3D geomechanical modeling of the Xianshuihe fault zone, SE Tibetan Plateau: Implications for seismic hazard assessment
Introduction
The Xianshuihe fault on the southeastern margin of the Tibetan Plateau is one of the most active intracontinental faults in the world (Fig. 1) (Allen et al., 1991). Geological and geodetic investigations show that this fault is a left-lateral strike-slip fault moving at a high rate of 10–20 mm/a (Allen et al., 1991; Bai et al., 2018; Bai et al., 2021; Gan et al., 2007; Shen et al., 2005), leading to frequent large earthquakes in this area. Since the year 1327, over 16 strong earthquakes of M > 6.5 have been recorded on different segments of the Xianshuihe fault (see Fig. 1), and 8 of these earthquakes reach a magnitude larger than 7.0 (Wen et al., 2008). The latest moderately strong earthquakes are the Kangding MS 6.3 and MS 5.8 earthquakes that occurred in 2014, and caused 5 deaths and a direct economic loss of approximately 700 million US dollars (Fang et al., 2015). However, some studies suggested that these two earthquakes did not fully release the energy accumulated in the focal area (Bai et al., 2018; Jiang et al., 2015), and a strong earthquake with a magnitude of MW 7.0 is still highly possible to strike the Kangding area (Bai et al., 2021).
In recent years, the great area of the Xianshuihe fault has witnessed an increasing number of key infrastructures being constructed, e.g., hydropower stations and the Sichuan-Tibet railway (Fig. 1), accompanied by a growing population. The increased human activities and properties greatly enhanced the demand for seismic hazard assessment for the Xianshuihe fault and its neighboring area. Seismic hazard of a region is often assessed based on knowledge of kinematics and stress state of dominating faults. Fault slip rates are commonly used to investigate the seismic activities of faults and to calculate the recurrence time of potentially damaging earthquakes; the distribution characteristics of stress along a fault plane can be used to directly outline high-stress zones, and provide useful information on the potential hypocenter area of future large earthquakes. Past studies have mainly focused on using fault slip rate (Bai et al., 2018; Bai et al., 2021; Chen et al., 2016; Chevalier et al., 2016) or stress state (Papadimitriou et al., 2004; Parsons et al., 2008; Shan et al., 2013; Toda et al., 2008) to assess the seismic hazard. For example, by using offset geomorphic features near Kangding with 10Be age date, Bai et al. (2021) obtained a Quaternary horizontal slip rate of 8–13.4 mm/a on the southeastern segment of the Xianshuihe fault and suggested that a high seismic hazard with an MW 7.0 earthquake exists on that segment, especially near the Kangding city. Papadimitriou et al. (2004) and Shan et al. (2013) calculated the changes of Coulomb Failure Stress (∆CFS) on the Xianshuihe fault caused by historical earthquakes and suggested that in general, the southeastern segment of the Xianshuihe fault has a high seismic hazard due to the positive ∆CFS.
However, using only kinematic or ∆CFS analysis may fail to give a reliable assessment of a fault's seismic hazard. For example, before the 2008 Wenchuan MS 8.0 earthquake, the Longmen Shan fault zone was assigned to have a moderate-to-low seismic hazard due to its low slip rate of 1–2 mm/a (Zhang et al., 1999). ∆CFS can only identify faults moving toward or away from failure, and using it solely to evaluate the potential of future earthquakes is known to have great uncertainty as the absolute level of crustal stress is generally unavailable (Toda et al., 2008). An important lesson learned from the Wenchuan MS 8.0 earthquake is that enhancing seismic hazard evaluation requires multi-source information about a fault from comprehensive observations (Zhang, 2013). However, so far the seismic hazard assessment for the Xianshuihe area has been conducted mostly based on a single information source, such as fault slip rate (Bai et al., 2018; Bai et al., 2021), ∆CFS (e.g., Shan et al., 2013), or historical seismic activity (Wen et al., 2008). Little attention has been paid to combining these information sources to give a comprehensive seismic hazard assessment. In addition, the sparse pointwise information on the fault slip rates (Bai et al., 2018; Bai et al., 2021; Chen et al., 2016) and stress measurements (Hu et al., 2017) distributed on the Xianshuihe fault also limits the reasonable seismic hazard assessment.
To improve the seismic hazard assessment, spatially continuous kinematics and stress information of the Xianshuihe fault is required. Fortunately, numerical modeling is such a powerful tool that can obtain the kinematics and stress of large regions simultaneously. In our previous study (Li et al., 2021, Li et al., 2022), a large-scale 3D geomechanical model that covers the eastern Tibetan Plateau was established. Based on the first-order features of these simulations, we have identified that the southeastern segment of the Xianshuihe fault has a stress environment that can generate large earthquakes. However, the geometry of the Xianshuihe fault implemented in the model was simplified as one almost vertical surface, and other secondary faults in/near the fault zone were ignored due to its low resolution. To test the inference of the seismic hazard on the southeastern segment of the Xianshuihe fault, a refined model that specifically focuses on the Xianshuihe fault and its adjacent area is needed. The detailed fault data of the SE Tibetan Plateau recently publicized by the China Seismic Experimental Site (CSES) (Lu, 2019) provide a solid foundation for such refined modeling.
