Open Geosciences (Oct 2024)
Vertical high-velocity structures and seismic activity in western Shandong Rise, China: Case study inspired by double-difference seismic tomography
Abstract
In this article, we collected the seismic phase arrival data (115°–120°E, 34°–39°N) of 2,833 local natural earthquakes above magnitude 1.0 recorded by 128 seismograph stations provided by the China Earthquake Networks Center covering the period from January 2008 to October 2023. We extracted the first arrival P- and S-wave arrival time data and obtained 26,351 P- and 26,349 S-wave absolute arrival times and 99,627 P-differential and 99,625 S-differential arrival times. Then, we determined 3-D P and S wave velocity structures under the Luxi region by using the double-difference tomography method. The results show lateral heterogeneities under the Luxi region, and the distribution of surface basins and uplift zones is associated with seismic velocities within the crust. The vertical section shows the widespread presence of vertical high-velocity bodies within the crust of the Luxi region, indicating seismological evidence of mantle upwelling in the region. Meanwhile, our imaging results also clearly indicate the presence of a significant low-velocity anomaly at depths of 13–17 km, which corresponds to the presence of a high-conductivity layer at that depth obtained from electromagnetic bathymetry. The transition zone between high and low velocities exists at a depth of 7–13 km, which plays an important role in the transfer of lithospheric stresses from the deep to the shallow part of the lithosphere. Combined with the results of the previous deep seismic wave velocity structure, petrology, and geological investigations, the deep dynamical background of the formation of slip tectonics and seismic mechanism in the Luxi area can be attributed to the go-slip activity of the Tan-Lu fault Zone, the subduction of the Pacific Plate, and the magmatism generated by mantle upwelling.
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