Seismic Source Parameters from a New Dial-up Seismological Network in Greece

—A regional dial-up PT telemetric network of eight digital short-period seismic stations has been in full operation since the beginning of 1995 in Greece. During the first year of full operation, three destructive earthquake sequences struck different regions of central and northern Greece. The dial-up network managed to successfully record more than 85% of these seismic events including foreshocks, main shocks and aftershocks, and 45 of these events were selected in order to determine their seismic source parameters by spectral analysis. The results show that seismic moment correlates very well with earthquake magnitude, fault radius and fault displacement. The determined scaling relations are in general agreement with those obtained by other studies for Greek earthquakes that used different methodologies. Since digital seismic instrumentation is now expanding in Greece, these first results from spectral analysis of digital short-period data can be considered useful for future seismic hazard studies.     

Ground Motion Modeling for Seismic Hazard Analysis in the Near-source Regime: An Asperity Model

—A new, yet simple, method using the asperity model to estimate ground motion in the near-source regime for probabilistic seismic hazard analyses is proposed in this study. This near-source model differs from conventional empirical attenuation equations. It correlates peak ground motions with the local contributing source in terms of the static stress drop released non-uniformly on the causative fault plane rather than with the whole seismic source in terms of magnitude. Here the model is simplified such that ground motions at a rock or firm soil site near extended vertical strike-slip faults are dominated by direct shear waves. The proposed model is tested by comparing its predictions with strong ground motion observations from the 1979 Imperial Valley and the 1984 Morgan Hill earthquakes. The results have revealed that ground motions in the near-source region can be adequately predicted using the asperity model with appropriate calibration factors. The directivity effect of ground motion in the near-source region is negligible for high-frequency accelerations. The cut-off frequency (?_max?) at a site is an important parameter in the near-source region. Higher values of ?_max yield higher estimates of peak ground accelerations. For high-frequency structures, ?_max should be carefully estimated. In the near- source region both non-uniform and uniform source models can produce non-stationary high-frequency ground motions. Peak motions may not be caused by the nearest sections of the fault (even if the uniform source model is considered).     

Diurnal periodicity of the representative earthquakes in Greece

The diurnal periodicity of seismic events of different energy from the Greece earthquake catalog was studied. Earthquake samplings of different energy with a known level of magnitude of completeness were compiled. Parameters of the diurnal periodicity of earthquakes in different time and magnitude intervals were analyzed. Significant diurnal periodicity of earthquakes with M ≤ 4.1 was revealed. The most important result of the paper is the discovery of the diurnal periodicity of the representative earthquakes with M = 3.2–4.1. The diurnal periodicity of representative earthquakes cannot be explained at the base of the prevailing hypothesis considering the diurnal periodicity of earthquakes as an apparent phenomenon resulting from diurnal changes in the real sensitivity of the seismic network due to diurnal variations of seismic noise.     

朝鲜核爆的Rayleigh波震级测量

利用1995年至2009年中国东北及邻近地区11个宽频带台站记录到的77个地震事件、3个化学爆炸和2次朝鲜核爆的区域地震资料,标定该区域台网的Rayleigh波震级.通过对8~25 s 周期的垂直分量Rayleigh波形进行分析,获取基于最大振幅的面波震级.计算82个区域事件不同周期的台基响应,经过台基校正后取最大振幅的面波震级为事件震级.2006年和2009年两次朝鲜核爆的面波震级分别为2.93±0.19和3.62±0.21.将地震和核爆事件的面波震级M_s与体波震级m_b(Lg)进行比较,发现根据该区域台网的数据利用M_s-m_b识别方法无法鉴别朝鲜地区的核爆与地震.朝鲜核爆的面波震级相对较大,使M_s-m_b识别方法失效,其原因可能是源区介质的不均匀性、由核爆炸冲击引发的深部的拉伸破坏被抑制,或者是近爆源区存在张性的构造预应力.假定核爆可能的埋藏深度范围是0.01~1.0 km,用Rayleigh波震级估计朝鲜核爆的当量,对2006年和2009年核爆当量的估值范围分别为0.42~3.17 kt和2.06~15.53 kt.     

Single-station estimates of the seismic moment of the 1960 Chilean and 1964 Alaskan earthquakes,using the mantle magnitudeM m

Measurements are taken of the mantle magnitudeM _m , developed and introduced in previous papers, in the case of the 1960 Chilean and 1964 Alaskan earthquakes, by far the largest events ever recorded instrumentally. We show that theM _m algorithm recovers the seismic moment of these gigantic earthquakes with an accuracy (typically 0.2 to 0.3 units of magnitude, or a factor of 1.5 to 2 on the seismic moment) comparable to that achieved on modern, digital, datasets. In particular, this study proves that the mantle magnitudeM _m does not saturate for large events, as do standard magnitude scales, but rather keeps growing with seismic moment, even for the very largest earthquakes. We further prove that the algorithm can be applied in unfavorable experimental conditions, such as instruments with poor response at mantle periods, seismograms clipped due to limited recording dynamics, or even on microbarograph records of air coupled Rayleigh waves.In addition, we show that it is feasible to use acoustic-gravity air waves generated by those very largest earthquakes, to obtain an estimate of the seismic moment of the event along the general philosophy of the magnitude concept: a single-station measurement ignoring the details of the earthquake's focal mechanism and exact depth.     

