Probabilistic seismic hazard assessment for Thailand

A set of probabilistic seismic hazard maps for Thailand has been derived using procedures developed for the latest US National Seismic Hazard Maps. In contrast to earlier hazard maps for this region, which are mostly computed using seismic source zone delineations, the presented maps are based on the combination of smoothed gridded seismicity, crustal-fault, and subduction source models. Thailand’s composite earthquake catalogue is revisited and expanded, covering a study area limited by 0°–30°N Latitude and 88°–110°E Longitude and the instrumental period from 1912 to 2007. The long-term slip rates and estimates of earthquake size from paleoseismological studies are incorporated through a crustal fault source model. Furthermore, the subduction source model is used to model the megathrust Sunda subduction zones, with variable characteristics along the strike of the faults. Epistemic uncertainty is taken into consideration by the logic tree framework incorporating basic quantities, such as different source modelling, maximum cut-off magnitudes and ground motion prediction equations. The ground motion hazard map is presented over a 10 km grid in terms of peak ground acceleration and spectral acceleration at 0.2, 1.0, and 2.0 undamped natural periods and a 5% critical damping ratio for 10 and 2% probabilities of exceedance in 50 years. The presented maps give expected ground motions that are based on more extensive data sources than applied in the development of previous maps. The main findings are that northern and western Thailand are subjected to the highest hazard. The largest contributors to short- and long-period ground motion hazard in the Bangkok region are from the nearby active faults and Sunda subduction zones, respectively.     

基于特大地震发生率的川滇地区地震危险性预测新模型

川滇地区是我国地震危险性较高的地区之一.本文基于对特大强震的风险性考虑,使用全球地震模型OpenQuake软件,建立了川滇地区地震危险性预测新模型.首先根据构造特征划分多个震源分区,并整理出这些震源分区内断层活动特征与滑动速率;基于震源分区和断层模型,使用GPS应变率转换成的锥形古登堡-里克特关系作为整个区域的地震积累率,并允许超过历史最大震级的特大地震的出现,结合活动断层滑动速率所积累的地震发生率,给出震源分区内断层地震源和背景地震源的地震发生率的比率分配关系;在活动断层分段上,保留了大型断裂或其主要部分,没有根据小的阶区来对断层进行详细分段,以便分配特大地震发生率;并使用地震率平滑方法分配背景地震发生率.最后在OpenQuake中加入地震动预测方程,计算出了川滇地区的PGA分布图,为区域地震危险性提供科学依据.     

新疆南部构造区带与地震活动状态研究

Based on the studies of earthquake activity, tectonic movement, crustal shortening rate, fault activity, local stress field and historical characteristics of strong earthquake activities in Xinjiang, we divide the south part of Xinjiang into 4 seismotectonic zones, namely, the eastern segment of south Tianshan seismic belt, the Kalpin block, the Kashi-Wuqia junction zone, and the west Kunlun Mountains seismic belt. Using earthquake catalogues from Xinjiang since 1900, and on the basis of integrity analysis of earthquake records in different magnitude ranges, the seismicity state of different seismotectonic zones is analyzed quantificationally by calculating the mean value of annual strain energy release, annual rate of earthquakes with different lower limits of magnitude, b-value, and the parameter m of accelerating strain release model. The characteristic indexes of seismicity state for each of the seismic tectonic zones are then determined, which provide a quantitative basis for earthquake tendency analysis and judgment.     

基于密集台阵研究龙门山断裂带南段地震空段的地震活动性

2016年12月—2018年4月间布设于汶川、芦山地震之间地震空段的密集监测台阵(LmsSGA)提供了密集的观测数据.通过拾取地震走时、初始定位,计算地方震级,得到了完备性震级为0级的地震目录.更加完备的地震目录为地震空段及周围地震活动的时空分布特征和孕震风险性评估提供了丰富的信息.重定位结果显示地震主要集中于龙门山断裂带深度为5～20km的孕震层内.地震活动频繁的汶川、芦山主震区,震源的空间分布模式与其早期余震相似,说明两次大地震的区域仍处于缓慢的应力调整阶段.青藏高原物质东向挤出受宝兴、彭灌杂岩阻挡,在两个杂岩体西北侧地震活动频繁.地震活动性分布显示汶川—茂县、映秀—北川断裂上存在一个清晰的长约30km,宽约20km的地震活动"空白"区域,与其下方因部分熔融而产生的低速体分布一致,我们推测熔融体的加温作用是导致空段内极低的地震活动性的主要原因.监测时段内仍观测到降雨变化率和地震数量呈反相关关系,再次证实了汶川—芦山地震间地震空段及邻区内季节性降雨对地震活动性存在一定调节作用.综合分析S波速度模型、历史强震活动及b值,我们推断地震空段东部的彭灌断裂中段及周围部分隐伏断层存在发生强震的风险.     

