随钻偶极远探测声场的辐射特性          下载免费PDF全文

曹景记  唐晓明  苏远大  魏周拓  庄春喜 《地球物理学报》2016,59(9):3503-3513

本文对偶极横波远探测技术在随钻测井中的应用进行了探讨.对于随钻远探测而言,井中声源向井外地层中的辐射性能是它的主控因素.本文从井孔内外声场出发,考察了随钻和电缆测井中偶极声源的辐射效率,即声源产生的辐射波能流与沿井传播的导波能流之比;分析了声源的远场辐射指向性;基于声源辐射与接收之间的互易性,快速模拟和处理了随钻测井下SH和SV横波远探测波形.研究结果表明,随钻条件下SH和SV横波的最大辐射效率受钻铤的影响较电缆的情况降低了70%左右,且横波最大辐射效率对应的优势激发频率也从电缆的3.5kHz降为2.5kHz左右;虽然随钻偶极的横波辐射效率明显降低,但由理论模拟的随钻远探测数据的成像结果可知,声源辐射到地层中的横波能量仍足以探测井外反射体,表明随钻偶极远探测技术在理论上是可行的,本文结果为随钻偶极远探测测井提供了理论依据.  相似文献   

乳山震群震源谱参数的稳健反演          下载免费PDF全文

郑建常  王鹏  徐长朋  许崇涛  刘凯  李冬梅  李翠芹 《地球物理学报》2016,59(11):4100-4112

本文引入截止频率f_(max)提出基于Brune模型的高频截止(High-Cut)模型,采用两步反演的方法来拟合求解震源谱的特征参数,并给出其误差范围;实际应用显示该模型的理论谱对观测谱有很好的拟合,可明显改善拐角频率识别的准确度.将该方法应用于2013—2015年的乳山震群,计算了乳山震群25次M_L≥3.0事件的震源参数(地震矩、破裂半径、应力降等),进一步对乳山震群的震源破裂特性进行了讨论.结果显示:拐角频率、应力降与震源尺度大小明显相关;高频衰减系数γ与震源破裂区的复杂程度以及破裂性质有关,当观测记录中混杂有其他事件的波形或微破裂时,高频衰减系数大于2,并且不确定性增大;截止频率f_(max)与地震大小存在一定相关性;使用Beresnev(2001)给出的震源半径计算公式,得到的乳山震群的结果显示与华北地区的经验关系较为一致;乳山震群的应力降明显偏小(最大不超过0.15 MPa),一方面反映了震中区域的构造应力水平,另一方面可能还意味着此次震群是一个相对非耗散型的脆性破裂过程,属于低摩擦应力的断层作用.  相似文献   

Analytical modelling of near‐source pulse‐like seismic demand for multi‐linear backbone oscillators          下载免费PDF全文

Georgios Baltzopoulos  Dimitrios Vamvatsikos  Iunio Iervolino 《地震工程与结构动力学》2016,45(11):1797-1815

Nonlinear static procedures, which relate the seismic demand of a structure to that of an equivalent single‐degree‐of‐freedom oscillator, are well‐established tools in the performance‐based earthquake engineering paradigm. Initially, such procedures made recourse to inelastic spectra derived for simple elastic–plastic bilinear oscillators, but the request for demand estimates that delve deeper into the inelastic range, motivated investigating the seismic demand of oscillators with more complex backbone curves. Meanwhile, near‐source (NS) pulse‐like ground motions have been receiving increased attention, because they can induce a distinctive type of inelastic demand. Pulse‐like NS ground motions are usually the result of rupture directivity, where seismic waves generated at different points along the rupture front arrive at a site at the same time, leading to a double‐sided velocity pulse, which delivers most of the seismic energy. Recent research has led to a methodology for incorporating this NS effect in the implementation of nonlinear static procedures. Both of the previously mentioned lines of research motivate the present study on the ductility demands imposed by pulse‐like NS ground motions on oscillators that feature pinching hysteretic behaviour with trilinear backbone curves. Incremental dynamic analysis is used considering 130 pulse‐like‐identified ground motions. Median, 16% and 84% fractile incremental dynamic analysis curves are calculated and fitted by an analytical model. Least‐squares estimates are obtained for the model parameters, which importantly include pulse period T_p. The resulting equations effectively constitute an R ? μ ? T ? T_p relation for pulse‐like NS motions. Potential applications of this result towards estimation of NS seismic demand are also briefly discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

