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1.
2.5-D modeling and inversion techniques are much closer to reality than the simple and traditional 2-D seismic wave modeling
and inversion. The sensitivity kernels required in full waveform seismic tomographic inversion are the Fréchet derivatives
of the displacement vector with respect to the independent anisotropic model parameters of the subsurface. They give the sensitivity
of the seismograms to changes in the model parameters. This paper applies two methods, called ‘the perturbation method’ and
‘the matrix method’, to derive the sensitivity kernels for 2.5-D seismic waveform inversion. We show that the two methods
yield the same explicit expressions for the Fréchet derivatives using a constant-block model parameterization, and are available
for both the line-source (2-D) and the point-source (2.5-D) cases. The method involves two Green’s function vectors and their
gradients, as well as the derivatives of the elastic modulus tensor with respect to the independent model parameters. The
two Green’s function vectors are the responses of the displacement vector to the two directed unit vectors located at the
source and geophone positions, respectively; they can be generally obtained by numerical methods. The gradients of the Green’s
function vectors may be approximated in the same manner as the differential computations in the forward modeling. The derivatives
of the elastic modulus tensor with respect to the independent model parameters can be obtained analytically, dependent on
the class of medium anisotropy. Explicit expressions are given for two special cases—isotropic and tilted transversely isotropic
(TTI) media. Numerical examples are given for the latter case, which involves five independent elastic moduli (or Thomsen
parameters) plus one angle defining the symmetry axis. 相似文献
2.
Krzysztof P. Teisseyre 《Acta Geophysica》2007,55(4):535-553
Analysis of a group of seismic events which took place in central Italy and have been recorded at the l’Aquila Observatory
reveals proportionality between the maximum seismic signal (the displacement velocity) and the maximum amplitudes of rotational
components. To compare the seismic events in the aspect of energy emitted as rotational motions, the rotation indices are
used; these indices help us also to differentiate between the results obtained for different frequency spectra.
In the adopted higher frequency range, 2.6–43 Hz, the relation between maximum displacement velocities and the rotation indices
is roughly reciprocal, while for the lower frequencies, 0.3–3 Hz, there is no clear relationship.
The share of rotation motions in the whole seismic energy emitted from the source varies during the seismic event. Research
on the rotational components hidden in the seismic field gives a new insight into the processes in the source. 相似文献
3.
In this paper, we attempt to use satellite gravity data and a new inversion method to study the lateral density anomaly distribution
in the mantle.
First, density difference Δρ(τ,θ,φ) is expanded in terms of a three—dimensional orthogonal function system, the coefficients of the expansion are to be determined.
Then, a set of observation equations is established from the relationship between density anomaly and disturbing geopotential.
In the equations the unknown vector contains the coefficients of density anomaly expansion, the observational vector is obtained
by computing geopotential perturbations using the potential coefficients of GEM10B, and a filtering process is done for the
observational values by properly selecting the harmonic degrees of geopotentical. Finally, the lateral density variations
in the lower mantle (670 km toCM boundary) are investigated. In this case, the degrees of disturbing geopotential are selected as 2–11, the truncated degrees
of density anomaly expansion are taken asL=6 andK=4, and the damping least squares method is used to solve the observation equations.
The resulting model shows the high level of density perturbations at 670 km discontinuity and core — mantle boundary, a high
— density zone circumscribing the Pacific and a lower—density region under the center of Pacific. These features are in agreement
with the three—dimensional seismic velocity variation features by Dziewonski (1984). In the Antarctic region and some parts
of Atlantic and Indian Ocean, however, the resulting density anomalies are negatively correlated with the seismic velocity
anomalies, the cause resulting in these phenomena is preliminarily analysed in this paper.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 53–65, 1991.
The principle and method represented in this paper can also be suitable to study the lateral density anomaly distribution
in the earth’s crust and the upper mantle. 相似文献
4.
Based on the time series of observational variations of the length of day (LOD) and seismic data in the world, the relations
of the decadal fluctuation and seasonal variation in the Earth’s rotation with global seismic activity are studied in this
paper. The results suggest that there are overall correlations on temporal scale and regional discrepancy on spatial scale
between global seismic activity and the Earth’s variable rotation, especially the seismic activity in the Eurasian seismic
zone (not including southeast Asia) and the Lower California-Eastern Alaska seismic zone correlating well with the Earth’s
variable rotation. According to the relations mentioned above, the observational data of the Earth’s rotation might provide
a referential basis for monitoring global seismic activity.
