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采用中日合作，分别布设于东川垂直竖井中地下200ｍ、100ｍ 和地面３个位置的高精度数字化地震仪记录的地方震资料（震中距8.5～95ｋｍ，震级ML1.3～5.1），用频谱比的分析方法计算了东川地区不同深度（－100ｍ 和地面）的场地放大因子．在８个频率（f ＝0.75，1.0，1.5，2，3，4，5和12Ｈｚ）上所对应的在-100ｍ 处的3个分向（N-S，E-W，U-D）的场地放大因子（与-200ｍ 处相比），当0.75Ｈｚ f 2Ｈｚ时，为1.0～1.49；当2Ｈｚ＜ f ＜12Ｈｚ时，为0.47～0.99；在地面，3个分向在8个频率上所对应的场地放大因子（与-200ｍ 处相比）均大于1，其值为1.6～7.63．-100ｍ 处的Ｓ波和尾波场地放大因子与地面的Ｓ波和尾波的场地放大因子的相关系数，当0.75Ｈｚ f 2Ｈｚ频段时，分别为0.82和0.81；当2Ｈｚ＜ f＜12Ｈｚ频段时，分别为0.47和0.45． 相似文献
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R. E. Abercrombie 《Pure and Applied Geophysics》1998,153(2-4):475-487
—Earthquake seismograms recorded by instruments in deep boreholes have low levels of background noise and wide signal bandwidth. They have been used to extend our knowledge of crustal attenuation both in the near-surface and at seismogenic depths. Site effects are of major importance to seismic hazard estimation, and the comparison of surface, shallow and deep recordings allows direct determination of the attenuation in the near-surface. All studies to date have found that Q is very low in the near-surface (～ 10 in the upper 100 m), and increases rapidly with depth. Unlike site amplification, attenuation at shallow depths exhibits little dependence on rock-type. These observations are consistent with the opening of fractures under decreasing lithostatic pressure being the principal cause of the severe near-surface attenuation. Seismograms recorded in deep boreholes are relatively unaffected by near-surface effects, and thus can be used to measure crustal attenuation to higher frequencies (≥ 100 Hz) than surface recordings. Studies using both direct and coda waves recorded at over 2 km depth find Q to be high (～ 1000) at seismogenic depths in California, increasing only weakly with frequency between 10 and 100 Hz. Intrinsic attenuation appears to be the dominant mechanism. These observations contrast with those of the rapidly increasing Q with frequency determined from surface studies in the frequency range 1 to 10 Hz. Further work is necessary to constrain the factors responsible for this apparent change in the frequency dependence of Q, but it is clearly unwise to extrapolate Q estimates made below about 10 Hz to higher frequencies. 相似文献
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在南北地震带地区,USGS全球地震目录中存在一些震源深度大于30km的地震.这些地震的震源深度是否可靠,对于研究这一地区的孕震机制、岩石圈强度和构造演化等科学问题具有重要意义.本文以南北地震带2012年发生的5个4~5级地震为例,利用区域地震台网的波形数据,基于sPL深度震相、短周期瑞利面波以及CAP等独立方法测定了其震源深度.结果表明:sPL深度震相和CAP方法给出的震源深度比较一致,差别小于2~3km,能够得到比较可靠的震源深度;短周期瑞利面波及其与P波振幅比也确定了地震震源深度较浅的特征.本文研究结果显示:宁夏会宁4.7级、云南富民4.8级和四川会东4.7级地震的震源深度约为8~12km左右,仍为发生于上地壳的地震,USGS地震目录给出的30km甚至更深的震源深度存在明显偏差;对于四川隆昌4.6和4.9级地震,本文给出的震源深度为1~2km,属于极浅源地震,USGS地震目录给出的10km和35km的震源深度结果尚需进一步改进. 相似文献
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由于印度-欧亚板块碰撞,位于板块边界带的喜马拉雅地区大震频繁,但对其活动性的认识仍十分有限.2015年4月25日尼泊尔中东部地区时隔80年再次发生8级地震,为研究板缘地震提供了一次难得机遇.本文用西藏和尼泊尔的GPS连续观测数据和全球分布的远震地震波记录联合反演此次特大地震的破裂过程,结果显示此次地震发生在印度板块与青藏高原接触边界面——喜马拉雅主滑脱断层上.北倾11°、近东西(295°)走向的断层面破裂约100km长(博卡拉到加德满都),130km宽(从加德满都深入我国西藏吉隆县),破裂以逆冲滑动为主,平均幅度达到2.4m,释放的地震矩高达9.4×1020 N·m.反演结果还显示,震源体主要破裂分布深度范围为5~25km,应无地表破裂,属于一次盲地震.基于GPS资料推测的地壳现今运动速率及1833年地震的震源位置,我们推测地震在此次地震破裂区域复发的周期可能为150~200a,而极震区以南的深部滑脱断层仍保持闭锁,未来仍有导致灾害性大震的可能性. 相似文献
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IntroductionSeismic wave is an important information source to analyze and study seismic source and internal structure of the earth. Studies of wave on different frequency ranges can provide many features of seismic source and internal structure of the earth. In recent years in quantitative study of seismic wave seismologists at home and abroad have developed a wide study field on the coda. Especially seismologists have done a lot of work in coda geneses, mechanism and its attenuation to explo… 相似文献
