天山与阴山─燕山造山带的深部结构和地震

天山与阴山-燕山是中国北部两个重要山系，它们几乎位于同一纬度。天山造山带是一个著名的地震活动带，而阴山-燕山断隆带历史上不但没有大地震发生，小地震也不多见，是一个地震空白区。这两个造山带地震活动性的差异与它们在时、空域中的构造环境相联系：中国的西部处于强烈的挤压环境，而东部为一伸展与走滑环境。天山造山带是中、新生代造山带，目前构造活动水平较高；而阴山-燕山造山带新生代以来已经成为东北稳定块体的一部分，其构造活动的鼎盛期已经过去，目前构造活动水平较低。地震的孕育、发生与深部构造环境密切相关。天山地震带的地壳内部，发育壳内高导层与低速层，地壳结构复杂；阴山-燕山造山带下面没有发现壳内高导层与低速层，整个地壳结构比较简单。壳内低速层、高导层的存在表明地质构造活动强烈，是地震带的重要标志之一，也是地震孕育、发生的深部动力学条件。

CONTRAST RESEARCH ON TIANSHAN OROGENIC BELT AND YINSHAN -YANSHAN OROGENIC BELT

Located at almost the same latitude, the Tianshan and the Yinshan - Yanshan are two important orogenic belts in northern China. The Tianshan orogenic belt within Chinese territory is situated in the northwestern China. It is also well known as a seismic zone. While the Yinshan - Yanshan orogenic belt is situated in the northeastern China. Small earthquakes have occurred scarcely in this belt, and no big one has taken place in the history which make this region a seismic blank area. The authors' research work shows that the differences in seis-micity are related to the tectonic environments. A compression envirorimnt exists in the north-western China and an extension environment in the northeastern China. As a Mesozoic and Cenozoic orogenic belt, the Tianshan orogenic belt exhibits a high tectonic activity at the mo-ment, while as a Proterozoic orogenic belt, the Yinshan - Yanshan orogenic belt has already passed its peak period of tectonic activity and only processes a lower level of tectonic activity at present. The development and occurrence of earthquakes are closely related to the deep struc-tures. The crust of the Tianshan orogenic belt develops the high conductivity layers and the correspondent lower velocity zones which make the crust to be very comlicated. In the Yin-shan- Yanshan orogenic belt, however, no high conductivity layers and lower velocity zone have been found there, so the crust structure is very simple. The existence of the high conduc-tivity layers and the lower velocity zones indicates that the tectonic activity is strong, which may provide a favourable condition for the development and occurrence of earthquakes.