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1.
The attenuation properties of the crust in the Koyna region of the Indian shield have been investigated using 164 seismograms
from 37 local earthquakes that occurred in the region. The extended coda normalization method has been used to estimate the
quality factors for P waves and S waves , and the single back-scattering model has been used to determine the quality factor for coda waves ( Q
c). The earthquakes used in the present study have the focal depth in the range of 1–9 km, and the epicentral distance vary
from 11 to 55 km. The values of
and Q
c show a dependence on frequency in the Koyna region. The average frequency dependent relationships ( Q = Q
0
f
n) estimated for the region are , and . The ratio is found to be greater than one for the frequency range considered here (1.5–18 Hz). This ratio, along with the frequency
dependence of quality factors, indicates that scattering is an important factor contributing to the attenuation of body waves
in the region. A comparison of Q
c and in the present study shows that for frequencies below 4 Hz and for the frequencies greater than 4 Hz. This may be due to the multiple scattering effect of the medium. The outcome of this
study is expected to be useful for the estimation of source parameters and near-source simulation of earthquake ground motion,
which in turn are required in the seismic hazard assessment of a region. 相似文献
2.
The attenuation of coda waves, Q
c
, has been estimated in Zarand, Jiroft, and Bam regions of east central Iran using a single back-scattering model of S-coda
envelopes. For this purpose, the recordings of 97 earthquakes by three seismic networks and a local strong ground motion network
have been used. In this research, the frequency-dependent Q
c
values are estimated at central frequencies of 1.5, 3, 6, 8, 12, 16, and 24 Hz using different lapse time windows from 20
to 60 s. The frequency-dependent relationships obtained are for Zarand, for Jiroft, and for Bam region. From the strong ground motion data, we obtain the relation . The Q
c
frequency-dependent relationship for the entire region of east central Iran from all data (both seismograms and accelerograms)
is . The average Q
c
values estimated and their frequency dependent relationships correlate well with a highly heterogeneous and highly tectonically
active region. Results also show that the attenuation is higher in Bam region compared to Zarand and Jiroft regions. 相似文献
3.
The seismic quality factor ( Q
c) and the attenuation coefficient ( δ) in the earth’s crust in southwest (SW) Anatolia are estimated by using the coda wave method based on the decrease of coda
wave amplitude by time on the seismogram. The quality factor Q
o, the value of Q
c at 1 Hz, and its frequency dependency η are determined from this method depending on the attenuation properties of scattered coda waves. δ is determined from the observations of amplitude variations of seismic waves. In applying the coda wave method, firstly,
a type curve representing the average pattern of the individual coda decay curves for 0.75, 1.5, 3.0, 6.0, 12.0, and 24.0 Hz
values was estimated. Secondly, lateral variation of coda Q and the attenuation coefficients for three main tectonic patterns
are estimated. The shape of the type curve is controlled by the scattering and attenuation in the crustal volume sampled by
the coda waves. The Q
o and η values vary from 30 to 180 and from 0.55 to 1.25, respectively for SW Anatolia. In SW Anatolia, coda Q– f relation is described by and δ = 0.008 km −1. These results are expected to help in understanding the degree of tectonic complexity of the crust in SW Anatolia. 相似文献
4.
