Viscoelastic stress change from the 1931 M_(w)7.8 Fuyun earthquake and its impacts on seismic activity around the Altai mountains

The 1931 M_(w)7.8 Fuyun earthquake occurred around the Altai mountains, an intracontinental deformation belt with limited active strain-rate accumulation. To explore whether seismic activity in this deformation belt was affected by stress interaction among different active faults, we calculate the Coulomb failure stress change(ΔCFS) induced by the Fuyun earthquake due to coseismic deformation of the elastic crust and postseismic viscoelastic relaxation of the lower crust and upper mantle. Numerical results show that the total ΔCFS at a 10-km depth produced by the Fuyun earthquake attains approximately 0.015-0.134 bar near the epicenter, and just before the occurrence of the 2003 M_(w)7.2 Chuya earthquake, which distances about 400 km away from the Fuyun earthquake. Among the increased ΔCFS,viscoelastic relaxation from 1931 to 2003 contributes to approximately 0.014-0.131 bar, accounting for>90% of the total ΔCFS. More importantly, we find that for the recorded seismicity in the region with a radius of about 270 km to the Fuyun earthquake from 1970 to 2018, the percentage of earthquakes that fall in positive lobes of ΔCFS resolved on the NNW-SSE Fuyun strike-slip fault, on the NWW-SEE Irtysh strike-slip fault, and on the NW-SE Kurti reverse fault is up to 67.22%-91.36%. Therefore, the predictedΔCFS suggests that the impact of the 1931 M_(w)7.8 Fuyun earthquake on seismic activity around the Altai mountains is still significant as to hasten occurrence of the 2003 M_(w)7.2 Chuya earthquake at a relatively far distance and to trigger its aftershocks in the near-field even after several decades of the mainshock.

Co-seismic Coulomb stress changes on the northern Tanlu fault zone caused by the Tohoku-Oki M_(W)9.0 earthquake

Based on the spherical earth dislocation theory and a fault slip model of the Tohoku-Oki M_(W)9.0 earthquake,the co-seismic Coulomb failure stress changes(ΔCFS)on the northern Tanlu fault zone at depths of 0–40 km are calculated.By comparing two sets of results from the spherical earth dislocation theory and the semi-infinite space one,the effect of earth curvature on the calculation results is analyzed quantitatively.First,we systematically summarize previous researches related to the northern Tanlu fault zone,divide the fault zone as detailed as possible,give the geometric parameters of each segment,and establish a segmented structural model of the northern Tanlu fault zone.Second,we calculate the Coulomb stress changes on the northern Tanlu fault zone by using the spherical earth dislocation theory.The result shows the Coulomb stress changes are no more than 0.003 MPa,which proves the great earthquake did not significantly change the stress state of the fault zone.Finally,we quantitatively analyze the disparities between the results of semi-infinite space dislocation theory and the spherical earth one.The average disparity between them is about 7.7%on the northern Tanlu fault zone and is 16.8%on the Fangzheng graben,the maximum disparity on this graben reaches up to 25.5%.It indicates that the effect of earth curvature can not be ignored.So it’s necessary to use the spherical earth dislocation theory instead of the semi-infinite space one to study the Coulomb stress change in the far field.

Coulomb stress and gravity changes associated with the 2016 Mw 7.8 Kaikoura Earthquake, New Zealand: Application for aftershock triggering and fault interaction process analysis

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.

Research on Frequency of the Aftershock Sequence of the Wenchuan Earthquake Based on Coseismic Coulomb Stress Change

By the aftershock frequency estimation method based on the calculation of coseismic static Coulomb stress changes and rate-and state-dependent fault constitutive law,we calculate the frequency of "direct "aftershocks of the Wenchuan earthquake related to coseismic static Coulomb stress changes in its aftershock zone and the areas nearby.It shows that the frequency is significantly lower than the truth in the main rupture zone,especially in the southern rupture zone,due to the decrease of stress level on the rupture plane of the main shock resulting from coseismic Coulomb stress change.The study also shows that the effect of the Coulomb stress change on the duration of aftershock activity is associated with the lower limit magnitude.The duration is about 15-16 months for aftershocks above ML4.0,and close to 60 months for aftershocks above ML3.5.In this period,the ratio of the"direct"aftershocks caused by coseismic Coulomb stress change ranges between 44.7% to48.6%,which suggests that,even in the "effective"period of coseismic Coulomb stress changes,about half of the aftershocks on the main shock rupture plane are independent of coseismic Coulomb stress changes.It is pointed out that those aftershocks may be related to the afterslip or the viscoelastic relaxation,which are time dependent cases.

