Detailed paleoseismic history of the Hinagu fault zone revealed by the high-density radiocarbon dating and trenching survey across a surface rupture of the 2016 Kumamoto earthquake,Kyushu, Japan

The NE-trending Hinagu fault zone, length 81 km, is one of the major active faults in Kyushu, Japan. From north to south, it is divided into three segments based on geomorphic features and paleoseismic behavior: the Takano-Shirahata, Hinagu, and Yatsushiro Sea segments. The 2016 Kumamoto earthquake produced a 6-km-long surface rupture with a dextral strike-slip displacement on the northern part of the Takano-Shirahata segment. Surface rupture, a faint east-side-up flexure with a vertical offset of less than 8 cm, was observed near the middle of the Takano-Shirahata segment. To examine past surface-rupturing earthquakes on the Takano-Shirahata segment, including rupture frequency and timing, we conducted a paleoseismic study with boring and trenching at Yamaide. A trench across the surface rupture exposed multiple fault strands associated with multiple surface-rupturing events that deformed several strata of fine-grained sediments. By structural and stratigraphic interpretation, high-density radiocarbon dating and tephra analysis, and Bayesian modeling, we constrained the timing of seven events, Events 1–7, to 0.84–1.25, 1.31–7.06, 9.99–11.0, 10.8–12.1, 12.0–13.0, 14.2–15.1, and before 14.8 kcal BP. Slip during Events 1–6 was obviously larger than the 2016 slip. The estimated average recurrence interval was about 2596–2860 years, but the interval between Events 2 and 3 was much longer than other intervals. Moreover, the vertical throw associated with Event 2 was larger than that of other events. This implies that the Takano-Shirahata segment has a period with rare larger earthquakes and a period with frequent smaller earthquakes. Some events might have produced ruptures on both the Takano-Shirahata and the northern part of the Hinagu segments simultaneously or in a short time. The variety of recurrence intervals suggests that the seismic activity has been affected by one or both activities of the Futagawa fault zone and the Hinagu segment.     

Outline of the fault zone drilling project by NIED in the vicinity of the 1995 Hyogo-ken Nanbu earthquake, Japan

Abstract Three boreholes, 1001 m, 1313 m and 1838 m deep, were drilled by the National Research Institute for Earth Science and Disaster Prevention (NIED) in the vicinity of the epicenter of the 1995 Hyogo-ken Nanbu (Kobe) earthquake to investigate tectonic and material characteristics near and in active faults. Using these boreholes, an integrated study of the in situ stress, heat flow, and material properties of drill cores and crustal resistivity was conducted. In particular, the Nojima–Hirabayashi borehole was drilled to a depth of 1838 m and directly intersected the Nojima Fault, and three possible fault strands were detected at depths of 1140 m, 1313 m and 1800 m. Major results obtained from this study include the following: (i) shear stress around the fault zone is very small, and the orientation of the maximum horizontal compression is perpendicular to the surface trace of faults; (ii) from the results of a heat flow study, the lower cut-off depth of the aftershocks was estimated to be roughly 300°C; (iii) cores were classified into five types of fault rocks, and an asymmetric distribution pattern of these fault rocks in the fracture zones was identified; (iv) country rock is characterized by a very low permeability and high strength; and (v) resistivity structure can be explained by a model of a fault extending to greater depths but with low resistivity.     

