Quick moment tensor solution for 6 April 2009,L'Aquila,Italy,earthquake

A Mw6.4 earthquake occurred in L＇Aquila, central Italy at 1：32：42 （UTC）, April 6, 2009. We quickly obtained the moment tensor solution of the earthquake by inverting the P waveforms of broadband recordings from the global seismographic network （GSN） stations using the quick technique of moment tensor inversion, and further inferred that the nodal plane of strike 132°, dip 53° and rake -103° is the seismogenic fault.

Coseismic slip distribution of 2009 L'Aquila earthquake derived from InSAR and GPS data

To better understand the mechanism of the Mw6.3 L＇Aquila （Central Italy） earthquake occurred in 2009, global positioning system （GPS） and interferometric synthetic aperture radar （InSAR） data were used to derive the coseismic slip distribution of the earthquake fault. Firstly, based on the homogeneous elastic half-space model, the fault geometric parameters were solved by the genetic algorithm. The best fitting model shows that the fault is a 13.7 km×14.1 km rectangular fault, in 139.3° strike direction and 50.2° southwest-dipping. Secondly, fixing the optimal fault geometric parameters, the fault plane was extended and discretized into 16× 16 patches, each with a size of 1 kmx 1 krn, and the non-uniform slip distribution of the fault was inverted by the steepest descent method with an appropriate smoothing ratio based on the layered crustal structure model. The preferred solution shows that the fault is mainly a normal fault with slight right-lateral strike slip, the maximum slip of 1.01 m is located in the depth of 8.28 km, the average rake is -100.9°, and the total geodetic moment is about 3.34× 1018 N.m （Mw 6.28）. The results are much closer than previous studies in comparison with the seismological estimation. These demonstrate that the coseismic fault slip distribution of the L＇Aauila earthauake inverted by the crustal model considering layered characters is reliable.

Processes of the displacement field change of the 2009 April 6 M_W6.3 L'Aquila earthquake using persistent scatterer and small baseline methods

Using a time series method that combines both the persistent scatterer and small baseline approaches, we analyzed 9 scenes Envisat ASAR data over the L＇Aquila earthquake, and obtained a Shocke＇s displacement field and its evolution processes. The results show that： （1） Envisat ASAR clearly detected the whole processes of displacement field of the L＇Aquila earthquake, and distinct variations at different stages of the displacement field. （2） Preseismic creep displacement → displacement mutation when faulting → constantly slowed down after the earthquake. （3） The area of the strongest deformation and ground rupture was a low-lying oval depression region to the southeast. Surface faulting within a zone of about 22 km× 14 km, with an orientation of 135°, occurred along the NW-striking and SW-dipping Paganica-S. Demetrio normal fault. （4） In analyzing an area of about 54 km x 59 km, bounded by north-south axis to the epicenter, the displacement field has significant characteristics of a watershed： westward of the epicenter shows uplift with maximum of 130 mm in line-of-sight （LOS）, and east of the epicenter was a region with 220 mm of maximum subsidence in the LOS, concentrating on the rupture zone, the majority of which formed in the course of faulting and subsequence.

Testing Geographical Methodology and Tools for the Study of Territories Damaged by Earthquakes. The Case of L’Aquila and Other Localities Three Years after the April 6th 2009 Event

In this paper, we discuss a geographical methodology supported by specific geo-technologies which we are testing for the study of territories damaged by the L’Aquila earthquake of 6 April 2009 and which can be used in similar situations. Subsequently, we provide an overview of the current situation and make a comparison between some aerial photographs obtained from an overflight in March 2012 and some photos made during our first field study in February 2010, in order to show the work undertaken or not during this period and to substantiate any considerations regarding the choices adopted and the necessary future planning. Moreover, we provide an example of the added value provided by the analysis of aerial photographs in both visible and thermal light for recognizing the provisional non-painted metal roofing of buildings in a post-earthquake urban area. In fact this technique can be useful for the rapid identification of damaged buildings and zones with provisional covering. In the present paper, we focus attention on L’Aquila town centre which provides a significant example of a “City of Stone” almost “minus” the presence of people.

