the design-basis for buildings on UC campuses.     

基于EMD和VARMA模型的地震动仿真

通过EMD方法将地震动分解成若干固有模态函数,提出了用固有模态函数的时变VARMA建模实现地震动仿真的思路。算例分析表明,该方法充分利用了固有模态函数的特性,解决了直接基于ARMA或VARMA模型建模的仿真方法所面临的模型判阶的难题,并可同时考虑地震动的强度和频率非平稳特性,使仿真地震动与实际地震动在能量时频分布特性上具有较好的一致性且样本统计性较好,弹性及弹塑性反应谱拟合精度较高。     

Suitable triggering algorithms for detecting strong ground motions using MEMS accelerometers

With the recent development of digital Micro Electro Mechanical System(MEMS) sensors, the cost of monitoring and detecting seismic events in real time can be greatly reduced. Ability of MEMS accelerograph to record a seismic event depends upon the efficiency of triggering algorithm, apart from the sensor′s sensitivity. There are several classic triggering algorithms developed to detect seismic events, ranging from basic amplitude threshold to more sophisticated pattern recognition. Algorithms based on STA/LTA are reported to be computationally efficient for real time monitoring. In this paper, we analyzed several STA/LTA algorithms to check their efficiency and suitability using data obtained from the Quake Catcher Network(network of MEMS accelerometer stations). We found that most of the STA/LTA algorithms are suitable for use with MEMS accelerometer data to accurately detect seismic events. However, the efficiency of any particular algorithm is found to be dependent on the parameter set used(i.e., window width of STA, LTA and threshold level).     

Numerical simulation of ground acceleration spectra and accelerograms for engineering application

A numerical approach to the earthquake ground motion analysis is proposed for regions where no accelerograms are available. Using Haskell matrix techniques, the response spectra of a layered substratum for SV waves were calculated and then multiplied by the spectra corresponding to Brune's type pulses. The ground acceleration spectra were obtained for different angles of pulse incidence at the substratum base. The spectrum shape depends upon the substratum response and the pulse shape, while its level was related to the maximum ground acceleration corresponding to the expected maximum intensity. Transformation of the ground spectra into the time domain produced numerical accelerograms for horizontal and vertical components and for different angles of pulse incidence. Finally, a standard statistical procedure was applied to obtain the design response spectra used in engineering applications.     

近断层地震动下设置BRB的双向减隔震桥梁地震反应

在近断层地震动下桥梁结构将发生较大反应,减隔震设计是减轻地震损伤的重要手段。提出了在桥梁双柱墩横桥向设置防屈曲支撑(BRB),在纵桥向设置铅芯橡胶支座(LRB)的双向减隔震体系。利用Midas Civil软件建立3种不同减隔震方式的桥梁结构模型:LRB仅单向,LRB双向与LRB联合BRB,运用非线性时程分析方法计算了桥墩反应(墩顶侧移角、残余位移角和曲率延性)、LRB支座变形和BRB的耗能特性等。结果表明:在近断层地震动输入下联合设置LRB和BRB的双向减隔震桥梁减震效果明显,相比其它2种方式,能有效降低墩柱的塑性变形及起到保护桥墩的作用。在横桥向,桥墩最大侧移角、残余位移角和最大曲率延性系数都显著降低。     

Stochastic simulation of regionalized ground motions using wavelet packets and cokriging analysis

Performance‐based earthquake engineering often requires ground‐motion time‐history analyses to be performed, but very often, ground motions are not recorded at the location being analyzed. The present study is among the first attempt to stochastically simulate spatially distributed ground motions over a region using wavelet packets and cokriging analysis. First, we characterize the time and frequency properties of ground motions using the wavelet packet analysis. The spatial cross‐correlations of wavelet packet parameters are determined through geostatistical analysis of regionalized ground‐motion data from the Northridge and Chi‐Chi earthquakes. It is observed that the spatial cross‐correlations of wavelet packet parameters are closely related to regional site conditions. Furthermore, using the developed spatial cross‐correlation model and the cokriging technique, wavelet packet parameters at unmeasured locations can be best estimated, and regionalized ground‐motion time histories can be synthesized. Case studies and blind tests using data from the Northridge and Chi‐Chi earthquakes demonstrate that the simulated ground motions generally agree well with the actual recorded data. The proposed method can be used to stochastically simulate regionalized ground motions for time‐history analyses of distributed infrastructure and has important applications in regional‐scale hazard analysis and loss estimation. Copyright © 2014 John Wiley & Sons, Ltd.     

Extraction of velocity pulses of pulse-like ground motions using empirical Fourier decomposition

Journal of Seismology - Pulse-like ground motions may have only a distinct strong pulse or multiple pulses within the velocity time-history. These intrinsic pulses are hidden in low-frequency...     

Representation of near-fault pulse-type ground motions

Near-fault ground motions with long-period pulses have been identified as critical in the design of structures. To aid in the representation of this special type of motion, eight simple pulses that characterize the effects of either the fling-step or forward-directivity are considered. Relationships between pulse amplitudes and velocity pulse period for different pulses are discussed. Representative ratios and peak acceleration amplification can exhibit distinctive features depending on variations in pulse duration, amplitude and the selected acceleration pulse shape. Additionally, response spectral characteristics for the equivalent pulses are identified and compared in terms of fixed PGA and PGV, respectively. Response spectra are strongly affected by the duration of pulses and the shape of the basic pulses. Finally, dynamic time history response features of a damped SDOF system subjected to pulse excitations are examined. These special aspects of pulse waveforms and their response spectra should be taken into account in the estimation of ground motions for a project site close to a fault.