鲜水河断裂带炉霍段的震后滑动与形变

1973年2月在鲜水河断裂带炉霍段发生了M7.6地震破裂.自那以来,先后在炉霍县虾拉沱布设了若干横跨该地震断层(1973年破裂带)的地壳形变观测系统,包括断层近场的短基线、短水准、蠕变仪、人工构筑物等,以及断层近-远场的GPS观测站.利用这些观测系统的长期观测资料,本文分析了鲜水河断裂带炉霍段的震后滑动/变形及其时、空变化特征,并建立起解释这些特征的动力学模式.研究表明:(1)1973年地震后的头5年,地震断层在虾拉沱场地表现为开放性质,近场的断层震后滑动以无震左旋蠕滑为主,速率达到10.27 mm/a,且伴有微量的拉张性蠕动作用;1979年以来,左旋蠕滑速率由5.3 mm/a逐渐减小到2.27 mm/a,减小的过程呈对数函数型,反映此阶段断层面已逐渐重新耦合、正朝闭锁的方向发展,并伴有部分应变积累.(2)1999年以来,地震断层两侧远场的相对左旋位移/变形速率为10 mm/a,远大于同时期断层近场(跨距40~144 m)的左旋蠕滑速率0.66~2.52 mm/a;远-近场位移/形变速率的显著变化发生在地震断层两侧各宽约30 km的范围,显示出这是与大地震应力应变积累—释放相关的断裂带宽度.(3)结合动力学背景与深部构造信息,本文对这里断层的震后位移/变形及其时、空变化的机理进行初步解释,要点是:震后约5年之后,由于逐渐增大的断层滑动/摩擦阻抗,上地壳脆性层中的断层面由震后初期的开放性质逐渐转向重新耦合、并朝闭锁的方向发展,但其两侧地块深部持续的延性相对运动拖拽着浅部脆性层发生相应的弹性位移/变形.(4)可估计再经历15~25年,研究断裂段将完全闭锁,即进入积累下一次大地震应力应变的震间闭锁阶段.     

Average slip rate,earthquake rupturing segmentation and recurrence behavior on the Litang fault zone,western Sichuan Province,China

The Litang fault zone (LFZ) is an important active fault within the northwestern Sichuan sub-block. To-gether with the Garzê-Yushu, Xianshuihe, and An-ninghe fault zones on its northern, eastern and south-eastern sides, the LFZ constitutes the lateral extrusion tectonic system in the southeastern part of the Qing-hai-Tibetan Plateau[1,2] (Fig. 1). According to instru-mental records, historical recordings and field investi- gation, an earthquake (Ms7.3) occurred on its middle to south se…     

龙门山断裂带地壳精细结构与汶川地震发震机理

利用2001年1月至2008年6月四川固定地震台网和临时地震台站记录到的大量P波到时资料,反演了龙门山断裂带及周边地区的地壳精细三维P波速度模型. 结果表明,汶川主震以北和以南地区的结构存在较大差异,以北地区的龙门山断裂带具有很强地壳不均匀性,这与该区发生了大量汶川地震的余震相一致. 这些结果有意义地改进了前人对龙门山断裂带仅为不同块体过渡带的认识. 汶川主震震源区下方存在有明显低波速异常体,表明流体可能存在于龙门山断裂带内. 这些流体可能直接影响汶川大震的形成. 本文的成像结果为下地壳流沿龙门山断裂带上浸提供了可靠的地震学证据.     

Internal structures and high-velocity frictional properties of a bedding-parallel carbonate fault at Xiaojiaqiao outcrop activated by the 2008 Wenchuan earthquake

This paper reports internal structures of a bedding-parallel fault in Permian limestone at Xiaojiaqiao outcrop that was moved by about 0.5 m during the 2008 Mw7.9 Wenchuan earthquake.The fault is located about 3 kn to the south from the middle part of Yingxiu-Beichuan fault,a major fault in the Longmenshan fault system that was moved during the earthquake.The outcrop is also located at Anxian transfer zone between the northern and central segments of Yingxiu-Beichuan fault where fault system is complex.Thus the fault is an example of subsidiary faults activated by Wenchuan earthquake.The fault has a strike of 243° or N63°E and a dip of 38°NW and is nearly optimally oriented for thrust motion,in contrast to high-angle coseismic faults at most places.Surface outcrop and two shallow drilling studies reveal that the fault zone is several centimeters wide at most and that the coseismic slip zone during Wenchuan earthquake is about 1 mm thick.Fault zone contains foliated cataclasite,fault breccia,black gouge and yellowish gouge.Many clasts of foliated cataclasite and black gouge contained in fault breccia indicate multiple slip events along this fault.But fossils on both sides of fault do not indicate clear age difference and overall displacement along this fault should not be large.We also report results from high-velocity friction experiments conducted on yellowish gouge from the fault zone using a rotary shear low to high-velocity frictional testing apparatus.Dry experiments at normal stresses of 0.4 to 1.8 MPa and at slip rates of 0.08 to 1.35 m/s reveal dramatic slip weakening from the peak friction coefficient of around 0.6 to very low steady-state friction coefficient of 0.1 0.2.Slip weakening parameters of this carbonate fault zone are similar to those of clayey fault gouge from Yingxiu-Beichuan fault at Hongkou outcrop and from Pingxi fault zone.Our experimental result will provide a condition for triggering movement of subsidiary faults or off-fault damage during a large earthquake.     

