Short- and long-term earthquake triggering along the strike-slip Kunlun fault, China: Insights gained from the Ms 8.1 Kunlun earthquake and other modern large earthquakes (original) (raw)
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Viscoelastic Triggering Between Large Earthquakes along the East Kunlun Fault System
Chinese Journal of Geophysics, 2003
We study stress transfer and triggering of large earthquakes along the East Kunlun fault system, northern Tibetan Plateau. Five M ≥7 earthquakes occurred along the fault zone during the past 70 years are considered: the 1937 M 7.5 Huashi Canyon, the 1963 MS7.1 Dulan, the 1973 MS7.3 Manyi, the 1997 MS7.5 Manyi, and the 2001 MW7.8 Kokoxili earthquakes.
Stress transfer and earthquake triggering along the Kunlun fault, western China
We study stress transfer and earthquake migration in the Kunlun fault system, northern Tibet. Five large earthquakes with Ms>=7 are considered: the 1937 M_s 7.5 Huashi Canyon earthquake, 1963 M_s 7.1 Dulan earthquake, 1973 M_s 7.3 Manyi earthquake, 1997 M_s 7.5 Manyi earthquake, and 2001 M_w 7.8 Kokoxili earthquake. We simulate seismically induced stress evolution in a layered visco-elastic medium using a dislocation modeling approach. Coulomb stress changes on fault planes of subsequent earthquake are evaluated. The result shows that prior to the Kokoxili earthquake the Coulomb stress on its fault plane was gradually built up by the occurrences of the previous 4 earthquakes and the visco-elastic relaxation of the crust. The Coulomb stress change resulted from the visco-elastic relaxation is found much larger than that due to the coseismic stress changes of the previous earthquakes. The Kokoxili earthquake has elevated the simulated Coulomb stress along the Xidatan-Dongdatan segm...
Earthquake Triggering along the Xianshuihe Fault Zone of Western Sichuan, China
Western Sichuan is among the most seismically active regions in southwestern China and is characterized by frequent strong (M ‡ 6.5) earthquakes, mainly along the Xianshuihe fault zone. Historical and instrumental seismicity show a temporal pattern of active periods separated by inactive ones, while in space a remarkable epicenter migration has been observed. During the last active period starting in 1893, the sinistral strike–slip Xianshuihe fault of 350 km total length, was entirely broken with the epicenters of successive strong earthquakes migrating along its strike. This pattern is investigated by resolving changes of Coulomb failure function (DCFF ) since 1893 and hence the evolution of the stress field in the area during the last 110 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic halfspace, and taking into account both the coseismic slip in strong (M ‡ 6.5) earthquakes and the slow tectonic stress buildup associated with major fault segments. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We evaluate whether these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. It was found that all strong earthquakes, and moreover, the majority of smaller events for which reliable fault plane solutions are available, have occurred on stress–enhanced fault segments providing a convincing case in which Coulomb stress modeling gives insight into the temporal and spatial manifestation of seismic activity. We extend the stress calculations to the year 2025 and provide an assessment for future seismic hazard by identifying the fault segments that are possible sites of future strong earthquakes.
We analyzed coseismic surface deformations associated with the 2001 Mw 7.8 Central Kunlun earthquake, which occurred on 14 November 2001 along the west (Kusai Lake) segment of the left-lateral strike-slip Kunlun fault in northern Tibet, China. Field investigations and analyses of satellite remote sensing imagery indicate that a 400-km-long coseismic rupture zone occurred along the pre-existing Kunlun fault zone. The coseismic surface rupture zone is mainly composed of sinistral shear faults, tensional cracks, mole tracks, and pull-apart sag ponds and grabens. Width of the coseismic surface rupture zone ranges from several meters to 1 km. This earthquake caused damage to the highway between Golmud and Lhasa, base of the Qinghai-Tibet railway, and temporary housing for railway construction workers. It also triggered snow and glacier avalanches. The analyses of coseismic surface deformational features and engineering damage provide us useful experience to evaluate possible engineering damage associated with future great earthquakes on strike-slip faults in highly populated and industrialized regions. Furthermore, it also provides us an unusual opportunity to understand the growth of geomorphic features due to repeated large seismic events along an active strike-slip fault.