This project is sponsored by the National Key Basic Research Project and the National Natural Science Foundation of China.
The English version is improved by Prof. Xin-Ling QIN, Institute of Geophysics, SSB, China. 相似文献
5.
Cities’ ability reducing earthquake disasters is a complex system involving numerous factors, moreover the research on evaluating
cities’ ability reducing earthquake disasters relates to multi-subject, such as earthquake science, social science, economical
science and so on. In this paper, firstly, the conception of cities’ ability reducing earthquake disasters is presented, and
the ability could be evaluated with three basic elements — the possible seismic casualty and economic loss during the future
earthquakes that are likely to occur in the city and its surroundings and time required for recovery after earthquake; based
upon these three basic elements, a framework, which consists of six main components, for evaluating city’s ability reducing
earthquake disasters is proposed; then the statistical relations between the index system and the ratio of seismic casualty,
the ratio of economic loss and recovery time are gained utilizing the cities’ prediction results of earthquake disasters which
were made during the ninth five-year plan; at last, the method defining the comprehensive index of cities’ ability reducing
earthquake disasters is presented. Thus the relatively comprehensive theory frame is set up. The frame can evaluate cities’
ability reducing earthquake disasters absolutely and quantitatively and consequently instruct the decision-making on reducing
cities’ earthquake disasters loss.
Foundation item: State Important Research Project of China (95130603). 相似文献
6.
Power spectral characteristics of the seismic activities before and after the seven large earthquake — Haicheng, Tangshan,
Lancang, Longling, Mabian, Puer and Songpan are studied by spectrum analysis method. The results show that they all have continuous
power spectrum and aperiodic behaviour. When the time away from the large earthquake occurrence, the characteristics of the
seismic activities are obviously accompanied by stochastic components. About one year before main shock, the moving orbits
constructed by spectrum amplitudes showed the contracting tendency. And the properties during that time may display as flicker
noise. One’s another time almost mixed whole phase space. But the essence of seismic activities after main shocks is a chaotic
state accompanied with much noises.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 276–281, 1993.
This subject is supported by the Chinese Joint Seismological Foundation. 相似文献
7.
8.
IntroductionThecrustaltectonicmovementisacomplicatedevolutionprocesswithtimeandspace.Spatially,themovementofcrustaltectoniciscloselyrelatedtotheinter-movementandinteractionofmulti-leveledcrustalblocksinacertainregionandtheirborderfaults.Temporally,themovementiscloselyrelatedtothatofmulti-leveledcrustalblocksandtimesequencedevelopmentofinteraction.Anearthquakeoccurrenceistheresultofsuddenruptureofcrustmediaundertheactionoftectonicstressfield,isalsoacomplicatedprocessinnercrust.Duetotheobviousi… 相似文献
9.
Shin Okamoto Nagahide Kani Masahiko Higashino Norihide Koshika Masayuki Kimizuka Mitsumasa Midorikawa Masanori Iiba 《地震工程与工程振动(英文版)》2002,1(2):213-225
The Building Standard Law of Japan and related Enforcement Order and Notifications have been substantially revised since the
year 2000 to introduce a performance-based regulatory and deregulation system for building control systems. Up to then, time-history
analyses were mandatory for isolated buildings and had to be specially approved by the Minster of the Ministry of Construction
(MOC). Simplified design procedures based on the equivalent linear method for seismically isolated buildings have been issued
as “Notification 2009 — Structural calculation procedure for buildings with seismic isolation” from MOC, and are now integrated
into the Ministry of Land, Infrastructure, and Transportation (MLIT). Along with Notification 2009, “Notification 1446 of
year 2000 — Standard for specifications and test methods for seismic isolation devices” was also issued. Buildings with heights
equal to or less than 60m and that are designed according to these Notifications, including base isolated buildings, only
need approval from local building officials, and no longer require the special approval of the Minister of MLIT. This paper
summarizes: 1) some statistics related to buildings with seismic isolation completed up to the end of 2001; 2) simplified
design procedures required by Notification 2009 of year 2000; and 3) performance of seismic isolation devices required by
Notification 1446 of year 2000. 相似文献
10.
