A multi-tiered earthquake hazard model for Australia

Earthquakes result from tectonic processes, and their distribution is strongly influenced by large-scale geology and the tectonic stress field. However, earthquake hazard estimates, particularly ground motion recurrence, have traditionally been computed using source models based primarily on instrumental and historical seismicity. In areas of low to moderate seismicity such as Australia, large earthquakes commonly occur in areas which have experienced little or no recent activity, making it difficult to develop source models based solely on seismicity.

The seismotectonic model developed for Australia that is presented here (AUS5) is based on geology, geophysics, tectonics and seismicity. The model was developed using a number of tiers of information, so that new information can easily be incorporated. The information used includes, but is not limited to, tectonic provinces, basins and ranges, gravity, magnetic, topography, and seismicity, all on a regional scale. On a local scale, for a site-specific earthquake hazard study, active faulting can be incorporated to provide fault source zones.

An earthquake hazard map showing peak ground acceleration with a 10% chance of exceedance in 50 years for southeastern Australia using the geologically defined seismotectonic model AUS5 is presented as an indication of how the model performs.     

Seismicity and seismoactive faults of Cuba

The first catalogue of active regional faults of Cuba is presented. The seismotectonic map of Cuba is a base for studying the seismicity in this region. Of the 30 faults studied, only twelve are active. The main seismotectonic structure is the Bartlett-Cayman fault system, which borders the eastern and southeastern seismotectonic units in this region. Approximately 70% of Cuban seismicity is concentrated here. The Cauto-Nipe, Cochinos and Nortecubana faults border other seismotectonic units. The Nortecubana fault is the only one associated with a tsunami. All the faults are segmented. The faults described are related to the current tectonic stress regime of the Northern Caribbean. All the available information (maps, sections and profiles, photos, geological and neotectonic data on seismicity and focal mechanisms) is supported by a GIS.     

Seismotectonics and seismicity of the Silakhor region, Iran

This paper deals with seismotectonic and seismicity of the Silakhor region that shows high seismic activity in western Iran. Silakhor is a vast plain with several villages and cities of Dorud and Borujerd and a small town of Chalanchulan that were destroyed and/or damaged many times by large earthquakes. This paper addresses the historical and instrumental earthquakes and their causative faults, seismotectonic provinces and seismotectonic zones of the region. Available seismic data were normalized by means of time normalization technique that resulted in the magnitude-frequency relation for the Silakhor area and estimation of the return period of earthquakes with different magnitudes. Some active faults in this region include the Dorud fault, the main Zagros thrust, the Galehhatam fault, the Sahneh fault and others. Among them, the Dorud fault is an earthquake fault and is the cause for most of the large and intermediate earthquakes in the region. The return period of large earthquakes with magnitudes greater than 7.0 (Ms) is very low, however, the occurrence of destructive earthquakes is greater in the region than in the neighboring provinces. The study proves the high seismicity of this zone and it is required to develop an accurate national plan for future building and reinforcement of the existing buildings in this region.     

Probabilistic seismic hazard assessment in the northeastern part of Algeria

This work involves updating the evaluation of seismic hazard in Northeast Algeria by a probabilistic approach. This reassessment attempts to resolve inconsistencies between seismic zoning in regional building codes and is further motivated by the need to refine the input data that are used to evaluate seismic hazard scenarios. We adopted a seismotectonic model that accounts for differences in interpretations of regional seismicity. We then performed a probabilistic assessment of regional seismic hazard in Northeast Algeria. Based on a homogeneous earthquake catalog and geological and seismotectonic data gathered in the first part of the study, a seismotectonic zoning map was created and seven risk areas were identified. For each area, peak ground acceleration hazard maps were produced. Details of the calculations are provided, including hazard curves at periods of 0.1, 0.2, 0.33, 0.5, 1.0, and 2.0 s and uniform hazard spectra at urban locations in the area, including Sétif, Constantine, Kherrata, Bejaia, and Jijel.     

