Kakioka观测台超低频地震地磁研究

地震是最严重的自然灾害之一。准确的地震预测可有效减轻地震灾害，一直以来都是地震工作者的奋斗目标。“是否存在有助于预测的地震前兆”是Science期刊创建125周年之际提出的125个最前沿科学问题之一。超低频地震地磁信号被认为是最具前景的地震短临前兆之一，受到广泛关注。然而，由于地震地磁信号本身较弱、孕震过程高度复杂，地震地磁研究仍面临一系列挑战：地震地磁信号通常混杂于空间场源之中难以精确提取；地震地磁信号与地震的时、空、强三要素对应关系不清，预测效能难以定量评估；地震地磁信号中的预测信息尚未得到有效应用。针对上述问题和挑战，本文利用日本Kakioka地磁台长达10年的超低频地磁观测数据和地震目录，开展地震地磁信号提取、统计显著性分析以及预测效能评估研究，并在此基础上探讨如何在预测模型中有效融合地震地磁信号中的预测信息，发挥磁场观测数据的应用价值。

第一，针对地震地磁信号弱、提取难的问题，开发了基于小波多元相干的台站间转换函数新方法。利用观测数据计算小波多元相干系数，通过设置相干度阈值筛选高信噪比数据；提出了新的窗长选取函数，实现了不同周期转换函数计算时间窗长的自适应选取，提升了转换函数计算精度。新方法解决了已有算法中存在的相干度计算窗长划分过于粗糙、有效样本数据少的问题，提升了转换函数计算稳定性和精度。合成数据和实测数据分析验证了新方法的有效性及稳定性，展现了新方法的优势。利用台站间转换函数，准确计算了Kakioka观测台磁场水平X、Y分量和垂向Z分量的外界空间场源信号，在此基础上实现了Kakioka台站局部磁场扰动的高精度识别和提取。

第二，针对地磁异常信号与地震对应关系不清的问题，开展了统计分析和预测效能评估。首先，利用新开发的台站间转换函数方法，构建了Kakioka台空间场源信号（周期小于940秒）变化模型值，计算了观测值与模型值残差，获取了Kakioka台站局部磁场变化。然后，计算了每日当地夜间2：30-4：00时间段磁场X、Y、Z三分量的局部磁场能量变化，并设置阈值定义磁场异常；最后，使用时序叠加法统计分析了Kakioka台磁场异常与区域地震活动的相关性及显著性，并利用Molchan误差图系统性地评估了磁场异常对区域地震活动的预测效能。结果表明Kakioka台的Z分量磁异常预测效能优于X分量和Y分量。Z分量磁异常总能量以及各周期（50秒/100秒/200秒/400秒）能量在地震前显著提升，预测效能均优于随机预测，其中总残差预测效能最佳。地磁异常对距离更远的地震样本预测效能明显下降，表明Kakioka台地磁异常信号与台站周围的地震更相关。为了进一步厘清地震地磁信号与地震时、空、强三要素对应关系，本研究提出了量化预测效能的新参数S*，利用数据驱动实现了对异常所指示的地震时间、位置和强度等参数的同步优化，获取了Kakioka台地磁异常与区域地震的关联特征。

第三，在上述工作基础上，本文对如何在实际地震预测中利用地震地磁信号进行了探讨。使用已有的点过程外激发模型，将基于台站间转换函数所得地磁异常作为激发源，通过适当的激发核函数，得到了随时间变化的地震发生率。赤池信息准则分析结果表明，基于地震地磁信号的外激发模型显著优于随机预测的泊松模型。进一步分析表明，外激发模型的信息增益随着震级下限的增加而增加，地震自激发模型（传染型余震模型）的信息增益随着震级下限的增加而减小，融合地震触发信息和地磁异常信息的综合地震模型预测效果最佳。

综上，本文分析了日本Kakioka地磁台长达10年的超低频地磁观测数据，开展了地震地磁信号提取、统计显著性分析、预测效能评估研究，并进行了应用探索。发展了基于小波多元相干的台站间转换函数新方法，提升了转换函数计算精度；提出了可系统性量化地磁异常预测效能的新参数；揭示了Kakioka台地磁异常与区域地震的关联特征；验证了综合地震预测模型的有效性并评估了其信息增益。相关研究成果可为中国地震科学试验场数据分析提供技术方法，有助于发掘观测资料在防灾减灾中的应用价值。

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