Static Coulomb Stress Changes and Triggering Interaction amongStrong Earthquakes in the Eastern Segment of North Qilian Mountain

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    Earthquakes are a natural phenomenon caused by sudden rupture and slippage of crustal rocks after stress reaches the point of rock failure.The coseismic dislocations of a major earthquake not only cause the stress state changes in adjacent areas, but also change the Coulomb stress.Research shows that a very small static Coulomb stress changes can trigger seismic activity (i.e.,earthquakes).Therefore,it is important to explore the relationship between Coulomb stress changes and earthquake triggering.First of all,we conducted primary research for strong earthquakes by Coulomb 3.3 on the static Coulomb stress changes with the primary study region being the eastern margin of north Qilian Mountain and adjacent area from 1561 to present. Meanwhile,we used cumulative and individual methods to calculate the Coulomb stress changes between foreshocks and aftershocks.Our results show that the next events,except Menyuan earthquake in 1986,would occur in the stress triggering area.The value of changes is between 0.1 bar and 4.066 bar,and trigger rate reached a high of 87.5%.In other instances,when the source fault is closed to receive fault,the former event can trigger the next.Secondly,according to the relationship between Coulomb stress changes and stress accumulation rate,we calculated the stress accumulated before the next event,not considering foreshocks.Finally,we assessed the future strong seismic hazard for this area according to earthquake migration and stress triggering.We used Okada’s method to calculate the change of static Coulomb failure stress among faults for the study area.In 1920 and 1927,two magnitude 8 earthquakes occurred,prior to the earthquakes the Coulomb stress significantly increased in the eastern side of Yunwu Mountain and western part of Jingtai-Tianzhu-Gulang.This suggests that an increase of Coulomb stress may forecast a triggered earthquake.It is noteworthy that the Tianzhu 6.2 earthquake occurred in the western part of the danger zone after two prior earthquakes.Considering the Coulomb stress triggering and the history of seismic activity,future earthquake risk should be strong in this area as well as the eastern side of Yunwu Mountain and Jinqianghe fault zone in the western part of Jingtai-Tianzhu-Gulang.This paper attempts to combine Coulomb stress adjustment and fracture characteristics with seismic activity.Results are consistent with other approaches in the Northeastern Qilian area,indicating that Coulomb stress changes can be used as an indicator of oncoming seismic activity. Application of this method will require further improvement to assess future seismic risk.

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  • Online: August 04,2014
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