The maximum magnitude of probable future earthquake in the target area is forecasted in this paper by synthetical analysis of tectonic structure,seismicity,stress and strain fields,based on data of the Chongqing urban active faults surveying. The maximum magnitude of probable future earthquake in the target area is 5.5≤ M S ≤6.0. We try to use the spatially smoothed seismicity method in weakly active area. Two seismic hazard models in weakly active area based on spatially smoothed seismicity method are proposed using strong seismic catalog and small seismic catalog. The completeness of these two catalogs is analyzed based on EMR(Entire Magnitude Range)method. And the seismic hazard(probability)in the target area is calculated using Poisson model. The results show that the seismic probability value for a single fault is relatively low and the possibility of destructive earthquake of magnitude above 5.5 in the target area is small. There are still some uncertainty and reliability for the results because of the hypnosis of the spatially smoothed seismicity model. However it should be noticed that the technique of seismic hazard calculation described in this paper based on spatially smoothed seismicity method is a new try and has potential application for the weakly active area such as Chongqing.

以重庆市活断层探测资料为基础,通过对该工作区的地震构造、地震活动性、构造应力场与形变场的分析,综合判定出目标区未来可能发生地震的最大震级为5.5≤ M S ≤6.0。尝试将地震空间光滑模型应用到弱活动区城市活断层地震危险性评价中,充分利用历史强震和微震目录,分别建立了2种地震空间光滑模型,并采用泊松模型,对目标区未来百年的地震危险性(发震概率)进行了定量分析。结果表明:单条断裂发震概率值较低,未来发生5.5级以上破坏性地震的可能性较小。

Estimation of sizes of potential earthquakes is required in long-term seismic hazard assessment.Such estimation is usually related to a single active fault segment with specific scale,and can be carried out by using an empirical relationship between magnitude and rupture-scale of earthquake.This type of empirical relationships published already for China mainland is established on data of surface ruptures along seismogenic active faults in West China.While,the special active tectonic environment in the region of North China makes it impossible to establish the same type of empirical relationships that are suitable for the region by using the surface-rupture data.Therefore,for North China,we should make an effort to develop the empirical relationships between earthquake magnitude and(sub-surface)source rupture-scale.In the latest 40 years,4 major earthquakes of magnitudes ≥7.0,7 strong ones of magnitudes 6.0 to 6.9 and tens of moderate ones(including aftershock events)of magnitudes 5.0 to 5.9,occurred in North China.For a part of these earthquakes,data or distribution patterns of aftershock sequences with good or high precision locations are available,and for many of these earthquakes,studies on source rupture processes and parameters have been carried out.These make it possible to establish preliminarily the empirical relationships between magnitude and rupture-scale for North China.For this purpose,from data of earthquakes that occurred in North China since 1965,we systematically collected and compiled the relevant rupture-scale parameters obtained from methods of analyzing seismic wave spectrum,coseismic crustal deformation and aftershock distribution,or available from published researches,including rupture length L,downdip rupture width W ,and rupture area A ( A = L × W ).We also re-determined the rupture-scale parameters for part of these earthquakes basing on aftershock distributions.In order to deal with uncertainties in the source rupture-scale parameters due to the use of various methods,and to take the main factors influencing the uncertainties into account,we broungt forward 8 criterions for determining the reliable parameters through further analyses and identification.With synthetic analyses basing on these criterions,we obtained reliable rupture-lengths of 34 earthquakes and reliable rupture-areas of 20 of the 34 earhtquakes.Focal mechanism data suggest that the absolute majority of the 34 ruptures are of strike-slip type.By using the least-square method,we further established two regression relationships between surface-wave magnitude M S and rupture-length L,and between magnitude M S and rupture-area A for seismogenic active faults.They are M S =3.821+1.860lg( L )and M S = 4.134+0.954lg( A ),respectively.A comparative analysis with previous empirical relationships of the same type suggests that the two new empirical relationships developed in this research are suitable very well for estimation of sizes of potential earthquakes on seismogenic active strike-slip faults in North China and in the urban area of Beijing and its surroundings.

