The Kaikoura earthquake on November 14,2016 is one of the largest and most complex earthquakes in New Zealand since 1947.Despite the fact that it has ruptured about 12 separate faults,triggered 2132 aftershocks within...The Kaikoura earthquake on November 14,2016 is one of the largest and most complex earthquakes in New Zealand since 1947.Despite the fact that it has ruptured about 12 separate faults,triggered 2132 aftershocks within one week of the mainshock and induced considerable stress changes,few studies have been conducted to comprensively investigate the characteristics.The current study examines the horizontal and vertical displacements as well as the stress and gravity changes,aftershock distributions and also find out whether these changes affect the surrounding regions along the complex fault systems.The study covers the entire area affected by the Kaikoura event,which includes the northern part of the South Island and the southern part of the North Island.The dislocation theory was employed to evaluate the coseismic slip model on the multiple faults.The displacement results revealed that the maximum horizontal displacement is about 6 m and the vertical about 2 m,which are reasonably consistent with earlier study findings.Besides,the stress and gravity changes are quite complicated and inhomogeneous as evidenced by our coseismic model,demonstrating the complexity of the Kaikoura earthquake as well.Almost all the aftershocks are distributed in places where the stress and gravity change are found to be significant.In order to investigate the stability of our stress change models,we applied different friction coefficients and receiver fault parameters.The results justify the friction coefficient(μ=0.4)and the receiver fault parameters(230°,70°,150°)are suitable to define good stress change estimates.According to the stress change results at 15 km depth,the northern parts of the mainshock region,Hundalee fault,Humps fault and Jordan thrust areas together with the Wellington area are closer to failure and situated in a seismic risk zone.The multidimensional analysis adopted in this paper is helpful for making decisions and applications of stress and gravity change models in assessing seismic hazards.展开更多
Numerous shallow earthquakes, including 24 th August Amatrice, 26 th October Visso, and 30 th October Norcia earthquakes, ruptured the segments of Mount Vettore-Gorzano fault system in the central Apennines(Italy) in ...Numerous shallow earthquakes, including 24 th August Amatrice, 26 th October Visso, and 30 th October Norcia earthquakes, ruptured the segments of Mount Vettore-Gorzano fault system in the central Apennines(Italy) in 2016. In order to investigate the stress perturbation and triggering patterns among the earthquake sequences, we introduce a more realistic nonplanar coseismic fault geometry model, which improve the rupture model by assimilating relocated aftershocks and the GPS observations. We adopt the seismic slip inversion program of the steepest descent method(SDM) to create the detailed coseismic rupture models and optimize Coulomb Failure Stress model by varying the coefficient of friction and received fault parameters. The results indicate that the nonplanar fault geometry model is more reflective of the deep slip of the coseismic rupture than planar model. As evidenced by the coseismic Coulomb stress changes caused by the three mainshocks at different depth slices, the stress loading mainly distributes on the active fault zones and the stress changes can well explain the spatial distribution of aftershocks. The first large Amatrice mainshock accelerates the occurrence of the Mw 5.9 Visso and Mw 6.6 Norcia earthquakes, with the positive stress changes at the hypocenter exceeding the stress triggering threshold(0.010×10^(6) Pa) and up to 0.015×10^(6) and 0.257×10^(6) Pa, respectively. Furthermore, the Mw 5.9 Visso earthquake as well encourages the occurrence of the Mw 6.6 Norcia event with the increased stress changes of 0.052×10^(6) Pa on the hypocenter. It is concluded that the stress transfer and accumulation play crucial roles on the linkage triggering mechanism among the mainshock-mainshock and mainshockaftershocks. Noteworthily, the cumulative stress changes on the southwest segment of the Norcia Fault(NF), the southeast parts of the Montereale Fault System(MFS) and Mount Gorzano Fault(MGF) of the main regions are up to(1.5~3.5) ×10^(6) Pa. The cumulative stress changes have not been released sufficiently by aftershocks, which may increase the seismic hazard in those regions.展开更多
