The 1986 Kermadec earthquake and its relation to plate segmentation
The 1986 Kermadec earthquake and its relation to plate segmentation
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1986 年克马德克地震及其与板块分割的关系
DOI：
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
S. Schwartz
中科院分区：
文献类型：
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作者：
H. Houston;H. Anderson;S. Beck;Jiajun Zhang;S. Schwartz
为了评估1986年10月20日Kermadec地震（Mw=7.7）的构造意义，我们进行了全面的分析，使用面波，体波和重新定位的余震的震源参数。振幅和相位谱从多达93瑞利波反演质心时间，深度和矩张量在两步算法。在一些反演中，时间函数被参数化以包括来自体波时间函数的信息。由此产生的源参数是稳定的相对于变化的速度和衰减模型假设，参数化的时间函数，并设置瑞利波。由此导出的面波震源机制（θ =275°，δ=61°，λ=156°）是一种不容易用俯冲构造解释的挤压-挤压机制。获得的地震矩为4.5×1020 N·m，震源深度为45±5 km，震源时间为13±3 s。方向性不能从表面波中分辨出来。震源持续时间短与大地震多形成鲜明对比，我们对震源机制和时间函数进行了P波和SH波同时反演。震源机制与面波机制基本一致。多个病灶机制仍然是一种可能性，但无法解决。体波表明滑动持续时间较短（15 ~ 20 s），60 s后出现二次力矩释放。从体波源谱计算地震辐射能量。根据地震能量计算的应力降约为30巴。用联合震源测定法（JHD）重新定位了主震后3个月内发生的60次余震。大多数余震都有下冲震源机制，似乎代表了主冲断层界面上的触发滑动。深度，相对较高的应力降，滑动持续时间短，以及真正的余震的缺乏是一致的下行板块内的板内断层。虽然不清楚滑动发生在哪个节面上，但有几个因素有利于大致E-W走向的平面。该事件发生在下行板块深度的一个主要分段附近、海沟的一个弯曲附近以及火山区沿东西向沿着80 km的右侧偏移附近。此外，该地区从1977年到1991年的所有事件与CMT震源机制类似的主震发生在主震震中附近，而不是形成一个平行于沟槽的伸长区一样，余震活动。我们将这一事件解释为俯冲板块的分割或撕裂过程的一部分。这种分割似乎与路易斯维尔海岭的俯冲有关，路易斯维尔海岭可能通过其浮力成为俯冲的障碍。
To evaluate the tectonic significance of the October 20, 1986 Kermadec earthquake (Mw=7.7), we performed a comprehensive analysis of source parameters using surface waves, body waves, and relocated aftershocks. Amplitude and phase spectra from up to 93 Rayleigh waves were inverted for centroid time, depth, and moment tensor in a two-step algorithm. In some of the inversions, the time function was parameterized to include information from the body-wave time function. The resulting source parameters were stable with respect to variations in the velocity and attenuation models assumed, the parameterization of the time function, and the set of Rayleigh waves included. The surface wave focal mechanism derived (ϕ=275°, δ=61°, λ=156°) is an oblique-compressional mechanism that is not easy to interpret in terms of subduction tectonics. A seismic moment of 4.5×1020 N-m, a centroid depth of 45±5 km, and a centroid time of 13±3 s were obtained. Directivity was not resolvable from the surface waves. The short source duration is in significant contrast to many large earthquakes.We performed a simultaneous inversion ofP andSH body waves for focal mechanism and time function. The focal mechanism agreed roughly with the surface wave mechanism. Multiple focal mechanisms remain a possibility, but could not be resolved. The body waves indicate a short duration of slip (15 to 20 s), with secondary moment release 60s later. Seismically radiated energy was computed from the body-wave source spectrum. The stress drop computed from the seismic energy is about 30 bars. Sixty aftershocks that occurred within three months of the mainshock were relocated using the method of Joint Hypocentral Determination (JHD). Most of the aftershocks have underthrusting focal mechanisms and appear to represent triggered slip on the main thrust interface. The depth, relatively high stress drop, short duration of slip, and paucity of true aftershocks are consistent with intraplate faulting within the downgoing plate. Although it is not clear on which nodal plane slip occurred, several factors favor the roughly E-W trending plane. The event occurred near a major segmentation in the downgoing plate at depth, near a bend in the trench, and near a right-lateral offset of the volcanic are by 80 km along an E-W direction. Also, all events in the region from 1977 to 1991 with CMT focal mechanisms similar to that of the Mainshock occurred near the mainshock epicenter, rather than forming an elongate zone parallel to the trench as did the aftershock activity. We interpret this event as part of the process of segmentation or tearing of the subducting slab. This segmentation appears to be related to the subduction of the Louisville Ridge, which may act as an obstacle to subduction through its buoyancy.