In this paper, we construct a more detailed three-dimensional (3D) geomechanical model including the latest geometric data of the fault system, inhomogeneous rock properties, tectonic forces, and gravity for the Xianshuihe fault and its adjacent area. A higher resolution spatially continuous kinematics and stress state of the study area is obtained and calibrated by comparison with model-independent data. Finally, based on the calibrated model results, we synthetically analyze the seismic hazard in the study area. The geological background and model setup of the study area is presented in Section 2. The modeled results and discussion of the seismic hazard potential in the study area are given in 3 Results, 4 Discussion, respectively. The conclusions are drawn in Section 5.
Section snippets
Geological background and model setup
The study area is located on the southeastern margin of the Tibetan Plateau, where active faults are extensively developed (Fig. 1). As the most important fault in the study area, the Xianshuihe fault plays a key role in understanding the tectonic evolution of the SE Tibetan Plateau. This mainly NW-SE-trending fault has a total length of about 350 km with a clockwise rotation of about 25° in the strike from northwest to southeast (Bai et al., 2021) (Fig. 1). Deep seismic sounding results show
Crustal horizontal velocities and fault slip rates
As mentioned in Section 2.4, in the beginning, the faults in the upper crust are set to be locked with an infinite effective friction coefficient. After a good fit between the modeled velocities and GPS measurements is achieved, the faults are changed to be unlocked with a low effective coefficient of friction, then the same boundary conditions as in Fig. 5 are imposed to finally obtain the long-term kinematics and stress evolution. We then compare the modeled results with model-independent
Discussion
From Bamei to Kangding, the Xianshuihe fault is divided into three branch faults, namely the Yalahe fault, the Selaha fault (the main active branch), and the Zheduotang fault (Fig. 9a). In our previous study (Li et al., 2021, Li et al., 2022), the first-order modeled results showed that the normal fault stress regime exists in the entire area between Bamei and Kangding, which is attributed to the clockwise rotation of the Xianshuihe fault. In this study, we constructed a smaller but more
Conclusions
In this study, we have established a refined 3D geomechanical model of the Xianshuihe fault and its adjacent area by using more detailed geological and geodetic data. The model considers the complexity of updated 3D fault geometry and provides a spatially continuous contemporary kinematics and crustal background stress field for the study area.
For the kinematic results, the modeled slip rate on the Xianshuihe fault is as high as 11 mm/a in the northwest segment and decreases southeastward to
Author-statement
Xianrui Li: Conceptualization, Investigation, Formal analysis, Writing - original draft Ke Gao: Funding acquisition, Project administration, Writing - review & editing Yu Feng: Writing - review & editing Chongyuan Zhang: Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work is supported by the Open Foundation of the United Laboratory of Numerical Earthquake Forecasting (Grant NO. 2020LNEF05), the China Postdoctoral Science Foundation (2021M691408) and the National Natural Science Foundation of China (NO. 41941018). We would like to thank editor Ramon Carbonell for managing the whole review process. We also thank three anonymous reviewers for their comments that helped us to improve the manuscript. Some figures were plotted using GMT (Wessel and Smith,
References (77)
- et al.
Linear elastic fracture mechanics explains the past and present evolution of the Aegean
Earth Planet. Sci. Lett.
(2004) - et al.
Southeastward increase of the late Quaternary slip-rate of the Xianshuihe fault, eastern Tibet. Geodynamic and seismic hazard implications
Earth Planet. Sci. Lett.
(2018) - et al.
Tectonic-geomorphology of the Litang fault system, SE Tibetan Plateau, and implication for regional seismic hazard
Tectonophysics
(2016) - et al.
The World Stress Map database release 2016: crustal stress pattern across scales
Tectonophysics
(2018) - et al.
Crustal stress pattern in China and its adjacent areas
J. Asian Earth Sci.
(2017) - et al.
Locking depth, slip rate, and seismicity distribution along the Daofu–Kangding segment of the Xianshuihe fault system, eastern Tibetan Plateau
J. Asian Earth Sci.
(2020) - et al.
Subsurface structure and spatial segmentation of the Longmen Shan fault zone at the eastern margin of Tibetan Plateau: evidence from focal mechanism solutions and stress field inversion
Tectonophysics
(2019) - et al.
