Coseismic displacement estimate of the 2013 <Emphasis Type="Italic">M</Emphasis><Subscript>S</Subscript>7.0 Lushan,China earthquake based on the simulation of near-fault displacement field

Usually, GPS observation provides direct evidence to estimate coseismic displacement. However, GPS stations are scattered, sparse and cannot provide a detailed distribution of coseismic displacement. Strong ground motion records share the same disadvantages as GPS in estimating coseismic displacement. Estimations from InSAR data can provide displacement distributions; however, the resolution of such methods is limited by the analysis techniques. The paper focuses on estimating the coseismic displacement of the M _S7.0 Lushan earthquake on April 20, 2013 using a simulation of the wave field based on the elastic wave equation instead of a quasi-static equation. First, the media and source models were constructed by comparing the simulated velocity and the record velocity of the ground motion. Then simulated static displacements were compared with GPS records. Their agreement validates our results. Careful analysis of the distribution of simulated coseismic displacements near the fault reveals more details of the ground motion. For example, an uplift appears on the hanging wall of the fault, rotation is associated with the horizontal displacement, the fault strike and earthquake epicenter provide the main control on motion near the faults, and the motion on the hanging wall is stronger than that on the footwall. These results reveal additional characteristics of the ground motion of the Lushan earthquake.     

用多种数据构建2008年汶川特大地震同震位移场

本文主要以GPS、精密水准观测和卫星SAR遥感图像分析2008年汶川特大地震同震位移特征.GPS数据包括:(1)四川盆地和川西高原地区各类国家等级GPS网点复测;(2)沿破裂带国家天文大地网GPS复测.前者推算的同震位移测定精度优于2 cm,后者6~8 cm.SAR遥感资料包括:(1)ALOS 卫星升轨相位干涉图像,精度优于8 cm;(2)ALOS和ENVISAT卫星影像合成的三维位移图,精度优于0.5 m.同震位移场显示,断层下盘(四川盆地)变形总体呈扇形集中指向震中,断层上盘(龙门山)变形总体上呈逆时针旋转态势,最大的实测水平位移5.5 m.汶川、理县、茂县等地测站位移指向破裂带方向,而平武、青川等地测站逐渐转变为平行,乃至远离破裂带方向,与汶川地震逆冲兼走滑的破裂特征一致.断层上盘大幅隆升,下盘靠近断层的区域以下沉为主,远场表现为幅度很小的隆升,垂直升降区域间,有一条与龙泉山断裂带平行的升降过渡带,调节龙泉断层的应力状态.用实测变形场检验多个地震波破裂模型表明,近场(距离断层50 km) 模型形变准确度可达40~50 cm, 远场精度优于5 cm.     

芦山地震地震动上下盘效应研究

2013年4月20日的芦山7.0级地震是继2008年5月12日汶川8.0级特大地震之后,发生在龙门山断裂带上的又一次大震级逆冲型地震.与汶川地震相比,芦山地震的发震断层没有地表出露,断层的滑动角更大,其逆冲性质更强烈.本文挑选了芦山地震中断层距小于200km的45条强震动记录,基于地震动衰减关系进行统计分析,对比了上盘和下盘台站地震动参数相对于衰减关系的对数残差.结果表明：芦山地震的上下盘效应明显,近断层上盘地震动的高频成分要高于同断层距的下盘;上盘地震动衰减要明显快于下盘.地震动衰减关系用简单的一个距离参数很难描述近场断层尺寸效应的影响,也很难模拟地震动上下盘效应.因此,在近场强地面运动模拟中,应多考虑有限断层模型,以模拟断层的尺寸效应.     

