Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile
Asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of Antofagasta, Chile
复制标题
智利安托法加斯塔地区b值和等静压残余异常网格揭示的凹凸体产生上地壳源
DOI：
10.1029/2006jb004796
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发表时间：
2007
影响因子：
--
通讯作者：
C. Krawczyk
中科院分区：
文献类型：
--
作者：
M. Sobiesiak;U. Meyer;S. Schmidt;H. Götze;C. Krawczyk
研究表明，1995年智利北部安托法加斯塔M(w) = 8.0地震断层上最大同震滑动（陡坡）的位置可以通过大逆冲地震余震序列的地震b值的空间分布来映射。这些高地震矩释放区和同时出现的高b值与Antofagasta地区重力均衡残差（IR）场异常是一致的。它们叠加在智利北部俯冲带的发震部分，预计上下板块的耦合最强。红外异常解释为侏罗纪-早白垩世大型岩基侵入上地壳所致。观测到的高地震b值、红外异常和地质构造之间的正相关关系使我们能够提出Antofagasta地区凹凸不平形成的力学模型。我们认为，岩基与作用在纳斯卡板块俯冲板块上的浮力共同作用，锁定了岩石所在的界面。这暗示了生糙体构造状况存在的长期条件。因此，安托法加斯塔周围的凹凸不平可能是静止的特征，至少在几个地震周期内是这样。因此，我们认为沿智利北部辐合边缘的红外异常可以作为未来大地震高矩释放和滑动的指示。
In our study we show that the locations of largest coseismic slip (asperities) on the fault plane of the M(w) = 8.0 1995 Antofagasta earthquake in Northern Chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake. These areas of high seismic moment release and concurrent high-b values are congruent with anomalies of the gravity isostatic residual (IR) field in the Antofagasta region. They are superimposed on the seismogenic part of the north Chilean subduction zone where the strongest coupling of the upper and lower plate is expected. The IR anomalies are interpreted to be caused by large Jurassic-Early Cretaceous batholiths which intruded into the upper crust. The observed positive correlations between high seismic b values, IR anomalies, and geologic structures enable us to propose a mechanical model for the generation of the asperities in the Antofagasta region. We suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the Nazca plate are responsible for locking the interface where the asperities are located. This implies long-term conditions for the existence of the asperity generating tectonic situation. Concequently, the asperities around Antofagasta could be stationary features, at least for several seismic cycles. Hence we propose that the IR anomalies along the north Chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes.