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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(MS>3.0)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.
Based on the geomagnetic data observed at about 7 km from the epicenter of the main shock on May 3-24, after the Lushan MS7.0 earthquake on April 20, 2013, the variation of the underground resistivity and the large aftershock (MS> 3.0) were analyzed. In order to ensure the reliability of the observed data for seismic anomaly analysis, based on the characteristics of the magnetotelluric method, a certain number of self-power spectra at each frequency point are obtained by using robust techniques and coherence factor constraints According to the distribution of apparent resistivity and phase curve, high-quality apparent resistivity and phase curve can be obtained after excluding the spectrum values causing the apparent resistivity and phase curve mutation. In addition, according to the curve shape and error distribution Data quality and eliminate the data that may be affected by the disturbance so as to obtain the apparent resistivity analysis result that truly reflects the change of the underground resistivity.The results show that the apparent resistivity value of the yx polarization mode during the observation period is generally non-monotonically increasing Trend, the largest increase of up to 27%; yx polarization mode apparent resistivity value of almost every relatively concentrated after a large set of aftershocks will have high value, while the larger during the larger aftershock cluster The apparent resistivity is low.Analysis of the resistivity effect of the earthquake originates from the change of the pore fluid in the microfracture from the physical mechanism. Therefore, it is inferred that the increase of the resistivity during the aftershock of the Lushan Earthquake is due to the stress recovery and porosity recovery Due.