利用强震数据获取汶川地震近断层地面永久位移

利用汶川地震中得到的靠近映秀—北川主断裂的64个强震台站的三分量记录数据, 对加速度记录进行基线校正的基础上获取近断层地面运动的永久形变位移, 并将由强震记录获取到的地面位移结果与GPS观测到的同震位移进行对比分析, 研究汶川M_S8.0地震的近断层地面运动的位移特征. 结果表明: ① 在靠近映秀—北川主断层的上盘和下盘, 东西相向的地面运动非常剧烈. 下盘的51SFB, 51MZQ和51JYH台东西向位移均为负(即地面运动向西), 其中51SFB台位移量最大, 达到1.49 m; 上盘的51WCW台位移向东, 位移量为1.26 m. ② 地面运动的位移分布主要表现为以龙门山断裂带的映秀—北川断裂为核心的相向运动, 东西方向上的永久位移要大于南北方向. 从断层机制上来讲, 断层的错动以逆冲运动为主(即逆冲位移要大于走滑分量的位移), 这与震源机制反演及地质考察的结果一致. ③ 大的地面永久位移集中分布在以龙门山断裂带为中心的狭长范围内, 离开发震断裂地面位移的衰减很快. 相比而言, 在发震断层的下盘一侧(即四川盆地)的地面位移的衰减比上盘一侧明显要快.      

Characteristics of amplitude and duration for near fault strong ground motion from the 1999 Chi-Chi, Taiwan Earthquake

A great number of free-field ground motion records are obtained during the 1999 Chi-Chi, Taiwan, earthquake. Records from 130 near fault free-field stations within 55 km to the causative fault surface are used as database, and characteristics of earthquake peak ground acceleration, velocity, displacement and duration are analyzed. According to this study, near fault ground motions are strongly affected by distance to fault, fault rupture directivity, site condition, as well as thrust of hanging wall. Compared with empirical strong ground motion attenuation relations used in China, US and Japan, the PGAs and PGVs recorded in this earthquake are not as large as what we have expected for a large earthquake as magnitude 7.6. However, the largest PGV and PGD worldwide were recorded in this event, which are 292 cm/s and 867 cm, respectively. Caused by nonlinear site effects of soil, peaks and corresponding ratios on E-class site were markedly different from those on other sites. Just as observed in historic earthquakes, fault rupture directivity effects caused significant differences between peaks of ground motion of two horizontal components, but took very slight effects on the duration of ground motion. The significant velocity pulses associated with large PGVs and PGDs, as well as large permanent displacements, which may result from the large thrust of the hanging wall, became the outstanding character of this event. Based on this study, we point out that 3D waveform modeling is needed to understand and predict near fault ground motion of large earthquakes.     

2016年8月24日意大利佩鲁贾MW 6.2级地震同震位移场估计和震源滑动模型反演

利用改进的自动经验基线校正方法SMBLOC,对2016年8月24日意大利佩鲁贾MW 6.2级地震震中周围约60 km内的近场强震记录进行基线校正并尝试给出同震位移场,与GPS观测结果进行对比分析,分别独立和联合两种资料反演震源滑动模型,并根据震源模型进一步给出全空间预测位移场分布.研究结果表明:(1)两种不同的资料给出的水平位移场幅值均为cm级,且均表明断层的错动以正断为主.(2)两种同震位移场分别独立和联合反演所得的震源静态滑动范围基本一致,最大滑动均发生在震中东北侧,强震模型表现出明显的双事件特征,较大滑动分布在震中东北侧和东南侧,GPS模型在震中东南侧的滑动相对较小,其双事件特征不明显.两种模型的最大滑动量分别为0.96 m和0.86 m,较为一致,反演的矩震级均在MW 6.3左右.(3)根据震源滑动模型计算所得的佩鲁贾地震全空间预测的水平同震位移场中最大位移分布区域与震后报告中受灾严重的地区基本一致.表明在一定的条件下,利用SMBLOC方法解算震级较小的MW 6.0左右地震强震记录的同震位移场,并反演震源滑动模型具有一定的可行性,且其同震位移场和滑动模型可为震后灾害快速评估、救援力量分配、余震趋势判定等快速应急响应工作提供参考依据.     

