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利用中、小容量气枪组成的立体气枪阵列延迟激发震源和海底地震仪(OBS)在我国北部浅海海域开展了人工地震深部地球物理探测试验.基于水深条件和压制水体虚反射、提升低频能量的需要,使气枪震源有足够的输出能量和高品质子波特性,研究了立体气枪阵列延迟激发震源工作机理,经远场子波理论模拟优选了组合参数并进行了海上试验工作.结果表明,中、小容量气枪组成的立体气枪阵列延迟激发震源,适应了浅水海域的激发环境,降低了由虚反射造成的局部陷波和干扰作用,有效地改善了OBS信号的品质,获得了Ps,Pg,PmP,Pn等多种震相.创新了由中、小容量气枪组成的立体气枪阵列延迟激发震源在浅海区OBS探测中的应用,也填补了南黄海海域深地震探测数据的空白,为南黄海、渤海深部地壳结构研究及含油气盆地形成演化研究提供了重要的基础资料. 相似文献
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Among engineers there is considerable interest in the real-time identification of “events” within time series data with a low signal to noise ratio. This is especially true for acoustic emission analysis, which is utilized to assess the integrity and safety of many structures and is also applied in the field of passive seismic monitoring (PSM). Here an array of seismic receivers are used to acquire acoustic signals to monitor locations where seismic activity is expected: underground excavations, deep open pits and quarries, reservoirs into which fluids are injected or from which fluids are produced, permeable subsurface formations, or sites of large underground explosions. The most important element of PSM is event detection: the monitoring of seismic acoustic emissions is a continuous, real-time process which typically runs 24?h a day, 7?days a week, and therefore a PSM system with poor event detection can easily acquire terabytes of useless data as it does not identify crucial acoustic events. This paper outlines a new algorithm developed for this application, the so-called SEED? (Signal Enhancement and Event Detection) algorithm. The SEED? algorithm uses real-time Bayesian recursive estimation digital filtering techniques for PSM signal enhancement and event detection. 相似文献
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Influencing factors of seismic signals generated by un-tuned large volume airgun array in a land reservoir 总被引：7，自引：0，他引：7 
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下载免费PDF全文 Meng Chen Wei Yang Weitao Wang Baoshan Wang Hongkui Ge Li Chen Yansheng Ding Jiyan Qiao Yong Chen 《地震科学（英文版）》2014,27(4):365-376
Un-tuned large volume airgun array in a water reservoir is recently proposed as a new way to generate seismic waves on land. It can be used to explore the earth velocity structure and its temporal variations as well. However, the characteristics of seismic signals (especially far-field signals) from an airgun array in a reservoir and its affecting factors (firing pressure, airgun towing depth, water level of the reservoir, etc.) has not been adequately studied. We analyzed the seismic data collected from field experiments at Binchuan Transmitting Seismic Station in 2011 and 2013 and found that (1) The similarity of seismic signals decrease with distance, which is most likely induced by the decay of signal amplitude and signal to noise ratio (SNR); (2) The amplitudes of far-field airgun signals are almost linearly proportional to the firing pressure; (3) The towing depth of airgun has less effects on the far-field signals; (4) The amplitudes of far-field airgun signals are proportional to the water level of the reservoir. 相似文献
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The distribution of some microelements (Sr, Si, Ba, Mo, Rb, and Mn) in the surface and deep-sea waters in various parts of the Caspian Sea is considered in comparison with the distribution of salt-forming macroelements. The observed mean concentrations of microelements and their variations over the sea area and with depth indicate to the presence of additional, other than Volga runoff, sources supplying Sr, Ba, U, Rb, and Mn to the Caspian Sea. 相似文献
