The Minxian-Zhangxian M6.6 earthquake,with a focal depth of 20 km,occurred at the boundary of Minxian and Zhangxian counties （34.5°N,104.2°E）,Dingxi city,Gansu Province,at 7：45 CST on July 22,2013.By 8：00 on July 29,1034 aftershocks occurred.Among them,nine above M3.0 include one M5.0～5.9,one M4.0～4.9,and seven M3.0～3.9 earthquakes.The strongest aftershock,which occurred at 9：12 on the date of the mainshock,attained MS5.6.Catastrophic damages caused by this earthquake are mainly attributed to poor residential structures erected by the government during a weak economy.The affected area was more than 10 000 km2 and involved in 6 cities and 13 counties ineluding Dingxi,Baiyin,Tianshui,Longnan,and Gannan Zang and Linxia Hui autonomous prefectures.Residents in Baoji,Hanzhong,Xianyang,Xi＇ an,Chengdu,and Mianyang felt this earthquake.The earthquake occurred at southeastern region of Gansu province,which is covered by very thick loess layer and exhibits complex topography such as steep,highly sloped mountains and crisscrossed ravines.It killed 95 people and injured 1 366.Secondary disasters caused by this earthquake include loess landslides,collapses,and pitfalls.Immediately following the earthquake,the China Earthquake Administration quickly organized field survey teams for seismicity monitoring,intensity studies,earthquake damage assessment,and scientific research,through which the first intensity distribution map of the Minxian-Zhangxian M6.6 earthquake was developed for conditions at 14：00 on July 24.The macroscopic epicenter of this earthquake,with an intensity of Ⅷ degrees,was located at Yongguang and Yongxing villages of Meichuan and Lalu Village of Hetuo.The long axes of intensity circled with an NW strike,in accordance with regional structures.This study discusses the basic parameters of this earthquake such as basic intensity distribution,damage features and seismogenic structure.This earthquake occurred at the eastern margin of the Qinghai-Tibetan Plateau at the intersection of the N-S seismic zone and the Kunlun-Qinling fault zone,which is the tectonic transformation zone between the NWW east-striking Kunlun fault and the northern margin of the western Qinling fault zone.We determined that the Hetuo fault,active since the late Pleistocene,passes through the extreme seismic area.Surface rupture phenomena such as landslides,ground fissures,earthquake pitfalls,sandblasting,and water oozing all exhibited zonal distribution along the Hetuo fault.The focal mechanism of this earthquake is consistent with the Hetuo fault.The strike of the nodal plane Ⅱ is 320° and 301.3°,as reported respectively by the Institute of Geophysics and the Institute of Geology,China Earthquake Administration,which also corresponds to the strike of the Hetuo fault.Moreover,the NE-dipping slip plane reported by the two agencies,51° and 57.3°,respectively,corresponds with the dipping direction of the Hetuo fault.Further,we determined that the Anjia Shan landslide slips laterally along a fault valley striking NW that resembles a long tongue with length and width of 310 m and 30～35 m,respectively.The plunge angel of fault striations on the slip plane is 12°～23°,and the main slip plane corresponds with the fault strike.Therefore,the Hetuo fault is seismogenic fault of the Minxian-Zhangxian M6.6 earthquake,which is a secondary fault,belongs to the Lintan-Tanchang fault zone.Three strong earthquakes above M6.0 have occurred near the epicenter of the Minxian-Zhangxian M6.6 earthquake on the Lintan fault,and two moderate earthquakes have occurred at this site in recent years,which include the Minxian M5.2 on November 13,2003,and the Minxian-Zhuoni M5.0 on September 7,2004.This earthquake represents the most recent activities of the Lintan-Tanchang fault zone.