为了建立适用于华北地区地震活断层的地震震级-震源破裂尺度经验关系,从1965年以来华北发生的地震中,系统整理出已由地震波谱、地形变、余震分布等方法获得和发表的震源破裂尺度参数,包括破裂长度 L 、破裂下倾宽度 W 以及破裂面积 A ( A = L × W ),同时还基于余震分布重新确定出部分地震的破裂尺度参数.针对来源于不同方法的破裂尺度参数的不确定性及其主要影响因素,提出通过进一步分析和鉴别来确定出可靠参数的8条原则.依据这些原则的综合分析,共获得34次地震的可靠破裂长度以及其中20次的破裂面积.震源机制解反映这些地震破裂以走滑型占绝大多数.我们进一步采用最小二乘法,分别建立起华北地区的面波震级 M S -破裂长度L的回归关系式 M S =3.821+1.860lg( L ) 以及面波震级 M S -断层破裂面积 A 的回归关系式 M S =4.134+0.954lg( A ).与已有同类关系式的比较分析表明:文中新建的2个关系式可较好地适用于华北以及首都圈地区的走滑型地震活断层的潜在地震强度评价.

For the M s 6.1 Panzhihua-Huili, Sichuan, earthquake sequence of Aug 30, 2008, this study determines the focal mechanism solutions of the mainshock event and the M L ≥4.0 aftershock events in the sequence using the CAP method and the broadband waveform records from the digital seismic networks of Sichuan and Yunnan. The result shows that the focal mechanism solution of the mainshock has two principal stress axes with low dip angles of M L ≥4.0 aftershocks have similar focal mechanism solutions with that of the mainshock. A preliminary analysis suggests that spatially the focal mechanism solutions of the M s 6.1 Panzhihua-Huili earthquake sequence of 2008 are coordinated with those of the previous events in the study region. This reflects that the 2008 sequence has been resulted from the left-lateral strike-slip faulting with a thrusting component along the nearly N-S-trending Hongge fault, under the SE- to SSE-ward horizontal motion of the Sichuan-Yunnan massif.

针对2008年8月30日在四川攀枝花—会理发生的 M s 6.1地震序列,本研究基于四川和云南两省数字地震台网的宽频带波形记录,采用CAP方法反演了该序列主震及 M L ≥4.0余震的震源机制解.结果显示:主震震源机制解的两个主应力轴仰角小于10°,其中,主压力轴方位为140°;节面之一走向185°、西倾83°、滑动角5°,显示左旋走滑略兼逆冲分量的断层作用性质.结合余震、烈度分布以及震区的活动构造,判定该节面代表了主震的发震断层面,相应的发震断层应是穿越震区的近南北向红格断裂(南段).本研究还获得主震震源机制解的最佳拟合误差深度为10 km,与该事件的定位结果相一致.该序列中6次 M L ≥4.0余震也具有与主震类似的震源机制解.分析初步表明:空间上,2008年攀枝花—会理 M s 6.1地震序列的震源机制解与研究区内更早地震的震源机制解具有良好的协调性,反映了该序列是在川滇地块SE-SSE向水平运动的背景下、沿近S-N向红格断裂发生左旋走滑略兼逆冲运动的结果.

Based on the differences of seismic activity,focal mechanism,geological structure,and hydrologic condition between reservoir induced seismicity(RIS)to natural earthquake,the basic features of reservoir induced earthquake from natural earthquake are studied statistically by the RIS database of 150 cases of reservoir induced earthquakes world-wide,and the results are shown as follows: ① Using statistical principle,we find that RIS occur in the areas near the reservoir banks in the impounding period,most of reservoir induced earthquake are distributed within a distance of 10km to the bank,with depth less than 10km,and a few events extend outwards as far as over 10km along fault zones,karst caves,and(thermal)springs; ②The frequency and magnitude of reservoir induced seismicity change with the reservoir water level. Most maximum magnitude earthquakes take place in the period before the first highest water level is reached,or in the following 2-3 impounding stages after the first highest water level,after then,a few would take place; ③The sequence of RIS is complete,usually as "foreshock-main shock-aftershock" or "foreshock-swarm-aftershock",most of them are microseisms of M L 1-3, so the b value is larger than natural earthquakes; ④ RIS differ from natural shocks in higher epicenter intensity,higher frequency of ground motion and higher peak ground acceleration,but faster attenuation with distance; ⑤The stress drop of RIS is smaller than that of natural earthquake of the same size,and the source size is larger; ⑥ The RIS occur in areas under lithological and geologic conditions of good permeability. Tensional fracture,tensional fault zone,unconsolidated fault plane,karst,and(thermal)springs are all good water penetration channels.

