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1.
《Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy》2000,25(9-11):731-735
The seismic wavefield associated to the ongoing eruptive activity at Stromboli volcano (Italy) is investigated using data from two small-aperture, short-period seismic arrays deployed on the northern and western flanks, located at about 1.7 km from the active craters. Two distinct approaches are used to analyze the recorded signals:
- 1.1) the zero-lag cross-correlation method is used to analyze the explosion quakes data, to estimate slowness and backazimuth as a function of lapse time;
- 2.2) multiple filter technique and phase matched filtering are used to estimate Rayleigh wave dispersion, to obtain a shallow velocity model of the two sites.
2.
A novel procedure is proposed to analyse continuous seismic signal on hourly scales to have a prompt discrimination among the different sources. Specifically, this approach is applied to a massive dataset recorded at Campi Flegrei caldera during the year 2006 when a swarm of volcano-tectonic earthquakes occurred. The convolutive independent component analysis is adopted to obtain a clear separation among meteo-marine microseism, anthropogenic noise, hydrothermal tremor in the absence of volcano-tectonic activity, whereas in non-stationary conditions a contribution connected to the corner frequency of the earthquakes emerges. A coarse-grained variable to be monitored continuously is introduced, i.e. the frequency associated with the maximum amplitude of the power spectral density of the deconvolutive independent components. That parameter is sensitive to the variation in the frequency bands of interest (e.g. that corresponding to the corner frequencies of volcano-tectonic events) and can be used as marker of the insurgence of seismic activity.
相似文献3.
To study factors that affect reliability of the derived vertical rotational ground motions (about vertical axis) from translational array waveforms, we have conducted a field test using explosion. The dataset was collected on March 4, 2008 from an active source experiment of the Taiwan Geodynamics Research project (TAIGER, 2008), in which 750 kg of explosives were set off about 500 m away from a specially designed seismic array in free field consisting of 8 tri-axial rotational sensors, 13 tri-axial accelerometers, and 12 six-channel, 24-bit dataloggers with GPS receivers. Our results show that the waveform fits were greatly improved when the explosion-induced crustal strains were less than 2 × 10−5 for our station configuration. As a result, our modeling for the large amplitude part of the mainshock was not entirely successful. However, we have successfully recovered the first order features of the later part of the vertical rotational ground motions using translational velocity waveforms in the 0.5–20 Hz bandwidth using the Spudich and Fletcher’s procedure (2009). Moreover, we used a modified Jaeger’s (1969) formula and derived similar rotational synthetics. We found that the best rotational rate waveform fits were derived using a station configuration of a dense, small-aperture, translational array combined with a few large-offset stations. A small-aperture array is needed to fulfill the uniform rotation assumption. However, inverting data from an array of small spatial dimension requires waveforms of high signal to noise ratio and high sampling rates. Surprisingly, large-offset translation stations provided additional constraints in time and space, helping to fit the low frequency waveforms. Using the inverted result, we forward predicted the vertical translational waveforms not used in the inversion and got excellent fits. This suggests that the inverted results are of good quality for predicting the complete translational ground motions, even though only horizontal components were used in the inversion. Array-derived or directly measured rotational ground motions can be used to predict translational ground motions in the near-by region. Lessons learned from this study could be helpful for future studies using translational ground motions to derive dynamic ground strains, tilts, and torsions. 相似文献
4.
A novel procedure is proposed to analyse continuous seismic signal on hourly scales to have a prompt discrimination among the different sources. Specifically, this approach is applied to a massive dataset recorded at Campi Flegrei caldera during the year 2006 when a swarm of volcano-tectonic earthquakes occurred. The convolutive independent component analysis is adopted to obtain a clear separation among meteo-marine microseism, anthropogenic noise, hydrothermal tremor in the absence of volcano-tectonic activity, whereas in non-stationary conditions a contribution connected to the corner frequency of the earthquakes emerges. A coarse-grained variable to be monitored continuously is introduced, i.e. the frequency associated with the maximum amplitude of the power spectral density of the deconvolutive independent components. That parameter is sensitive to the variation in the frequency bands of interest (e.g. that corresponding to the corner frequencies of volcano-tectonic events) and can be used as marker of the insurgence of seismic activity. 相似文献
5.