Regional seismicity triggered by the M_s=7.8 Tangshan event on July 28, 1976 and the stati cstress field change

We studied the seismicity before and after the M_s=7.8 Tangshan event on July 28, 1976 (39°28'N, 1 18° 11'E) and the results show that in 3 regions outside of the source zone, seismicity rate increasing were observed, which was significant in 0.99 significance level using Z-statistic test and was proposed to be triggered by the M_s=7.8 Tangshan earthquake. The magnitude of the greatest triggered event was 5.5. The epicenter distances of these earthquakes were several ten kilometers to 300 km. The static stress change △CFS of Coulomb failure was calculated using an elastic dislocation model in half space and the △CFS on the major rupture directions in these three regions were positive.

Seismicity changes and numerical simulation of coseismic deformation following the 2022 M_(s)6.8 Luding earthquake in Sichuan,China

The Xianshuihe fault is a major tectonic boundary between the Sichuan-Yunnan rhombic and Bayanhar blocks in Southwest China.With an average left-lateral strike-slip movement of 10–15 mm/yr,it is a fast-moving strike-slip continental fault.On September 5,2022,the Ms6.8 Luding earthquake occurred along the Moxi segment of the Xianshuihe fault,reaching a maximum intensity of IX and resulting in a significant number of casualties and severe property damage.This earthquake broke the long-standing seismic quiescence of the Xianshuihe fault,which lasted for more than 40 years,and was followed by a significant number of aftershocks.An outstanding question is how the behavior of the Xianshuihe fault and major earthquakes changed following this mainshock.In this study,we examined the changes in regional seismicity following the Luding earthquake and identified the potential for future strong earthquakes along the Xianshuihe fault.We used a finite element numerical method to simulate the environment of the seismogenic fault and its adjacent areas.In addition,we used the coseismic slip model of the Luding earthquake with the split-node method to calculate how the stress and strain fields in the surrounding area were affected by the2022 mainshock.Coulomb stress changes were resolved in the main faults,and the seismicity of adjacent faults was analyzed in conjunction with the observed seismic data.The results indicate that regional tectonic movement primarily occurred to the southeast along the Moxi segment.The stress field is approximately north-south in tension and east-west in compression.Variation in the stress field in the epicentral region of the Luding earthquake exceeded 1 MPa.The maximum displacement of the coseismic deformation field was concentrated between Moxi town and Tuanjie village,and the Coulomb stress of the fault zone in this region experienced the largest decrease.However,the b-value of the Gutenberg-Richter magnitude-frequency relationship at the epicenter and the surrounding area exhibited an abnormal pattern of decrease-decrease-increase,indicating that the regional stress may not be fully released.This earthquake increased the Coulomb stress in other segments of the Xianshuihe,Anninghe,and Daliangshan faults,whereas the Coulomb stress in the Longmenshan and Xiaojinhe fault zones decreased.In addition,it triggered a series of normal-fault,moderate-sized earthquakes in nearby areas.The Dagangshan reservoir,located~20 km from the epicenter of the Luding earthquake,received an increase of~5.3 MPa in the tensile stress along the NWW-SEE direction.The Xiluodu Reservoir,located approximately 225 km from the epicenter,was less affected by this earthquake,and the seismic activity near the reservoir remained relatively unchanged.In this study,post-earthquake seismicity in the vicinity of the Ms6.8 Luding earthquake was analyzed and predicted by numerical simulation,providing a scientific basis for earthquake prediction and disaster reduction.

