Analysis of seismic attenuation in the earthquake swarm area near Werdau

西波希米亚/沃格特兰的震群区过去和现在都是密集的地球科学调查的对象。然而，很少有人注意到，到目前为止，其他小震群地区的周围的主要活动区，以及连接到莱比锡-雷根斯堡断层带。在这里提交的项目中，我们建议对韦尔道（萨克森西部）附近最北端的已知震群区进行详细分析。我们的目标是揭示差异和相似之处，以及可能的联系，这两个群地震区，并最终提高我们的理解流体诱发的地震活动在陆内设置。为了对被认为是震群原因的流体进行成像，我们将利用当地地震反演韦尔道震群区域的三维地震衰减结构。在第一步中，我们将应用辐射传输理论来分离固有吸收和散射衰减，分析衰减的频率依赖性，以及反演详细的源谱和频率依赖的地震计场地响应因子。为了求解辐射传输的弹性方程，我们将首次应用改进的蒙特-卡罗算法，该算法能够分别反演不同深度的固有衰减和散射衰减。要做到这一点，我们将扩展一个领先的现有算法，允许在任意深度依赖的速度和衰减模型的能量传播的计算。这种算法将是有用的超出这个特定的项目，以获得可靠的1D地壳衰减模型。在第二步中，我们将对P波和S波进行3D衰减层析成像，以检测流体含量增加的区域。辐射传输理论和衰减层析成像两种技术的结合是另一个技术目标。首次将两种方法的各自优势结合起来，开发出优化的联合反演策略。结果将与现有的速度模型（vP和vP/vS）进行比较，并共同解释。这种对地下流体流动进行成像的技术及其与流体诱发地震活动的联合解释也将在本项目之外发挥重要作用。特别是，我们指的是与地下的技术使用和人为流体引起的地震活动，例如在地热发电厂，碳捕获和封存，以及水力压裂的背景下的社会相关性。

The earthquake swarm area of West-Bohemia/Vogtland was and is an object of intense geoscientific investigations. However, little attention has been paid so far to other small swarm earthquake areas in the surroundings of this main zone of activity as well as to the connection to the Leipzig-Regensburg fault zone. In the project submitted here, we propose to carry out a detailed analysis of the northernmost known earthquake swarm area near Werdau (western Saxony). The goal is to reveal differences and similarities as well as possible connections between both swarm earthquake areas, and finally, to improve our understanding of fluid induced seismicity in intracontinental settings. To image the fluids, which are believed to be the cause of the earthquake swarms, we will invert for the 3D seismic attenuation structure of the Werdau earthquake swarm area using local earthquakes. In a first step, we will apply radiative transfer theory to separate intrinsic absorption and scattering attenuation, to analyze the frequency dependence of attenuation, as well as to invert for detailed source spectra and for frequency dependent seismometer site response factors. To solve the elastic equation of radiative transfer we will apply, for the first time, an improved Monte-Carlo algorithm, which is able to separately invert for intrinsic and scattering attenuation in different depths. To do so, we will extend one of the leading existing algorithms to allow the computation of energy propagation in arbitrary depth dependent velocity and attenuation models. Such kind of algorithms will be useful beyond this particular project, to obtain reliable 1D attenuation models of the Earth's crust. In a second step, we will conduct a 3D attenuation tomography for P- and S-waves, to detect areas of increased fluid content. The combination of the two techniques of radiative transfer theory and attenuation tomography is another technical goal. The respective strengths of the two methods will be combined for the first time, to develop an optimized joint inversion strategy. Results will be compared with existing velocity models (vP and vP/vS ) and jointly interpreted. Such techniques to image fluid flow in the subsurface and its joint interpretation with fluid induced seismicity will play a major role also beyond this project. Especially, we refer to the social relevance with respect to the technical use of the subsurface and to anthropogenic fluid induced seismicity, e.g. in the context of geothermal power plants, carbon capture and sequestration, as well as hydraulic fracturing.