Anisotropy Effects on Microseismic Event Location 总被引:2,自引:0,他引:2
Seismic anisotropy in sedimentary environments is significant—microseismic waveforms often show strong shear-wave splitting,
with differences reaching 40% between horizontally and vertically-polarized shear-wave velocities. Failure to account for
this anisotropy is shown to result in large microseismic event location errors. A method is presented here for determining
the five elastic parameters of a homogeneous, vertical transverse-isotropic (VTI) model from calibration shot data. The method
can also use data from mining-induced seismic events, which are then simultaneously located. This simple model provides a
good fit to arrival times from coal-environment data, and results in dramatic shifts in interpreted event locations. 相似文献
11.
Matthew Patrick David Wilson David Fee Tim Orr Don Swanson 《Bulletin of Volcanology》2011,73(9):1179-1186
The first eruptive activity at Kīlauea Volcano’s summit in 25 years began in March 2008 with the opening of a 35-m-wide vent
in Halema‘uma‘u crater. The new activity has produced prominent very-long-period (VLP) signals corresponding with two new
behaviors: episodic tremor bursts and small explosive events, both of which represent degassing events from the top of the
lava column. Previous work has shown that VLP seismicity has long been present at Kīlauea’s summit, and is sourced approximately
1 km below Halema‘uma‘u. By integrating video observations, infrasound and seismic data, we show that the onset of the large
VLP signals occurs within several seconds of the onset of the degassing events. This timing indicates that the VLP is caused
by forces—sourced at or very near the lava free surface due to degassing—transmitted down the magma column and coupling to
the surrounding rock at 1 km depth. 相似文献
12.
Krzysztof P. Teisseyre 《Acta Geophysica》2011,59(1):5-28
Three seismic events in L’Aquila region and one in western Greece have been chosen for comparative analysis of two kinds of
seismic motions, spin and twist. These torque components of the seismic field were detected in horizontal plane with the rotational
seismometers. Homologous parts were sought in the signals of spin and twist components — curve of one component was compared
to the other directly and after transformations: phase-shifting and sign reversal. To achieve better clarity, these operations
were done on the data divided into several descendant signals with the use of band-pass filtration. Conformities of spin and
twist, revealed in this way, are assumed to be results of distant processes in the source, where relations between rotational
and shear motions include retardations. 相似文献
13.
In this paper, we show how to estimate the phase velocities of multi-mode signals as present in 2-D shallow seismic surveys
along a seismic line with the help of a method that is based on the deformation of the wavelet spectra of the seismic traces.
In analogy with frequency-wavenumber (f–k) analysis, we perform “frequency-velocity” analysis using the correlations between phases of the wavelet spectra. Our method
has two tuning parameters — the parameter of an analyzing wavelet and the parameter of a threshold operation. Numerical and
experimental examples are presented to illustrate how the method accurately extracts the phase velocity from single- and multi-mode
signals. 相似文献
14.
O. K. Kedrov E. O. Kedrov N. A. Sergeyeva L. P. Zabarinskaya V. R. Gordon A. B. Chulkov 《Izvestiya Physics of the Solid Earth》2010,46(11):974-999
The Method of Dynamic Calibration (MDC) of stations of the International Monitoring System (IMS) was developed for calibrating
regions where no underground nuclear explosions were carried out, with the purpose of providing conditions for implementation
of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) in nontrivial cases. Initially, the MDC had been presented in [Kedrov,
2001; Kedrov et al., 2001; Kedrov O.K. and Kedrov E.O., 2003] and then considered in detail in [Kedrov et al., 2008]. The
core of MDC relates to adapting diagnostic parameters for the identification of underground nuclear explosions (UNE) and earthquakes
elaborated for the region of Eurasia, taken as a basic region (BR), for other researched regions that differ from BR in the
character of the attenuation of seismic waves. The unique characteristic of this method lies in the fact that calibration
of diagnostic parameters with the help of attenuation coefficients b
Δ at varied source-station traces is implemented using only natural seismicity data within the limits of an explored region
and does not require special underground chemical explosions. The MDC algorithm is implemented in the research program ”Kalibr”,
which was tested by using the experimental data from Eurasia region. It is shown in this work that MDC can be used for calibration
of regions where a very low level of natural seismicity is observed. According to the results of the calibration of diagnostic
parameters at IMS stations in several regions of North America, Africa, and Asia, the approximate classification of propagation
conditions for seismic signals at source-station traces in platform and tectonically active regions is made. The results for
the development of two research programs, “Spektr” and “Signal”, are presented; this software is intended for automation of
calculation procedures for spectral diagnostic parameters of UNEs’ and earthquakes’ identification by amplitude spectra of
P waves and by the maximal amplitudes of P, S, and LR signals. The application of these programs allowed us to accelerate the whole calibration procedure for a particular source-station
trace using the ”Kalibr” program. 相似文献
15.