考虑俯冲带潜在震源区的地震危险性算法研究及在中国海域的应用

本文研究了俯冲带潜在震源区离散化方法及考虑俯冲带高震级地震震源破裂面和震源深度的场点地震动计算方法，推导了俯冲带潜在震源区地震危险性计算公式，并使用中国海域及邻区地震危险性模型进行地震危险性试算。结果表明，本文建立的考虑俯冲带潜在震源区的地震危险性算法能够实现场点地震危险性计算时对俯冲带高震级地震震源破裂面和震源深度的考虑。     

中国海域地震区划及关键问题研究

国家重点研发计划项目《海域地震区划关键技术研究》已实施3年，进入项目结题阶段，已形成海域地震区划方法与技术体系，研究成果为即将开展的中国海域地震区划图编制工作提供技术支撑。项目组分析和探讨了海域地震区划研究基础与存在的问题，结合所关注的关键科学和技术问题，介绍和分析了主要研究成果和进展，包括海域断裂活动性探测和地震构造、中国海域与邻区地震目录及地震活动特征、海域地震动特性及衰减模型、海域场地条件及对地震动的影响、海域地震区划图编制方法与技术等；编制了一系列相关图件、数据库和计算软件，包括中国东部和南部海域活动构造框架图、3个典型海域（位于黄海、台湾海峡、南海内）地震构造图、中国海域及邻区统一地震目录、中国海域潜在震源区划分图与考虑不确定性的对比方案及考虑三维潜源模型的地震危险性分析软件；建立了中国海域及邻区俯冲带地震构造模型、基于地震动观测记录和地震模拟数据的南海俯冲带板内地震动衰减关系、利用强震动加速度记录结合宽频带速度记录的俯冲带板缘与板内地震的地震动长周期反应谱衰减关系，提出了以场地覆盖土层厚度及土层等效剪切波速为指标的大陆架场地分类方法及相应的场地地震动参数调整方案；最后形成了海域地震区划图编制原则、技术要求和技术方法体系，完成了海域地震区划图编制规程（初稿）的编制工作，基本完成了3个典型海域地震区划图的编制工作。     

Seismic hazard assessment for derivation of earthquake scenarios in Risk-UE

The main features of the Risk-UE project approach to assessing the ground-shaking (and related hazards) distribution within urban areas are described, as a basis for developing seismic damage scenarios for European cities. Emphasis was placed in the project on adoption of homogeneous criteria in the quantitative treatment of seismicity and in constructing the ground-shaking scenarios, despite wide differences in amount and quality of data available for the cities involved. The initial steps of the approach include treatment of the regional seismotectonic setting and the geotechnical zonation of the urban area, while the hazard assessment itself takes the form of both a deterministic analysis, and of a probabilistic, constant-hazard spectra analysis. Systematic 1D site response analyses were used, mostly in the softer soil zones, to modify (when needed) the obtained ground motion maps. Earthquake induced hazard effects, such as liquefaction and landsliding, are also briefly dealt with at the end.     

Seismic hazard impact of the Lower Tagus Valley Fault Zone (SW Iberia)

The seismic hazard of SW Iberia is composed of two contributions: offshore, large to very large events on the plate boundary between Africa and Eurasia such as the Lisbon earthquake of 1755 or the Gorringe Bank earthquake of 1969; and onshore, moderate to strong intraplate earthquakes on inherited crustal fractures. One of these zones of crustal weakness is the Lower Tagus Valley (LTV) fault zone, which displays the highest level of seismic hazard in Western Iberia. In this paper we review the active tectonics and seismicity of the LTV, integrating previous geophysical data with recent results of paleoseismological investigations, and discuss its impact on the seismic hazard of SW Iberia. We conclude that the seismic zonation for hazard assessment currently in force in the building code is biased towards the scenario of distant offshore rupture, and does not take adequately into account the LTV seismic source.     

