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1.
Multifractal measures of earthquakes in west Taiwan 总被引:1,自引:0,他引:1
The generalized fractal dimension for epicentral distribution of earthquakes in west Taiwan is measured. The entire area is first divided into two zones, i.e., north and south zones, after which the two zones are further separated into three subzones for the former and two for the latter. The logC
q
(r) versus logr function, whereC
q
(r) is the generalized correlation integral andr is the distance between two epicenters, shows that a linear relation between logC
q
and logr exists in the range ofr smaller thanr
c
. The value ofr
c
is 25 km for the north zone, 40 km for the south and 12 km for the three north subzones. The valuesr
c
=25 and 40 km are almost the smallest ones of the width of epicentral distributions of the north and south zones, respectively. The value ofr
c
=12 km for the three north subzones is approximately the smallest size of the cluster of epicenters. For the plots of two south subzones, the pattern of data points does not bend in the range ofr in consideration, and, thus, there is not such a critical radius. TheD
q
–q relations forq=0, 1, 2,..., 15 are constructed for the two zones and five subzones. Results show significant multifractality and a spatial variation in multifractality for epicentral distributions of earthquakes in west Taiwan. 相似文献
2.
This study is to evaluate the applicability of estimating the one-dimensional horizontal hydraulic diffusivity of an unconfined
aquifer with time-dependent fluctuation of lateral head and vertical recharge boundaries using observed water level spectra.
Different models of boundary condition are imposed to evaluate the statistical significance between the calculated hydraulic
diffusivity (ξ′) with the given hydraulic diffusivity (ξ). The auto-spectra of the water level in observation wells tapping the same aquifer
are closely related to those at the disturbed boundaries. For an aquifer with a constant hydraulic diffusivity, the water
level fluctuation in the monitoring wells is linearly related to the water level spectra observed at the boundaries. The spectral
density function of aquifer hydraulic head varies inversely with specific yield (S
y) and directly with recharge. Given small variation in water level spectra at the disturbed boundaries, the water level fluctuation
in the aquifer is affected by the recharge condition and the aquifer spectral density function is sensitive to S
y. Using an iterative technique to estimate ξ from 1400 sets of given parameters, 99% of the ξ′/ξ values deviated within only one order of magnitude with the model length (L) being equal to 1 km and 10 km. For L equal to 100 m, approximately 82% of the ξ′/ξ population falls within two orders of magnitude. Therefore, spectral analysis of aquifer hydraulic head response can be
used to estimate the hydraulic diffusivity of an unconfined aquifer which is affected by periodic variations in recharge and
head at boundaries. 相似文献
3.
Abstract We consider the growth of disturbances to large-scale zonally-asymmetric steady states in a truncated spectral model for forced and dissipated barotropic flow. A variant of the energy method is developed to optimize the instantaneous disturbance energy growth rate. The method involves solving a matrix eigenvalue problem amenable to standard numerical techniques. Two applications are discussed. (1) The global stability of a family of steady states is assessed in terms of the Ekman damping coefficient r. It is shown that monotonic global stability (i.e., every disturbances energy monotonically decays to zero) prevails when r≥rc . (2) Initially fastest-growing disturbances are constructed in the r<rc regime. Particular attention is paid to a subregion of the r<rc regime where initially-growing disturbances exist despite stability with respect to normal modes. Nonlinear time-dependent simulations are performed in order to appraise the time evolution of various disturbances. 相似文献
4.
Starting with dislocation model, using the result of the fracture mechanics: the slip displacement at the crack tip is proportional
to the length of the crack and the applied ambient shear stressτ
0
2
, we consider the dislocation in the earthquake to be the slip displacement at the crack tip and have obtained the analysis
expresses of displacement and velocity pulse for the circular crack and have calculated the seismic wave energy radiated by
earthquake. The seismic wave energyE ∞M
0
τ
0
2
f(v)
r
, i. e.E is proportional to the seismic momentM
0 and the square of the ambient shear stressτ
0
2
and increases with the rupture velocityv
r
.