Seismic coda wave attenuation ( $ Q_{\text{c}}^{ - 1} $ ) characteristics in the Garhwal region, northwestern Himalaya is studied using 113 short-period, vertical component seismic observations from local events with hypocentral distance less than 250?km and magnitude range between 1.0 to 4.0. They are located mainly in the vicinity of the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT), which are well-defined tectonic discontinuities in the Himalayas. Coda wave attenuation ( $ Q_{\text{c}}^{ - 1} $ ) is estimated using the single isotropic scattering method at central frequencies 1.5, 3, 5, 7, 9, 12, 16, 20, 24 and 28?Hz using several starting lapse times and coda window lengths for the analysis. Results show that the ( $ Q_{\text{c}}^{ - 1} $ ) values are frequency dependent in the considered frequency range, and they fit the frequency power law ( $ Q_{\text{c}}^{ - 1} \left( f \right) = Q_{0}^{ - 1} f^{ - n} $ ). The Q 0 ( Q c at 1?Hz) estimates vary from about 50 for a 10?s lapse time and 10?s window length, to about 350 for a 60?s lapse time and 60?s window length combination. The exponent of the frequency dependence law, n ranges from 1.2 to 0.7; however, it is greater than 0.8, in general, which correlates well with the values obtained in other seismically and tectonically active and highly heterogeneous regions. The attenuation in the Garhwal region is found to be lower than the Q c ?1 values obtained for other seismically active regions of the world; however, it is comparable to other regions of India. The spatial variation of coda attenuation indicates that the level of heterogeneity decreases with increasing depth. The variation of coda attenuation has been estimated for different lapse time and window length combinations to observe the effect with depth and it indicates that the upper lithosphere is more active seismically as compared to the lower lithosphere and the heterogeneity decreases with increasing depth. 相似文献
5.
Strombolian-type volcanic activity is characterized by a series of gas bubbles bursting at the top of a magma column and leading
to the ejection of lava clots and gas emission at the surface. The quantitative analysis of physical parameters (e.g., velocity,
size, and mass fluxes) controlling the emission dynamics of these volcanic products is very important for the understanding
of eruption source mechanisms but remains difficult to obtain in a systematic fashion. Ground-based Doppler radar is found
to be a very effective tool for measuring ejecta velocities at a high acquisition rate and close to the emission source. We
present here a series of measurements carried out at Mt. Etna’s Southeast crater, using an L-band volcanological Doppler radar,
during the 4 July 2001 Strombolian eruptions. Doppler radar data are supplemented by the analysis of video snapshots recorded
simultaneously. We provide here a set of physical parameters systematically retrieved from 247 Strombolian explosions spanning
15 min and occurring during the paroxysm of the eruption from 21:30 to 21:45 UT. The time-average values give a maximum particle
velocity of
Vmaxp = 94.7±24 \text m/ s V_{{\max }}^p = {94}.{7}\pm {24} {\text{m/s}} , a bulk lava jet velocity of
V\textPW - rad = 37.6±1.9 \text m/ s {V_{{{\text{PW - rad}}}}} = {37}.{6}\pm {1}.{9} {\text{m/s}} , and an initial gas velocity at the source vent of
V0g = 118.4±36 \text m/ s V_0^g = {118}.{4}\pm {36} {\text{m/s}} . The time-averaged particle diameter is found to be about
D\textPW - rad = 4.2±2.1 \text cm {D_{{{\text{PW - rad}}}}} = {4}.{2}\pm {2}.{1} {\text{cm}} . The volume and mass gas fluxes are estimated from time-averaged source gas velocities over the sequence duration at
Qvg = 3 - 11 ×10 3\text m3\text/ s Q_v^g = {3} - {11} \times {1}{0^{{3}}}{{\text{m}}^{{3}}}{\text{/s}} and
Qmg = 0.5 - 2 ×10 3\text kg/ s Q_m^g = 0.{5} - {2} \times {1}{0^{{3}}}{\text{kg/s}} , respectively. 相似文献
6.
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
7.
We analyze the strong motion accelerograms of the moderate ( M
w = 6.1), March 31, 2006, Darb-e-Astane earthquake of western Iran and also those of one of its prominently recorded, large
( M
w = 5.1) foreshock and ( M
w = 4.9) aftershock. (1) Using derived SH-wave spectral data, we first objectively estimate the parameters W o\mathit{\Omega} _{\rm o} (long period spectral level), f
c (corner frequency) and Q( f) (frequency dependent, average shear wave quality factor), appropriate for the best-fit Brune ω
− 2 spectrum of each of these three events. We then perform a non-linear least square analysis of the SH-wave spectral data to
provide approximate near-field estimates of the strike, dip, and rake of the causative faults and also the seismic moment,
moment magnitude, source size, and average stress drop of these three events. (2) In the next step, we use these approximate
values and an empirical Green’s function approach, in an iterative manner, to optimally model the strong ground motion and
rupture characteristics of the main event in terms of peak ground acceleration/velocity/displacement and duration of ground
shaking and thereby provide improved, more reliable estimates of the causative fault parameters of the main event and its
asperities. Our near-field estimates for both the main moderate event and the two smaller events are in good conformity with
the corresponding far-field estimates reported by other studies. 相似文献
8.