汶川地震形成位移场的空间分布

采用Yoshimitsu Okada及Steketee的断裂位错模型和汶川地震现有成果,通过坐标转换和合成矢量的方法将断裂位错模型用于映秀—北川断裂、灌县—安县断裂和北川—青川断裂组成的断裂系统的错动研究中,理论上计算龙门山近断裂地区的水平位移场(包括沿走向和垂直走向方向)和垂直位移场从震源到地表的分布.模型参数源于现有的研究成果和野外实地考察,计算得到的地表位移场与先前研究成果,包括GPS实测数据,具有的近似性表明了模型的正确性.但GPS只能测定地表水平和垂直变形,对于地下变形情况及其分布却无法描述;目前对于地下变形的研究主要基于对大量仪器记录的地震资料进行反演或通过野外观测进行推测;但是反演多集中于空间较大范围,这样虽可阐述断裂运动引起的大范围位移趋势,而对于震源附近空间介质位移的描述却略显粗糙;同时,野外观测误差较大.本文通过理论模型计算汶川地震中近断裂区域(距断裂50km)内的位移及分布.由计算发现在近断裂区域内垂直位移场和垂直走向方向位移场变化趋势一样,幅值都是从震源到地表逐渐减小;沿断裂走向方向的水平位移场从震源到地表逐渐变大,同时计算还表明位移场的变化在断裂上盘比下盘剧烈,余震分布主要集中于断裂上盘,这说明余震分布和位移剧烈程度存在某种相关性.     

日本熊本MW7.0地震同震位移场和震源滑动模型反演

利用2016年4月16日日本熊本M_W7.0地震震中周围94个近场强震动台的观测资料和新近改进的强震经验基线校正方法SMBLOC,尝试解算并绘制了一个内陆M7左右走滑型地震的同震位移场全貌,并反演了其震源滑动模型.与日本国土地理院(GSI)公布的该地震57个GPS同震位移结果的比较显示,两种完全不同资料、不同解算方法给出的水平同震位移场的最大幅值均为100 cm左右,均呈右旋走滑为主兼具部分正断分量的震源机制.强震最大水平和垂直永久位移分别为104.5 cm和58.0 cm, 分别出现在震中东北侧的KMMH162台和KMM005台.两种资料单独以及联合反演的震源滑动模型均表明,此次地震为北东侧破裂为主并呈双事件特征,且主要滑动均不在初始破裂点附近, 而是集中于第二次事件周围,即距离初始破裂点东北侧约20 km处的走向长约40 km、倾向宽约20 km的范围内.基于强震和GPS模型所得的最大滑动量分别为5.10 m和5.87 m,量级一致,反演矩震级均为M_W7.1左右;主破裂区近地表滑动量比野外调查结果略微偏大,可能与数值效应有关.此外,还利用不同方法得到的解算结果比较了熊本地震特有的12组台间距在3 km以内的GPS-强震台站对各自的三分量同震位移,其结果表明对于M7左右的地震而言,SMBLOC方法解算同震位移时方向和幅值的可靠性下限约为2 cm.      

芦山MS7.0地震前水平位移和同震水平位移研究

本文利用“中国地壳运动观测网络（二期）”多个GPS连续观测站观测数据处理结果,将2013年4月20日四川芦山MS7.0地震区域参考框架同震水平位移与全球参考框架同震水平位移进行比较,结果表明两组框架解一致,说明两种参考框架均可当作位错参考框架,也即全球参考框架同震水平位移也可视为区域参考框架同震水平位移．区域参考框架下GPS连续观测站地震前的水平位移和同震水平位移结果表明,震前数年,SCTQ站西侧的GPS站构造运动十分显著,而该站水平位移却很小,即出现反常的闭锁．但该站的同震水平位移使其弹性回跳至正常构造水平位移水平,因此SCTQ站震前的位移闭锁是水平位移空间分布中的异常,是芦山MS7.0地震的前兆．水平位移时空变化表明,该站震前和震时位移完全符合里德的弹性回跳理论．区域参考框架中位移时间系列和同震水平位移的综合研究有助于对芦山地震地壳运动前兆的认识和解释．尽管本文未能直接采用其它GPS连续观测站的资料,但结合本文和其它研究结果可以证实,震中附近其它站地震前后的变化与SCTQ站类似．基于芦山地震前水平位移和同震水平位移及其与前兆关系的研究,本文进一步讨论了GPS监测网的布设、 数据处理和分析等问题．      

2013年四川芦山MS7.0地震近断层强地面运动模拟及烈度分布估计

2013年4月20日在我国四川省发生了芦山M_S7.0地震,地震给当地群众的生命财产安全带来了巨大的损失,其中最严重的破坏发生在震中附近的芦山、宝兴等地区.根据地震发生的快速反演结果,及发震断层面上滑动位移的分布情况,构建有限断层模型,对近断层区域的强地面运动进行初步计算,并基于强地面运动的模拟结果给出震区烈度分布的初步估计.模拟结果显示：模拟烈度图显示极震区的烈度在IX级左右,VI级烈度影响范围大致为16000 km²,该结果与中国地震局于4月27日给出的震区实测烈度图一致程度较高.强烈地震发生后,基于近断层强地面运动模拟计算的结果,可以给出相对合理的地震烈度分布情况估计,对震区震情判定及救灾工作具备较高的现实意义.     

