瀑布沟水库区域地震的重新定位

利用双差定位方法对瀑布沟水库区域内2006-10-13~2013-07-31之间发生的3 784个地震进行了重新定位,获得了3 601个地震的重新定位结果,到时残差平均为0.12 s,E-W、N-S和U-D三个方向上平均定位误差分别为0.15 km、0.17 km和1.10 km。重新定位结果显示,在研究区域内的西南方向和水库流域,地震分布密集,这个区域处于鲜水河断裂中南段、安宁河断裂北段和大凉山断裂北段的位置,此区域内地震震源深度主要分布在5~30km间,表明该区域的地震主要是构造活动引起的,而水库库区内地震震源深度主要分布在0~5 km区间,分布比较集中,该地区的地震为水库诱发和人工爆破引起的地震。     

大凉山断裂带南段滑动速率估计

大凉山断裂带是川滇活动块体东边界的重要组成部分,其活动速率的估计不仅对评价青藏高原东南边缘的地壳运动和变形模型具有重要理论意义,还对大凉山地区的地震危险性评价和地震中长期预测具有重要的应用价值。通过对大凉山断裂带南段交际河断裂和布拖断裂的详细野外调查、典型构造地貌GPS精细测量以及断错地貌的时间约束,获得大凉山断裂带南段全新世以来的滑动速率为2.5～4.5mm/a,交际河断裂平均滑动速率略大于布拖断裂的滑动速率。对比滑动速率发现,大凉山断裂带南段与鲜水河-小江断裂系中段西支的安宁河、则木河断裂带的水平滑动速率相当,表明大凉山断裂带活动强度不低于安宁河和则木河断裂带,随着大凉山断裂带逐渐取代安宁河和则木河断裂在鲜水河-小江断裂系中的作用,大凉山断裂带的活动强度将增强。     

新生的大凉山断裂带——鲜水河-小江断裂系中段的裁弯取直

部分由于缺乏破坏性地震记录,部分由于处于边远山区,作为鲜水河-小江断裂系一部分的大凉山断裂带长期被研究者们忽视,以至于在描述该断裂系时,往往不把大凉山断裂带算在其中．造成大凉山断裂带被忽视的另一个重要的原因是该断裂带是一条新生的构造带,新生性决定了其成熟度低于鲜水河-小江断裂系中的其他断裂带,所反映的线性断裂地貌特征不如其他断裂带明显．两年多详细的遥感解译和野外调查结果表明大凉山断裂是一条新生的断裂带：（1）具有复杂几何结构的大凉山断裂带无论是连续性还是成熟度都明显低于鲜水河．小江断裂系中的其他断裂带;（2）大凉山断裂带南、北两段的活动性高于中段,而且北段的左旋位错量是南段的3倍,小震活动在中段也存在一个明显的空区,说明大凉山断裂带还没有完全贯通,尚处于从两端向中间发展的早期阶段;（3）大凉山断裂带上地质体反映的总位错和水系的位错基本相同,说明大凉山断裂带开始于该地区水系成型之后,而鲜水河-小江断裂系中其他断裂带上的总位错远大于水系所反映的位错;（4）探槽揭示的古地震事件和用断错地貌和GPS观测结果估计的水平滑动速率3～4mm／a,都表明大凉山断裂带与安宁河、则木河断裂带一样也是一条强震构造带;（5）在滑动速率大致相当的情况下,并假定各断裂带在整个发育历史中滑动速率基本不变,大凉山断裂带产生11km的滑移量需要2．7～3．7Ma,而安宁河和则木河断裂带完成47～53km的位错量需要12～18Ma．进一步推断,新生的大凉山断裂带产生于鲜水河-小江断裂系中段的“裁弯取直”,而“裁弯取直”是由于青藏高原南东块体相对刚性的顺时针旋转造成的．随着“裁弯取直”的持续发展,大凉山断裂带将可能逐渐取代安宁河和则?     