The intrinsic dissipation and scattering attenuation in southwestern (SW) Anatolia, which is a tectonically active region,
is studied using the coda waves. First the coda quality factor ( Qc) assuming single scattering is estimated from the slope of the coda-wave amplitude decay. Then the Multiple Lapse Time Window
(MLTW) analysis is performed with a uniform earth model. Three non-overlapping temporal data windows are used to calculate
the scattered seismic energy densities against the source-receiver distances, which, in turn, are used to calculate separate
estimates of the intrinsic and scattering factors. In order to explore the frequency dependency, the observed seismograms
are band pass-filtered at the center frequencies of 0.75, 1.5, 3.0, 6.0 and 12.0. The scattering attenuation ( Qs−1) is found lower than the intrinsic attenuation ( Qi−1) at all frequencies except at 0.75 Hz where the opposite is observed. Overall the intrinsic attenuation dominates over the
scattering attenuation in the SW Anatolia region. The integrated energy curves obtained for the first energy window (i.e.,
0–15 s) are somewhat irregular with distance while the second (i.e., 15–30 s) and third (i.e., 30–45 s) data windows exhibit
more regular change with distance at most frequencies. The seismic albedo B0 is determined as 0.61 at 0.75 Hz and 0.34 at 12.0 Hz while the total attenuation factor denoted by Le−1 changes in the range 0.034–0.017. For the source-station range 20–180 km considered the scattering attenuation is found strongly
frequency dependent given by the power law Qs−1 = 0.010* f−1.508. The same relations for Qi−1, Qt−1 (total), Qc−1 and
(expected) hold as Qi−1 = 0.0090* f−1.17, Qt−1 = 0.019* f−1.31, Qc−1 = 0.008* f−0.84 and
respectively. Compared to the other attenuation factors Qc−1 and
are less dependent on the frequency. 相似文献
9.
In this paper the application of an edge detection technique to gravity data is described. The technique is based on the tilt
angle map (TAM) obtained from the first vertical gradient of a gravity anomaly. The zero contours of the tilt angle correspond
to the boundaries of geologic discontinuities and are used to detect the linear features in gravity data. I also present that
the distance between zero and
±p\mathord | / |
\vphantom p4 4 \pm {\pi \mathord{\left/ {\vphantom {\pi 4}} \right. \kern-\nulldelimiterspace} 4} pairs obtained from the TAM corresponds to the depth to the top of the vertical contact model. Alternatively, the half distance
between
- p\mathord | / |
\vphantom p4 4 - {\pi \mathord{\left/ {\vphantom {\pi 4}} \right. \kern-\nulldelimiterspace} 4} and
+ p\mathord | / |
\vphantom p4 4 + {\pi \mathord{\left/ {\vphantom {\pi 4}} \right. \kern-\nulldelimiterspace} 4} radians is equal to the depth to the same model. I illustrate the applicability of the present method by gravity data due
to buried vertical prisms, imaging the positions of the edges of the prisms. The results obtained from the theoretical data,
with and without random noise, have been discussed. The analysis of the TAM has been demonstrated on a field example from
the Kozaklı-Central Anatolian region, Turkey, and the location and depth of the edges of the structural uplifts of the Kozaklı graben are imaged. The results indicated
that depth values from these sources have ranged between 0.2 and 0.6 km. I have also compared the Euler deconvolution technique
with the TAM images obtained from the first vertical gradient of residual gravity anomaly. Both techniques have agreed closely
in detecting the horizontal location and depth of the uplift edges in the subsurface with good precision. 相似文献
10.
