地震研究

祁连—海原断裂带强震库仑应力演化特征研究^*

孟令媛¹,张竹琪^2,周龙泉¹,臧阳¹

(1.中国地震台网中心,北京 100045; 2.中国地震局地质研究所地震动力学国家重点实验室,北京 100029)

Research on Cumulative Coulomb Stress Evolution Characteristic of Strong Earthquakes along the Qilian-Haiyuan Fault Zone

MENG Lingyuan¹,ZHANG Zhuqi²,ZHOU Longquan¹,ZANG Yang¹

(1.China Earthquake Networks Center,Beijing 100045,China)(2.State Key Laboratory of Earthquake Dynamics,Institute of Geology,CEA,Beijing 100029,China)

Keywords：Qilian-Haiyuan Fault Zone; viscoelastic relaxation; Burgers model; cumulative coulomb stress evolution

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参考文献

研究祁连—海原断裂带及其附近区域自1920年海原M_S8.5地震后至今发生的6次M_S≥7.0强震间的相互触发关系,基于Burgers体构建粘弹性介质模型,模拟同震和震后库仑应力的演化过程; 进一步针对祁连山北缘断裂带、西秦岭北缘断裂带及六盘山断裂带3条主要断裂带,分别计算自1920年至今6次强震在这3条断裂带上近百年尺度的应力累积。结果表明:1927年古浪M_S8.0地震受到1920年海原M_S8.5地震同震和震后库仑应力的共同加载,1954年民勤M_S7.0地震和1990年共和M_S7.0地震均受到之前发生强震的库仑应力的累积加载影响; 西秦岭北缘断裂位于6次强震震后的综合累积应力卸载区,六盘山断裂带则位于累积应力加载区。研究强震间库仑应力演化特征及其对周围断裂带的较长时间尺度的累积影响,需要合理考虑粘弹性松弛效应下的震后库仑应力的累积作用,也可结合地震活动性进一步为明确危险断层段提供合理的参考。

Firstly,we study the triggering relation of six strong M_S≥7.0 earthquakes after Haiyuan M_S8.5 earthquake in 1920 along the Qilian-Haiyuan Fault Zone and its adjacent area since 1920,such as the 1920 Haiyuan M_S8.5 earthquake,the 1927 Gulang M_S8.0 earthquake,the 1932 Changma M_S7.6 earthquake,the 1954 M_S7.3 Shandan earthquake,the 1954 Minqin M_S7.0 earthquake,and the 1990 Gonghe M_S7.0 earthquake.Secondly,we establish the viscoelastic medium model based on Burgers model to simulate the co-seismic and post-seismic cumulative coulomb stress changes.Finally,we calculated the stress accumulation in the last hundred years of 6 strong earthquakes on the north Qilian-Mountain Fault,the north Western-Qinling Fault and Liupan-Mountain Fault.The results shows that the 1927 Gulang M_S8.0 earthquake was triggered by the loading of both co-seismic and post-seismic coulomb failure stresses of the 1920 Haiyuan M_S8.5 earthquake,and the 1954 Minqin M_S7.0 earthquake and the1990 Gonghe M_S7.0 earthquake were both influenced by the loading of cumulative coulomb stress of their previous earthquakes.The north Western-Qinling Fault was located in the stress unloading zone cumulated by the total 6 strong earthquakes with the viscoelastic relaxation till 2015,and the Liupan-Mountain Fault located in the cumulative stress loading zone.It needs to point out that studying the coulomb stress changes of strong earthquakes and their cumulative effect on the surrounding fault zone in the long time scale,it need to consider the cumulative effect of post-seismic coulomb stress under the effect of viscoelastic relaxation and provide reference for determining the risk segment combining with seismic activity.

引言
1 研究方法和原理
2 模型构建
3 计算结果分析
4 讨论
5 结论

图1 Kelvin体(a)、Maxwell体(b)和Burger体(c)模型示意图<br/>Fig.1 Sketch map of Kelvin body model(a),Maxwell body model(b),and Burgersbody model(c)

图1 Kelvin体(a)、Maxwell体(b)和Burger体(c)模型示意图
Fig.1 Sketch map of Kelvin body model(a),Maxwell body model(b),and Burgersbody model(c)

表1 本研究所采用的地壳与上地幔模型参数<br/>Tab.1 Parameters of crust and upper mantle model used in this study

表1 本研究所采用的地壳与上地幔模型参数
Tab.1 Parameters of crust and upper mantle model used in this study

图2 祁连—海原带6次强震震源位置及时间迁移示意图<br/>Fig.2 The sketch map of the location of the hypocenters of the six strong earthquakes investigated in this study in Qilian-Haiyuan Fault and their time migration

图2 祁连—海原带6次强震震源位置及时间迁移示意图
Fig.2 The sketch map of the location of the hypocenters of the six strong earthquakes investigated in this study in Qilian-Haiyuan Fault and their time migration

表2 本研究所用的强震震源模型参数<br/>Tab.2 Strong earthquake source and rupture parameters used in this study

表2 本研究所用的强震震源模型参数
Tab.2 Strong earthquake source and rupture parameters used in this study

图3 1920年海原地震对1927年古浪地震同震(a)及震后(b)库仑应力影响<br/>Fig.3 The co-seismic dislocations(a)and the post-seismic viscoelastic relaxation(b)of coulomb stress changes on the fault plan of the 1927 Gulang earthquake associated with the 1920 Haiyuan earthquake