川滇菱形块体东边界断层闭锁程度与滑动亏损动态特征研究

利用1999—2007期和2009—2013期中国大陆GPS速度场数据,采用DEFNODE负位错反演程序估算了川滇菱形块体东边界——鲜水河—安宁河—则木河—小江断裂带在汶川地震前后的断层闭锁程度和滑动亏损空间分布动态变化特征,讨论了汶川地震对该断裂系统的影响范围和程度,并结合b值空间分布和地震破裂时-空结果分析了断裂系统的强震危险段.结果表明,汶川地震前鲜水河断裂最南端为完全闭锁(闭锁深度25km),中南段地表以下10~15km深度为强闭锁状态,中北段基本处于蠕滑状态;安宁河断裂最南端闭锁很弱,其余位置闭锁深度为10~15km;则木河断裂除最南端闭锁较弱以外,其余位置基本为完全闭锁;小江断裂在巧家以南、东川以南、宜良附近、华宁以北等四处位置闭锁较弱,其余位置为强闭锁.10年尺度的GPS速度场反演所得断层闭锁程度所指示的强震危险段,主要为鲜水河断裂道孚—八美段、安宁河断裂中段、则木河断裂中北段、小江断裂北段东川附近、小江断裂南段华宁—建水段,该结果与地质尺度的断层地震空区和30年尺度的b值空间分布所指示的危险段落具有一致性.汶川地震后断裂带远、近场速度分布和块体运动状态发生变化,这种区域地壳运动调整使得负位错模型反演得到的断裂带闭锁情况发生一定变化.汶川地震前后川滇菱形块体东边界平行断层滑动亏损速率均为左旋走滑亏损,且在安宁河断裂北端、则木河断裂中北段滑动亏损速率最大;除鲜水河断裂中南段与最南端和小江断裂东川附近以外,其余断裂震后滑动亏损速率均有所增加.垂直断层滑动亏损速率既有拉张亏损也有挤压亏损,且鲜水河断裂最南端由震前挤压转变为震后拉张,其余断裂除了安宁河断裂和小江断裂中段与最北端存在挤压滑动亏损速率外均为拉张速率.     

安宁河—则木河断裂带和大凉山断裂带孕震深度研究及其地震危险性

安宁河—则木河断裂带及东侧的大凉山断裂带作为大凉山次级块体西侧与东侧边界,具有发生大地震的活动构造背景.本文意在用有限的形变数据和地震数据两种资料评估大凉山次级块体边界断裂带的孕震深度及其地震危险性.采用弹性半空间模型对安宁河断裂、则木河断裂和大凉山断裂带滑动速率和闭锁深度进行了详细分析;计算了90%、95%和99%不同分位数的小震深度下界值并与GPS得到的闭锁深度进行对比,分析二者异同点.结果显示,安宁河断裂北段闭锁深度为6.2 km,不到90%分位小震震源深度16 km的一半,表明该段在1952年M_S6³/₄地震后,断层逐渐趋于闭锁;而在6~16 km深度主要以小地震和无震滑动两种形式释放能量,存在深部蠕滑运动.大凉山断裂北段在0~10 km范围内完全闭锁,而10~25 km闭锁程度较弱.安宁河断裂南段、则木河断裂、大凉山断裂中段和南段均处于完全闭锁阶段,闭锁深度接近90%分位数小震深度的下界值,标准差约为0.94 km.此外,A、B、C三个剖面的反演结果表明大凉山次级块体的运动自北向南具有顺时针旋转特性,与川滇块体顺时针运动特征吻合.大凉山次级块体北、中、南三段边界断裂及块体内部总的滑动速率分别为9.8 mm·a^-1、8.9 mm·a^-1和8.4 mm·a^-1,呈自北向南递减趋势.大凉山断裂南段布拖断裂和交际河断裂积累的能量分别能够发生一次矩震级为M_W7.5的地震,离逝时间已经接近地震平均复发间隔,未来100年大地震的发震概率分别为7.1%和5.9%,应对其地震危险性给予重视.     

