辽宁海城NW向构造全新世活动特征及古地震研究
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摘要
<正> 一、引言辽宁省海城位于我国东北下辽河平原与辽东山地交界地带,地质构造属于华北断块区下辽河块陷与辽东块隆的分界。中国东部著名的郯庐断裂带向北过渤海进入辽东湾后,大致沿下辽河凹陷东界向北继续延伸。70年代中期以前,NNE向断裂一直被认为是该地区活跃的构造。1975年海城地区发生的7.3级地震改变了人们的认识。该次地震的等震线、震源机制、地震地表破裂、中小地震活动及地震前后的地形变测量资料表明,NW向
A NW-trending, 41km long, Holocene active fault belt has been discovered in Haicheng area, Liaoning province, based on airphoto interpretation and field investigation. The fault is located on the southeast side of the 1975 Haicheng Earthquake seismic zone, and appears as a linear negative landform consisting of a series of drainage divides of short gullies. The short gullies have systematically been offset left-laterally. By trenching and dating, the results show that the latest activities of the fault occurred in the period of 5,000～ 7,000 a.B.P. According to its geographical position, we suggest that this newly discovered fault can be named as the "Lamufanggou-Dafangshen Fault". The surface ruptures of the fault were scaled greater than that of the 1975 Haicheng earthquake. Besides, we have discovered two fault-scarplets cutting Holocene river terrace near Chagou Village. Each of the scarplets is 3.5～4.0 m in height, indicating that two paleo-events had occurred since 5,000 a.B.P. In general, at least 2～3 paleo-earthquakes had occurred in this region before the 1975 Haicheng earthquake; the average recurrence interval of strong earthquakes has been 2500～3500 a.
A NW-trending, 41km long, Holocene active fault belt has been discovered in Haicheng area, Liaoning province, based on airphoto interpretation and field investigation. The fault is located on the southeast side of the 1975 Haicheng Earthquake seismic zone, and appears as a linear negative landform consisting of a series of drainage divides of short gullies. The short gullies have systematically been offset left-laterally. By trenching and dating, the results show that the latest activities of the fault occurred in the period of 5,000～ 7,000 a.B.P. According to its geographical position, we suggest that this newly discovered fault can be named as the "Lamufanggou-Dafangshen Fault". The surface ruptures of the fault were scaled greater than that of the 1975 Haicheng earthquake. Besides, we have discovered two fault-scarplets cutting Holocene river terrace near Chagou Village. Each of the scarplets is 3.5～4.0 m in height, indicating that two paleo-events had occurred since 5,000 a.B.P. In general, at least 2～3 paleo-earthquakes had occurred in this region before the 1975 Haicheng earthquake; the average recurrence interval of strong earthquakes has been 2500～3500 a.
引文
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[5] 王挺梅等,海城地震地质构造背景和发震构造的填图,地质科学,No.3,1976。
[6] 赵文峰,海城地震背景与发震构造,地震研究,No.2,1981。
[7] 钟以章等,从海城地震裂缝特征探讨1975年海城7． 3级地震的发震构造,中国地震断层研究,乌鲁木齐:新疆人民出版社,1988。
[8] 任纪舜等,中国大地构造及其演化,北京:科学出版社,1983。
[9] 袁宗印,华北新生代沉积与断块构造,华北断块区的形成与发展,北京:科学出版社,1984。
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