In frequency domain, integrating the square of source velocity spectrum derived from our the scaling law model, we have also
obtained the seismic wave energyE released by earthquake and earthquake radiated effficiencyη.E ∞M
0
τ
0
2
also. If takingτ
0 = 10.0 MPa, E=4.79M
0. This result is consistent with the estimate by Vassiliou and Kanamori (1982). Theη=5.26%. The distribution of the seismic wave energy is that most of the energy contains in the frequency range between the
first corner frequencyf
c1 and thirdf
c3, amount to 92.3% the energy in the rangef<f
c1 is about 3.85% and 3.85% whenf>f
c3. Thef
c3 is about 8Hz forM ⩾ 6, thus most of radiated energy is below 2Hz. This phenomenon had been verified by Vassiliou Kanamori.
Previous results show the energy radiated by earthquake to be strongly dependent on ambient shear stress.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 146–152, 1993.
This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledged.
The authors are also grateful to Professor Klussmann and Mr. Hasthoff for their lots of help. 相似文献
5.
In the paper, we introduce Allegre's scaling-rule theory of rock fracture and the probability to develop a method for predicting earthquake occurrence time on its basis. As an example, we study the characteristics of seismological precursors (seismic spatial correlation length and coda Qc) associated with the earthquake (M=6.1) occurred in Shandan-Minle, Gansu Province. The results show an increasing trend of seismic spatial correlation length and coda Qc before the earthquake. And a power exponent relation is used to fit the increasing variation form of these two parameters. The study has provided a basis for creating a method and finding indexes to predict the earthquake occurrence time by using the monitored seismic spatial correlation length and coda Qc. 相似文献
6.
This paper examines a model for estimating canopy resistance rc and reference evapotranspiration ETo on an hourly basis. The experimental data refer to grass at two sites in Spain with semiarid and windy conditions in a typical Mediterranean climate. Measured hourly ETo values were obtained over grass during a 4 year period between 1997 and 2000 using a weighing lysimeter (Zaragoza, northeastern Spain) and an eddy covariance system (Córdoba, southern Spain). The present model is based on the Penman–Monteith (PM) approach, but incorporates a variable canopy resistance rc as an empirical function of the square root of a climatic resistance r* that depends on climatic variables. Values for the variable rc were also computed according to two other approaches: with the rc variable as a straight‐line function of r* (Katerji and Perrier, 1983, Agronomie 3 (6): 513–521) and as a mechanistic function of weather variables as proposed by Todorovic (1999, Journal of Irrigation and Drainage Engineering, ASCE 125 (5): 235–245). In the proposed model, the results show that rc/ra (where ra is the aerodynamic resistance) presents a dependence on the square root of r*/ra, as the best approach with empirically derived global parameters. When estimating hourly ETo values, we compared the performance of the PM equation using those estimated variable rc values with the PM equation as proposed by the Food and Agriculture Organization, with a constant rc = 70 s m?1. The results confirmed the relative robustness of the PM method with constant rc, but also revealed a tendency to underestimate the measured values when ETo is high. Under the semiarid conditions of the two experimental sites, slightly better estimates of ETo were obtained when an estimated variable rc was used. Although the improvement was limited, the best estimates were provided by the Todorovic and the proposed methods. The proposed approach for rc as a function of the square root of r* may be considered as an alternative for modelling rc, since the results suggest that the global coefficients of this locally calibrated relationship might be generalized to other climatic regions. It may also be useful to incorporate the effects of variable canopy resistances into other climatic and hydrological models. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
7.