Introspection on improper seismic retrofit of Basilica Santa Maria di Collemaggio after 2009 Italian earthquake

The 2009 L’Aquila, Italy earthquake highlighted the seismic vulnerability of historic masonry building structures due to improper ＂strengthening＂ retrofit work that has been done in the last 50 years. Italian seismic standards recommend the use of traditional reinforcement techniques such as replacing the original wooden roof structure with new reinforced concrete （RC） or steel elements, inserting RC tie-beams in the masonry and new RC floors, and using RC jacketing on the shear walls. The L’Aquila earthquake revealed the numerous limitations of these interventions, because they led to increased seismic forces （due to greater additional weight） and to deformation incompatibilities of the incorporated elements with the existing masonry walls. This paper provides a discussion of technical issues pertaining to the seismic retrofit of the Santa Maria di Collemaggio Basilica and in particular, the limitations of the last （2000） retrofit intervention. Considerable damage was caused to the church because of questionable actions and incorrect and improper technical choices.

Location of Tibetan earthquakes──a nonlinear approach by a simplex optimized technique

An advanced earthquake location technique presented by Prugger and Gendzwill (1988) was introduced in this paper. Its characteristics are: 1) adopting the difference between the mean value by observed arrival times and the mean value by calculated travel times as the original reference time of event to calculate the traveltime residuals, thus resulting in the 'true' minimum of travel-time residuals; 2) choosing the L1 norm statistic of the residuals that is more suitable to earthquake location; 3) using a simplex optimized algorithm to search for the minimum residual value directly and iteratively, thus it does not require derivative calculations and avoids matrix inversions, it can be used for any velocity structures and different network systems and can solve out hypocentral parameters (λ, ,h) rapidly and exactly; 4) original time is further derived alone, so the trade-off between focal depth and original time is avoided. All these prominent features make us obtain more accurate Tibetan earthquake locations in the rare network condition by using this method. In this paper, we examined these schemes for our mobile and permanent networks in Tibet with artificial data sets,then using these methods, we determined the hypocentral parameters of partial events observed in the field work period of this project from July 1991 to September 1991 and the seven problematic earthquakes during 1989 - 1990. The hypocentral location errors may be estimated to be less than 3. 6 km approximately. The events with focal depth more than 40 km seem to be distributed in parallel to Qinghai-Sichuan-Yunnan arc structural zone.

联合Envisat和ALOS卫星影像确定L′Aquila地震震源机制

2009年4月6日意大利L′Aquila地区发生了Mw6.3级地震,该地震造成了300余人的人员死亡.本文联合不同波长、不同入射倾角的升降轨Envisat和ALOS卫星的差分干涉数据对该地震进行震源机制解的反演研究.研究首先对卫星雷达影像进行二通差分干涉处理,获取了覆盖L′Aquila地震震区的完整InSAR同震形变场,然后结合四叉树和均匀采样方法对原始观测数据进行降采样.在此基础上,联合GPS形变观测数据,利用弹性半空间矩形和三角位错模型,以及断层自动剖分技术对断层面进行最优离散剖分,反演获取了发震断层的精确几何参数和最优断层滑动分布,结果显示分布式三角位错滑动模型能够很好地解释观测到的地表形变场.反演结果表明发震断层是一个以正倾滑为主兼有少量右旋走滑的盲断层;基于观测数据最优确定的断层单元的最短边长为0.4km,最长边长为6.3km;此次地震的滑动分布主要发生在5～14km深度的范围内,最大滑移量为1.07m,释放的能量为3.43×1018 N.m(Mw6.32),与地震学的研究结果非常一致.

2009年4月6日意大利拉奎拉(L′Aquila)M_W 6.3地震的破裂过程——视震源时间函数方法与直接波形反演方法比较

通过对视震源时间函数方法和直接波形反演方法在意大利拉奎拉(L′Aquila)M_w 6.3地震破裂过程反演中的应用,分析比较了两种方法的特点.视震源时间函数结果表明,这次地震的破裂过程由两次子事件组成,其中第二次子事件的多普勒效应显著,表明破裂主要朝震中的东南方向传播.分别采用视震源时间函数方法和滑动角固定以及滑动角可变的直接波形反演方法对拉奎拉地震时空破裂过程进行反演所得到的结果一致表明:断层面上有两块滑动量集中的区域,分别位于震源处和沿走向(132°)方向距震源5～10 km处,最大滑动量分别约为1.2 m和1.0 m.破裂持续时间约为9.5 S.最大滑动速率达0.6～0.7 m/S,快速的破裂和上盘下盘效应导致了拉奎拉城的严重破坏.

