ABSTRACT

We use the eikonal equation‐based seismic travel‐time tomography method to image the source areas of the 2008 Wenchuan earthquake and the 2013 Lushan earthquake in the Longmenshan fault zone. High‐resolution VP and VS models are obtained by inverting 75,686 P‐wave and 74,552 S‐wave travel times of local earthquakes during the period from 2009 to 2018. The tomographic models reveal strong crustal velocity heterogeneities in the study area. A significant velocity contrast exists across the Longmenshan fault zone: The western Songpan–Ganzi block is a high‐velocity body, whereas the eastern Sichuan basin is a low‐velocity anomaly. The hypocenter of the 2008 Wenchuan earthquake is between a high‐velocity and a low‐velocity anomaly. Beneath the Wenchuan mainshock, there is a significant low‐velocity structure in the lower crust. The 2013 Lushan earthquake occurred in rocks associated with a high‐velocity anomaly. A distinct low‐velocity zone with low seismicity is imaged between the 2008 Wenchuan earthquake and the 2013 Lushan earthquake, where the crustal ductile deformation is likely to occur. The Baoxing complex to the northwest of the Lushan hypocenter exhibits as a high‐velocity anomaly, which may be a carrier of stress accumulation and more prone to seismic activities in the future.

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