There is no single method available for estimating the seismic risk in a given area, and as a result most studies are based
on some statistical model. If we denote by Z the random variable that measures the maximum magnitude of earthquakes per unit time, the seismic risk of a value m is the probability that this value will be exceeded in the next time units, that is, R(m)=P(Z>m). Several approximations can be made by adjusting different theoretical distributions to the function R, assuming different distributions for the magnitude of earthquakes. A related method used to treat this problem is to consider
the difference between the times of occurrence of consecutive earthquakes, or inter-event times. The hazard function, or failure
rate function, of this variable measures the instantaneous risk of occurrence of a new earthquake, supposing that the last
earthquake happened at time 0. In this paper, we will consider the estimation of the variable that measures the inter-event
time and apply nonparametric techniques; that is, we do not consider any theoretical distribution. Moreover, because the stochastic
process associated with this variable can sometimes be non-stationary, we condition each time by the previous ones. We then
work with a multidimensional estimation, and consider each multidimensional variable as a functional datum. Functional data
analysis deals with data consisting of curves or multidimensional variables. Nonparametric estimation can be applied to functional
data, to describe the behavior of seismic zones and their associated instantaneous risk. The applications of estimation techniques
are shown by applying them to two different regions and data catalogues: California and southern Spain. 相似文献
6.
Accuracy of predicting pile capacities by pile driving formulas have been investigated. Five test piles were driven up to
a depth of about 9 m of clay deposit and the penetrations due to final blows were recorded. The pile bearing capacity of each
pile was predicted using 6 different pile driving formulas and the predicted pile capacity was compared with measured pile
capacity from the pull up tests. Hiley formula, Modified Engineering News Record (ENR) formula, Janbu formula, Dutch formula,
Danish formula, and Gates formula were used. The performance and accuracy of each formula was evaluated and the correlation
coefficient of each pile driving formula was determined for a more accurate pile capacity prediction. Methods used to evaluate
the performance of each formula were; (1) the best fit line for Q
p versus Q
m (2) cumulative probability for Q
p/Q
m and (3) the arithmetic mean and standard deviation for Q
p/Q
m. From the study, it was found that using Dutch formula provided the most accurate pile capacity estimate compared to the
other formulas with an average of 7% deviation from value obtained from the field pull up test. It was followed by the Danish
formula, Janbu formula, Hiley formula, Modified ENR formula, and Gates formula. The ability to predict the accuracy of estimating
pile capacity using an appropriate method is very important and valuable to contractors, developers, geotechnical engineers,
and manufacturers. 相似文献
7.
ABSTRACTThe main sources of uncertainty in the soil specification and mechanical behaviour consist of the lithological and heterogeneous randomness of soil deposits. It is quite obvious that the cone penetration testing (CPT) data and the variation of soil characteristics are not stationary. Hence, this paper investigates a new approach to realise a CPT data, taking both sources of uncertainty into consideration. In this regard, the first part of this study illustrates a simple approach to stratify the CPT data, using the Eslami–Fellenius chart of classification. In the second part, the non-stationary algorithm of generating random field is introduced to generate a multi-layer random field. This algorithm takes account of each layer’s statistical properties (i.e. standard deviation, mean, and the trend value), separately. To validate the proposed approach, 41 case histories from different worldwide sites, have been regenerated by considering both the stationary and non-stationary algorithms. The correlation coefficient between real and realised CPT data has been employed to show that the proposed non-stationary algorithm can simulate the CPT data more accurately in comparison with the stationary algorithm. 相似文献
8.