2013年7月22日7时45分,在甘肃省定西市岷县和漳县交界（34.5°N,104.2°E）发生了一次MS6.6地震,震源深度20 km.截至7月29日8时,甘肃岷县、漳县MS6.6地震共记录到余震1 034次,其中3.0级以上余震9次,包括5.0～5.9级1次,4.0～4.9级1次,3.0～3.9级7次.其中最大余震为发生在7月22日9时12分的MS5.6地震.地震造成95人死亡,1 366人受伤.震区地处青藏高原与西秦岭陇南山地接壤区,黄土覆盖较厚,地形起伏较大,山坡陡峭,沟壑纵横,地震引发了黄土滑坡、崩塌和塌陷等次生灾害.另外,震区经济发展较为落后,房屋结构差,土木结构房屋所占比例较高,抗震性能差,是这破坏较重的主要原因.受灾范围涉及定西市、白银市、天水市、陇南市、甘南藏族自治州和临夏回族自治州等6个市（州）13个县,面积约1万多km2.甘肃天水、兰州、陇南、白银,陕西的宝鸡、汉中、咸阳、西安及四川成都、绵阳等地都有震感.地震发生后,中国地震局迅速组织地震现场考察队赶赴灾区,进行震情监测、烈度评定、震害损失评估和科学考察等工作,并于7月24日14时发布了甘肃岷县漳县6.6级地震烈度图.本次地震宏观震中位于岷县梅川镇永光、永星村和禾驮乡的拉路村一带,极震区烈度为Ⅷ度.烈度长轴走向为北西向,与区域构造线相一致.本文归纳总结了岷县、漳县MS6.6地震的基本参数、烈度分布、震害特征和发震构造背景等基本特征.本次地震发生在青藏高原东缘的甘东南地区,该区是南北地震带与昆仑山—秦岭断裂带等活动构造交汇部分部位,也是北西西向的东昆仑断裂与西秦岭北缘断裂之间的构造转换区.地震发生在靠近临潭—宕昌断裂一侧.通过野外地质调查,发现通过极震区有一条断层,即禾驮乡断层为活动断层,为晚更新世活动断层.包括滑坡、地裂缝、地震陷坑和喷沙冒水等地表破坏现象沿断层成带状分布.在震源机制解方面,且震源机制解也与该断层相吻合.中国地震局地球物理研究所给出节面Ⅱ走向为320°,与禾驮乡断层相一致.中国地震局地质研究所给出的是301.3°,也基本与其吻合.两个单位所给出的滑动面倾向为51°和57.3°,皆为向北东倾,与禾驮乡断层倾向也相一致.另外发现安家山滑坡长约310m,宽约30 ～ 35 m,沿断层谷地呈长舌形向北西做水平滑动,滑动面上擦痕侧俯角为12°～23°,主滑动面走向与断层走向相一致.说明禾驮乡断层为此次地震的发震断层,该断层属于区域上临潭—宕昌断裂的次级断层,该断裂历史上在本区内曾发生过3次6级以上强震,近期又发生过2003年11月13日岷县5.2级地震和2004年9月7日岷县—卓尼5.0级地震.此次地震是临潭—宕昌断裂进一步活动的结果.

On July 4, 2006, a magnitude 5.1 earthquake occurred at Wen′an, ~100 km south of Beijing, which was felt in Beijing metropolitan area. To better understand the regional tectonics, we have inverted local and teleseismic broadband waveform data to determine the focal mechanism of this earthquake. We selected waveform data of 9 stations from the recently installed Beijing metropolitan digital Seismic Network (BSN). These stations are located within 600 km and cover a good azimuthal range to the earthquake. To better fit the lower amplitude P waveform, we employed two different weights for the P wave and surface wave arrivals, respectively. A grid search method was employed to find the strike, dip and slip of the earthquake that best fit the three-component records of P and surface waveforms recorded (the tangential component of the P-wave arrivals was not used). Synthetic waveforms were computed with an F-K method. Two crustal velocity models were used in the synthetic calculation to reflect a rapid east-west transition in crustal structure observed by seismic and geological studies in the study area. The 3D grid search results in reasonable constraints on the fault geometry and the slip vector with a less well determined focal depth. As such we combined teleseismic waveform data from 8 stations of the Global Seismic Network in a joint inversion. Clearly identifiable depth phases (pP, sP) recorded by the teleseismic stations obviously provided a better constraint on the resulting source depth. The results from the joint inversion indicate that the Wen′an earthquake is mainly a right-lateral strike slip event (-150°) which occurred on a near vertical (dip, ~80°) NNE trending (210°) fault. The estimated focal depth is 14~15 km, and the moment magnitude is 5.1. The estimated fault geometry here agrees well with aftershock distribution and is consistent with the major fault systems in the area which were developed under a NNE-SSW oriented compressional stress field.