Physicochemical and microbiological characteristics of the bathing waters in Varna’s Black Sea coastal area were investigated
during year 2007 at 23 monitoring stations. Most of the determined physicochemical parameters—pH, mineral oils, surface active
substances, phenols, dissolved oxygen, nutrients and microbiological parameters—“Total coliforms”, “Faecal coliforms”, “Faecal
streptococci” were in compliance with the guidline’ limits and exhibited good water quality. Ammonium and phosphate’s pollution
above the limits was determined at the South beach, Officers beach and Central beach situated in Varna’s central bathing zone.
For the period of 13.08 to 24.10.2007—70% of the South beach samples analyzed for NH4+ exceeded the limits 60 times and the concentrations of PO43− exceeded the limits 17.5 times. Some deviations from the guidline’ limits regarding the microbiology were exhibited at the
same beaches. A conclusion is made that the area of study is not yet seriously threatened, in spite of the rapid recreation
during the last years. 相似文献
16.
V. M. Ovtchinnikov P. B. Kaazik D. N. Krasnoshchekov 《Izvestiya Physics of the Solid Earth》2012,48(3):211-221
Experimental data on the differential travel time t
BC–t
DF of seismic waves PKPDF and PKPBC in the Earth’s core under Africa and Australia are analyzed. The differential travel-time residuals beneath Africa in a narrow
range of angles from 21° to 25° between the direction of the seismic ray in the core and the Earth’s rotation axis exhibit
a scoop-shaped peculiarity not accounted for by cylindrical anisotropy in the inner core. A model with a 0.2–0.8% P-wave velocity anomaly with a radius of 1375 km in the cylindrical region in the outer core is proposed, which closely fits
the experimental data. We suggest that the velocity anomaly is generated by the dynamical processes occurring in the outer
core, namely, the growth of the inner core and the convection in the outer core, both leading to the formation of a low-density
anomaly in the outer core. 相似文献
17.
M. I. Yaroshevich 《Izvestiya Physics of the Solid Earth》2011,47(7):636-640
A possible influence of tropical cyclones on seismic activity in the cyclonic zone of the northwestern Pacific is considered.
There is no direct and sufficiently reliable method for calculating the degree of impact of tropical cyclones on the Earth’s
crust. Therefore, a sort of inverse problem is solved in the investigation: a possible qualitative influence of tropical cyclones
on seismic activity is estimated from its intra-annual dynamics. It is established that for territories of the cyclonic zone,
the intra-annual dynamics of cyclonic and seismic activities are similar. Low monthly mean values of the cyclonic and seismic
energies are attained in July–October, whereas in the continental territories under consideration (Central Asia), the seismic
activity is higher in January–March. The results obtained suggest that cyclones can affect the seismic regime in the cyclonic
zone of the northwestern Pacific. 相似文献
18.
