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首页> 外文期刊>Pure and Applied Geophysics >Gradual Fault Weakening with Seismic Slip: Inferences from the Seismic Sequences of L'Aquila, 2009, and Northridge, 1994
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Gradual Fault Weakening with Seismic Slip: Inferences from the Seismic Sequences of L'Aquila, 2009, and Northridge, 1994

机译：具有地震滑动的逐渐断层弱化：根据拉奎拉（L'Aquila），2009和诺斯里奇（1994）的地震序列推论

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We estimate seismological fracture energies from two subsets of events selected from the seismic sequences of L'Aquila (2009), and Northridge (1994): 57 and 16 selected events, respectively, including the main shocks. Following ABERCROMBIE and RICE (Geophys J Int 162: 406-424, 2005), we postulate that fracture energy (G) represents the post-failure integral of the dynamic weakening curve, which is described by the evolution of shear traction as a function of slip. Following a direct-wave approach, we compute mainshock-/aftershock-source spectral ratios, and analyze them using the approach proposed by MALAGNINI et al. (Pure Appl. Geophys., this issue, 2014) to infer corner frequencies and seismic moment. Our estimates of source parameters (including fracture energies) are based on best-fit gridsearches performed over empirical source spectral ratios. We quantify the source scaling of spectra from small and large earthquakes by using the MDAC formulation of WALTER and TAYLOR (A revised Magnitude and Distance Amplitude Correction (MDAC2) procedure for regional seismic discriminants, 2001). The source parameters presented in this paper must be considered as pointsource estimates representing averages calculated over specific ruptured portions of the fault area. In order to constrain the scaling of fracture energy with coseismic slip, we investigate two different slip-weakening functions to model the shear traction as a function of slip: (i) a power law, as suggested by ABERCROMBIE and RICE (Geophys J Int 162: 406-424, 2005), and (ii) an exponential decay. Our results show that the exponential decay of stress on the fault allows a good fit between measured and predicted fracture energies, both for the main events and for their aftershocks, regardless of the significant differences in the energy budgets between the large (main) and small earthquakes (aftershocks). Using the power-law slip-weakening function would lead us to a very different situation: in our two investigated sequences, if the aftershock scaling is extrapolated to events with large slips, a power law (a la Abercrombie and Rice) would predict unrealistically large stress drops for large, main earthquakes. We conclude that the exponential stress evolution law has the advantage of avoiding unrealistic stress drops and unbounded fracture energies at large slip values, while still describing the abrupt shear-stress degradation observed in high-velocity laboratory experiments (e.g., DI TORO et al., Fault lubrication during earthquakes, Nature 2011).
机译：我们从L'Aquila（2009）和Northridge（1994）的地震序列中选出的两个事件子集来估计地震破裂能：分别包括主要地震在内的57个和16个选定事件。遵循ABERCROMBIE和RICE（Geophys J Int 162：406-424，2005），我们假设断裂能（G）代表动态弱化曲线的破坏后积分，其通过剪切牵引力的演变来描述。滑。遵循直接波方法，我们计算主震源/余震源的频谱比，并使用MALAGNINI等人提出的方法对其进行分析。 （Pure Appl。Geophys。，此问题，2014年）推断角频率和地震矩。我们对震源参数（包括裂缝能量）的估算是基于对经验震源光谱比进行的最佳拟合网格搜索。我们使用WALTER和TAYLOR的MDAC公式（针对区域地震判别的修订的幅度和距离幅度校正（MDAC2）程序，2001）来量化小地震和大地震的谱源缩放比例。本文提出的震源参数必须视为点震源估算值，代表在断层区域特定破裂部分上计算出的平均值。为了用同震滑移来限制裂缝能量的缩放比例，我们研究了两种不同的滑移弱化函数，以将剪切力作为滑移的函数进行建模：（i）幂律，如ABERCROMBIE和RICE所建议（Geophys J Int 162 ：406-424，2005），和（ii）指数衰减。我们的结果表明，断层应力的指数衰减使得无论是主要事件还是余震，断裂能量的测量值和预测值都能很好地拟合，而不管大型（主要）和小型（主要）能源预算的显着差异如何。地震（余震）。使用幂律滑差减弱函数将导致我们遇到一种截然不同的情况：在我们研究的两个序列中，如果将余震标度外推到发生大滑差的事件，则幂律（la Abercrombie和Rice）将预测出不切实际的大大型主要地震的应力下降。我们得出的结论是，指数应力演化定律的优点是避免了在大滑移值下不切实际的应力降和无限制的断裂能，同时仍然描述了在高速实验室实验中观察到的突然的切应力降解（例如DI TORO等，地震期间的故障润滑，《自然》，2011年）。

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