汶川地震发震断层破裂触发过程   总被引：3，自引：1，他引：2       下载免费PDF全文

贺鹏超  沈正康 《地球物理学报》2014,57(10):3308-3317

2008年汶川大地震造成北川断裂、彭灌断裂、小渔洞断裂等多条断裂的破裂,呈现出复杂的破裂过程. 对此,以往地震学的研究没有对于各个发震断层的破裂先后顺序给出充分论证. 本文计算由于断层破裂在其他断层段上造成库仑应力的变化,根据其相互触发关系确定断层可能的破裂顺序. 结果表明,各断裂带可能的发震顺序为:主震在北川断裂南端(小渔洞断裂以南的北川断裂虹口段)起始,造成北川断裂的后续段落龙门山镇-清平段和彭灌断裂同时破裂,进而触发小渔洞断裂发生破裂.  相似文献   

Spatial-temporal Variations of H2 Concentration in Soil Gas in the Seismic Fault Zone Produced by the Wenchuan MS 8.0 Earthquake     

Zhou Xiaocheng  Shi Hongyu  Chen Chao  Zeng Linghua  Sun Fengxia  Li Jing  Chen Zhi  Lü  Chaojia  Huang Dan  Du Jianguo 《地球科学进展》2017,32(8):818-827

Degassing of Hydrogen (H₂) from fault may be a good indicator of fault activity. The concentration of H₂ in soil gas in the seismic surface rupture zone produced by the Wenchuan M_S 8.0 earthquake was investigated in twenty three measuring regions in order to explore the relationship between the spatio-temporal variations of H₂ concentration in soil gas along the seismic rupture zone and the vertical displacements and aftershocks activities. The results indicated: ① the sources of H₂ were directly related to from the release of natural gas reservoirs; ②the average concentration of H₂ in soil gas spatially decreased from Yingxiu to Nanba; ③the magnitudes of the H₂ concentration anomalies declined significantly with time. It is very significant to study the variation tendency of atmospheric environment with further research of degassing of H₂ from faults.  相似文献   

Near‐source seismic demand and pulse‐like records: A discussion for L'Aquila earthquake     

Eugenio Chioccarelli  Iunio Iervolino 《地震工程与结构动力学》2010,39(9):1039-1062

Rupture directivity effects in ground motion are known since many years to both seismologists and earthquake engineers, i.e. in sites that are in a particular geometrical configuration with respect to the rupture, the velocity fault‐normal signals may show a large pulse which occurs at the beginning of the record and contains the most of energy. The results are waveforms different from ordinary ground motions recorded in the far field or in geometrical conditions not favorable with respect to directivity. Current attenuation laws are not able to capture such effect well, if at all, and current probabilistic seismic hazard analysis is not able to predict the resulting peculiar spectral shape. Moreover, it is believed that structures with dynamic behavior in a range of periods related to the pulse period may be subjected to underestimated seismic demand. In the paper this is investigated and increments in both elastic and inelastic seismic actions are quantified using a large dataset of records, from the next generation attenuation project (NGA), in which a fraction is comprised of velocity pulses identified in other studies. These analyses employ recently developed tools and procedures to assess directivity effects and to quantify the associated threat in terms of seismic action on structures. Subsequently, the same tools are used in one of the first attempts to identify near‐source effects in the data recorded during a normal faulting earthquake, the mainshock of the recent Abruzzo (central Italy) sequence, leading to conclude that pulse‐like effects are likely to have occurred in the event, that is (1) observation of pulse‐like records in some near‐source stations is in fair agreement with existing predictive models, (2) the increment in seismic demand shown by pulse‐like ground motion components complies with the results of the analysis of the NGA data, and (3) seismic demand in non‐impulsive recordings is generally similar to what expected for ordinary records. The results may be useful as a benchmark for inclusion of near‐source effect in design values of seismic action and structural risk analysis. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The displacement coefficient method in near‐source conditions          下载免费PDF全文

Georgios Baltzopoulos  Eugenio Chioccarelli  Iunio Iervolino 《地震工程与结构动力学》2015,44(7):1015-1033

