Late Quaternary episodic displacement on a sackung scarp in the central Spanish Pyrenees. Secondary paleoseismic evidence?

A sackung scarp has been investigated by trenching in the central Spanish Pyrenees. This feature is located 18 km to the SW of the North Maladeta Fault, which is the most probable source of the M_w 5.3 Vielha earthquake of 1923. Three displacement events have been inferred for the trenched sackung based on colluvial wedge stratigraphy and fault truncation. The increasing amount of deformation in each successive faulting event may be related to the progressive weakening of the slope through time. A minimum vertical slip rate of 0.19 mm/yr has been calculated for the sackung scarp. Several arguments suggest that the episodic displacement of the analysed sackung is controlled by strong seismic shaking: (a) Spatial association of the sackung features with the North Maladeta Fault; (b) Episodic displacement with a millennial recurrence (5.6 kyr) consistent with the expectable earthquake recurrence interval for a low slip rate fault, like the neighbouring North Maladeta Fault. Demonstrating in future investigations that the sackung features in the area constitute archives of large paleoearthquakes would be of great interest for seismic hazard assessments. They might help to improve the catalogue of paleoearthquakes and might provide information on earthquake recurrence intervals and the age of the most recent event (MRE).     

Emergency shelter capacity estimation by earthquake damage analysis

Taiwan is located on the Pacific Ring of Fire and thus experiences many detectable earthquakes annually. The damage resulting from these earthquakes affects the government and local citizens financially and endangers lives. As the political and economic capital of Taiwan, Taipei has a high population density. Assessing the seismic effects in Taipei, therefore, is a crucial issue requiring immediate attention. In this study, Taiwan Earthquake Loss Estimation System (TELES) software for analyzing potential earthquakes was used to simulate earthquake events at potential faults in the Taipei area. The TELES analysis theory was used to analyze seismic events and to predict building damage and displacement of citizens in each Taipei administrative district. The analytical results are then compared with the capacity of temporary shelters currently planned by the government. Finally, our conclusions and recommendations are presented. Hopefully, the results of this study can provide a useful reference for relevant organizations when developing earthquake disaster prevention policies.     

Review of paleoseismological and active fault studies in Taiwan in the light of the Chichi earthquake of September 21, 1999

This paper reviews the research on active and earthquake faults in Taiwan conducted prior and after the 1999 Chichi earthquake. The Chichi earthquake plays as a turning point of the relevant studies, since the 1999 coseismic surface rupture exactly follows preexisting fault scarps, created in turn by previous seismic events along the Chelungpu Fault. This fact indicates that the precise mapping on the other active faults is fundamental to predict the location of surface rupture caused by large future earthquakes. Since 1999, many trenching studies have been carried out along the Chichi earthquake fault. A few of them demonstrates that the penultimate event is as young as probably only 200–430 years old; however, some others show a rather old age of several hundreds years or even older for the last faulting event before 1999. More trenching studies are necessary for such a long fault in order to understand the possible segmentation features and the correlation of the paleoseismic events identified along the entire fault length. In addition, we further discuss the offshore faulting associated with seismic event along the eastern coast of Taiwan, where the multiple Holocene terraces are well known.     

基于形变观测分析中国台湾东部花东纵谷断层运动特征

花东纵谷断层是中国台湾动力作用和地壳运动变形最强烈的断层之一,其断层运动特征和强震危险程度一直备受学者的关注。文中分别以同震地表位移、1992-1999年震间形变数据为约束,反演2003年成功MW 6.8地震同震位错分布和花东纵谷断层震间运动特征。结果表明：花东纵谷断层北段处于强闭锁状态（闭锁率高达0.9）,闭锁深度深（约27 km）;南段闭锁程度较弱（闭锁率约0.5）,闭锁深度较浅（约12 km）;中段闭锁程度与闭锁深度介于南北段之间。另一方面,2003年成功MW 6.8地震微观震中位于震间无震滑移区与闭锁区的过渡带附近。依据同震位错、震间断层运动反演结果,以及历史强震破裂分布特征,分析认为,花东纵谷断层南北段运动方式存在差异性,北段主要以强震形式运动,南段以蠕滑和地震两种形式运动。自1951年花莲-台东ML 7.3地震序列后,花东纵谷断层南段、中段和北段至2016年所累积的矩能量分别等价MW 6.4、MW 7.0、MW 7.4地震;若发生级联破裂,整个断层至2016年所累积的矩能量等价MW 7.5地震。     