—The coda Q, Q c ?, have been estimated for the Koyna region of India. The coda waves of 76 seismograms from thirteen local earthquakes, recorded digitally in the region during July–August, 1996, have been analyzed for this purpose at nine central frequencies viz., 1.5, 2.0, 3.0, 4.0, 6.0, 8.0, 12.0, 16.0 and 24.0 Hz using a single backscattering model. All events with magnitude less than 3 fall in the epicentral distances less than 60 km and have focal depths which range from 0.86 to 9.43 km. For the 30 sec coda window length the estimated Q c values vary from 81 to 261 at 1.5 Hz and 2088 to 3234 at 24 Hz, whereas the mean values of Q c with the standard error vary from 148 ± 13.5 at 1.5 Hz to 2703 ± 38.8 at 24 Hz. Both the estimated Q c values and their mean values exhibit the clear dependence on frequency in the region and a frequency dependence average attenuation relationship, Q c = 96 f 1.09, has been obtained for the region, covering an approximate area of 11500 km 2 with the surfacial extent of about 120 km and depth of 60 km.¶Lapse time dependence of Q c has also been studied for the region, with the coda waves analyzed at five lapse time windows from 20 to 60 sec duration with the difference of 10 sec. The frequency dependence average Q c relationships obtained at these window lengths Q c = 66 f 1.16 (20 sec), Q c = 96 f 1.09 (30 sec), Q c =131 f 1.04 (40 sec), Q c = 148 f 1.04 (50 sec), Q c = 182 f 1.02 (60 sec) show that the frequency dependence (exponentn) remains mostly stationary at all the lapse time window lengths, while the change in Q 0 value is significant. Lapse time dependence of Q c in the region is also interpreted as the function of depth. 相似文献
11.
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=126 f1.03 (40–70 sec) and Qc=122 f1.02 (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
12.
The attenuation properties of the crust in the Chamoli region of Himalaya have been examined by estimating the frequency-dependent relationships of quality factors for P waves (Q α) and for S waves (Q β) in the frequency range 1.5–24 Hz. The extended coda normalization method has been applied on the waveforms of 25 aftershocks of the 1999 Chamoli earthquake (M 6.4) recorded at five stations. The average value of Q α is found to be varied from 68 at 1.5 Hz to 588 at 24 Hz while it varies from 126 at 1.5 Hz to 868 at 24 Hz for Q β. The estimated frequency-dependent relations for quality factors are Q α = (44 ± 1)f (0.82±.04) and Q β = (87 ± 3)f (0.71±.03). The rate of increase of Q(f) for P and S waves in the Chamoli region is comparable with the other regions of the world. The ratio Q β/Q α is greater than one in the region which along with the frequency dependence of quality factors indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of attenuation relation for S wave estimated here (Q β = 87f 0.71) with that of coda waves (Q c = 30f 1.21) obtained by M andal et al. (2001) for the same region shows that Q c > Q β for higher frequencies (>8 Hz) in the region. This indicates a possible high frequency coda enrichment which suggests that the scattering attenuation significantly influences the attenuation of S waves at frequencies >8 Hz. This observation may be further investigated using multiple scattering models. The attenuation relations for quality factors obtained here may be used for the estimation of source parameters and near-source simulation of earthquake ground motion of the earthquakes, which in turn are required for the assessment of seismic hazard in the region. 相似文献
13.
The local earthquake waveforms recorded on broadband seismograph network of Institute of Seismological Research in Gujarat,
India have been analyzed to understand the attenuation of high frequency (2–25 Hz) P and S waves in the region. The frequency
dependent relationships for quality factors for P ( Q
P) and S ( Q
S) waves have been obtained using the spectral ratio method for three regions namely, Kachchh, Saurashtra and Mainland Gujarat.
