Crustal lg attenuation within the North China Craton and its: Surrounding regions

We report on a broad-band high-resolution attenuation model for the North China Craton and surrounding regions based on regional Lg-wave data. Vertical broad-band waveforms recorded at 39 stations from 176 crustal earthquakes are collected to extract the Lg-wave amplitude spectra between 0.05 and 10.0Hz. We use the dual-station method to generate a preliminary Q_Lg model and use it as the initial model. Then, we combine the dual- and single-station data together to jointly invert the Q_Lg distribution and Lg source excitation functions. These inversions are conducted independently at individual frequencies without using any a priori assumption about the frequency dependences in Q_Lg and source terms. The maximum spatial resolution is approximately 1° × 1° in well-covered areas for frequencies between 0.05 and 2.0Hz. The Q_Lg image is then used to determine the relationship between the attenuation and different geological structures. Results show an average Q₀ (1Hz Q_Lg) of 374 for the entire North China Craton with an increasing trend from east to west. Average Q₀ values are 337, 361 and 421 for the east, central and west blocks, respectively. For the surrounding regions, the Eastern Tibetan plateau has a very low Q₀ of 188, while the Northeast China Plate and the Tianshan-Xingmeng fold belts are characterized by high Q₀ values of 506 and 424, respectively. We also investigate regional variations of the Lg attenuation in low-frequency band between 0.2 and 1.0Hz.