环境应力场在确定地震危险区中的作用

THE ROLE OF AMBIENT STRESS FIELDS IN DETERMINING SEISMIC RISK REGIONS

从位错模式出发，应用断裂力学的成果，作者在世界上首次导出了体波震级ｍ＿ｂ，环境剪应力值τ＿０（或构造剪应力值，或初始剪应力值，而不是应力降）和地震矩Ｍ＿０之间的依赖关系式。这个公式提供了直接利用震源参数大量计算构造剪应力场量值的可能性。作者认为构造剪应力场是控制地震发生的主要因素，即出现高应力值地震的地区是容易发生强震（Ｍ≥６．０）的地区，是地震危险区。作者计算了１９８７年以来发生在中国境内所有ｍ＿ｂ≥３．８地震的剪应力值，并据此划出了未来三年内我国大陆地区的强震危险区，同时给出了震级范围。１９９２年４月—１９９４年１月３１日，中国大陆地区共发生９次Ｍ＿ｓ≥６．０的地震，其中有８次落在事先划定的危险区内，只有１次在危险区外。

From the dislocation model,the authors of this paper have for the first time in the world de-duced the dependence relationship between body wave magnitudes(m_b),ambient shear stress va-lues τ_0 (or tectonic shear stress values,or initial shear stress values rather than stress drop)andseismic moment(M_0)by applying the achievements in fracture mechanics.The relationship hasopened up possibilities for calculating large numbers of magnitudes of tectonic shear stress fieldsby directly using seismic source parameters.They believe that tectonic shear stress fields are themain factors controlling earthquake occurrence,that is to say,the areas where earthquakes occurwith high stress values are seismic risk areas, being liable to strong earthquakes(M≥6.0). Theauthors have calculated the shear stress values of all the earthquakes with,m_b≥3.8 occurring inChina since 1987, and on the basis of the results, they have marked out the strong earthquake riskregions in the Chinese mainland in the next three years,giving the range of magnitudes simuta-neously. From April 1992 to January 31,1994,altogether nine earthquakes with M_s≥6. 0 occurredin the Chinese mainland,eight of them occurred in the previously designated risk regions,only oneof them occurred out of the risk regions.