数值模拟静态应力扰动下的断层失稳:结果分析兼与Dieterich模型和Coulomb模型的对比

基于大量岩石力学实验,Dieterich和其他研究者(Dieterich,1978;Ruina,1983)首先提出了描述岩石摩擦过程的速率-状态摩擦定律(R-S摩擦定律).如今R-S摩擦定律已成为研究地震成核等地震演化机制的有效手段.Dieterich(1992,1994)最早提出了描述受静态剪应力扰动后断层失稳时间提前或推后的余震触发机制的解析模型.现在Dieterich模型已经成为解释余震随时间衰减规律的Omori定律等地震观测现象的有力工具.与之相对应,广泛使用的Coulomb应力失稳模型也可以给出断层受到静态剪应力扰动后,断层失稳时间的提前和推后量.Dieterich模型和Coulomb应力失稳模型基于不同的物理方法,所以在进行地震危险性评估时,二者均有各自的局限性.本文利用R-S摩擦定律控制的1-D弹簧-滑块模型,模拟计算了理论地震循环以及在不同静态剪切应力扰动下,失稳时间的提前和推后量的变化情况,然后将计算得到的时间提前和推后量分别与Dieterich模型和Coulomb模型的相应计算结果进行了定量化对比和差异性分析,并给出了相应的解释.数值模拟结果显示,对于R-S摩擦定律在参数不变的条件下,断层模型失稳时间的提前和推后量的大小强烈依赖于静态剪应力扰动的大小和作用时间,而且绝对值相同的正、负向静态剪应力扰动造成的失稳时间的提前和推后量的变化情况并不完全一致.在震后松弛/滑移阶段和闭锁阶段,时间提前和推后量是常数,且随静态剪应力扰动绝对值的增大而增大,两者的比值接近于1.0,这与Dieterich模型和Coulomb模型的结果是一致的,相应的差值小于两模型结果的10%.而在自加速阶段,模拟计算结果则存在与Dieterich模型和Coulomb模型结果不同的特征.首先,在自加速阶段模拟计算结果均偏离Coulomb模型,而且时间提前和推后量的比值小于1.0,相异于Coulomb模型的论断.不过当受到正向静态剪应力扰动后,Dieterich模型的结果和模拟计算结果是一致的,最大相差量不超过Dieterich模型结果的7%,可接近0.对于负向静态剪应力扰动,当其绝对值较小时,Dieterich模型的结果很接近模拟计算结果,相差量不超过该结果的14%.但对于绝对值较大的情况,模拟计算结果远大于Dieterich模型的结果,最大可达Dieterich模型结果的35倍,这是由于负向静态剪应力扰动后使得Ω=δ·θ/dc1的条件不再成立,进而使得Dieterich模型不再成立.总的来说,与模拟计算相比Dieterich模型可以很好地描述1-D断层受扰后失稳时间提前和推后量的变化情况,并且可以体现出正、负静态剪切应力扰动后失稳时间提前量和推后量变化的差异性,而Coulomb模型则不能完整地给出受到静态剪应力扰动后断层失稳时间提前或推后的估计值.

Stress triggering" between different rupture events in several earthquakes

Most strong earthquakes have complex rupture processes. As an approximation, each earthquake can be described as two or more subevents of rupture with time interval of several seconds to several days. In order to discuss the relationship between different subevents, we investigated the rupture process of the 1966 Xingtai, the 1976 Tangshan, the 1990 Gonghe and the 1996 Lijiang earthquake by calculating the static Coulomb failure stress changes produced by the first subevent. The calculation of static stress changes produced by fault slip is based on the formulation of Okada (1992). The result suggests that the static Coulomb failure stress changes (ΔCFS) produced by the first subevent have 'triggering' effect on the subsequent subevents which locate in the region where the Coulomb stress change produced by the first event is positive, with the order of magnitude 10-2 [similar to] 10-1 MPa.

Crustal Stress Evolution over the Past 700 Years in North China and Earthquake Occurrence

