A note on the M w 6.3 earthquake in Iceland on 29 May 2008 at 15:45 UTC     

R. Sigbjörnsson  J. Th. Snæbjörnsson  S. M. Higgins  B. Halldórsson  S. Ólafsson 《Bulletin of Earthquake Engineering》2009,7(1):113-126

This preliminary study aims to investigate a M _w 6.3 earthquake that occurred in South Iceland on Thursday 29 May 2008 at 15:45 UTC. The epicentre was in the Olfus District between the towns of Selfoss and Hveragerdi. This study examines the data recorded and the damage observed immediately after the event. Horizontal accelerations of up to 80%g were recorded in the epicentral region and there is visual evidence that the vertical acceleration exceeded 1 g. The PGA data is compared to a ground motion estimation model developed for the South Iceland earthquakes in June 2000. In general the basic properties of this event are found to be similar to the characteristics of the South Iceland earthquakes in June 2000. The duration of strong-motion is short and the intensity attenuates rapidly with increasing distance. The earthquake action resisted by buildings in the near fault area is inspected through evaluation of elastic as well as inelastic response spectra. The vast majority of structures seemed to withstand the strong-motion fairly competently and without significant visual damage due firstly to the low-rise, predominantly reinforced concrete or timber, style of buildings. Secondly, the short duration of strong-motion contributed to the endurance of structures.  相似文献   

Migration for velocity and attenuation perturbations   总被引：1，自引：0，他引：1  

Bobby Hak  Wim A. Mulder 《Geophysical Prospecting》2010,58(6):939-952

Migration maps seismic data to reflectors in the Earth. Reflections are not only caused by small‐scale variations of the velocity and density but also of the quality factor that describes attenuation. We investigated scattering due to velocity and attenuation perturbations by computing the resolution function or point‐spread function in a homogeneous background model. The resolution function is the migration image of seismic reflection data generated by a point scatterer. We found that the resolution function mixes velocity and attenuation parameter perturbations to the extent that they cannot be reconstructed independently. This is true for a typical seismic setting with sources and receivers at the surface and a buried scatterer. As a result, it will be impossible to simultaneously invert for velocity and attenuation perturbations in the scattering approach, also known as the Born approximation. We proceeded to investigate other acquisition geometries that may resolve the ambiguity between velocity and attenuation perturbations. With sources and receivers on a circle around the scatterer, in 2D, the ambiguity disappears. It still shows up in a cross‐well setting, although the mixing of velocity and attenuation parameters is less severe than in the surface‐to‐surface case. We also consider illumination of the target by diving waves in a background model that has velocity increasing linearly with depth. The improvement in illumination is, however, still insufficient to remove the ambiguity.  相似文献   

Calibration of the specific barrier model to Iranian plateau earthquakes and development of physically based attenuation relationships for Iran   总被引：1，自引：0，他引：1  

H. Zafarani  M. Mousavi  As. Noorzad  A. Ansari 《Soil Dynamics and Earthquake Engineering》2008,28(7):550-576

Earthquake ground-motion relationships for soil and rock sites in Iran have been developed based on the specific barrier model (SBM) used within the context of the stochastic modeling and calibrated against up-to-date Iranian strong-motion data. A total of 171 strong-motion accelerograms recorded at distances of up to 200 km from 24 earthquakes with moment magnitudes ranging from Mw 5.2 to 7.4 are used to determine the region-specific source parameters of this model. Regression analysis was conducted using the “random effects” methodology that considers both earthquake-to-earthquake (inter-event) variability and within-earthquake (intra-event) variability to effectively handle the problem of weighting observations from different earthquakes. The minimization of the error function in each iteration of the “random effects” procedure was performed using the genetic algorithm method. The residuals are examined against available Iranian strong-motion data to confirm that the model predictions are unbiased and that there are no significant residual trends with distance and magnitude. No evidence of self-similarity breakdown is observed between the source radius and its seismic moment. To verify the robustness of the results, tests were performed to confirm that the results are unchanged if the number of observations is changed by removing different randomly selected datasets from the original database. Stochastic simulations, using the derived SBM, are then performed to predict peak ground-motion and response spectra parameters for a wide range of magnitudes and distances. The stochastic SBM predictions agree well with the new empirical regression equations proposed for Iran, Europe and Middle East in the magnitude–distance ranges well represented by the data. It has been shown that the SBM of this study provides unbiased ground-motion estimates over the entire frequency range of most engineering interests (1–10 Hz) for the Iranian earthquakes. Our results are also important for the assessment of hazards in other seismically active environments in the Middle East and Mediterranean regions.  相似文献   