Contemporary kinematics in the eastern Tibetan Plateau: insights from 3D geomechanical modeling
Tectonophysics
(2021) - et al.
Contemporary background stress field in the eastern Tibetan Plateau: insights from 3D geomechanical modeling
Tectonophysics
(2022) - et al.
Paleoseismic events and recurrence interval along the Beichuan–Yingxiu fault of Longmenshan fault zone, Yingxiu, Sichuan, China
Tectonophysics
(2013)
Coulomb stress evolution along Xianshuihe–Xiaojiang Fault System since 1713 and its interaction with Wenchuan earthquake, May 12, 2008
Earth Planet. Sci. Lett.
A theory for in situ stresses in isotropic and transversely isotropic rock
Int. J. Rock Mech. Min. Sci. Geomech. Abstr.
Historical pattern and behavior of earthquake ruptures along the eastern boundary of the Sichuan-Yunnan faulted-block, southwestern China
Phys. Earth Planet. Inter.
Holocene activity and paleoseismicity of the Selaha Fault, southeastern segment of the strike-slip Xianshuihe Fault Zone, Tibetan Plateau
Tectonophysics
3D crustal stress state of Western Central Europe according to a data-calibrated geomechanical model
Solid Earth
Field study of a highly active fault zone: the Xianshuihe fault of southwestern China
Geol. Soc. Am. Bull.
Spatial slip rate distribution along the SE Xianshuihe fault, eastern Tibet, and earthquake hazard assessment
Tectonics
Empirical relations between elastic wavespeeds and density in the earth’s crust
Bull. Seismol. Soc. Am.
Improved correlation between the static and dynamic elastic modulus of different types of rocks
Mater. Struct.
Late quaternary slip-rates and slip partitioning on the southeastern Xianshuihe Fault system, Eastern Tibetan Plateau
Acta Geol. Sin.
Multisegment rupture hazard modeling along the Xianshuihe Fault Zone, Southeastern Tibetan Plateau
Seismol. Res. Lett.
Basic characteristics of active tectonics of China
Sci. China Earth Sci.
The geological tectonic foundation of Minya Gongkar and its characteristic glacial landforms
J. Chengdu Univ. Sci. Technol.
Preliminary Report on the 22 November 2014 Mw6.1/Ms6.3 Kangding Earthquake, Western Sichuan, China
Seismol. Res. Lett.
Improving earthquake rupture forecasts using California as a guide
Seismol. Res. Lett.
Long-term time-dependent probabilities for the third Uniform California Earthquake Rupture Forecast (UCERF3)
Bull. Seismol. Soc. Am.
Present-day crustal motion within the Tibetan Plateau inferred from GPS measurements
J. Geophys. Res.
Late Quaternary Paleoseismology and Faulting Behavior of the Internal and Western Boundary Faults of Northwest Sichuan Subblock
Discussion on the recent active feature of the Fubianhe fault
Sichuan Earthquake
Lower friction of the Xianshuihe-Xiaojiang fault system and its effect on active deformation around the south-eastern Tibetan margin
Terra Nova
Numerical Modelling of the Absolute Stress State in the Marmara Region - A Contribution to Seismic Hazard Assessment
Geomechanical model of the Marmara Sea region—II. 3-D contemporary background stress field
Geophys. J. Int.
Stress field sensitivity analysis in a sedimentary sequence of the Alpine foreland, northern Switzerland
Solid Earth
Holocene activity on Yunongxi fault and Liuba M6.2 earthquake in Kangding, Sichuan
Earthquake Res. China
Long-term elasticity in the continental lithosphere; modelling the Aden Ridge propagation and the Anatolian extrusion process
Geophys. J. Int.
Numerical modeling of correlation between slip rate and fault geometry on the southeastern segment of the Xianshuihe fault zone
Earthquake Res. Sichuan
Geodetic imaging of potential seismogenic asperities on the Xianshuihe-Anninghe-Zemuhe fault system, southwest China, with a new 3-D viscoelastic interseismic coupling model
J. Geophys. Res.
Applying 3D inversion of single-profile magnetotelluric data to identify the Shade and Yunongxi faults
Seismol. Geol.
Cited by (10)
Contemporary crustal kinematics in the Guangdong-Hong Kong-Macao Greater Bay Area, SE China: Implications for the geothermal resource exploration
2024, Journal of Asian Earth SciencesAsymmetric Bilateral Rupture of the 2022 Ms 6.8 Luding Earthquake on a Continental Transform Fault, Tibetan Border, China
2023, Seismological Research LettersRapid estimation of disaster losses for the M6.8 Luding earthquake on September 5, 2022
2023, Science China Earth SciencesStudy on the Applicability of Various In-situ Stress Inversion Methods and Their Application on Sinistral Strike-Slip Faults
2023, Rock Mechanics and Rock Engineering