Fault interaction and earthquake occurrence have attracted much attention in seismological community during recent years. Many studies have shown that the rupture of one fault could encourage or discourage earthquake nucleation on a neighboring fault, depending on the relative geometry of the two faults and the earthquake rupture mechanisms. In this paper, we simulate the evolutionary process of cumulative Coulomb failure stress change （ CCFSC ） in North China since 1303, manifested by secular tectonic stress loading and occurrence of large earthquakes. Secular tectonic stress loading is averaged from crustal strain rates derived from GPS. Fault rupture parameters of historical earthquakes are estimated as follows： the earthquake rupture length and the amount of slip are derived based on their statistical relationships with the earthquake intensity distribution and magnitude, calibrated using parameters of instrumentally measured contemporary earthquakes. The earthquake rake angle is derived based on geologically determined fault orientational parameters and seismically estimated orientation of regional tectonic stresses. Assuming a layered visco-elastic medium, we calculate stress evolution resulting from secular tectonic loading and coseismic and postseismic deformation. On the eve of each large earthquake, the accumulated stress field is projected to the fault surface of that earthquake and the CCFSC is evaluated to assess the triggering effect of CCFSC. Forty-nine earthquakes with M≥6.5 have occurred in North China since 1303. Statistics shows that 39 out of the 48 subsequent events were triggered by positive CCFSC, yielding a triggering rate of 81.3%. If we use the accumulative stress field to evaluate the CCFSC for the M ≥ 5.0 earthquakes that occurred in North China since 1303, we find that 75.5% of those events were triggered. The triggering rate for the M ≥ 5.0 earthquakes after the 1976 Ninghe earthquake is up to 82.1%. The triggering rates can be higher if corrections are made for some aftershocks which were wrongly identified as occurring in stress shadow zones because of errors in parameter estimates of historical earthquakes. Our study shows a very high correlation between positive CCFSC and earthquake occurrences. Relatively high CCFSC in North China at present is concentrated around the Bohai Sea, the west segment of the Northern Qinling fault, the western end of the Zhangjiakou-Bohai Sea seismic zone, and the shiyuan basin, Shanxi graben, suggesting relatively higher earthquake potential in these areas.

Research on seismic stress triggering

This paper briefly reviews basic theory of seismic stress triggering. Recent development on seismic stress triggering has been reviewed in the views of seismic static and dynamic stress triggering, application of viscoelastic model in seismic stress triggering, the relation between earthquake triggering and volcanic eruption or explosion, other explanation of earthquake triggering, etc. And some suggestions for further study on seismic stress triggering in near future are given.

Study on Stress Triggering During the Activity Process of the Jiashi Strong Earthquake Swarm

The Bachu-Jiashi earthquake of MS6.8 occurred on February 24,2003,about 20km from the southeast of the 1997～1998 Jiashi seismic region in Xinjiang,and its aftershocks are rich and strong.Did the 1997～1998 Jiashi strong earthquake swarm trigger the Bachu-Jiashi MS6.8 earthquake? The Atushi earthquake of MS6.7 occurred in 1996,and the 1997～1998 Jiashi strong earthquake swarm occurred about 70km from the Atushi earthquake 10 months later.Did the Atushi earthquake of M-S6.7 encourage the 1997～1998 Jiashi strong earthquake swarm? There were 9 earthquakes with M-S6.0 from 1996 to 1997 in the Jiashi seismic region,how did they act on each other? To answer the above questions,the article studies the triggering effect of the activity process of the whole Jiashi earthquake swarm from the 1996 Atushi earthquake of M-S6.7,the 1997～1998 Jiashi strong swarm to the 2003 Bachu-Jiashi earthquake of M-S6.8,and analyzes the seismicity characteristics around the Jiashi region.The results show that the 1996 Atushi earthquake of M-S6.7 encouraged the 1997～1998 Jiashi strong swarm to some extent,the accumulative Coulomb stress change from the previous M-6.0 earthquakes of the Jiashi strong swarm had certain triggering effects on the following M-6.0 events,and the Coulomb stress change converted from the Jiashi strong swarm strongly encouraged the 2003 Bachu-Jiashi earthquake with M-S6.8.

2022年墨西哥米却肯州7.6级地震序列的触发关系及发震动力学探讨

2022年9月19日墨西哥米却肯州发生M_(W)7.6地震,该地震位于北美板块与科科斯板块交汇处。为进一步研究本次地震对周围断层和后续地震的影响,剖析该地震的孕震背景和发生条件,首先使用包括USGS在内的多个国外地震机构得到的墨西哥M_(W)7.6地震以及后续的两次M_(W)>5.0地震的震源机制解,分别计算出震源机制中心解,然后通过计算主震产生库伦破裂应力变化来研究本次地震对后续两次地震的触发作用,最后收集了1976年1月1日至2022年5月31日发生在本次地震附近的M_(W)≥4.9的29条震源机制解数据,反演该地区的构造应力场,并模拟在局部构造及其作用下产生的各种断层形状及相对正应力和剪应力的分布情况。研究结果表明:①震源机制中心解表明主震和6.8级余震为逆冲型地震,而5.8级余震的震源机制为正断型地震;②本次地震对5.8级和6.8级余震的库伦破裂力变化均超过0.01MPa的阈值,表明这两次强余震可能是在主震的触发下发生的;③震源区应力场的主压应力轴为NNE-SSW向,主张应力轴近乎垂直。本地震序列的断层破裂近乎沿应力场的最大剪应力平面发生,最大限度地释放了构造运动积累的应力。

