Spatial and Temporal Variations in Earthquake Stress Drops between the 2008 Wenchuan and 2013 Lushan Earthquakes

Abstract

As a case study of spatial and temporal variations in earthquake stress drops between the 2008 Ms 8.0 Wenchuan and 2013 Ms 7.0 Lushan earthquakes, we computed 1828 stress-drop values for earthquakes with magnitudes 1.7 ≤ M L ≤ 5.0 during an eight-year time span before and after major earthquakes. We divide the study area into three subregions (the southern segment of the Longmen Shan fault zone; the southwestern junction of the Longmen Shan and Sichuan Basin; and the southwestern margin of the Sichuan Basin) and calculate individual event stress drops in each. The results show that regions of alternating high and low stress drop are found on either side of the southwestern segment of the Longmen Shan fault zone. During the two-year period after the 2008 Ms 8.0 Wenchuan earthquake, the stress state of the southern Longmen Shan fault shows no significant change. A marked increase in stress level appears about 18 months before the 2013 Ms 7.0 Lushan earthquake near the Lushan hypocenter zone. Two months after the Ms 7.0 event, the stress drops suddenly attenuate, with significantly less seismic energy release per event. We find that changes in the patterns of high and low stress drop values are consistent with the process of stress accumulation or transfer from the pre-mainshock to postmainshock periods. The results indicate that major earthquakes are the dominant cause of temporal and spatial evolution in stress levels. Stress drop variations show obvious temporal and spatial patterns that may suggests subtle changes in the character of stress fields on faults and spatial variations related to local intense compression and tectonic effects.

The Small and Moderate Earthquake Parameters Training Catalog on the Main Faults in Sichuan, China

“…Previous studies [66] show that changes in the patterns of high and low stress drop values are in line with the process of stress accumulation or transfer from the pre-mainshock to post-mainshock periods. Taking the LMS fault zone as a case study, we have re-evaluated the stress drop values of small and medium earthquakes occurring from 2013 to 2018 (Figure 9) and from 2019 to 2023 (Figure 10).…”

Unveiling Temporal Cyclicities in Seismic b-Values and Major Earthquake Events in Japan by Local Singularity Analysis and Wavelet Methods

“…This cyclic pattern is not only reflected in the majority of seismic events but is also prominent in major earthquakes. Several factors may contribute to this result: firstly, high-intensity earthquakes play a crucial role in crustal destruction and stress release [33,34]. Situated at the junction of multiple tectonic plates, the buildup and release of crustal stress through earthquakes are natural responses of Japan's geological structure.…”

Variation of Thermal Infrared Brightness Temperature Anomalies in the Madoi Earthquake and Associated Earthquakes in the Qinghai-Tibetan Plateau (China)

“…Considering the geodynamic evolution, the overall force status of the Qinghai-Tibetan Plateau varies across the area, roughly with 90 °E as the boundary. Due to the extrusion of the Indian subcontinent, the stress in the west of the 90 °E showed a tendency to continue with a northward movement, whereas in the east of the 90 °E the stress continued in an eastward direction (Chen, YT, et al, 1996;Hui et al, 2012;Wu et al, 2020), causing the eastern edge of the Qinghai-Tibetan Plateau to become the front end of power transmission. Consequently, tectonic activity is concentrated in this area.…”