阿尔金断裂东北段敦煌阳关断裂晚第四纪活动性及其强震危险性影响分析

阿尔金断裂系东北段阳关断裂的晚第四纪活动性与强震危险性关系到敦煌地区及相关文物古迹的防震减灾问题.基于高分辨率卫星影像对阳关断裂几何展布特征进行解译,采用差分GPS、无人机航空摄影测量方法、古地震探槽方法以及OSL测年方法对两个研究点进行了详细研究,对其定量活动参数进行了初步限定.结果显示,阳关断裂东段运动形式主要表现为挤压逆冲,最新的一次地震事件可能发生在距今43.5~12.1 ka之间,表明阳关断裂东段至少在晚更新世以来有过活动,并且具有发生M_w6.6强震的潜能及危险性.如果发生类似强度的地震,敦煌主城区的烈度至少在Ⅵ以上,阳关土遗址地区则会达到Ⅸ.因此,阳关断裂应该是该区防震减灾重点关注的发震断层之一.      

PGA distributions and seismic hazard evaluations in three cities in Taiwan

This study first presents the series of peak ground acceleration (PGA) in the three major cities in Taiwan. The PGAs are back-calculated from an earthquake catalog with the use of ground motion models. The maximums of the 84th percentile (mean?+?one standard deviation) PGA since 1900 are 1.03, 0.36, and 0.10?g, in Taipei, Taichung, and Kaohsiung, respectively. Statistical goodness-of-fit testing shows that the series of PGA follow a double-lognormal distribution. Using the verified probability distribution, a probabilistic analysis was developed in this paper, and used to evaluate probability-based seismic hazard. Accordingly, given a PGA equal to 0.5?g, the annual exceedance probabilities are 0.56, 0.46, and 0.23?% in Taipei, Taichung, and Kaohsiung, respectively; for PGA equal to 1.0?g, the probabilities become 0.18, 0.14, and 0.09?%. As a result, this analysis indicates the city in South Taiwan is associated with relatively lower seismic hazard, compared with those in Central and North Taiwan.     

Seismogenic Tectonics and Dynamics of the 2011 Ms5.9 Yingjiang Earthquake in Yunnan,China

In the southern South–North Seismic Zone, China, seismic activity in the Yingjiang area of western Yunnan increased from December 2010, and eventually a destructive earthquake of Ms5.9 occurred near Yingjiang town on 10 March 2011. The focal mechanism and hypocenter location of the mainshock suggest that the Dayingjiang Fault was the site of the mainshock rupture. However, most of foreshocks and all aftershocks recorded by a portable seismic array located close to the mainshock occurred along the N–S-striking Sudian Fault, indicating that this fault had an important influence on these shocks. Coulomb stress calculations show that three strong(magnitude ≥5.0) earthquakes that occurred in the study region in 2008 increased the coulomb stress along the plane parallel to the Dayingjiang Fault. This supports the Dayingjiang Fault, and not the Sudian Fault, as the seismogenic fault of the 2011 Ms5.9 Yingjiang earthquake. The strong earthquakes in 2008 also increased the Coulomb stress at depths of ≤5 km along the entire Sudian Fault, and by doing so increased the shallow seismic activity along the fault. This explains why the foreshocks and aftershocks of the 2011 Yingjiang earthquake were located mostly on the Sudian Fault where it cuts the shallow crust. The earthquakes at the intersection of the Sudian and Dayingjiang faults are distributed mainly along a belt that dips to the southeast at ~40°, suggesting that the Dayingjiang Fault in the mainshock area also dips to the southeast at ~40°.     

东昆仑断裂带库赛湖段晚第四纪古地震研究*

对东昆仑断裂带库赛湖段进行了断错地貌填图和古地震探槽揭露研究。除2001年昆仑山口西8.1级地震外,共揭露出9次古地震事件,它们的年龄分别为31900±1923aB.P. , 27990±1681aB.P. , 23635±1427aB.P. , 20345±1225aB.P. , 16865±1018aB.P. , 12935±774aB.P. , 9730±592aB.P. , 6955±425aB.P.和3100±201aB.P.;古地震重复间隔分别为3910±2554a,4355±2205a,3290±1881a,3480±1593a,3930±1279a,3205±975a,2775±728a,3855±470a和3100±201a。研究结果表明,库赛湖段晚第四纪古地震活动具有准周期性,其平均重复间隔为3544±416a。发生在距今3100年前的倒数第1次古地震事件的离逝时间与重复间隔非常接近,这意味着2001年11月14日发生在库赛湖段的8.1级大地震为该断裂地震活动在准周期上的再现。高的滑动速率和长周期复发间隔表明库赛湖段活动习性以重复发生大地震为特征。     