新版地震区划图地震活动性模型与参数确定

地震活动性模型和地震动预测模型是概率地震危险性分析的两个核心。在新版地震区划图中,依据板内地震活动空间不均匀性分布的特点,在概率地震危险性分析方法(CPSHA)中采用了由地震统计区、背景潜在震源区和构造潜在震源区构成的三级层次性潜在震源区模型,并构建了相应的地震活动性模型。本文在论述CPSHA方法及其地震活动性模型基本概念的基础上,重点介绍了新版地震区划图地震活动性模型的三级潜在震源区模型的构成、地震活动性假定和基本特点,同时,也对新版地震区划图地震活动性模型的重要参数确定思路、方法与结果进行了介绍。本文将为更好地认识与理解我国新版地震动参数区划图提供有益的参考。     

Seismotectonic Study on the West Part of the Interaction Zone Between Southern Tianshan and Northern Tarim

The interaction zone between southern Tianshan and northern Tarim is located at the northeast side of Pamir. It is a region with high seismicity. We constructed a seismotectonic model for the west part of this zone from geological profiles, deep crust seismic detection and earthquake focal mechanisms data. Based on the synthesized geological features, deep crust structure, and earthquake focal mechanisms, we think that the main regional tectonic feature is that the Tianshan tecto-lithostratigraphic unit overthrusts on the Tarim block. The Tianshan tectonic system includes the Maidan fault and thrust sheets in front of the fault; The Tarim tectonic system includes the underground northern Tarim margin fault, conjugate faults in basement and overthrust fault in shallow. The northern Tarim margin fault is a high angle fault deep in the Tarim crust, adjusting different trending deformation between Tianshan and Tarim. It is a major active fault that can generate large earthquakes. The other faults, such as the Tianshan overthrust system and the Tarim basement faults in this area may generate moderately strong earthquakes with different styles.     

2008年汶川8.0级地震发生的历史与现今地震活动背景

为了了解2008年5月12日四川汶川M_S8.0地震发生的地震活动背景,本文综合历史与现代地震资料,从南北地震带中段及其邻区的视野研究了汶川地震前1~2千年的强震活动性,以及震前20年的地震活动性背景.结果主要表明：（1）至少在2008年之前的1100~1700年中,龙门山断裂带未发生M≥7的地震,相对其南、北两侧的其他活动断裂带（或段）形成一个地震空区,2008年汶川M_S8.0地震发生在该空区中;（2）17世纪以来,在由龙门山断裂带大部分地区、川北岷江-虎牙断裂带以及甘南文县-武都断裂带组成的巴颜喀拉块体东边界上共发生了12次M=6.5~8.0地震,显示出一个已持续了近400年、逐渐加速的应变能释放过程,2008年汶川M_S8.0地震属于该过程中两次巨大地震之一;（3）汶川地震前20年,龙门山断裂带中、南段不存在背景地震活动的平静,反而显示出比曾经发生过1879年M_S8地震的甘南文县-武都断裂带还略高的地震活动背景水平;（4）2008年汶川地震的强度远远超出龙门山断裂带的历史最大地震,说明仅基于数百年至一、两千年的历史地震记载,远不足以正确评估较低滑动速率的、大型活动断裂带的潜在地震危险性.     

地震活动性层次结构分析及危险区预测方法

对地震活动性进行层次结构分析可划分出不同的地震区带,中国大陆的地震活动可分为9个地震区带,分析各个区带的地震活动性可作出某一活跃期强震发生主体地区的判别,对某一个地震区带的地震活动进行层次结构分析可作出地震危险区预测。用震源面投影图代替点投影的震中分布图可更合理地解释一个构造带上强震的发生过程,更清楚地勾画出未来强震的孕震范围。对强震破裂区闭锁段、背景空区、孕震空区的关系用实测震例进行了解释。     

