Study On The Influence Characteristics Of Resistivity Anisotropy Of Seismogenic Structure

Earthquakes pose a great threat to the safety of human life and property.In order to reduce the damage caused by earthquakes,it is very important to strengthen the monitoring of moderate and strong earthquakes.At present,the electromagnetic method is one of the important means for the monitoring of earthquake precursor anomalies.During the "Ninth Five-Year Plan" and "Tenth Five-Year Plan" period,our country implemented the digital transformation and network construction of seismic electromagnetic stations,which enriched the data quantity and improved the data quality,and it has made a significant contribution to the development of seismic electromagnetic research in our country.The direct current(DC)method is one of the main seismic electromagnetic monitoring methods,and it has a history of nearly 60 years of observation.We usually establish georesistivity stations in open and flat places with few interference sources.After long-term and continuous observation of georesistivity,we can delineate anomalies and predict earthquakes.Previous studies have pointed out that changes in the geoelectric properties of seismogenic structures can lead to resistivity anisotropy in the subsurface medium near the surface,which leads to anisotropic changes in the resistivity observed by georesistivity stations in different directions.A large number of studies have shown that before moderate and strong earthquakes,most of the georesistivity stations within 150km of the epicenter will have short-term anomalies,which manifest as synchronous or asynchronous decline;at the same station,the variation of georesistivity values in different directions will also show anisotropy.The regularity of observation data is closely related to the distribution of seismogenic structures and subsurface fault zones.In this paper,three-dimensional seismogenic structure models are established,and the DC anisotropy program based on the unstructured finite element method is used for forward modeling to explore the influence of the geoelectric properties of the seismogenic structure on the change of the georesistivity anisotropy.Through the DC circular scan with the fault zone model,it is recognized that the existence of the fault zone will cause the anisotropy of the georesistivity at different measuring directions.Through the numerical simulation of the change of georesistivity in a large-scale fault zone model,it is recognized that the georesistivity at different positions and different directions will show anisotropy with the change of the geoelectric properties of the fault zone.This paper considers that the change of georesistivity and the cause of anisotropy are related to the change of geoelectric properties in the fault zone and the formation of cracks under the action of stress,and combined with the simulation analysis of the main stations of the Tangshan earthquake.After calculation,the simulated data is consistent with the trend of the measured data,which proves the rationality of the conjecture.