2014年新疆于田MS7.3地震同震位移及位错反演研究

利用于田震中300 km范围内的1个GPS连续站和12个GPS流动站数据,解算得到了2014年新疆于田M_S7.3地震地表同震位移,并反演了发震断层滑动分布,探讨此次地震对周边断裂的影响.地表同震位移结果显示,GPS观测到的同震位移范围在平行发震断裂带的北东-南西向约210 km,垂直发震断裂带的北西-南东方向约为120 km,同震位移量大于10 mm的测站位于震中距约120 km以内;同震位移特征整体表现为北东-南西方向的左旋走滑和北西-南东方向的拉张特征,其中在北东-南西方向,I069测站位移最大,约为32.1 mm,在北西-南东方向,XJYT测站位移最大,约为28.1 mm;位错反演结果表明,最大滑动位于北纬36.05°,东经82.60°,位于深部约16.6 km,最大错动量为2.75 m,反演震级为M_W7.0,同震错动呈椭圆形分布,以左旋走滑为主并具有正倾滑分量,两者最大比值约为2.5：1,同震错动延伸至地表,并向北东方向延伸,总破裂长度约50 km,地表最大错动约1.0 m;同震水平位移场模拟结果显示贡嘎错断裂、康西瓦断裂和普鲁断裂等不同位置主应变特征具有差异性,这种差异特征是否影响断裂带以及周围区域的应力构造特征,值得关注.     

THE COSEISMIC VERTICAL DISPLACEMENTS OF SURFACE RUPTURE ZONE OF THE 1556 HUAXIAN EARTHQUAKE

Coseismic displacement plays a role in earthquake surface rupture, which not only reflects the magnitude scale but also has effect on estimates of fault slip rate and earthquake recurrence intervals. A great historical earthquake occurred in Huaxian County on the 23^rd January 1556, however, there was lack of surface rupture records and precise coseismic vertical displacements. It's known that the 1556 Huaxian earthquake was caused by Huashan front fault and Weinan plateau front fault, which are large normal faults in the east part of the southern boundary faults in Weihe Basin controlling the development of the basin in Quaternary. Here, we made a study on three drilling sites in order to unveil the coseismic vertical displacements. It is for the first time to get the accurate coseismic vertical displacements, which is 6m at Lijiapo site of Huashan front fault, 7m at Caiguocun site, and 6m at Guadicun site of Weinan plateau front fault. These coseismic displacements measured based on same layers of drilling profiles both at footwall and hanging wall are different from the results measured by former geomorphological fault scarps. It's estimated that some scarps are related with the nature reformation and the human beings' activities, for example, fluviation or terracing field, instead of earthquake acticity, which leads to some misjudgment on earthquake displacements. Moreover, the vertical displacements from the measurement of geomorphological scarps alone do not always agree with the virtual ones. Hence, we assume that the inconsistency between the results from drilling profiles and geomorphological scarps in this case demonstrates that the fault scarp surface may have been demolished and rebuilt by erosion or human activities.     

芦山7级地震的同震位移估计和震源滑动模型反演尝试

利用自动经验基线校正方法,分析2013年4月20日芦山M_S7.0级地震13个近场强震动台的观测资料,以估算同震位移场分布,并据此反演了震源滑动模型.经与GPS结果比较,两种不同方法给出的芦山7级地震的水平近场同震位移场幅度都不超过cm级,均显示为典型的逆冲型地震（兼有少量左旋走滑错动）.强震最大水平和垂直永久位移分别为4.9 cm和4.4 cm,分别出现在51YAM台和51QLY 台.两种资料反演的震源滑动模型虽显示多事件特征,但主要滑动均集中在第一次事件,即初始滑动点两侧的走向长约30 km、倾向长约25 km的相对集中的较小范围内,强震和GPS模型的最大滑动量分别为1.14 m和1.09 m,较为一致.其余子事件滑动量小且分布零散,不能排除其数值效应的因素.反演矩震级均在M_w6.7左右,地表破裂应该不明显.文章还讨论了目前在我国利用近场强震动记录估计M_w6~7级地震同震位移场存在的困难和问题,为今后类似工作提供参考.     

