1997年伽师强震群活动的近场定点形变异常特征

对１９９７年伽师强震群前后的近场宁点形变资料和卡尔曼滤波结果的前兆异常进行了分析,结果表明,震前短临异常较为明显。通过密切跟踪,在后续强震的预报中发挥了重要作用。文中还对异常与孕震构造和应力场的关系进行了讨论。     

1997年新疆伽师强震群发展过程中发震断层间相互作用的影响

1997年发生在新疆伽师的强震群迄今仍在持续活动，从1997年1月21日震群发生至1997年10月18日，共发生5级以上地震15次.震群发生前，该地区几乎没有地震活动.根据伽师震群地震的精确定位结果及震源机制解，我们设定该震群的发震构造是一组NNW（北北西）向的雁形右旋走滑断层和一组NE（北东）向雁形正倾滑断层.并以此作为模拟该区域理论地震活动的力学模型，开展震群区域理论地震活动的模拟研究.模拟结果证实了断层间的相互作用或应力传递能产生震群活动的猜测，并对伽师震群中为何部分地震的震源机制是正断层进行了合理解释.进一步推测伽师位于地壳厚度的陡变带也可能是引起该地区地震活动丛集发生的原因.     

伽师强震群震源机制与区域应力场特征

利用所搜集新疆地震台网各种短周期Pg 和Pn 波初动方向资料和中国数字地震台网(CDSN)、全球数字地震台网(GDSN)及中亚地区部分资料,计算了新疆阿图什1996年6. 9级和1998年6. 0级地震、伽师1997~ 1998年6次强震,以及M_S≥ 4. 0中小地震震源机制解48个。结合伽师强震群地震时空分布、地震烈度,对该区域应力场进行了探讨。结果表明,该区域应力场主压应力方向为SW-NE向。     

利用尾波包络线反演方法研究伽师强震群区地壳的非均匀结构

以单次散射模型、球形辐射源、一维线性速度模型为基础计算理论包络线,通过尾波归一化方法把理论与观测包络线结合起来形成非线性方程组,用迭代最小二乘方法反演伽师强震群区的散射系数空间分布.结果表明,伽师强震群区下方中上地壳中存在明显的非均匀结构.在10~25 km各深度图像上,研究区中部都存在一低散射系数区,这个低散射系数区在10 km、15 km深度被高散射系数区包围,在20 km深度仅其东侧存在高散射系数区.1997年的7次M_s≥6.0级地震发生在研究区中部的低散射系数区内或低散射系数区向高散射系数区过渡带的低散射系数一侧.     

Fracture characteristics of the 1997 Jiashi, Xinjiang, China, earthquake swarm inferred from source spectra

Broadband P and S waves source spectra of 12 MS5.0 earthquakes of the 1997 Jiashi, Xinjiang, China, earthquake swarm recorded at 13 GDSN stations have been analyzed. Rupture size and static stress drop of these earthquakes have been estimated through measuring the corner frequency of the source spectra. Direction of rupture propagation of the earthquake faulting has also been inferred from the azimuthal variation of the corner frequency. The main results are as follows: ①The rupture size of MS6.0 strong earthquakes is in the range of 10～20 km, while that of MS=5.0～5.5 earthquakes is 6～10 km.② The static stress drop of the swarm earthquakes is rather low, being of the order of 0.1 MPa. This implies that the deformation release rate in the source region may be low. ③ Stress drop of the earthquakes appears to be proportional to their seismic moment, and also to be dependent on their focal mechanism. The stress drop of normal faulting earthquakes is usually lower than that of strike-slip type earthquakes. ④ For each MS6.0 earthquake there exists an apparent azimuthal variation of the corner frequencies. Azimuthally variation pattern of corner frequencies of different earthquakes shows that the source rupture pattern of the Jiashi earthquake swarm is complex and no uniform rupture expanding direction exists.     