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In western India during the Bhuj earthquake (Mw 7.6) on January 26, 2001, the Anjar City at ~30 km southwest of Bhuj experienced three types of damage scenario: severely damaged, less damaged and non-damaged. Similar damage patterns were also observed for the 1819 (Mw 7.8) and the 1956 (Mw 6.0) earthquakes. Microtremor array measurements were conducted in and around the Anjar city to examine the strength of soil structures and damage pattern. Significant differences are observed in frequencies and amplitudes in horizontal-to-vertical spectral ratio (HVSR) using microtremor measurements. The severely- damaged site shows two peak amplitudes: 2.8 at 1.2 Hz; and 4.0 at 8.0 Hz. The less-damaged site also shows two amplitudes: 2.5 and 2.1 at 1.4 Hz; and 2.0 Hz, respectively. The non-damaged site, on the other hand, shows that the HVSR curves become almost flatter. Similar results for three types of damage scenario based on analyses of earthquake records are also observed for the study area. The microtremor array measurements has revealed shear wave velocity Vs≥400 m/s at 18 m depth in the non-damaged, at 40 m in the less-damaged and at 60 m depth in the severely-damaged sites. The site amplitudes and the Vs values show a good correlation with the soil characteristics and damage pattern, suggesting that strength of soil layers at varying depths is a dictating factor for the estimate of the earthquake risk evaluation of the area under study. 相似文献
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The Q-factor estimates of the Earth’s crust and upper mantle as the functions of frequency (Q(f)) are obtained for the seismic S-waves at frequencies up to ~35 Hz. The estimates are based on the data for ~40 earthquakes recorded by the Kislovodsk seismic station since 2000. The magnitudes of these events are MW > 3.8, the sources are located in the depth interval from 1 to 165 km, and the epicentral distances range from ~100 to 300 km. The Q-factor estimates are obtained by the methods developed by Aki and Rautian et al., which employ the suppression of the effects of the source radiation spectrum and local site responses in the S-wave spectra by the coda waves measured at a fixed lapse time (time from the first arrival). The radiation pattern effects are cancelled by averaging over many events whose sources are distributed in a wide azimuthal sector centered at the receiving site. The geometrical spreading was specified in the form of a piecewise-continuous function of distance which behaves as 1/R at the distances from 1 to 50 km from the source, has a plateau at 1/50 in the interval from 50–70 km to 130–150 km, and decays as \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {\sqrt R }}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\sqrt R }$}}\) beyond 130–150 km. For this geometrical spreading model and some of its modifications, the following Q-factor estimates are obtained: Q(f) ~ 85f0.9 at the frequencies ranging from ~1 to 20 Hz and Q(f) ~ 75f1.0 at the frequencies ranging from ~1 to 35 Hz. 相似文献
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Introduction It is well known that the occurrence of moderate and strong earthquakes and the distribution of seismically active belts are most directly related to deep crustal faults. Therefore, studying geometrical spreading and physical state of medium of deep crustal faults has always been a major subject in earthquake science. It is not only of great significance to the understanding of deep structural background and seismogenic mechanism of strong earthquakes, but also of great help to se… 相似文献