Study on equivalent velocity pulse of nearfault ground motions

Introduction By analyzing earthquake motions, we could find that earthquake motions near the causativefault have two characteristics. One is the remarkable directivity effect. The amplitude of thefault-normal component is larger than that of the fault-parallel one; the other is obvious pulse mo-tions. Bertero, et al (1977) studied the earthquake records of the 1971 San Fernando earthquake.They first pointed out that some ground motions recorded near the causative fault is characterizedb…     

Rating damage potential of ground motion records

In this study, a total of 115,246 ground motions recorded during earthquakes of Moment magnitudes ranging from M_w 5.0 to M_w 9.0 are analyzed statistically. A total of 21 ground motion parameters characterising the recorded acceleration time histories are used in the analysis. Classification of these parameters through statistical correlation is reported and a parameter called "distance from zero-amplitude axis," or d_Z-A, is formulated in the principal component space. The ability for d_Z-A to rate the damage potentials of strong motion records is evaluated through correlation of d_Z-A with Japan Meteorological Agency(JMA) instrumental seismic intensities. This parameter can be used to rate damage potential of any strong motion record irrespective of the magnitude and location of the earthquake. It can also be used in selecting ground motion records of appropriate damage potential in seismic design and probabilistic analysis.     

Monofractal and multifractal approaches in investigating scaling properties in temporal patterns of the 1983-2000 seismicity in the western Corinth graben, Greece

Much recent work has been focused on understanding the statistical properties of time-occurrence series of earthquakes. Investigating into the patterns of seismic sequences reveals evidence of scaling features in temporal behavior. This is shown in the clustering properties of seismicity of the western Corinth graben, Greece from 1983 to 2000. Power-law behavior has been found by means of Allan factor analysis and Fourier spectra for the earthquake sequence, with consistent values for the scaling exponents, that decrease with the threshold magnitude. The analysis of the temporal variation of the scaling exponent, performed with different threshold magnitudes, reveals an enhancing of the clusterization in correspondence to larger events. The multifractal analysis of the temporal distribution of the events has shown a decrease of the intermittent character with the threshold magnitude.     

会昌地震台数字与模拟地震波形和震级的对比初探

通过会昌台数字与模拟地震记录到的多个地震事件进行对比分析，认为前者在记录带宽、获取更多的地震动物理量、记录波形能力及可操作性等方面具有显著的优势，数字观测完全可以取代模拟观测；对两种记录计算的地震震级进行了对比与统计分析，发现数字记录近震的震级比远震的偏差要大，远震震级可直接与全国地震目录接轨。     

Accounting for site effect in probabilistic assessment of seismic hazard for Romania and Bucharest: a case of deep seismicity in Vrancea zone

The paper presents recent achievements in evaluations of site-dependent seismic hazard in Romania and the capital city of Bucharest caused by the Vrancea focal zone (SE-Carpathians). The zone is characterized by a high rate of occurrence of large earthquakes in a narrow focal volume at depths 60–170 km. The database that was used for the hazard evaluation includes parameters of seismicity, ground-motion source scaling and attenuation models (Fourier amplitude spectra), and site-dependent spectral amplification functions. Ground-motion characteristics were evaluated on the basis of several hundred records from more than 120 small magnitude (M 3.5–5) earthquakes occurred in 1996–2001 and a few tens of acceleration records obtained during four large (M 7.4, 7.2, 6.9 and 6.3) earthquakes. The data provide a basis for probabilistic seismic hazard assessment in terms of peak ground acceleration, peak spectral acceleration and MSK intensity using Fourier amplitude spectra for various exceedance probabilities or average return periods. It has been shown that the influence of geological factors plays very important role in distribution of earthquake ground-motion parameters along the territory of Romania.     