Georgia Poursoulis Agnès Levret Nathalie Lambert Alain Rideaud Bruno Helly 《Journal of Seismology》2006,10(4):511-526
Archaeological techniques and methodology are used to identify seismic traces and disorders in ancient buildings. Clear evidence could be identified as direct seismic consequences or as communities’ technical answers for repair or reinforcement of buildings in order to reduce their vulnerability. This methodology is called “archaeological reading of buildings.” It is based on the identification of different construction phases, modifications and past events (human actions or natural phenomena) suffered by buildings during their life. The data read from the buildings are successively observed, identified, described, and recorded, following the principal of archaeological stratigraphy, in order to explain the buildings history. The seismic pathologies are identified according to detailed engineering knowledge of the behaviour of buildings during seismic motion. In this case study, our approach is applied to the historical city of Manosque, located in a seismic area along the “Moyenne–Durance” active fault. As a result of historical researches (Quenet G, Baumont D, Scotti O, Levret A, Ann Geophys, 47(2/3):583–595, 2004), many historical documents gave evidence about this earthquake’s effects. Among these documents, was an exceptional one: the record of a survey made in Manosque by bricklayers a few days after the 14th August 1708 shock. This gave us specific information concerning the seismic damage caused in the town of Manosque and was the starting point to validate the method. In the present paper, the archaeological reading of buildings method is illustrated by two specific cases: the Charité building in Manosque and the Sainte-Agathe chapel in Saint-Maime village. The buildings suffered various modifications during many centuries. This complicates the application of the method, however the observations made from the buildings correlate well with the indications deduced from written sources, validating our approach. The study highlights the necessity to cross correlate different field data in the frame of a multidisciplinary approach in order to obtain valuable results concerning details of seismic damage, its approximate dating by architectural chronology and the communities’ reaction in terms of repairs and reinforcement techniques. 相似文献
19.
Besides generating seismic waves, which eventually dissipate, an earthquake also generates a static displacement field everywhere within the Earth. This global displacement field rearranges the Earth’s mass thereby causing the Earth’s rotation and gravitational field to change. The size of this change depends upon the magnitude, focal mechanism, and location of the earthquake. The Sumatran earthquake of December 26, 2004 is the largest earthquake to have occurred since the 1960 Chilean earthquake. Using a spherical, layered Earth model, the coseismic effect of the Sumatran earthquake upon the Earth’s length-of-day, polar motion, and low-degree harmonic coefficients of the gravitational field are computed. Using a model of the earthquake source that is composed of five subevents having a total moment-magnitude M
w
of 9.3, it is found that this earthquake should have caused the length-of-day to decrease by 6.8 microseconds, the position of the Earth’s generalized figure axis to shift 2.32 milliarcseconds towards 127° E longitude, the Earth’s oblateness J
2 to decrease by 2.37 × 10−11 and the Earth’s pear-shapedness J
3 to decrease by 0.63 × 10−11. The predicted change in the length-of-day, position of the generalized figure axis, and J
3 are probably not detectable by current measurement systems. But the predicted change in oblateness is perhaps detectable if other effects, such as those of the atmosphere, oceans, and continental water storage, can be adequately removed from the observations. 相似文献
20.
S. Marzorati C. Ladina E. Falcucci S. Gori M. Saroli G. Ameri F. Galadini 《Bulletin of Earthquake Engineering》2011,9(3):841-868
The April 6, 2009 L’Aquila earthquake was responsible for an “anomalous”, relatively high degree of damage (i.e. Is 7 MCS
scale) at Castelvecchio Subequo (CS). Indeed, the village is located at source-to-site distance of about 40 km, and it is
surrounded by other inhabited centres to which considerably lower intensities, i.e. Is 5–6, have been attributed. Moreover,
the damage was irregularly distributed within CS, being mainly concentrated in the uppermost portion of the old village. Geophysical
investigations (ambient seismic noise and weak ground motions analyses) revealed that site effects occurred at CS. Amplifications
of the ground motion, mainly striking NE–SW, have been detected at the uppermost portion of the carbonate ridge on which the
village is built. Geological/structural and geomechanical field surveys defined that the CS ridge is affected by sets of fractures,
joints and shear planes—mainly roughly NW–SE and N–S trending—that are related to the deformation zone of the Subequana valley
fault system and to transfer faults linking northward the mentioned tectonic feature with the Middle Aterno Valley fault system.
In particular, our investigations highlight that seismic amplifications occur where joints set NW–SE trending are open. On
the other hand, no amplification is seen in portions of the ridge where the bedrock is densely fractured but no open joints
occur. The fracture opening seems related to the toppling tendency of the bedrock slabs, owing to the local geomorphic setting.
These investigations suggest that the detected amplification of the ground motion is probably related to the polarization
of the seismic waves along the Castelvecchio Subequo ridge, with the consequent oscillation of the rock slabs perpendicularly
to the fractures azimuth. 相似文献