中国大陆地震震源分布特征的初步研究

PRELIMINARY STUDY ON DISTRIBUTION CHARACTERISTICS OF EARTHQUAKE SOURCES IN THE CHINESE MAINLAND

本文讨论了中国大陆内部１９７０年以来ＭＬ≥３．０级并给出震源深度的地震的分布特征。根据对１类测定精度的４７５７次地震深度的统计表明，约９１％的地震发生在小于３０ｋｍ的深度内，位于峰值深度段５－２５ｋｍ内的地震约占７５％。从带深度的１类和２类精度地震震中分布来看，它们多成条带状分布于构造地块周围，如青藏块体东缘和东北边缘，鄂尔多斯块体四周等。地震深度分布还显现出区域性特征：在帕米尔、天山地区存在大于６０ｋｍ的壳下地震；青藏高原内部地震深度为１０－３０ｋｍ；鄂尔多斯南北两侧为５－３０ｋｍ，西侧５－５０ｋｍ，东侧１０－４０ｋｍ；华北地震小于５０ｋｍ；渤海地震在１０－５３ｋｍ之间；东南沿海地震深度小于４０ｋｍ。本文还根据地震震源的空间分布特征提出了可以进一步研究的问题。

In this paper, the distribution characteristics of ML≥3.0 earthquakeswith focal depths in Chinese mainland since 1970 are discussed.The statistics of focal depths of 4757 events with determining precision of the first class show that about 91% of the events occurred within depths less than 30 km and 75% of the events lay in peak depths of 5-25km.Theepicentres of the events with determining precision of the first and second classes were distributed in belts around tectonic blocks, such as, east margin and northeast margin of the Qinghai-Tibet block and all around thd Ordos block. Depth distribution shows the regional feature:there were subcrustal earthquakes with depths over 60km in Pamier and Tianshan regions; the focal depths of the events in the interior of Qinghai-Tibet plateau were 1030km; the focal depths were 5-30km in the both south and north sides of Ordos, 550km, the west side and 10-40km,the east side;the focal depths of the events In north China were less than 50km; the focal depths of the events in Bohai Sea were 10-53km and the focal depths of the events in the coastal waters of southeast China were less than 40km.Some problems which can be further studied have also been given on the basis of space distribution characteristics of earthquake sources.