S-wave velocity structure beneath Changbaishan volcano inferred from receiver function

The S wave velocity structure in Changbaishan volcanic region was obtained from teleseismic receiver func-tion modeling. The results show that there exist distinct low velocity layers in crust in volcano area. Beneath WQD station near to the Tianchi caldera the low velocity layer at 8 km depth is 20 km thick with the lowest S-wave velocity about 2.2 km/s. At EDO station located 50 km north of Tianchi caldera,no obvious crustal low velocity layer is detected. In the volcanic re-gion,the thickness of crustal ...     

The velocity structure of crust and uppermantle in the Wudalianchi volcano area in—ferred from the receiver function

The Wudalianchi volcano is a modern volcano erupted since the Holocene.Its frequent occurrence of the small earthquake is considered to be indicator of active dormancy volcano.The S wave velocity structure is inferred from the receiver function for the crust and upper mantle of the Wudalianchi volcano area.The results show that the low velocity structure of Swave is widely distributed undemeath the volcano area and part of the low-velocity-zone located at shallow depth in the Wudalianchi volcano area.The low velocity structure is related to the seismicity.The Moho interface is not clear undemeath the volcano area,which may be regard to be an nec-essary condition for the lava upwelling.Therefore,we infer that the Wudalianchi volcano has the deep structural condition for the volcano activity and may be alive again.     

Mapping crustal S—wave velocity structure with SV—component receiver function method

In this article,we analyze the characters of SV-component receiver function of teleseismic body waves and its advantages in mapping the S-wave velocity structure of crust in detail.Similar to radial receiver function,SV-component receiver function can be obtained by directly deconvolving the P-component from the SV-component of teleseismic recordings.Our analyses indicate that the change of amplitude of SV-component receiver function against the change of epicentral distance is less than that of radial receiver function.Moreover,the waveform of SV-component receiver function is simpler than the radial receiver function and gives prominence to the PS converted phases that are the most sensitive to the shear wave velocity structure in the inversion.The synthetic tests show that the convergence of SV-component receiver function inversion is faster than tnat of the radial receiver function inversion.As an example,we investigate the S-wave velocity structure beneath HIA sta-tion by using the SV-component receiver function inversion method.     

Three-dimensional seismic velocity tomography of the upper crust in Tengchong volcanic area, Yunnan Province

Introduction Tengchong is one of youngest volcanic areas in Chinese mainland. Since Pliocene, the volcanoes have erupted several times. Nowadays, the thermal activity is very intensive there. The possibility of re-eruption and the reserve of geothermal energy in the area are the questions to which the publics pay much attention, and the volcanists and seismologists dedicated. HAN, et al (1996) reviewed all of the studies carried out in Tengchong area. In the late 1990s, an integrative volca…     

A study on deep structure using teleseismic receiver function in Western Yunnan

1 Tectonic environment and geophysical background There are two kinds of continental-oceanic contacts relationship: the Atlantic and the Pacific type. The Atlantic type is characterized by extension and lower relative activity. The continent nearby the ocean is stable and its edge is of extension and block tectonics. Europe, Africa and American belong to this kind. The Pacific type is characterized by compression and shear com-pression. The continent near the ocean is more active than othe…     

利用远震接收函数反演重庆地震台下方的速度结构

选取重庆地震台2010年至2012年记录的60个远震宽频带数字地震记录,采用频率域反褶积法获得台站的接收函数,采用H-Kappa叠加方法反演台站下方的地壳厚度和泊松比,作为台站下方波速反演的约束条件,以减少反演的非唯一性.计算结果显示,重庆地震台下方地壳厚度为42 km,与中国大陆中西部地区Moho面深度在38-45 km保持一致.该研究对增强该区的深部地质构造特征、分析孕震机制等具有积极意义.     

The crustal structure of Norway from inversion of teleseismic receiver functions

Teleseismic body waves from seismic broadband and short periodstations were used to investigate the crustal structure of Norwaythrough inversion of the receiver functions. The Moho depths ofthe Baltic Shield are quite well known from previous studiesincluding seismic experiments and spectral ratio technique.However, the results on the details of the crustal structure areinconsistent. This study provided more detailed crustalstructure information at 16 locations than previously known andgenerally confirmed Moho depth results obtained in earlier studies. Significant differences are seen at a few sites. The Moho for the various sites was found at depths between28 and 44 km. In summary, the crustal thicknessincreases from the West Coast of Norway, away from thecontinental margin, towards the centre of the Baltic Shield andfrom Southwest to the Northeast. This corresponds to theincreasing age of the crust. The P velocities in the crust atmost sites show a gradual increase from about 6.0 to 7.1 km/s, withoutclear layering.     

腾冲火山区S波速度结构接收函数反演

腾冲火山区临近印度板块与欧亚板块碰撞、俯冲的边界, 火山活动与构造环境关系密切. 采用远震接收函数反演的方法揭示了该区域的深部结构特征. 结果显示, 腾冲火山区S波低速结构明显受到NE向大盈江断裂的影响, 断裂的南部存在明显的S波低速结构, 断裂的北部低速结构不十分明显. 火山区存在浅部的低速结构, 低速结构与地震活动性存在对应关系. 证实了低速结构是火山区热活动的直接因素, 并认为腾冲火山区存在再次活动的基本条件.     