2006年7月4日，在距离北京100 km左右的文安地区，发生了 M w =5.1级地震，引起了北京地区的强烈震感.为了更好的认识区域构造，我们利用近震及远震波形反演的方法得到了此次文安地震的震源机制.选择了北京数字地震台网的9个地震台，震中距小于600 km，台站的方位角覆盖较好.为了更好地利用信号相对较弱的P波信号，对于一个地震记录，本文分别截取出P波和面波两个部分，分别给予不同的权重进行反演，结合格点搜索的方法，得到了与记录P波及面波三分量对应较好的地震的方位角、倾角和滑移角.同时考虑到北京西北地区地壳较厚，本文在利用 F-K 方法计算近震理论波形的时候，对不同的方位角，采用了不同的地壳速度模型.随后结合远震信号中的直达P、pP、sP波形得到了分辨率较高的地震震源深度.反演结果表明，此次文安地震是一个较为典型的走滑型地震，方位角为210°，倾角80°，滑移角-150°，地震的深度为14~15 km，地震的震级为( M w =5.1).反演结果与断层的几何分布、余震分布及北京地区北北东向应力场有很好的一致性.

Based on digital seismic waveform records of 10 regional broadband stations in Northeastern China and using the generalized "Cut and Paste" (gCAP) method, we obtained full moment tensors of the deep earthquakes occurred on February 10, 2010 and May 10, 2011 near the China-Russia border. In comparison with moment tensor results provided by international agencies for global earthquakes, our results for the 2011 deep earthquake confirmed the Global Centroid-Moment-Tensor (gCMT) result, i.e., it has a significant non-double couple component. This study shows that the gCAP method works very well for obtaining reliable focal mechanisms of deep earthquakes. We also determined the regional stress regime using 23 gCMT solutions of deep earthquakes between 1977 and 2010 within our study area by the Linear Stress Inversion with Bootstrapping resampling method. The regional stress shows that the anomalous non-double couple source component of the 2011 deep earthquake was caused by the dynamic effect of the Japan subduction zone in response to the tectonic stress adjustment after the 11 March 2011 M-w 9. 0 Tohoku-oki earthquake.

本研究利用中国区域宽频地震台的波形数据,应用gCAP (generalized Cut And Paste)方法反演了2010年2月18日和2011年5月10日中国东北中俄边界附近发生的两个深震的矩张量解,与全球地震矩张量测定机构的结果对比分析,证实了2011年5月深震具有显著的补偿线性单力偶矢量(CLVD)成分,表明基于区域波形资料的gCAP反演可获得较可靠的深震震源机制结果.结合研究区1977—2010年的深震震源机制数据反演确定的日本俯冲带前缘的区域应力场方向,分析认为2011年5月深震的非同寻常震源机制,可能是由于日本东北近海 M w 9.0地震造成南东东向拉张应力的变化而造成的,属于日本俯冲带动力作用过程中的响应活动.