Stress evolution and fault interactions before and after the 2008 Great Wenchuan earthquake
Tectonophysics, 2010
The 12 May 2008 Wenchuan earthquake (Mw 7.9) ruptured ∼ 300 km of the Longmen Shan fault, claiming ∼ 90,000 lives and devastating many cities in the Sichuan province, China. The coseismic stress changes due to the Wenchuan earthquake have been studied in kinematic models using the inferred coseismic fault slips, but the cause of the fault slips, the impact of other large earthquakes, and the mechanical interactions between the faults in eastern Tibet are uncertain. Here we explore these issues using a three-dimensional viscoelastoplastic dynamic model that calculates the regional stresses from tectonic and topographic loading, and simulates earthquakes and their stress perturbations. Our calculated coseismic changes of the Coulomb stress associated with the Great Wenchuan earthquake are similar to those in previous models. However, we show that the cumulative Coulomb stress changes, hence the implied earthquake risks, are significantly different when previous large earthquakes in the region are included in the model. Particularly, we show that in spite of stress increase from the Wenchuan earthquake, the southeastern segments of the Xianshuihe fault stay in a stress shadow because of the stress release by six M ≥ 6.9 events in this part of the Xianshuihe fault since 1893. We also found that interseismic locking on the Xianshuihe fault can increase the loading rate on the Longmen Shan fault by up to ∼ 50 Pa/year.
Geophysical Journal International, 2014
The East Kunlun Fault zone, striking E-W to WNW-ESE, has been recognized as one of the largest and most active left-lateral strike-slip faults in the China continent. Presently, the Maqin-Maqu segment (MMS) is recognized as a seismic gap on the East Kunlun Fault. Since several highly populated counties are close to this region, understanding stress transfer and accumulation along this segment is important for hazard assessment along the MMS. In this study, we calculated the stress evolution along the MMS of the East Kunlun Fault zone during 1879-2008 by integrating coseismic effects, viscoelastic relaxation and tectonic loading. It is observed that the stress accumulation on the western part of the Maqin segment has been effected by the 1937 Tuosuo Lake earthquake, the stress on the eastern part of the Maqin segment. Also, the western part of the Maqu segment was relaxed by the 1947 Dari earthquake, and the stress loading on the eastern part of Maqu segment was increased by both the 1879 Wudu and 2008 Wenchuan earthquakes. It is observed that, compared to coseismic static stress changes, the post-seismic viscoelastic relaxation process has played a more important role on stress accumulation in the Maqu segment. The increased stress on the Maqin and Maqu segment is consistent with tectonic loading over 160 and 250 yr, respectively, which we expect will lead to future earthquakes and associated seismic hazard on these segments.
Visco-elastic stress triggering model of Tangshan earthquake sequence
Acta Seismologica Sinica, 2008
We calculated the Coulomb failure stress change generated by the 1976 Tangshan earthquake that is projected onto the fault planes and slip directions of large subsequent aftershocks. Results of previous studies on the seismic failure distribution, crustal velocity and viscosity structures of the Tangshan earthquake are used as model constraints. Effects of the local pore fluid pressure and impact of soft medium near the fault are also considered. Our result shows that the subsequent Luanxian and Ninghe earthquakes occurred in the regions with a positive Coulomb failure stress produced by the Tangshan earthquake. To study the triggering effect of the Tangshan, Luanxian, and Ninghe earthquakes on the follow-up small earthquakes, we first evaluate the possible focal mechanisms of small earthquakes according to the regional stress field and co-seismic slip distributions derived from previous studies, assuming the amplitude of regional tectonic stress as 10 MPa. By projecting the stress changes generated by the above three earthquakes onto the possible fault planes and slip directions of small earthquakes, we find that the "butterfly" distribution pattern of increased Coulomb failure stress is consistent with the spatial distribution of follow-up earthquakes, and 95% of the aftershocks occurred in regions where Coulomb failure stresses increase, indicating that the former large earthquakes modulated occurrences of follow-up earthquakes in the Tangshan earthquake sequence. This result has some significance in rapid assessment of aftershock hazard after a large earthquake. If detailed failure distribution, seismogenic fault in the focal area and their slip features can be rapidly determined after a large earthquake, our algorithm can be used to predict the locations of large aftershocks.