基金financially supported by the National Key Research Program of China“Collaborative Precision Positioning Project”(No.2016YFB0501900)the National Natural Science Foundation of China(No.41374032)。
文摘The Kaikoura earthquake on November 14,2016 is one of the largest and most complex earthquakes in New Zealand since 1947.Despite the fact that it has ruptured about 12 separate faults,triggered 2132 aftershocks within one week of the mainshock and induced considerable stress changes,few studies have been conducted to comprensively investigate the characteristics.The current study examines the horizontal and vertical displacements as well as the stress and gravity changes,aftershock distributions and also find out whether these changes affect the surrounding regions along the complex fault systems.The study covers the entire area affected by the Kaikoura event,which includes the northern part of the South Island and the southern part of the North Island.The dislocation theory was employed to evaluate the coseismic slip model on the multiple faults.The displacement results revealed that the maximum horizontal displacement is about 6 m and the vertical about 2 m,which are reasonably consistent with earlier study findings.Besides,the stress and gravity changes are quite complicated and inhomogeneous as evidenced by our coseismic model,demonstrating the complexity of the Kaikoura earthquake as well.Almost all the aftershocks are distributed in places where the stress and gravity change are found to be significant.In order to investigate the stability of our stress change models,we applied different friction coefficients and receiver fault parameters.The results justify the friction coefficient(μ=0.4)and the receiver fault parameters(230°,70°,150°)are suitable to define good stress change estimates.According to the stress change results at 15 km depth,the northern parts of the mainshock region,Hundalee fault,Humps fault and Jordan thrust areas together with the Wellington area are closer to failure and situated in a seismic risk zone.The multidimensional analysis adopted in this paper is helpful for making decisions and applications of stress and gravity change models in assessing seismic hazards.
基金This work is funded by Sichuan Science and Technology Program(No.2020GZYZF0010)National Natural Science Foundation of China(No.41374032.No.41704028).
文摘Numerous shallow earthquakes, including 24 th August Amatrice, 26 th October Visso, and 30 th October Norcia earthquakes, ruptured the segments of Mount Vettore-Gorzano fault system in the central Apennines(Italy) in 2016. In order to investigate the stress perturbation and triggering patterns among the earthquake sequences, we introduce a more realistic nonplanar coseismic fault geometry model, which improve the rupture model by assimilating relocated aftershocks and the GPS observations. We adopt the seismic slip inversion program of the steepest descent method(SDM) to create the detailed coseismic rupture models and optimize Coulomb Failure Stress model by varying the coefficient of friction and received fault parameters. The results indicate that the nonplanar fault geometry model is more reflective of the deep slip of the coseismic rupture than planar model. As evidenced by the coseismic Coulomb stress changes caused by the three mainshocks at different depth slices, the stress loading mainly distributes on the active fault zones and the stress changes can well explain the spatial distribution of aftershocks. The first large Amatrice mainshock accelerates the occurrence of the Mw 5.9 Visso and Mw 6.6 Norcia earthquakes, with the positive stress changes at the hypocenter exceeding the stress triggering threshold(0.010×10^(6) Pa) and up to 0.015×10^(6) and 0.257×10^(6) Pa, respectively. Furthermore, the Mw 5.9 Visso earthquake as well encourages the occurrence of the Mw 6.6 Norcia event with the increased stress changes of 0.052×10^(6) Pa on the hypocenter. It is concluded that the stress transfer and accumulation play crucial roles on the linkage triggering mechanism among the mainshock-mainshock and mainshockaftershocks. Noteworthily, the cumulative stress changes on the southwest segment of the Norcia Fault(NF), the southeast parts of the Montereale Fault System(MFS) and Mount Gorzano Fault(MGF) of the main regions are up to(1.5~3.5) ×10^(6) Pa. The cumulative stress changes have not been released sufficiently by aftershocks, which may increase the seismic hazard in those regions.
