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Structural Setting and Seismogenesis Mechanism of the 16th September 2021 Luxian Ms6.0 in the Southern Sichuan Basin, China

Description: 

The Ms6.0 earthquake occurred in Luxian, Sichuan Province, on September 16, 2021, breaking the largest magnitude ever recorded in the inner Sichuan Basin. The epicenter of the earthquake is located in a syncline of Huayingshan thrust-fold belt in southern Sichuan and southern Sichuan's important shale gas mining area. Using two high-resolution seismic reflection profiles passing through the epicenter of the Ms6.0 earthquake, combined with regional geological and drilling data, the geological structure model of the earthquake area is established. Based on the focal mechanism solutions of this earthquake and adjacent area, the analysis of the seismogenic structure and the seismogenic mechanism is carried out.

The results show that the structural styles are decoupled vertically. The gypsum layer of the Middle Cambrian Gaotai Formation and the Silurian shale are typical detachment layers. NE, NE, and NEE striking blind salt-related detachment anticlines and thrust faults are widely developed from the Cambrian gypsum layer to the Silurian shale, indicating the characteristics of multi-directional structural superposition. The buried depth, attitudes, and properties of this fault system in the north of Luxian are consistent with the coseismic fracture surface of shallow earthquakes, indicating that the Cambrian gypsum layer to the Silurian shale should be the main seismogenic layer in the sedimentary cover, and its blind structures strongly susceptible on the local stress field. The Luxian Ms6.0 epicenter is stuck in the triangle area where NE, NNE, and NEE striking faults converge, and its strike of coseismic rupture surface and the direction of principal stress is very different from that of regional faults and principal stresses. We suggest that under the conditions of regional stress slow loading and local stress disturbance, the Middle Cambrian gypsum layer and its complex blind fault system interacted with each other, forming local stress concentration, resulting in Ms6.0 seismic activity in the syncline region.

Session: Tectonics and Seismicity of Stable Continental Interiors [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Weikang Zhang

Student Presenter: Yes

Invited Presentation: 

Authors