Lapse time and frequency-dependent attenuation characteristics of coda waves in the Northwestern Himalayas 总被引:1,自引:0,他引:1
We analyzed the local earthquakes waveform recorded on a broadband seismic network in the northwestern Himalayan Region to
compute lapse time and frequency dependence of coda Q (Q
c). The observed Q
c values increase with increasing lapse time at all frequency bands. The increase in Q
c values with lapse time is attributed to an increase in Q
c with depth. This implies that attenuation decreases with increasing depth. The approximate radius of medium contributing
to coda generation varies from 55 to 130 km. By comparing the Q
c values with those from other regions of the world, we find that they are similar to those obtained from tectonically active
regions. The estimated Q
c values show a frequency-dependent relationship, Q
c = Q
0
f
n
, where Q
0 is Q
c at 1 Hz and n represents degree of frequency dependence. They represent the level of heterogeneity and tectonic activity in an area. Our
results show that northwest Himalayas are highly heterogeneous and tectonically very active. Q
0 increases from 113 ± 7 to 243 ± 10 and n decreases from 1.01 ± 0.05 to 0.85 ± 0.03 when lapse time increases from 30 to 70 s. As larger time window sees the effect
of deeper part of the Earth, it is concluded that Q
0 increases and n decreases with increasing depth; i.e., heterogeneity decreases with depth in the study area. 相似文献
8.
Stress Sensitivity of Seismic and Electric Rock Properties of the Upper Continental Crust at the KTB
We test the hypothesis that the general trend of P-wave and S-wave sonic log velocities and resistivity with depth in the pilot hole of the KTB site Germany, can be explained by the progressive
closure of the compliant porosity with increasingly effective pressure. We introduce a quantity θc characterizing the stress sensitivity of the mentioned properties. An analysis of the downhole measurements showed that estimates
of the quantitiy θc for seismic velocities and electrical formation factor of the in situ formation coincide. Moreover, this quantity is 3.5 to 4.5 times larger than the averaged stress sensitivity obtained from
core samples. We conclude that the hypothesis mentioned above is consistent with both data sets. Moreover, since θc corresponds approximately to the inverse of the effective crack aspect ratio, larger in situ estimates of θc might reflect the influence of fractures and faults on the stress sensitivity of the crystalline formation in contrast to
the stress sensitivity of the nearly intact core samples. Finally, because the stress sensitivity is directly related to the
elastic nonlinearity we conclude that the elastic nonlinearity (i.e., deviation from linear stress-strain relationship i.e.,
Hooke's law) of the KTB rocks is significantly larger in situ than in the laboratory. 相似文献
9.
Coda Q in the Kachchh Basin, Western India Using Aftershocks of the Bhuj Earthquake of January 26, 2001 总被引:1,自引:0,他引:1
S. C. Gupta Ashwani Kumar A. K. Shukla G. Suresh P. R. Baidya 《Pure and Applied Geophysics》2006,163(8):1583-1595
QC-estimates of Kachchh Basin in western India have been obtained in a high frequency range from 1.5 to 24.0 Hz using the aftershock
data of Bhuj earthquake of January 26, 2001 recorded within an epicentral distance of 80 km. The decay of coda waves of 30
sec window from 186 seismograms has been analysed in four lapse time windows, adopting the single backscattering model. The
study shows that Qc is a function of frequency and increases as frequency increases. The frequency dependent Qc relations obtained for four lapse-time windows are: Qc=82 f1.17 (20–50 sec), Qc=106 f1.11 (30–60 sec), Qc=126f1.03 (40–70 sec) and Qc=122f1.02 (50–80 sec). These empirical relations represent the average attenuation properties of a zone covering the surface area of
about 11,000, 20,000, 28,000 and 38,000 square km and a depth extent of about 60, 80, 95, 110 km, respectively. With increasing
window length, the degree of frequency dependence, n, decreases marginally from 1.17 to 1.02, whereas Q0 increases significantly from 82 to 122. At lower frequencies up to 6 Hz, Qc−1 of Kachchh Basin is in agreement with other regions of the world, whereas at higher frequencies from 12 to 24 Hz it is found
to be low. 相似文献
10.
The null distribution of the lag-k sample serial correlation coefficient (r
k
, k=1,2,3) was investigated by Monte Carlo simulation. For a time series with normal, exponential, Pearson 3, EV1 (Gumbel), or
generalized Pareto (GP) distribution type, the null distribution of its r
k
can be approximated by the normal distribution with mean −1/(n−k) and variance 1/(n−1). But for a time series with the lognormal, EV2 or EV3 (Weibull) distribution type, the null distribution of r
k
is skewed distributed. In such cases, a simulation technique is suggested to construct percentile confidence intervals at
a given significance level. 相似文献
11.
