Probabilistic multi-segment rupture seismic hazard along the Xiaojiang fault zone, southeastern Tibetan Plateau

Abstract

• Multi-segment rates depend on the historical seismicity and segment parameters. • Historical seismicity rates, fault slip rates, and fault segmentation model determine the multi-segment rupturing rates for each fault segment. • Modeled seismicity rates show multi-segment rupturing earthquakes easily occur around the middle section of the Xiaojiang fault. The Xiaojiang fault is an active boundary fault on the southeastern Tibetan Plateau. Historical earthquake records indicate that the Xiaojiang fault has been struck by at least four multi-segment rupturing events. Why and where the Xiaojiang fault is prone to multi-segment earthquakes need to be well studied. To investigate the multi-segment seismic hazard of the Xiaojiang fault, we divide the Xiaojiang fault, the nearby Qujiang fault, and Jianshui fault, into 34 fault segments according to the new geological mapping results. We build four possible multi-segment rupture combination models, and then analyze the geological studies to select appropriate fault slip rates. We use the selected fault slip rates and the Magnitude-Frequency relationship to model the future seismicity rates for these rupture combinations. We find that the multi-segment rupture combination model developed from the historical rupture events that did not rupture through the step-over with a 12-km-width and the adjoining segments with strike difference ≥28°, showing the effectiveness of consuming the strain accumulation on the fault in our calculation. Finally, we calculate the Peak Ground Acceleration (PGA) values from the compatible multi-segment rupture combination model. Our results show that the PGA value is relatively lower around the middle section of the Xiaojiang fault, which agrees with the multi-segment rupturing tendency from historical seismicity and paleo-earthquakes studies. The high probabilities of the multi-segment rupturing for the Xiaojiang fault are determined by the fault segment distribution based on the new geological mapping results.