芦山M_S7.0地震余震期间大地电磁视电阻率变化

发布时间：2018-04-24 18:21

本文选题：芦山地震 + 较大余震　；参考：《地震学报》2017年01期

【摘要】：以2013年4月20日芦山MS7.0地震震后5月3—24日距主震震中约7km处所观测到的大地电磁数据为基础,分析地下电阻率变化与较大余震(MS3.0)活动的关系.为确保用于地震异常分析的观测数据的可靠性,基于大地电磁方法的特点,使用稳定估算(robust)技术和相干度因子约束等方法得到各频点一定数量的自功率谱和互功率谱,再根据视电阻率和相位曲线的分布形态,剔除引起视电阻率和相位曲线突变的谱值之后得到高质量的视电阻率和相位曲线.此外,根据曲线形态和误差分布来判断数据质量,剔除可能受到干扰影响的数据,以获得能够真实地反映地下电阻率变化的视电阻率分析结果.结果显示:观测期内的yx极化模式的视电阻率值总体呈非单调的增大趋势,最大增幅达27%;yx极化模式的视电阻率值几乎在每个相对集中的较大余震丛集后均会出现高值,而较大余震丛集期间对应的则是视电阻率低值.从物理机制上分析地震的电阻率效应源于微裂隙内孔隙流体的变化,故推测芦山地震余震期间电阻率的增加趋势是由于震后应变释放区应力恢复和孔隙度恢复所致.
[Abstract]:Based on the magnetotelluric data observed from the epicentre of the Lushan MS7.0 earthquake from May 3-24 to the epicenter of the main shock on April 20, 2013, the relationship between the variation of underground resistivity and the activity of larger aftershock M S 3.0) is analyzed. In order to ensure the reliability of observational data for seismic anomaly analysis, based on the characteristics of magnetotelluric method, a certain number of self-power spectrum and cross-power spectrum are obtained by using the technique of stable estimation robust) and the constraint of coherence factor. Then according to the distribution form of apparent resistivity and phase curve, the high quality apparent resistivity and phase curve are obtained by excluding the spectral value that causes the abrupt change of apparent resistivity and phase curve. In addition, the quality of the data is judged according to the curve shape and error distribution, and the data which may be affected by the interference are excluded to obtain the results of apparent resistivity analysis which can truly reflect the change of underground resistivity. The results show that the apparent resistivity of YX polarization mode increases in a non-monotonic trend in general during the observation period, and the maximum increase of apparent resistivity in YX polarization mode is as high as nearly every relatively concentrated large aftershock cluster. However, the low apparent resistivity corresponds to the larger aftershock cluster. Based on the analysis of the physical mechanism, the resistivity effect of the earthquake originates from the change of pore fluid in the micro-fissure, so it is inferred that the increasing trend of resistivity during the aftershock of the Lushan earthquake is due to the stress recovery and porosity recovery in the post-earthquake strain release area.
【作者单位】：中国地震局地质研究所地震动力学国家重点实验室;
【基金】：中国地震局地质研究所基本科研业务“芦山科考”专项(IGCEA1305) 国家自然科学基金(41204056,41374077,41074047)共同资助
【分类号】：P315.722

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