This electronic supplement includes 1) the earthquake hazard map of the region, 2) more details of the models for calculating changes of stress, and 3) elastic block models for calculating seismic moments.
We used the three-dimensional visco-elasto-plastic finite element model of Luo and Liu (2010) to calculate coseismic and postseismic Coulomb stress changes shown in Figure 2. The finite element mesh and boundary conditions are shown in Figure S2.
Earthquakes are simulated as the result of strain softening when rocks in the fault zone are loaded to their yield stress (Jaeger et al., 2007; Yin and Zhang, 1982). To avoid the influence of arbitrary initial conditions (zero initial stress), we loaded the model domain to a quasi-steady state to produce a background stress field. The predicted background stress is validated by its consistency with the regional stress field indicated by earthquake focal mechanisms.To model historic earthquakes, we used their moment releases, estimated from their magnitudes, to constrain coseismic slip.
The method and model used for balancing moment on the regional faults are given by Wang et al. (2010). We used a three-dimensional elastic block model (Meade, 2007) and GPS data (Gan et al., 2007) to calculate slip rates on simplified fault systems in the Tibetan Plateau and surrounding regions (Figure S3). With the slip rates and the optimal locking depths for each faults determined by χ2 fitting, we calculated the rate of moment (M0) accumulation on each fault segment: M0=μ|s|A, where s is the slip, A is the area of locked fault plane, and μ is the shear modulus. Moment deficit or surplus is derived from comparison of moment accumulation with seismic moment release by previous large earthquakes (Table S1) on the fault segments over the same periods.
Figure S1. Earthquake hazard map by Global Seismic Hazard Assessment Program. Empty star is the epicenter of the 2008 Wenchaun earthquake (rupture zone outlined by solid lines); solid star and the enclosing box show the epicenter and rupture zone of the 2013 Lushan earthquake.
Figure S2. Geodynamic model for calculating stress changes by earthquakes. (a) Mesh and boundary conditions for the three-dimensional finite element model. (b) Finite element representation of the fault zones. LMSF: Longmenshan fault; HYF: Haiyuan fault; KLF: Kunlun fault; MJF: Minjiang fault; XSHF: Xianshuihe fault; ANHF: Anninghe fault.
Figure S3. Elastic block model (solid lines) and GPS velocities relative to stable Eurasia (arrows with error ellipse at 95% confidence interval).
Table S1. Earthquakes of M ≥ 6.0 used in stress and moment calculations.
| Region | Date | Magnitude (Ms) | Epicenter | Location* | |
|---|---|---|---|---|---|
| Longitude | Latitude | ||||
| Eastern Kunlun fault | 1879-07-01 | 8.0 | 104.7 | 33.2 | south of Wudu |
| 1881-07-20 | 6.5 | 104.6 | 33.6 | Lixian | |
| 1937-01-07 | 7.5 | 97.6 | 35.5 | Tuosuo | |
| 1963-04-19 | 7.0 | 97.0 | 35.7 | Alake | |
| 1971-03-24 | 6.3 | 98.10 | 35.45 | Tuosuo Lake | |
| Longmen Shan-Minshan fault | 1933-08-25 | 7.5 | 103.7 | 32.0 | Diexi |
| 1938-03-14 | 6.0 | 103.6 | 32.3 | south of Songpan | |
| 1941-06-12 | 6.0 | 102.5 | 30.1 | Luding | |
| 1958-02-08 | 6.2 | 104.3 | 31.7 | Beichuan | |
| 1960-11-09 | 6.8 | 103.66 | 32.78 | Zhangla | |
| 1970-02-24 | 6.2 | 103.2 | 30.6 | Dayi | |
