库尔勒5.8级和库车6.0级地震地方震尾波持续时间比的初步研究

选用地方震尾波长度两水平分量的算术平均值与垂直分量之比τ_H/τ_ v作为参量,分析处理了库尔勒1978年4月22日5.8级地震前后库尔勒地震台65型地震仪所记录的104个地方震,以及库车1979半3月29日6.0级地震前后新源地震台维开克型地震仪所记录的128个地方震。取地震前几分钟噪声水平的两倍(毫米数)作为噪声带确定尾波的结止时间。所取地方震震中距Δ小于200公里,震级区间取0.7≤M_L≤4.5。结果表明,在库尔勒5.8级地震前一个多月库尔勒台的τ_H/τ_V出现了一定的低值变化,而在库车6.0级地震前利用新源台求出的τ_H/τ_V变化不太明显,略有异常显示。     

岫岩5.4级地震前后尾波振动持续时间比的演化特征

本文在前人工作的基础上，从地震波的动力学特性出发，利用尾波振动持续时间比τH/τv方法，对1999年11月29日岫岩Ms5．4地震前后地震活动的演化特征进行了详细研究。结果发现在岫岩Ms5．4地震前，距震中相对较近台站记录到的尾波振动持续时间比一rH／TV存在一定程度的异常显示，而距震中较远外围地区的台站记录到的一τH／τv震前无明显的异常反应。认为尾波振动持续时间比τH／τv从统计意义上提供了研究介质物理性质的较好方法，对短临地震预报具有一定的参考意义。     

中等强度地震前后尾波衰减特征

本文处理了1981年11月邢台5.8级、1980年8月林县4.7级,1983年11月荷泽5.9级、1984年5月黄海6.3级四个中等强度地震前后的序列资料,讨论了红山、林县、嘉祥、南通地震台所记录到的各次地震前后,小震尾波两水平分量持续时间对数lgτ与两水平分量S波最大振幅SH的关系及尾波振动持续时间比τ_H/τ_z随时间的变化。结果表明,邢台、林县、荷泽地震前后它们的变化形态基本一致,即震前低值、震后高值,然后逐渐恢复正常;黄海与前三个地震的变化形态不同,即震前出现高值现象。本文对它们的变化特征进行了初步讨论。     

青海昆仑山口西8.1级地震前的尾波持续时间和地震频次

2001年11月14日青海省昆仑山口西发生了8.1级大地震，震后，分析了青海省大武地震台尾波持续时间、门源地震台记录的地震频次，发现昆仑山口西8.1级地震前大武地震台的尾波持续时间明显存在低值异常、门源地震台观测到的地震频次出现了高值异常。得出青海昆仑山口西8.1级地震前有地震月频次高值异常，地震发生在尾波低值异常期的结论。     

乌鲁木齐地区尾波衰减特征初探

一、引言本文分别采用区域观测台网的DD-1和65仪器两种记录,对乌鲁木齐及附近地区的尾波衰减特征进行了初步探讨,同时,将所得结果与京津和川滇地区作了对比分析。最后,对于中强震前尾波衰减系数K及振动持续时间比τ_H/τ_V可能出现的前兆变化进行了讨论。     

1981年盈江地震尾波的变化特征

本文以盈江1981年7月7日(M_s=5.4级)及8月14日(M_s=5.1级)两次地震前后的序列地震资料为基础,探讨了腾冲地震台所记录到的盈江序列地震的尾波在震前及震后两水平分量持续时间的对数logτ与两水平分量S波最大振幅S_H的变化关系及尾波振动持续时间比τH/τZ随时间的变化情况。本文叙述了这二个特征量的测定方法并给出了结果。从结果中可以看出这二个特征量在盈江地震前后的变化是明显的。     

中等地震前地震波异常特征

本文利用P波初动符号,垂直向P波、S波最大振幅比,尾波衰减系数a值,尾波持续时间比τ_b/τ_v及尾波衰减速率p值等方法研究了1990年10月25日乌苏5.2级地震波异常曲时空变化特征。结果表明,地震波参数的分析可以提取中强地震前的异常信息。     

新疆南天山部分地区尾波衰减特征

分析1988年库尔勒和阳霞台地震尾波资料发现,地方震尾波衰减系数α值、尾波持续时间比τ值,在中强震前确有异常显示。     

2022年青海门源MS6.9地震前地下流体异常特征分析

对2022年1月8日青海门源M_S6.9地震前,震中附近地下流体观测资料及异常特征进行分析,结合震前预测过程进行了回顾性总结。结果表明：门源地震震中500 km范围内存在9项异常,其中8项为中短期异常,均出现在震前6个月;异常在空间上分布不均匀,主要集中于震中南部200 km范围内;本次门源地震与2016年门源M_S6.4地震和2021年玛多M_S7.4地震前的地下流体异常存在一定的相同性及差异性变化。     

建立尾波持续时间震级统一标度的设想

本文从地震矩和尾波掠过时间(Lapse time)的关系,提出与矩震级标度一致的尾波持续时间震级统一标度公式 M_w=logτ+0.1(△/τ)+F(τ)。它适用于各台测定 M_L≤5.0级地震的矩震级。     

Attenuation characteristics of coda waves and estimation of Q c values in eastern China

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.     

Regional characteristics of coda attenuation after the lancang-Gengma earthquake

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 theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ _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 factorA _o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM ₀=lgA ₀(f)+17.6,M _D=0.67lgA ₀(f)+1.21 and logM ₀=1.5M _D+15.79. In addition, the rates of amplitude attenuationβ _s andβ _m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ _s/β_m=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL 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 inherentQ _i and scatteringQ _s, testify to this areas having lowQ-values correspond to stronger scatterings. The Chinese version of this paper appeared in the Chinese edition ofActa 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.     

