Seismic Tomography

Utilizing over 31 000 Lg waveforms from 136 crustal earthquakes recorded at 346 regional stations, we conduct detailed tomographic mappings of the Lg Q structure across Eastern Asia in a frequency range from 0.5 to 4.0 Hz. By improving the standard two-station (TS) method, we ef fecti vel y correct non-unity site response ratios using site responses estimated at individual stations. This innovative approach combines the flexible recording geometry of the TS method with the precision of reversed two-station (RTS) and reversed two-event (RTE) methods, producing a comprehensive data set devoid of source and site effects for Q tomography. To address unsolvable 3-D structural effects in the Lg spectral amplitude modelling, we justify these as modelling errors with a Gaussian distribution. This approach supports our SVD-based tomographic method, allowing for effective inversion of attenuation parameters and quantitative assessment of model resolution and errors. Our results reveal a complex relationship between Lg Q and the tectonic characteristics of Eastern Asia. In wellresolv ed re gions, low Qo (1-Hz Q) values correspond to areas with high heat flow, partial melt, thick sediment and recent tectonic-thermal activities, in contrast to high Qo values in stable, ancient crusts lacking recent tectonic activity. Rift basins are characterized by low Lg Qo , whereas flexural basins generally have high Qo basements. We also note that postformation factors, such as sedimentation and crustal flow intrusion, significantly impact Qo values. Fur ther more, Lg Q shows a complex frequency relationship, though the po wer-la w approximation with positive power η remains useful. The frequency dependence power η is inversely related to Qo : the regions with low Q o typically have high η and vice versa. This study provides reliable attenuation tomographic and relative site response models for Lg waves in Eastern Asia, pertinent for relative geophysical studies.