On 22 Nov. 2014, an M 6.3 earthquake hit Kangding County in Sichuan Province, southwestern China. 3 days later, another M 5.8 earthquake occurred in the same region, about 10 km southeastwards from the epicenter of the M 6.3 mainshock. Both earthquakes were on the NW-striking Xianshuihe fault zone where no M ≥6.0 earthquakes were reported after the 1982 M 6.0 Ga nz i event. From the relocated aftershock distribution and focal mechanism solutions, we aim to analyze the seismogenic structure of the 2014 M 6.3 Kangding earthquake sequence. Along with the analysis on the characteristics of the strong earthquake ruptures and the spatial distribution of the relocated small earthquakes, we will further discuss the future strong-earthquake risk between Daofu and Kangding on the central segment of the Xianshuihe fault zone.Based on the digital waveform data from China National Seismic Network and Sichuan Regional Network, the Kangding earthquake sequence was relocated by a multi-step locating method developed by Long et al. The focal mechanism solutions and the centriod depths of the M 6.3 and M 5.8 earthquakes were inverted simultaneously by the gCAP (generalized Cut and Paste) moment tensor inversion method. The spatial-temporal distribution of the M ≥6.5 strong earthquake ruptures since 1725 and the focal depth distribution of relocated small earthquakes from Jan. 2001 to Oct. 2014 along the central-southern segment of the Xianshuihe fault zone were used to identify the potential seismogenic region of the next strong earthquakes on the segment between Daofu and Kangding.The epicentral relocation of the M 6.3 mainshock is at 101.69°E、30.27°N, and its initial rupture depth is about 10 km, while the centroid depth is 9 km; the relocated M 5.8 earthquake is at 101.73°E、30.18°N with the initial rupture depth at about 11 km and the centroid depth of 9 km. The moment tensor solutions from gCAP method show that the two events are dominated by the double-couple component. The parameters of the best double-couple solutions are as follows, strike 143°, dip 82°, rake -9° for nodal plane Ⅰ, and strike 234°, dip 81°, rake -172° for nodal plane Ⅱ for the M 6.3 earthquake. For the M 5.8 earthquake, the parameters are listed as, strike 151°, dip 83°, rake -6° for the nodal plane Ⅰ, and strike 242°, dip 84°, rake -173° for the nodal plane Ⅱ. Most aftershocks during the first 3 days were distributed on the NW side of the M 6.3 mainshock, and majority of the aftershocks after M 5.8 earthquake were concentrated around the epicenter of the M 5.8 event. The average focal depth of the 459 relocated earthquakes of the sequence is about 9 km. Focal depth distribution reveals that the sequence mainly concentrated in the depth range of 6~11 km and most of the aftershocks are shallower than the M 6.3 and M 5.8 earthquakes. The seismic source scale is estimated to be about 30 km in length and 4 km in width with 6 km in depth according to the aftershock distribution. On the space-time diagram of the historical M ≥6.5 strong earthquake ruptures, we observe a gap on the Selaha fault of the central Xianshuihe fault zone, where no M ≥6.5 earthquakes occurred since the 1748 M 6 1 / 2 event. Aseismic gap below the depth 7 km between Kangding and Tagong and a low-seismicity region below the depth 2 km between Tagong and Songlinkou were identified on the vertical cross-section of the relocated small earthquakes since 2001 along the central-southern segment of the Xianshuihe fault zone.The nodel planeⅠof the focal mechanism solution was interpreted as the coseismic rupture plane for the M 6.3 and M 5.8 earthquakes based on the aftershock distribution and the fault strike. Both earthquakes are of left-lateral strike-slip faulting with some normal component. The relocated M 6.3 earthquake and its aftershocks during the first three days are on the NW-striking Selaha fault with a near-vertical dip angle of 82°, while the M 5.8 earthquake and its adjacent aftershocks are on the northern portion of the NW-striking Zheduotang fault with a dip angle of 83°, implying that the M 5.8 earthquake on the Zheduotang fault may be induced by the M 6.3 earthquake in the adjacent Selaha fault. The scarce aftershock region around the M 6.3 mainshock may belong to a relatively large asperity where the accumulated energy was totally released as the M 6.3 mainshock occurred. The 2014 M 6.3 Kangding earthquake sequence occurred within the Selaha strong-earthquake rupture gap between Qianning and Kangding. Due to the duration of quiescence longer than the estimated average recurrence interval for the M 7 earthquakes, we propose that the ruptures of the M 6.3 and M 5.8 earthquakes are too limited to fill up the gap, posing future M 7 earthquake risk on the Selaha and its adjacent Qianning segments along the central segment of the Xianshuihe fault zone. Since most area of the previous seismic gap below the depth 7 km between Kangding and Tagong along the central-southern Xianshuihe fault zone was filled by the 2014 M 6.3 Kangding earthquake sequence, and the most likely place of future strong earthquake occurrence will be below the segment between Tagong and Songlinkou where low seismicity is observed.