Basement interface structural characteristics beneath Jiashi strong earthquake swarm area in Xinjiang, China

The seismic data obtained from high resolution seismic refraction profile in Jiashi strong earthquake swarm area in Xinjiang, China were further processed with ray hit analysis method and more complete basement interface struc-tural characteristics beneath Jiashi strong earthquake swarm area were determined. The results show that there are two clear basement interfaces at the upper crust in Jiashi strong earthquake swarm area. The first one with buried depth ranging from 2.6 km to 3.3 km presents integral and continuous structure, and it appears an inclined plane interface and smoothly rises up toward Tianshan Mountain. The second basement interface with buried depth from 8.5 km to 11.8 km, is the antiquated crystalline basement of Tarim basin. Near the post number of 37 km, the bur-ied depth of the crystalline basement changed abruptly by 2.5 km, which maybe result from an ultra crystalline basement fault. If taking this fault as a boundary, the crystalline basement could be divided into two parts, i.e. the southwestern segment with buried depth about 11.5 km, and the northeastern segment with buried depth approxi-mately from 8.5 km to 9.0 km. That is to say, in each segment, the buried depth changes not too much. The north-east segment rises up as a whole and upheaves slightly from southwest to northeast, which reflects the upper crustal deformation characteristics under the special tectonic background at the northwestern edge of Tarim basin.     

A priliminary study on the sequence characteristics and focal mechanism solution of the Jiashi strong earthquake swarm

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Tomographic determination of the upper crustal structure in the Jiashi strong earthquake swarm region

IntroductionBetween January and April of 1997, 7 earthquakes with M(6.0 occurred successively in Jiashi, Xinjiang. The continual occurrence of strong earthquakes within such a small area and in such a short period of time is exceptional for intraplate earthquakes. The Jiashi earthquake swarm took place on the northeast side of the Pamirs, where the Tarim basin, South Tianshan and West Karakoram meet (HU, et al, 1989). This is also a place where a number of active faults develop, so it is…     

Stress interactions between normal faults and adjacent strike-slip faults of 1997 Jiashi earthquake swarm

During a 4-month period starting from 21 January, 1997, an earthquake swarm of seven major events (Ms≥6.0) struck the Jiashi region at the northwestern corner of the Tarim Basin in Xinjiang,, China. Previous relocation studies suggested that these strong earthquakes had occurred along at least two parallel rupture zones. According to the relocated hypocenters and focal mechanisms of the events, we have constructed fault models for these seven earthquakes to calculate the Coulomb stress changes produced by each of these events. Furthermore, we extended our model calculations to include an ad- jacent 1996 Ms=6.9 Artushi earthquake, which occurred one year before the Jiashi earthquake swarm. Our calculations show that the Coulomb stress change caused by the preceding events was around 0.05 MPa at the hypocenter of the 4th event, and higher than 0.08 MPa at the hypocenters of the 2nd, 3rd, 5th and 6th events. Our results reveal a Coulomb stress interactive cycle of earthquake triggering between two adjacent normal and strike-slip faults.     

伽师强震群区震源细结构的深地震反射探测研究

穿过伽师强震群的深地震反射剖面提供了研究区从地表直至莫霍界面的地壳细结构图像.探测结果表明：研究区上、下地壳分界面埋深约20～30 km,莫霍界面埋深约52～58 km.上地壳内部存在着两种截然不同的反射图像.上地壳上部为沉积盖层,厚度约8～9 km,盖层内部反射成层分布,显示了稳定而连续的沉积特点;上地壳下部则为“反射透明”背景下存在的叠层状反射带.下地壳内部呈现明显的反射性质,具体体现在上、下地壳分界面和莫霍间断面都表现为具有一定持续时间的多循环反射叠层结构特征.时间剖面上所有反射事件由北东向南西下倾的整体图像直观地反映了塔里木盆地地壳变形而向西昆仑下插入的事实.剖面47km桩号附近,上地壳下部至壳幔过渡带以上地壳范围内存在一条高倾角的深断裂,具有走滑性质,本研究认为该深断裂与1997年伽师强震群的发生密切相关,推断它为伽师强震群的发震构造.而时间剖面上壳幔过渡带反射的连续性则说明该断裂没有向下穿过莫霍面.存在于上地壳上部的两条高倾角的浅部断层可能对应于地质推测的麦盖提—下苏洪断裂带,它们与位于其下方的地壳深断裂构成了伽师强震群可能的深、浅构造关系.     