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Elision and infiltration groundwater of the Northern Caspian basin are described. It is shown that a zone of elision brines with a high formation pressure exists under the Caspian Sea. These brines are shown to penetrate from below the Caspian Sea into the underground beds, carry fluids, and facilitate the formation of hydrocarbon fields. 相似文献
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T. A. Aliev A. M. Abbasov G. G. Mamedova G. A. Guluev F. G. Pashaev 《Seismic Instruments》2013,49(1):64-80
Robust noise technologies for analyzing a seismic acoustic signal that allow using its noise as a carrier of information at the beginning of abnormal seismic processes preceding an earthquake are proposed. A station which receives seismic acoustic signals from the deep strata of the earth with the help of 3–6 km-deep steel bores of dormant oil wells has been designed based on this technology. It monitors the beginning of the latent period of the earthquake development. The experiments carried out at these stations on Qum Island in the Caspian Sea since May 1, 2010 and in the town of Shirvan in the southern region of Azerbaijan since November 20, 2011 confirmed the reliability and validity of the monitoring results and identification of the earthquake in the radius of 300–500 km with a 10–15 h lead as compared to conventional seismic stations. 相似文献
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Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment 下载免费PDF全文
下载免费PDF全文 Valeriya Shulakova Roman Pevzner J. Christian Dupuis Milovan Urosevic Konstantin Tertyshnikov David E. Lumley Boris Gurevich 《Geophysical Prospecting》2015,63(1):55-69
4D seismic is widely used to remotely monitor fluid movement in subsurface reservoirs. This technique is especially effective offshore where high survey repeatability can be achieved. It comes as no surprise that the first 4D seismic that successfully monitored the CO2 sequestration process was recorded offshore in the Sleipner field, North Sea. In the case of land projects, poor repeatability of the land seismic data due to low S/N ratio often obscures the time‐lapse seismic signal. Hence for a successful on shore monitoring program improving seismic repeatability is essential. Stage 2 of the CO2CRC Otway project involves an injection of a small amount (around 15,000 tonnes) of CO2/CH4 gas mixture into a saline aquifer at a depth of approximately 1.5 km. Previous studies at this site showed that seismic repeatability is relatively low due to variations in weather conditions, near surface geology and farming activities. In order to improve time‐lapse seismic monitoring capabilities, a permanent receiver array can be utilised to improve signal to noise ratio and hence repeatability. A small‐scale trial of such an array was conducted at the Otway site in June 2012. A set of 25 geophones was installed in 3 m deep boreholes in parallel to the same number of surface geophones. In addition, four geophones were placed into boreholes of 1–12 m depth. In order to assess the gain in the signal‐to‐noise ratio and repeatability, both active and passive seismic surveys were carried out. The surveys were conducted in relatively poor weather conditions, with rain, strong wind and thunderstorms. With such an amplified background noise level, we found that the noise level for buried geophones is on average 20 dB lower compared to the surface geophones. The levels of repeatability for borehole geophones estimated around direct wave, reflected wave and ground roll are twice as high as for the surface geophones. Both borehole and surface geophones produce the best repeatability in the 30–90 Hz frequency range. The influence of burying depth on S/N ratio and repeatability shows that significant improvement in repeatability can be reached at a depth of 3 m. The level of repeatability remains relatively constant between 3 and 12 m depths. 相似文献