冀东南堡油田设计地震动参数研究

新发现的冀东南堡油田位于地震和断裂活动较强的渤海湾地区,抗震设防问题不容忽视。本文分析了油田所在地区的地震活动和地震构造环境,并在此基础上划分出了潜在震源区,确定了地震动衰减关系,进行了地震危险性分析。然后根据油田周边相关工程的工程地质条件特征,建立了场地土动力模型,进行了土层地震反应计算,确定了场地设计地震动参数。结果表明,局部场地条件对地震动峰值和反应谱的影响较大,需对场地工程地质条件进行详细研究。     

我国台湾岛的地震构造特征

本文在简要地论述了台湾岛及其周围地区的地质构造、重力异常、地壳结构和地震活动等特征的基础上划分了地震构造带,对台湾岛上7级以上强震的发震构造条件作了初步讨论,最后用板块构造观点探讨了本区地震的构造成因     

Faulting, shallow seismicity and seismic hazard analysis for the Costa Rican Central Valley

Faulting, shallow seismicity (0–30 km), and seismic hazard of the Costa Rican Central Valley were analyzed. Faults in the study area are oriented northwest or northeast. There is an active fault system in the south flank of the Central Volcanic Ridge and another in the north flank of the Talamanca Ridge. Faults of these systems have generated 15 destructive earthquakes in the area during the last 228 years all of them shallow and their locations show one cluster near the Poas Volcano and another southward the Central Valley. These earthquakes have damaged cities of the Central Valley, two of them destroyed Cartago city and almost 1000 people were killed. Regarding recent seismicity, there are three main seismic sources at the Central Volcanic Ridge: Irazu, Bajo de la Hondura and Poas and other three in the Talamanca Ridge: Puriscal, Los Santos and Pejibaye.A seismic hazard map for the Metropolitan Area of San José has been elaborated, based on local tectonic and seismic information. The area for the hazard computation covers an area of 20×15 km² and includes the zone where the most population and socioeconomic activities are concentrated. The computation analysis are based on areas zones and faults, each one characterized by recurrence parameters, geometry, minimum and maximum magnitude and source depth. A recent local spectral attenuation model, which includes relations for shallow crustal sources and subduction zone earthquakes, has been applied in this study. The seismic hazard results are presented in terms of contour plots of estimated peak ground acceleration (PGA) for bedrock conditions for return period of 50, 100 and 500 years. In the Central Park of San Jose City the following PGA values were found: 0.29g for 50 years, 0.36g for 100 years, and 0.53g for 500 years.     

Spatial Separation of Large Earthquakes, Aftershocks, and Background Seismicity: Analysis of Interseismic and Coseismic Seismicity Patterns in Southern California

We associate waveform-relocated background seismicity and aftershocks with the 3-D shapes of late Quaternary fault zones in southern California. Major earthquakes that can slip more than several meters, aftershocks, and near-fault background seismicity mostly rupture different surfaces within these fault zones. Major earthquakes rupture along the mapped traces of the late Quaternary faults, called the principal slip zones (PSZs). Aftershocks occur either on or in the immediate vicinity of the PSZs, typically within zones that are ??2-km wide. In contrast, the near-fault background seismicity is mostly accommodated on a secondary heterogeneous network of small slip surfaces, and forms spatially decaying distributions extending out to distances of ??10?km from the PSZs. We call the regions where the enhanced rate of background seismicity occurs, the seismic damage zones. One possible explanation for the presence of the seismic damage zones and associated seismicity is that the damage develops as faults accommodate bends and geometrical irregularities in the PSZs. The seismic damage zones mature and reach their finite width early in the history of a fault, during the first few kilometers of cumulative offset. Alternatively, the similarity in width of seismic damage zones suggests that most fault zones are of almost equal strength, although the amount of cumulative offset varies widely. It may also depend on the strength of the fault zone, the time since the last major earthquake as well as other parameters. In addition, the seismic productivity appears to be influenced by the crustal structure and heat flow, with more extensive fault networks in regions of thin crust and high heat flow.     

