Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011
Comparison of postseismic afterslip models with aftershock seismicity for three subduction-zone earthquakes: Nias 2005, Maule 2010 and Tohoku 2011
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DOI：
10.1093/gji/ggu292
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发表时间：
2014-11
影响因子：
2.8
通讯作者：
D. Lange;J. Bedford;M. Moreno;F. Tilmann;J. Báez;M. Bevis;F. Krüger
中科院分区：
文献类型：
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作者：
D. Lange;J. Bedford;M. Moreno;F. Tilmann;J. Báez;M. Bevis;F. Krüger
我们关注2010年2月27日智利中部莫勒8.8级地震后地震与震后总余滑之间的关系。首先，我们计算了余震活动释放的累积滑移。我们通过总结根据比例关系估计的余震区和滑移来实现这一点。将累积地震滑移与余滑模型进行比较，结果表明，个别余震的地震滑移局部超过了大地约束下的倒转余滑模型。由于余滑模型隐含了来自余震的位移，这反映了余滑模型抹杀实际滑动模式的趋势。然而，它也表明，一些较大余震的局部滑动超过了无震滑动，尽管余震的总等效力矩比余震的累积力矩大得多。这种影响在2010年的毛勒地震和2011年的东北地震中看起来很弱，可以通过考虑地震活动和余滑模型的不确定性来解释。尽管存在不确定性，2005年尼亚斯地震的震中地区被建议释放一大部分力矩，几乎是纯粹的地震。因此，这些余震不是单纯由余滑驱动的，而是它们的滑移区可能受到了地震间载荷和主震破裂的应力作用。在第二步中，我们将2010年Maule断裂的巨型断裂划分为不同的单元，并计算每个单元中心50公里内发生的余震数量作为时间的函数。然后，我们将这个数字与随时间变化的余震模型进行比较，方法是将每个单元格的“余震与余震比”(ASAR)定义为时间t的余滑与余震计数作图时最佳拟合线的斜率。虽然我们发现大多数地震区的余滑和余震之间存在线性关系，但ASAR在巨型逆冲的下倾和沿走向方向上都有显著的变化。我们将ASAR的空间分布与地震耦合、同震滑动和布格重力异常的空间分布进行了比较，发现在每种情况下都没有显著的相关性。
We focus on the relation between seismic and total postseismic afterslip following the Maule Mw 8.8 earthquake on 2010 February 27 in central Chile. First, we calculate the cumulative slip released by aftershock seismicity. We do this by summing up the aftershock regions and slip estimated from scaling relations. Comparing the cumulative seismic slip with afterslip models we show that seismic slip of individual aftershocks exceeds locally the inverted afterslip model from geodetic constraints. As the afterslip model implicitly contains the displacements from the aftershocks, this reflects the tendency of afterslip models to smear out the actual slip pattern. However, it also suggests that locally slip for a number of the larger aftershocks exceeds the aseismic slip in spite of the fact that the total equivalent moment of the afterslip exceeds the cumulative moment of aftershocks by a large factor. This effect, seen weakly for the Maule 2010 and also for the Tohoku 2011 earthquake, can be explained by taking into account the uncertainties of the seismicity and afterslip models. In spite of uncertainties, the hypocentral region of the Nias 2005 earthquake is suggested to release a large fraction of moment almost purely seismically. Therefore, these aftershocks are not driven solely by the afterslip but instead their slip areas have probably been stressed by interseismic loading and the mainshock rupture. In a second step, we divide the megathrust of the Maule 2010 rupture into discrete cells and count the number of aftershocks that occur within 50 km of the centre of each cell as a function of time. We then compare this number to a time-dependent afterslip model by defining the ‘afterslip to aftershock ratio’ (ASAR) for each cell as the slope of the best fitting line when the afterslip at time t is plotted against aftershock count. Although we find a linear relation between afterslip and aftershocks for most cells, there is significant variability in ASAR in both the downdip and along-strike directions of the megathrust. We compare the spatial distribution of ASAR with the spatial distribution of seismic coupling, coseismic slip and Bouguer gravity anomaly, and in each case we find no significant correlation.