以水库诱发地震震例数据库为基础，借鉴统计学原理，分析了全球已发震水库的150个震例在地震活动性、震源机制、构造地质和水文地质等方面的主要特征。研究结果表明：水库诱发地震发生在水库周围并在蓄水过程中，多数在距库岸10km范围之内、震源深度 b 值多在1左右；水库诱发地震具有较高的震中烈度、地震动频率和地面峰值加速度，但随距离增加烈度衰减很快；水库地震应力降明显小于同一级别的天然地震应力降，震源尺度大于同一级别的天然地震；水库诱发地震的发震地段具有良好的库水渗透的岩性条件和构造条件，张性断裂带、未胶结的断裂面、岩溶、（温）泉等成为库水的渗透通道。

Statistical study of earthquakes in the past, due to the small-medium size magnitude earthquake associated with surface rupture are rare, considers that only the earthquakes beyond magnitude 6 1/2 could produce surface ruptures in the most cases. Identification of paleoseismic events is also often based on this assumption. In this paper, we summarized 56 historical moderate size earthquakes worldwide, which have clearly documented about surface ruptures from 1950 to 2014.Results show that the magnitude lowest limit of the earthquake associated with surface rupture may be lower than the 6 1/2 , probably is about 5, even can be as low as 3.6 under extreme conditions. Additionally, from the view of theory and practice, this paper explored the effect of control factors on surface rupture, so as to indicate that the shallow focal depth is one of the most important factors for small-medium size earthquake associated with surface rupture, also included are the high heat flow values, tensile tectonic environment and active fault with weak friction strength. Although the probability that small magnitude earthquake produces surface rupture is low, it is not impossible. In the interpretation of paleoearthquake events, it also cannot overgeneralize that the corresponding earthquake magnitude must be 6.5 or greater as long as the fracture appeared, while ignoring the possibility of some moderate size earthquakes.

以往的地震统计研究中, 由于中小地震产生地表破裂的震例缺乏, 多数研究者认为在大多数情况下, 当地震震级 M >6 1/2 时才会产生地表破裂。基于上述统计认识, 古地震探槽中破裂的出现也认为更可能是由 M 6 1/2 以上地震造成的。收集了1950—2014年全球范围内有明确记录产生地表破裂的56个中小强度震例, 发现伴有地表破裂地震的震级下限可能在5级左右, 极端情况下震级可以低至3.6级。同时, 从理论和经验的角度, 探讨地表破裂的控制因素, 发现震源深度较浅是中小强度地震产生地表破裂的1个重要原因, 此外高热流值和拉张的构造环境、摩擦强度较弱的活动断裂也是低震级事件破裂达到地表的有利条件。因此, 虽然中小震级地震产生地表破裂的概率较低, 但并非完全不可能。古地震探槽解译时, 也不能绝对地认为只要有破裂出现, 就一定是6.5级以上地震所为, 而忽视古地震探槽揭示中等震级地震事件的可能性。