Li Lei Tan Jingqiang Zhang Dazhou Malkoti Ajay Abakumov Ivan Xie Yujiang 《Computational Geosciences》2021,25(5):1565-1578
Seismic modeling plays an important role in geophysics and seismology for estimating the response of seismic sources in a given medium. In this work, we present a MATLAB-based package, FDwave3D, for synthetic wavefield and seismogram modeling in 3D anisotropic media. The seismic simulation is carried out using the finite-difference method over the staggered grid, and it is applicable to both active and passive surveys. The code package allows the incorporation of arbitrary source mechanisms and offers spatial derivative operators of accuracy up to tenth-order along with different types of boundary conditions. First, the methodological aspects of finite-difference method are briefly introduced. Then, the code has been tested and verified against the analytical solutions obtained for the homogeneous model. Further, the numerical examples of layered and overthrust models are presented to demonstrate its reliability.
相似文献9.
A TEM and RUM study of the inherent displacive flexibility of the fresnoite framework structure type
A careful electron diffraction study has been made of the incommensurately modulated room-temperature phases of the fresnoites
Ba2TiGe2O8 (BTG) and Ba2TiSi2O8 (BTS) and used to determine their (3+1)- and (3+2)-dimensional superspace group symmetries. The primitive primary modulation
wave vectors in both materials are found to occur close to the same position in the parent Brillouin zone, near ∼0.3〈110〉
p
*+1/2c
p
st
. A rigid unit mode (RUM) analysis of the inherent displacive structural flexibility of the ideal fresnoite framework structure
type is then carried out in an attempt to understand the significance of this particular modulation wave vector. Six zero-frequency
RUM modes and two close to zero frequency quasi-RUM (Q-RUM) modes are found to exist for any modulation wave vector. These
RUM modes are all primarily associated with rotations of the constituent TO4 (T=Si or Ge) tetrahedra and TiO5 square pyramids around in-plane i.e. perpendicular to c rotation axes. A seventh RUM mode involving rotation of the constituent rigid polyhedra around c combined with shifts in the basal plane is found but only at a very specific modulation wave vector q∼0.30〈110〉
p
*
, in close agreement with the condensed RUM mode found in the electron diffraction study. It is the condensation of just such
a RUM mode that appears to play a major role in the various incommensurately modulated structures observed in Ba2TiGe2O8, Ba2TiSi2O8 and Sr2TiSi2O8, respectively.
Received: 26 November 2001 / Accepted: 25 May 2002
Present address: Y. Tabira Materials Characterization Laboratory Mitsui Mining & Smelting Co. Ltd. 1333-2 Haraichi, Ageo, Saitama 362-0021,
Japan 相似文献
10.
In relation to the assessment of earthquake-induced landslide hazard, this paper discusses general principles and describes
implementation criteria for seismic hazard estimates in landslide-prone regions. These criteria were worked out during the
preparation of a hazard map belonging to the official Italian geological cartography and they are proposed as guidelines for
future compilation of similar maps. In the presented case study, we used a procedure for the assessment of seismic hazard
impact on slope stability adopting Arias intensity Ia as seismic shaking parameter and critical acceleration a
c
as parameter representing slope strength to failures induced by seismic shaking. According to this procedure, after a preliminary
comparison of estimated historical maximum values of Ia with values proposed in literature as landslide-triggering thresholds, a probabilistic approach, based on the Newmark’s model,
is adopted: it allows to estimate the minimum critical acceleration a
c
required for a slope to keep under a prefixed value, the probability of failures induced by seismic shakings expected in
a given time interval. In this way, one can prepare seismic hazard maps where seismic shaking is expressed in an indirect
way through a parameter (the critical acceleration) representing the “strength” that seismic shakings mobilise in slope materials
(strength demand) with a prefixed exceedance probability. This approach was applied to an area of Daunia (Apulia—southern
Italy) affected by frequent landslide phenomena. The obtained results indicate that shakings with a significant slope destabilisation
potential can be expected particularly in the north-western part of the area, which is exposed to the seismic activity of
Apennine tectonic structures. 相似文献
11.