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基于青藏高原东北缘密集宽频带野外流动观测台阵以及固定台站资料,利用双差层析成像方法对地震位置和研究区的地壳速度结构进行了反演.最终用于联合反演的地震事件合计9644个.结果显示青藏高原东北缘速度结构具有明显的横向不均匀性.从整体上看,青藏高原地区表现为低速异常,鄂尔多斯表现为高速异常,而扬子地块亦表现为高速异常.不同深度处速度结构表现不一致,同一深度处P波速度结构和S波速度结构也有明显差异.由西秦岭北缘断裂带、临潭-宕昌断裂以及礼县-罗家堡断裂围限的地震活动强烈的区域中,P波速度结构由深度0 km时呈现的低速异常,逐渐过渡到5 km时高低速相间分布的特征;而S波速度结构在此区域中,由近地表0 km时高低速相间分布的特征,逐渐过渡到30 km时几乎表现为低速异常.2017年8月8日九寨沟7级地震所在的塔藏断裂、岷江断裂和雪山断裂围限区域,在深度20 km处的P波速度结构和周围存在明显差异,九寨沟地震处于高速异常与低速异常的过渡带内.此外,2013年7月22日发生在青藏高原东北缘的岷漳县6.6级地震,震源区所在的临潭-宕昌断裂附近的P波速度结构在15 km深度处也有明显特征,震源位置所在区域也处于高低速过渡带.该区域这种地壳内部高低速过渡带可能是应力比较容易积累而发生中强地震的一个重要场所. 相似文献
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Seismic data recorded in the upper mantle triplication distance range between 10° and 30° are generated by wave propagation through complex upper mantle structure. They can be used to place constraints on seismic velocity structures in the upper mantle, key seismic features near the major discontinuities, and anisotropic structure varying with depth. In this paper, we review wave propagation of the upper mantle triplicated phases, how different key seismic features can be studied using upper mantle triplicated data, and the importance of those seismic features to the understanding of mantle temperature and composition. We present two examples of using array triplicated phases to constrain upper mantle velocity structures and detailed features of a certain discontinuity, with one for a shallow event and the other for deep events. For the shallow event, we present examples of how the array triplication data can be used to constrain several key properties of the upper mantle: existence of a lithospheric lid, existence of a low velocity zone beneath the lithospheric lid, and P/S velocity ratio as a function of depth. For deep events, we show examples of how array triplication data can be used to constrain the detailed structures of a certain discontinuity: velocity gradients above and below the discontinuity, velocity jumps across the discontinuity and depth extents of different velocity gradients. We discuss challenges of the upper mantle triplication study, its connection to other approaches, and its potential for further studying some other important features of the mantle: the existence of double 660-km discontinuities, existence of low-velocity channels near major discontinuities and anisotropy varying with depth. 相似文献
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利用区域地震台网数字波形资料,对2017年9月23日朝鲜ML3.4地震进行地震矩张量反演计算与参数稳定性评估,获得了此次地震的震源机制解.结果表明,地震矩心深度为3 km,标量地震矩为1.34×1014 N·m,矩震级为MW3.4.地震矩张量结果分解后,双力偶分量（DC）为96.4%,补偿线性矢量偶极分量（CLVD）为-0.8%,震源体体积变化的各向同性分量（ISO）为-2.8%.主压应力P轴方位角为144°,倾角为74°,主张应力T轴方位角为341°,倾角为15°.其中一个节面的参数为：走向248°,倾向60°,滑动角-94°.地震震源体积变化分量很小,震源机制类型属于典型的由断层剪切位错引起的正断层型地震事件,且主张应力T轴方向与区域近地表应变率场方向一致.由于朝鲜2017年9月3日核试验释放的能量对局部区域应力场进行了扰动,致使核试验场附近地壳岩体处于破裂的临界状态,2017年9月23日朝鲜ML3.4地震事件可能是区域应力场作用下的一次山体滑动事件. 相似文献