| 1973-08-11 | 6.5 | 103.9 | 32.93 | Huanglong | |
| 1976-08-16 | 7.2 | 104.13 | 32.61 | Songpan | |
| 1976-08-22 | 6.7 | 104.4 | 32.6 | Songpan | |
| 1976-08-23 | 7.2 | 104.3 | 32.5 | Songpan | |
| Xianshuihe fault | 1893-08-29 | 7.2 | 101.5 | 30.6 | Daofu |
| 1904-08-30 | 7.0 | 101.1 | 31.0 | Daofu | |
| 1919-05-29 | 6.3 | 100.5 | 31.5 | Daofu | |
| 1919-08-26 | 6.2 | 100.0 | 32.0 | Ganze | |
| 1923-03-24 | 7.2 | 100.8 | 31.3 | Daofu | |
| 1930-04-28 | 6.0 | 100.0 | 32.0 | Ganze | |
| 1932-03-07 | 6.0 | 101.8 | 30.1 | Kangding | |
| 1955-04-14 | 7.5 | 101.9 | 30.0 | Kangding | |
| 1967-08-30 | 6.8 | 100.3 | 31.6 | Luhuo | |
| 1967-08-30 | 6.6 | 100.23 | 31.63 | Luhuo | |
| 1973-02-06 | 7.6 | 100.24 | 31.5 | Luhuo | |
| 1973-02-08 | 6.0 | 100.5 | 31.6 | Luhuo | |
| 1981-01-24 | 6.9 | 101.1 | 31.0 | Daofu | |
| 1982-06-16 | 6.0 | 99.75 | 31.86 | Ganze | |
| Anninghe fault | 1489-01-03 | 6.8 | 102.21 | 28.00 | Xichang |
| 1536-03-29 | 7.5 | 102.19 | 28.23 | Xichang | |
| 1952-09-30 | 6.8 | 102.18 | 28.41 | Mianning | |
| Outsider the fault | 1920-12-16 | 8.5 | 105.7 | 36.7 | Haiyuan |
| 1935-07-26 | 6.0 | 101.1 | 33.3 | Jiuzi | |
| 1941-10-08 | 6.0 | 102.3 | 31.7 | Heishui | |
| 1947-03-17 | 7.7 | 99.5 | 33.3 | Dari | |
| 1949-06-15 | 6.0 | 100.0 | 33.3 | Banma | |
| 1952-11-01 | 6.0 | 101.0 | 33.3 | Jiuzi | |
| 1989-09-22 | 6.5 | 102.51 | 31.58 | north of Xiaojin | |
| 1995-12-18 | 6.2 | 97.3 | 34.6 | Guoluo | |
Shaded events are included in the stress calculations for Figure 2c-d.
*Earthquake data sources: (Chen et al., 1994; Division of Earthquake Monitoring and Prediction, 1999; Wen et al., 2008).
Chen, S., Wilson, C. J. L., Deng, Q., Zhao, X., and Luo, Z., (1994), Active Faulting and Block Movement Associated with Large Earthquakes in the Min Shan and Longmen Mountains, Northeastern Tibetan Plateau, Journal of Geophysical Research-Solid Earth, 99, no. B12, 24025-24038.
Division of Earthquake Monitoring and Prediction, C. S. B., 1999, Catalog of Chinese historical strong earthquakes (1912-1990 Ms > 4.7), Beijing, China Seismological Press.
Gan, W., Zhang, P., Shen, Z., Niu, Z., Wang, M., Wan, Y., Zhou, D., and Cheng, J., (2007), Present-day crustal motion within the Tibetan Plateau inferred from GPS measurements, Journal of Geophysical Research-Solid Earth, 112, no. B08416, doi:10.1029/2005JB004120.
Jaeger, J. C., Cook, N. G. W., and Zimmerman, R. W., 2007, Fundamentals of Rock Mechanics, Blackwell Publishing, 261-262.
Luo, G., and Liu, M., (2010), Stress evolution and fault interactions before and after the 2008 Great Wenchuan Earthquake, Tectonophysics, doi:10.1016/j.tecto.2009.1012.1019.
Meade, B. J., (2007), Present-day kinematics at the India-Asia collision zone, Geology, 35, no. 1, 81-84.
Wang, H., Liu, M., Shen, X., and Liu, J., (2010), Balancing seismic moment in eastern Tibet: Implications for the Great 2008 Wenchuan Earthquake, Tectonophysics, doi:10.1016/j.tecto.2009.1009.1022. 10.1016/j.tecto.2009.09.022.
Wen, X., Ma, S., Xu, X., and He, Y., (2008), Historical pattern and behavior of earthquake ruptures along the eastern boundary of the Sichuan-Yunnan faulted-block, southwestern China, Physics of the Earth and Planetary Interiors, 168, 16-36. 10.1016/j.pepi.2008.04.013.
Yin, Y.-Q., and Zhang, H., (1982), A mathematical model of strain softening in simulating earthquake, Acta Geophysica Sinica, 25, no. 5, 414-423.
[ Back ]
