Study On Surface Permanent Displacement Of Active Faults

Large-scale surface rupture is caused by the recent earthquakes such asWenchuan earthquake,Jiji earthquake,Kunlunshan earthquake and Turkey izmitEarthquake. Huge losses were caused because of the great damage to thebridges, roads, dams and so on. So,research of surface rupture of active fault isthe focus in the field of geotechnical earthquake engineering. Research ondistribution of permanent surface displacement has great engineeringsignificance and theoretical value to earthquake preparedness and disasterreduction.The mechanism and process of earthquake occurrence are analyzed in thispaper.Physical process of earthquake occurrence is described in mathematicaland physical way, which is the process of local buckling or material damage ofinterface of unstable system composed by faults and septate block affected bygeological processes.Tectonic stress and strong earthquake are closely related. In this paper,application and achievements of GPS in the research of geodynamics aresummarized and dynamic environment of mainland China and nearby regionsis introduced. Xianshuihe fault,Longmenshan fault and Dongkunlun fault arechosen as the research objects, then dynamics of crustal movement is applied tosimulate the motion state of fault before and after the nearest destructiveearthquakes---Kunlunshan earthquake,Wenchuan earthquake and Yushuearthquake. The results show that there is relation between stress, strain anddeformation behavior and earthquake and strong earthquakes may happen inthe northwest of Xianshuihe fault, southwest and northwest ofYingxu-beichuan fault according to preliminary inference.There is regularity for earthquake occurrence in active structure of oneregion. The common model of earthquake occurrence and its scope ofapplication is analyzed comparatively. Basing on the former research results,the method and steps to choose earthquake occurrence model are put forwardfor the appointed active fault. Considering the historical earthquakeand supplementary earthquake sequence confirmed by trial trench, models ofearthquake occurrence of several rupture are given as follows: the averagerecurrence time interval of eartahquake which magnitude is greater than orequal to7.0in Xianshuihe fault is41years and the magnitude of characteristicearthquake is712. The average recurrence time interval of eartahquake whichmagnitude is greater than or equal to7.0in Xiaojiang fault is58years and themagnitude of characteristic earthquake is712.Seismic risk of fault in the future can be estimated considering thesimulation results of dynamics of crustal movement and earthquake occurrence model of fault. The method to evaluate the surface displacement caused byearthquake can be considered in the ways of near field and far field. For nearfield, probability analysis method of permanent surface displacement is usedbasing on Cornell vibration framework of surface. And also, the relationbetween magnitude and rupture scale, the distribution model of permanentdisplacement and the method to evaluate the maximum permanentdisplacement of surface based on the Lee displacement attenuation model areall considered. Then, permanent displacement along rupture zone of theWenchuan earthquake is studied with statistics and the applicability ofdistribution model of permanent displacement is demonstrated. Then, themethod is applied to analyze the Xianshuihe fault and the value of themaximum permanent displacement of near field is obtained.The method to evaluate the permanent displacement of the fault in the farfield is put forward based on Mindlin solution. It is applied to the XianshuiheFault.And displacement field of surface is calculated in a limited range of thefault. The results showed that the displacement distribution of the site which isfar26km from the fault is relatively homogeneous.The relative displacement ofthree directs are1cm,1cm,2cm.In a word, physical process of earthquake occurrence is analyzed andearthquake of fault, seismic geology, tectonic stress and GPS observation dataare also analyzed comprehensively. The key point of earthquake occurrence iscalculated by using the geodynamics. Earthquake occurrence model isconfirmed and then its risk is confirmed in the future according to the statisticalrelation among the paleoseismic, historical and modern earthquakes. In thispaper taken Dagangshan dam as engineering background, surface permanentdisplacement of fault is evaluated. At last, a set of evaluation system is putforward for permanent surface displacement of active fault which can beapplied to the engineering seismology.