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Burying receivers for improved time‐lapse seismic repeatability: CO2CRC Otway field experiment 
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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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上地幔温度是控制地幔流变性和动力学过程的关键参数之一.本文利用高分辨率S波地震层析成像速度结果,基于岩石温度与地震波速度的关系,研究了华北地区上地幔50~300 km深度范围内的温度分布和"热"岩石圈厚度.为了验证结果的可靠性,本文用计算的上地幔60 km深度处的温度作为底面约束,得到了相应的地表热流.计算地表热流与观测地表热流之间符合程度较好,相对误差大部分都在地表热流观测误差范围之内.通过对上地幔的温度分布进行分析,我们研究发现:(1)在上地幔浅部,温度与地表构造之间有很好的对应关系.在小于170 km的深度上,温度呈现东高西低的分布态势.温度较高的区域集中在东部的河淮盆地、渤海湾盆地、华北平原和中部陆块的交界处、西部鄂尔多斯高原北缘的银川―河套地堑以及阴山地区,同时,这些地区的岩石圈厚度也相应较薄,大约为80~100 km;(2)西部的鄂尔多斯高原是整个华北地区岩石圈地幔温度最低的地区,比东部地区低200~400 ℃,岩石圈厚度相应最厚,平均岩石圈厚度达到140~150 km,最厚处超过160 km.(3)在170 km以下的软流圈地幔部分,温度分布发生反转,西部温度高于东部,表明东、西部陆块在地质历史时期经历了不同的深部地幔动力学过程. 相似文献
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Records of the Niigata Chuetsu-Oki earthquake (July, 16, 2007, M w?=?6.6, depth ~17?km) and its aftershocks from seismic vertical arrays deployed at the territory of the Kashiwazaki-Kariwa nuclear power plant (~15?km from the fault) are used to study the soil behavior down to ~250?m during strong ground motion. Nonlinear models of soil behavior during the main shock and six aftershocks are constructed, and stresses and strains induced by the strong motion in the soil layers at various depths are estimated. The data are processed using the method developed by Pavlenko and Irikura (Bull Seismol Soc Am 96(6): 2131–2145, 2003) and previously applied for studying the soil behavior in near-fault zones during the 1995 Kobe and 2000 Tottori earthquakes. A rather good agreement between the recorded and simulated acceleration time histories testifies to the validity of the obtained vertical distributions of stresses and strains in soil layers. In the upper, softer layers (~45?m) at the territory of the plant, the shear moduli were reduced by ~30–35% during the main shock and by ~1.5–3% during the aftershocks. The constructed models of soil behavior can be used in scenario earthquake shaking maps of Japan where, based on source modeling parameters, the level of strong motion can be evaluated for the territory of the power plant in future earthquakes with various magnitudes and fault planes. Using methods of stochastic finite-fault modeling of ground motions from the Chuetsu-Oki earthquake, we estimated input motion to the soil layers during the main shock and found that it differs from the imposed motion (recorded by the deepest sensor of the vertical array) by slightly decreased (by a factor of ~1.2) low-frequency (f?<?10?Hz) spectral components. 相似文献
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A 3-D crustal geoelectric model of the Ukrainian Shield (USh) is constructed from magnetic variation data. High electrical conductivity anomalies with resistivities of 1–100 Ω m are located at depths of up to 30 km from the basement surface. A high conductivity layer with ρ = 25 Ω m and with its upper boundary at a depth of 70 km is supposed to exist in the upper mantle of the southwestern USh. 相似文献
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Ying Li Hans‐Joachim Massonne Arne Willner Hong‐Feng Tang Cong‐Qiang Liu 《Island Arc》2008,17(4):577-590