基于地震安全性评价的广东省地震危险性分析

地震安全性评价是防震减灾的重要措施之一。地震危险性分析是地震安全性评价的基础。论文利用安全性评价基本理论和方法对广东省的地震危险性进行分析。以广东省历史上发生的中强地震目录作为研究基础,分析了广东省的地质构造特点和断裂特点,划分潜在地震源、确定地震活动性参数,建立了地震发生概率模型,通过计算得出地震带的综合影响。研究结果表明广东省内具有发生7.5、 6.5、 6.0、 5.5级级段地震的发震条件,其中沿海地区是广东省中、强地震的主要发震区域。     

Evolution of Stress Fields and Faulting in Seismic Zones

—Measurements indicate that stress magnitudes in the crust are normally limited by the frictional equilibrium on pre-existing, optimally oriented faults. Fault zones where these limitations are frequently reached are referred to as seismic zones. Fault zones in the crust concentrate stresses because their material properties are different from those of the host rock. Most fault zones are spatially relatively stable structures, however the associated seismicity in these zones is quite variable in space and time. Here we propose that this variability is attributable to stress-concentration zones that migrate and expand through the fault zone. We suggest that following a large earthquake and the associated stress relaxation, shear stresses of a magnitude sufficient to produce earthquakes occur only in those small parts of the seismic zone that, because of material properties and boundary conditions, encourage concentration of shear stress. During the earthquake cycle, the conditions for seismogenic fault slip migrate from these stress-concentration regions throughout the entire seismic zone. Thus, while the stress-concentration regions continue to produce small slips and small earthquakes throughout the seismic cycle, the conditions for slip and earthquakes are gradually reached in larger parts of, and eventually the whole, seismogenic layer of the seismic zone. Prior to the propagation of an earthquake fracture that gives rise to a large earthquake, the stress conditions in the zone along the whole potential rupture plane must be essentially similar. This follows because if they were not, then, on entering crustal parts where the state of stress was unfavourable to this type of faulting, the fault propagation would be arrested. The proposed necessary homogenisation of the stress field in a seismic zone as a precursor to large earthquakes implies that by monitoring the state of stress in a seismic zone, its large earthquakes may possibly be forecasted. We test the model on data from Iceland and demonstrate that it broadly explains the historical, as well as the current, patterns of seismogenic faulting in the South Iceland Seismic Zone.     

Discussion on Characteristics of Crustal Deformation along the Zhangjiakou-Bohai Sea Seismotectonic Zone

INTRODUCTIONThe Zhangjiakou-Penglai fault zone has drawnextensive attentionfromseismologists and geologistssince it was determinedinthe1980’s(Zheng Binghua,et al.,1981).Ma Xingyuan,et al.(1989)consideredit asthe north boundaryof North China sub-block.Int…     

南北地震带地壳结构多参数成像及强震触发机制研究

通过反演由大量的纵、横波地震数据组成的综合数据集,获得了南北地震带地壳的多参数三维精细结构,探讨和分析了南北地震带的高地震活动性和强震频发的原因.成像结果表明,尽管1976年松潘一平武地震(M7.2)与2008年汶川地震(M8.0)以及2013年芦山地震(M7.0)均发生在高速、低泊松比异常区域,并且在其震源的下方均有一低速、高泊松比异常区域.我们认为,上述三个地震的触发与流体侵入导致的地壳形变之间有密切的联系.1955年炉霍地震(M7.4)和1973年康定地震(M7.1)均发生在鲜水河断裂带上,其震源中心区域表现为低速、高泊松比异常,可以解释为下地壳中的流体沿断层面上涌.在震源区的周边区域兼有高速、高泊松比异常,低速、高泊松比异常以及高速、低泊松比异常,可能分别与含流体的岩石、沿断裂带发育的变质岩以及坚硬的克拉通块体对应.流体的侵入不仅能够改变断层面上的应力情况,还能降低岩石骨架的岩石力学强度,进而触发地震.1970年云南通海大地震(M7.1)发生在哀牢山一红河断裂带附近的曲江断裂上,其震源处于高速度、低泊松比异常与低速度、高泊松比异常之间的边界区域,被认为是流体挤压后的应变能积累,最终导致脆性破裂,以至于发生地震.根据本次研究获得的多参数结构图像,结合前人的研究成果,我们认为南北地震带地壳强烈形变与流体侵入是造成该区域地震活动性较高及强震频发的两个主要因素.