构建了等直径不同裂隙密度和等裂隙密度不同裂隙直径两组物理模型,进行不同围压条件下多方向的超声波速度测试,并运用Hudson理论进行了理论模型计算。结果显示,计算与实测结果吻合较好。随围压的增大,纵、横波速度均近线性增加,纵、横波各向异性基本保持不变;裂隙密度从2%增大到6%,纵波速度不同程度降低,其中慢纵波降低幅度相对较大,快横波变化不明显,而慢横波则大幅降低。随着裂隙密度的增大,纵、横波各向异性均增大,且横波各向异性增加速率大于纵波;裂隙直径从2 mm增大到3 mm,快纵波速度增加很小,慢纵波增加明显,横波速度均不发生改变。随着裂隙直径的增大,纵波各向异性逐渐降低,横波各向异性保持不变。最后结合试验结果分析了Hudson理论在不同深度进行参数预测的必要条件。研究结果有助于油气生产、地下水的开采与控制、污染处理等。 相似文献
12.
An important issue of using the multiple-point (MP) statistical approach for reservoir modeling concerns the integration of
auxiliary constraints derived, for instance, from seismic information. There exist two methods in the literature for these
non-stationary MP simulations. One is based on an analytical approximation (the “τ-model”) of the conditional probabilities that involve auxiliary data. The degree of approximation with this method depends
on the parameter τ, whose inference is difficult in practice. The other method is based on the inference of these conditional probabilities
directly from training images. This method classifies the auxiliary data into a few classes. This classification is in general
arbitrary and therefore inconvenient in practice, especially in the case of continuous auxiliary constraints. In this paper,
we propose an alternative method for performing non-stationary MP simulations. This method accounts for the data support in
the modeling procedure and allows, in particular, continuous auxiliary data to be integrated into MP simulations. This method
avoids the major limitations of the previous methods, namely the use of an approximate analytical model and the reduction
of the auxiliary data into a limited number of classes. This method can be easily implemented in the existing MP simulation
codes. Numerical tests show good performance of this method both in reproducing the geometrical features of the training image
and in honouring the auxiliary data. 相似文献
13.
In order to better constrain and define the microseismic activity at the north Evoikos Gulf and its surrounding area we deployed an onshore/offshore seismic array consisting of 31 three-component seismic digital stations. The array was active from 30 June to 24 October 2003, and covered an area of 2500 km2. We located more than 2000 seismic events ranging from 0.7 to 4.5 ML by using six stations as a minimum in order to define the foci parameters. Recorded seismicity delineated three major zones of deformation: from south to north, the Eretria–Parnis–eastern Corinthiakos zone, the Psachna–Viotia zone, and the Northern Sporades–North Evia–Bralos zone. Alignments of the recorded seismicity follow the tectonic trends and their orientation in the above zones. The whole area accommodates the stress field between the North Aegean Trough and the Corinthiakos Gulf. Rate of deformation intensifies from north to south, as revealed also by historical and instrumental seismicity. The successive change of orientation between the two stress fields fragments the crust in relatively small units and the fault systems developed do not permit the generation of major earthquakes in the north Evoikos area and its immediate vicinity. This is also supported by the instrumental seismicity of the last century. Larger events reported in historical times are probably overestimated.Most seismic activity is crustal. Subcrustal events were recorded mainly below the Lichades area and are interpreted as the consequence of the subduction of the Ionian oceanic lithosphere below the Hellenides. The Lichades volcano is the most northern end of the Hellenic volcanic arc.At present the highest seismic activity is associated with the Psachna region of north Evia that has been continuously active since 2001. Considering, however, the development of the seismic activity during the last decade, there has been a sequence of large events, i.e., Parnis in 1999, Skyros in 2001 and Psachna in 2001–2003. This demonstrates the fact that the tectonic deformation in all this area is intense and important for the accommodation of the stress field of the North Aegean Trough to that of the Corinthiakos Rift. 相似文献
14.
Analytical study of ground motion caused by seismic wave propagation across faulted rock masses 
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下载免费PDF全文 Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions. 相似文献
15.
