Attenuation Characteristics of Near-Source Ground Motions from Temporary Observations of Small Earthquakes in Yunnan Province, China

The temporary strong-motion observation in Yunnan Province, southwestern China, has obtained a valuable batch of near-source recordings from many small earthquakes from 2008 to 2018. Based on the 546 well-processed strong-motion recordings with R = 4–35 km, which were obtained at 56 temporary strong-motion stations in 198 small earthquakes with ML=2.0–4.3 in Yunnan Province, we established ground-motion attenuation models for peak ground acceleration and peak spectral accelerations (PSAs) at periods of 0.1–2.0 s and investigated the attenuation characteristics of the near-source ground motions of small events. Our model includes the source term represented by the quadratic functional form of M, the magnitude-dependent geometrical spreading term, and the local site effects on the horizontal ground motions. The predicted medians by our model can well describe the distance attenuation of the near-source ground motion observed in the small events. The attenuation model in this study well represents the dependence of geometrical spreading on both the magnitude and the oscillator period that is the larger the magnitude and the longer the period, the weaker the geometrical spreading. Our model was compared with the Sun19 model for small aftershocks in the Jinggu, Yunnan Province earthquake sequence and the Zhang22 model for moderate-to-large earthquakes in western China. Our model shows the weaker attenuation rate with distance and the weaker source effects, compared with the Sun19 model. Similarly, there is the weaker geometrical spreading for PSAs at periods greater than 0.5 s in our model than in the Zhang22 model.