Finite element simulation of deformation and stress changes of Kalpin-Kemin fault system in the Southwest Tianshan Orogenic Belt

Under the shadow of the far-field effect of the India-Eurasia collision,the Tianshan orogenic belt underwent tectonic re-activation in the Cenozoic,accompanied by strong tectonic deformation and frequent large earthquakes.Bounded by two rigid cratonic blocks located in its north and south,a series of marginal foreland fold-and-thrust belts are developed within the Tianshan orogenic belt and continue to develop to the bilateral pull-apart basins.Meanwhile,the faults in the orogenic belt are reactivated.The deformation caused by thrust-related structure accounts for larger than 50%of the total convergence of the Tianshan Mountains,which results in the most active structure with large earthquakes in the Tianshan area.Therefore,it is of great significance to study the dynamic process of the newly generated and reactivated thrust-nappe structures in Tianshan orogen via numerical modeling.This paper selects a classical cross-section profile in the western segment of the Southwest Tianshan Mountains,which contains the Kalpin-Maidan-Nalati-Kemin fault system from the south to the north.We attempt to establish a two-dimensional plane strain,viscoelastic finite element model,by treating the regional faults as a whole fault system and considering the topography,fault geometry,and GPS data.The displacement and stress fields of the model are retrieved,the short-term cumulative deformation field of the overall fault system is analyzed,and the rate of Coulomb failure stress change of each fault is also considered.The results show that the deformation is concentrated in the middle and southern parts of the Southwest Tianshan Mountains.In contrast,the deformation of the Kemin fault in the north is relatively small.According to the Coulomb failure stress changes of these four faults and the historical earthquake catalog,the potential seismicity of each fault is qualitatively analyzed.Our preliminary results suggest that the possibility of large earthquake occurrence is higher in the Kalpin fault,Maidan fault,and Nalati fault but lower in the Kemin fault in the near future。

地震应力触发研究

介绍地震应力触发基本理论.从地震静态和动态应力触发、粘弹性模型在地震应力触发中的应用、火山喷发或爆炸与地震触发及地震触发的其它解释等几个方面,综述近年来地震应力触发的研究进展,并对地震应力触发研究近期的发展进行展望.

鲜水河断裂带库仑应力演化与强震间关系

以鲜水河断裂带为研究区,首先验证了该断裂带上1893年以来M6.7以上地震的相互触发作用,然后采用更符合实际的分层黏弹介质模型研究强震震后黏滞松弛引起的库仑应力变化对后续地震的影响,并基于负位错理论计算鲜水河断裂带10个断层段的震间长期构造加载作用引起的断层上的应力积累.在此基础上,讨论同震、震后、震间效应引起的累积库仑应力变化与区域强震活动的关系,给出断层上库仑应力随时间的演化.结果表明,鲜水河断裂带上1893年以来发生的7次强震均在其前面一系列强震及构造应力加载的驱使下发生,同震、震后、震间三方面效应均引起了鲜水河断裂带不可忽略的库仑应力变化.对断层上的库仑应力状态的研究,可进一步为揭示地震的发生规律、找寻危险断层段提供线索.

华北地区700年来地壳应力场演化与地震的关系研究

目前地震断层相互作用问题已引起地震学家的广泛关注。许多研究表明一条断层的破裂可以影响附近其他断层趋于破裂的进程 ,两条断层间的确切作用取决于它们的相对位置、破裂机制、错动量和介质力学性质。本研究给出了华北地区 70 0年来由于长期构造加载及地震断层错动导致的累积库仑破裂应力变化 (ΔCCFS)的演化过程。长期构造加载场由GPS观测得到的地壳平均应变率场给出。关于历史地震断层破裂参数的估算 ,根据的是华北地区有现代仪器记录的大震资料归算地震烈度与断层破裂长度、震级和地震矩的统计关系 ;根据地质调查得到的地震断层走向、倾角以及本地区的构造应力场方向估计滑动角。考虑粘弹性成层介质地壳模型 ,计算长期构造加载和地震形变 (同震及震后介质粘弹性驰豫变形 )造成的累积应力场变化。将累积应力场变化投影到后续地震断层面和滑动方向上得到ΔCCFS ,并研究其对后续地震发生的触发作用。对 130 3年以来华北地区发生的 4 9个M≥ 6 5地震研究结果表明 :ΔCCFS对 4 8个后续地震中的 38个有触发作用 ,触发率达到 79 2 %。应用当今累积应力场变化于华北地区 130 3年～ 2 0 0 3年发生的M≥ 5地震 ,我们发现触发率达到 75 5 % ,于 1976年以来发生的M≥ 5地震触发率达 82 1%。