The use of nonlinear static procedures for performance‐based seismic design (PBSD) and assessment is a well‐established practice, which has found its way into modern codes for quite some time. On the other hand, near‐source (NS) ground motions are receiving increasing attention, because they can carry seismic demand systematically different and larger than that of the so‐called ordinary records. This is due to phenomena such as rupture forward directivity (FD), which can lead to distinct pulses appearing in the velocity time‐history of the ground motion. The framework necessary for taking FD into account in probabilistic seismic hazard analysis (PSHA) has recently been established. The objective of the present study is to discuss the extension of nonlinear static procedures, specifically the displacement coefficient method (DCM), with respect to the inelastic demand associated with FD. In this context, a methodology is presented for the implementation of the DCM toward estimating NS seismic demand, by making use of the results of NS‐PSHA and a semi‐empirical equation for NS‐FD inelastic displacement ratio. An illustrative application of the DCM, with explicit inclusion of NS‐pulse‐like effects, is given for a set of typical plane R/C frames designed under Eurocode provisions. Different scenarios are considered in the application and nonlinear dynamic analysis results are obtained and discussed with respect to the static procedure estimates. Conclusions drawn from the results may help to assess the importance of incorporating NS effects in PBSD. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Response spectra for nuclear structures on rock sites considering the near-fault directivity effect     

Longjun Xu  Shengchao Yang  Lili Xie 《地震工程与工程振动(英文版)》2010,9(3):357-365

Near-fault ground motions, potentially with large amplitude and typical velocity pulses, may significantly impact the performance of a wide range of structures. The current study is aimed at evaluating the safety implications of the near-fault effect on nuclear power plant facilities designed according to the Chinese code. To this end, a set of nearfault ground motions at rock sites with typical forward-directivity effect is examined with special emphasis on several key parameters and response spectra. Spectral comparison of the selected records with the Chinese and other code design spectra was conducted. The bi-normalized response spectra in terms of different corner periods are utilized to derive nuclear design spectra. It is concluded that nuclear design spectra on rock sites derived from typical rupture directivity records are significantly influenced both by the earthquake magnitude and the rupture distance. The nuclear design spectra specified in the code needs to be adjusted to reflect the near-fault directivity effect of large earthquakes.  相似文献   

织金煤田西南矿区菱铁矿产出形态及指相意义   总被引：1，自引：0，他引：1  

周国正 《中国煤炭地质》2009,(5):17-19

织金煤田西南矿区龙潭组、长兴组广泛发育菱铁矿层。在前人研究成果的基础上,对菱铁矿层赋存特征及沉积相进行了分析,认为区内菱铁矿可归纳为9种形态,其产出的沉积相有草甸相、沙泥潮坪相、淡化泻湖相、沿坝砂坝相、开阔海碳酸盐台地潮坪相,且多数形态具有指相意义。这一结论对区内沉积环境研究起到重要作用。  相似文献   

Influence of interaction between small asperities on various types of slow earthquakes in a 3-D simulation for a subduction plate boundary   总被引：3，自引：1，他引：2  

Keisuke Ariyoshi  Takane Hori  Jean-Paul Ampuero  Yoshiyuki Kaneda  Toru Matsuzawa  Ryota Hino  Akira Hasegawa 《Gondwana Research》2009,16(3-4):534-544

Recently, the occurrence of slow earthquakes such as low-frequency earthquakes and very low-frequency earthquakes have been recognized at depths of about 30 km in southwest Japan and Cascadia. These slow earthquakes occur sometimes in isolation and sometimes break into chain-reaction, producing tremor that migrates at a speed of about 5–15 km/day and suggesting a strong interaction among nearby small asperities. In this study, we formulate a 3-D subduction plate boundary model with two types of small asperities chained along the trench at the depth of 30 km. Our simulation succeeds in representing various types of slow earthquakes including low-frequency earthquakes and rapid slip velocity in the same asperity, and indicates that interaction between asperities may cause the very low-frequency earthquakes. Our simulation also shows chain reaction along trench with propagation speed that can be made consistent with observations by adjusting model parameters, which suggests that the interactions also explain the observed migration of slow earthquakes.  相似文献