17:15 〜 18:45
[SSS06-P04] Study on stress characteristics in the vicinity of Lushan M5.8 earthquake in 2022
キーワード：Focal Mechanism Solution, Strong Aftershocks, Stress of Aftershock area
On June 1, 2022, a M5.8 earthquake occurred in Lushan County, Sichuan Province, China, with a focal depth of 12km. The epicenter was located in the southern section of the Longmenshan fault zone, about 9.7km from the Lushan M 6.6 earthquake on April 20, 2013, at its northwest end. The source mechanism solutions obtained by using different velocity models show that the earthquake is a thrust rupture event with a NE trend, which is basically consistent with the trend of Shuangshi-Dachuan fault in seismic research. According to the USGS, the focal mechanism solution of the Lushan M 6.6 earthquake is a NE thrust rupture, and it is clear that the focal mechanism solution of the two earthquakes is very similar. After the fine location of the aftershock of the M5.8 Lushan earthquake, the results show that the main earthquake is located in the southernmost part of the sequence, and the NW profile results show that the depth is deeper in the southeast end and gradually shallower to the northwest. Its distribution is basically consistent with the distribution of the early aftershocks of the 6.6 Lushan M earthquake, so it is considered that the earthquake was a strong earthquake that occurred in the aftershock region of the 6.6 Lushan M earthquake.
We have made statistics on the occurrence of strong earthquakes in the aftershock area of M7 or above in Sichuan and Yunnan, and found that the occurrence of strong earthquakes in the aftershock area after many years is rare. Preliminary analysis shows that this phenomenon may be related to the change of its stress state. Therefore, based on the initial motion and amplitude ratio of P-wave, the focal mechanism of small and medium-sized earthquakes in the aftershock region after the 2013 Lushan M6.6 earthquake is solved, and the regional stress field is solved on this basis. The calculation results show that the distribution of stress field in the region before the 2022 Lushan M5.8 earthquake has a good correspondence with the fault where the aftershock is located. The M6.6 earthquake in 2013 was a thrust type rupture, but the stress state near the fault where it was located was mainly strike-slip after the main earthquake occurred, while the fault on the north side was a thrust. In 2022, a M5.8 earthquake occurred on the thrust fault. This result may indicate that the stress state near the fault in the aftershock region of a large earthquake may change with the occurrence of a small earthquake, and we should focus on the fault where the stress state continues to maintain the thrust, in this case, a strong aftershock occurred near the fault.
We have made statistics on the occurrence of strong earthquakes in the aftershock area of M7 or above in Sichuan and Yunnan, and found that the occurrence of strong earthquakes in the aftershock area after many years is rare. Preliminary analysis shows that this phenomenon may be related to the change of its stress state. Therefore, based on the initial motion and amplitude ratio of P-wave, the focal mechanism of small and medium-sized earthquakes in the aftershock region after the 2013 Lushan M6.6 earthquake is solved, and the regional stress field is solved on this basis. The calculation results show that the distribution of stress field in the region before the 2022 Lushan M5.8 earthquake has a good correspondence with the fault where the aftershock is located. The M6.6 earthquake in 2013 was a thrust type rupture, but the stress state near the fault where it was located was mainly strike-slip after the main earthquake occurred, while the fault on the north side was a thrust. In 2022, a M5.8 earthquake occurred on the thrust fault. This result may indicate that the stress state near the fault in the aftershock region of a large earthquake may change with the occurrence of a small earthquake, and we should focus on the fault where the stress state continues to maintain the thrust, in this case, a strong aftershock occurred near the fault.