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A New Perspective on the Origin of Seismic and Tectonic Activity of the Sichuan Basin, Central China

Description: 

The Sichuan Basin, adjacent to the eastern margin of the Tibetan Plateau, has long intrigued geologists and seismologists due to its complex tectonic and seismic activity. While existing models, such as upper crustal thickening and low-to-middle crust channel flow, explain aspects of plateau growth and tectonic extrusion, they fail to fully account for the internal seismicity of the basin and the weak tectonic activity preceding major earthquakes like the 2008 Mw 7.9 Wenchuan event. To address these gaps, we present a novel framework for understanding the tectonic and seismic dynamics of the Sichuan Basin.

Integrating geological evidence, focal mechanism solutions, GPS measurements, and geomorphic analyses, we identify a counterclockwise rotation of the basin’s crystalline basement—initiated ~12 million years ago—driven by the lateral extrusion of the Chuan-Dian fragment at the southeastern margin of the Tibetan Plateau. This rotation is facilitated by interactions between two dominant fault systems: the left-lateral Xianshuihe fault, which accommodates southeastward motion, and the Longmenshan fault belt, responsible for oblique compression and thrusting. These processes lead to strain partitioning, reactivation of NE-SW transpressional faults, and decoupling of the sedimentary cover from the crystalline basement.

Earthquakes predominantly occur at depths of 8–25 km within the rigid basement, as demonstrated by events like the 2008 Wenchuan earthquake. This highlights the role of fault discontinuities and rotational dynamics in accommodating strain. Our findings enhance the understanding of the occurrence of right-lateral shearing during the Wenchuan earthquake and the high frequency of seismic events within the rigid Sichuan Basin block, thereby contributing to the development of improved seismic risk models and early warning systems for tectonically active regions worldwide.

Session: Unusual Earthquakes and Their Implications [Poster]

Type: Poster

Date: 4/16/2025

Presentation Time: 08:00 AM (local time)

Presenting Author: Zhe

Student Presenter: No

Invited Presentation: 

Poster Number: 17

Authors