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1.
The digital seimograph network set up by China and France in Zhangye of China had been operated in 1988. The Zhangye network
is situated in the middle segment of Hexi corridor and Qilina mountain, which was regarded as a monitoring earthquake area.
Using the records of Zhangye digital network theQ-values in and around Minle basin have been measured. The results of this study showed that theQp-values range from 500 to 780, andQs-values range from 230 to 460. TheQ-values of inside of Minle basin are higher than that around the basin. The greater parts of moderate and strong earthquakes
occurred along tectonic belts around the Minle basin. Moreover, TheQ-values increased with the depth of penctration of wave ray. The attenuation of S wave is stronger than P wave in shallow
layer of crust. Some problems ofQ-value change versus time before and after Sunan eathquake (M
s=5.7) have been also disscussed. These results can be applied to study and to monitor seismic danger of the Minle monitoring
area.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 296–302, 1993. 相似文献
2.
3.
Based on the scattering coda model by which local and regional earthquakes are interpreted (K. Aki, 1969), and using observational coda data of 68 aftershocks of the 1985 Luquan, Yunnan earthquake registered by the VGK seismographs installed at 12 stations in the Yunnan regional short-period network, theQ-values of coda waves are calculated respectively for 6 time intervals. It is observed that within the frequency range of 0.40–1.65 Hz of the observed data, theQ-values are closely related with the frequencies and the calculated codaQ ranges between 80–240 with the coefficient of frequency dependence η=0.45. The calculated source factorsB(f> p) of the coda waves which indicate the scattering strength are mostly within the order 10?23–10?24. Areas with lowQ-values present high scattering. It should be noted that by comparing data obtained before and after the Luquan earthquake, clear changes can be detected in theQ-values measured at stations close to the epicentral region, and that theQ-values of the aftershock coda are less than about one half of the pre-shock values. It may be mentioned that the time-dependent regional variations of theQ-values might possibly bring about practical significance in earthquake prediction. Moreover, aftershock focal parameters are determined. Through discussions on the quantitative relations between the focal parameters, we get: 1gE=1.59M L+ 11.335;E=(2.10 × 10?5)M 0; length of focal rupturea=0.40?0.80 km for 3.0≤M L<5.0 events; stress drop Δσ=(6.0–130) ×105 Pa. Through interpretation of the data, we have also learned the important characteristics that there is no linear relation between the stress drops and the earthquake magnitudes. 相似文献
4.
Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), theQ
R
of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino-Korean paraplatform
in this paper. TheQ
β
models of the crust and upper mantle are respectively obtained for the 4 paths, with the aid of stochastic inverse method.
It shows that in the eastern Sino-Korean paraplatform, the average crustalQ
β
is about 200, and that there exists a weak attenuation layer in the middle crust (about 10–20 km deep) which is possibly
related to earthquake-prone layer. A strong attenuation layer (lowQ) of 70 km thick extensively exists in the uppermost mantle, with the buried depth about 80 km. The averageQ
R
of fundamental mode Rayleigh wave is between the value of stable tectonic region and that of active tectonic region, and
much close to the latter.
Contribution No. 96A0001, Institute of Geophysics, SSB, China.
Funded by the Chinese Joint Seismological Science Foundation. 相似文献
5.
Based on the long period surface wave data recorded by the China Digital Seismograph Network (CDSN), theQ R of fundamental mode Rayleigh wave with periods from 10 s to 146 s is determined for the eastern Sino-Korean paraplatform in this paper. TheQ β models of the crust and upper mantle are respectively obtained for the 4 paths, with the aid of stochastic inverse method. It shows that in the eastern Sino-Korean paraplatform, the average crustalQ β is about 200, and that there exists a weak attenuation layer in the middle crust (about 10–20 km deep) which is possibly related to earthquake-prone layer. A strong attenuation layer (lowQ) of 70 km thick extensively exists in the uppermost mantle, with the buried depth about 80 km. The averageQ R of fundamental mode Rayleigh wave is between the value of stable tectonic region and that of active tectonic region, and much close to the latter. 相似文献
6.
