Abstract
Although the Zhaotong–Ludian fault is a seismically active zone located in the boundary between the Sichuan–Yunnan block and the South China block, it has not experienced a large earthquake greater than Mw 7 since at least 1700. On 3 August, 2014, an Mw 6.1 earthquake (the Ludian earthquake) ruptured the Zhaotong active belt in Ludian County, Yunnan province, China. This earthquake was the largest earthquake recorded in the region since 2000, and it provides us with a unique opportunity to study the active tectonics in the region. The analysis of the aftershocks showed that two conjugate faults could have been involved in the event. We first used Global Positioning System (GPS) data and C-band RADARSAT-2 imagery to map the coseismic surface deformation. We then inverted the derived coseismic deformation for the slip distribution based on the constructed conjugate fault model. Finally, the coulomb failure stress due to the Ludian earthquake was estimated to investigate the potential seismic hazards in this region. Our investigations showed that the Ludian earthquake was mainly a bilateral rupture event. The major slip of the main shock was located at depths of 0–5 km, which is close but does not superpose with the aftershocks that are mostly located at depths of 5–20 km. Interestingly, the seismic moment released by the aftershocks (6.9 × 1018 N∙m) was greater than that of the main shock (2.6 × 1018 N∙m). This evidence suggests that the accumulated elastic strain at depths of 0–20 km could have been fully released by the Ludian earthquake and its subsequent aftershocks. Furthermore, our analysis of the coulomb failure stress changes due to the main shock showed that the aftershocks could be the result of dynamic triggering rather than static triggering.
Highlights
The northeastern Yunnan rift zone is a seismically active region, located along the western boundary of the Sichuan–Yunnan Block and the eastern margin of the Qinghai–Tibet Plateau
These findings suggest that the elastic strain accumulated in the interseismic cycle in the seismogenic region could have been fully released by the main shock and the subsequent aftershocks
The earthquake showed a complex deformation pattern, and a conjugate fault was deemed to be responsible for its occurrence
Summary
The northeastern Yunnan rift zone is a seismically active region, located along the western boundary of the Sichuan–Yunnan Block and the eastern margin of the Qinghai–Tibet Plateau. The Zhaotong–Ludian fault is located in the southeastern margin of the Qinghai–Tibet Plateau (Figure 1) This fault is a dextral strike-slip fault [2] and is a part of the boundary zone between Sichuan and Yunnan provinces. The GPS velocity field shows that the regional deformation is significant and is mainly dominated by NW-oriented tectonic stress (Figure 1) [2,3,4]. Centroid Moment Tensor (GCMT) Project all revealed a left-lateral strike-slip faulting mechanism (Table 1, Figure 1). This is to be expected, considering the dominant extensional tectonic setting. Ludian earthquake, because it is a thrust and right-lateral strike-slip fault.
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