An improved assessment of the geodetic/seismic deformation in the Southeastern Tibetan Plateau and its implications for regional seismic hazard

Abstract

To better understand the moment deficit and seismic coupling in the Southeastern Tibetan Plateau, we jointly analyzed the seismic catalogs and GNSS observations to improve the assessment of earthquake hazards in the area. This study involved an updated GNSS velocity field in a unified reference frame which is used to determine the strain field, and compiled several earthquake catalogs to estimate the Gutenberg-Richer parameter a-value and b-value, as well as the maximum earthquake magnitude in each seismic zone; in addition, the seismogenic thickness in the study region is also estimated. Through these products, we obtained the geodetic moment accumulation rate, seismic moment release rate, and the ratio between them. Our results show that the northern region - including the central-northern segment of the Xianshuihe fault, the Longmen Shan fault, and adjacent areas, and the southern region – including the Menglian fault, Nantinghe fault, and Lancangjiang fault, as well as neighboring regions, have higher seismic coupling indices (>0.8), indicating that these areas may represent fully coupled seismic source zones, the future earthquake hazard in these areas may be lower compared to areas with low seismic coupling. In contrast, in the southern portion of the Xianshuihe fault, the Anninhe-Zemuhe fault, the Daliangshan fault, the southern part of the Jinshajiang fault, as well as the middle-northern part of the Red River fault and nearby regions, the seismic coupling is notably low (<0.3), indicating significant seismic moment deficit and possibly considerable stress accumulation or long-term aseismic deformation in these areas. These areas have a moment deficit of 6.7–7.0 magnitude earthquakes or accumulating seismic moment energy equal to 0.4–1.0 missing earthquakes (M = 7). In addition, the XJF zone has deficit magnitudes ranging from 6.8 to 7.0 or 0.5–1.0 missing earthquakes (M = 7) during the longer catalog period. We classify these areas using a “red-yellow-gray” label system, designating areas with strong earthquake potential and high urgency as red, where future earthquake hazards should be noted. These findings are consistent with the earthquake hazard model, providing valuable insight into potential seismic activity. Taking into account the moment deficit and missing earthquakes estimated by the combination of the geodetic and seismology data, our approach can be applied to the seismic hazard assessment in the Tibetan Plateau or mainland China.