利用2018年伽师小震群强震动记录分析区域场地特征

2018年9月伽师地区发生震群事件,连续发生18次M3.0地震,最大震级M 5.5,获取大量强震动记录,初步分析此次震群强震动记录特征、记录峰值比、场地地震反应,结果发现:加速度记录峰值在震中距30 km范围内衰减较快,震中距30—100 km范围内衰减平缓;强震动加速度记录峰值水平向与垂直向比值为1—3,均值约1.5;场地共振频率为0.48—1.56 Hz,平均放大倍数为8.4—9.5。     

Fine upper crustal structure of Jiashi strong earthquake swarm region in Xinjiang inferred from high resolution seismic refraction profile data

Introduction Jiashi-Artux area in southwest Xinjiang is one of the most active earthquake provinces at pre-sent in Chinese mainland. In the last century, about 3/4 strong earthquakes in Chinese mainland hit this area, and especially from January 21 to April 16 in 1997, 7 earthquakes with the magnituderanging from 6.0 to 6.9 occurred in a very small area of 9 km×18 km near Jiashi (ZHU et al, 1998). It has never taken place before in Chinese mainland that a series of strong earthquakes shoo…     

1997-1998年伽师强震群震源区应力场特征

利用1997-1998年伽师强震群中强地震震源机制系统聚类及震源区应力场反演,得到以下主要结果:(1)伽师强震群中强地震主要以走滑和正断层为主,伽师震源区主压应力方向为NNE或近NS向,与相邻的柯坪块体区域构造应力场方向不一致;伽师强震群的破裂面沿NEE方向,属左旋破裂;(2)4~5级中强地震应力场反演得到最大主压应力轴为NNE向,最小主压应力轴为NWW向,中等主应力轴倾角为65°,比较直立;(3)伽师强震群震源区应力场在强震前后经历了一系列变化。最后对所得结果进行了一定的讨论。     

伽师强震群活动过程的应力触发作用研究

2003年2月24日位于1997~1998年伽师震区东南约20km的新疆巴楚-伽师地区发生了MS6·8地震,其余震丰富、强度大。1997~1998年伽师强震群的发生是否会对2003年巴楚-伽师MS6·8地震产生触发作用?1996年阿图什发生MS6·7地震,时隔10个月距其70km处又发生了伽师强震群,1996年阿图什地震的发生是否有利于1997~1998年伽师强震群的发生?1997~1998年伽师震区接连发生9次6级以上地震,伽师强震群中各强震之间会产生怎样的影响?针对上述问题,本文结合伽师周围地区地震活动特征分析研究了自1996年阿图什MS6·7地震及1997~1998年伽师强震群至2003年巴楚-伽师MS6·8地震在整个伽师强震群活动过程中的应力触发作用。研究结果表明:1996年阿图什MS6·7地震在一定程度上有利于1997~1998年伽师强震群的发生;伽师强震群中先发生的6级地震产生的累加静态库仑破裂应力变化对后续6级地震有一定触发作用;1997~1998年伽师强震群折合为1次地震产生的静态库仑破裂应力变化表明,其对2003年巴楚-伽师MS6·8地震触发作用明显。     

1997年新疆伽师强震群序列活动特征

以１９９７年伽师强群序列基础资料,分析了其频度衰减特征,ｈ值动态演化,强震群动态发生过程以及序列各参数的动态演变与强,余震发生的关系,最后给出伽强震群中长,中,短和临震预报的新思路,同时讨论了实施强震群动态跟踪临震预报的可能性。     

