Statistical Research On Ionospheric Plasma Anomalies Related To Earthquakes

Earthquake is one of the most serious natural disasters faced by humanity,and earthquake prediction is a global scientific problem.Therefore,conducting sufficient research on earthquakes to reduce their harm is urgently needed at present.During the process of earthquake generation,a series of physical or chemical signals generated by plate tectonic movements affect the crust,which can cause abnormal changes in the ionosphere through the coupling of layers.With the development of space technology,observing earthquakes from space provides new ideas for earthquake monitoring and prediction research and has been highly anticipated by scientists.Since the beginning of the 21 st century,the specialized DEMETER and CSES satellites launched for earthquake monitoring have provided important data resources for studying earthquake-ionosphere anomalies,greatly advancing our understanding of the coupling mechanism between earthquakes and the ionosphere.However,due to the complexity of earthquake mechanisms,there is no unified understanding of earthquake-ionosphere anomalies yet,and therefore,more attempts and explorations are still needed.This article conducted a statistical study on ionospheric plasma anomalies related to earthquakes based on the night-side ion density data observed by the DEMETER satellite’s Ionospheric Plasma Analyzer(IAP)from 2005 to 2010.First,a stable background field spatiotemporal variation model was constructed,and using the sliding quartile method and superimposed epoch analysis on the spatiotemporal changes in the background model,the perturbation changes of ion density above the epicenter relative to the background field were extracted.The main research conclusions are as follows:(1)Analysis of ion density background characteristicsA global spatial distribution map of ion density was constructed for every month between 2005 and 2010,using the global grid method.The study found that the spatial distribution of Ni is non-uniform,with high values typically appearing in the magnetic equator and mid-to-high latitudes of the northern and southern hemispheres.The spatial distribution also shows significant seasonal features that are similar within the same season but have different distribution characteristics across different seasons.In particular,there is a reversal of the north-south hemisphere structure during the spring and autumn months.The spatial distribution of ion density shows distinct features,including the WN4 structure,Mid-latitude Summer Nighttime Anomaly(MSNA),and Weddell Sea Anomaly(WSA).The distribution pattern shows regular changes with variations in solar activity and season.Using the time series method,ion density time series was constructed for different geomagnetic latitude regions from 2005 to 2010.The study showed that ion density time series exhibited a significant annual cycle at the same latitude,with different features depending on latitude.The trend of change in ion density in low-latitude regions was consistent in both hemispheres,while in mid-to high-latitude regions,the annual change trend was opposite in the northern and southern hemispheres.There was a high correlation between the long-term trend of ion density in mid-to low-latitude regions and the trend of F10.7,although the correlation in mid-to high-latitude regions was somewhat lower.(2)Analysis of the Characteristics of Global Earthquakes with Mw≥7 from2005 to 2010This paper analyzes the characteristics of 75 global earthquakes with Mw≥7from 2005 to 2010,using the fixed orbit analysis method and excluding data with missing or invalid information.Anomalies are defined as continuous disturbance,a change in amplitude exceeding 50%,and occurring during periods of geomagnetic activity.The study found four types of anomalies: positive,negative,both positive and negative,and no significant change.Among the 75 earthquakes,59(74.7%)had Ni disturbances before or after the earthquake,with positive anomalies being dominant(89.3%),and only six earthquakes showing negative anomalies.Anomalies mostly occurred within seven days before and after the earthquake,especially concentrated around the earthquake occurrence.Additionally,19 earthquakes without anomalies were analyzed and found mostly to be deep-focus earthquakes below 7.6 magnitude.Therefore,the study suggests that there is a strong correlation between anomalous responses and earthquake source depth,with shallow-focus earthquakes being more easily detectable than deep-focus earthquakes.(3)Analysis of Statistical Characteristics of Anomalous Phenomena in Global Earthquakes with Mw≥4.8 from 2005 to 2010After defining and strictly selecting data related to earthquakes,the stacking epoch method was used to conduct statistical analysis on 10,320 earthquakes with Mw≥4.8 worldwide.The statistical results were tested through multiple methods,such as classifying by different magnitudes,earthquake source depths,and designing random earthquakes.The study found that ion density would exhibit enhanced fluctuations under the influence of earthquakes.According to the histogram analysis of anomalous changes,the distribution of positive anomalies deviated significantly from the Gaussian distribution,indicating a stronger correlation with earthquakes.The increase of ion density anomalies mostly occurred three to five days,nine to ten days,thirteen to fourteen days,and on the day of the earthquake occurrence.The relationship between Dobrovolsky’s seismic radius and the range of anomalies indicated that there is a difference between the disturbance range in the ionosphere and the formula for the seismic radius.For earthquakes with 4.8 ≤M<6.0,disturbances mainly occur within the R range,while for stronger earthquakes above magnitude 6,the anomalous range may exceed the seismic radius R.The statistical results for different magnitudes showed that the larger the magnitude,the wider the range of anomalous disturbances.The statistical results for different earthquake source depths showed that shallow-focus earthquakes had the most significant disturbances,concentrated in the epicenter and northern regions,while mid-shallow focus earthquakes also showed notable disturbances but scattered.Deep-focus earthquakes had the least noticeable disturbances.Moreover,the statistical results of designed random earthquakes did not show any regularity and even displayed unreasonable anomalous phenomena,which verified the reliability of the statistical results.