The earthquakes recorded at nine stations of Kachchh, five stations of Saurashtra and one station in mainland Gujarat have
been used for this analysis. The estimated relations for average Q
P and Q
S are: Q
P = (105 ± 2) f
0.82 ± 0.01, Q
S = (74 ± 2) f
1.06 ± 0.01 for Kachchh region; Q
P = (148 ± 2) f
0.92 ± 0.01, Q
S = (149 ± 14) f
1.43 ± 0.05 for Saurashtra region and Q
P = (163 ± 7) f
0.77 ± 0.03, Q
S = (118 ± 34) f
0.65 ± 0.14 for mainland Gujarat region. The low Q (<200) and high exponent of f (>0.5) as obtained from present analysis indicate the predominant seismic activities in the region. The lowest Q values obtained for the Kachchh region implies that the area is relatively more attenuative and heterogeneous than other
two regions. A comparison between Q
S estimated in this study and coda Q ( Qc) previously reported by others for Kachchh region shows that Q
C > Q
S for the frequency range of interest showing the enrichment of coda waves and the importance of scattering attenuation to
the attenuation of S waves in the Kachchh region infested with faults and fractures. The Q
S/ Q
P ratio is found to be less than 1 for Kachchh and Mainland Gujarat regions and close to unity for Saurashtra region. This
reflects the difference in the geological composition of rocks in the regions. The frequency dependent relations developed
in this study could be used for the estimation of earthquake source parameters as well as for simulating the strong earthquake
ground motions in the region. 相似文献
14.
The Q-factor estimates of the Earth’s crust and upper mantle as the functions of frequency ( Q( f)) are obtained for the seismic S-waves at frequencies up to ~35 Hz. The estimates are based on the data for ~40 earthquakes recorded by the Kislovodsk seismic station since 2000. The magnitudes of these events are MW > 3.8, the sources are located in the depth interval from 1 to 165 km, and the epicentral distances range from ~100 to 300 km. The Q-factor estimates are obtained by the methods developed by Aki and Rautian et al., which employ the suppression of the effects of the source radiation spectrum and local site responses in the S-wave spectra by the coda waves measured at a fixed lapse time (time from the first arrival). The radiation pattern effects are cancelled by averaging over many events whose sources are distributed in a wide azimuthal sector centered at the receiving site. The geometrical spreading was specified in the form of a piecewise-continuous function of distance which behaves as 1/ R at the distances from 1 to 50 km from the source, has a plateau at 1/50 in the interval from 50–70 km to 130–150 km, and decays as \({\raise0.7ex\hbox{$1$} \!\mathord{\left/ {\vphantom {1 {\sqrt R }}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${\sqrt R }$}}\) beyond 130–150 km. For this geometrical spreading model and some of its modifications, the following Q-factor estimates are obtained: Q( f) ~ 85 f0.9 at the frequencies ranging from ~1 to 20 Hz and Q( f) ~ 75 f1.0 at the frequencies ranging from ~1 to 35 Hz. 相似文献
15.
Based on the single scattering model of coda power spectrum analysis, digital waveform data of 50 events recorded by the real-time
processing system of the Chengdu telemetry network are analyzed to estimate the Q
c values of earth medium beneath the Chengdu telemetry network for several specified frequencies. It is found that the Q
c shows the frequency dependency in the form of Q
c = Q
0
f
n in the range of 1.0 to 20.0Hz. Estimated Q
0 ranges from 60.83 to 178.05, and n is found to be 0.713 to 1.159. The average value of Q
0 and n are 117 and 0.978 respectively. This result indicates the strong frequency dependency of the attenuation of coda waves beneath
the Chengdu telemetry network. Comparing with the results obtained in other regions of the world, it is found that Q
0
−1 value and its change with frequency are similar to those in regions with strong tectonic activity.
This subject is supported by the Ministry of Personnel, China for partly sponsoring. 相似文献
16.