Possible evidence of remotely triggered and delayed seismicity due to the 2001 Bhuj earthquake (Mw?=?7.6) in western India

Remote triggering by large earthquakes at regional distances is a globally observed phenomenon. However, there are no reports of observations of dynamic triggering at regional distances of several source lengths associated with the large Mw?=?7.6 Bhuj earthquake of January 26, 2001, in western India. In the present study, a swarm of over 140 microearthquakes that occurred about 500?km southeast of Bhuj, in the geothermal province of the Western Ghats in the Deccan volcanic province (DVP) of India, immediately after the occurrence of the Bhuj earthquake in 2001 is investigated. The post-Bhuj seismicity (M?<?2.0) occurred in three bursts spread over 2?months with each burst of intense activity lasting for 2?C3?days. All the three bursts of seismicity occurred in the same volume along a 5-km-long NW?CSE trending fault. The temporal coincidence and the sudden rise in seismicity that interrupts the characteristically low background seismicity strongly suggest that the Bhuj earthquake may have remotely triggered this activity. The triggered seismicity began approximately 2.5?h after the onset of the Bhuj mainshock and continued well after the passage of the surface waves, suggesting that the dynamic stresses possibly gave rise to secondary time-dependent mechanisms leading to the triggering. It is proposed that the triggered and delayed seismicity is possibly a consequence of the redistribution in pore fluid pressure due to the Bhuj earthquake. This is the first documented observation of remotely triggered seismicity at regional distances due to the Bhuj earthquake.     

Time-dependent seismicity in China

Precise zonation of the territory of China has been performed based on the active known faults, type of faulting and seismicity level. One hundred and forty seven seismogenic regions were defined, forming 10 larger seismic areas, and the seismotectonic characteristics in each one of them were investigated in detail. After checking for data accuracy and completeness of the shallow earthquakes (h≤60 km), the regional time and magnitude predictable model was applied and the model parameters were estimated. Based on the model applicability in the studied area, probabilities for the occurrence of strong (M≥6.0) earthquakes during the next 10 years were calculated for each seismogenic region. Statistical tests have been used proving the superiority of the model in comparison with the time independent one, as well as in comparison with the actual earthquake occurrence.     

Loading of a seismic zone to failure deforms nearby volcanoes: a new earthquake precursor

The South Iceland Seismic Zone (SISZ) was loaded to failure in June 2000, resulting in two M6.6 earthquakes. The SISZ is an E–W‐trending zone with an overall sinistral movement. Numerical models indicate that, when the SISZ is loaded to failure, there are stress concentrations at its ends: tensile in the north‐east and south‐west quadrants, and compressive in the north‐west and south‐east quadrants. These model predictions fit well with observations. Geodetic measurements indicate considerable compression, uplift and associated intense seismicity in recent years in the volcanoes of Hengill and Eyjafjallajokull, located in the quadrants of compression, whereas there have been unusually frequent eruptions in the past decades in the Hekla Volcano, located in one of the quadrants of extension. The models predict that following the large June 2000 earthquakes, stress relaxation within the SISZ should lead to stopping of the intense seismicity and deformation in the volcanoes of Hengill and Eyjafjallajokull, again in agreement with observations. However, when similar episodes of deformation and seismicity start again, particularly in the Hengill Volcano, a large earthquake would be expected within several years in the SISZ. The numerical models, and the deformation and seismic data, indicate that monitoring of ‘soft’ inclusions such as volcanoes (many with magma chambers) in the vicinity of a seismic zone may serve as precursors to large earthquakes.     

Deformation and displacement fields of the Himalayan arc,seismicity and large earthquake hazards in its eastern segment and vicinity

The Himalayan arc is a type of plate margin similar to an island arc and is a world-famous region of tectonic and seismic activities, where a series of large earthquakes have occurred in historical time. In this paper, the vertical deformation and horizontal displacement fields of the Himalayan arc are theoretically derived from the viewpoint of the collision between the Indian and Eurasian plates. In the light of the observed data, the seismicity, earthquake focal mechanism, seismotectonic and geomorphological features of the arc and its vicinity are reasonably explained. The characteristics of seismicity and the possibility of earthquakes with magnitude above 8 occurring in this region in the future are studied.     

