西北太平洋俯冲带多震相深部细结构成像与我国东北火山深层动力过程

The northwestern Pacific plate subduction has a significant impact on the geological structure in Northeastern Asia. It produced a series of tectonic systems including Japan islands, Japan sea, the Songliao basin, the great Xing'anling and Ji-Hei fold zones, accompanying many Quaternary volcanoes (i.e., the Changbaishan and Wudalianchi volcanoes) and deep earthquakes in Northeastern China. However, some scientific issues are still unclear, such as the frontal edges of the western Pacific subducting slab in the mantle transition zone, and the existence of the certain correlation between volcanoes and between volcano and deep earthquakes. This is because in the study region the Wudalianchi volcanic area has a sparse distribution of permanent seismic stations and was passed by a linear network of portable stations, which leads to be hard to delineate a clear seismic image under the region. Later seismic phases have different ray paths from first phase and can sample the deep structure not ordinarily sampled by first phase, which is of great significance to improve the spatial resolution of the model. Therefore, in this study we will make 2-D portable seismic observations around the Wudalianchi volcano to be complimentary to the insufficiency of existing observation data, develop multiple phase tomography technique, and conduct investigations of body-wave and surface tomography, seismic anisotropy, and receiver function analysis, trying to obtain the detailed structure down to the mantle transition zone beneath the northwestern Pacific subduction zone including the Japan Sea. This may reveal the deep dynamics of the volcano (including the Wudalianchi volcano) formation and deep earthquake generation beneath Northeastern China.

西北太平洋板块俯冲对东北亚地质构造产生重大影响，形成了日本岛弧、日本海、松辽盆地和大兴安岭及吉黑褶皱等构造体系，在我国东北还伴随有长白山火山和五大连池火山等第四纪活火山与深源地震活动。然而，西北太平洋俯冲板块在地幔转换带内的前缘位置、火山与火山、火山与深源地震之间是否存在有机关联性尚不清楚，可能由于研究区内五大连池火山区固定台站稀疏，而流动台网又以线性方式穿过，致使研究区清晰的深部结构图像难以刻划。后续震相有着与初至震相不同的射线路径，可采集到初至震相难以反映的深部结构信息，这对提高模型空间分辨率有着重要影响。本研究拟围绕五大连池火山开展二维流动地震观测，以补充已有观测资料的不足，发展多震相成像技术，开展体波成像、面波成像、各向异性和接收函数研究，获取西北太平洋俯冲带包括日本海下方深至地幔转换带的壳幔细结构与岩石圈变形特征，以揭示我国东北火山包括五大连池火山形成和深源地震发生的深层动力过程

受太平洋板块西向深俯冲影响，中国东北分布有很多第四纪活火山，但其深部起源及其之间关系并不十分清楚。为此，围绕五大连池火山开展了宽频带密集流动地震观测，开展了西北太平洋俯冲带特别是中国东北地区三维地幔成像、背景噪声成像、Lg衰减成像、SKS分裂分析、接收函数成像和Pn波成像以及青藏高原东缘与天山造山带等地区深部结构与动力学过程的对比研究。结果显示，五大连池火山下方5-15 km深度以浅为明显低波速异常，而其下地壳却存在明显高波速异常，据此提出五大连池火山具有“间歇性”地幔岩浆供给的新认识；五大连池火山及周边地区快波方向和分裂时间均存在着以火山为中心东南向开口的“U”形结构特征，可能与五大连池火山下方具有较强垂向上升流、而其南北两侧存在较强地幔水平流但受大兴安岭较厚岩石圈阻挡有关；在长白山、镜泊湖和五大连池火山及阿巴嘎和哈拉哈火山群下方Moho明显深于周边地区，特别是长白山火山下方Moho深达40 km，且接收函数随地震事件反方位角变化明显，暗示长白山火山下方地壳内存在复杂的岩浆作用。中国东北火山区上地幔顶部存在明显Pn波低速异常，且一些低速异常被高速异常所分隔，但被各向异性快播方向所连接，暗示在现今或历史构造演化过程中这些火山区可能存在关联性，提出东北火山存在物质与能量交换的动力学模型。全矩张量解显示，2013年松原震群以逆冲机制为主但伴随着明显体积压缩分量，而2018年震群则为走滑型。同时，地震主要发生在相对高波速异常区，但震源区下方却存在明显低波速异常，这些低波速异常可能代表了流体作用。这些结果表明，中国东北地区火山形成和地震发生均是与太平洋板块深俯冲至地幔转换带形成的“大地幔楔”结构中的动力学过程密切相关。在JGR、GJI、PEPI等期刊发表学术论文33篇。培养了多名研究生和1名博士后。学术交流40余人次。获得中国地震局防震减灾成果奖一等奖等学术奖励。

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