汶川地震前龙门山断裂带闭锁程度和滑动亏损分布研究

利用1999—2007期GPS水平速度场数据,采用Defnode负位错反演程序估算了龙门山断裂在汶川地震前的闭锁程度和滑动亏损分布,结合龙门山断裂带附近地表水平应变率场结果,综合分析了震前地壳变形特征.反演结果表明,震前龙门山断裂中北段处于完全闭锁状态,闭锁深度达到21 km(闭锁比例0.99)左右,垂直断层方向的挤压滑动亏损速率约为2.2 mm/a,平行断层方向的右旋滑动亏损速率约为4.6 mm/a.龙门山断裂南段只有地表以下12 km闭锁程度较高(闭锁比例0.99),垂直断层方向滑动亏损速率约为1.4 mm/a,平行断层方向滑动亏损速率约为4.6 mm/a;在12~16 km处闭锁比例约为0.83,垂直断层方向滑动亏损速率约为1.2 mm/a,平行断层方向滑动亏损速率约为3.8 mm/a;在16~21 km处闭锁比例约为0.75,垂直断层方向滑动亏损速率约为1.1 mm/a,平行断层方向滑动亏损速率约为3.5 mm/a.在21~24 km处整条断裂均逐步转变为蠕滑.上述反演结果与区域应变计算获得的龙门山断裂带中北段整体应变积累速率较低、南段应变积累速率较高相一致,均表明中北段闭锁程度高、南段闭锁程度稍低,该特征可以较好地解释汶川地震时从震中向北东向单向破裂现象.     

汶川地震前龙门山断裂带闭锁程度和滑动亏损分布研究

利用1999—2007期GPS水平速度场数据,采用Defnode负位错反演程序估算了龙门山断裂在汶川地震前的闭锁程度和滑动亏损分布,结合龙门山断裂带附近地表水平应变率场结果,综合分析了震前地壳变形特征.反演结果表明,震前龙门山断裂中北段处于完全闭锁状态,闭锁深度达到21 km(闭锁比例0.99)左右,垂直断层方向的挤压滑动亏损速率约为2.2 mm/a,平行断层方向的右旋滑动亏损速率约为4.6 mm/a.龙门山断裂南段只有地表以下12 km闭锁程度较高(闭锁比例0.99),垂直断层方向滑动亏损速率约为1.4 mm/a,平行断层方向滑动亏损速率约为4.6 mm/a;在12~16 km处闭锁比例约为0.83,垂直断层方向滑动亏损速率约为1.2 mm/a,平行断层方向滑动亏损速率约为3.8 mm/a;在16~21 km处闭锁比例约为0.75,垂直断层方向滑动亏损速率约为1.1 mm/a,平行断层方向滑动亏损速率约为3.5 mm/a.在21~24 km处整条断裂均逐步转变为蠕滑.上述反演结果与区域应变计算获得的龙门山断裂带中北段整体应变积累速率较低、南段应变积累速率较高相一致,均表明中北段闭锁程度高、南段闭锁程度稍低,该特征可以较好地解释汶川地震时从震中向北东向单向破裂现象.     

2013年芦山MS7.0地震的地震地质 灾害和发震断裂探讨

在对2013年4月20日芦山M_S7.0地震灾区大量地震地质灾害实地考察及调查的基础上, 总结了滑坡、 崩塌、 砂土液化、 地裂缝、 地表变形等地震地质灾害的分布及发育特点, 探讨了地震地质灾害与发震断裂之间的关系. 极震区和重灾区的崩塌和滑坡特别严重, 是地震巨大破坏作用的外在表现形式; 砂土液化点较少, 分布范围和规模有限; 地裂缝和地表变形并非真正意义上的地震地表破裂带. 根据极震区和重灾区地震地质灾害的分布和发育特点, 认为芦山地震最有可能的发震断裂为龙门山前山断裂的双石—大川断裂, 也有可能是龙门山山前隐伏断裂的大邑断裂, 还有可能是双石—大川断裂与大邑断裂两者共同触发的结果.      

Resistivity mapping using the VLF-MT method around surface fault ruptures of the 1995 Hyogo-ken Nanbu earthquake, Japan

Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo-ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF-MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR-0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo-ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.     