In this paper, the "spectral amplitude ratio method" (SAR), "energy method" (EN) and "coda wave method" (CW) are used to calculate theQ value variations of gneiss in the preparing rupture process. The obtained results show that the variation state ofQ values by SAR features the shape of relative stability—gradual increment to the maximum—then decrement and final rupture. The variation state ofQ values by EN is just contrary to that by SAR, i. e. with the shape of stability—decrement—increment—and final rupture. The varation state ofQ values by CW is similar to that by EN, its main frequency features the shape of relatively high value—decrement to the minimum—increment—and final rupture. But to the high frequency (higher than the main frequency), the variation state ofQ values features the shape of the stable value-increment to the maximum-decrement-and final rupture. At the same time, the results by coda wave amplitude spectrum show that, when stress reaches 70% of rupture stress, the high frequency component of S wave rapidly reduces (Q c increasing); at the time of impending the main rupture, the main frequency component reduces with a large scale (Q c increasing again), this may be the reason which causes the different variation states of two codaQ values. The result of amplitude spectra of P, S (initial wave) waves also show that with the appearance of microcracks the frequency band of S wave turn to be narrow, the high frequency component is reduced quickly, i. e. the S wave spectra have different variation states with different frequency components. That is why theQ s obtained by different methods have different variation characteristics. 相似文献
7.
Source parameters and characteristics of regional attenuation of Tangshan aftershocks are studied by using digital records
of Tangshan aftershocks. An inversion method of P wave spectra to reduce influence on the ambiguity in the estimates of parameters
by the usual spectrum analysis method is developed. By testing with digital simulation data and applying to actual data, it
is confirmed that the method is usable.
Source parameters of the Tangshan Luanxian area are obtained by using records of 35 earthquakes at 5 stations.Q values of P wave and high frequency decay rate γ of source spectrum at 5 stations are obtained. TheQ values range from 408 to 847, and the mean value is 520; whiley ranges from 1.54 to 3.22, and the mean value is 2.41.
In the studies of spectra of the micro-earthquakes in the Luanxian area, that stress drop increases with increasing earthquake
moment is found.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 430–441, 1991. 相似文献
8.
An earthquake withM=6.5 happened on January 15, 2000 in Yao’an of Yunnan Province. After the earthquake, a temporary digital network with 6 detectors around the epicenter area was set up. 402 aftershocks were located more precisely. According to coda short recording observed, the coda averaging quality factor has been acquired via Sato’s single scattering model analyses,Q c(f)=49f 0.95,f=1.5～20.0 Hz, which has the attenuation characteristics of high structural active region. 相似文献
9.
Prantik Mandal 《Pure and Applied Geophysics》2007,164(1):135-160
Delineation of the top sedimentary structure and its Qs vs. Qp relationship using the travel-time difference of direct S and converted Sp phase is key to understanding the seismic hazard
of any sedimentary basin area. We constructed filtered displacement waveforms from local ETNA Episensor acceleration recordings
as well as local velocity recordings of aftershocks of the 2001 Bhuj earthquake recorded by the Kachchh seismological network
of the National Geophysical Research Institute (NGRI), Hyderabad, India during 2001–2004. Stations are within 15–70km of epicenters,
and the resulting displacement waveforms are generally simple, displaying prominent P, Sp, and S wave pulses. Particle motion
of P and S waves suggest near-vertical raypaths consistent with preliminary depth estimates. The direct S wave on the horizontal
component is characterized by lower frequency content than the converted Sp phase on the vertical component. This difference
in frequency content between S and Sp phases can be explained in terms of different attenuation effects for P and S waves