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v--v Continuous seismic threshold monitoring is a technique that has been developed over the past several years to assess the upper magnitude limit of possible seismic events that might have occurred in a geographical target area. The method provides continuous time monitoring at a given confidence level, and can be applied in a site-specific, regional or global context.¶In this paper (Part 1) and a companion paper (Part 2) we address the problem of optimizing the site-specific approach in order to achieve the highest possible automatic monitoring capability of particularly interesting areas. The present paper addresses the application of the method to cases where a regional monitoring network is available. We have in particular analyzed events from the region around the Novaya Zemlya nuclear test site to develop a set of optimized processing parameters for the arrays SPITS, ARCES, FINES, and NORES. From analysis of the calibration events we have derived values for beam-forming steering delays, filter bands, short-term average (STA) lengths, phase travel times (P and S waves), and amplitude-magnitude relationships for each array. By using these parameters for threshold monitoring of the Novaya Zemlya testing area, we obtain a monitoring capability varying between mb 2.0 and 2.5 during normal noise conditions.¶The advantage of using a network, rather than a single station or array, for monitoring purposes becomes particularly evident during intervals with high global seismic activity (aftershock sequences), high seismic noise levels (wind, water waves, ice cracks) or station outages. For the time period November-December 1997, all time intervals with network magnitude thresholds exceeding mb 2.5 were visually analyzed, and we found that all of these threshold peaks could be explained by teleseismic, regional, or local signals from events outside the Novaya Zemlya testing area. We could therefore conclude within the confidence level provided by the method, that no seismic event of magnitude exceeding 2.5 occurred at the Novaya Zemlya test site during this two-month time interval.¶As an example of particular interest in a monitoring context, we apply optimized threshold processing of the SPITS array for a time interval around 16 August 1997 mb 3.5 event in the Kara Sea. We show that this processing enables us to detect a second, smaller event from the same site (mb 2.6), occurring about 4 hours later. This second event was not defined automatically by standard processing. 相似文献
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自2006年至2017年,朝鲜民主主义人民共和国在中朝边界地区的试验场进行了6次地下核试验.本文综合报道根据东北亚地区的宽频带数字地震资料利用地震学方法对这六次地下核爆炸的研究.结果表明,朝鲜地下核试验在区域台网产生的地震记录具有典型浅源爆炸的特征.针对上述资料发展了处理核爆数据的方法并据此得出各次朝鲜核爆的地震学参数,包括事件识别、当量测定、以及震中相对定位等.对6次核爆和4次天然地震P/S类型谱振幅比的统计分析表明,2 Hz以上台网平均谱振幅比可以正确地将朝鲜核爆从天然地震中识别出来,从而有效监测在朝鲜半岛进行的当量大于0.5 kt的地下核试验.同时也发现,建立在体波-面波震级比之上的识别方法不适用于朝鲜核试验场.通过建立中朝边界地区基于Lg波的体波震级系统,计算了各次朝鲜核试验的体波震级mb（Lg）,并由此估计了它们的地震学当量,其值介于0.5 kt至60 kt之间.由于缺少爆炸埋藏深度的数据,上述当量有可能被低估,因而有必要对深度影响做进一步研究.以第一次爆炸的位置为参考震中,利用Pn波相对走时数据和高精度相对定位方法获得了各次核爆在试验场中的精确定位. 相似文献
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在哈萨克斯坦的5个现代化数字地震台阵中,4个小孔径同心圆结构的IMS简约型台阵建设、维护方便,全方位监测能力强,1个十字型结构中等孔径台阵,因对特定方位敏感,对更远距离已知核试验点监测能力更强。台阵观测场地均处于完整稳定的构造块体,内部岩石迁移性良好,噪声水平低,保证了对远处微弱地震信号的监测及各子台信号的相似性。地震检波器良好的性能,保证了台阵的地震信号记录质量和数据研究基础。采用卫星传输方式,有效保证了数据的实时性。哈萨克斯坦的地震台阵,其选址、布局、仪器、数据传输等台阵建设,为中国地震台阵发展建设提供了经验借鉴。 相似文献
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利用首都圈数字地震台网接收人工地震信号,进行地下结构研究具有重要意义.但人工震源释放的能量小,激发的地震波以短周期为主,因此本文较全面地研究了地震台网对短周期微弱信号（1～20 Hz）的检测能力：(1) 分析了台网的背景噪声,结果表明基岩台址的地震台噪声比沉积盖层台址的地震台噪声低约13 dB,这相当于近1个震级的检测阈值;夜间的噪声比白天低约5 dB;噪声有逐年增高的趋势,2006年比2001年噪声提高约4 dB.(2 )分析了在台网内进行的药量为25 kg的陆地井下爆破实验,一次爆破相当于0.69级（ML）的天然地震,有18个地震台可辨认爆炸产生的Pg、Pm或Pc波;离爆破点218 km的基岩台,仍可以接收到振幅只有1.6 nm 的Pm波,这个结果可为地震勘探实际工作提供参考.(3) 研究了台网外核爆试验的信号特征,2006年发生在朝鲜的地下核试验是一次检验台网检测微弱信号能力的好机会.波形记录经1～5Hz滤波后,台网中噪声小的18个基岩台可以清晰辨认核爆破产生的P波或Lg波,P波平均振幅为16 nm,计算的平均震级为mb4.3,和NEIC给出的震级相同;分析还表明背景噪声是影响台站信号检测能力的主要因素之一. 相似文献
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Avadh Ram 《Physics of the Earth and Planetary Interiors》1982,28(3):242-250
