单台Lg尾波Q_(Lg)~c的测量研究

将单台记录叠加频谱比法（简称SSR法）应用于震中距小于500km的区域地震Lg尾波为lHz下的值,n是与频率f有关的指数)的提取之中·为了检验方法的稳定性和可靠性,我们选用两组发生在不同地区的地震记录．一组是1989-10-18大同主震（ML＝5．9）的15个余震,北京遥测地震台网记录到的信噪比较高的Lg尾波序列。另一组是秦岭造山带数字流动地震观测台网记录到的1995年甘肃平凉两次地震信噪比较高的Lg尾波序列．每一组地震的震源参数基本相同,即它们到某一特定台站的路径几乎相同,得到的　可以认为是不受震源影响的地震一台站路径上的平均衰减效应·两区域　的测量结果表明：（1）尽管两个地震观测台网所用观测仪器不同,每个台站的观测条件不同,所记录的地震也不尽相同,但对Q₀和,的拟合结果线性程度都比较高,说明SSR法是稳定的;（2）同一震群的不同地震到某一特定台站测得的结果基本一致,即Q₀值及其平均值大都在其标准差范围之内,说明SSR法是可靠的。（3）对同一地震不同方位各台站的Lg尾波测量结果可以看出,穿过不同构造区的Q₀值存在明显差...     

Moment magnitudes of two large Turkish earthquakes on February 6, 2023 from long-period coda

Two large earthquakes (an earthquake doublet) occurred in south-central Turkey on February 6, 2023, causing massive damages and casualties. The magnitudes and the relative sizes of the two mainshocks are essential information for scientific research and public awareness. There are obvious discrepancies among the results that have been reported so far, which may be revised and updated later. Here we applied a novel and reliable long-period coda moment magnitude method to the two large earthquakes. The moment magnitudes (with one standard error) are 7.95±0.013 and 7.86±0.012, respectively, which are larger than all the previous reports. The first mainshock, which matches the largest recorded earthquakes in the Turkish history, is slightly larger than the second one by 0.11±0.035 in magnitude or by 0.04 to 0.18 at 95% confidence level.     

应用Sato、Aki模型对比分析内蒙古东北地区尾波Q值

选取2016年3月—2019年6月内蒙古地震监测台网记录的925条内蒙古东北部及邻近地区地震数据,从中挑选133次M_L≥2.0且记录清晰、信噪比较高的地震事件,利用Sato模型、Aki模型,分别计算该区域地震尾波平均Q值,并拟合得到Q值对频率的依赖关系,其中：(1)Sato模型：Q_C(f)=(64.11±29.15)f~((0.8914±0.0772));(2)Aki模型：Q_C(f)=(258.4±65)f~((0.6815±0.1435))。结果表明,利用2种模型计算的该区域地震尾波Q值分布具有一致性,且Q值与依赖指数η成反比关系,分析认为,尾波Q值高低分布与地震活动性及地质构造有关。     

基于Sato模型的内蒙古东北部地区尾波Q值

基于Sato模型,采用2016年3月至2018年6月内蒙古东北部及临近地区发生的526次地震事件,挑选M_L≥2.0、记录清晰且信噪比较高的102次地震事件,拟合得到内蒙古东北部地区尾波Q值,得到Q_C(f)=(64.74±29.09)f^{(0.8925±0.0765});Q值与依赖指数η成反比,且该区北部Q值偏高,南部Q值偏低,可能与地质构造及地震活动性有关。     

影区地震的识别与定位

通过分析西安地震台近几年各个方向记录到的影区地震,详细阐述 Lg1、Lg2波的确认方法,运用 Matlab对数据进行分析,给出S波与 Lg1、Lg2波的走时关系式,提高影区地震的分析速度和准确度,为单台大震速报和日常分析提供借鉴经验。     

Detecting remotely triggered temporal changes around the Parkfield section of the San Andreas fault

Detecting temporal changes in fault zone properties at seismogenic depth have been a long-sought goal in the seismological community for many decades.Recent studies based on waveform analysis of repeating earthquakes have found clear temporal changes in the shallow crust and around active fault zones associated with the occurrences of large nearby and teleseismic earthquakes.However,repeating earthquakes only occur in certain locations and their occurrence times cannot be controlled,which may result in inadequate sampling of the interested regions or time periods.Recent developments in passive imaging via auto-and cross-correlation of ambient seismic wavefields (e.g.,seismic noise,earthquake coda waves) provide an ideal source for continuous monitoring of temporal changes around active fault zones.Here we conduct a systematic search of temporal changes along the Parkfield section of the San Andreas fault by cross-correlating relatively high-frequency (0.4-1.3 Hz) ambient noise signals recorded by 10 borehole stations in the High Resolution Seismic Network.After using stretch/compressed method to measure the delay time and the decorrelation-index between the daily noise cross-correlation functions (NCCFs),we find clear temporal changes in the median seismic velocity and decorrelation-index associated with the 2004 M6.0 Parkfield earthquake.We also apply the same procedure to the seismic data around five regional/teleseismic events that have triggered non-volcanic tremor in the same region,but failed to find any clear temporal changes in the daily NCCFs.The fact that our current technique can detect temporal changes from the nearby but not regional and teleseismic events,suggests that temporal changes associated with distance sources are very subtle or localized so that they could not be detected within the resolution of the current technique (～0.2%).     

利用Aki模型对宁夏及邻区尾波Q值分布特征的研究

从2008年1月至2013年12月宁夏地震台网记录的665次ML≥2.0地震的数字地震波形资料中,选取波形记录清晰、噪声水平满足计算条件的数字地震波形记录,利用Aki模型,计算宁夏及邻区各区域尾波Q值,并与前人已有结果进行对比,得到该区尾波Q值的分布特征。结果表明:宁夏及邻区尾波Q值整体呈北高南低分布;吴忠、灵武地区该值相对较高,与该区域存在高速区相对应;阿拉善左旗西南该值较低;中卫、海原及附近地区该值相对较低,认为与该区域地壳深部的高温度与高热流值有关。     

辽宁海城-岫岩地区尾波Q值研究

本文利用Sato单次散射模型,研究1999年至2007年辽宁海城-岫岩地区尾波Q值随时间的变化情况及1999年岫岩5.4级地震和2000年5.1级两次中强地震发生阶段该地区的尾波Q值变化。计算结果表明:该区在地震活跃阶段,Qc值随时间变化起伏较大,平均值相对较高,在岫岩5.4级主震前有短时升高现象,之后Qc值并没有明显的降低,直到强余震序列结束之后Qc值逐步降低,趋于平稳,通过对比该区在地震活跃阶段与平静阶段的Qc值变化,可以为未来该区的强震预测提供参考依据。