Coda wave attenuation quality factor Qc is estimated in the northeastern region of India using 45 local earthquakes recorded
by regional seismic network. The quality factor Qc was estimated using the single backscattering model modified by Sato (J
Phys Earth 25:27–41, 1977), in the frequency range 1–18 Hz. The attenuation and frequency dependence for different paths and the correlation of the
results with geotectonics of the region are described in this paper. A total of 3,890 Qc measurements covering 187 varying
paths are made for different lapse time window of 20, 30, 40, 50, 60, 70, 80, and 90 s in coda wave. The magnitudes of the
analyzed events range from 1.2 to 3.9 and focal depths range between 7 and 38 km. The source–receiver distances of the selected
events range between 16 and 270 km. For 30-s duration, the mean values of the estimated Qc vary from 50 ± 12 (at 1 Hz) to
2,078 ± 211(at 18 Hz) for the Arunachal Himalaya, 49 ± 14 (at 1 Hz) to 2,466 ± 197 (at 18 Hz) for the Indo-Burman, and 45
± 13 (at 1 Hz) to 2,069 ± 198 (at 18 Hz) for Shillong group of earthquakes. It is observed that Qc increases with frequency
portraying an average attenuation relation for the region. Moreover, the pattern of Qc − 1 with frequency is analogous to the estimates obtained in other tectonic areas in the world, except with the observation that
the Qc − 1 is much higher at 1 Hz for the northeastern region. The Qc − 1 is about 10 − 1.8 at 1 Hz and decreases to about 10 − 3.6 at 18 Hz indicating clear frequency dependence. Pertaining to the spatial distribution of Qc values, Mikir Hills and western
part of Shillong Plateau are characterized by lower attenuation. 相似文献
17.
The attenuation of coda waves in the earth’s crust in southwest (SW) Anatolia is estimated by using the coda wave method, which is based on the decrease of coda wave amplitude in time and distance. A total of 159 earthquakes were recorded between 1997 and 2010 by 11 stations belonging to the KOERI array. The coda quality factor Q c is determined from the properties of scattered coda waves in a heterogeneous medium. Firstly, the quality factor Q 0 (the value of Q c at 1 Hz.) and its frequency dependency η are determined from this method depending on the attenuation properties of scattered coda waves for frequencies of 1.5, 3.0, 6.0, 8.0, 12 and 20 Hz. Secondly, the attenuation coefficients ( δ) are estimated. The shape of the curve is controlled by the scattering and attenuation in the crustal volume sampled by the coda waves. The average Q c values vary from 110 ± 15 to 1,436 ± 202 for the frequencies above. The Q 0 and η values vary from 63 ± 7 to 95 ± 10 and from 0.87 ± 0.03 to 1.04 ± 0.09, respectively, for SW Anatolia. In this region, the average coda Q– f relation is described by Q c = (78 ± 9) f 0.98±0.07 and δ = 0.012 km ?1. The low Q 0 and high η are consistent with a region characterized by high tectonic activity. The Q c values were correlated with the tectonic pattern in SW Anatolia. 相似文献
18.
In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered
respectively at the 4 short period stations installed near the foci shortly after the M7.6 Lancang and M7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and the Q
c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study
shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and
northern areas. The southern area presents a faster attenuation ( Q
c=114), whereas the northern area shows a slower attenuation ( Q
c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear
relation between the coda source factor A
o( f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lg M
0=lg A
0( f)+17.6, M
D=0.67lg A
0( f)+1.21 and log M
0=1.5 M
D+15.79. In addition, the rates of amplitude attenuation β
s and β
m are respectively calculated using the single scattering and multiple scattering models, and the ratio β
s/β m=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free path L of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations
which can distinguish between the inherent Q
i and scattering Q
s, testify to this areas having low Q-values correspond to stronger scatterings.
The Chinese version of this paper appeared in the Chinese edition of Acta Seismologica Sinica, 14, 71–82, 1992.
