Constraints on upper plate deformation in the Nicaraguan subduction zone from earthquake relocation and directivity analysis
Constraints on upper plate deformation in the Nicaraguan subduction zone from earthquake relocation and directivity analysis
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地震重定位和方向性分析对尼加拉瓜俯冲带上板块变形的约束
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发表时间：
2010
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通讯作者：
Victor Gonzalez
中科院分区：
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作者：
S. W. French;Linda M. Warren;Karen M. Fischer;G. Abers;Wilfried Strauch;J. M. Protti;Victor Gonzalez
在中美洲俯冲带尼加拉瓜段，书架断裂被认为是响应科科斯板块斜向俯冲而发生的加勒比板块变形的主要样式。该模型的一个关键要素是弧形正走滑断层的左旋运动。2005年8月3日，在尼加拉瓜奥梅特佩岛附近发生了里氏6.3级地震及其广泛的前震和余震序列。为了确定在主震中破裂的断裂面，我们重新定位了主震、前震和余震震源，并利用图昌宽带地震实验的波形分析了主震源的方向性。对波形互相关法确定的P和S事件对的起震时间和差分走时，应用双差分方法进行重新定位分析。重新定位的震中定义了一个大致垂直的地震活动平面，走向为N60°E。该平面与主激震源机构的两个节面之一对齐。方向性分析是基于16个图赞台的波形进行的，结果表明，N60°E走向主震节面上的破裂与数据吻合最好。位移和方向性分析确定N60°E垂直节面为主震断层面，与书架模型所要求的断裂样式一致。在主震断裂面以南、走向为N350°E-N355°E的第二个断裂面，在主震后5h开始发生地震活动，说明主震断裂面所传递的应力的影响。2005年8月地震发生之前，附近的康塞普西翁火山于2005年7月28日小规模喷发。然而，当地的地震活动并不能为地震触发或通过地应力传递触发主震提供证据。
In the Nicaraguan segment of the Central American subduction zone, bookshelf faulting has been proposed as the dominant style of Caribbean plate deformation in response to oblique subduction of the Cocos plate. A key element of this model is left‐lateral motion on arc‐normal strike‐slip faults. On 3 August 2005, a Mw 6.3 earthquake and its extensive foreshock and aftershock sequence occurred near Ometepe Island in Lake Nicaragua. To determine the fault plane that ruptured in the main shock, we relocated main shock, foreshock, and aftershock hypocenters and analyzed main shock source directivity using waveforms from the TUCAN Broadband Seismic Experiment. The relocation analysis was carried out by applying the hypoDD double‐difference method to P and S onset times and differential traveltimes for event pairs determined by waveform cross correlation. The relocated hypocenters define a roughly vertical plane of seismicity with an N60°E strike. This plane aligns with one of the two nodal planes of the main shock source mechanism. The directivity analysis was based on waveforms from 16 TUCAN stations and indicates that rupture on the N60°E striking main shock nodal plane provides the best fit to the data. The relocation and directivity analyses identify the N60°E vertical nodal plane as the main shock fault plane, consistent with the style of faulting required by the bookshelf model. Relocated hypocenters also define a second fault plane that lies to the south of the main shock fault plane with a strike of N350°E–N355°E. This fault plane became seismically active 5 h after the main shock, suggesting the influence of stresses transferred from the main shock fault plane. The August 2005 earthquake sequence was preceded by a small eruption of a nearby volcano, Concepción, on 28 July 2005. However, the local seismicity does not provide evidence for earthquake triggering of the eruption or eruption triggering of the main shock through crustal stress transfer.