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

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