This study is partly supported by the Seismological Science Foundation of the State Seismological Bureau of China, and the
present English version of the paper is translated from its Chinese original by Wenyi Xia, Seismological Bureau of Yunnan
Province. 相似文献
19.
Wave tank experiments with long internal waves of elevation, of different initial length l, moving in a two-fluid system, interacting with a weak slope of 0.045 rad, show an onshore flow of the dense water, at the undisturbed pycnocline-slope intersection, of duration $11.3\sqrt{l/g'}Wave tank experiments with long internal waves of elevation, of different initial length l, moving in a two-fluid system, interacting with a weak slope of 0.045 rad, show an onshore flow of the dense water, at the
undisturbed pycnocline-slope intersection, of duration 11.3?{l/g￠}11.3\sqrt{l/g'} (g′ reduced gravity). This period corresponds to that of a strong bottom current event measured in the stratified ocean at the
Ormen Lange gas field, at 850 m depth, lasting for 24 hrs, corresponding to 11.2?{l/g￠}11.2\sqrt{l/g'}, using the width l = 300 km of the Norwegian Atlantic Current (NAC) at the site as length scale, suggesting a lateral sloshing motion of the
NAC causing the event. The onshore velocity of the dense fluid has a maximal velocity of 0.4?{g￠h2}0.4\sqrt{g'h_2} in laboratory and 0.5 ms-1=0.3?{g￠h2}^{-1}=0.3\sqrt{g'h_2} in the field (h
2 mixed upper layer thickness). Run-up of the dense fluid, beyond the undisturbed pycnocline-slope intersection, has initially
a front velocity of 0.35?{g￠h2}0.35\sqrt{g'h_2}, corresponding to the velocity of the head of a density current on a flat bottom. Due to disintegration, an initially depressed
pycnocline results in comparatively smaller run-up and velocity. While moving past the turning point, a dispersive wave train
is formed in the back part of the depression wave, developing by breaking into a sequence of up to eight boluses moving by
the undisturbed pycnocline-slope intersection. 相似文献
20.
A new estimate of the fracture parameters of earthquakes is provided in this paper. By the Muskhelishvili method (1953) a number of basic relations among fracture-mechanics parameters are derived. A scheme is proposed to evaluate the slip weakening parameters in terms of fault dimension, average slip, and rise time, and the new results are applied to 49 events compiled in the earthquake catalogue of Purcaru and Berckhemer (1982). The following empirical relations are found in the paper: $$\begin{gathered} \frac{{\tau _B - \tau _f }}{{\tau _\infty - \tau _f }} = 2.339 \hfill \\ {{\omega _c } \mathord{\left/ {\vphantom {{\omega _c } {W = 0.113}}} \right. \kern-\nulldelimiterspace} {W = 0.113}} \hfill \\ \log G_c \left( {{{dyne} \mathord{\left/ {\vphantom {{dyne} {cm}}} \right. \kern-\nulldelimiterspace} {cm}}} \right) = 2 \log L (km) + 6.167 \hfill \\ \log \delta _c (cm) = 2 \log L (km) - 1.652 \hfill \\ \end{gathered} $$ where G c is the specific fracture energy, ω c the size of the slip weakening zone, δ c the slip weakening displacement, τ B ? τ f the drop in strength in the slip weakening zone, τ ∞? τ f the stress drop, L the fault length, and W the fault width. The investigation of 49 shocks shows that the range of strength drop τ B ? τ f is from several doze to several hundred bars at depth h<400 km, but it can be more than 10 3 bars at h>500 km; besides, the range of the size ω c of the strength degradation zone is from a few tenths of a kilometer to several dozen kilometers, and the range of the slip weakening displacement δ c is from several to several hundred centimeters. The specific fracture energy G c is of the order of 10 8 to 10 11 erg cm ?2 when the moment M 0 is of the order of 10 23 to 10 29 dyne cm. 相似文献
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