运用古地震数据评价东昆仑断裂带东段未来百年的强震危险性

通过收集、整理和分析青藏高原东北部22条断裂带上古地震定量数据,拟定了该区的地震复发概率密度函数.根据此函数对区内东昆仑断裂带东段不同段落上未来100年内强震原地复发的条件概率进行了初步研究.结果表明,该断裂带上自西向东的3个破裂段中,玛沁段和塔藏段未来20、50、100年的复发概率值介于0.76%~7.36%之间,玛曲段未来20、50年的复发概率值介于2.0%~5.26%,属于低概率事件;玛曲段未来100年的复发概率值为10.82%,属于中概率事件;整个段未来100年内至少发生一次7级以上强震的联合概率可达21.87%,属于中概率事件.考虑到概率模型的不确定性,进一步对各段进行了危险性的定性分类,综合评价认为玛沁段在未来百年内发生大震的危险性较低,玛曲段和塔藏段未来百年发生大震的危险性较高.最后将本文拟合的概率密度函数与传统通用函数计算的条件概率值进行比较,发现通用的复发概率函数随着自变量t/R的增大,因变量P的反映不如本文拟合函数的敏感.     

Great earthquake at 7.3 ka inferred from tsunami deposits in the Sukumo Bay area,Southwestern Japan

Tsunami deposits in Kyushu Island, Southwestern Japan, have been attributed to the 7.3 ka Kikai caldera eruption, but their origin has not been confirmed. We analyzed an 83-cm-thick Holocene event deposit in the SKM core, obtained from incised valley fill in the coastal lowlands near Sukumo Bay, Southwestern Shikoku Island. We confirmed that the event deposit contains K-Ah volcanic ash from the 7.3 ka eruption. The base of the event deposit erodes the underlying inner-bay mud, and the deposit contains material from outside the local terrestrial and marine environment, including angular quartz porphyry from a small inland exposure, oyster shell debris, and a coral fragment. Benthic foraminifers and ostracods in the deposit indicate various habitats, some of which are outside Sukumo Bay. The sand matrix contains low-silica volcanic glass from the late stage of the Kikai caldera eruption. We also documented the same glass in an event deposit in the MIK1 core, from the incised Oyodo River valley in the Miyazaki Plain on Southeastern Kyushu. These two 7.3 ka tsunami deposits join other documented examples that are widely distributed in Southwestern Japan including the Bungo Channel and Beppu Bay in Eastern Kyushu, Tachibana Bay in Western Kyushu, and Zasa Pond on the Kii Peninsula as well as around the caldera itself. The tsunami deposits near the caldera have been divided into older and younger 7.3 ka tsunami deposits, the younger ones matching the set of widespread deposits. We attribute the younger 7.3 ka tsunami deposits to a large tsunami generated by a great interplate earthquake in the Northern part of the Ryukyu Trench and (or) the Western Nankai Trough just after the late stage of the Kikai caldera eruption and the older 7.3 ka tsunami deposits to a small tsunami generated by an interplate earthquake or Kikai caldera eruption.     

Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan, China,that caused the 2008 Wenchuan earthquake

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake, at an outcrop in Hongkou, Sichuan province, China. Present work is a part of comprehensive project of Institute of Geology, China Earthquake Administration, trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties. Outcrop studies could be integrated with those performed on samples recovered from fault zone drilling, during the Wenchuan Earthquake Fault Scientific Drilling (WFSD) Project, to understand along-fault and depth variation of fault zone properties. The hanging wall side of the fault zone consists of weakly-foliated, clayey fault gouge of about 1 m in width and of several fault breccia zones of 30–40 m in total width. We could not find any pseudotachylite at this outcrop. Displacement during the Wenchuan earthquake is highly localized within the fault gouge layer along narrower slipping-zones of about 10 to 20 mm in width. This is an important constraint for analyzing thermal pressurization, an important dynamic weakening mechanism of faults. Overlapping patterns of striations on slickenside surface suggest that seismic slip at a given time occurred in even narrower zone of a few to several millimeters, so that localization of deformation must have occurred within a slipping zone during coseismic fault motion. Fault breccia zones are bounded by thin black gouge layers containing amorphous carbon. Fault gouge contains illite and chlorite minerals, but not smectite. Clayey fault gouge next to coseismic slipping zone also contains amorphous carbon and small amounts of graphite. The structural observations and mineralogical data obtained from outcrop exposures of the fault zone of the Wenchuan earthquake can be compared with those obtained from the WFSD-1 and WFSD-2 boreholes, which have been drilled very close to the Hongkou outcrop. The presence of carbon and graphite, observed next to the slipping-zone, may affect the mechanical properties of the fault and also provide useful information about coseismic chemical changes.     

