Abstract: The crystalline basement velocity structure of Changbaishan Tianchi volcanic area is established by using Three-Dimensional Finite-Difference method and Pg data from four wide-angle reflection/refraction profiles and one three-dimensional array which was deployed in Changbaishan Mountain area. This paper presents the characteristics of the velocity structure of crystalline basement and the interface with 5.9～6.0km/s P-wave velocity in the crystalline basement. Inversion results reveal that the velocity of surface layer in the southern part is higher than that in the northern part of the studied area. In general, the depth of crystalline basement of the studied area is within the range of 2.0～3.0km, with the deepest of about 4.0km and the shallowest of about 1 5km near Songjiang. There are two low velocity areas in this region, one is beneath the Protection Station of Tianchi volcano, and the other is located beneath Erdaobaihe and Chixi Protection Station. In these two areas the depths of crystalline basement are about 4.0km. We found that the intense lateral variation of velocity and depth of crystalline basement in the seismic profile coincides well with the location of fault. Therefore, it is suggested that the intense lateral variation of velocity and the abrupt change of the depths of crystalline basement can be taken as an indication of the occurrence of fault.

Key words: Changbaishan Tianchi volcanic area, velocity structure, crystalline basement, Finite Difference Method

摘要： 利用在长白山天池火山区布设的4条深地震测深剖面和1个三维地震透射台阵的Pg波资料,用有限差分方法反演了该地区的基底速度结构。对该地区的基底速度结构特征及P波速度5.9～6.0km/s所对应的结晶基底的界面形态、深度等进行了讨论。反演结果表明,长白山天池火山区基底深度变化不大,一般为2.0～3.0km,最深处位于天池火山口下和二道白河-池西之间;最浅处位于松江附近,约为1.5km。同时发现天池火山口下及二道白河-池西保护站之间是两处低速区,结晶基底深度为4.0km,其中二道白河-池西保护站之间的低速区对应于地质构造上的地堑构造。提出基底速度横向变化剧烈和基底深度突变的特征可以作为断层存在的一种标志。

关键词: 长白天池火山区, 结晶基底速度结构, 基底深度, 有限差分层析成像