Seismic Wave Attenuation in Germany's Deep Borehole Area from VSP Data

Pujol该项目涉及使用VSP（垂直地震剖面）数据确定地震波衰减，该数据记录在德国目前正在钻探的超深井旁边的一个4公里深的试验井中（预计深度在10至12公里之间）。尽管进行了广泛的研究，但衰减机制并没有得到很好的理解，甚至其测量也受到不确定性的困扰，因为波的振幅也被波的传播效应所改变，通常只是近似已知的。因此，VSP数据以最小的干扰提供了观测地震波振幅和形状实际变化的最佳机会。德国深钻计划对这一提议的重要性是双重的。该钻孔是在结晶岩中钻出的极少数钻孔之一。关于这类岩石的衰减信息很少。(2)收集了多个不同震源的零偏移VSP数据集。炸药、振动器和冲击源已被用来产生P波和S波。这是一个特殊的数据集，将用于研究震源类型和波的频率内容对衰减测量的影响，由于无法获得数据，迄今为止对这一问题进行的研究很少或没有。虽然使用VSP数据测量衰减(Q)是最可靠的技术，并且获得Q的数值是一个相当简单的过程，但是有许多因素会影响测量结果。事实上，不同的测量方法（例如，光谱比、上升时间），甚至锥形窗的选择都可能影响结果。此外，由于薄层的散射和滤波作用，波在真实地球中的传播会影响波的振幅和频率含量。因此，本研究的主要目标将是计算可靠的内禀Q值并研究影响它的因素。这将是关于晶体岩石衰减的最详细信息，对于校准衰减非常有用，这些衰减可能是通过分析井区内收集的高质量反射地震数据确定的。* * *

9219208 Pujol This project involves the determination of seismic wave attenuation using VSP (Vertical Seismic Profiling) data recorded in a 4-km-deep pilot borehole next to the super-deep borehole currently being drilled in Germany (expected to reach between 10 and 12 km). In spite of extensive research, attenuation mechanisms are not well understood, and even its measurement is plagued with uncertainty, as wave amplitudes are also modified by wave propagation effects generally only approximately known. For this reason, VSP data offer the best chance to observe the actual change in the amplitude and shape of seismic waves with the minimum amount of interference. The importance of the German deep- drilling program for this proposal is two-fold. (1) The borehole is one of the very few drilled in crystalline rocks. Very little information about attenuation in this type of rocks is available. (2) Several zero-offset VSP data sets for different seismic sources have been collected. Explosive, vibrator, and impact sources have been used to generate P and S waves. This is an exceptional data set that will be used to study the influence of the type of source and the frequency content of the waves on the measurement of attenuation, a matter on which little or no research has been carried out so far because of the unavailability of data. Although the measurement of attenuation (Q) using VSP data is the most reliable technique and getting a number for Q is a rather straightforward procedure, there are a number of factors that affect the measurements. In fact, different methods of measurement (e.g., spectral ratio, rise time) and even the choice of a tapering window may affect the results. In addition, wave propagation in the real earth affects wave amplitudes and frequency content because of scattering and the filtering effect of thin layers. For this reason, the main goal of this research will be the computation of reliable intrinsic Q values and a study of the factors that affect it. This will be the most detailed information on attenuation in crystalline rocks and will be extremely useful to calibrate the attenuation that may be determined from the analysis of high-quality reflection seismic data collected in the borehole area. ***