in the unconsolidated sediments. The Sp phase is generated by S-to-P phase conversion at the base of Mesozoic sediments of
the Kachchh basin. Travel-time inversion (VELEST) of 2565 P and 2380 S arrivals from 658 well located aftershocks recorded
at 8–14 three-component local seismic stations led to 1 D velocity models indicated very slow sediments in the upper 0–2 km
depth range (Vp: 2.92 km/s and Vs: 0.90 km/s) and an increasing trend of velocities with depth at 2–40 km depth. The estimated
sediment thicknesses beneath 12 accelerograph and 6 seismograph sites from the estimated velocity model and the travel-time
difference between S and converted Sp phases reaches a maximum of (1.534 ± 0.117) km beneath Bandri (near the location of
2001 Bhuj mainshock) and attains a minimum sediment thickness of (0.858 ± 0.104) km beneath Ramvav and Burudia. The spectral
ratios between Sp and S from 159 three-component accelerograms have been used to study seismic wave attenuation in the Kachchh
rift basin. The estimated Qs vs. Qp relations for 12 accelerograph sites vary from Qs = 0.184 Qp (at Chobari) to Qs = 0.505 Qp (at Dudhai). For stations Chobari, Chopdwa, Jahawarnagar, Vondh and Tapar, the spectral ratio slopes and hence the calculated
Qs vs. Qp relations are effectively the same, and the correlation coefficients are quite high (0.91–0.93). Stations Adhoi, Manfara,
New Dudhai, Dudhai and Sikara have similar Qs vs. Qp relationships to each other and also have high correlation coefficients (0.78–0.87). The spectral ratios for stations Anjar
and Ramvav are small and poorly constrained, resulting in less reliable Qs vs. Qp relations. This could be due to noisy data, fewer available waveforms, or scattering due to velocity heterogeneities and/or
interface irregularities. 相似文献
10.
A seismic coda wave from local earthquakes is an indication of heterogeneity in the crust and upper mantle, and codaQ (Q
c
) is the parameter defining the temporal decay of the coda wave. ButQ
c
estimates obtained with the conventional least-square method are not based on any solid statistical background, assuming the Gaussian distributiona priori. In this study, we propose a statistically reliable estimation method of estimatingQ
c
using the maximum likelihood method, and show its validity and usefulness with the data from the 1986 Joint Seismological Research in the western Nagano Prefecture. We found first that theQ
c
estimation with the maximum likelihood method is statistically valid and its reliability can be checked with the -square test. Next,Q
c
around Ohtaki village, within the studied area, is estimated using the maximum likelihood method. The averageQ
c
value at low frequencies (up to 2 Hz) is one of the lowest in the world, which is in harmony with the geological setting of the site condition directly above an active fault. 相似文献
11.
Ichiro Nakanishi 《Physics of the Earth and Planetary Interiors》1979,19(4):337-347
36 pairs of multiply-reflected ScS waves from deep earthquakes around Japan are analyzed to investigate the anelastic properties of the mantle on the continental and oceanic sides of the dipping slab. The average Q-value for shear waves passing through the mantle on the oceanic side is found to be 226 in the frequency range 10–40 mHz. This Q-value is in good agreement with the Q models SL8 (Anderson and Hart, 1978) and QBS (Sailor and Dziewonski, 1978) which have been derived from free oscillation data. Assuming that the Q-value for the mantle deeper than 400 km on the continental side of the Japanese Arc is the same as that for the model SL8, we obtain a value of Q = 53 in the upper mantle above the dipping slab beneath the Sea of Japan. Higher Q-values are obtained for the mantle behind the northern Izu-Bonin arc. 相似文献
12.
Observations and studies of electromagnetic waves during the approaching of earthquakes 总被引：1，自引：0，他引：1
This article introduces the practical observation results of pre-earthquake electromagnetic radiations at the network of monitoring
stations in Jiangsu region in resent years and discusses the electromagnetic wave precursors during the approaching period
of earthquakes based on the observations of the electromagetic radiation signals before theM
s 6.0 Liyang earthquake of 1979 in Jiangsu province, theM
s 5.9 Heze earthquake of 1983 in Shandong province and theM
s 6.2 South Yellow Sea earthquake of 1984. 相似文献
13.
