Seismological analyses of the 2010 March 11, Pichilemu, Chile Mw 7.0 and Mw 6.9 coastal intraplate earthquakes
Seismological analyses of the 2010 March 11, Pichilemu, Chile Mw 7.0 and Mw 6.9 coastal intraplate earthquakes
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2010年3月11日智利皮奇勒姆7.0级和6.9级沿海板内地震的地震学分析
DOI：
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发表时间：
2014
期刊：
影响因子：
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通讯作者：
D. Comte
中科院分区：
文献类型：
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作者：
J. Ruiz;G. Hayes;D. Carrizo;H. Kanamori;A. Socquet;D. Comte
2010年3月11日，智利中部发生了一系列大型浅层大陆地壳地震。两次正断层活动发生在皮奇勒木镇附近，震级分别为Mw7.0和Mw6.9，相隔仅15 min。这些类型的大型板内内陆地壳地震在智利俯冲带上方很少见，更好地了解它们与2010年2月27日马乌莱M_w 8.8地震的关系非常重要，该地震破坏了邻近的巨型逆冲断层板块边界。我们提出了一个广泛的地震学分析，这些地震都使用地震和区域数据。我们通过W-相位反演计算这两个事件的地震矩张量，并测试对各种反演参数的敏感性，以评估解决方案的稳定性。第一个事件发生在格林尼治时间14时39分，受到很好的约束，显示出一个走向为N145°E的断层面，倾向角为55°SW，与余震位置的趋势和其他已发表的结果一致。地震的Teleseophilic有限断层反演显示，沿断层南部沿着有一个大的滑动带，与所报告的余震空间密度有很好的相关性。第二次地震（格林尼治标准时间14时55分）似乎已经破裂了一个断层，该断层从前一次破裂的断层向南分支，位于第一次地震的上盘内。在区域到震中距离（Δ > 10°）处模拟地震图是相当具有挑战性的，因为两次地震的观测地震波场重叠，增加了第二次地震的明显复杂性。我们进行点源和扩展源反演在区域和非线性距离，评估模型的灵敏度，导致故障的方向，尺寸和震源位置的变化。结果表明，第二次地震的震源机制具有更陡的倾角和相对于前一次地震略顺时针旋转的走向。这种在大型正断层上盘具有次级破裂的地质断层配置在伸展地质体制中是常见的。我们认为，这两次地震形成了一个典型的正断层发散展布的一部分，次级断层连接到主断层的深度。为了确定这两个事件滑动的空间和时间细节的更多信息，我们收集了近断层地震和大地测量数据。通过对近断层合成地震图的正演模拟，我们建立了一个具有断层上空间分布滑动的k^（−2）震源运动学模型，该模型在一阶上解释了同震静态位移GPS矢量和最近站点的短周期地震仪观测。第一次地震的结果与地球物理模拟的震源机制一致，震级为M_w 6.97。类似地，第二次地震的近断层模型表明，破裂是沿沿着一个正断层发生的，M_w 6.90，其特征是倾角更陡（倾角= 74°），走向相对于前一次地震顺时针旋转（走向= 155°）。
On 2010 March 11, a sequence of large, shallow continental crust earthquakes shook central Chile. Two normal faulting events with magnitudes around M_w 7.0 and M_w 6.9 occurred just 15 min apart, located near the town of Pichilemu. These kinds of large intraplate, inland crustal earthquakes are rare above the Chilean subduction zone, and it is important to better understand their relationship with the 2010 February 27, M_w 8.8, Maule earthquake, which ruptured the adjacent megathrust plate boundary. We present a broad seismological analysis of these earthquakes by using both teleseismic and regional data. We compute seismic moment tensors for both events via a W-phase inversion, and test sensitivities to various inversion parameters in order to assess the stability of the solutions. The first event, at 14 hr 39 min GMT, is well constrained, displaying a fault plane with strike of N145°E, and a preferred dip angle of 55°SW, consistent with the trend of aftershock locations and other published results. Teleseismic finite-fault inversions for this event show a large slip zone along the southern part of the fault, correlating well with the reported spatial density of aftershocks. The second earthquake (14 hr 55 min GMT) appears to have ruptured a fault branching southward from the previous ruptured fault, within the hanging wall of the first event. Modelling seismograms at regional to teleseismic distances (Δ > 10°) is quite challenging because the observed seismic wave fields of both events overlap, increasing apparent complexity for the second earthquake. We perform both point- and extended-source inversions at regional and teleseismic distances, assessing model sensitivities resulting from variations in fault orientation, dimension, and hypocentre location. Results show that the focal mechanism for the second event features a steeper dip angle and a strike rotated slightly clockwise with respect to the previous event. This kind of geological fault configuration, with secondary rupture in the hanging wall of a large normal fault, is commonly observed in extensional geological regimes. We propose that both earthquakes form part of a typical normal fault diverging splay, where the secondary fault connects to the main fault at depth. To ascertain more information on the spatial and temporal details of slip for both events, we gathered near-fault seismological and geodetic data. Through forward modelling of near-fault synthetic seismograms we build a kinematic k^(−2) earthquake source model with spatially distributed slip on the fault that, to first-order, explains both coseismic static displacement GPS vectors and short-period seismometer observations at the closest sites. As expected, the results for the first event agree with the focal mechanism derived from teleseismic modelling, with a magnitude M_w 6.97. Similarly, near-fault modelling for the second event suggests rupture along a normal fault, M_w 6.90, characterized by a steeper dip angle (dip = 74°) and a strike clockwise rotated (strike = 155°) with respect to the previous event.
影响因子：
5.3
作者：
Lange, Dietrich;Tilmann, Frederik;Beck, Susan
通讯作者：
Beck, Susan