Ground motion characteristics of the Chi‐Chi earthquake of 21 September 1999

The purpose of this paper is to investigate the ground motion characteristics of the Chi‐Chi earthquake (21 September 1999) as well as the interpretation of structural damage due to this earthquake. Over 300 strong motion records were collected from the strong motion network of Taiwan for this earthquake. A lot of near‐field ground motion data were collected. They provide valuable information on the study of ground motion characteristics of pulse‐like near‐field ground motions as well as fault displacement. This study includes: attenuation of ground motion both in PGA and spectral amplitude, principal direction, elastic and inelastic response analysis of a SDOF system subjected to near‐field ground motion collected from this event. The distribution of spectral acceleration and spectral velocity along the Chelungpu fault is discussed. Based on the mode decomposition method the intrinsic mode function of ground acceleration of this earthquake is examined. A long‐period wave with large amplitude was observed in most of the near‐source ground acceleration. The seismic demand from the recorded near‐field ground motion is also investigated with an evaluation of seismic design criteria of Taiwan Building Code. Copyright © 2000 John Wiley & Sons, Ltd.     

ANALYSIS ON THE CHARACTERISTICS OF DURATION AND PERIOD OF GROUND MOTION OF THE LUSHAN EARTHQUAKE BASED ON THE STATION RECORDS

Based on 60 records from the 20 stations within 100km to the epicenter of Lushan earthquake, the predominant period, period of peak response spectrum, duration of ground motion, and source duration are investigated. By the study, we conclude that within 100km to the epicenter, the scope of predominant period is 0.013~0. 275s in EW, NS and UD direction; the scope of period of peak response spectrum for 5% damping ratio is 0.03~0.65s; the scope of 90% ground motion durations is 5. 1~35. 9s; the scope of averaging source duration is 6.41 (EW), 6.05 (NS) and 5.47s (UD). Furthermore, based on the ground motion duration calculated by 20 stations dada, the predictive curve and equation of ground motion duration is regressed and compared with the recent equation of ground motion duration by Bommer (2009). We find that the ground motion durations of most stations are larger than predictively mean value by Bommer (2009), which means that the source effect of Lushan earthquake is relatively larger. Lastly, by the contour figure of ground motion duration and source duration, we conclude that the directivity character of duration is relatively apparent in NE direction. The relatively larger source duration and ground motion duration in NE direction indicate more energy release in the main shock of Lushan earthquake, which perhaps causes the relatively less aftershocks in this direction. The duration has no hanging wall effect, which perhaps results from the blind-reverse fault structure of Lushan earthquake.     

2004年苏门答腊地震的几个断层滑动模型的全球同震位移对比

2004年苏门答腊大地震后,不同作者根据地震波和/或GPS观测,提出了不同的断层错动模型.在利用同震位移观测资料反演断层滑动模型时,由于使用半无限空间均匀介质模型或半无限空间分层介质模型,一般只能利用近场位移GPS观测约束,无法利用远场资料,这些模型有时差别颇大,如何区别这些模型的优劣是一个仍尚未解决的问题.本文采用等效体力有限元方法,在考虑地球球形和分层的条件下,对四个不同作者提供的2004年苏门答腊地震的断层滑动模型计算全球同震位移.由于采用了球形模型,所以不仅可以把四个模型的近场位移计算结果与GPS数据进行对比,而且可以把远场位移计算结果与GPS数据进行对比.我们发现,垂直位移对断层滑动模型的依赖性小于水平位移.四个模型计算的近场位移与GPS位移符合程度均较好,但是四个模型计算的远场位移与GPS位移符合情况有很大不同,其中Chlieh等（2007）模型在近场与远场符合程度均很好,是四个模型中最好的.另外还探讨了断层反演数据资料、断层几何模型以及地球模型对计算结果的影响.对于特大地震,全球同震位移观测与计算值吻合程度的好坏是衡量断层滑动模型的合理性的一个重要依据.     

