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Spatial and Temporal Variations in the Moment Tensor Solutions of the 2008 Wenchuan Earthquake Aftershocks and Their Tectonic Implications
Author(s) -
Lin X.,
Dreger D.,
Ge H.,
Xu P.,
Wu M.,
Chiang A.,
Zhao G.,
Yuan H.
Publication year - 2018
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1002/2017tc004764
Subject(s) - aftershock , geology , seismology , focal mechanism , tectonics , moment tensor , thrust fault , fault (geology) , thrust , slip (aerodynamics) , cauchy stress tensor , seismic moment , geodesy , moment (physics) , deformation (meteorology) , oceanography , physics , classical mechanics , thermodynamics
Following the mainshock of the 2008 M8 Wenchuan Earthquake, there were more than 300 M L ≥ 4.0 aftershocks that occurred between 12 May 2008 and 8 September 2010. We analyzed the broadband waveforms for these events and found 160 events with sufficient signal‐to‐noise levels to invert for seismic moment tensors. Considering the length of the activated fault and the distances to the recording stations, four velocity models were employed to account for variability in crustal structure. The moment tensor solutions show considerable variations with a mixture of mainly reverse and strike‐slip mechanisms and a small number of normal events and ambiguous events. We analyzed the spatial and temporal distribution of the aftershocks and their mechanism types to characterize the structure and the deformation occurring in the Longmen Shan fold and thrust belt. Our results suggest that the stress is very complex at the Longmen Shan fault zone. The moment tensors have both a spatial segmentation with two major categories of the moment tensor of thrust and strike slip; and a temporal pattern that the majority of the aftershocks gradually migrated to thrust‐type events. The variability of aftershock mechanisms is a strong indication of significant tectonic release and stress reorganization that activated numerous small faults in the system.