Study On Seismic Fractal In Chongqing

Earthquake is a kind of geological disasters that brings great threat to the safety of human life and property.Compared with other natural disasters,earthquakes cause more serious losses to human society.China is one of the most severely threatened countries in the world due to the earthquake disaster.Due to its special geographical location and complex terrains in the periphery of the North-South Seismic Belt,Chongqing can easily induce seismic secondary disasters,such as landslide,collapse,debris flow.The frequent earthquake disaster hinders the social and economic development of our country to a great extent.Therefore,strengthening the research on earthquake disaster is of great significance to regional disaster prevention and mitigation and urban sustainable development.The emergence of fractal theory provides a new research idea for earthquake disaster.Many scholars at home and abroad apply the fractal method to explore the space-time propagation characteristics and earthquake prediction of earthquake,but the research scope is mainly confined to some strong earthquakes,and there are few studies on the fractal of earthquakes in small and medium-sized earthquake-prone areas.Based on the Chongqing time-space fractal study,the seismic activity characteristics are revealed from mesoscopic space scale.This not only provides a reference for earthquake prevention and disaster reduction in Chongqing,but also is a beneficial attempt for the prediction of moderate-strong earthquakes.Based on the seismic data above 2 magnitudes from 1993 to 2015 in Chongqing City and the"Chongqing Seismotectonic Map",taking the Seismotectonic zones as the statistical unit,this paper uses fractal theory and spatial analysis and other related methods to calculate seismic spatiotemporal fractal dimension.Then,the spatiotemporal fractal features of the seismic activity of the fractured zone are analyzed and compared.Finally,based on the geological tectonic setting of Chongqing,the relationship between seismic fractal features of Chongqing and the geological structures is discussed systematically.The main contents and conclusions of this paper are as follows:(1)Time-fractal characteristics of earthquakes in Chongqing are discussed systematically.There is a positive correlation between the size of information dimension and magnitude of earthquake and the frequency of M?3 earthquakes in each tectonic area;The time-varying characteristics of the information dimension before and after the strong earthquake and the sensible earthquake in each tectonic area are different;The D_q value of each tectonic area increases with the decrease of the value of q,and D_q value of different q areas spears abnormal before the strong earthquake,however,the anomalous characteristics of D_q-q curve before the onset of sensitive earthquake are not obvious.;The D_q-t curve can well reveal the fractal features of the time structure of moderate-strong earthquakes,but it can not describe the fractal features of the time structure of sensitive earthquakes.;The multifractal spectrum of seismic time structure appears anomalous feature,which can be used as a method to verify the spectrum of generalized dimension.The time-fractal feature of multiple earthquake areas can indirectly reflect the seismic fractal characteristics of the entire study area.(2)The special fractal characteristics of earthquake in Chongqing are discussed systematically.The information dimension of earthquake can indirectly reflect the degree of seismic activity in the tectonic area;the D_q value of the spatial distribution of seismicity increases first and then decreases with the increase of q,and the seismic activity in dense area is more complicated than the sparse area;The spatial distribution pattern of earthquake points is different and the larger the information dimension of the structural area is,the closer to aggregation distribution the spatial distribution of seismic points is;The occurrence of moderately strong earthquakes does not occur when the distribution of small earthquakes is the most concentrated,but after or before.(3)The relationship between spatiotemporal fractal features and geological structural areas in Chongqing is discussed systematically.The multifractal characteristics of seismic spatial distribution in each tectonic zone are not as obvious as the multifractal characteristics of time series;The stronger seismic activity,the larger the fractal dimension value is,the more obvious is the spatiotemporal fractal characteristics of seismic activity.(4)The relationship between seismic spatial fractal and active faults in Chongqing is discussed systematically.The earthquakes in Chongqing mainly occurred near the basement fault or at the intersection of basement faults;The more complex the fault zones in the tectonic zone,the larger the seismic intensity is and the larger the fractal values of the corresponding fault zones are;The larger the range of the buffer zone is,the larger the value of seismic information dimension is;The information dimension in the buffer zone has the same positive correlation with the magnitude 4 or above earthquakes;The seismic activity in Rongchang area is affected by the Huayingshan basement fault zone and the Cenozoic tectonic stress field,and may also be related to deep well water injection and the reactivation of faults caused by it.