2014年11月22日在NW向鲜水河断裂带中南段四川康定县发生 M 6.3级地震,11月25日在该地震震中东南约10 km处再次发生 M 5.8级地震. 基于中国国家数字地震台网和四川区域数字地震台网资料,采用多阶段定位方法对本次康定 M 6.3级地震序列进行了重新定位; 利用gCAP(generalized Cut And Paste) 矩张量反演方法获得了 M 6.3和 M 5.8级地震的震源机制解与矩心深度,分析了本次地震序列的发震构造,并结合历史强震破裂时空分布和2001年以来小震重新定位结果,对鲜水河断裂带中段强震危险性进行了初步探讨. 获得的主要结果如下:(1) M 6.3级主震震中位于101.69°E、30.27°N,震源初始破裂深度约10 km,矩心深度9 km; M 5.8级地震震中位于101.73°E、30.18°N,初始破裂深度约11 km,矩心深度9 km. gCAP矩张量反演结果揭示这两次地震双力偶分量占主导, M 6.3级地震的最佳双力偶解节面Ⅰ走向143°/倾角82°/滑动角-9°,节面Ⅱ走向234°/倾角81°/滑动角-172°. M 5.8级地震最佳双力偶解节面Ⅰ走向151°/倾角83°/滑动角-6°,节面Ⅱ走向242°/倾角84°/滑动角-173°. 依据余震分布长轴展布与断裂走向,判定节面Ⅰ为发震断层面, M 6.3和 M 5.8级地震均为带有微小正断分量的左旋走滑型地震. (2) 序列中重新定位的459个地震平均震源深度约9 km,地震主要集中分布在6~11 km深度区间,余震基本发生在 M 6.3和 M 5.8级地震震源上部. 依据余震密集区展布范围,推测本次康定地震的震源体尺度长约30 km、宽约4 km、深度范围约6 km. M 6.3级主震震源附近的余震稀疏区可能是一个较大的凹凸体(asperity),在主震中能量得以充分释放. (3) 最初3天的余震主要分布在 M 6.3级地震NW侧;而 M 5.8级地震之后的余震主要集中在其震中附近. M 6.3级地震以及最初3天的绝大部分余震发生在倾角约82°近直立的NW走向色拉哈断裂上; M 5.8级地震与其后的多数余震发生在倾角约83°近直立的NW走向折多塘断裂北端走向向北偏转部位, M 5.8级地震可能是 M 6.3级地震触发相邻的折多塘断裂活动所致. (4) 康定 M 6.3与 M 5.8级地震发生在鲜水河断裂带乾宁与康定之间的色拉哈强震破裂空段,本次地震破裂尺度较小,尚不足以填补该强震空段. 色拉哈段以及相邻的乾宁段7级地震平静时间均已超过其平均复发周期估值,未来几年存在发生7级地震的危险. 康定 M 6.3级地震序列基本填补了震前存在于塔公与康定之间的深部小震空区,未来强震发生在塔公至松林口段深部小震稀疏区内的可能性很大.

青藏高原东北缘所在的柴达木-祁连活动地块内的晚第四纪活动构造可以划分为主边界左旋剪切构造带、块内次级右旋剪切构造带和挤压会聚构造带等三种基本类型。在区域北东向构造应力作用下,块体发生了NE向的挤压缩短、顺时针方向的旋转和向SEE方向的挤出等构造变形。在块体内部形成了挤压推覆构造、次级剪切构造、剪切压扁构造和弧形挤出构造等四种典型的构造转换方式,实现不同方向与不同性质活动构造之间的转换平衡。