Internal structure of Longmenshan fault zone at Hongkou outcrop,Sichuan,China,that caused the 2008 Wenchuan earthquake

This paper reports the internal structures of the Beichuan fault zone of Longmenshan fault system that caused the 2008 Wenchuan earthquake,at an outcrop in Hongkou,Sichuan province,China.Present work is a part of comprehensive project of Institute of Geology,China Earthquake Administration,trying to understand deformation processes in Longmenshan fault zones and eventually to reproduce Wenchuan earthquake by modeling based on measured mechanical and transport properties.Outcrop studies could be integrate...     

基于小震定位与震源机制解信息的阿尔金断裂带东段构造转换研究

阿尔金断裂带东段地区的造转换及其动力学机制研究一直是地学工作者关注的焦点.本文利用双差定位法获取研究区域2008—2017年间6013次地震事件的精确定位数据;整理筛选前人震源机制解36个,并采用P/S波振幅比方法计算获得221个以及CAP方法获得25个震源机制解信息.选择野马河—大雪山断裂作为研究区构造转换研究的突破口,综合小震定位数据与震源机制解信息,并开展野外地质调查进行验证,清晰刻画出该断裂的深部构造形态以及现今的运动特征：由阿尔金断裂带向祁连山方向过渡,断层产状由近直立逐渐转变为倾向南,倾角变缓,震源机制解由走滑性质为主转变为逆冲性质为主,是一个连续渐变的过程,为研究区的构造转换研究提供了直接证据.     

In situ stress measurements in NIED boreholes in and around the fault zone near the 1995 Hyogo-ken Nanbu earthquake, Japan

Abstract The 1995 Hyogo-ken Nanbu (Kobe) earthquake, M 7.2, occurred along the north-east–south-west trending Rokko–Awaji Fault system. Three boreholes of 1001 m, 1313 m and 1838 m deep were drilled in the vicinity of the epicenter of the earthquake. Each borehole is located at characteristic sites in relation to active faults and the aftershock distribution. In particular, the Nojima–Hirabayashi borehole [Hirabayashi National Research Institute for Earth Science and Disaster Prevention (NIED) drilling] in Awaji Island was drilled to a depth of 1838 m, approximately 320 m southeast from the surface rupture of the Nojima Fault, and it crosses fracture zones below a depth of 1140 m. In situ stress measurements by the hydraulic fracturing method were conducted in these boreholes within 1.5 years after the earthquake. Measurement results suggest the following: (i) Differential stress values are very small, approximately 10 MPa at a depth of 1000 m at each site; (ii) the orientation of maximum horizontal compression is almost the same in the boreholes, perpendicular to the surface trace of the faults, north-west–south-east; (iii) fault types estimated from the state of stress differ among these sites; and (iv) the differential stress value just beneath the fault fracture zone decreases abruptly to one-half of that above the fault zone in the Hirabayashi NIED drilling. These features support the idea that the shear stress along the Rokko–Awaji Fault system decreased to a low level just after the earthquake.     

东昆仑断裂带东端的构造转换与2017年九寨沟MS7.0地震孕震机制

2017年四川九寨沟M_S7.0地震是继2008年汶川M_S8.0地震和2013年芦山M_S7.0地震之后,青藏高原东缘在不到十年的时间内发生的第三个震级M_S7.0以上的强震.这次地震发生在东昆仑断裂带东端,作为青藏高原东北缘的一条大型左旋走滑断裂带,东昆仑断裂带与东端其它构造之间的转换关系仍不清楚,因区内地质构造和地形复杂,东昆仑断裂带东端的主要构造仍缺少深入的研究.本文在总结区域地震构造活动特征、历史地震和现代地震基础上,通过东昆仑断裂带东端已有的和最近开展的活动构造定量研究结果,并结合现今GPS变形场资料和2017年九寨沟M_S7.0地震灾害特征分析,发现东昆仑断裂带最东段塔藏断裂上的左旋走滑除了一小部分继续向东传播转移到文县断裂带上外,大部分转化为其南侧的龙日坝断裂带北段、岷江断裂和虎牙断裂上的近东西向地壳缩短,这可能是岷山隆起的构造机制,而2017年九寨沟M_S7.0地震正是左旋走滑的东昆仑断裂带在东端继续向东扩展的结果.

