衰减、场地响应等地震波传播相关信息综合研究

【作者】 朱新运；

【导师】 陈运泰；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理， 2011， 博士

【摘要】 地震激发的波,经过传播路径、仪器、场地等因素的调制作用成为台站地震记录,即台站记录是震源、路径、仪器、场地等多种因素的耦合,而基于地震记录研究震源信息、路径衰减、场地响应等则是逆向的解耦过程。基于地震学理论、通过各种计算技术,从地震波形资料中解析出关于地震震源力学参数、地震波传播介质及台站场地响应信息是地震研究的重要内容,也是认识地震孕育、发生、发展过程,了解地震孕育背景构造特征等的有效途径。本文在地震学前沿理论方法基础上使用最新计算机技术开展以下三个方面的工作。本文第一部分,在逆向双台谱比法的基础上,提出了基于谱比法的地震波衰减与场地响应联合反演方法。与逆向双台谱比法相比,该方法对数据条件限制降低,增加了可用数据量,获得地震波衰减参数外,还同时获得场地响应参数。使用该方法,选取首都圈台站记录的同区域小震资料,评估首都圈台站场地响应,计算相应研究区地震波衰减参数。研究表明,在1Hz～6Hz频率范围内,基岩台场地响应小、平坦且稳定,土层台对低频率波放大作用高于对高频率波的放大作用,地震波衰减参数与区域地震活动性相关。同样使用该方法,选取浙江省区域地震台网台站记录的台湾地震波形资料,评估浙江省丘陵地带基岩台站场地响应,计算了穿越台湾海峡较单一路径Lg波衰减参数,通过区域地震记录震级偏离情况对该研究场地响应结果的可靠性进行了检验。第二部分基于弱散射的尾波理论开展地震波尾波衰减研究。文章详细阐述了基于Aki模型及Sato模型的尾波衰减参数计算的原理方法,定量分析不同滤波器及相关性能、地震波噪声、数据采样、尾波流逝时间等对计算结果的影响。根据计算特点,针对Aki模型在数据采样方面提出了动态采样方法,针对Sato模型提出了最佳线形段自动判断算法。研究表明,利用动态采样代替固定窗长的静态采样方法,在拟合数据段较短的情况下,结果更稳定。利用浙江、宁夏及首都圈台网近年来记录的数字地震波资料,研究相应地区地震波尾波衰减特征,并结合地震活动情况,研究了地震波衰减参数与区域地震活动的关系,对研究结果的可靠性进行了论证。研究发现,Q0大小除了与射线穿过区域地震活动性、地震地质条件有关外,与台站位置所处的局部地形及地震地质构造有关。地震活动程度越高、地震波衰减越快,衰减参数Q0值越小。研究中,我们发现地震波衰减参数Q0与η具有负相关关系。小震序列对相应区域介质衰减的影响表现为,衰减参数η趋势性降低,而Q0不具有趋势性特征。根据数据条件,使用基于Sato模型计算的衰减参数Q0构建区域衰减参数图像,分析华北区域历史大震活动与衰减参数图像的关系,结果表明,研究区Ms7级以上地震均发生在低Q0区或Q0高梯度递变区。第三部分为综合研究部分。在这一部分,使用浙江珊溪水库地震序列波形资料,开展了地震定位、小震震源参数、地震波衰减、综合段层面解等研究。在地震定位方面提出了在虚波走时方程基础上的遗传算法定位,由此得到的定位结果与浙江省台网用hypo81方法定位结果相比,走时残差大幅降低,定位质量明显提高。基于虚波走时方程,将非线性方程线性化,求解获得震源位置及虚波速度初值,之后计算初值走时残差,由走时残差的标准偏差的2倍计算在经度、纬度、深度及虚波速度产生的最大误差,构造遗传种群,利用遗传算法进行二次定位,获得地震定位的最终结果。利用该方法,对浙江珊溪水库震群进行重新定位,结果表明：地震基本上集中发生在一个近乎垂直的北西向的断层面内,断层面走向136°,倾角87°。小震综合面解获得的结果与定位结果基本一致；震源深度平均4.7km,最大深度9.5km,最浅1.7km,地震震中呈北西向狭窄条带分布,沿北西方向地震震源深度趋势性增大,在条带西北端有大约3.5km的地震不连续空段;利用Borun模型计算的小震震源参数结果表明,该震群地震震源参数没有表现出明显有别于构造地震的特征,地震应力降多在0.33 MPa左右,平均应力降为0.88MPa,根据应力降空间分布的情况判断,该地震条带西北端地震活动不连续段处于应力降低值区。根据数据处理要求,本研究自主开发了界面友好、功能完善,数据输入、输出及参数配置操作方便实用的数字地震波处理软件,软件运行节省内存、速度快、流程可控。更多还原