以形变观测为约束的芦山M_S7.0地震孕震机理数值模拟研究

本文以2013年4月20日芦山MS7.0地震前后在震中附近开展的形变观测研究结果为约束,利用震区天然地震成像、大地电磁测深、人工地震探测剖面、余震精确定位、震源破裂过程、地质考察、GPS观测、构造应力场等结果,建立了芦山地震震中及邻近地区的深浅部构造二维有限元数值模型,探讨了青藏高原向东挤出运动、区域地形特征、地壳内低速带和滑脱面、震区主要断裂带活动等可能因素对芦山地震孕育和破裂的控制作用.模拟结果显示,汶川地震后的青藏高原东部物质相对四川盆地运动速率增大是引发或加快芦山地震发生的主要动力学控制因素,龙门山断裂带西侧上中地壳内部低速带和滑脱面的存在是控制芦山地震震源位置的重要条件,其他因素则是控制龙门山断裂带长时间尺度区域构造活动的动力学因素;同时本文给出了主震破裂为复杂"y"型双破裂面的同震位移,模拟计算的地表垂直位移与观测结果一致,进一步支持了余震精确定位提出的主震为"y"型破裂面的推测.     

Seismic rotational displacement of gravity walls by pseudo-dynamic method: Passive case

Prediction of the seismic rotational displacements of retaining wall under passive condition is an important aspect of design in earthquake prone region. In this paper, the pseudo-dynamic method is used to compute the rotational displacements of rigid retaining wall supporting cohesionless backfill under seismic loading for the passive earth pressure condition. The proposed method considers time, phase difference and effect of amplification in shear and primary waves propagating through both the backfill and the retaining wall. The influence of ground motion characteristics on rotational displacement of the wall is evaluated. Also the effects of variation of parameters like wall friction angle, soil friction angle, amplification factor, shear wave velocity, primary wave velocity, period of lateral shaking, horizontal and vertical seismic accelerations on the rotational displacements are studied. The rotational displacement of the wall increases substantially with increase in amplification of both shear and primary waves, time of input motion, period of lateral shaking and decreases with increase in soil friction angle, wall friction angle. The rotational displacements of the wall also increase when the effect of wall inertia is taken into account. Results are provided in graphical form.     

Rupture model of the 2013 M_W 6.6 Lushan (China) earthquake constrained by a new GPS data set and its effects on potential seismic hazard

Vertical records are critically important when determining the rupture model of an earthquake, especially a thrust earthquake. Due to the relatively low fitness level of near-field vertical displacements, the precision of previous rupture models is relatively low, and the seismic hazard evaluated thereafter should be further updated. In this study, we applied three-component displacement records from GPS stations in and around the source region of the 2013 MW6.6 Lushan earthquake to re-investigate the rupture model.To improve the resolution of the rupture model, records from both continuous and campaign GPS stations were gathered, and secular deformations of the GPS movements were removed from the records of the campaign stations to ensure their reliability. The rupture model was derived by the steepest descent method(SDM), which is based on a layered velocity structure. The peak slip value was about 0.75 m, with a seismic moment release of 9.89 × 10~(18) N·m, which was equivalent to an M_W6.6 event. The inferred fault geometry coincided well with the aftershock distribution of the Lushan earthquake. Unlike previous rupture models, a secondary slip asperity existed at a shallow depth and even touched the ground surface. Based on the distribution of the co-seismic ruptures of the Lushan and Wenchuan earthquakes, post-seismic relaxation of the Wenchuan earthquake, and tectonic loading process, we proposed that the seismic hazard is quite high and still needs special attention in the seismic gap between the two earthquakes.     

近断层地震动的基本特征

本文对近断层地震动的基本特征作了详细分析,这些基本特征主要包括近断层强地震动的集中性、地表破裂、地面永久变形、破裂的方向性效应、近断层速度大脉冲和上盘效应。这些特征虽然在一次地震中不一定同时出现,但它们是已经被强震观测资料和数值模拟证实了的,在模拟和预测近断层地震动时,必须充分考虑这些特点,合理的近断层地震动模拟或预测模型和方法应当在结果中再现这些特点。