2020年呼和浩特市和林格尔M_(L)4.5地震破裂方向性测定及发震构造分析

本文基于区域数字地震台网波形数据,在三维空间内利用gCAP反演方法获得2020年3月30日和林格尔M_(L)4.5地震矩心的空间精细位置为40.131°N, 111.922°E,深度为13 km。最佳震源机制解节面Ⅰ为走向279°,倾角41°,滑动角-27°;节面Ⅱ为走向30°,倾角72°,滑动角-127°;矩震级MW3.98。采用双差定位法对主震和余震序列进行重定位,获得19个地震事件的重定位结果。研究表明,主震震源参数为40.136°N, 111.858°E,震源深度为11.718 km;余震序列沿NW—SE方向双向扩展,地下破裂长度约为4.6 km;深度剖面显示,主震位于余震区中部,主破裂同时向上和向下扩展,深度分布范围为4~17 km。利用Hypocenter-Centroid方法对地震发震断层进行快速判断,20组测定结果均显示NW走向的节面Ⅰ为发震断层面。综合震源区地质构造、余震序列分布、区域构造应力场及三维地壳结构等研究结果,推断和林格尔M_(L)4.5地震的发震断层是一条沿NW向延伸的隐伏断裂。本次地震是一次左旋走滑、带正断分量的事件。地震发生于地壳内波速高低转换的过渡区,位于偏高速体一侧。综合分析认为,流体物质的涌入是引发2020年和林格尔M_(L)4.5地震的关键因素,而复杂的断层结构不仅为流体运移提供了通道,且控制着地震的发生及地震序列的空间展布。

The Basilica of Santa Maria di Collemaggio in L＇Aquila： Modern Provisional Measures

The case in analysis is Santa Maria di Collemaggio, the church symbol of the town of L＇Aquila and the most important example of Romanesque style in Abruzzi, tragically damaged by the earthquake in 2009. The following paper starts with an accurate analysis of the Basilica, whose historical, stylistical cultural characteristics make it an unicum in the whole urban environment. The authors tried to identify in which way these values have been compromised or altered after the earthquake through several analysis （surveys, historical researches etc.） aiming at the recognition of collapses, the cracks profile, the structural transformations caused by the provisional measures： the goal is to provide a kind of Basilica ＂cognitive manual＂ that will be useful for the future interventions. This first analysis allowed to understand many aspects： on the one hand, the constructive phases and which damages were caused by past careless interventions of restoration, drawing attention to the vulnerability elements of the Basilica; on the other hand, the innovative technologies and materials of the post-seismic provisional measures and their exact location.

Paleoseismological trenching and seismic hazard assessment of the Bozkurt Segment of the Maymundağı Fault, Acıgöl Graben, SW Türkiye

The Acıgöl Graben in SW Turkey,ca.50-55 km in length and 11-15 km in width,formed during the Miocene to Quaternary periods.This graben is bounded by active normal faults of MaymundağıFault(MF)to the northwest and the GemişFault Zone(GFZ)to the southeast that have triggered significant earthquakes,causing considerable damage.This study focuses on the Bozkurt segment of the MF,which caused a damaging earthquake(Mw 6.0)in 2019 and another significant earthquake in 1886 during historical times.A paleoseismological trench survey along the Bozkurt segment revealed at least two faulting events,with the last event producing a vertical displacement of 0.25 m.The Optical Stimulated Luminescence(OSL)dating indicates that the last earthquake occurred 3.13±0.33 ka BP,while the penultimate earthquake occurred 4.0±0.72 ka BP.These dates correspond to a long-term slip rate of approximately 0.36±0.11 mm/a and a mean recurrence interval of 2.08 ka,short-term slip rate 0.78±0.16 mm/a and recurrence interval of 0.96 ka,and compatible with the mean sedimentation rate of 0.26 mm/a,calculated from drill logs in Acıgöl basin-fill.Considering the 6 km length of the Bozkurt segment and its vertical displacement of 0.25 m in the last event,this segment has the potential to generate earthquakes ranging from 5.6 to 5.9 Mw.Long-term slip rates derived from geomorphological data are 0.56 mm/year to the north and 0.64 mm/a to the south of the graben,indicating higher subsidence on the southern margin.These rates are in accordance with the slip rates calculated from the paleoseismological trench survey and sedimentation rate from the drill-log.These indications show that the Bozkurt segment is an active Holocene fault with relatively long recurrence intervals and low-slip rate.Consequently,the paleoseismological studies in combination with geomorphological data are important tool to assess seismic hazards and to define the characteristics of individual fault segments.