【Abstract】 Seismic record is a record coupled with seismic source, path, instrument and site. Study on seismic source information, path attenuation, site response and so on based on seismic records is the reverse of the decoupling process. It is an important content of seismic research to extract characteristics of seismic mechanical parameters, propagation media characteristics, site characteristics from seismic record, based on the theory of seismology, through a variety of computing technology. And it is effective way to understand the process of earthquake preparation, development, occurs and the background and other structural features of earthquake preparation. In this study, three areas of work were carried out based on the latest cutting-edge computer technology and the cutting-edge seismology theory methods.In the study, on the basis of the reverse two-station spectral ratio method, a joint inversion method which allows simultaneous determination of Lg wave attenuation and site response from spectral amplitude ratios was developed. Compared with the reverse two-station spectral ratio method, this method reduced the data constraints, increased the amount of available data, obtain the site response parameters, besides the seismic wave attenuation parameters. This is the first part of this research and is the groundbreaking work in this study. The method was used successfully for estimating site response of Zhejiang seismic network statgions and Metropolitan area seismic network station, and applied to invert for the parameters of Lg wave attenuation corresponding region. The comparison with other results suggested that our results are highly reliable.In the second part, the study on seismic coda attenuation was carried out based on weak scattering theory of coda. The principle and method of coda attenuation parameter calculation based on Aki and Sato model were elaborated, and the effect of different filters and their properties, seismic noise, data sampling, coda lapse time on the calculation results were analyzed quantitatively. According to the calculation features, the dynamic sampling method was proposed for Aki model, and the best linear segment automatically determining algorithm was proposed for Sato model. Studies on calculation method have shown that the result used dynamic sampling method was more stable than that used static sampling when the fitting data were shorter. If the selection of filter and its properties didn’t cause the waveform distortion, it would not affect the result.Selecting the digital seismic data recorded by Zhejiang region earthquake network, Ningxia region earthquake network and metropolitan earthquake network in recent years, we calculated Qc(f) value of coda in relative region, polyfited relationship between Qc(f) value and frequency in corresponding region. Considering the seismic activity, we studied the relationship between the attenuation parameters of seismic wave and the seismic activity. According to the data We constructed Qo images and analyzed the relationship between images and region’s historical seismic activity in northern China.Studies have shown that the value of the coda Qo was related to not only local topography and geological structure near the location of the stations but also the seismic activity, seismic-geology of the region that the seismic wave pass through. The higher the level of seismic activity, the faster seismic wave attenuation, coda Qo is smaller. In the study, we found that the coda attenuation parameter Qo is negatively correlated withη. The effect of small earthquake sequences on the attenuation of the media in corresponding region has shown that the attenuation parametersηdropped with tendency, but Qo didn’t have the characteristics of tendency.In the third part, we selected the digital seismic data of Shanxi reservoir earthquake recorded by fixed stations and temporary stations, With these data we carried out on the earthquake location, a small local earthquake source parameters, attenuation of seismic waves, integrated surface solutions of small earthquakes and other research. In the earthquake location, the nonlinear virtual travel time equation was linearized and solved, and the source position, initial virtual velocity and travel time residuals were obtained. Then taking two times the standard deviation as a time residuals to calculate maximum error generated from longitude, latitude, depth and virtual velocity. The genetic population was structured using the maximum error and the end result of earthquake location was obtained by genetic algorithm. Using this method, the results significantly reduce travel time residuals, location quality has improved significantly compared to with the results of Zhejiang Province Network hypo81 positioning. Reservoir earthquake location shows that:the earthquake is largely concentrated in a nearly vertical, north west of the fault plane, whose normal and north angle of 46°, and east angle of 44°, and vertical angle of 87°. The result is in agreement with that of small earthquake comprehensive mechanism solution. The average depth of the earthquake 4.7km, maximum depth of 9.5km, the minimum depth of 1.7km. Epicenter was northwest narrow band distribution, and focal depth increased along the northwest direction. There is a seismic discontinuities space segment at about 3.5km the northwest end of the strip. The characteristics source parameters obtained by using the Brun model significantly different from that tectonic earthquakes. Seismic stress drop is about more than the 0.33 MPa, the average stress drop 0.88Mpa. According to the stress drop spatial distribution, the seismic discontinuities space segment at the northwest end of the strip is a low stress drop one.According to the data processing requirements, this study developed a user-friendly digital seismic processing software, The software is fully functional, data input, output and parameter configuration easy to operate, the software is running to save memory, speed, flow control.更多还原