青藏高原昆仑—汶川地震系列与巴颜喀喇断块的最新活动

青藏高原是中国最主要的地震活动区之一。最近十多年来,在青藏高原中部连续发生了1997年西藏玛尼Ms7.5级地震、2001年青海昆仑山Ms8.1级地震、2008年3月新疆于田Ms7.3级地震和5月四川汶川Ms8.0级地震及2010年青海玉树Ms7.1级地震,它们相继发生于青藏断块区巴颜喀喇断块四周边界活动断裂带上,是该断块最新活动的结果。发生于断块南北边界断裂上的3次地震都是走滑断裂错动的结果,发生在断块东南端的汶川地震则是挤压逆冲断裂的产物,而西北端的于田地震则呈现出张性特征,它们共同反映青藏断块区巴颜喀喇条状断块向东南方向滑动的最新活动。自1900年以来,青藏断块区和巴颜喀喇断块的强震活动表现出多期活动和区域性转移的特征,20世纪早期Ms7.0级以上强地震活动的主体地区在青藏断块区北部边界构造带,中期转移到高原南部喜马拉雅板块边界构造带和断块区南部断块,最近十多年来则在巴颜喀喇断块及周缘边界断裂上活动。青藏高原这种块体活动和地震活动与澳大利亚-印度板块对亚洲大陆的推挤作用相关,因而,青藏高原和巴颜喀喇断块的强震活动与澳-印板块边界苏门答腊强震活动相对应。目前苏门答腊地区强震活动仍在继续,因此,近期对巴颜喀喇断块及青藏高原南部地区的强震活动和强震危险性仍需加以注意。

Recent tectonic activity of Bayankala fault-block and the Kunlun-Wenchuan earthquake series of the Tibetan Plateau

The Tibetan Plateau is a major region of earthquake activity in China.Five major earthquakes occurred in the Tibetan Plateau during the last decade.They are the 1997 Mani earthquake of magnitude Ms 7.5 in Xizang,the 2001 Kunlun Mountains earthquake of magnitude Ms 8.1 in Qinghai,the 2008 Yutian earthquake of magnitude Ms 7.3 in Xingjiang,the 2008 Wenchuan earthquake of magnitude Ms 8.0 in Sichuan,and the 2010 Yushu earthquake of magnitude Ms 7.1 in Qinghai.All of them occurred around the boundaries of the Bayankala fault-block of the Tibetan fault-block region and represented most recent activity of the block.Earthquakes occurred on the northern and southern boundaries of the block are strike-slip faulting events.The Wenchuan earthquake on its eastern boundary is a reverse faulting event.The Yutian earthquake on the western boundary is a normal faulting event.The kinematics of these events suggest the southeastward movement of the Bayankala fault-block.Major regional seismicity in the Tibetan fault-block region and the Bayankala fault-block has shown the multi-period activities and migration from one region to another since 1900.Most of strong earthquakes occurred along the northern boundary of the Tibetan fault-block region in the early period of the last century,took place mostly along the southern boundary of the region in the middle period of the last century,and were located around the Bayankala fault-block during the last decade.This pattern of seismic activity and fault-block motions in the Tibetan fault-block region and the Bayankala fault-block may relate to the compression and penetration of the Australia-Indian plate into the Eurasian plate.Thus,the earthquake activity in the Tibetan Plateau and in the Bayankala fault-block may also relate to strong earthquake activity in Sumatra along the boundary of the Australia-Indian plate.Because great earthquakes are still occurring in the Sumatra region,great attention should be paid to the great earthquake risks in the Bayankala fault-block and the southern part of the Tibetan Plateau.