A Study On Seismogenic Structure Of LinDian Earthquake

On July25,2005, the devastating MS5.1earthquake jolted lindian county ofHeilongjiang province, with great influence to oil field p roduction and life. Daqing isan important energy base, occupies an important place in the national economy. So,the research of Lindian earthquake has important practical significance.This research, with considerable difficulty, is the first study, filling the gaps inDaqing seismic study of seismogenic structure, mainly devoted to natural earthquakeseismogenic structure. This study laid the foundation for future studies, and alsoaccumulated the necessary natural earthquake research experience. The studyprogressed the comparisons and analysises of31sequences of Lindian earthquake,Qianan earthquake and both sides of Kaiyuan-Chifeng，arrived at the conclusion thatthe earthquake sequence characteristics is major-after shocks, and there is a little ofafter-schock. The results, analysing of the distribution of the principal advantagestress direction, realize the predominant direction of P is NE45°in Songliao basin andsurrounding areas, and the predominant direction of T is NW30°, to be orthogonal,there for, the predominant direction of stress is NEE.Re-processing of Songliao Basincover and the deep structure with the Songliao Basin and its surroundings’seismicgeological structure and basic geophysical field, interpreting of3-d and2-d seismicwork area in Northern Songliao Basin,showed that Lindian earthquake epicenter laidin the interchange of Sunwu-Shuangliao fracture, or Da’an-Dude fracture, andBinzhou fracture.By vertical projection in Binzhou fracture section，find out thedepthof Lindian’s eismogenic structure is6.432s. This times research also carried outthat the Lindian epicenter is13.84km deep, based on heavy, magnetic, electric andseismic and drilling data, and combined with geological section seismology researchresults,by the method of combine the Sectional fixed Vo and matchingβtime-depthconversion.Achieved following results:1. Binzhou fracture continuous activated in The formation of Songliao basin,giveing rise to the reason of settlement differences between both sides. The nature ofNW strike-slip made it become seismogenic structure easier. And most of the historyearthquakes were NE. so Binzhou fracture very likely is the seismogenic structure ofLindian earthquake.2. The quasi-periodicity is20years in Songliao basin and surrounding areas3.The deep regional gravity results show: Songliao base is balanced and stable, the main reason of Lindian earthquake is the variation of stresses caused by regionaltectonic stress field and the crust’s nonuniformity.4. The top surface and surrounding areas of detachment layer is earthquakeprincipal part.depth at10-17km.5. The internal causes of Lindian earthquake are detachment surface, geothermalanomaly, fracture and rock mass. The external cause is regional tectonic stress field.