The attenuation of P- and S-waves in Southeastern Sicily was estimated by applying two different methods in time and frequency domains. We analyzed waveforms from about 290 local events (0.6≤ML≤4.6) recorded at a three-component digital network.By applying the pulse broadening method to the first P-wave pulse, we found an average Qp value of ca. 140. The application of the frequency decay method provided a Qp value of ca. 120, in the low-frequency band (3-9 Hz). Conversely, in the high frequency range (16-27 Hz) the average Qp is significantly larger (ca. 640). The frequency decay method was also applied to S-waves spectra. In the low frequency range (2-5 Hz) the estimated average Qs is ca. 190. As for Qp, also Qs, in the high frequency range (16-27 Hz), is larger (ca. 700). These results evidenced a frequency dependence of both the quality factors Qp and Qs, as commonly observed in tectonically active zones characterized by high degree of heterogeneity. 相似文献
14.
Based on the single scattering model of seismic coda waves, we have calculated theQ-factor in Beijing and its surrounding regions by means of calculating the power density spectrum in frequency domain with
a fixed time window. The digital seismic data of 69 earthquakes from Beijing Telemetered Seismographic Network are used. These
earthquakes were recorded from January 1, 1989 to December 31, 1990 at 20 stations. This paper shows the variations of the
codaQ-factors in the studied region with different sites, frequency and lapse time, and the temporal change of the codaQ-factors in these two years. The results indicate that codaQ-factor depends strongly on the lapse time and frequency. It is assumed that whenQ
C=Q
0fη, for the three time windows of 15–30s, 30–60s and 60–90s, the average values ofQ
0 are 48, 115 and 217; and the average values ofη are 0. 89, 0.91 and 0.74, respectively.
Contribution No. 95A0009, Institute of Geophysics, SSB, China.
This work is a contract subject 85-04-01-02 of the State Seismological Bureau, China. 相似文献
15.
—Attenuation properties of the lithosphere around the Koyna-Warna seismic zone is studied by estimating the coda-Q c from 30 local earthquakes of magnitude varying from 1.5 to 3.8. An average lapse time of 65 sec used in the single scattering model sampled a circular area with an average radius of 114 km. The estimated Q c values show a frequency-dependent relation, Q c =169 f?0.77, and range from 169 at 1 Hz to 1565 at 18 Hz. A comparison of worldwide Q studies reveals that for a large frequency range the Q for active regions is low as compared to that for stable regions. However, South Carolina and Norway are exceptions in that their Q is low in the low frequency range while New England and North Iberia are exceptions as they have a Q value similar to that for active regions like Spain, Turkey, Italy and Garhwal Himalaya (STIH), in the higher frequency range. In contrast to this, the Q for the Koyna-Warna area, which belongs to a stable region, is low in the entire frequency range as compared to the stable regions and similar to the active STIH regions. 相似文献
16.
We studied the applicability of two types of existing three-dimensional (3-D) basin velocity structure models of the Osaka
basin, western Japan for long-period ground motion simulations. We synthesized long-period (3–20 s) ground motions in the
Osaka basin during a M6.5 earthquake that occurred near the hypothetical Tonankai earthquake source area, approximately 200 km
from Osaka. The simulations were performed using a 3-D finite-difference method with nonuniform staggered grids using the
two basin velocity structure models. To study the ground motion characteristics inside the basin, we evaluated the wave field
inside the basin using the transfer functions derived from the synthetics at the basin and a reference rock site outside the
basin. The synthetic waveforms at the basin site were obtained by a convolution of the calculated transfer function and the
observed waveform at the reference rock site.
