Abstract
Abstract. It is well-established that the post-seismic slip results from the combined contribution of seismic and aseismic processes. However, the partitioning between these two modes of deformation remains unclear due to the difficulty of inferring detailed and robust descriptions of how both evolve in space and time. This is particularly true just after a mainshock when both processes are expected to be the strongest. Using state-of-the-art sub-daily processing of GNSS data, along with dense catalogs of aftershocks obtained from template-matching techniques, we unravel the spatiotemporal evolution of post-seismic slip and aftershocks over the first 12 h following the 2015 Mw 8.3 Illapel, Chile, earthquake. We show that the very early post-seismic activity occurs over two regions with distinct behaviors. To the north, post-seismic slip appears to be purely aseismic and precedes the occurrence of late aftershocks. To the south, aftershocks are the primary cause of the post-seismic slip. We suggest that this difference in behavior could be inferred only a few hours after the mainshock. We finish by showing that this information can potentially be obtained very rapidly after a large earthquake, which could prove to be useful in forecasting the long-term spatial pattern of aftershocks.
Highlights
One of the most perceptible expressions of the post-seismic activity following a large earthquake is the occurrence of aftershocks
Their temporal behavior is welldescribed by the Omori–Utsu law (Omori, 1894; Utsu et al, 1995), which states that the frequency of aftershocks decays as a power law with time after the mainshock
We only explore values that are plus or minus 15◦ from the rake angle of the mainshock given by the Global Centroid Moment Tensor (GCMT) catalog (i.e., 109◦)
Summary
One of the most perceptible expressions of the post-seismic activity following a large earthquake is the occurrence of aftershocks. Their temporal behavior is welldescribed by the Omori–Utsu law (Omori, 1894; Utsu et al, 1995), which states that the frequency of aftershocks decays as a power law with time after the mainshock. Miller (2020) proposes that the decay rate of aftershock sequences reflect the ability of the medium to heal co-seismic and post-seismic perturbations, influencing the circulation of fluids and the temporal evolution of aftershocks. The geometrical complexity of the fault zones has been proposed to explain the emergence of the Omori–Utsu law for aftershock sequences (Ozawa and Ando, 2021). It has been argued that power laws might not be suited to explain the temporal evolution of aftershocks with, for instance, Mignan (2015) suggesting that stretched exponential functions fit the observations better
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