Three-dimensional P and S wave velocity models of the crust under the Granada Basin in Southern Spain are obtained with a spatial resolution of 5 km in the horizontal direction and 2 to 4 km in depth. We used a total of 15407 P and 13704 S wave high-quality arrival times from 2889 local earthquakes recorded by both permanent seismic networks and portable stations deployed in the area. The computed P and S wave velocities were used to obtain three-dimensional distributions of Poisson's ratio (σ) and the porosity parameter (Vp×Vs). The 3-D velocity images show strong lateral heterogeneities in the region. Significant velocity variations up to ±7% in P and S velocities are revealed in the crust below the Granada Basin. At shallow depth, high-velocity anomalies are generally associated with Mesozoic basement, while the low-velocity anomalies are related to the neogene sedimentary rocks. The south–southeastern part of the Granada Basin exhibits high σ values in the shallowest layers, which may be associated with saturated and unconsolidated sediments. In the same area, Vp×Vs is high outside the basin, indicating low porosity of the mesozoic basement. A low-velocity zone at 18-km depth is found and interpreted as a weak–ductile crust transition that is related to the cut-off depth of the seismic activity. In the lower crust, at 34-km depth, a clear slow Vp and Vs anomalous zone may indicate variations in lithology and/or with the rigidity of the lower crust rocks. 相似文献
16.
Robert Kirby 《Computational Geosciences》2003,7(3):197-214
In this paper, residual-based a posteriori error bounds are derived for the mixed finite element method applied to a model second order elliptic problem. A global upper bound for the error in the scalar variable is established, as well as a local lower bound. In addition, due to the fact that the scalar and vector variables are approximated to equal order accuracy, the dual problem may be modified to give an upper bound for the vector variable. Some comments on estimating more general error quantities are also made. The estimate effectively guides adaptive refinement for a smooth problem with a boundary layer, as well as detects the need to refine near a singularity. 相似文献
17.
S.K. Guha 《Tectonophysics》1979,52(1-4)
There have been instances of premonitory variations in tilts, displacements, strains, telluric current, seismomagnetic effects, seismic velocities ( Vp, Vs) and their ratio (Vp/Vs), b-values, radon emission, etc. preceding large and moderate earthquakes, especially in areas near epicentres and along faults and other weak zones. Intensity and duration (T) of these premonitory quantities are very much dependent on magnitude (M) of the seismic event. Hence, these quantities may be utilised for prediction of an incoming seismic event well in advance of the actual earthquake. In the recent past, tilts, strain in deep underground rock and crustal displacements have been observed in the Koyna earthquake region over a decade covering pre- and postearthquake periods; and these observations confirm their reliability for qualitative as well as quantitative premonitory indices. Tilt began to change significantly one to two years before the Koyna earthquake of December 10, 1967, of magnitude 7.0. Sudden changes in ground tilt measured in a watertube tiltmeter accompanied an earthquake of magnitude 5.2 on October 17, 1973 and in other smaller earthquakes in the Koyna region, though premonitory changes in tilt preceding smaller earthquakes were not so much in evidence. However, changes in strains in deep underground rock were observed in smaller earthquakes of magnitude 4.0 and above. Furthermore, as a very large number of earthquakes (M = 1–7.0) were recorded in the extensive seismic net in the Koyna earthquake region during 1963–1975, precise b-value variations as computed from the above data, could reveal indirectly the state of crustal (tectonic) strain variations in the earthquake focal region and consequently act as a powerful premonitory index, especially for the significant Koyna earthquakes of December 10, 1967 (M = 7.0) and October 17, 1973 (M = 5.2). The widespread geodetic and magnetic levelling observations covering the pre- and postearthquake periods indicate significant vertical and horizontal crustal displacements, possibly accompanied by large-scale migration of underground magma during the large seismic event of December 10, 1967 in the Koyna region (M = 7.0). Duration (T) of premonitory changes in tilt, strains, etc., is generally governed by the equation of the type logT = A + BM (A and B are statistically determined coefficients). Similar other instances of premonitory evidences are also observed in micro-earthquakes (M = − 1 to 2) due to activation of a fault caused by nearby reservoir water-level fluctuations. 相似文献
18.