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 Ms6.7 encourage the 1997 - 1998 Jiashi strong earthquake swarm？ There were 9 earthquakes with Ms6.0 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 Ms6.7, the 1997 - 1998 Jiashi strong swarm to the 2003 Bachu-Jiashi earthquake of Ms6.8, and analyzes the seismicity characteristics around the Jiashi region. The results show that the 1996 Atushi earthquake of Ms6.7 encouraged the 1997 - 1998 Jiashi strong swarm to some extent, the accumulative Coulomb stress change from the previous M6.0 earthquakes of the Jiashi strong swarm had certain triggering effects on the following M6.0 events, and the Coulomb stress change converted from the Jiashi strong swarm strongly encouraged the 2003 Bachu-Jiashi earthquake with Ms6.8.     

The shock event of October 6, 1597 is a strong deep earthquake

A special earth shock event was recorded at 22 counties of the 7 provinces of eastern China on October 6, 1597, and 2 volcanic eruptions and seismic activities were recorded in Sanshui county, Xianjingbeidao, Korea at that day and the 3rd day. Because of the large range of this shock, low intensity, slow attenuation and no extreme-earthquake area, its epicenter and focus could not be determined onthe scientific-technological conditions at that time. In the Seismological Catalogue of China (GU, 1983) published in 1983, its epicenter was determined to be in the Bo Sea (38.5°N, 120.0°E), its magnitude was 7; and it was changed into 7.5 in the later Seismological Catalogue of Beijing; someone estimated it over 7(HUAN, 1989); someone thought that, it was a very large earthquake, might be a extraordinarily serious large one according to the scale of sensational range, reaching 8 (SHI, et al, 1985). The authors think that, the disputes on its magnitude and epicenter, and on deep or shallow earthquake show the complicities of this problem; further discussions about it will be helpful to the study on the seismic activity of the northern China area.     

伽师强震系列应力场的转向过程

自1997～2003年,新疆伽师地区相继发生多次强震. 取哈佛大学公布的伽师强震系列CMT(矩心矩张量解)解资料,由滑动矢量拟合法反演区域应力场. ＣＭＴ解的系统聚类分析表现出3个阶段的时序特征. 分析震源区应力场发现,1997年3月1日至2003年1月4日期间新疆伽师地区的应力场发生变化,2003年2月24日起,又恢复到基本应力场的方向,从而完成从基本应力场－变化应力场－基本应力场一次完整变动过程. 结合区域受力状况和构造背景,讨论了新疆伽师强震系列应力场变化的成因,并且认为伽师强震系列具有体破裂的特征.     

伽师强震群与加兹里强震群对比研究

对比研究了新疆伽师强震群与乌兹别克斯坦加兹里强震群,发现两者不但在分段上极为相似,而且随时间的发展在能量释放的分配形式上也极为相似,且余震都呈共轭分布,主要地震迁移呈多侧扩展型,强震群序列中各次主要地震的发生表现出一定的的继承性特征,强震前中小地震出现平静。从频度及强度上看,两次强震群第一组强震发生后余震频度及强度较低,第二组强震发生后余震频度及强度较高,第三组强震发生后余震频度及强度最高。     

2013年10月吉林省前郭强震群研究

从2013年10月31日开始,不到一个月的时间吉林省前郭县就发生了5次5级以上地震,最大地震为11月23日的Ms5．8地震。根据震源机制解、余震序列特征、震中区地质构造特点以及历史地震情况,对这次强震群的发震条件进行探讨。认为震源区位于松辽盆地中部滑脱面上部的推覆构造系内,我国东北块体应力应变状态受2011年日本9级巨震影响,应力使滑脱面上部的隐伏铲形断层面组发生错动,从而发生这次隅露群．