川滇块体东边界活动断裂的大地震活动特征分析

活动断裂的活动习性是认识活动断裂应变加载及释放随时间、空间变化的关键所在，也是研究区域运动学、动力学和科学评价地震危险性的重要基础。安宁河断裂、大凉山断裂与鲜水河断裂呈倒“Y”字形交于石棉一带，共同协调了鲜水河断裂向SE的应变传递，2022年鲜水河断裂磨西段发生了泸定M_S6.8地震后，安宁河断裂和大凉山断裂的地震危险性再次引起了人们的关注。本文通过梳理分析这3条断裂相关的古地震和历史大地震资料，得出以下认识：(1)安宁河断裂和鲜水河断裂磨西段近4 000 a来的大地震平均复发间隔约为700 a，大凉山断裂则为524 a；(2)鲜水河断裂磨西段和安宁河断裂的古地震活动表现为丛集特征，大凉山断裂的古地震活动则表现为准周期特征；(3)近4 000 a来三条断裂在200 a时间窗内的大地震活动表现出准同步性，在时空上有相互影响的特征。     

海南岛及邻区地震精确定位及断裂构造分析

利用双差地震定位法对2000~2012年海南岛及邻区ML≥1.0的1 035次地震进行重新定位,得到了820次地震的重定位结果。结果显示:重新定位后的结果大大改善了原地震定位的精度,且部分震群更加集中密集,并向断裂带趋近;震源深度分布更为合理,精定位前震源深度绝大多数位于10 km处,而精定位后发散分布于地下20 km内,近似呈正态分布形态,优势分布深度为5~15 km;重定位后的地震呈现垂直条带分布特征,体现了断裂带的运动构造,更加符合断裂带的地震活动特点。     

四川大凉山断裂带的晚第四纪平均滑动速率

大凉山断裂带呈近南北向或北北西展布于安宁河、则木河断裂东侧的大凉山腹地，是一条连接鲜水河、小江断裂的贯通性全新世活动断裂，全长约280km。航、卫片解译及野外实地考察结果表明，大凉山断裂带由海棠-越西、普雄河、布拖及交际河四条次级断裂呈羽列组合而成，晚第四纪以来的平均左旋滑动速率在3mm／a左右。     

2010年以来四川地区中强地震震源机制反演及深度确定

2008年5月12日四川龙门山断裂带发生了汶川8.0级地震,之后四川境内发生了两次7.0级地震(其中一个是芦山地震),为了研究汶川地震之后龙门山断裂带及周边区域的地震活动性,本研究收集了国家地震台网和四川区域地震台网2010年1月1日—2017年12月31日四川地区发生的17次M≥5.0地震以及120多次5.0>M≥4.0地震的波形资料,利用波形拟合法反演了震源机制解及区域应力场.反演结果显示,位于龙门山断裂带上的地震,震源机制以逆冲型为主,鲜水河断裂带地震震源机制以走滑型为主,而川滇块体西南部的理塘断裂、金沙江断裂附近,震源机制解以正断层为主.根据震源机制解反演得到的龙门山地区、鲜水河地区的主压应力场方向为WNW、近EW向.川滇块体的巴塘、理塘等地区,其主压应力轴方向为12°左右,接近SN向,且仰角接近40°左右.本研究利用面波振幅谱特征对震源深度进行了精确定位,定位结果与中国地震台网中心(CENC),美国地震调查局(USGS),国际地震中心(ISC)等机构地震目录进行了对比.结果显示,四川地区强震震源深度主要分布在20km以上的中上地壳.龙门山地区震源优势分布在10～20km,鲜水河断裂地震震源深度在10km左右,川滇块体西南部的理塘断裂,巴塘断裂,金沙江断裂等地区,震源深度一般在5～10km范围.     

大凉山断裂带与安宁河-则木河断裂带的地震活动性分析

通过对比分析,研究了大凉山断裂带和安宁河-则木河断裂带的地震活动性。认为在历史上安宁河-则木河断裂带的地震活动无论是频次还是强度都高于大凉山断裂带,这与活断层及古地震研究的结论是一致的。而且,地震活动性分段比较的结果显示,普格附近的空段2和冕宁附近的空段1发生强震的可能性最大,其次为西昌钝角交汇区．另外,需要注意强震前先发生中强震的可能性。     

Precise Location of Earthquakes at the Eastern Boundaries of the Sichuan-Yunnan Rhombic Block