门源地倾斜异常的深入分析

应用形态法、差分法、契氏拟合法对１９８４—１９９５年门源倾斜的资料做了系统的分析、总结，对其２００ｋｍ范围内的中强地震的震前异常进行了分析，发现在１９８６年门源６．４级、１９９０年共和７．０级地震前趋势性异常比较显著，且异常幅度大、持续时间长，而在一些５级左右地震前异常不明显。并且发现在中强地震前门源倾斜ＮＳ向有一个减速过程，这似与以往总结的震例有所区别。并在此基础上对门源倾斜的映震能力作了评价，且提出了未来一个时期的地震趋势。     

Application of scaling-rule theory in crustal rock fracture to studying characteristics of seismological precursors associated with M=6.1 Shandan-Minle earthquake

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.     

青藏高原东北部强震成组孕震特征初探

通过对1986年门源6．4级地震以来青藏高原东北部发生的一系列6级强震时空分布特征的研究，提出了这些地震为成组孕震的观点，并从背景空区、诱发地震、地震活动增强及前兆异常的突变等方面论证了成组孕震的可能性。     

Coda wave attenuation in the Parecis Basin,Amazon Craton,Brazil: sensitivity to basement depth

Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor (Q _c) of coda waves modeled using Q_c = Q₀ f^hQ_{\rm c} =Q_{\rm 0} f^\eta , where Q ₀ is the coda quality factor at frequency of 1 Hz and η is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239–252, 2008), based in the temporal attenuation coefficient, χ(f) instead of Q(f), given by the equation c(f)=g+\fracpfQ_e \chi (f)\!=\!\gamma \!+\!\frac{\pi f}{Q_{\rm e} }, for the calculation of the geometrical attenuation (γ) and effective attenuation (Q_e^-1 )(Q_{\rm e}^{-1} ). Q _c values have been computed at central frequencies (and band) of 1.5 (1–2), 3.0 (2–4), 6.0 (4–8), 9.0 (6–12), 12 (8–16), and 18 (12–24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin Q_c = (98±12)f^(1.14±0.08)Q_{\rm c} =(98\pm 12)f^{(1.14\pm 0.08)}, for the surrounding shield Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)}, and for the whole region of Porto dos Gaúchos Q_c = (99±19)f^(1.17±0.02)Q_{\rm c} =(99\pm 19)f^{(1.17\pm 0.02)}. Using the independent frequency model, we found: for the cratonic zone, γ = 0.014 s^− 1, Q_e^-1 = 0.0001Q_{\rm e}^{-1} =0.0001, ν ≈ 1.12; for the basin zone with sediments of ~500 m, γ = 0.031 s^− 1, Q_e^-1 = 0.0003Q_{\rm e}^{-1} =0.0003, ν ≈ 1.27; and for the Parecis basin with sediments of ~1,000 m, γ = 0.047 s^− 1, Q_e^-1 = 0.0005Q_{\rm e}^{-1} =0.0005, ν ≈ 1.42. Analysis of the attenuation factor (Q _c) for different values of the geometrical spreading parameter (ν) indicated that an increase of ν generally causes an increase in Q _c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, Q_c = (78±23)f^(1.17±0.14)Q_{\rm c} =(78\pm 23)f^{(1.17\pm 0.14)} (in the deepest part of the basin), than in the basement, Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.     

Lateral variations of coda Q and attenuation of seismic waves in Southwest Anatolia

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.     

Attenuation of High Frequency P and S Waves in the Gujarat Region,India

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.     

Frequency characteristics of coda and determination of medium parameters in Lingwu region, China

In this paper, considering the influences of source spectrum, the scattering property of medium and instrument response on the dominant frequency of coda, a method of using the coda of local earthquake to determine the correlation length of medium andQ-value is given. We find the following formula as: {fx719-1} wheret* =t/Q, f is the dominant frequency of coda,u ₁ andu ₂ are the parameters depend on the correlation length and the corner frequency of the source spectrum respectively,I(f) is a function of instrument response. If the source parameter is given, we can obtain the correlation length andQ-value by means of the inversion of observed curves off-t of coda. We processed the data of coda wave of more than 40 earthquakes from 1982 to 1989 in Lingwu region, China, determined the correlation length andQ-value, and preliminarily studied the temporal change of correlation length before and after moderately strong earthquakes. The result suggests that there are indications that the correlation length of medium decreases before the moderate earthquake. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 62–70, 1992.     

Q and high-frequency strong motion spectra

Empirical scaling equations for Fourier amplitude spectra of strong ground motion are used to describe A₀ and τ in the assumed (high-frequency) shape of strong motion amplitudes: FS(_φ) = A₀e-^πτφ. The res of computed A₀ and τ with other related estimates of spectral amplitudes; (2) smooth decay of strong motion spectral amplitudes up to φ = 25 Hz, without an abrupt low-pass filtering of high frequecies; and (3) good agreement with other estimates of the regionally specific attenuation of high-frequncy seismic waves.As the recorded strong earthquake shaking in the western United States typically samples only the shallow (10 km) and local (100km) characteristics of wave attenuation, the processed strong motion accelerograms can be used as the most direct means of describing the nature of the high-frequency attenuation of the entire strong motion signal for use in earthquake engineering applications. Seismological body wave, Lg and coda wave estimates of Q sample different volumes of the crust surrounding the station, and involve different paths of the waves. These differences must be carefully documented and understood before the results can be used in earthquake engineering characterization of strong motion amplitudes.