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

9219208 Pujol该项目涉及使用在德国目前正在钻探的超深钻孔(预计达到10至12公里)旁边的4公里深的试点钻孔中记录的垂直地震剖面数据来确定地震波的衰减。尽管有广泛的研究，但衰减机制还不是很清楚，甚至它的测量也充满了不确定性，因为波的幅度也会受到波传播效应的影响，通常只有大约知道。因此，VSP数据提供了最好的机会，以最小的干扰量观察地震波的幅度和形状的实际变化。对于这一提议，德国深井钻探计划的重要性是双重的。(1)这个钻孔是在结晶岩中钻出的极少数几个孔之一。关于这类岩石中衰减的信息很少。(2)采集了不同震源的零炮检距VSP数据集。爆炸、可控震源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含量对衰减测量的影响，由于数据不可用，迄今为止对这一问题的研究很少或根本没有开展。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，但仍有许多因素影响测量。事实上，不同的测量方法(如频谱比、上升时间)甚至是锥形窗口的选择都可能影响结果。此外，由于薄层的散射和滤波效应，波在真实地球中的传播会影响波的幅度和频率含量。因此，这项研究的主要目的将是计算可靠的固有Q值，并研究影响它的因素。这将是关于结晶岩中衰减的最详细信息，对于校准可能通过分析在井区收集的高质量反射地震数据而确定的衰减将非常有用。***

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. ***