Pseudosections for two sediments and one basalt calculated in the system K2O–Na2O–CaO–MgO–FeO–Fe2O3–Al2O3–TiO2–SiO2–H2O for the P–T range 10 to 35 kbar, 300 to 900°C give useful insights into the amount of H2O released from oceanic crust in subduction zones. In cold subduction zones (20 kbar–300°C to 35 kbar–500°C) hydrous minerals storing 3 to 4 wt% H2O are still present in metasediments at depths of 120 km. In the same environment, metabasite releases 1 wt% H2O in the depth range 100 to 120 km, but 4.5 wt% H2O is transported to greater depths. In hot subduction zones (300°C hotter than the cold subduction zone at 100 km depth), dehydration events of metasediments in the depth range 50 to 80 km correspond to the breakdown of chlorite and paragonite. In the calculations no further water is released at greater depths because the modal content of phengite, the only hydrous mineral phase at these depths, remains almost constant. For the same P–T path, metabasite shows continuous dehydration between 40 and 80 km releasing almost 3 wt% H2O. At 120 km depth less than 0.4 wt% of H2O remains. In an average modern subduction zone (～6°C/km) most dehydration of sediments occurs at depths of 70 to 100 km and that of basalts at depths of 80 to 120 km. Only 1.3 wt% H2O in metasediments and 1.6 wt% H2O in metabasalt has the potential to be subducted to depths greater than 120 km. The dehydration behavior of sediments concurs with the generally held idea that subduction zone fluids are most effectively transported to great depths by cold subduction. In hot subduction zones, such as those characteristic of early Earth, most H2O carried by oceanic crust is liberated at depths less than 120 km and, thus, would not contribute to island‐arc magmatism. 相似文献
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盆地内快速剧烈的构造作用可导致热异常,在利用盆地热历史揭示深部动力学过程时,需消除热异常的影响. 本文根据瞬时热传导原理,校正了渤海湾盆地渤中坳陷低热异常,准确地约束了盆地深部动力学状态. 对渤中坳陷内3口典型井进行热流校正结果表明,渤中坳陷古近纪以来快速沉积导致其现今（~60.9 mW·m-2）未达到热平衡（低热异常）. 校正后的热流值平均约为67.4 mW·m-2,比现今高5~10 mW·m-2. 利用校正后的热流值计算得到的渤中坳陷的“热”岩石圈的平均厚度约为70 km,比修正前的厚度（82~100 km）减少了13~28 km. 相似文献
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利用日本ALOS-2和欧空局Sentinel-1A卫星获得的尼泊尔地震同震形变场,结合GPS同震位移数据,联合反演了断层滑动分布特征和空间展布.结果表明:尼泊尔地震的同震形变场主要集中在150km×100km的范围内,且分为南北两个相邻的形变中心,南形变中心的视线向抬升量约为1.2m,北形变中心的视线向沉降量约为0.8m,均位于发震断层上盘.位于形变抬升区的KKN4和NAST两个GPS站,抬升量和南向运动量均达到了m级,而远离震区的其他GPS台水平和垂直观测量均在1cm以内.联合反演得到的断层位错分布主要集中在沿走向150km,沿倾向70km的范围内,最大滑动量为5.59m,平均滑动量为0.94m.断层面倾角在浅部约为7°,随着深度增加,倾角逐渐变大,到垂直深度20km时倾角接近12°;5月12日MW7.2级余震位于主震破裂区的"凹"型滑动缺损区域;主震破裂区的上边界与MBT空间位置十分吻合,主震破裂区主要集中的MBT以北50~60km处,垂直深度为8~9km,倾角为9°,继续向北时主震破裂面以10°~12°的倾角向深延伸,在18~20km可能与MHT交汇.因此,初步判定MBT为此次地震的发震断层. 相似文献
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ELECTRICAL STRUCTURE OF UPPER CRUST IN THE SOURCE REGION OF JINGGU YUNNAN MS6.6 EARTHQUAKE AND THE SEISMOGENIC ENVIRONMENT 下载免费PDF全文
下载免费PDF全文 The October 7, 2014 MS6.6 earthquake in southwest of Jinggu in the southwestern Yunnan Province occurred as the result of shallow strike-slip faulting within the crust of the Eurasia plate in the broad plate boundary region between the India and Eurasia plates. The strike of fault plane is 140°, and the aftershock distribution shows that the rupture plane is also NNW-trending. Tectonics of the region are controlled by the convergence of the India plate with Eurasia, which has driven the uplift of the Himalayas to the west of this earthquake, and has caused the formation of numerous intraplate continental transform structures in the surrounding region. The pattern of elastic-wave radiation from the earthquake is consistent with the shock occurring either as the result of right-lateral faulting on a northwest-trending fault or as the result of left-lateral faulting on a northeast trending fault. Faults of both types have been mapped in southwestern Yunnan, and it is unclear at this time which type of fault hosted this event. Magnetotelluric survey line is across Jinggu earthquake zone. The advanced data processing and analysis technology of MT is employed and the quantitative data from field surveys are analyzed to acquire the reliable electrical model. The MT data are inverted using nonlinear conjugate gradient (NLCG) inversion algorithm. At last, the interpretation of the electrical model is performed considering the geology and the other geophysical data. Based on the final inversion model of the target profile, it is found that:(1) Electrical structure of the source region can be divided into four layers:The surface is relatively low resistivity layer(0~5km), consisting mainly of Mesozoic and Cenozoic Basin sedimentary rocks, the value of resistivity is 100Ω·m; The high resistivity layer(5~10km) in upper crust mainly consists of Proterozoic metamorphic rocks, with resistivity higher than 1 000Ω·m; there are the upper crust high-conductivity layer(15~25km) and crust-mantle transition zone(blow 25km); (2) The focal depth of the Jinggu earthquake is about 10km, which locates in the interface between high resistivity layer and high-conductivity layer; (3) Most of the focal depths of the aftershocks are in the range of 5km and 10km, and the two depths(5km & 10km) are corresponding to the resistivity gradient belt. 相似文献
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There is general agreement that calc-alkaline volcanic rocks at convergent plate margins are genetically related to the process of subduction (Ringwood, 1974; Maaloe and Petersen, 1981; Hawkesworth et al., 1997). However, opinions on the mode and site of generation of primary magma for island arc volcanism differ substantially. The site of generation of calc-alkaline magma is thought to be either in the mantle wedge (Plank and Langmuir, 1988; McCulloch and Gamble, 1991) or in the subducting slab (White and Dupré, 1986; Defant and Drummond, 1990; Edwards et al., 1993; Ryan and Langmuir, 1993). We present seismological evidence in favour of the latter concept. A distinctive seismicity pattern around and under the Krakatau volcano was identified during systematic studies of the SE Asian convergent plate margins by means of global seismological data. A column-like cluster of events, probably associated with the dynamics of the volcano, is clearly separated from the events in the Wadati-Benioff zone. The accuracy of hypocentral determinations of the events of the cluster does not differ from the accuracy of the events belonging to the subducting slab. The depths of the cluster events vary from very shallow to about 100 km without any apparent discontinuity. On the other hand, there is a pronounced aseismic gap in the Wadati-Benioff zone directly beneath the volcano at depths between 100-150 km. The Krakatau cluster connects this aseismic gap to the volcano at the surface. The pervasive occurrence of earthquakes in the continental wedge between the subducting slab and the Earth surface bears witness to the brittle character of the continental lithosphere and casts doubt on the existence of large-scale melting of mantle material. The aseismic gap (Hanu and Vank, 1985), interpreted by us as a partially melted domain occurring in subducted slabs in practically all active subduction zones that reach depths greater than 100 km, is here used as evidence for the location of the primary source region of island arc volcanics in the subducting plate. 相似文献
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低温热年代学数据是一个与热历史过程紧密相关的资料类型,与高温年代学不同,低温热年代学表观年龄本身在很多情况下没有直接的地质意义.当且仅当样品线性持续冷却的情况下,表观年龄才可以被直接解释为样品经过其封闭温度的大致时间.因此,只有结合地质约束通过对低温热年代学数据进行热历史模拟才能更好地揭示其所蕴含的地质信息.对川东北地... 相似文献