For the problem of matrix compaction and melt segregation a general mush continuity equation is derived, which explicitly
expresses the coupling between the melt percolation and the inelastic matrix deformation and closes the governing equation
set. Besides, a general equation is obtained, which describes the change in the volume of pore space due to all the possible
reasons (inelastic matrix deformation, the phase transitions, and the advection of porosity by the matrix flow). The features
of the isothermal melt segregation inside a partially molten zone are demonstrated using one-dimensional (1D) numerical solutions.
It follows from the solutions that the pattern and the characteristic time of the melt segregation inside a partially molten
zone of thickness L are controlled by the segregation parameter γ
c
= (L/δ
c
)2, where the compaction length δ
c
= k(φ0)η/(φ0μ) depends on the permeability, k, the value of characteristic porosity, φ0, and the viscosities of the matrix, η, and melt, μ. The solutions demonstrate that at any value of γ
c
, layers that are highly enriched in melt compared to the maximum initial porosity are formed in the upper part of the zone.
At the same time, the evolution of the system and the segregation time differ considerably in the limits of γ
c
≪ γ* and γ
c
≫ γ*, where γ* depends on the boundary and initial conditions of the problem, and γ* is about 80 for the problem of melt segregation inside a partially molten zone with the maximum in the initial melt distribution
located in the middle of the zone. At γ
c
≪ γ*, which corresponds to the segregation of low-viscosity ultrabasic melts (kimberlites, carbonatites), all the melt accumulates
to the roof of the zone, and the segregation time does not depend on the matrix permeability and melt viscosity and decreases
with an increase in the thickness of the zone as L
−1. The latter can be the reason for the formation of clusters of the same age and same composition eruptions characteristic
of the kimberlite provinces. In the opposite limiting case, γ
c
≫ γ*, the segregation time does not depend on the matrix viscosity and scales as L with a wave sequence forming in the upper part of the zone, which, probably, elucidates the origin of the rhythmical layering
of the large tholeiitic basalt plutons. 相似文献
12.
J. Zhu M. G. Satish 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(3):228-243
Stochastic analysis of one- and two-dimensional flow through a shallow semi-confined aquifer with spatially variable hydraulic
conductivity K represented by a stationary (statistically homogeneous) random process is carried out by using the spectral technique. The
hydraulic head covariance functions for flows in a semi-confined aquifer bounded by a leaky layer above and an impervious
stratum below are derived by assuming that the randomness forcing the head variation to originate from the hydraulic conductivity
field of the aquifer. The head covariance functions are studied using two convenient forms of the logarithmic hydraulic conductivity
process. The results demonstrate the significant reduction in the head variances and covariances due to the presence of a
leaky layer. The hydraulic head correlation distance is also reduced greatly due to the presence of the leaky layer. 相似文献
13.
For short-period near-earthquake records in eastern China, from the empirical attenuation formula of coda ground motion amplitudeA with timeτ: lgA=G−2. 235 lgτ, using the single scattering theory modified with epicentral distance, we obtain the curve family of corrected coda amplitudeA
c(r,t), andω/2Q
c values for each time interval of coda. From this,Q
c(f,h) values, which correspond to each observational average frequency and sampling depth, are calculated. The results substantially
agree with those observationalQ
c values in Yunnan, Beijing and central Asia. 相似文献
14.
Valerio Lombardo Maria Fabrizia Buongiorno Stefania Amici 《Bulletin of Volcanology》2006,68(7-8):641-651
The simultaneous solution of the Planck equation (involving the widely used “dual-band” technique) using two shortwave infrared (SWIR) bands allows for an estimate of the fractional area of the hottest part of an active lava flow (f
h) and the background temperature of the cooler crust (T
c). The use of a high spectral and spatial resolution imaging spectrometer with a wide dynamic range of 15 bits (DAIS 7915) in the wavelength range from 0.501 to 12.67 μm resulted in the identification of crustal temperature and fractional areas for an intra-crater hot spot at Mount Etna, Italy. This study indicates the existence of a relationship between these T
c and f
h extracted from DAIS and Landsat TM data. When the dual band equation system is performed on a lava flow, a logarithmic distribution is obtained from a plot of the fractional area of the hottest temperature vs. the temperature of the cooler crust. An entirely different distribution is obtained over active degassing vents, where increases in T
c occur without any increase in f
h. This result indicates that we can use scatter plots of T
c vs. fh to discriminate between different types of volcanic activity, in this case between degassing vents and lava flows, using satellite thermal data. 相似文献
15.
