Analysis of seismic attenuation in the earthquake swarm area near Werdau

西波希米亚/沃格特兰震群地区过去是，现在也是密集的地球科学调查对象。然而，到目前为止，很少有人注意到这一主要活动区周围的其他小震群地震区以及与莱比锡-雷根斯堡断裂带的联系。在这里提交的项目中，我们建议对维尔道(西萨克森州)附近最北端的已知震群区域进行详细分析。其目的是揭示两个震群地震区之间的异同和可能的联系，并最终提高我们对陆内流体诱发地震活动的理解。为了对被认为是震群原因的流体成像，我们将使用当地地震来反演维尔道震群地区的3D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本征吸收和散射衰减，分析衰减的频率相关性，以及反演详细的震源谱和频率相关的地震计场地响应系数。在求解弹性辐射传输方程时，我们将首次应用一种改进的蒙特卡罗算法，该算法能够分别对不同深度的本征衰减和散射衰减进行反演。为此，我们将扩展现有的主要算法之一，以允许计算任意深度相关的速度和衰减模型中的能量传播。这种算法将在这个特定项目之外发挥作用，以获得可靠的地壳一维衰减模型。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。首次将这两种方法的各自优势结合起来，开发出一种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，并进行联合解释。这种成像地下流体流动的技术及其与流体诱发地震活动的联合解释也将在该项目之外发挥重要作用。我们特别提到地下技术利用和人为流体引起的地震活动的社会相关性，例如在地热发电厂、碳捕获和封存以及水力压裂方面。

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.