Intraplate seismotectonic features of North China

Intraplate earthquakes in North China are characterized by shallow depth, large magnitude and high frequency. Obviously, the zonal distribution of earthquakes is closely related to recent active faults and Cenozoic graben and rift systems.The active faults are mainly oriented NNE with right-lateral movements, and partially oriented NW with left-lateral movements.The Hetao-Yinchuan graben, Fenhe-Weihe graben and North China Plain rift systems often reflect crustal thinning and mantle uplift.According to the data concerning crustal deformation, particularly the movement patterns of faulting, crustal taphrogenesis and earthquake surface rupture, it is suggested that a shearing-extension mechanism could be considered as a cause of the formation of seismotectonic structures in North China since the Early Cenozoic Era.Graben and rift systems also developed in Northeast and South China. They formed earlier than the graben and rift systems in North China, however, and their activity has decreased during the Quaternary period. It is reasonable that the seismicity in Northeast and South China is not as strong as that in North China.     

Seismic Hazard Studies in the U.K.: Source Specification Problems of Intraplate Seismicity

Although the U.K. is in an area of only low to moderate seismicity, the seismic hazard is sufficient to pose a threat to sensitive structures such as chemical plants and nuclear facilities. In quantifying the level of hazard by conventional probabilistic methodology, however, some problems arise in attempting to interpret earthquake data in terms of geological structure and faults. In the U.K., not only is it impossible to identify any demonstrably active faults, but also it is extremely difficult to discern any relationship between the pattern of seismicity and local or regional geological structure.This study discusses the use of two zonation approaches which complement each other in such a way that the general character and trend of seismicity is preserved. In one approach, the zonation is informed by the structural geology, where possible; geological zonation is avoided if it produces sources with heterogeneous seismicity. In the other approach, the record of past earthquakes is divided up into very small zones around individual epicentres or groups of epicentres, the size of each zone usually being proportional to the uncertainty in the epicentral determination of the appropriate event. This zonation preserves an observed tendency of some British earthquakes to repeat themselves. It is suggested that, in intraplate areas such as the U.K., it is often inappropriate to attempt to model individual fault sources. No faults in the U.K. are provably active. Because an earthquake of moderate size can occur on a very short fault segment, it is impractical to restrict fault modelling to major features. Even the two largest U.K. faults, suspected to be active, pose problems in attributing historical seismicity to them as distinct features.     

云南宁蒗地区铜厂河铜矿构造控矿规律研究

宁蒗地区铜厂河铜矿主干控矿构造为SN向断裂体系，起着导矿、配矿、容矿的作用。矿区NWW向F1断裂为阻矿构造，铜矿化均产于其下盘（南盘）；NE向F2，F3断裂将本区分成三个不同矿化特征的矿段，其东、中矿段是寻找隐伏－半隐伏铜矿体的有利地段。由于构造活动的多期次和构造形变的分带性，矿区铜矿具显著的成矿多期、多阶段性和矿化体水平－垂直分带性规律。     

Seismotectonic Reactions to the Arc-continent Convergence in Central Philippines

Abstract. High seismic activity in the Philippines originates from tectonic convergence related to surface and subsurface seismotectonic features. Based on earthquake data, the archipelago can be divided into the seismically-active Philippine Mobile Belt and the aseismic North Palawan Block. The latter represents a rifted continental fragment of the Eurasian margin that juxtaposed with the rest of island arc units in central Philippines. Earthquake hypocenter plots on planar and in vertical profiles show that the seismic events are associated with known seismotectonic features. In addition, data suggest that the collision zone between the North Palawan Block and the Philippine Mobile Belt is characterized by a decreased amount of hypocenters at > 100 km depths. Although field evidence favors the presence of a subducted slab or slabs beneath western central Philippines, these are difficult to image using the present seismicity distribution dataset.     

Cautious neotectonic hypotheses for assessing the seismic hazard in northeastern Italy

A simplified tectonic scheme for hazard purposes was recently adopted for northeastern Italy, introducing large generalized seismogenic areas containing systems of complex geometry faults. This scheme considers only major faults with documented seismic activity. In the present analysis, a different tectonic scheme, with linear elements as seismogenic sources, is presented. The assessment of the regional seismic hazard is done with the fault rupture model, its most important advantage being the recognition that the length of fault rupture during an earthquake is an important consideration in probabilistic calculations of seismic hazard. Moreover, some structures with no associated seismicity but with notable neotectonic activity are considered, and their contribution to the results investigated. Important uncertainties such as those in the maximum possible magnitude of future earthquakes, in the location of the fault, in the focal depth, and in the attenuation law are accounted for in the calculations and their influence studied. The results identify a seismic belt running from Lake Garda to Friuli and along the Yugoslav coast and are very similar to those already known for Friuli, with the largest values corresponding to the zone around Gemona. Some slight differences in the shape of the areas of equal acceleration are probably due to the delineation of the seismic sources of the proposed model. For a cautious elaboration, some neotectonic lines without present seismicity were added into the fault model. Their contribution is negligible in the areas of highest acceleration, but increases remarkably in the areas where acceleration is not expected to exceed the medium values.     

