Spatial and Temporal Variations in the Moment Tensor Solutions of the 2008 Wenchuan Earthquake Aftershocks and Their Tectonic Implications

Abstract

Following the mainshock of the 2008 M8 Wenchuan Earthquake, there were more than 300 ML ≥ 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.

A Gravity Study of the Longmenshan Fault Zone: New Insights Into the Nature and Evolution of the Fault Zone and Extrusion‐Style Growth of the Tibetan Plateau Since 40 Ma

“…Earthquake focal depths here are constrained within the crust (transect L in Figures a and b). Whereas the M7.9 Wenchuan earthquake, located close to the intersection of the Fubianhe Fault (the bounding fault between the Danba and Songpan blocks) and the LFZ, showed a complex focal mechanism (e.g., Lin et al, ; Nakamura et al, ), the magnitude 6.7 Ya'an earthquake showed a dominant thrust component (Figure ).…”

Spatial and Temporal Stress Variations before and after the 2008 Wenchuan Mw 7.9 Earthquake and its Implications: A Study based on Borehole Stress Data

“…The WCEQ and its strong aftershocks were undoubtedly responsible for the disturbance and redistribution of the stress field and seismicity. Previous studies have attempted to determine the stress changes induced by the WCEQ through conducting in situ stress measurements (Wu Z et al, 2013;Meng et al, 2015a, b;Wang et al, 2015), or systematic analyses of seismic data, such as focal mechanism and shear wave splitting (e.g., Zhang et al, 2015;Gao et al, 2018;Lin et al, 2018;Yang et al, 2018). Furthermore, Coulomb stress changes have been simulated to demonstrate earthquake triggers in neighboring regions (Parsons et al, 2008;Toda et al, 2008;Luo and Liu, 2010;Liu M et al, 2014;Zhu, 2016).…”

Spatiotemporal Evolution of Earthquakes in Longmenshan Fault and Adjacent Area, before and after the 2008 Wenchuan Earthquake

“…Before the Wenchuan earthquake, studies on the Longmenshan fault mainly focused on the fault slip rates [2]. After the Wenchuan earthquake, studies on the Longmenshan fault mainly concentrated on the seismogenic process [3,4], stress state [5,6], coseismic surface rupture [7], kinematic characteristics [8][9][10][11], and deep tectonic environment [12][13][14][15] of the fault area. Liu et al [16] and Yin et al [17] analysed the spatiotemporal distribution of the early aftershocks following the Wenchuan earthquake.…”