ABSTRACT We apply seismic full waveform inversion to SH‐ and Love‐wave data for investigating the near‐surface lithology at an archaeological site. We evaluate the resolution of the applied full waveform inversion algorithm through ground truthing in the form of an excavation and sediment core studies. Thereby, we investigate the benefits of full waveform inversion in comparison with other established methods of near‐surface prospecting in terms of resolution capabilities and interpretation security. The study is performed in a presumed harbour area of the ancient Thracian city of Ainos. The exemplary target is the source of a linear magnetic anomaly oriented perpendicular to the coast, which was found in a previous magnetic gradiometry survey, suggesting a mole. The SH‐wave full waveform inversion recovered a subsurface SH‐wave velocity model with submeter resolution showing lateral and vertical velocity variation between 40 and 150 m/s. To tame the non‐linearity of the full waveform inversion, a sequential inversion of frequency bands has to be combined with time‐windowing in order to separate the Love wave from the reflected SH wavefield. We compare the full waveform inversion results with multichannel analysis of surface waves, standard seismic reflection imaging, electrical resistivity tomography and electromagnetic induction. It turns out that the respective depth sections are correlated to a certain degree with the full waveform inversion results. However, the structural resolution of the other geophysical methods is significantly lower than for the full waveform inversion. An exception is the reflection seismic imaging, which shows the same resolution as full waveform inversion but can only be interpreted together with the full waveform inversion–based velocity model. An archaeological excavation as well as coring data allows ground truthing and a direct understanding of the geophysical structures. The results show that the target was a sort of near‐surface trench of about 3–4 m width and 0.8 m to 1.0 m depth, filled with silty sediment, which differs from the layered surrounding in colour and composition. The ground truthing revealed that only SH‐wave full waveform inversion and seismic reflection imaging could image the trench and sediment structure with satisfying lateral and depth resolution. We emphasize that the velocity distribution from SH‐wave full waveform inversion agrees closely with the excavated subsurface structures, and that the discovered changes in seismic velocity correlate with changes in the sand content in the respective sediment facies sequences. The study demonstrated that SH‐wave full waveform inversion is capable to image structural and lithological changes in the near subsurface at scales as low as 0.5 m, thus providing the high resolution needed for archaeological and geoarchaeological prospection.

中文翻译：

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用 SH 波表征粉砂质到细砂质沉积物：与其他地球物理方法相比的全波形反演

摘要 我们将地震全波形反演应用于 SH 和 Love 波数据，以研究考古遗址的近地表岩性。我们以挖掘和沉积岩心研究的形式通过地面实况评估应用的全波形反演算法的分辨率。因此，我们研究了全波形反演与其他已建立的近地表勘探方法相比在分辨率能力和解释安全性方面的优势。该研究是在色雷斯古城艾诺斯的假定海港区进行的。示例性目标是垂直于海岸的线性磁异常源，这是在先前的磁梯度测量中发现的，表明存在鼹鼠。SH波全波形反演恢复了亚米级分辨率的地下SH波速度模型，显示横向和垂直速度变化在40到150 m/s之间。为了抑制全波形反演的非线性，必须将频带的顺序反演与时间窗口相结合，以便将洛夫波与反射的 SH 波场分开。我们将全波形反演结果与表面波的多通道分析、标准地震反射成像、电阻率层析成像和电磁感应进行了比较。结果表明，各个深度段与全波形反演结果有一定的相关性。然而，其他地球物理方法的结构分辨率明显低于全波形反演。一个例外是反射地震成像，它显示出与全波形反演相同的分辨率，但只能与基于全波形反演的速度模型一起解释。考古发掘以及取芯数据允许进行地面实况和对地球物理结构的直接了解。结果表明，该目标为一种近地表海沟，宽度约为3-4 m，深度为0.8-1.0 m，充满粉质沉积物，颜色和成分与层状环境不同。地面实况表明，只有 SH 波全波形反演和地震反射成像才能以令人满意的横向和深度分辨率对海沟和沉积物结构进行成像。我们强调，SH波全波形反演的速度分布与挖掘的地下结构非常吻合，并且发现的地震速度变化与各个沉积相序列中含砂量的变化相关。研究表明，SH波全波形反演能够以低至0.5 m的尺度对近地表的结构和岩性变化进行成像，从而为考古和地质考古勘探提供所需的高分辨率。