南海及邻区新构造运动表现特征及其主控因素

南海具有复杂的地质构造背景,扩张结束以后,新构造运动活跃,但各区域新构造运动发生的时间及运动特征有较大差异。本文综合分析了南海各区域构造演化事件、现今构造格局及新构造运动的基本特征,认为南海新构造运动的起始时间为中中新世（约15 Ma）较合理。在此基础上,收集和整理了南海及邻区最新的地质和地球物理资料,对南海海域新构造期地层差异升降、活动断裂、天然地震以及岩浆活动等新构造表现形式进行了综合分析,系统总结了南海新构造运动特征,并根据活动断裂、天然地震以及岩浆活动等特征和分布规律分析,认为南海海域新构造的表现形式之间存在较大的耦合性。本文根据新构造运动表现形式在空间分布的不平衡性,将南海及邻区划分为1个强构造活动区、3个中等强度构造活动区以及1个弱构造活动区,并结合研究区应力场特征分析,认为南海新构造运动主要受控于东部菲律宾海板块和太平洋板块对东亚大陆边缘的持续俯冲碰撞作用。     

Morphometric evidence of seismicity around Wagad and Gedi Faults, eastern Kachchh, Gujarat

Recent studies suggest that the eastern Kachchh is a potential zone for major earthquakes in the near future. Particularly, the E-W trending faults are considered capable of generating large magnitude earthquakes is further indicated by the recent concentration of the earthquake shocks, which, show two prominent clustering around west and north of the Wagad upland. In view of this, the conventional morphometric analyses of a terrain bounded by the E-W trending North Wagad Fault (NWF) and the Gedi Fault (GF) has been undertaken to ascertain the influence of seismicity in the evolution of the drainage basin. The study suggests that the fifth order drainage basins responded to the seismicity associated with both the NWF and GF. However, compared to the GF, the NWF seems to be more active. In addition to this, based on the stream morphology, we could identify two lineaments trending N-S and E-W. The former appears to be associated with the activity along the Manfara Fault (MF), whereas, the later seems to be the splays of the NWF. Further, a preferential westward shift of the streams suggests left lateral displacement of the E-W trending faults. Overall it can be suggested that the terrain is in juvenile stage implying tectonic instability.     

Geomorphic expression of neotectonic activity in a low relief area in an Airborne Laser Scanning DTM: A case study of the Little Hungarian Plain (Pannonian Basin)

The NW corner of the Little Hungarian Plain, which lies at the junction of the Eastern Alps, the Pannonian Basin and the Western Carpathians, is a neotectonically active region linking the extrusional tectonics of the Eastern Alps with the partly subsiding Little Hungarian Plain. The on-going deformation is verified by the earthquake activity in the region. An extremely flat part of the area, east of Neusiedlersee, the so-called Seewinkel, has been investigated with Airborne Laser Scanning (ALS, also known as airborne LiDAR) techniques, resulting in a digital terrain model (DTM) with a 1 m grid resolution and vertical precision of better than 10 cm. The DTM has been compared with known and inferred neotectonic features.Potential neotectonic structures of the DTM have been evaluated, together with geological maps, regional tectono-geomorphic studies, geophysical data, earthquake foci, as well as geomorphological features and the Quaternary sediment thickness values of the Seewinkel and the adjacent Parndorfer plateau. A combined evaluation of these data allows several tectonic features with a relief of < 2 m to be recognized in the DTM. The length of these linear geomorphological structures ranges from several hundred meters up to several kilometers. The most prominent feature forms a 15 km long, linear, 2 m high NE–SW trending ridge with gravel occurrences having an average grain size of ca. 5 cm on its top. We conclude this feature to represent the surface expression of the previously recognized Mönchhof Fault. In general, this multi-disciplinary case study shows that ALS DTMs are extremely important for tectono-geomorphic investigations, as they can detect and accurately locate neotectonic structures, especially in low-relief areas.     

