Lithosphere Anisotropy of Prydz Bay, Antarctica: From Ocean Bottom Seismometer Long Term Observation
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摘要: 为了研究南极普里兹湾岩石圈深部应力场及其动力学,采用S波分裂旋转相关法,对中国第31次南极科学考察成功回收的3个站位海底地震仪数据(5个远震记录)进行了反演,获得了普里兹湾洋陆过渡带岩石圈各向异性特征.结果表明,台站所在区域各向异性显著,在较小的范围内存在明显的空间差异,快S波偏振方向变化范围是N40°E ~ N60°E,快慢波时间延迟变化范围为0.2~1.3 s.洋盆的各向异性主要取决于海底扩张地幔流作用,大陆及附近的各向异性主要受上地幔顶部残留构造的影响,而中间过渡带各向异性层厚度较小集中在地壳内,它可能受海底扩张地幔流和残留构造共同作用.Abstract: In order to understand better the stress field and dynamics characteristic of the lithosphere at Prydz bay in the Antarctica, rotation-correlation shear wave splitting method is used to study 5 earthquakes recorded by three ocean bottom seismometers recovered at Prydz bay during the 31th Chinese Antarctic Research Expedition to obtain the anisotropy characteristics of the continent and ocean transition of Prydz bay in this paper. Our inversion results show strong anisotropy in the lithosphere of Prydz bay with spatial differences in small scale. The fast shear wave polarization directions are from N40°E to N60°E, fast and slow shear wave times delay are from 0.2 s to 1.3 s. We think that the anisotropy at the oceanic part is dominated by the mantle flow of mid-ocean ridge spreading, while the continental part is dominated by the relic structural fabric of the ancient lithosphere at the top of the upper mantle, and the middle zone with shallower and thinner anisotropy layer may be influenced by the both reasons above.
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Key words:
- Prydz bay /
- anisotropy /
- shear wave splitting /
- ocean bottom seismometer /
- marine geology
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图 1 (a)研究区在全球的位置和地震震中分布,(b)OBS站位分布
SEIR的扩张方向为NE-SW向(Baran et al., 2005)
Fig. 1. (a) The location of study area and the positions of earthquake hypocenters, (b) positions of OBSs for long term earthquake observation
图 3 OBS1站位事件2的S波分裂反演结果及分析
a.旋转相关计算前的快慢波波形;b.旋转相关计算后的快慢波波形;c.旋转相关计算前的质点运动轨迹;d.旋转相关计算后的质点运动轨迹;e.反演结果,横轴δt为时间延迟,纵轴φ为偏振方向,两个极值点分别代表快波(δt>0) 和慢波(δt<0) 的结果,极值点对应的纵轴值分别为快波和慢波的偏振方向,横轴值分别为快慢波的时间延迟.如e图中快慢波的时间延迟为0.9 s,快波方向为N42°E,慢波方向为N138°E
Fig. 3. S wave splitting inversion results and analysis for earthquake No. 2 recorded by OBS1
图 4 OBS1站位事件3的S波分裂反演结果及分析
相关说明同图 3;e图中的快慢波时间延迟为0.8 s,快S波偏振方向为N40°E
Fig. 4. S wave splitting inversion results and analysis for earthquake No. 3 recorded by OBS1
图 5 OBS2站位事件2的S波分裂反演结果及分析
相关说明同图 3;e图中的快慢波时间延迟为0.4 s,快S波偏振方向为N44°E
Fig. 5. S wave splitting inversion results and analysis for earthquake No. 2 recorded by OBS2
图 6 OBS5站位事件2的S波分裂反演结果及分析
相关说明同图 3;e图中的快慢波时间延迟为0.2 s,快S波偏振方向为N56°E
Fig. 6. S wave splitting inversion results and analysis for earthquake No. 2 recorded by OBS5
图 7 普里兹湾区域S波分裂反演得到的快波方向和时间延迟
陆地台站的信息来源于Reading and Heintz(2008)
Fig. 7. S wave splitting inversion results of fast wave polarization directions and the times delay between fast and slow waves at Prydz bay
表 1 地震事件与S波分裂反演结果
Table 1. Earthquake events and S wave splitting inversion results
地震事件编号 发震时间
(格林威治时间)纬度(°) 经度(°) 震源深度(km) 地震震级(Ms) OBS1 OBS2 OBS5 d1 φ1 t1 d2 φ2 t2 d5 φ5 t5 1 2013-04-06
T04:42:35.860Z-3.517 138.476 66.0 7.0 77.314 - - 77.200 44 0.2 77.795 52 0.5 2 2013-05-23
T17:19:04.750Z-23.009 -177.232 173.7 7.4 76.884 42 0.9 76.683 44 0.4 76.046 56 0.2 3 2013-06-05
T04:47:26.240Z-11.401 166.299 39.0 6.1 81.023 40 0.8 80.989 - - 80.840 - - 4 2013-06-16
T02:51:35.750Z-56.280 -27.443 91.2 5.5 44.287 40 1.3 43.947 - - 42.998 - - 5 2013-07-15
T14:03:39.880Z-60.857 -25.070 11.0 7.3 39.879 - - 39.521 - - 38.522 60 0.8 注:d1,d2,d5分别代表OBS1,OBS2和OBS5对某一地震事件的震中距,单位为°;φ1,φ2,φ5分别代表OBS1,OBS2和OBS5对某一地震事件的快波方位角,单位为°;t1,t2,t5分别代表OBS1,OBS2和OBS5对某一地震事件的快慢波时间延迟,单位为s;“-”为未记录或未得到结果. -
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