The quality factor Q is a dimensionless measure of the energy loss per cycle of a wave field, and a proper understanding of this factor is important in a variety of fields, from seismology, geophysical prospecting to electrical science. Here, the focus is on viscoelasticity. When interpreting experimental values, several factors must be taken into account, in particular the shape of the medium (rods, bars or unbounded media) and the fact that the measurements are made on stationary or propagating modes. From a theoretical point of view, the expressions of Q may differ due to different definitions, the spatial dimension and the inhomogeneity of the wave, i.e. the fact that the vectors of propagation (or wavenumber) and attenuation do not point in the same direction. We show the difference between temporal and spatial Q, the relationships between compressional and shear Q, the dependence on frequency, the case of poro-viscoelasticity and anisotropy, the effect of inhomogeneous waves and various loss mechanisms, and consider the analogy between elastic and electromagnetic waves. We discuss physical theories describing relaxation peaks, bounds on Q and experiments showing the behaviour of Q as a function of frequency, saturation and pore pressure. Finally, we propose an application example where Q can be used to estimate porosity and saturation.

品质因数 Q 是波场每个周期能量损失的无量纲度量，正确理解该因数在地震学、地球物理勘探到电学等各个领域都很重要。这里，重点是粘弹性。在解释实验值时，必须考虑几个因素，特别是介质的形状（棒、棒或无界介质）以及测量是在静止或传播模式下进行的事实。从理论角度来看，由于定义、空间维度和波的不均匀性，即传播向量（或波数）和衰减向量不指向同一方向，Q的表达式可能会有所不同。我们展示了时间和空间 Q 值之间的差异、压缩 Q 值和剪切 Q 值之间的关系、对频率的依赖性、孔隙粘弹性和各向异性的情况、非均匀波的影响和各种损耗机制，并考虑弹性和电磁之间的类比波浪。我们讨论描述松弛峰值、Q 界限的物理理论，以及显示 Q 作为频率、饱和度和孔隙压力函数的行为的实验。最后，我们提出了一个应用示例，其中 Q 可用于估计孔隙度和饱和度。