Fine S wave velocity structure beneath Iwate volcano, northeastern Japan, as derived from receiver functions and travel times

A genetic algorithm inversion of receiver functions derived from a dense seismic network around Iwate volcano, northeastern Japan, provides the fine S wave velocity structure of the crust and uppermost mantle. Since receiver functions are insensitive to an absolute velocity, travel times of P and S waves propagating vertically from earthquakes in the subducting slab beneath the volcano are involved in the inversion. The distribution of velocity perturbations in relation to the hypocenters of the low-frequency (LF) earthquakes helps our understanding of deep magmatism beneath Iwate volcano. A high-velocity region (dV_S/V_S=10%) exists around the volcano at depths of 2–15 km, with the bottom depth decreasing to 11 km beneath the volcano’s summit. Just beneath the thinning high-velocity region, a low-velocity region (dV_S/V_S=−10%) exists at depths of 11–20 km. Intermediate-depth LF (ILF) events are distributed vertically in the high-velocity region down to the top of the low-velocity region. This distribution suggests that a magma reservoir situated in the low-velocity region supplies magma to a narrow conduit that is detectable by the hypocenters of LF earthquakes. Another broad low-velocity region (dV_S/V_S=−5 to −10%) occurs at depths of 17–35 km. Additional clusters of deep LF (DLF) events exist at depths of 32–37 km in the broad low-velocity zone. The DLF and ILF events are the manifestations of magma movement near the Moho discontinuity and in the conduit just beneath the volcano, respectively.     

Seismological study on the crustal structure of Tengchong volcanic-geothermal area

Introduction The Tengchong volcanic-geothermal area is located on the northeast edge of the collision zone between Indian and Eurasian plates, and belongs to Eurasian volcanic zone (the MediterraneanHimalayanSoutheast Asia volcanic zone). In Tengchong area, the Quaternary volcanic, geothermal and seismic activities are all intensive. These phenomena have been drawing the attention of many geoscientists in the world. Their studies are concerned with geology, geophysics, geochemistry, and cr…     

Crustal structure of northeastern Tibet inferred from receiver function analysis

Sponsored by National Science & Technology Committee, the cooperation between China Academy of Geoscience and Institute of Geophysics and Tectonics, University Joseph, France conducted a lithospherical experiment using 40 Minititan 3-component and 13 CEIS 1-component seismometers along the road from Gonghe to Yushu in Qinghai Province during 5 months after June, 1998. The interested area is on the north of Bangong- Nujiang fault, the east of Qaidam basin, the south of Center Qilian fault and the west of Longmenshan fault. And the profile across most tectonic parts of Eastern Tibet such as Southern Qilian, Eastern Kunlun fault, Bayan Har terrane, Jinshajiang suture (Figure 1), which is the first seismological profile across Eastern Tibet (Qinghai-Tibet) and will be beneficial on the comparison with the results of its center parts, especially on the understanding of the effect of the thousands-kilometer-faraway collision between Eurasia Plate and Indian Plate on the uplifting of south and north part of Eastern Kunlun fault, and on the thickening of crust and the feature of deep structure of Qilian mountain on the north of Tibet Plateau.     

人工神经网络系统在接收函数反演中的应用

为使接收函数的反演更为简便,本文提出了一种基于人工神经网络误差反传(BP)算法的接收函数反演新方法,该方法采用人工神经网络反演系统,避免了接收函数反演过程中复杂的地震响应计算及耗时的雅可比矩阵计算,只需经过学习训练就能够解决复杂的实际问题,而且具有记忆功能,这使接收函数的反演工作具有延续性和可继承性.理论数据的反演计算结果表明,该方法是切实可行的.     

2-D crustal structure of Changbaishan-Tianchi volcanic region determined by seismic traveltime inversion

IntroductionTrial-and-error forward modeling of wide-angle seismic reflection/refraction traveltimes for 2-D velocity structure is extremely time-consuming, even for experienced data interpreters. For wide-angle seismic reflection/refraction experiments that consist of numerous shots along a single line, it is quite difficult through repeated trial-and-error forward modeling to construct a 2-D model that fits the data within acceptable limits (Cerveny, et al, 1977; ZHANG, et al, 200 . In ad…     

Three—dimensional P velocity structure in Beijing area

A detail three-dimensional P wave velocity structure of Beijing,Tianjin and Tangshan area(BTT area)was deter-mined by inverting local earthquake data.In total 16 048 Pwave first arrival times from 16048 shallow and mid-depth crustal earthquakes,which occurred in and around the BTT area from 1992to 1999were used.The first arrival times are recorded by Northern China Unived Telemetry Seismic Network and Yanqing-Huailai Digital Seismic Network.Hypocentral parameters of 1 132 earthquakes with magnitude ML=1.7-6.2 and the three-dimensional P wave velocity structure were obtained simultaneously.The inversion result reveals the com-plicated lateral heterogeneity of P wave velocity structure around BTT area.The tomographic images obtained are also found to explain other seismological observations well.     