We investigate the crustal velocity structure of the Sichuan basin based on ambient noise tomography using continuous waveform data recorded by the Chongqing telemetry network and other permanent stations in the region from January to December of 2012. By extracting the dispersion information of Rayleigh waves from empirical Green functions (EGFs), we invert the phase velocity of surface waves for periods from 5 s to 40 s and further estimate S-wave velocity in 3-dimensions. The results of phase velocity at periods of 5 s and 10 s indicate that the Sichuan basin is characterized by thick sedimentary layers, of which the thickness is relatively small in the central basin. The phase velocity at periods around 20 s mainly reflects the S-wave velocity structure in middle crust, which demonstrates increasing velocity with increasing depth. The phase velocity at the period about 35 s is totally high indicating that the Yangtze plate has a rigid lower crust in the region. Particularly, the distinct high velocity anomalies around the Wuling Mountains from Jishou to Changde are most likely related to the paleo-volcanic chain of Jiangnan paleo-continent activity which caused a large amount of basic and ultrabasic mantle material intruded into the crust. With greater mechanical strength, it plays a certain impediment to southward escaping of material on the west of the Wuling Mountains. gradient zone of gravity anomalies (Yunnan-Guizhou Plateau and the mountainous topography of the west of Hubei and Hunan), which is just located in the transition zone of the second step and the third step of China's topography. The obtained 3-dimensions S-wave velocity model is corresponding to the main geological structures within and surrounding the Sichuan basin, and thus it is meaningful for further study on the deep structure and seismicity in the region.

本文利用三峡库区重庆遥测台网及邻近地区台网2012年1月至12月期间的连续波形记录，通过噪声互相关，提取了这些台站间的经验格林函数.并通过获取的经验格林函数瑞利面波频散信息，反演出该区域5~40 s瑞利面波相速度分布.周期5 s及10 s的相速度分布结果显示：四川盆地具有较厚的沉积盖层，其中盆地中部沉积层相对偏浅.而周期20 s及35 s的相速度分布结果显示：中下地壳的扬子克拉通整体呈现较高的相速度分布，具有相对坚硬的中下地壳结构.这其中吉首—常德的武陵山区附近出现明显高速异常，可能与江南古陆古火山岛链（雪峰—九岭弧形古火山群）活动有关，火山活动导致大量的基性-超基性幔源物质侵入地壳，造成了武陵山重力异常，并一定程度上阻挡了云贵高原和湘鄂西部的物质向南逃逸；在地形上，此处恰好对应我国地形第二阶梯向第三阶梯的过渡带，并将华南地块分隔为东西两大部分.最后我们在瑞利面波相速度成像的基础上，反演出该区域三维剪切波速度分布，结果显示四川盆地周边的龙门山、米仓山、大巴山、七曜山和大娄山等地质构造与地壳剪切波速度结构具有明显对应关系.研究结果有助于深入研究该区的深部地质构造特征与地震发生机理.

Study on structure of earthquake source regions is one aspect of earthquake geology, which has relatively small spatial-scale but needs to know more details about seismogenic structures of specific historical events and potential events. Most of shallow-focus and tectonio-genic earthquakes on continents usually nucleate at 10 to 30km below the earth's surface. Such a depth is not able to be reached from studies only using data and methods of geology, geomorphology, or only from analyses of remote sense imagery. It needs studies of coupling deep and shallow structures by combining data from geological investigations and seismological survey, as well as from inspections of multi-geophysical techniques. The study region of this article is the middle to western portion of the Hetao graben system in Inner Mongolia, China, which is an active boundary belt separating the Ordos and Yanshan blocks, and a large-scale seismogenic tectonic zone dominantly under tensional-stress in the northwestern North China. Along the system, at least two great earthquakes occurred in the historical time, and reportedly some lines of evidence of paleo-earthquakes have been found. Since the 20th century 4 strong events with magnitudes 6.0 to 6.4 have taken place in the Hetao graben system. The most recent two of the 4 are the M S 6.0 Wuyuan earthquake on Aug. 25, 1979 and the M S 6.4 Baotou earthquake on May 3, 1996, respectively. For seismogenic structures of the two, although relevant studies were made mainly based on analyzing the relation between aftershock's and seismic intensity's distributions and surface faults or "faults" inferred just from remote sensing images, queries still remain in the corresponding conclusions because information used in these studies are limited to the surface and far from the event's nucleation depths. Based on the previous studies, this study collects and combines more information available of active tectonics, petroleum seismic survey and relocated earthquake distribution, as well as seismic intensities and focal mechanism solutions of the mainshocks, further constructs and analyzes two seismo-tectonic profiles across the individual source regions of the two events, and then re-determines seismogenic faults of the two events. The author concludes that the M S 6.0 Wuyuan earthquake of 1979 occurred as a result of normal faulting along the main one of the Sertengshan piedmont fault zone, which trends in near west-east and dips southward, and the M S 6.4 Baotou earthquake of 1996 was produced by oblique-slip normal faulting along an unnamed blind fault that hides beneath the Wulashan horst, strikes west-northwest and dips south-southwest. The new conclusion is able to march and explain, to the maximum extent, the relevant information and phenomena in the individual source regions, including surface and subsurface active tectonics, aftershock, seismic intensity distributions and focal mechanism solutions of the mainshocks, and coseismic macro ground damages (as cracks yielded in bedrocks of the Wulashan horst during the 1996 mainshock). The only one phenomenon that cannot be completely explained is that about 2/5 of the area of the meizoseismal zone(with intensity Ⅷ) of the 1996 Baotou earthquake lies north(the foot wall)of the seismogenic fault determined in this study. In addition, case study of the seismogenic structure of the Baotou earthquake suggests that secondary active normal faults or oblique-slip normal faults may exist beneath horsts within large-scale active grabens, and they would have ability to produce strong earthquakes.

