Stress distribution and geometry of the subducting Nazca plate in northern Chile using teleseismically recorded earthquakes
Stress distribution and geometry of the subducting Nazca plate in northern Chile using teleseismically recorded earthquakes
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使用远震记录的地震研究智利北部俯冲纳斯卡板块的应力分布和几何形状
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发表时间：
1995
期刊：
影响因子：
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通讯作者：
G. Suárez
中科院分区：
文献类型：
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作者：
D. Comte;G. Suárez
摘要
使用从 15 次地震 (mb± 5.5) 和 1962 年至 1993 年间发生的 212 个有报告的震源机制事件的长周期 P、SV 和 SH 波形反演获得的震源机制解，分析了沿智利北部俯冲纳斯卡板块的应力分布。进行了联合震源测定，以控制在远震距离记录的 261 个事件 (mb± 5.0) 的深度。沿俯冲板片上部从拉应力场到压应力场的变化与耦合区的最大深度范围相关。这种变化发生在智利北部距海沟±200-250公里处，深度±60.10公里处。该深度大于逆冲板间事件观测到的最大深度（40 ± 10 km），这可能意味着，在 40 至 60 km 的深度，大的低倾角逆冲事件不会成核。然而，地震滑移可能延伸至 40 公里深度。瓦达蒂-贝尼奥夫带的浅倾角（深度达 60 公里）并未显示出沿海沟走向的变化。然而，在距离海沟超过 200-250 公里处观察到板块逐渐向南变平。这种变化是在南纬 21° 左右观察到的，可能与比在该纬度以北观察到的岩石圈更年轻、可能更有浮力有关。三个主要地震活动群之间有两个间隙；这些差距显然与下降的岩石圈中的分离无关。第一个簇位于发震板间接触面的内部和下方，其特征是稀有的张力活动上的逆断层和逆冲断层事件。在第二组中，远震事件中压缩地震活动很少，并且位于正常断层事件下方。第三组对应于紧张事件。因此，这些地震活动间隙可能与俯冲板片中从压缩应力场到张应力场的交替变化有关。
SUMMARY
The stress distribution along the subducting Nazca plate in northern Chile is analysed using focal mechanism solutions obtained from the inversion of long-period P, SV, and SH waveforms of 15 earthquakes (mb± 5.5), and from 212 events with reported focal mechanisms, which occurred between 1962 and 1993. A joint hypocentral determination was carried out to control the depth of 261 events (mb± 5.0) recorded at teleseismic distances. A change from tensional to compressional stress field along the upper part of the subducting slab is associated with the maximum depth extent of the coupled zone. This change occurs in northern Chile at ±200-250 km from the trench, at depths of ±60.10 km. This depth is larger than the maximum depth observed for the thrusting interplate events (40 ± 10 km), probably meaning that, at depths of between 40 and 60 km, large low-dip angle thrust events do not nucleate. Seismic slip, however, probably extends down to 40 km in depth. The shallow dip angle (up to 60 km in depth) of the Wadati-Benioff zone does not show variations along the strike of the trench. However, a gradual southward flattening of the slab is observed at distances greater than 200–250 km from the trench. This change, observed from about 21°S, could be associated with a younger and probably more buoyant lithosphere than that observed to the north of this latitude. There are two gaps located between the three main clusters of seismicity; these gaps are clearly not related to detachments in the descending litosphere. The first cluster is located in and beneath the seismogenic interplate contact, and is characterized by reverse and thrust faulting events over a scarce tensional activity. In the second cluster, the compressional seismicity is scarce for teleseismic events and is located beneath the normal faulting events. The third cluster corresponds to tensional events. Therefore, these gaps in seismicity could be associated with alternating changes from compressional to tensional stress field in the subducting slab.