滇西南地区地壳速度结构的区域波形反演

Crustal velocity structure under southwestern Yunnan from regional waveform inversion

利用中国地震局地壳应力研究所于2010~2011年在滇西南地区布设的宽频带流动地震台所记录的三分量高质量波形资料,采用小生境遗传算法通过波形反演,获得了研究区P波速度模型.结果显示,滇西南地区地壳厚度为38~43 km,上地幔顶部平均速度为7.9 km/s,地壳速度存在明显的横向不均匀性.思茅地块的上地壳和下地壳厚度均呈现出明显的由南向北、自东向西增厚趋势,说明该地块地壳增厚由上地壳和下地壳共同增厚形成.腾冲地块中地壳和下地壳的平均厚度及速度均小于保山地块和思茅地块,思茅地块部分路径上的下地壳和上地幔速度均较低,可能与印度板块东向俯冲引起地幔热物质上涌等动力过程密切相关.这些结果对于认识青藏高原形成与演化动力过程提供重要地震学约束.

High-quality three-component waveform data were recorded at portable broadband seismic stations deployed in southwestern Yunnan by the Institute of Crustal Dynamics, China Earthquake Administration during 2010 and 2011. These data were used to obtain a regional P-wave velocity model through waveform inversion using the Niching Genetic algorithm. The results show a crustal thickness of about 38–43 km and an average upper mantle velocity of 7.9 km/s, suggesting strong lateral heterogeneities in the crustal velocity. In the Simao block, both the upper and lower crust show a clear trend of thickening from south to north and from east to west. This implies that the crustal thickening is caused by simultaneous thickening of the upper and lower crust. The average thickness and velocity beneath the Tengchong block are lower than those under the Baoshan and Simao blocks. The velocities are lower in both the lower crust and uppermost mantle along some paths in the Simao block. This phenomenon is closely related to the upwelling of hot material caused by the eastward subduction of the Indian plate. These results provide important seismic constraints that will improve our understanding of the formation and evolutional processes of the Tibetan Plateau.