Fore‐arc deformation controls frequency‐size distribution of megathrust earthquakes in subduction zones
Fore‐arc deformation controls frequency‐size distribution of megathrust earthquakes in subduction zones
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弧前变形控制俯冲带巨型逆冲地震的频率-震级分布
DOI：
10.1029/2009jb006359
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发表时间：
2009
影响因子：
--
通讯作者：
O. Oncken
中科院分区：
文献类型：
--
作者：
M. Rosenau;O. Oncken
准周期性大逆冲地震时，俯冲带的地震构造变形似乎遵循相当简单的时空模式，弧前盆地位于大滑动区之上。为了研究长期变形与地震行为之间可能的耦合关系，我们使用压粒状楔块作为俯冲带前弧覆盖在发震大逆冲上的模拟模型，这些楔块覆盖在速率和状态相关的摩擦界面上。对于不同的孕震带几何形状，我们分析了相对于永久应变积累的变形时间序列和相当于大震的幕式滑动事件的频率大小分布。我们观察到，在几十个模拟地震周期中，楔形的永久变形集中在深度不稳定滑动的外围。对于上倾限制孕震带模型，这导致构造楔分割，其特征是弹性域覆盖在不稳定基底滑动带上。随着分割的演变，偶发性滑动事件的频率大小分布从更随机的、类似古腾堡-里希特的事件（b值~ 0.6）发展到更周期性的、特征性的事件（b值<0.1）。对应的递归区间变异系数（Cv）从变形楔形的Cv≈0.6降低到分段楔形的Cv≈0.3。因此，从实验中我们推断出弧前构造和大逆冲地震发生之间存在正反馈，从而使系统从随机状态变为更确定的状态。我们的实验观测表明，从现有的地震记录中可以明显看出，大俯冲地震的准周期性复发是一个与弧前楔的地震构造分割有内在关系的长期特征。
[1] Seismotectonic deformation in subduction zones seems to follow rather simple spatiotemporal patterns with fore-arc basins overlying the areas of large slip during quasiperiodic megathrust earthquakes. To study the possible coupling between long-term deformation and earthquake behavior, we use compressive granular wedges overlying a rate- and state-dependent frictional interface as analogue models of subduction zone fore arcs overlying a seismogenic megathrust. For different seismogenic zone geometries, we analyze deformation time series with respect to the accumulation of permanent strain and frequency-size distributions of episodic slip events equivalent to great (M > 8) earthquakes. We observe that permanent deformation in the wedges localizes at the periphery of unstable slip at depth over tens of simulated seismic cycles. For updip-limited seismogenic zone models, this leads to structural wedge segmentation characterized by an elastic domain overlying the zone of unstable basal slip. Along with the evolution of segmentation the frequency-size distributions of episodic slip events develop from more random, Gutenberg-Richter-like events (b value ∼0.6) toward more periodic, characteristic events (b value <0.1). Corresponding coefficients of variation (Cv) of recurrence intervals decrease from Cv ≈ 0.6 in deforming wedges to Cv ≈ 0.3 in segmented wedges. From the experiments we thus infer a positive feedback between fore-arc tectonics and megathrust seismogenesis which brings the system from a stochastic to a more deterministic state. Our experimental observations imply that the quasiperiodic recurrence of great subduction earthquakes evident from existing earthquake records is a long-term feature intrinsically related to the seismotectonic segmentation of the fore-arc wedges.