山东地区中小地震概率预测实践

基于时间相依的地震复发间隔混合概率模型,开展山东地区中、短期尺度上的中小地震的概率预测实践,1年的检验结果显示,3、4级中小地震基本发生在此前给出的地震危险性高概率区。研究认为,该方法在日常地震会商中应用效果较好,并有望为破坏性地震的概率预测提供参考。     

Crust and upper mantle structure beneath Bohai Sea inferred from receiver function study

We analyzed teleseismic waveforms recorded by 36 stations near Bohai Sea region and obtained 2 248 high quality receiver functions.The crustal thickness (H) and average crustal vP/vS ratio (κ) as well as the Poisson's ratios beneath 34 stations were estimated using the H-κ stacking method.The results indicate that crustal thicknesses near the Liaoning province range from 30.0 to 35.5 km,and the corresponding vP/vS ratios vary from 1.72 to 1.89 which corresponds to Poisson's ratio with a range from 0.243 to ...     

Crustal structure beneath Qiangtang and Lhasa terrane from receiver function

To determine the crustal structure in central Tibet, we used teleseismic waveform data recorded by 18 stations in the INDEPTH-Ⅲ seismic array across the central Tibet from the central Lhasa terrane to the central Qiangtang terrane. The S-wave velocity structures beneath stations are determined by inverting the stacked radial receiver function using the GA method. The first order features in the receiver function are modeled. Our results show that the Moho in Qiangtang is about 8 km shallower than that in Lhasa terrane along the INDEPTH-Ⅲ profile. It maybe suggests the northward subduction of the Lhasa mantle lid beneath the Qiangtang terrane is affected by the India-Asia collision. We conclude that there exist low velocity zone in the middle crust across the northern Lhasa and Qiangtang terrane, which can be related to the high temperature upper mantle beneath that.     

Crustal structure of northeastern margin of the Tibetan Plateau by receiver function inversion

Using seismic data of about one year recorded by 18 broadband stations of ASCENT project,we obtained 2547 receiver functions in the northeastern Tibetan Plateau.The Moho depths under 14 stations were calculated by applying the H-κ domain search algorithm.The Moho depths under the stations with lower signal-noise ratio(SNR) were estimated by the time delay of the PS conversion.Results show that the Moho depth varies in a range of ~40–60 km.The Moho near the Haiyuan fault is vague,and its depth is larger than those on its two sides.In the Qinling-Qilian Block,the Moho becomes shallower gradually from west to east.To the east of 105°E,the average depth of the Moho is 45 km,whereas the west is 50 km or even deeper.Combining our results with surface wave research,we suggest a boundary between the Qinling and the Qilian Mountains at around 105°E.S wave velocities beneath 15 stations have been obtained through a linear inversion by using Crust2.0 as an initial model,and the crustal thickness that was derived by H-κ domain search algorithm was also taken into account.The results are very similar to the results of previous active source studies.The resulting figure indicates that low velocity layers developed in the middle and lower crust beneath the transition zone of the Tibet Block and western Qinling,which may be related to regional faults and deep earth dynamics.The velocity of the middle and lower crust increases from the Songpan Block to the northeastern margin of Tibetan Plateau.Based on the velocity of the crust,the distribution of the low velocity zone and the composition of the curst(Poisson's ratio),we infer that the crust thickening results from the crust shortening along the direction of compression.     

Crust and uppermost mantle structure of the Ailaoshan-Red River fault from receiver function analysis

S-wave velocity structure beneath the Ailaoshan-Red River fault was obtained from receiver functions by using teleseismic body wave records of broadband digital seismic stations. The average crustal thickness, Vp/Vs ratio and Poisson’s ratio were also estimated. The results indicate that the interface of crust and mantle beneath the Ailaoshan-Red River fault is not a sharp velocity discontinuity but a characteristic transition zone. The velocity increases relatively fast at the depth of Moho and then increases slowly in the uppermost mantle. The average crustal thickness across the fault is 36―37 km on the southwest side and 40―42 km on the northeast side, indicating that the fault cuts the crust. The relatively high Poisson’s ratio (0.26―0.28) of the crust implies a high content of mafic materials in the lower crust. Moreover, the lower crust with low velocity could be an ideal position for decoupling between the crust and upper mantle.     

Determination of S-wave velocity structure using microtremors and spac method applied in Thessaloniki (Greece)

Array measurements of microtremors at 16 sites in the city of Thessaloniki were performed to estimate the V_s velocity of soil formations for site effect analysis. The spatial autocorrelation method was used to determine phase velocity dispersion curves in the frequency range from 0.8–1.5 to 6–7 Hz. A Rayleigh wave inversion technique (stochastic method) was subsequently applied to determine the Vs profiles at all the examined sites. The determination of V_s profiles reached a depth of 320 m. Comparisons with V_s values from cross-hole tests at the same sites proved the reliability of the SPAC method. The accuracy of the V_s profiles, the ability to reach large penetration depths in densely populated urban areas and its low cost compared to conventional geophysical prospecting, make Mictrotremor Exploration Method very attractive and useful for microzonation and site effects studies. An example of its application for the site characterization in Thessaloniki is presented herein.