Probabilistic aftershock hazard assessment I: numerical testing of methodological features   总被引：1，自引：1，他引：0  

František Gallovič  Johana Brokešová 《Journal of Seismology》2008,12(1):53-64

Probabilistic aftershock hazard assessment (PAHA, Wiemer, Geoph Res Lett 27:3405–3408, 2000), provided for California within the frame of the STEP project, is based on a methodology, two features of which are addressed in detail: (1) the parameters of Omori’s law and (2) application of attenuation relations in evaluating peak ground velocity exceedence probability. Concerning the first point, we perform a simple parametric study. We assume the generalized Omori’s law by Shcherbakov et al. (Geoph Res Lett 31:L11613, 2004), in which characteristic time c scales with aftershock magnitude. The study shows that, among all the parameters, the hazard is most sensitive to the choice of m* (controlling the overall aftershock productivity) and least sensitive to the scaling of c. We also conclude that the hazard is mainly due to very early (less than 1 day) aftershocks. As regards the second point, we employ various attenuation relations from different tectonic areas to study their effect on the hazard analysis. We conclude that the resulting variations are relatively large, comparable to those obtained for varying m*.  相似文献   

Strong motion uncertainty determined from observed records by dense network in Japan   总被引：2，自引：1，他引：1  

Nobuyuki Morikawa  Tatsuo Kanno  Akira Narita  Hiroyuki Fujiwara  Toshihiko Okumura  Yoshimitsu Fukushima  Aybars Guerpinar 《Journal of Seismology》2008,12(4):529-546

The variation of ground motions at specific stations from events in six narrow areas was inspected by using K-NET and KiK-net records. A source-area factor for individual observation stations was calculated by averaging ratios between observed values for horizontal peak acceleration and velocity, as well as acceleration response spectra for 5% damping, and predicted values using a ground-motion model (usually known as an attenuation relation) by Kanno et al. (Bull Seismol Soc Am, 96:879–897, 2006). Standard deviations between observed and predicted amplitudes after the correction factor are less than 0.2 on the logarithmic scale and decrease down to around 0.15 in the short-period range. Intra-event standard deviation clearly increases with decreasing distance due to differing paths around near source area. Standard deviations may increase with amplitude or decrease with magnitude; however, both amplitude and magnitude of the data are strongly correlated with distance. The standard deviation calculated in this study is obviously much smaller than that of the original ground-motion model, as epistemic uncertainties are minimized by grouping ground motions at specific stations. This result indicates that the accuracy of strong ground motion prediction could be improved if ground-motion models for specified region are determined individually. For this to be possible, it is necessary to have dense strong-motion networks in high-seismicity regions, such as K-NET and KiK-net.  相似文献   

Pilot‐Scale Degradation of Organic Contaminants in a Continuous‐flow Reactor by the Helielectro‐Fenton Method     

Juan Casado  Jordi Fornaguera 《洁净——土壤、空气、水》2008,36(1):53-58

The feasibility of pilot‐scale mineralization of organic pollutants in wastewaters using the Electro‐Fenton® process is demonstrated. The treatment was applied in a continuous‐flow reactor, to solutions of nitrobenzene, 2,4‐D and benzoic acid and to actual wastewaters from a fine chemicals company along with a pulp and paper company. The results showed mineralization yields from 60 to 84% by simply applying the Electro‐Fenton® process. When a subsequent exposure to sunlight was carried out (Helielectro‐Fenton method), this mineralization almost went to completion, except for the effluent from the fine chemicals industry.  相似文献   

印尼强地震引起的同震形变波   总被引：11，自引：1，他引：10  

牛安福  吉平  高福旺  孟国杰 《地震》2006,26(1):131-137

研究了2004年12月26日及2005年3月29日印尼苏门答腊8.7和8.5级地震引起的同震地倾斜、 地应变、 体应变和重力波变化及衰减过程特征, 给出了不同仪器进行的同类观测同震波衰减特性的差异及不同区域衰减过程相近等特性。 对同震形变波衰减特性的研究有助于认识仪器工作参数、 观测点附近的观测环境等对观测结果的影响及理解强地震衰减过程是有意义的。  相似文献   

Seismic attenuation,normal moveout stretch,and low‐frequency shadows underlying bottom simulating reflector events          下载免费PDF全文