Touhuanping Fault, an active wrench fault within fold-and-thrust belt in northwestern Taiwan, documented by spatial analysis of fluvial terraces

This study aims at the recent activity and development of an active wrench fault, the Touhuanping Fault in northwestern Taiwan. Northwestern Taiwan has been proposed in a current situation between the mature to waning collision in terms of tectonic evolution. The main drainage in this area, the Chungkang River, flows close to the trace of the fault mentioned above. We examined various types of deformation of fluvial terraces along the Chungkang River as a key to understanding the nature and rate of the late Quaternary tectonics. The E–W trending Touhuanping Fault has long been mapped as a geological boundary fault, but its recent activity was suspected. Field survey revealed that its late Quaternary activity is recorded in the offset fluvial terraces. Our result shows dextral slip and vertical offset with upthrown side on the south, and activated at least twice since the emergence of terrace 4 (older terrace 3 with OSL date of ca. 80 ka). Total amount of offset recorded in the Touhuanping terrace sequence is 15 m for dextral and 10 m for vertical offset. Estimated recurrence time of earthquake rupture may be a few tens of thousand years. Uplift on the upthrown side of the Touhuanping Fault also resulted in the formation of drowned valleys which were graded to terrace 4. Other deformation features, such as back-tilting, westward warping, and a range-facing straight scarp, were also identified. A second-order anticline roughly parallel to the Touhuanping Fault is suggested to be the origin of the northward tilting on terrace 3; it could have resulted from a flower structure on the Touhuanping Fault at shallow depth. This may demonstrate that the buried segment of the Touhuanping Fault has also been active since 80 ka. In the northern study area, the westward warping at terrace 2 probably represents late Quaternary activity of another NE–SW trending Hsincheng Fault.     

Influence of slow active faults in probabilistic seismic hazard assessment: the northwestern margin of the València trough

Areas of low strain rate are typically characterized by low to moderate seismicity. The earthquake catalogs for these regions do not usually include large earthquakes because of their long recurrence periods. In cases where the recurrence period of large earthquakes is much longer than the catalog time span, probabilistic seismic hazard is underestimated. The information provided by geological and paleo-seismological studies can potentially improve seismic hazard estimation through renewal models, which assume characteristic earthquakes. In this work, we compare the differences produced when active faults in the northwestern margin of the València trough are introduced in hazard analysis. The differences between the models demonstrate that the introduction of faults in zones characterized by low seismic activity can give rise to significant changes in the hazard values and location. The earthquake and fault seismic parameters (recurrence interval, segmentation or fault length that controls the maximum magnitude earthquake and time elapsed since the last event or T_e) were studied to ascertain their effect on the final hazard results. The most critical parameter is the recurrence interval, where shorter recurrences produce higher hazard values. The next most important parameter is the fault segmentation. Higher hazard values are obtained when the fault has segments capable of producing big earthquakes. Finally, the least critical parameter is the time elapsed since the last event (T_e), when longer T_e produces higher hazard values.     

Teleseismic finite-fault inversion of two <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> = 6.4 earthquakes along the East Anatolian Fault Zone in Turkey: the 1998 Adana and 2003 Bingöl earthquakes

The East Anatolian Fault Zone is a continental transform fault accommodating westward motion of the Anatolian fault. This study aims to investigate the source properties of two moderately large and damaging earthquakes which occurred along the transform fault in the last two decades using the teleseismic broadband P and SH body waveforms. The first earthquake, the 27 June 1998 Adana earthquake, occurred beneath the Adana basin, located close to the eastern extreme of Turkey’s Mediterranean coast. The faulting associated with the 1998 Adana earthquake is unilateral to the NE and confined to depths below 15 km with a length of 30 km along the strike (53°) and a dipping of 81° SE. The fixed-rake models fit the data less well than the variable-rake model. The main slip area centered at depth of about 27 km and to the NE of the hypocenter, covering a circular area of 10 km in diameter with a peak slip of about 60 cm. The slip model yields a seismic moment of 3.5?×?10¹⁸ N-m (M_w???6.4). The second earthquake, the 1 May 2003 Bingöl earthquake, occurred along a dextral conjugate fault of the East Anatolian Fault Zone. The preferred slip model with a seismic moment of 4.1?×?10¹⁸ N-m (M_w???6.4) suggests that the rupture was unilateral toward SE and was controlled by a failure of large asperity roughly circular in shape and centered at a depth of 5 km with peak displacement of about 55 cm. Our results suggest that the 1998 Adana earthquake did not occur on the mapped Göksun Yakap?nar Fault Zone but rather on a SE dipping unmapped fault that may be a split fault of it and buried under the thick (about 6 km) deposits of the Adana basin. For the 2003 Bingöl earthquake, the final slip model requires a rupture plane having 15° different strike than the most possible mapped fault.     