图3 1920年海原地震对1927年古浪地震同震(a)及震后(b)库仑应力影响
Fig.3 The co-seismic dislocations(a)and the post-seismic viscoelastic relaxation(b)of coulomb stress changes on the fault plan of the 1927 Gulang earthquake associated with the 1920 Haiyuan earthquake

图4 祁连—海原带及附近区域1920年以来强震的震后粘弹松弛效应引起的累积库仑应力变化(①～⑥依次为1920年海原地震、1927年古浪地震、1932年昌马地震、1954年山丹地震、1954年民勤地震和1990年共和地震)(a)海原地震及古浪地震震后粘弹松弛效应在昌马地震断层面上的累积库仑应力变化;(b)山丹地震前3次强震震后粘弹松弛效应在其断层面上共同产生的累积库仑应力变化;(c)民勤地震前4次强震震后粘弹松弛效应在其断层面上共同产生的累积库仑应力变化;(d)共和地震前5次强震震后粘弹松弛效应在其断层面上共同产生的累积库仑应力变化
Fig.4 Cumulative coulomb stress changes caused by the post-seismic viscoelastic relaxation of previous strong earthquakes in the Qilian-Haiyuan Fault and its adjacent region since 1920(① to ⑥ are 1920 Haiyuan earthquake,1927 Gulang earthquake,1932 Changma earthquake,1954 Shandan earthquake,1954 Minqin earthquake and 1990 Gonghe earthquake respectively)(a)coulomb stress changes on the 1932 Changma earthquake fault plane associated with the post-seismic viscoelastic relaxation of the 1920 Haiyuan earthquake and the 1927 Gulang earthquake;(b)coulomb stress changes on the 1954 Shandan earthquake fault plane associated with the post-seismic viscoelastic relaxation of three strong earthquakes before 1954 Shandan earthquake;(c)coulomb stress changes on the 1954 Minqin earthquake fault plane associated with the post-seismic viscoelastic relaxation of four strong earthquakes before 1954 Minqin earthquake;(d)coulomb stress changes on the 1990 Gonghe earthquake fault plane associated with the post-seismic viscoelastic relaxation of four strong earthquakes before 1990 Gonghe earthquake

表3 本研究计算的3条断裂带的潜在断层破裂面(接收断层)参数<br/>Tab.3 Receiver fault plane parameter of the three boundary faults in this study

表3 本研究计算的3条断裂带的潜在断层破裂面(接收断层)参数
Tab.3 Receiver fault plane parameter of the three boundary faults in this study

图5 祁连—海原带及附近区域6次强震自1920年至今在祁连山北缘断裂带(F1)(a)、西秦岭北缘断裂带(F2)(b)、六盘山断裂带(F3)(c)上的累积库仑应力变化(①～⑥同图4)<br/>Fig.5 Cumulative coulomb stress changes on the north Qilian-Mountain Fault(F1)(a),the north Western-Qinling Fault(F2)(b),Liupan-Mountain Fault F3)(c)caused by the all the six earthquakes in the Qilian-Haiyuan Fault and its adjacent area since 1920(the illustration of ① to ⑥ are same as in Fig.4)

图5 祁连—海原带及附近区域6次强震自1920年至今在祁连山北缘断裂带(F1)(a)、西秦岭北缘断裂带(F2)(b)、六盘山断裂带(F3)(c)上的累积库仑应力变化(①～⑥同图4)
Fig.5 Cumulative coulomb stress changes on the north Qilian-Mountain Fault(F1)(a),the north Western-Qinling Fault(F2)(b),Liupan-Mountain Fault F3)(c)caused by the all the six earthquakes in the Qilian-Haiyuan Fault and its adjacent area since 1920(the illustration of ① to ⑥ are same as in Fig.4)

图6 1970～2012年本研究中3条目标断层及附近区域ML≥3.0地震分布(中国地震台网中心精定位结果)<br/>Fig.6 Distributions of the ML≥3.0 earthquakes along the 3 boundary faults and their adjacent region from 1970 to 2012 in this study(relocation results of the earthquake from China Earthquake Network Center)

图6 1970～2012年本研究中3条目标断层及附近区域ML≥3.0地震分布(中国地震台网中心精定位结果)
Fig.6 Distributions of the ML≥3.0 earthquakes along the 3 boundary faults and their adjacent region from 1970 to 2012 in this study(relocation results of the earthquake from China Earthquake Network Center)

图7 1970～2012年沿祁连山北缘断裂带(F1)(a)、西秦岭北缘断裂带(F2)(b)、六盘山断裂带(F3)(c)3条目标断层发生的ML≥0.0小震深度剖面图(中国地震台网中心精定位结果)<br/>Fig.7 Distributions of focal depth profiles of ML≥0.0 small earthquakes from 1970 to 2012 along the traces of the 3 boundary faults,such as the north Qilian-Mountain Fault(F1)(a),the north Western-Qinling Fault(F2)(b),Liupan-Mountain Fault(F3)(c)(relocation results of the earthquake from China Earthquake Network Center)

图7 1970～2012年沿祁连山北缘断裂带(F1)(a)、西秦岭北缘断裂带(F2)(b)、六盘山断裂带(F3)(c)3条目标断层发生的ML≥0.0小震深度剖面图(中国地震台网中心精定位结果)
Fig.7 Distributions of focal depth profiles of ML≥0.0 small earthquakes from 1970 to 2012 along the traces of the 3 boundary faults,such as the north Qilian-Mountain Fault(F1)(a),the north Western-Qinling Fault(F2)(b),Liupan-Mountain Fault(F3)(c)(relocation results of the earthquake from China Earthquake Network Center)