Evidence of significant forward rupture directivity aggravated by soil response in an Mw6 earthquake and the effects on monuments

While strong directivity effects have been mostly recognized in M_w > 6.5 earthquakes, the paper investigates the case of a strong such effect in a relatively small‐magnitude event on 3 February 2014 in the island of Cephalonia, Greece. The second of two events (both of M_w ≈ 6) produced a pernicious accelerogram in the region's main town, Lixouri. The paper provides evidence from geology, interferometry, and seismology to convince that the motion was the result of constructive interference in front of the direction of rupture of the obliquely‐strike‐slip fault. The nature of the record is explored to demonstrate that its frequency content, its high velocity pulse, and its strong fault‐normal (FN) favorable polarity are associated with directivity. Moreover, the broad spectral acceleration peak (of 1.7 g) of the FN motion, centered at a period (T ≈ 1.4 s) which almost coincides with the period of the velocity pulse, is shown to have also been affected by soil amplification, in quantitative agreement with Bray et al. (2009). Such a directivity‐and‐soil‐affected motion explains much of the profound damage to monuments, slopes, and harbor quaywalls. In particular, toppling (as well as excessive rotation and sliding) of nearly‐all the tombstones in Lixouri cemetery are shown to correlate well with characteristics of the FN component of motion. By contrast, the excellent performance of the building stock — despite the destructive shaking that prevailed — is persuasively attributed to conservatively‐robust construction practices of the past and the high base shear coefficient of the strict latest (2000) seismic code. Copyright © 2017 John Wiley & Sons, Ltd.     

Discrimination of earthquakes and explosions using multi-fractal singularity spectrums properties

A new method of discrimination of seismic records from earthquakes and explosions is proposed which is based on using properties of their multi-fractal singularity spectrums. The efficiency of the method is illustrated by analysing seismic records from the region of Aswan Dam in Egypt. Current pattern of seismicity in the Upper Egypt is composed by three types of records: tectonic earthquakes, reservoir-induced earthquakes and seismic events generated by quarry blasts. To discriminate quarry blasts from earthquakes of both natures, multi-fractal analysis of records were used. Singularity spectrum support width and multi-fractal generalised Hurst exponents were calculated for all seismic events in the selected data set from a given area. The linear Bayesian discriminator using these characteristics of seismic records provides correct classification for 93 % of earthquakes records and for 99 % of quarry blasts records.     

The use of teleseismic P-wave complexity for seismic event screening – results determined from GRF and GERESS array data

Seismic data recorded at the broad-band teleseismic GRF array and theshort-period regional GERESS array, which is a designated IMS primarystation, are analyzed to determine the effectiveness of teleseismic P-wave complexity for the purpose of seismic event screening within theframework of Comprehensive Nuclear-Test-Ban Treaty verification. For theGRF array, seismic waveform data from nearly 200 nuclear explosions havebeen recorded since its installation in the late 1970's, which were studiedalong with several thousand earthquakes from the last few years.Additionally, we investigated teleseismic P wave complexity for a similarnumber of earthquakes recorded at GERESS. However, owing to itsoperation starting in 1991, only a limited number of nuclear explosionseismograms are available for study.For nuclear explosions, complexity does not exceed levels of 0.3 except fora number of events from the Nevada Test Site recorded only at the GRFarray and located at a large distance where PcP may interfere with the initialP wavelet. Since all events with complexity at GRF larger than 0.3 areexclusively located on Pahute Mesa within the Nevada Test Site,near-source geology or topography must play a dominant role for theseincreased complexity values, while PcP may not contribute significantly tothe high-frequency energy measured by the complexity parameter.Although many earthquakes show complexities below this level, for morethan 25% of the earthquakes investigated the complexities determined arelarger than 0.7, thus showing distinctly larger values than nuclearexplosions. Therefore, this percentage may be screened as earthquakes fromall seismic events detected. As currently only about half of the eventsdetected by the global IMS network are screened out based on focal depthand the m _b :M _s criterion, teleseismic P-wavecomplexity may contribute significantly to the task of seismic eventscreening.     

Empirical attenuation relationship for Arias Intensity

Arias Intensity is a ground motion parameter that captures the potential destructiveness of an earthquake as the integral of the square of the acceleration–time history. It correlates well with several commonly used demand measures of structural performance, liquefaction, and seismic slope stability. A new empirical relationship is developed to estimate Arias Intensity as a function of magnitude, distance, fault mechanism, and site category based on 1208 recorded ground motion data from 75 earthquakes in active plate‐margins. Its functional form is derived from the point‐source model, and the coefficients are determined through non‐linear regression analyses using a random‐effects model. The results show that for large magnitude earthquakes (M > 7) Arias Intensity was significantly overestimated by previous relationships while it was underestimated for smaller magnitude events (M ? 6). The average horizontal Arias Intensity is not significantly affected by forward rupture directivity in the near‐fault region. The aleatory variability associated with Arias Intensity is larger than that of most other ground motion parameters such as spectral acceleration. However, it may be useful in assessing the potential seismic performance of stiff engineering systems whose response is dominated by the short‐period characteristics of ground motions. Copyright © 2003 John Wiley & Sons, Ltd.     