Structure of pseudotachylyte vein systems as a key to co-seismic rupture dynamics: the case of Gavilgarh–Tan Shear Zone,central India

The secondary fractures associated with a major pseudotachylyte-bearing fault vein in the sheared aplitic granitoid of the Proterozoic Gavilgarh–Tan Shear Zone in central India are mapped at the outcrop scale. The fracture maps help to identify at least three different types of co-seismic ruptures, e.g., X–X′, T₁ and T₂, which characterize sinistral-sense shearing of rocks, confined between two sinistral strike-slip faults slipping at seismic rate. From the asymmetric distribution of tensile fractures around the sinistral-sense fault vein, the direction of seismic rupture propagation is predicted to have occurred from west-southwest to east-northeast, during an ancient (Ordovician?) earthquake. Calculations of approximate co-seismic displacement on the faults and seismic moment (M ₀) of the earthquake are attempted, following the methods proposed by earlier workers. These estimates broadly agree to the findings from other studied fault zones (e.g., Gole Larghe Fault zone, Italian Alps). This study supports the proposition by some researchers that important seismological information can be extracted from tectonic pseudotachylytes of all ages, provided they are not reworked by subsequent tectonic activity.     

Probability-based damage assessment for reinforced concrete bridge columns considering the corrosive and seismic hazards in Taiwan

In this paper, we consider the time at which earthquake events occur when analyzing seismic structural damage to a deteriorating RC bridge within a specified period. Because the uncertainty exists in the occurrence time of earthquake events, Monte Carlo simulation is applied. The proposed procedure for evaluating the exceedance probability, which corresponds to a specified limit state, is then applied to a case study of RC bridges in Taiwan to demonstrate its applicability. This study selects three typical RC bridges located in the Taipei Basin, Taiwan, to analyze exceedance probabilities of specified damage states during various specified periods and then discusses the cumulative damage effect on the exceedance probabilities of specified damage states. Additionally, for the chloride-induced deteriorating bridges at various distances to the sea in Suao, Taiwan, the effects of the deterioration and seismic structural damage on the exceedance probabilities of specified damage states are demonstrated and discussed. The proposed assessment procedure can help engineers understand whether the deterioration would accelerate the declining seismic performance of bridges and shorten their serviceability-related and safety-related service lives, as well as provide reference for repairing RC bridges and retrofitting their seismic performance.     

The Seismogenic Structure and Deformation Mechanism of the Lushan (Mw 6.6) Earthquake,Sichuan, China

On April 20 th, 2013, an earthquake of magnitude MW 6.6 occurred at Lushan of Sichuan on the southern segment of the Longmenshan fault zone, with no typical coseismic surface rupture. This work plotted an isoseismal map of the earthquake after repositioning over 400 post–earthquake macro–damage survey points from peak ground acceleration(PGA) data recorded by the Sichuan Digital Strong Earthquake Network. This map indicates that the Lushan earthquake has a damage intensity of IX on the Liedu scale, and that the meizoseismal area displays an oblate ellipsoid shape, with its longitudinal axis in the NE direction. No obvious directivity was detected. Furthermore, the repositioning results of 3323 early aftershocks, seismic reflection profiles and focal mechanism solutions suggests that the major seismogenic structure of the earthquake was the Dayi Fault, which partly defines the eastern Mengshan Mountain. This earthquake resulted from the thrusting of the Dayi Fault, and caused shortening of the southern segment of the Longmenshan in the NW–SE direction. Coseismal rupture was also produced in the deep of the Xinkaidian Fault. Based on the above seismogenic model and the presentation of coseismic surface deformation, it is speculated that there is a risk of more major earthquakes occurring in this region.     

