Seismic structure and b-value in the focal area of the 8th January 2022 Menyuan, Qinghai M-S 6. 9 earthquake

On 8th January 2022, the M-S 6. 9 earthquake occurred in Menyuan County, Qinghai Province, China. Basing on the tomographic results of the NE Tibetan Plateau with a horizontal resolution of 0.3 degrees, we present tomographic images of the middle-upper crust around the focal area, including seismic velocity (V-P and V-S) and Poisson's ratio (sigma), and estimate structures of crack density (epsilon) and saturation rate (xi) using the obtained V-P, V-S and sigma values. Our results reveal that the Menyuan M-S 6. 9 earthquake is located close to the edge parts of the high velocity zones where V-P and V-S change abruptly, as well as the patterns of sigma and xi indicating. Distributions of seismic parameters (a, b, a/b) of the Lenglongling fault zones around the focal area share similar characters to those along the Longmenshan-Minshan fault zones with low-b, low-a and high-a/b values before the strong earthquakes. Crack density (epsilon) on the north of the Lenglongling fault is much higher than that on the south in the shallow crust, which may cause larger surface ruptures on the north of the Lenglongling fault by field survey after the earthquakes.