On 20 June and 9 August 2011 two M s 5.2 earthquakes occurred in the Tengchong volcanic area, and we call them the double earthquakes because both their origin times and earthquake hypocenters are all close to each other. For better understanding the rupture mechanism of these double earthquakes, we inferred their full moment tensor solutions and relocated their seismic sequences. Using the arrival times collected from observation bulletins and obtained from the waveform cross-correlation method, we relocated the M s 5.2 double earthquake sequences with the double-difference location algorithm. These data were recorded by the CEA Crustal Institute temporary and Yunnan provincial permanent seismic stations. We obtained the full moment tensor solutions of double earthquakes with the generalized Cut and Paste (gCAP) inversion method. The gCAP method includes the parameters ζ and χ representing the strengths of the ISO and CLVD terms, respectively.Our results show that the epicenters of these double earthquakes are located west of the Longchuanjiang fault, and their aftershocks are a column tilted toward the Tengchong volcanic area with depth. The 20 June and 9 August M s 5.2 2011 double earthquakes are a kind of earthquakes with the volume-closed rupture mechanism having an obvious non-double-couple component, and the latter is much weaker in the non-double-couple component. The bootstrap test shows the values of the parameters ζ and χ are all located in their 95% confidence intervals, which demonstrates the reliability of non-double-couple components in our results. These results suggest that the M s 5.2 double earthquakes and their aftershocks are closely associated with the crustal magmatism under the Tengchong volcano and the Longchuanjiang fault provides a channel for hot material upwelling. We conclude that the occurrence of double earthquakes could be closely related to the obvious reduction in the rupture volume of the first earthquake,which leads to the extrusion of fluids that affect the fault again.

本研究联合使用观测震相到时和波形互相关数据,采用双差法对2011年6月20日与8月9日发生在云南腾冲的5.2级双震及其余震序列进行重定位,并采用gCAP(generalized Cut and Paste)方法反演了该双震全矩张量解.结果显示,双震震中位于龙川江断裂的西侧,余震序列在深度上为一个倾斜的柱状体,且倾向腾冲火山区;6月20日和8月9日5.2级地震均表现为体积缩小的闭合型破裂,包含有显著的非双力偶成分,但后者包含的非双力偶成分相对明显减小.这些结果表明,云南腾冲5.2级双震及余震活动可能与火山下方的地壳岩浆作用密切相关,龙川江断裂为热物质向上运移提供了通道,而双震型地震的发生可能与首次地震的破裂体积缩小挤出的流体作用于断裂密切相关.

On July 22,2013,the Minxian-Zhanxian M S 6.6 earthquake occurred at the central-northern part of the South-North Seismic Belt. In the area,complicated structural geometries are controlled by major strike-slip fault zones,i.e.the Eastern Kunlun Fault and the Northern Frontal Fault of West Qinling. The distribution of related seismic disasters,namely,the ellipse with its major axis trending NWW,is in good accord with the strike of the Lintan-Tanchang Fault. Severe damages in the meizoseismal area of the Minxian-Zhangxian M S 6.6 earthquake are located within the fault zone. So it is considered that the earthquake related damages are closely related to the complicated geometry of the Lintan-Tanchang Fault,and it also indicates that the earthquake is the outcome of joint action of its secondary faults. Based on field investigations,and by integrating the results of previous studies on active tectonics,structural deformation and geophysical data,it can be inferred that the southward extension of the Northern Frontal Fault of West Qinling and the northeastward extrusion of the Eastern Kunlun Fault in the process of northeastward growth of Tibetan plateau are the main source of tectonic stress. Basic tectonic model is provided for strong earthquake generation on the Lintan-Tanchang Fault.

2013年7月22日,甘肃岷县漳县 M S 6.6地震发生在南北地震带的中北段,东昆仑断裂和西秦岭北缘断裂是该地区复杂多样的构造几何特征中2条主要的边界控制断裂。这次地震的震害分布与临潭-宕昌断裂的走向基本一致,为长轴走向NWW的椭圆,极震区内严重破坏范围也完全位于该断裂带内,这与临潭-宕昌断裂复杂的几何结构密切相关,也说明地震的发生是多条次级断裂共同作用的结果。综合分析认为,受西秦岭北缘断裂带向南侧的扩展和青藏高原向NE扩展过程中东昆仑断裂带的NE向挤压作用共同影响下的临潭-宕昌断裂是这次地震的发震构造。