华北地区1900-1970年5级以上地震发震位置与震源机制研究

本文通过整理世界地震台网1900-1970年世界台站震相报告,对该时期发生在我国华北地区震级5级以上强震的震源位置及震源机制（断层面解）进行了测量.具体开展了以下三点工作：（1）使用1900-1970年之间Shide Circulars（BAASSC,1900-1912）,《国际地震资料汇编》（ISS）和EHB Bulletin的震相到时,对该时间范围内的22个地震事件重新定位,得到了21个地震事件的可靠结果;（2）使用1933年至1970年之间ISS的P波初动,对该时间范围内的15个地震事件求解震源机制解,得到了其中12个地震事件的震源机制解的可靠结果,从而丰富了华北地区基于全球地震台网观测的1900-1970年历史强震目录震源机制资料;（3）基于华北地区地震地质及区域构造应力场研究结果,推断了华北地区M≥5.0的部分缺乏地震资料观测的历史地震断层面参数,并对这种方法推断的断层面参数的可靠性进行了讨论.     

Effect of isolation on fragility curves of highway bridges based on simplified approach

The trend of isolating highway bridges is on the rise after the recent large earthquakes in Japan, the United States, and other countries. Recent investigation shows that isolated systems perform well against seismic forces as the substructures of such systems experience less lateral forces due to energy dissipation of the isolation device. Hence, it is anticipated that there might be an effect on fragility curves of highway bridges due to isolation. In this study, 30 isolated bridge models were considered (and they were designed according to the seismic design code of highway bridges in Japan) to have a wider range of the variation of structural parameters, e.g. pier heights, weights, and over-strength ratio of structures. Then, fragility curves were developed by following a simplified procedure using 250 strong motion records, which were selected from 5 earthquake events that occurred in Japan, the USA, and Taiwan. It is observed that the level of damage probability for the isolated system is less than that of the non-isolated one for a lower level of pier height. However, having the same over-strength ratio of the structures, the level of damage probability for the isolated system is found to be higher for a higher level of pier height compared to the one of the non-isolated system. The proposed simple approach may conveniently be used in constructing fragility curves for a class of isolated bridge structures in Japan that have similar characteristics.     

多种表征强震动记录特性的参数对比分析

为研究强震动记录的破坏特性,对多条国内外常用的强震动记录的特性参数进行了对比分析.结果表明,强震动记录特性参数之间的相关件很小;PGA(PGV)和EPA(EPV)大小关系受震级和震中距影响较大;VSI较ASI能够更准确的评价强震动记录的破坏特性;与其它参数相比,强震动记录破坏强度参数(PD)同时考虑了地震加速度、时间和...     

基于强震监测记录的冶勒大坝动力反应特性初步分析

冶勒沥青混凝土心墙堆石坝最大坝高为124.5m,坝址区地震烈度高,地质条件复杂。大坝上布设了9台强震仪组成的强震监测台阵,自2005年12月开始投入运行至2014年12月底共获得有效记录57次,其中包括汶川地震、攀枝花地震和芦山地震记录。对典型强震记录进行时域分析和频谱分析,初步总结了冶勒大坝的动力反应特性。研究结果表明,大坝坝顶部位的动力反应主要以放大为主,并且随着底部PGA的减小,坝体放大倍数明显增大;由于地震动本身震源特性、传播途径的差异,大坝在不同地震中动力反应的频谱特性明显不同,但多次记录均显示土石坝体有较为明显的滤波作用。     

Tall building performance‐based seismic design using SCEC broadband platform site‐specific ground motion simulations

The scarcity of strong ground motion records presents a challenge for making reliable performance assessments of tall buildings whose seismic design is controlled by large‐magnitude and close‐distance earthquakes. This challenge can be addressed using broadband ground‐motion simulation methods to generate records with site‐specific characteristics of large‐magnitude events. In this paper, simulated site‐specific earthquake seismograms, developed through a related project that was organized through the Southern California Earthquake Center (SCEC) Ground Motion Simulation Validation (GMSV) Technical Activity Group, are used for nonlinear response history analyses of two archetype tall buildings for sites in San Francisco, Los Angeles, and San Bernardino. The SCEC GMSV team created the seismograms using the Broadband Platform (BBP) simulations for five site‐specific earthquake scenarios. The two buildings are evaluated using nonlinear dynamic analyses under comparable record suites selected from the simulated BBP catalog and recorded motions from the NGA‐West database. The collapse risks and structural response demands (maximum story drift ratio, peak floor acceleration, and maximum story shear) under the BBP and NGA suites are compared. In general, this study finds that use of the BBP simulations resolves concerns about estimation biases in structural response analysis which are caused by ground motion scaling, unrealistic spectral shapes, and overconservative spectral variations. While there are remaining concerns that strong coherence in some kinematic fault rupture models may lead to an overestimation of velocity pulse effects in the BBP simulations, the simulations are shown to generally yield realistic pulse‐like features of near‐fault ground motion records.