Abstract:

This paper studies the linear concentrated distribution of geomagnetic diurnal induced current and the spatial distribution characteristics of short-term in-situ recurrence anomalies in the 1~3 years before the 2016 Zadoi M6.2 earthquake, the 2017 Jiuzhaigou M7.0 earthquake and the 2017 Milin M6.9 earthquake. The main conclusions are as follows:
(1)The overlapping segment anomalies occurring within 1~3 years before strong earthquakes usually have the phenomenon of seismic gaps. The overlapping segment gap is a large high-resistance body and also a hard body(hard inclusion)in the seismogenic model of hard body. Overlapping segment gap and seismic gap are the detection results of hard body with different depth distribution range by different physical detection methods. The distribution range of hard body is delineated by seismic gap in the upper and middle crust and overlapping segment gap in the middle-lower crust and upper mantle. The overlapping segment gaps occurred within 1~3 years before strong earthquakes, which are the anomalies in the third stage of the seismogenic model. The seismic gap before strong earthquakes has different stages. For example, background gaps are formed decades of years before strong earthquakes, and the gaps formed again about 1 year before the earthquakes.
(2)The overlapping segment anomalies occurring within 1~3 years before strong earthquakes reflect the formation of short-time high conductive current channels in the high conductive layers among high resistance bodies. These short-time high conductive current channels are caused by the mutually detached slip events with up-arching property among the high-resistivity bodies located in the middle-lower crust and upper mantle, resulting from the upwelling of deep thermal fluid. They are the events in which the energy in the middle-lower crust and upper mantle migrates to the hard body in the seismogenic model of hard body, while the seismic gap events are the ones in which the energy in the middle-upper crust migrates to the hard body before the earthquake.
(3)Based on the results of seismic high-pressure fluid experiments in recent years, and combined with the mechanism of overlapping segment seismic anomalies, it is considered that each sealed high-pressure fluid in the seismogenic fault of the source body will not rupture at the same time in the impending earthquake stage. The original free water in the fault, the sealed high-pressure fluid broken in the earlier stages, and the high-pressure thermal fluid upwelling into the fault in the deep may make the seismogenic fault of the source body full of free water, and may form a high-conductivity current channel in the fault with impending earthquake significance. The high-conductivity current channel may be a real impending earthquake anomaly. Obviously, it is found that the high-conductivity current channel in the fault in the impending earthquake stage has practical significance for the short-term and impending earthquake prediction.
(4)The detachment slip events detected from the overlapping segment anomalies are located below the strong earthquake source, which is similar to the phenomenon that slow earthquake zone is located below the earthquake zone. Although the relationship between slow earthquakes and earthquake above them is unclear, some scholars believe that slip events produce stress accumulation on the surface of locked plates. A slip event may trigger a destructive earthquake, that is, a high-incidence period of intermittent tremors and slips can produce a peak period of seismicity. The above views on slow earthquakes are similar to the relationship between the linear overlapping segment anomalies of induced current associated with geomagnetic diurnal variation and earthquakes. The detachment slip events detected from the overlapping segment anomalies may be similar to the inter-plate slow earthquake or slow slip involving the upwelling and migration of thermal fluid under the continent, but this speculation needs to be demonstrated based on the research results of seismology.

Key words: geomagnetic diurnal variation, induced current, thermal fluid, upwelling, detached slip, seismogenic mode, hard body, slow earthquake

摘要：

文中研究了2016年杂多6.2级、 2017年九寨沟7.0级和2017年米林6.9级地震前1~3a内地磁日变化感应电流的线状集中分布和短期原地重现异常的空间分布特征, 发现线状感应电流的重叠段有围空现象, 并依据重叠段异常产生的机理丰富和完善了坚固体孕震模式, 获得的主要结论包括: 1)重叠段空区是坚固体在中-下地壳和上地幔分布范围的反映, 这与地震空区是坚固体在中-上地壳分布范围的反映相类似, 重叠段空区是发生在震前1~3a、 坚固体孕震模式第3阶段的异常; 2)重叠段异常是中-下地壳和上地幔高阻体之间出现带有上拱性质的相互拆离滑动事件导致的高阻体之间高导层出现的短时间高导电流通道, 其中上述拆离滑动事件是由深部热流体上涌引起的, 它是坚固体孕震模式中发生在中-下地壳和上地幔的能量向坚固体运移的事件; 3)临震阶段震源体孕震断层内的各个密封高压流体不会同时破裂, 早期破裂的密封高压流体与深部上涌进入断层内的高压热流体及断层内原有的自由水可能使得断层内遍布自由水, 并在震源体孕震断层内形成有临震意义的高导电流通道, 发现临震阶段震源体孕震断层内的高导电流通道对地震短临预报具有现实意义; 4)重叠段异常探测发现的中-下地壳和上地幔拆离滑动事件可能是大陆下方有热流体上涌运移参与的慢地震, 但这一推测还需要基于测震学原理的研究结果加以论证。

关键词: 地磁日变化, 感应电流, 热流体, 上涌, 拆离滑动, 孕震模式, 坚固体, 慢地震