Stress changes on major faults caused by M w7.9 Wenchuan earthquake, May 12, 2008
Science in China Series D: Earth Sciences, 2009
On May 12, 2008, a magnitude 7.9 earthquake ruptured the Longmenshan fault system in Sichuan Province, China, collapsing buildings and killing tens of thousands people. As predicted, aftershocks may last for at least one year, and moreover, large aftershocks are likely to occur. Therefore, it is critical to outline the areas with potential aftershocks before reconstruction and re-settling people as to avoid future disasters. It is demonstrated that the redistribution of stress induced by an earthquake should trigger successive seismic activity. Based on static stress triggering theory, we calculated the coseismic stress changes on major faults induced by the Wenchuan earthquake, with elastic dislocation theory and the multilayered crustal model. We also discuss the stress distribution and its significance for future seismic activity under the impact of the Wenchuan earthquake. It is shown that coulomb failure stress (CFS) increases obviously on the Daofu-Kangding segment of the Xianshuihe Fault, the Maqu and Nanping segment of the Eastern Kunlun Fault, the Qingchuan Fault, southern segment of the Minjiang Fault, Pengxian-Guanxian Fault, Jiangyou-Guangyuan Fault, and Jiangyou-Guanxian Fault. The increased stress raises the probability of earthquake occurrence on these faults. Since these areas are highly populated, earthquake monitoring and early disaster alarm system are needed. CFS increases with a magnitude of 0.03-0.06 MPa on the Qingchuan Fault, which is close to the northern end of the rapture of Wenchuan earthquake. The occurrence of some strong aftershocks, including three events with magnitude higher than 5.0, indicates that the seismic activities have been triggered by the main shock. Aftershocks seem to migrate northwards. Since the CFS change on the Lueyang-Mianxian Fault located on the NEE of the Qingchuan Fault is rather small (±0.01 MPa), the migration of aftershocks might be terminated in the area near Hanzhong City. The CFS change on the western Qinling Fault is around 10 Pa, and the impact of static triggering can be neglected. The increment of CFS on the Pengxian-Guanxian Fault and Beichuan-Yingxiu Fault southwest to the main rupture is 0.005-0.015 MPa, which would facilitate earthquake triggering in these areas. Very few aftershocks in these areas indicate that the accumulated stress has not been released sufficiently. High seismic risk is predicated in these areas due to co-seismic CFS loading. The Wenchuan earthquake released the accumulated CFS on the Fubianhe Fault, the Huya Fault, the Ha'nan-Qingshanwan Fault, and the Diebu-Bailongjiang Fault. The decrement of CFS changes on the Longquanshan Fault east to Chengdu City is about 0.002 MPa. The seismic activity will be depressed by decrement of CFS on these faults.
1] As the most destructive seismic episode ever known in eastern Taiwan, the 1951 M L 7.3 Hualien -Taitung earthquake series consisted of sequential ruptures along four distinct fault segments. It provides a good opportunity to study earthquake triggering processes along an active fault at an oblique arc-continent collision boundary. This sequence initiated on 21October 1951 with the M L 7.3 Hualien main shock and a group of M6+ aftershocks nearby. The M L 6.0 Chihshang earthquake occurred 34 days later and 100 km away from the main shock. The M L 7.3 Yuli earthquake followed 3 m later and 5 km away from the Chihshang event. Two days later, the M L 6.0 Taitung earthquake shocked a region 40 km away from the preceding M6 event and completed the sequence. The first triggered rupture outside the main shock area did not occur on the nearby Yuli fault segment but occurred 100 km away at the Chihshang fault. Calculations of static Coulomb stress change show that most of the major aftershocks were located in areas of enhanced static stress change. However, the stress transfer alone cannot explain triggering across 100 km. With the rate/state stress transfer model, we computed the temporal order of encouraged ruptures on different segments along the collision boundary. The results show that 34 days following the major shocks in Hualien, the Chihshang segment had a higher M6+ (M R 6) earthquake probability due to its significantly higher (at least an order of magnitude) background seismicity rate than the other two segments. After the Chihshang event, the rate/state model predicted a higher M6+ earthquake probability in the Yuli segment, also matching the observation. In this case, the Yuli segment was triggered ahead of the Taitung segment because of its larger increase in Coulomb stress change.