Ali Osman Öncel Ian Main Ömer Alptekin Patience Cowie 《Pure and Applied Geophysics》1996,147(1):147-159
We investigate the nature of temporal variations in the statistical properties of seismicity associated with the North Anatolian Fault Zone between longitudes 31°–41°E during the instrumental period 1900–1992. Temporal variations in the seismicb value and the fractal (correlation) dimensionD
c
of earthquake epicenters are examined for earthquakes of magnitudeM
S
4.5, using sliding windows of 100 consecutive events.b varies temporally between 0.6 and 1.0, andD
c
between 0.6 and 1.4, both representing significant fluctuations above the errors in measurement technique. A strong negative correlation (r=–0.85) is observed betweenb andD
c
, consistent with previous observation of seismicity in Japan and southern California. Major events early in this century (M
S
7) are associated with lowb and highD
c
, respectively consistent with greater stress intensity and greater spatial clustering of epicenters—both implying a greater degree of stress concentration at this time. 相似文献
16.
G. Christakos V. Papanicolaou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2000,14(6):471-478
Permissibility of a covariance function (in the sense of Bochner) depends on the norm (or metric) that determines spatial
distance in several dimensions. A covariance function that is permissible for one norm may not be so for another. We prove
that for a certain class of covariances of weakly homogeneous random fields, the spatial distance can be defined only in terms
of the Euclidean norm. This class includes commonly used covariance functions. Functions that do not belong to this class
may be permissible covariances for some non-Euclidean metric. Thus, a different class of covariances, for which non-Euclidean
norms are valid spatial distances, is also discussed. The choice of a coordinate system and associated norm to describe a
physical phenomenon depends on the nature of the properties being described. Norm-dependent permissibility analysis has important
consequences in spatial statistics applications (e.g., spatial estimation or mapping), in which one is concerned about the
validity of covariance functions associated with a physically meaningful norm (Euclidean or non-Euclidean). 相似文献
17.
Spatial variation in soil resistance to flowing water erosion along a regional transect in the Loess Plateau 总被引:4,自引:0,他引:4
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The factors influencing soil erosion may vary with scale. It remains unclear whether the spatial variation in soil erosion resistance is controlled by regional variables (e.g. precipitation, temperature, and vegetation zone) or by local specific variables (e.g. soil properties, root traits, land use, and farming operations) when the study area enlarges from a hillslope or catchment to the regional scale. This study was performed to quantify the spatial variations in soil erosion resistance to flowing water under three typical land uses along a regional transect on the Loess Plateau and to identify whether regional or local specific variables are responsible for these changes. The results indicated that the measured soil detachment capacities (Dc) of cropland exhibited an irregular trend along the regional transect. The Dc of grassland increased with mean annual precipitation, except for two sites (Yijun and Erdos). The measured Dc of woodland displayed an inverted ‘U’ shape. The changes in rill erodibility (Kr) of three land uses were similar to Dc, whereas no distinguishable trend was found for critical shear stress (τc). No significant correlation was detected between Dc, Kr and τc, and the regional variables. The spatial variation in soil erosion resistance could be explained reasonably by changes in soil properties, root traits, land use, and farming operations, rather than regional variables. The adjustment coefficient of Kr for grassland and woodland could be well simulated by soil cohesion and root mass density (R2 = 0.70, P < 0.01), and the adjustment coefficient of critical shear stress could be estimated with aggregate stability (R2 = 0.57, P < 0.01). The results are helpful for quantifying the spatial variation in soil detachment processes by overland flow and to develop process‐based erosion model at a regional scale. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
18.
