SUMMARY The largest earthquake recorded in South Korea occurred in Gyeongju on 2016 September 12. Since then, understanding the geological structures near the Gyeongju earthquake's epicentre has been demanded. As a preliminary step to understand the geological structures around the epicentre, a 3-D audio-magnetotelluric (AMT) survey was conducted. These 3-D AMT data were imaged through data processing and inversion. However, because the AMT data acquired in Gyeongju were very noisy, conventional imaging procedures did not yield reliable results. To obtain a reliable model inverted from such noisy data, we propose various imaging strategies: an additional data processing technique using the Nyquist diagram after conventional data processing and several inversion strategies related to the selection of data, the weighting of the data, the constraints on the model parameter vector and the Lagrange multiplier used for the regularization. By applying the additional data processing step and several inversion strategies, we were able to successfully invert the noisy field data. The inversion results verify that the data-screening procedure applying the Nyquist diagram remarkably improves the results compared with those obtained using only conventional data processing. The imaging strategies proposed in this case study can be used to image noisy MT/AMT field data for other regions.

中文翻译：

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解释在韩国庆州获得的 3-D 嘈杂音频-大地电磁数据的成像策略：数据处理和反演

摘要 韩国记录的最大地震于 2016 年 9 月 12 日发生在庆州。从那时起，就要求了解庆州地震震中附近的地质结构。作为了解震中周围地质结构的初步步骤，进行了 3-D 音频-大地电磁 (AMT) 调查。这些 3-D AMT 数据通过数据处理和反演成像。然而，由于在庆州获得的 AMT 数据非常嘈杂，传统的成像程序并没有产生可靠的结果。为了从这些噪声数据中获得可靠的模型，我们提出了各种成像策略：在常规数据处理之后使用奈奎斯特图的附加数据处理技术以及与数据选择、数据权重相关的几种反演策略，模型参数向量的约束和用于正则化的拉格朗日乘数。通过应用额外的数据处理步骤和几种反演策略，我们能够成功地反演嘈杂的现场数据。反演结果证实，与仅使用常规数据处理获得的结果相比，应用奈奎斯特图的数据筛选程序显着改善了结果。本案例研究中提出的成像策略可用于对其他区域的噪声 MT/AMT 场数据进行成像。反演结果证实，与仅使用常规数据处理获得的结果相比，应用奈奎斯特图的数据筛选程序显着改善了结果。本案例研究中提出的成像策略可用于对其他区域的噪声 MT/AMT 场数据进行成像。反演结果证实，与仅使用常规数据处理获得的结果相比，应用奈奎斯特图的数据筛选程序显着改善了结果。本案例研究中提出的成像策略可用于对其他区域的噪声 MT/AMT 场数据进行成像。