Based on the seismic station data sets from Sichuan and Yunnan provinces, we employed a multi-step seismic location method (Hypo2000 + Velest + HypoDD) to precisely locate the 7,787 earthquakes that occurred during 2010-2015 along the eastern boundaries of the Sichuan-Yunnan rhombic block, namely from southern Dawu to the Qiaojia segment. The final results show that location precision is greatly advanced and epicenter distribution exhibits good consistency with the linear distribution of the seismic faults. Earthquake distribution is quite intensive at the intersection region in the southern segment of the Xianshuihe fault, the Anninghe fault zone, the Xiaojinhe fault zone and the Daliangshan fault zone to the east. The depth profile of seismicity shows a clear stepwise activity along the active seismic fault zones. The profile crossing the faults of the Xianshuihe, Anninghe, and Daliangshan presents a complex interaction among faults near the multiple faults intersection region, Shimian, where the earthquakes are obviously divided into two groups in depth. Earthquakes are very rare at the depth of 15km-20km, which is consistent with the region of the plastic rheology between 14km-19km calculated by Zhu Ailan et al.,(2005).     

A seismic gap on the Anninghe fault in western Sichuan,China

Through integrated analyses of time-varying patterns of regional seismicity, occurrence background of strong and large historical earthquakes along active faults, and temporal-spatial distribution of accu- rately relocated hypocenters of modern small earthquakes, this paper analyzes and discusses the im- plication of a 30-year-lasting seismic quiescence in the region along and surrounding the Anninghe and Zemuhe faults in western Sichuan, China. It suggests that the seismic quiescence for ML≥4.0 events has been lasting in the studied region since January, 1977, along with the formation and evaluation of a seismic gap of the second kind, the Anninghe seismic gap. The Anninghe seismic gap has the background of a seismic gap of the first kind along the Anninghe fault, and has resulted from evident fault-locking and strain-accumulating along the fault during the last 30 years. Now, two fault sections either without or with less small earthquakes exist along the Anninghe fault within the An- ninghe seismic gap. They indicate two linked and locked fault-sections, the northern Mianning section and the Mianning-Xichang section with lengths of 65 km and 75 km and elapsed time from the latest large earthquakes of 527 and 471 years, respectively. Along the Anninghe fault, characteristics of both the background of the first kind seismic gap and the seismicity patterns of the second seismic gap, as well as the hypocenter depth distribution of modern small earthquakes are comparable, respectively, to those appearing before the M=8.1 Hoh Xil earthquake of 2001 and to those emerging in the 20 years before the M=7.1 Loma Prieta, California, earthquake of 1989, suggesting that the Anninghe seismic gap is tending to become mature, and hence its mid- to long-term potential of large earthquakes should be noticeable. The probable maximum magnitudes of the potential earthquakes are estimated to be as large as 7.4 for both the two locked sections of the Anninghe fault.     

四川活断层分段与强震危险性概率预测

本文主要根据断层的几何结构、活动强度与断层上最大地震破裂长度等对四川境内几主要活断层的晚第四纪，特别是全新世以来的活动性进行了分段，并采用概率复发模型对各活动段在未来３０年内强震的复发概率进行了预测。     

Segmentation of Active Faults and Risk Probability Prediction of Strong Earthquakes in Sichuan Province

Based on geometric structure,active strength,and maximum seismic rupture length along the fault in the late Quaternary or Holocene,this paper presents the segmentation of main active faults in Sichuan Province and uses the recurrence probability model to predict the recurrence probabilities of strong earthquakes along each segment during next 30 years.The results indicate that earthquakes with M=7.0 or greater may happen along Qiajiao segment,Qianning segment,and Selaha segment of Xianshuihe fault zone,the segment from Xichang to Mianning and Yejidong segment of Anninghe fault zone; earthquakes with M=6.0 or greater may happen along the segment from Maowen to Caopuo of Longmenshan fault zone and Xiaoyanjing segment of Anninghe fault zone.     