2021年6月17日承德M_(L)3.6地震重新定位及震源机制解研究

2021年6月17日河北省承德市双桥区发生M_(L)3.6地震。基于河北区域数字地震台网资料,采用双差定位算法重新定位该地震序列,获得了精确震中分布。利用小震拟合法计算得到该次地震对应断层面参数为:走向63.76°,倾角70.52°。采用CAP方法反演获得了主震的最佳单位震源参数、矩张量解和双力偶解。其中,最佳断层面解为:走向63.4°,倾角52.8°。根据断层中心解计算,确定最终发震断层面参数为走向63.59°,倾角61.66°,与该区域的双塔山—双峰寺断裂吻合。考虑区域构造特征,推测本次地震可能由主张应力在该断裂上挤压而诱发,属于一个典型的正断层活动。本次研究为确定承德地震的发震构造及该地区的应力场状态提供了重要依据。

中长期地震危险性概率预测中的统计检验方法Ⅱ:N-test和L-test方法

本文介绍了国际"地震可预测性合作研究"CSEP计划中,用于地震概率预测模型检验的N-test和L-test方法的基本原理、发展动态。以地震活动平滑模型(smoothed seismicity model)在新疆天山中部地区的中长期预测结果为例,本文尝试使用N-test和L-test统计检验方法对预测结果进行评价。结果表明,上述方法能够较好地评价预测结果,并有助于构建更为科学合理的地震预测模型及相关参数设置。

L波段InSAR数据观测的北京及其周边2007—2010年间累计地壳形变基本特征

地壳形变是评估地震灾害和地质灾害的重要依据之一。北京及其周边地区的形变状况一直以来缺乏全面、可靠的观测数据,阻碍了对该地区这两种灾害的客观认识。本研究利用L波段InSAR形变观测数据,调查北京及其周边190km×150km范围内,约3年时间内的累积地壳形变,详细给出北京地区2007—2010年间的地壳形变基本特征,为认识该地区的灾害提供参考。研究结果显示,该地区主要地壳形变源为地下水开采造成的地面沉降,观测时间内累积的最大雷达视线向形变达到了37.6cm。地面沉降的严重影响,以及大气噪声的干扰,造成活动构造变形很难从现有数据定量分辨出来,但可以确定在此观测期间内较大尺度(长度>50～100km)的断层活动及其构造变形比较微弱,对北京地区的地壳形变贡献较小。最重要的一点是,北京地区的地壳形变呈条块状分布,清晰显示地面沉降与活动构造,特别是NW走向的南口—孙河断层,存在较强的相关性。

2018年安徽无为M_(L)4.1地震地下流体前兆异常特征

对2018年4月6日无为M_(L)4.1地震前的地下流体前兆异常特征以及该地震的震源机制解进行了分析,结果表明,无为地震前的异常分布在距震中64~233 km范围内,这些异常在时间进程上,可分为中期趋势背景异常和短临异常,主要以中期趋势背景异常为主。这些中期趋势背景异常均表现为水位的破年变变化。从空间演化上看,2018年安徽无为M_(L)4.1地震前出现的中期趋势背景异常沿着长江破碎带有序分布。这种比较明显的异常群体性特征为地震预测提供了较好的依据。震源机制解结果显示,节面I的走向为NE向,节面Ⅱ的走向NW向。反演的震源机制的P轴(主压轴)方向为NE向(70°),倾角近水平(7°)。无为地震震源机制解所得主压应力作用方向与无为地震前异常展布方向相同。这说明地震孕育过程中区域应力加载作用和流体前兆响应具有密切关系。