本文详细讨论了羌塘盆地二十多年来二维地震勘探所取得的进展。羌塘盆地除发育背景干扰外,还发育多种面波散射、线性干扰、折射波和多次折射波;检波器大组合能压制背景和面波散射干扰,但不能压制速度较高的线性干扰、折射波和多次折射波。最佳激发因素为常规可控震源振动台次3台1次,驱动幅度70%,扫描频率6～84Hz,扫描长度18s;低频可控震源振动台次2台1次,驱动幅度60%,扫描频率1. 5～84Hz,扫描长度16s;大吨位可控震源振动台次2台1次,驱动幅度70%,扫描频率6～84Hz,扫描长度16s。炸药震源为单井高速层下7m激发,最浅井深18m,药量18kg;组合方式激发为2口井×15m×12kg或3口井×12m×8kg。尽管可控震源单炮的能量、信噪比、频谱及子波一致性与炸药震源相比较并不占优,但可控震源激发在高密度高覆盖采集条件下仍能获得等同于或明显优于井炮激发质量的地震剖面资料。从"环保、安全、经济、高效"上考虑,羌塘盆地宜采用可控震源和井炮联合的宽线高密度高覆盖采集方案,3L3S或2L3S,960次以上覆盖为可控震源最佳观测系统;2L3S,360次左右覆盖为井炮震源最佳观测系统。北羌塘坳陷构造稳定,容易获取高品质地震资料,南羌塘坳陷构造过于复杂,资料信噪比低,可能不太适合开展地震勘探工作。文章最后还讨论了冻土层静校正和激发接收方面存在的问题及解决方案。 相似文献
19.
We delineate shallow structures of the Mozumi–Sukenobu fault, central Japan, using fault zone waves generated by near-surface explosions and detected by a seismometer array. Two explosive sources, S1 and S2, were placed at a distance of about 2 km from the array, and the other two, S3 and S4, were at a distance of about 4 km. Fault zone head waves and fault zone trapped waves following direct P wave arrivals were clearly identified in the seismograms recorded by a linear seismometer array deployed across the fault in a research tunnel at a depth of 300 m. Synthetic waveforms generated by a 3-D finite-difference (3-D FD) method were compared with observed fault zone waves up to 25 Hz. The best fitting model indicates a 200-m-wide low-velocity zone extending at least to shot site S1 located 2 km east of the seismic array with a 20% decrease in the P wave velocity relative to the wall rock. The width of the low-velocity zone is consistent with the fault zone defined by direct geological observation in the research tunnel. However, the low-velocity zone should disappear just to the east of the site S1 to explain the observed fault zone waves for shot S3 and S4 located 4 km east of the seismometer array. Yet the observation and the simulation show notable trapped wave excitation even though shots S3 and S4 are outside the fault zone. These results indicate that (1) the effective waveguide for seismic waves along the fault does not exist east of source site S1 although the surface traces of the fault are observed in this region, and (2) considerable trapped waves can be excited by sources well outside the fault zone. These results highlight the along-strike variability in fault zone structure. 相似文献
20.
Seismic ray direction anomalies and relative residuals of earthquakes recorded at Gauribidanur array
Slowness and azimuthal anomalies provide valuable information about lateral inhomogeneities within the crust and mantle of the earth. Over 300 earthquakes (distance range 14°–36° and azimuth 0°–360°) recorded at Gauribidanur seismic array (GBA) in southern India, were analysed using adaptive processing techniques. Slowness anomalies upto 1·3 sec/deg and azimuthal anomalies upto 8° have been observed in the present analysis. Slowness anomaly patterns for Java trench, Mid-Indian oceanic ridge earthquakes are more consistent as compared to the events originating in the Himalayan and Hindukush regions. A significant feature of the azimuthal anomaly pattern was the distinct absence of any positive anomalies from earthquakes occurring in mid-oceanic ridge. These anomalies have also been analysed as a function of epicentral distance and are mainly attributed to the transition zones occurring between 400–700 km depth ranges in the Indian upper mantle regions. Relative residuals between the stations of GBA have very little dependence on azimuth and distance. An anomalous structure beneath the array in the direction of the Java trench region (azimuth 116–126°) has been postulated on the basis of large systematic slowness vectors observed. 相似文献