在内蒙古河套断陷带中—西段，1979年8月和1996年5月分别发生了五原6.0级地震和包头6.4级地震。针对这2次地震的发震构造，在前人研究工作的基础上，进一步集成活动构造、石油物探、重新定位的地震分布、烈度分布以及震源机制解等信息进行分析，构建通过这2次地震震源区的地震构造剖面，并重新确定了相应的发震断层。结果表明：1979年五原6.0级地震更可能是走向近EW、倾向S的色尔腾山山前主断层发生正断层作用的结果；而1996年包头6.4级地震更可能是乌拉山凸起之下的一条走向NWW、倾向SSW的无名隐伏断层发生斜滑正断层作用的结果。对这2次地震发震构造的新认识，能够最大程度符合并解释各自震源区的地表活动构造、余震分布、主震的烈度分布与震源机制解以及主震时的地面宏观破坏等现象。惟一不能完全解释的是包头地震的极震区（Ⅷ度区）面积约有 2/5 位于所判定的发震断层北侧（下盘）。另外，包头地震发震构造的例子显示出在大型活动断陷带内部的相对凸起区之下，也可能存在具有发生强震能力的活动性正断层或斜滑正断层。

Lower Paleozoic marine shale is widely distributed in Southeast Chongqing and features in large thickness,shallow burial depth and high organic abundance.The information from Well Yuke 1 helps us to well understand the characteristics and gas potential of the dark shale.The thickness of dark shale in the Cambrian Niutitang Formation is 50.2 m in total.Our studies reveal that the shale has favorable hydrocarbon accumulation conditions,with an average total organic carbon content( TOC ) of 5.63% and an average vitrinite reflectance( R o ) of 3%.Calculation through logging analysis,isothermal adsorption test and linear regression shows that the total gas content of the shale is within the range of 1.0-3.5 m 3 /t.Well Yuke 1 demonstrates that the Niutitang Formation dark shale is characterized by high organic content,high maturity and large gas content,indicating great potential of shale gas resources.

渝东南地区广泛发育下古生界海相页岩,具有发育范围广、厚度大、埋藏深度较浅、有机质丰度高等特点。渝科1井位于四川盆地东南部外缘,揭示了渝东南地区富有机质页岩的发育特征和含气特点。该井钻揭下寒武统牛蹄塘组页岩层总厚50.2 m。研究表明:牛蹄塘组页岩具有有利的页岩气成藏条件,有机碳含量平均值为5.63%,成熟度( R o )主体分布在3%左右。利用测井数据、等温吸附实验、线性回归等多种方法对页岩含气量进行分析和计算,得到牛蹄塘组页岩总含气量在1.0～3.5 m 3 /t。渝科1井揭示了渝东南地区发育的牛蹄塘组富有机质页岩具有高有机碳含量、高成熟度、高含气量的特点,该地区具有较大的页岩气资源潜力。

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.