完全库仑破裂应力变化与云南龙陵震群序列的应力触发

计算和研究了1976年云南龙陵Ms7.3、Ms7.4双主震产生的完全库仑破裂应力变化及其对后续震群序列的动态和静态应力触发作用.结果显示,龙陵第2主震受到了第1主震的动态和静态库仑破裂应力的触发作用.龙陵双主震的13个后续强余震中,发生在龙陵三角形块体内部的强余震,90%都受到了第1或第2主震的动态库仑破裂应力触发或静态库仑破裂应力触发作用,发生在三角形块体外部的强余震,2/3受到了第2主震的动态库仑破裂应力触发作用.从触发作用的强度和范围上看,第2主震的动态和静态库仑破裂应力触发作用都大于第1主震.就近场而言,受到龙陵双主震的动态和静态库仑破裂应力触发作用的余震数目相当,但动态库仑破裂应力的触发作用范围大于静态库仑破裂应力.

汶川M_S8.0巨震产生的完全库仑破裂应力变化及其强余震群

计算和研究了2008年5月12日四川汶川MS8.0巨震在其强余震断层面上产生的完全库仑破裂应力变化,分析了该变化对强余震的动态和静态应力触发作用。结果显示,汶川主震后15天内发生的7次MW≥5.5强余震均受到了动态和静态库仑破裂应力的综合触发作用。

汶川M_S 8.0地震库仑破裂应力变化及断层危险性初步研究

利用四川省汶川MS8.0地震的震源机制解及滑动分布模型,反演了由汶川地震造成的同震库仑破裂应力变化;从余震效应与断层相互作用的角度对库仑破裂应力变化进行了分析。结果显示:基于滑动分布模型反演的库仑破裂应力变化能较好地反映与余震分布的对应关系,以最大余震断层面参数(走向/倾角/滑动角:204°/56°/98°)为接收断层,反演结果最佳,83%M>4的余震均发生于库仑应力增加约0.01MPa的区域;库仑破裂应力变化的主要特征为断层北盘大部分区域为库仑破裂应力下降区,断层南盘主要为增加区,断层两端均显示库仑破裂应力变化增加,且分别沿NE和SW两个方向发展。最后,基于活断层分布模型,计算由此次地震造成的已存断层面上的库仑破裂应力变化,结果显示多条左旋走滑断裂库仑破裂应力变化值增加。

南北地震带北部5次(1561～1920年)M≥7级地震触发关系研究

以南北地震带北部的青藏高原东北边缘与华北构造区过渡部位为例,通过建立地震构造模型,计算静态库仑破裂应力改变量（ΔCFS）,研究了该区1561-1920年360年间5次M≥7级地震之间的触发过程.结果表明,在1561年罗山东麓71/4级地震之后,下一次地震无一例外地发生在前面地震产生的应力触发区（ΔCFS〉0）.在4条被触发的发震断裂中,有3条发震断裂的平均ΔCFS〉0.2×10^5Pa,最大可达0.62×10^5Pa,超出目前普遍认为触发应力阀值（0.1×10^5Pa）.根据断裂库仑破裂应力变化量（ΔCFS）和构造应力累计率（δτ）,计算获得了下一次地震发生的提前量（ΔT）,地震活动提前量最大可以达到160a.在一条重要活动构造带或地区上,一次地震发生对下一次地震的触发缩短了地震重复发生所需要的累积时间,使得地震可以提前发生,这一方面使得某一特定的发震断裂在时间尺度表现出准周期性,另一方面使得空间上不同发震断裂的地震活动表现出丛集发生的现象.此项研究有助于认识断裂间相互作用特点、揭示地震丛集发生规律以及预测未来地震危险区.