José M. Carcione  Ayman N. Qadrouh  Hervé Perroud  Davide Gei  Jing Ba  Stefano Picotti 《Geophysical Prospecting》2018,66(5):857-871

In many cases, the seismic response of bottom‐simulating reflectors is characterised by low frequencies called “low‐frequency shadow”. Generally, this phenomenon is interpreted as attenuation due to partial saturation with free gas. Actually, this frequency loss may have multiple causes, with a normal moveout stretch as a possible candidate. To analyse this phenomenon, we compute synthetic seismograms by assuming a lossy bottom‐simulating layer, with varying quality factor and thickness, bounded by the upper hydrate‐brine/gas‐brine and lower gas‐brine/brine interfaces. First, we estimate the shift of the centroid frequency of the power spectrum as a function of the travelled distance of the seismic pulse. Then, we perform one‐dimensional numerical experiments to quantify the loss of frequency of the seismic event below the bottom‐simulating reflector as a function of the quality factor of the bottom‐simulating layer and its thickness (due to wave interference). Then, we compute shot gathers to obtain the stacked section, with and without the normal moveout stretch correction and with and without the presence of wave attenuation in the bottom‐simulating layer. The results indicate that the low‐frequency shadow due to the normal moveout stretch is stronger than that due to attenuation and may constitute a false indicator of the presence of gas. In fact, often, the low‐frequency shadow overlies events with higher frequencies, in contradiction with the physics of wave propagation. This is particularly evident when the low‐frequency shadow is so extensive that the presence of high frequencies below cannot be justified by the acquisition geometry.  相似文献   

Attenuation of marine seismic interference noise employing a customized U-Net     

Jing Sun  Sigmund Slang  Thomas Elboth  Thomas Larsen Greiner  Steven McDonald  Leiv-J. Gelius 《Geophysical Prospecting》2020,68(3):845-871

Marine seismic interference noise occurs when energy from nearby marine seismic source vessels is recorded during a seismic survey. Such noise tends to be well preserved over large distances and causes coherent artefacts in the recorded data. Over the years, the industry has developed various denoising techniques for seismic interference removal, but although well performing, they are still time-consuming in use. Machine-learning-based processing represents an alternative approach, which may significantly improve the computational efficiency. In the case of conventional images, autoencoders are frequently employed for denoising purposes. However, due to the special characteristics of seismic data as well as the noise, autoencoders failed in the case of marine seismic interference noise. We, therefore, propose the use of a customized U-Net design with element-wise summation as part of the skip-connection blocks to handle the vanishing gradient problem and to ensure information fusion between high- and low-level features. To secure a realistic study, only seismic field data were employed, including 25,000 training examples. The customized U-Net was found to perform well, leaving only minor residuals, except for the case when seismic interference noise comes from the side. We further demonstrate that such noise can be treated by slightly increasing the depth of our network. Although our customized U-Net does not outperform a standard commercial algorithm in quality, it can (after proper training) read and process one single shot gather in approximately 0.02 s. This is significantly faster than any existing industry denoising algorithm. In addition, the proposed network processes shot gathers in a sequential order, which is an advantage compared with industry algorithms that typically require a multi-shot input to break the coherency of the noise.  相似文献   

基于夜光遥感影像的粤港澳地区城市发展时空格局演变     

赵丽娴  李长辉  宋杨  李熙 《热带地理》2020,40(2):243-253

将VIIRS时间序列夜光遥感影像首次应用于粤港澳地区,结合LandScan ^TM人口分布图等辅助数据,采用夜间灯光统计、位序-规模法则以及由基尼系数构建的夜光发展指数等方法,在地市级、区县级2种尺度上对其城市发展空间格局进行分析,探究其城市规模的时空演变情况。结果发现,2012—2018年粤港澳地区所有城市的夜光总量均呈现出增长的态势,但中小城市的增速明显高于大城市,汕尾市的夜光增长率高达310.35%。在位序-规模分析中,地市级与区县级的q值在2012—2018年分别下降了16.86%和13.52%,城市规模分布趋于分散的力量大于趋于集中的力量,城市间规模发展日趋平衡。夜光发展指数同样随时间的变化逐渐降低,城市内部夜光与人口之间的分配水平差距正逐渐弥合,中小城市的发展相对更快。同时,夜光发展指数下降最为显著的几个地级市均位于粤东地区,说明粤东地区近年来正展现出强劲的发展态势。  相似文献