Using the double-difference algorithm, we relocated the Ludian M(s)6.5 mainshock and its 647 aftershocks during 3 to 7 August 2014 and finally obtained 471 relocated earthquakes. Our results show that the focal depth of main shock is 13.3 km, which is close to the initial rupture depth of the main shock. The aftershock sequence presents an asymmetric conjugate shape with lengths of 17 km in the EW direction and of 22 km in the NW direction. Small earthquakes are predominately located above 10 km depth, and extend toward the shallow parts above 10 km depth along the southeast and eastwest directions of conjugate faults from the main shock. In addition, distribution of small earthquakes also shows that the seismogenic fault has a high dip and is the NW Baogunao-Xiaohe fault that is one branch of the Zhaotong-Ludian fault. Because the mainshock centroid depth can provide important evidence for understanding the serious disaster caused by the mainshock, we determined 5 focal mechanism solutions (M-s >=-4.0) including the main shock using the gCAP(generalized Cut And Paste) method. Our results show that the centroid depth of the main shock is only 5 km, which is consistent with the 2 similar to 8 km depth of larger slip in the obtained rupturing process. The conjugate rupture and shallower centroid depth of main shock could be the important causes for the serious disaster of this earthquake.

本研究采用双差定位法对2014年 8月3日至7日期间鲁甸 M S 6.5级主震及647个余震序列进行重新定位，得到471个重定位结果.结果显示，主震的震源深度为13.3 km，与破裂过程显示的初始破裂深度较为接近，余震序列呈现出近东西向-北西向的不对称共轭状分布，近东西向长约17 km，而北西向长约22 km，小震优势分布深度为10 km以上，且由主震处沿共轭断层分别向东南向和近东西向逐渐往10 km深度以上的浅部迁移.小震分布还展示出发震断层高倾角分布，且与昭通—鲁甸断裂分支断裂包谷垴—小河断裂活动相关.由于主震破裂的质心深度可为深入认识本次地震灾害严重提供重要证据，为此我们采用gCAP（generalized Cut And Paste）方法反演了包括主震在内共5个4.0级以上地震的震源机制解，结果显示主震质心深度仅约5.0 km，与已有破裂过程显示的较大滑移量处于2~8 km之间的深度一致.本次主震错断了互为共轭的两条断裂，这种共轭破裂模式与矩心深度较浅，可能为本次地震致灾严重的重要原因.

Based on the fundamental theory of earthquake location, it is found that the data recorded at nearby stations are applicable in double difference relocation algorithm, but not in other relative location algorithms. Equation derivation and simulated calculation demonstrate that double difference algorithm allows us to get the absolute locations of earthquakes with certain accuracy by using the nearby station phase arrivals. The errors of relative location become larger when using the nearby station records alone than that using the distant station records. Combining the nearby and distant station records, the best locations are obtained. In the case that hypocenter depth is far less than the epicenter distance without depth phases available, only the relative epicenter distribution could be obtained accurately by double difference method, the depth determined would be not stable. The relocation test of a part of aftershocks in Jiashi earthquake sequence verified the effect of nearby station records on the double difference algorithm mentioned above.

从地震定位的基本原理出发，分析认为近台资料可用于双差定位算法，但不能用于其他相对定位方法.在此基础上，通过分析和模拟计算表明，应用近台资料时，双差法有可能给出一定精度的地震绝对位置.但仅采用近台资料时，相对位置的误差会比使用远台资料时有所增加.近台和远台资料的联合使用，有利于得到较为精确的定位结果.当震源深度远小于震中距时，如果没有深度震相的参与，只能得到误差较小的震中相对分布，深度的相对位置仍有较大的误差.对2003年新疆伽师地震余震序列中部分余震的重新定位试验，验证了近台资料对双差定位算法的上述影响.