2022年青州M_(L)4.1地震前后的重力场变化分析

以2022年青州M_(L)4.1地震为研究目标,根据先前学者总结的区域重力场变化在大震孕育发生中的异常特征,通过计算相邻两期重力变化、累计重力变化的方式,分析了震中附近变化的空间尺度和数量级。本文分析了区域重力场变化显著地区的测点单点变化情况,包括高炳西、济南站、王坟及庙子等测点,以及高炳西场地南北两测点重力差的变化情况。根据高炳西场地南北两测点周边干扰情况,包括降水量、地面沉降、地形改正等,分析了该两测点重力差变化的原因。本文认为青州ML4.1地震发震前后的重力场有变化,且该变化与地震孕育发生导致的地下物质迁移有关。

某L型不规则隔震结构减震分析与研究

将基础隔震引入不规则结构中,以某L型不规则结构为例,建立了三维基础隔震实体模型,通过调整隔震层刚心位置,使其与上部质心尽量重合,解决了不规则结构的扭转问题,对隔震与相应的非隔震结构进行不同地震波作用下的非线性动力时程分析.分析表明:采用基础隔震的L型不规则结构能够通过调整刚心与质心的相对位置来减轻扭转带来的震害;采用基础隔震的L型不规则结构可以获得较好的减震效果;结构在罕遇地震下能够保持较好的结构性能和使用功能.

平面L形框剪结构剪力墙布置方案

建筑平面为L形的结构,由于其几何形状的不对称性,其剪力墙的合理布置一直是工程设计中的难点,在高烈度区更是如此。本文以平面L形框架-剪力墙结构为研究对象,通过分析软件PKPM和ETABS对所设计的结构进行建模及分析,讨论剪力墙的位置、数量和长度等对结构抗震性能的影响。计算结果表明:综合考虑剪力墙对结构扭转效应和剪力墙自身内力的控制,是进行平面L型框架-剪力墙结构剪力墙布置的先决条件,对结构设计具有重要意义。

磁流变阻尼器受控平面L形框架结构的多维减震

磁流变阻尼器(magnetorheological damper, MRD)广泛应用于土木工程减震防灾领域。为研究加入MRD框架结构的多维减震性能和扭转震动特性,采用MATLAB软件开发了未控和MRD受控平面L形框架结构的空间计算模型程序,在三向地震荷载作用下分别对未控和MRD受控模型进行了动力时程分析,对结构典型节点X、Y、Z向的位移时程响应、加速度时程响应、结构的各层位移、加速度、层间位移角以及空间扭转震动响应进行对比。结果表明:用MATLAB开发的未控和MRD受控平面L形框架结构的空间计算模型程序能有效计算结构的多维地震响应;MRD可以有效减小平面L形框架结构的多维位移和加速度时程响应;MRD可以有效减小平面L形框架结构的各层最大位移、加速度和层间位移角;合理地布置MRD能够稳定地发挥耗能作用,并能有效减小平面L形框架结构的扭转震动响应。

2021-09-29宁夏中宁M_(L)3.6地震震源参数测定

基于宁夏区域地震台网资料,采用初至P震相定位法测定2021-09-29中宁M_(L)3.6地震震源深度,同时利用gCAP反演方法测定该地震震源机制解及矩张量解,然后根据震源机制与应力场模拟方法计算现今应力场体系在中宁M_(L)3.6地震震源机制两个节面的相对剪应力和正应力。结果表明,初至P震相定位法和gCAP方法测定的中宁M_(L)3.6地震震源深度均为11 km,震源机制节面Ⅰ走向242°、倾角63°、滑动角8°,节面Ⅱ走向148°、倾角83°、滑动角153°,矩张量解结果表明该地震的双力偶成分占全矩张量解的97.07%,表明该地震为天然地震。结合震中附近2009年以来M_(L)1.0以上地震重定位后的空间分布、区域地质构造和相对剪应力等分析推测,中宁M_(L)3.6地震发震断层可能与天景山断裂东南段附近NNW向断裂薄弱带有关,该地震是在青藏高原东北缘NE向挤压作用下,沿着NNW向断裂剪切滑动引起的一次右旋走滑型地震事件。