长白山天池火山岩浆系统分析

针对外媒报道长白山天池火山在近2年内有可能喷发的言论,在长白山天池火山区布测了一条长度约为103 km的二维大地电磁测深观测剖面,对火山区深部电性结构进行探测研究.由于研究区内不明来源的电磁干扰非常强,对数据采用了远参考处理、Robust处理、Rhoplus分析、张量阻抗分解和基于一维层状介质电阻率与相位互算方法等先进处理技术,获取到一批在强干扰区质量较为可靠的电磁数据,利用数据计算分析了长白山天池火山区二维构造走向和感应矢量特征,采用NLCG二维反演技术对资料进行了二维反演解释,并将反演结果与前人探测结果进行了对比分析.探测结果表明:在天池火山口下方存在明显的直立型岩浆通道,岩浆通道在下方约5~8 km位置形成关闭;在火山口下方往北方向附近,在埋深位置约7 km深处存在一个明显的低阻异常体,电阻率小于10 Ωm,且与岩浆通道对接,推测其可能是地表浅部发育的岩浆囊;在长白山山门附近C07-C09号测点之间和C04-C05号测点之间,在埋深约7~17 km深处发现近直立型低阻带,低阻带与下方低阻体直接相连,推测低阻带内赋存有活动的岩浆;随着埋深的增加,从天池火山口南部约20 km位置往北方向,在埋深13~30 km之间壳内广泛发育明显的低阻异常体,推测其可能是活动的岩浆囊.反演结果与前人探测结果整体电性特征相似,但又局部不同.

Analysis of magma chamber at the Tianchi volcano area in Changbai mountain

According to South Korean media's comments that the Tianchi volcano in Changbai Mountain is likely to erupt in coming 2 years, we carried out an MT sounding observation profile about 103 km long at Tianchi volcano area for detecting the deep electrical structures. Since the electromagnetic interference from unknown sources is very strong in the research area, we used a number of advanced data processing techniques including remote reference, Robust processing, Rhoplus analysis, impedance tensor decomposition, and a mutual approximate calculation method between apparent resistivity and phase, finally obtained high-quality and more reliable electromagnetic data in the strong interference areas. Then we analysed the two dimensional structural trend and characteristics of induction vector at Tianchi volcano area in Changbai Mountain, using NLCG inversion technique to interpret the inversion data, then compared the inversion results with previous exploration results. The results show that there is an obvious magma channel at the bottom of Tianchi volcano, the magma channel is closed in depth about 5~8 km. At the bottom of the crater, near the north direction about 7 km deep exists an obvious low resistance body, the resistivity is less than 10Ωm, connected with the magma channel. It is inferred that it may be the developing magma chamber in shallow surface. The abnormal region is between stations C07-C09 near the entrance gate of Changbai mountain and between C04-C05 station, there are two obvious nearly vertical low resistivity zones existing in the depth of about 7~17 km, connecting with below low resistance body directly, it is inferred that the low resistivity zone contains the magma. As the depth increases, the crust low resistivity anomaly bodies are widely developed in the depth of 13km to 30km, north to the position of 20 km south from Tianchi volcano, which may be the active magma chamber. Comparing the inversion results with the previous exploration results, the electrical characteristics are overall similar, but locally different.