中国东南沿海地区地震的精定位研究

应用中国地震台网229个台站在2008至2017年期间记录的9826个地震事件体波走时数据,采用地震双差定位方法反演了中国东南沿海地区的地震位置。结果显示,东南沿海地区构造活动对地震活动有控制作用。在现今活动较强的块体边缘,地震活动集中呈条带状线性分布,优势方向与构造带方向一致;在现今活动性较弱的块体内部,地震分布离散或稀疏,无成带分布现象。在广东南澳岛北部出现两处线性分布的地震,长度分别约200和40 km,走向均为北偏东70°。其位置与前人根据重力资料推测的断裂位置一致,由于无已知断裂构造与其对应,此处可能是尚未发现的隐伏断裂。在南澳岛南部海域巴士断裂与滨海断裂交汇处,地震沿断裂大量聚集,剖面显示滨海断裂倾向为东南且倾角大。新丰江水库地震深度均在12 km内,较构造地震的深度浅。     

STUDY ON SOURCE PARAMETERS OF THE 8 AUGUST 2017 M7.0 JIUZHAIGOU EARTHQUAKE AND ITS AFTERSHOCKS,NORTHERN SICHUAN

On August 8, 2017, a strong earthquake of M7.0 occurred in Jiuzhaigou County, Aba Prefecture, northern Sichuan. The earthquake occurred on a branch fault at the southern end of the eastern section of the East Kunlun fault zone. In the northwest of the aftershock area is the Maqu-Maqin seismic gap, which is in a locking state under high stress. Destructive earthquakes are frequent along the southeast direction of the aftershocks area. In Songpan-Pingwu area, only 50~80km away from the Jiuzhaigou earthquake, two M7.2 earthquakes and one M6.7 earthquake occurred from August 16 to 23, 1976. Therefore, the Jiuzhaigou earthquake was an earthquake that occurred at the transition part between the historical earthquake fracture gap and the neotectonic active area. Compared with other M7.0 earthquakes, there are few moderate-strong aftershocks following this Jiuzhaigou earthquake, and the maximum magnitude of aftershocks is much smaller than the main shock. There is no surface rupture zone discovered corresponding to the M7.0 earthquake. In order to understand the feature of source structure and the tectonic environment of the source region, we calculate the parameters of the initial earthquake catalogue by Loc3D based on the digital waveform data recorded by Sichuan seismic network and seismic phase data collected by the China Earthquake Networks Center. Smaller events in the sequence are relocated using double-difference algorithm; source mechanism solutions and centroid depths of 29 earthquakes with M_L≥3.4 are obtained by CAP method. Moreover, the source spectrum of 186 earthquakes with 2.0≤M_L≤5.5 is restored and the spatial distribution of source stress drop along faults is obtained. According to the relocations and focal mechanism results, the Jiuzhaigou M7.0 earthquake is a high-angle left-lateral strike-slip event. The earthquake sequence mainly extends along the NW-SE direction, with the dominant focal depth of 4~18km. There are few shallow earthquakes and few earthquakes with depth greater than 20km. The relocation results show that the distribution of aftershocks is bounded by the M7.0 main shock, which shows obvious segmental characteristics in space, and the aftershock area is divided into NW segment and SE segment. The NW segment is about 16km long and 12km wide, with scattered and less earthquakes, the dominant focal depth is 4~12km, the source stress drop is large, and the type of focal mechanism is complicated. The SE segment is about 20km long and 8km wide, with concentrated earthquakes, the dominant depth is 4~12km, most moderate-strong earthquakes occurred in the depth between 11~14km. Aftershock activity extends eastward from the start point of the M7.0 main earthquake. The middle-late-stage aftershocks are released intensively on this segment, most of them are strike-slip earthquakes. The stress drop of the aftershock sequence gradually decreases with time. Principal stress axis distribution also shows segmentation characteristics. On the NW segment, the dominant azimuth of P axis is about 91.39°, the average elevation angle is about 20.80°, the dominant azimuth of T axis is NE-SW, and the average elevation angle is about 58.44°. On the SE segment, the dominant azimuth of P axis is about 103.66°, the average elevation angle is about 19.03°, the dominant azimuth of T axis is NNE-SSW, and the average elevation angle is about 15.44°. According to the fault profile inferred from the focal mechanism solution, the main controlling structure in the source area is in NW-SE direction, which may be a concealed fault or the north extension of Huya Fault. The northwest end of the fault is limited to the horsetail structure at the east end of the East Kunlun Fault, and the SE extension requires clear seismic geological evidence. The dip angle of the NW segment of the seismogenic fault is about 65°, which may be a reverse fault striking NNW and dipping NE. According to the basic characteristics of inverse fault ruptures, the rupture often extends short along the strike, the rupture length is often disproportionate to the magnitude of the earthquake, and it is not easy to form a rupture zone on the surface. The dip angle of the SE segment of the seismogenic fault is about 82°, which may be a strike-slip fault that strikes NW and dips SW. The fault plane solution shows significant change on the north and south sides of the main earthquake, and turns gradually from compressional thrust to strike-slip movement, with a certain degree of rotation.     

