论文部分内容阅读
本文基于地震活动是现代地质构造运动之产物,以及对我国及邻区现代构造条件的认识,指出了构造类比中值得关注的7个问题,提出了发震构造识别方法的新建议,其主要结果如下:(1)发震构造宜定义为,“在现代构造条件下,曾发生或可能发生地震的地质构造”。(2)我国及邻区的现代地质构造同第四纪以来的新构造运动是一脉相承,密不可分的。其中,①现代构造应力场具有明显的区域特征,而且从中更新世以来是基本稳定的;②组成我国大陆不同新构造类型的活动地块(构造单元)之间,存在包括地壳和上地幔横向非均匀性的构造格架差异;③大陆内部各活动地块之间,也存在不同的现代构造形变特征;④宜将中更新世的构造形迹作为与地震活动有关的现代构造形迹看待。(3)在进行构造类比时值得关注的问题有:①宜按活动断裂当前所处的发育阶段来评价其潜在地震;②断裂活动时代并非识别发震构造的充分条件,只有符合现代构造条件的粘~滑断裂,才应识别为大地震的发震构造;③只有同现代构造应力场相适应的先存构造,才可能孕育和发生地震;④对于某些单一断层参数与震级关系的统计结果,未考虑各地震构造区之间现代构造条件和断裂发育阶段的差异,则难以用于构造类比;⑤凡有新生代玄武岩(β6)出露的地段,有可能只发生6.5级以下的地震;⑥地震同地表断裂形迹之间没有必然的联系,尤其仅有断层物质特性分析或测年结果可用时,宜慎重对待为妥;⑦构造类比方法仅适用于识别与先存构造继承性活动有关的发震构造,对于活动地块内部新生或隐伏的发震构造仍无能为力。(4)对于发震构造识别方法的建议是:①以新构造单元为基础划分地震构造区;②按历史重演原则识别曾发生过地震的构造,即凡有较可靠中强以上地震震中、有小地震成丛或呈带分布、或有可信古地震遗迹的地段,均宜识别出符合现代构造条件的发震构造;③根据地震构造区内曾发生过不同震级档地震的构造标志,再按类比原则推断可能的发震构造;④综合评定地震构造区的极限地震,并以此作为区内发震构造最大潜在地震的阀限。
Based on the fact that the seismic activity is a product of modern geological tectonic movement and the understanding of the conditions of modern tectonics in China and its neighboring areas, the paper points out seven problems that deserve attention in structural analogies and proposes new suggestions for seismogenic structures identification. The main results As follows: (1) Seismogenic structure should be defined as “the geological structure of an earthquake that has occurred or may occur under the conditions of modern tectonics”. (2) The modern geological structure in our country and its neighboring areas is inextricably linked with the neotectonic movement since Quaternary. Among them, ① the modern tectonic stress field has obvious regional characteristics and has been basically stable since the middle Pleistocene; ② between the active parcels (tectonic units) that constitute the new tectonic types in mainland China, there are horizontal crustal structures including crust and upper mantle Homogeneity; ③ There are also different characteristics of modern tectonic deformation between the various continents within the continent; ④ It is appropriate to regard the mid-Pleistocene tectonic trace as a modern structural trace related to seismic activity. (3) The issues worthy of attention in the construction of analogy are as follows: (1) The potential earthquakes should be evaluated according to the current development stage of the active fault; (2) the age of fault activity is not a sufficient condition for identifying seismogenic structures; (3) It is only possible to identify the seismogenic structure of a major earthquake as a viscous-slippery fault. ③ Only the preexisting structure adapted to the modern tectonic stress field can breed and generate an earthquake. ④For some single-layer fault statistics and magnitude relationships , It is hard to be used for tectonic analogy without considering the difference of the modern tectonic setting and fault development stage between the seismotectonic areas. (5) Where there is any exposed Cenozoic basalt (β6), it is probable that only an earthquake below 6.5 will occur; ⑥ There is no necessary relationship between earthquakes and surface rupture. Especially when only the characteristics of the fault material or the dating results are available, it should be treated with caution. ⑦ The construction analogy is only applicable to the identification of the inheritance of preexisting structures Seismogenic structures are still powerless to new or buried seismogenic structures within the active massif. (4) Suggestions for identifying seismogenic structures are: (1) dividing the seismic structure based on the new tectonic units; (2) recognizing the structure of the earthquakes occurred according to the principle of historical reenactment, that is, According to the tectonic markers of earthquakes with different magnitudes occurred in the seismic tectonic zone, the earthquakes that conform to the conditions of modern tectonics should be identified. According to the principle of analogy, the possible seismogenic structures can be deduced. (4) The limit earthquakes in the seismic tectonic area are comprehensively evaluated and used as the limit of the maximum potential earthquakes in the seismogenic structures in the area.