用INDEPTH资料研究青藏高原岩石层构造

根据INDEPTH宽频带数字地震资料，用接收函数方法与面波频散研究青藏高原的岩石层构造Ｍü〔ū浠挥牒铣傻卣鹜迹侗鸬卣鸺锹嫉腜-S转换波震相，构制P-S转换波剖面。捎枚嗟婪瘩藁际酰釉墩鹛宀úㄐ沃刑崛√ㄕ窘邮蘸２捎枚肷⑿〔ū浠欢越邮蘸鞑ㄐ畏囱荩岷厦娌ㄆ瞪⒎囱菅芯壳嗖馗咴沂乖斓暮嵯虮浠暗退俨惴植肌

Based on teleseismic P waveform data provided by INDEPTH, multi-channel deconvoution, wavelet transformation inversion, ray back-projection migration, wave equation modeling and imaging, and Kirchhoff migration are presented for receiver function study, more then 3000 receiver functions are recoverved from INDEPTH teleseismic waveform data, the crust and upper mantle velocity structure beneath the Tibetan is obatained, and also the migration and stacking profile of receiver function is also presented. Our study reveals several important pheonomena for the crust and upper mantle structure beneath the Tibet plateau. The velocity structure takes a gradient zone across the Bangong?Niujiang suture, there is a low-velicity-zone from upper to middle crust across both the Qiangtang and Lahsa terrens, a low-velocity-zone is also located beneath the topmost mantle of the Qiangtang terran. A strong P-to-S converted phase, dipping to the north, exists in the mid-to-lower crust beneath the Lahsa terren, in contrast, another P-to-S converted phase, dipping to the south, exists in the mid-to-lower crust beneath the Qiangtang terran. Above all, there is a north-dipping P-to-S converted phase in the upper mantle of the Lahsa terran, a strong "brightness spot" is also detected in the topmost mantle of Qiangtang terren. Both of the 410km and 660km upper mantle discontinuities obviously dip northward. We put forward a "double crustal subduction and lithospheric mantle delamination" model to explain the observed seismic pheonomena. We infer that the double-thickness crust of Tibetan plateau is caused by double subduction of Inidan and Eurasian crusts, and that Inidan lithospheric mantle is delaminated from its upper part beneath the Lahsa terren. The low upper mantle velocity may indicate the existence of sub-plume beneath the northern Tibet.