1927年古浪8级大震及其周边地区三维地壳P波速度结构特征

本文联合利用甘肃及周边测震台网记录的古浪及周边地区4592次地震的P波绝对到时资料和相对到时资料,采用双差地震层析成像方法反演了古浪震源区高分辨率的三维P波速度精细结构.结果显示,浅部P波速度分布与地表地质之间具有很好的对应关系.皇城—双塔断裂带在6 km以上深度表现为高速异常带,而在6~15 km逐渐转换为明显的低速特征,之后再次转换为高速体.震区下部在10~20 km深度有一个尺度约200 km²的低速异常体,地震发生时破裂首先在该低速体发生,与主震空间位置非常吻合.主震区的岩石结构主要由奥陶纪变质砂岩、石英岩和加里东期的花岗岩等坚硬岩体组成.这种坚硬岩体对应的P波速度结构为高速体,有利于能量积累.武威盆地在20 km以上深度表现为明显的低速异常,在25 km深度之下,整体显示为高速体,表现出稳定块体的特征.表明武威盆地中下地壳和上地幔顶部已插入到冷龙岭隆起带之下.震区小震重新定位发现,皇城—双塔断裂带东、西两段表现出不同的力学运动性质,西段以逆冲运动为主,地震主要发生在断裂的下盘.而东段地震却主要发生在上盘,断层活动以局部拉张为主.我们还首次发现在皇城—双塔断裂带的中段与主破裂呈垂直方向存在有在主震发生时新产生的一条共轭断层,基于小震的断层面参数反演显示该断裂是一高倾角运动性质以右旋为主兼具正断的断裂.     

滇南及临近地区基底结构——镇康—泸西深地震测深剖面结果

位于南北地震带南段的云南地区是中国大陆内部地震活动最强的地区之一,近年来该区地震活动频繁,展开对该区的探测与研究对人们认识地震孕震背景及板块相互运动具有重要意义.在中国地震局"中国地震科学台阵探测——南北地震带南段"行业专项的支持下,2011年底中国地震局地球物理勘探中心在滇南沿镇康—泸西一线布设一条近东西向的深地震宽角反射/折射探测剖面.该探测剖面跨越三江褶皱系、扬子地台、华南地块等多个地质构造单元,同时穿越南汀河断裂、澜沧江断裂、红河断裂带、小江断裂带等多个重要断裂带.探测剖面长600km,沿线共布设11个炮点和400余台三分量地震数字仪进行爆破和接收.本文利用有限差分和时间项方法对沿线11炮初至波资料进行了计算处理,获取了探测剖面的基底速度结构.研究结果表明:沿线不同地质构造单元基底界面形态起伏变化剧烈,其深度在1.0~7.0km范围内变化,速度横向不均匀性明显.在测线西端地表速度约4.6km·s-1,基底深度较浅,起伏变化不大;地表速度在三江褶皱系下降至4.3km·s-1,而基底埋深达7.0km左右.在扬子地台基底埋深有一个缓慢的变浅,基底深度约5.0km,地表速度约4.5km·s-1.测线在东端进入华南块体,基底深度迅速变浅,甚至出露于地表,地表速度增至约5.2km·s-1.在速度等值线变化剧烈的地方与该区分布的断裂带有很好的对应关系,尤其是在红河断裂带两侧速度等值线及界面形态变化剧烈,该特征在首波的记录截面图上也能清晰的体现.本结果为进一步研究该区强震发生背景及深部动力学意义提供了重要的科学依据.