拉萨和羌塘地块地震活动和热前兆现象及其机理研究

Seismicity and Precursory Heat Anormaly in the Lasa and Qiangtang Blocks

青藏地块活动区南部的II级拉萨和羌塘地块内部的M≥6.5强震活动比北部的巴颜喀拉、柴达木和祁连II级地块内部明显活跃,这可能与拉萨和羌塘地块处于地壳厚度较大、较高的热状态和较低的正断层剪切强度等地学背景下,导致地壳强度较弱有关。拉萨和羌塘地块内部两次拉张性正断层活动的强震(2008年于田7.3级和当雄6.6级)前热异常的震例,可能与临震前孕震区及邻近断层带扩容,以及中下地壳低速层熔融物质或流体的进入有关。

There are relatively active strong seismicity inside the second-order Lasa and Qiangtang blocks compared with other blocks in the first-order Qing-Zang active block region, which might be related to the weaker crust strength due to thicker crust, higher heat and lower shear strength on normal fault there. Inside the second-order Lasa and Qiangtang active blocks, cases of abnormal heat phenomenon have been observed before two strong earthquakes（M7. 3 Yutian earthquake and M6. 6 Danxion earthquake in 2008） , which might be related to the dilatation in the faults of earthquake preparation region and nearby, where melting material and liquid enter into from the low velocity layer in uppermiddle crust.