唐山地震区域构造背景和发震模式的讨论

1976年7月28日3点42分在我国河北省唐山地区发生了7.8级强烈地震。地震的发生,是有它的区域构造背景和震区的构造条件的。深入研究这个问题,对认识地震的形成、孕育和发生是十分有意义的。唐山地震震中与深大断裂没有表现直接的联系,而是分布在不引入注目的北东向断裂上。其控制因素我们认为是包围震区的边界断裂起了重要作用。边界断裂的存在使被围限的北东向断裂得到了暂时的平衡,形成相对“闭锁”区段。当区域应力场急剧变化时,“闭锁”就被突破,产生大地震。     

雷琼地区新构造运动的特征

雷琼地区系广东省雷州半岛和海南岛的简称。以王五-文教断裂为界,本区可分为两部分:北部的雷州半岛和琼北,通称“雷琼坳陷”,为新第三纪和早更新世大幅度沉降区,兼有剧烈而频繁的火山活动和地震活动,是本文讨论的重点;南部是以五指山为中心的隆起区,发育多级剥夷面,由隆起中心向海呈阶梯状下降,该区隆起幅度虽大,却基本上没有火山活动,地震活动亦弱(图1)。本文根据若干典型的第四系剖面、火山活动、¹⁴C测年数据、测震及地形变等资料,初步探讨雷琼地区新构造运动的基本特征。     

以精定位背景地震活动与震源机制解研究郯庐断裂带中南段现今活动习性

郯庐断裂带是中国东部板内一条规模最大的强构造变形带与地震活动断裂带,其断裂结构与历史地震活动性具明显的分段活动性。文中通过沿郯庐断裂带中南段的历史地震活动性、精定位背景地震活动性与震源机制解分析,讨论了断裂带的深部几何结构与现今活动习性。现今地震活动在中段主要沿1668年郯城MS 8地震破裂带线性分布,线性条带在泗洪-诸城间延伸约340 km长,为1668年地震长期缓慢衰减的余震序列活动。大震地表破裂遗迹与精定位地震分布都揭示出郯庐断裂带中段的两条全新世活动断裂昌邑-大店断裂与安丘-莒县断裂以右阶斜列的形式共同参与了1668年郯城MS 8地震破裂。精定位震源剖面刻画出两条断裂结构面呈高角度相背而倾,其中昌邑-大店断裂倾向SE,安丘-莒县断裂倾向NW,两条断裂在深部没有合并汇聚。余震活动所代表的1668年地震震源破裂带是郯庐断裂带中现今尚未闭锁的安全段落,对应于高b值段。而未发生破裂的安丘以北段,小震活动不活跃,b值低,现今可能已成为应力积累的闭锁段。震源机制解揭示的断裂应力状态在中段以NE向主压应力为主,表现为右旋走滑活动性质,且存在少量正断分量,南段转为以NEE至近EW向为主,存在少量的逆冲分量。在中段与南段的转折处宿迁-嘉山段,主压应力方向垂直断裂带走向呈NWW向,反映出局部以挤压为主的应力特征,其中泗洪-嘉山段也是历史地震未破裂段,现今小震活动不活跃,因此该段可能更易于应力积累。精定位小震活动在郯庐断裂与北西向断裂相交汇处聚集,反映出北西向断裂的新活动性,以及郯庐断裂带现今的逆冲作用。在断裂带南端,精定位背景地震活动沿与其相交汇的襄樊-广济断裂带东段呈北西向线性分布,表明了该段的现今活动性。     

海城地震地质构造背景与发震构造的探讨

前言 一九七五年二月四日,我国辽宁省海城县发生了一次7.3级强烈地震。由于这次地震预报和预防工作的成功极大地减少了伤亡损失,取得了预报和预防破坏性地震的一些很有意义的经验。它充分显示了经过无产阶级文化大革命之后,我国地震工作在毛主席革命路线指引下取得的新成就。 这次海城地震是我国东北有记载以来第一个七级以上的浅源地震。在宏观调查的基础上,我们先后两次对震区及其邻近地区进行了地震地质考察。