Abstract

We present relocated seismicity and crustal tomographic images for the regions around the 2014 Ms 6.5 Ludian earthquake based on double‐difference tomography. The 2014 Ludian earthquake occurred in a complex fault system within the region bounded by the Chuandian Rhomb block and the Yangtze block. Most of the relocated aftershocks were found in the depth range between 3 and 15 km, distributed on two different faults that were nearly perpendicular to each other. This geometry suggests that the faulting of the mainshock is structurally complicated. Checkerboard resolution test confirms the reliability of tomographic images at depths ranging from 6 to 15 km because the velocity structure is not well resolved at depth shallower than 3 km. Our tomographic results are generally consistent with major tectonic features of the region. Velocity contrasts are identified across the major faults. Low compressional wave velocity (VP) anomaly in the source region of the Ludian earthquake is surrounded by higher VP zone, consistent with a weaker fault zone than the surrounding country rock. Most of the aftershocks occurred in the low VP and low Poisson’s ratio area, and are constrained by the faults ruptured by the mainshock. Poisson’s ratio manifests the significant crustal heterogeneity as compared to the body‐wave tomographic images. We interpret the anomalously low Poisson’s ratio zones as high quartz content rocks in the vicinity of the Ludian earthquake, whereas high VP anomalies in the surrounding areas indicate the dominance of granitic and metamorphic rocks. Based on the aftershocks’ distribution and the seismic structure, there are possible seismic gaps in the aftershock zones and are capable of causing seismic hazards in the future.

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