Southeast Gansu province along the central-northern portion of the South-North Seismic Belt, the tectonic activities and deformation pattern are closely related to the northeastward growth of the Tibetan Plateau. Complicated structural geometries were controlled by both Eastern Kunlun and West-Qinling Northern Faults, and outward growth of the NE Tibet continuously contributes to the regional active deformation. In recent years, intermediate-strong earthquakes occurred frequently, calling for a detailed analysis. By integrating both structural and historical seismicity studies, and combining geophysical, seismological and field investigations, we conclude that northward indenting and eastward movement along the Eastern Kunlun Fault is the main tectonic stress source, and also it provides the basic setting and mechanism to generate strong earthquakes. Left-lateral slip and its bi-flanking thrusting 'flower structure' of the West-Qinling Northern Fault contributed to the frequent occurrence of intermediate-strong earthquakes along the Lintan-Tanchang fault to the south. Minxian-Zhangxian M(S)6. 6 earthquake on July 22, 2013 along the central-eastern Lintan-Dangchang fault is a consequence of differential activity due to heterogeneous segments.

位于南北地震带中北段的甘东南地区，其构造变形和构造活动特征与青藏高原向北东方向的扩展密切相关，该地区复杂的构造几何形态主要受控于东昆仑断裂和西秦岭北缘断裂，区域新构造运动主要动力来源于青藏高原向北东的扩展.近年来，甘东南地区中强地震频发，本文主要通过对该地区构造活动特征、历史地震等资料的综合分析讨论，结合地球物理、地震学和野外调查等资料，认为青藏高原东北部东昆仑断裂的向北挤压和向东的运动是该地区构造应力集中的主要原因，也是该地区中强地震的主要孕震环境和机制，而西秦岭北缘断裂的走滑及向南北两侧逆冲“花状构造”是临潭—宕昌断裂带上中强地震频繁发生的一个重要动力因素.2013年7月22日发生在甘肃岷县—漳县的 M S 6.6级地震正好位于临潭—宕昌断裂带中东段上，是该断裂分段不均匀活动的结果.

This paper presents the three-dimensional crustal seismic wave velocity structure in the region 32°~40°N, 100°~108°E reconstructed through seismic tomographic inversion. We use 38 052 arrival time data of 〖AKP-〗, 〖AKS-〗, Pm, Sm, Pn and Sn phases recorded from 2 032 earthquakes with M≥1.5 occurred from 1980 to 2000 and the Moho interface topography data from deep seismic sounding. The 3-D tomographic image clearly reveals that the crust structure of this region consists of four layers. The top layer (about 0~3 km) has a velocity gradient about 0.2 s-1 that corresponds to the sediments. The second layer (about 3~17 km) is the upper crust with a velocity gradient about 0.1 s-1 at top and relative large lateral velocity variation as well as lower velocity blocks at bottom. The third layer (about 17~36 km) is the middle crust with velocity gradient 0.03 s-1. The lower crust forms the fourth layer (about 36 km-Moho), which is thick in the west and thin in the east. The thickness of this layer gradually reduces from the Qinghai-Tibetan plateau to the Erdos platform and the Yangtze paraplatform with different velocity gradient at different location.

本文用1980—2000年M≥1.5的2 032个天然地震事件的38 052个〖AKP-〗、〖AKS-〗、Pm、Sm、Pn和Sn震相到时及人工地震测深给出的Moho面形态资料，利用地震层析技术反演了32°~40°N, 100°~108°E区域内地壳地震波速度结构.从层析成像图象中可以得到，本区的地壳可分成4个层位.第1层（埋深约在0~3 km）为沉积层， 速度梯度约为0.2 s-1；第2层（埋深约在3~17 km）为上地壳, 其顶部速度梯度约为0.1 s-1, 下部速度横向变化较大且存在低速块体；第3层（埋深约在17~36 km）为中地壳， 速度梯度约为0.03 s-1；第4层（埋深约在36 km—Moho）为下地壳, 是一个契形层，总的趋势是西厚东薄，青藏高原较厚逐渐向鄂尔多斯地块和扬子准地台方向变薄，各处的地震波速度梯度不尽相同.