About fifty earthquakes in the distance range 40–70° and azimuthal range 45–120° from the Celebes, Philippines, Mariana and Kurile Island regions, and recorded at Gauribidanur seismic array in southern India, were used in the present study. Measurements on slowness and apparent azimuths were made on the first 30 s of the short period P-wave trains using an adaptive processing technique. Analysis of this data set has revealed no strong evidence for any triplications in the travel-time curve over the ranges in question. The P-wave velocity increases continuously with an almost uniform gradient below 1000 km depth range and is in very close agreement with the JB model. Almost all the observed slowness values of the events were anomalously low and consistent suggesting that they are caused by some azimuthal dependent structure near the array. 相似文献
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The Ludian County of Yunnan Province in southwestern China was struck by an MS6.5 earthquake on August 3, 2014, which was another destructive event following the MS8.0 Wenchuan earthquake in 2008, MS7.1 Yushu earthquake in 2010, and MS7.0 Lushan earthquake in 2013. National Strong-Motion Observation Network System of China collected 74 strong motion recordings,which the maximum peak ground acceleration recorded by the 053 LLT station in Longtoushan Town was 949 cm/s2 in E–W component. The observed PGAs and spectral ordinates were compared with ground-motion prediction equation in China and the NGA-West2 developed by Pacific Earthquake Engineering Researcher Center. This earthquake is considered as the first case for testing applicability of NGA-West2 in China. Results indicate that the observed PGAs and the 5 % damped pseudo-response spectral accelerations are significantly lower than the predicted ones. The field survey around some typical strong motion stations verified that the earthquake damage was consistent with the official isoseismal by China Earthquake Administration. 相似文献
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Comparison of crustal and upper mantle heterogeneity in different time periods: Indonesian subduction zone to northern Australia 下载免费PDF全文
下载免费PDF全文 Earthquake events from the Indonesian subduction zone recorded in northern Australia show a long and high-frequency coda associated with both P and S waves. Regional events recorded by Warramunga array in northern Australia can separate out wave propagation through the mantle by focusing on the coherent signal across the medium-aperture array. Most of the incoherent wave components result from structures in the vicinity of the array with small-scale lengths of 1–2 km or smaller. The coherent phases with relatively rapid changes in waveforms are associated with the scattering of seismic waves by crustal and mantle heterogeneity, but in some case can be related to structural effects near the source. As the depth of the source increases, the coherent portion of the seismic wavefield tends to become much simpler, which suggests that the heterogeneity tends to weaken at depth with larger-scale length. We compare the coherent signal features of earthquakes from the Indonesian subduction zone that have occurred in recent years with those in the early 1980s, first studied by Kennett (Phys Earth Planet Inter 47: 319–332, 1987). The general characteristics of the coherent signal variation with depth in recent years are the same as those observed in 1980s, but the variations are larger. This change suggests a stringer variation in heterogeneity with depth than before, which may bear important information about the dynamic processes and evolution of the crust and upper mantle. 相似文献