     

巴颜喀拉块体北和东边界大地震序列的关联性与2008年汶川地震

2008年汶川地震发生在巴颜喀拉块体的东边界.为了探讨区域动力学背景与该地震发生的关系,本文基于活动构造、震源机制解、GPS站速度、地震破裂展布以及历史大地震活动等资料分析巴颜喀拉块体北、东两个边界断裂系统的运动、变形以及大地震序列发生的关联性.结果表明:由于受到华南地块的阻挡,巴颜喀拉块体朝东-南东方向的 "逃逸"运动—表现为该块体北边界的左旋走滑断层作用—在该块体的东边界转换成为逆冲或缩短兼走滑断层作用,亦即该块体的运动对其东边界断裂系统具有显著的"加载"作用.这种加载作用也反映在该块体北和东两个边界大地震序列发生的关联性上.19世纪中-晚期至2001年期间,一个由8次事件组成的大地震序列使巴颜喀拉块体北边界总长度的2/3破裂,该序列同时具有加速应变释放以及事件的间隔逐渐缩短的特征,反映最晚自1902年以来该块体发生了加速运动.作为对这一加速运动的响应,巴颜喀拉块体东边界大约自1933年以来发生一个由3次事件组成的大地震序列,也显示出加速释放以及事件的间隔逐渐缩短的特征;2008年汶川地震正是该响应序列中的最新事件.东边界的响应型大地震序列的发生至少滞后于北边界的数十年,可能与该块体的非刚性运动有关.另外,这两个大地震序列的事件序次-时间关系有助于分析该块体北与东边界的中-长期地震危险性.     

利用余震震中分析芦山MS7.0 地震发震构造

对2013年4月20日芦山M_S7.0地震主震震中周边29个地震台记录到的震后一年多的微、 小余震,利用Hypo71绝对定位方法进行定位,获得了约1960次地震的震源位置. 结果显示,芦山地震余震在平面上主要沿双石—大川分支断裂及其周边分布,在垂向上主要集中在大约5—20 km深度之间的两条余震交叉带上. 其中一条余震带倾向NW,倾角在12 km左右深度发生变化,浅部倾角较陡,该余震带延伸至地表与双石—大川分支断裂和新开店断裂之间的推测隐伏断裂位置相重合; 另一条余震带倾向SE,其延伸至地表的位置与双石—大川断裂非常接近,但与该断裂倾向相反. 主震震源位置与两条余震带相交的位置接近,且芦山地震主震的两个节面产状与这两条余震带的深部几何形态正好对应, 表明芦山地震主震可能是两条余震带所对应的两条断裂同时活动的结果.      

2016年阿克陶MW6.6地震的同震断层滑动分布及库伦应力变化

2016年11月25日新疆阿克陶地区发生的M_W6.6地震,对当地人民生命造成一定的危害。基于Sentinel-1数据获取该地震的视线向同震形变场,采用贝叶斯方法反演单一断层走向为106.9°、倾角为73.8°、震源深度为17.35 km,在此断层几何模型基础上,以最速下降梯度法（Steepest Descent Method,SDM）反演滑动分布,结果表明断层面上存在两个滑动峰值,其中位于断层西侧的最大滑动量为0.66 m,深度为11.7 km,位于断层东侧的最大滑动量为0.83 m,深度为7.5 km,根据反演结果模拟LOS形变,其最大残差为~5 cm。构建倾角分别为70.79°和55.33°的双断层几何模型,并根据双断层几何模型反演了滑动分布,结果表明单一断层模型与双断层模型的滑动分布具有一致性,但是最大滑动量值有所不同,相对于单一断层模型的滑动分布而言,双断层模型的滑动量在西侧增大,其值为0.68 m;而在东侧减小,其值为0.77 m;最大残差降低了约2 cm。双断层模型库伦应力增加区域与余震的分布比较吻合。