First, we estimated the appropriate Q values for the sediment layers. Assuming that the Q value depends on the S wave velocity V
S and period T, it was set to Q = (1/3V
S)(T
0/T) where V
S is in m/s and the reference period T
0 is 3.0 s. Second, we compared the synthetics and the observations using waveforms and pseudovelocity response spectra, together
with a comparison of the velocity structures of the two basin models. We also introduced a goodness-of-fit factor to the pseudovelocity
response spectra as an objective index. The synthetics of both the models reproduced the observations reasonably well at most
of the stations in the central part the basin. At some stations, however, especially where the bedrock depth varies sharply,
there were noticeable discrepancies in the simulation results of the models, and the synthetics did not accurately reproduce
the observation. Our results indicate that the superiority of one model over the other cannot be determined and that an improvement
in the basin velocity structure models based on simulation studies is required, especially along the basin edges. We also
conclude that our transfer function method can be used to examine the applicability of the basin velocity structure models
for long-period ground motion simulations. 相似文献
17.
G-A. Tselentis 《Pure and Applied Geophysics》1998,153(2-4):703-712
—Intrinsic (Q i -1) and scattering (Q s -1) attenuation parameters have been determined in the seismically active region of W. Greece, which is continuously monitored by the University of Patras microearthquake network. One hundred and twenty-three local and shallow earthquakes close to the recording stations have been used and Wennerberg’s (1993) approach has been adopted. Results for 1 to 12 Hz range show that Q i -1 is higher than Q s -1 and coda Q values are close to Q i ?, indicating that coda Q can be a reasonable estimate of intrinsic Q. 相似文献
18.
Jian Zeng Tian-Chang Chen Wei-Bin Han Jun Fan Si-Hua Zheng Akira Hasegawa Shigeki Horiuchij Satoshi Matsumoto 《地震学报(英文版)》1997,10(3):313-320
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
19.
A. Ugalde L. G. Pujades J. A. Canas A. Villaseñor 《Pure and Applied Geophysics》1998,153(2-4):685-702
—Northeastern Venezuela has been studied in terms of coda wave attenuation using seismograms from local earthquakes recorded by a temporary short-period seismic network. The studied area has been separated into two subregions in order to investigate lateral variations in the attenuation parameters. Coda-Q ?1 (Q c ?1) has been obtained using the single-scattering theory. The contribution of the intrinsic absorption (Q i ?1) and scattering (Q s ?1) to total attenuation (Q t ?1) has been estimated by means of a multiple lapse time window method, based on the hypothesis of multiple isotropic scattering with uniform distribution of scatterers. Results show significant spatial variations of attenuation the estimates for intermediate depth events and for shallow events present major differences. This fact may be related to different tectonic characteristics that may be due to the presence of the Lesser Antilles subduction zone, because the intermediate depth seismic zone may be coincident with the southern continuation of the subducting slab under the arc. 相似文献
20.
Heavily populated by Beijing and Tianjin cities, Bohai basin is a seismically active Cenozoic basin suffering from huge lost by devastating earthquakes, such as Tangshan earthquake. The attenuation (QP and QS) of the surficial Quaternary sediment has not been studied at natural seismic frequency (1?10 Hz), which is crucial to earthquake hazards study. Borehole seismic records of micro earthquake provide us a good way to study the velocity and attenuation of the surficial structure (0?500 m). We found that there are two pulses well separated with simple waveforms on borehole seismic records from the 2006 MW4.9 Wen'an earthquake sequence. Then we performed waveform modeling with generalized ray theory (GRT) to confirm that the two pulses are direct wave and surface reflected wave, and found that the average vP and vS of the top 300 m in this region are about 1.8 km/s and 0.42 km/s, leading to high vP/vS ratio of 4.3. We also modeled surface reflected wave with propagating matrix method to constrain QS and the near surface velocity structure. Our modeling indicates that QS is at least 30, or probably up to 100, much larger than the typically assumed extremely low Q (~10), but consistent with QS modeling in Mississippi embayment. Also, the velocity gradient just beneath the free surface (0?50 m) is very large and velocity increases gradually at larger depth. Our modeling demonstrates the importance of borehole seismic records in resolving shallow velocity and attenuation structure, and hence may help in earthquake hazard simulation. 相似文献