Zhiping Song Xiangchu Yin Shirong Mei Yucang Wang Can Yin Huihui Zhang Langping Zhang 《Pure and Applied Geophysics》2006,163(9):1991-2009
Based on the three-dimensional elastic inclusion model proposed by Dobrovolskii, we developed a rheological inclusion model
to study earthquake preparation processes. By using the Corresponding Principle in the theory of rheologic mechanics, we derived
the analytic expressions of viscoelastic displacement U(r, t) , V(r, t) and W(r, t), normal strains εxx (r, t), εyy (r, t) and εzz (r, t) and the bulk strain θ (r, t) at an arbitrary point (x, y, z) in three directions of X axis, Y axis and Z axis produced by a three-dimensional inclusion in the semi-infinite rheologic medium defined by the standard linear rheologic
model. Subsequent to the spatial-temporal variation of bulk strain being computed on the ground produced by such a spherical
rheologic inclusion, interesting results are obtained, suggesting that the bulk strain produced by a hard inclusion change
with time according to three stages (α, β, γ) with different characteristics, similar to that of geodetic deformation observations, but different with the results of
a soft inclusion. These theoretical results can be used to explain the characteristics of spatial-temporal evolution, patterns,
quadrant-distribution of earthquake precursors, the changeability, spontaneity and complexity of short-term and imminent-term
precursors. It offers a theoretical base to build physical models for earthquake precursors and to predict the earthquakes. 相似文献
19.
S. D’Amico D. Caccamo F. Parrillo C. Lagana F. M. Barbieri 《Izvestiya Physics of the Solid Earth》2010,46(4):317-326
The purpose of this work is to highlight some methodological aspects related to the observation of possible anomalies in the
temporal decay of aftershocks temporal series following a mainshock with magnitude M ≥ 7.0. In this paper we present the results for the Taiwan seismic sequence started on 20 September 1999 (M = 7.7) by tuning some seismic parameters that show considerable variations during the aftershock decay process. In here we
also present the results obtained using a fractal approach for the seismic sequence. Earthquakes belong to a class of phenomena
known as multifractals. In general it is important to define the fractal dimension D, but sometimes is not useful if we are describing a natural phenomenon; so it is necessary to define D
0 called box-counting dimension and D
2 called correlation dimension, usually D
0 ≥ D
2. In the elaborations of the fractal dimensions, for this sequence, we have obtained values lesser than 1, with a greater
tendency of aftershocks to clusterize in time before a large aftershock. This is coherent with the possible existence of seismic
anomalies, that could occur before the large aftershock. We also report the results obtained by using the delta/sigma method
described firstly in [Caccamo et al., 2005] and later applied to different seismic sequence. The observed temporal series
of the aftershocks per day can be considered as a sum of a deterministic and a stochastic contribution. If the decay can be
modeled as a non-stationary Poissonian process, the number of aftershocks in a small time interval Δt is the mean value n(t) Δt, with a standard deviation (δ = √n(t)Δt. Investigating both aftershock behavior and a wide spectrum of parameters may find the key to explain better the mechanism
of seismicity as a whole. 相似文献
20.
Ergodicity is a behavior generally limited to equilibrium states and is here defined as the equivalence of ensemble and temporal
averages. In recent years, effective ergodicity is identified in simulated earthquakes generated by numerical fault models
and in real seismicity of natural fault networks by using the Thirumalai-Mountain metric. Although the effective ergodicity
is already reported for Taiwanese seismicity, an immediate doubt is the unrealistic gridded sizes for discretizing the seismic
data. In this study, we re-examined the effective ergodicity in Taiwanese seismicity by using reasonable gridded sizes which
corresponded with the location errors in the real earthquake catalogue. Initial time and magnitude cut-off were examined for
the validity of ergodic behavior. We found that several subsets extracted from Taiwanese seismicity possessed effectively
ergodic intervals and all terminations of these ergodic intervals temporally coincided with the occurrences of large earthquakes
(M
L
< 6.5). We thus confirm the ergodicity in the crustal seismicity by using the Thirumalai-Mountain metric. 相似文献