南海北缘钻探选址：滨海断裂带大型海洋地质灾害研究

滨海断裂带是南海北缘的一条大型活动断裂带，其位置靠近我国华南沿海地区。滨海断裂带全长超过1200 km，包括西段（北部湾- 阳江），中段（珠江口）和东段（粤东- 福建）。其西段和东段历史上至少曾发生过4次大地震（M7+），中段目前是一个大地震空区。在经济高速发展和人口高度密集的今天，如果滨海断裂带再次发生大地震并触发海啸，必将对我国华南沿海地区造成灾难性破坏。由于缺乏完整的历史地震记录和针对古地震的钻孔沉积研究，目前尚不清楚滨海断裂带大地震的准确次数、空间分布和复发周期，以及中段大地震空区的主要原因（断层蠕滑或大地震周期较长），因此无法有效评估该断裂带的大地震破裂分段和灾害风险。本研究总结了滨海断裂带的构造特征、重点描述了3次历史大地震及引发的灾害影响，和国际上针对海底大地震的钻探研究经验。根据这些信息，本文建议在断裂带的西段、中断和东段进行大洋钻探，获取穿过断层带的关键沉积和岩石样品，利用沉积古地震方法重建滨海断裂带东段和西段的大地震历史和复发周期，研究断层带的岩石物理性质，揭示滨海断裂中段大地震空区的成因，解析断层分段式破裂的原因，为我国海洋防灾减灾提供重要的科学依据。     

东昆仑断裂带西大滩段全新世古地震研究*

对东昆仑断裂带西大滩段进行了断错地貌填图和古地震探槽揭露,共揭露出6次古地震事件,它们的年龄分别为10302±651aB.P. , 8650±500aB.P. , 7160±506aB.P. , 2830±170aB.P. , 1985±121aB.P.和1540±92aB.P. ;古地震重复间隔分别为1652±820a,1490±711a,4330±534a,845±209a和445±152a。研究发现,西大滩段全新世古地震活动具有丛集现象和重复间隔时间的分段性,第1丛集期在10300~7100aB.P.期间,平均重复间隔1571±543a,第2丛集期在2800~1500aB.P.期间,重复间隔400~800a左右,平均重复间隔645±129a,两个丛集期间隔4300a。西大滩段全新世地震活动规律对昆仑山地区未来地震危险性评估具有重要意义。     

Characteristics of the 1912 co-seismic rupture along the North Anatolian Fault Zone (Turkey): implications for the expected Marmara earthquake

Evidence of right‐lateral offsets associated with the 1912 earthquake (M_w 7.4) along the North Anatolian Fault (Gaziköy–Saros segment) allow us to survey (using DGPS) the co‐seismic and cumulative slip distribution. The damage distribution and surface breaks related with the earthquake show an elongated zone of maximum intensity (X MSK) parallel to the fault rupture on land but this may extend offshore to the north‐east and south‐west. Detailed mapping of the fault using topographic maps and aerial photographs indicates the existence of pull‐apart basins and pressure ridges. At several localities, the average 1912 offset along strike is 3.5–4 m and cumulative slip is 2–6 times that of individual movement. The fault rupture geometry and slip distribution suggest the existence of three subsegments with a combined total length of 110–120 km, a fault length and maximum slip similar to those of the 1999 Izmit earthquake. The amount of slip at the north‐easternmost section and in the coastal region of the Sea of Marmara reaches an average 4 m, thereby implying the offshore extension of the 1912 rupture. The results suggest that the 1912 event generated up to 150 km of surface faulting, which would imply a M_w 7.2–7.4 earthquake and which, added with rupture lengths of the 1999 earthquakes, help to constrain the remaining seismic gap in the Sea of Marmara.     

Seismic slip rates,potential subsurface rupture areas and seismic potential of the Vienna Basin Transfer Fault

The Vienna Basin Transfer Fault (VBTF) is a slow active fault with moderate seismicity (I _max~8–9, M _max~5.7) passing through the most vulnerable regions of Austria and Slovakia. We use different data to constrain the seismic potential of the VBTF including slip values computed from the seismic energy release during the 20th century, geological data on fault segmentation and a depth-extrapolated 3-D model of a generalized fault surface, which is used to define potential rupture zones. The seismic slip of the VBTF as a whole is in the range of 0.22–0.31 mm/year for a seismogenic fault thickness of 8 km. Seismic slip rates for individual segments vary from 0.00 to 0.77 mm/year. Comparing these data to geologically and GPS-derived slip velocities (>1 mm/year) proofs that the fault yields a significant seismic slip deficit. Segments of the fault with high seismic slip contrast from segments with no slip representing locked segments. Fault surfaces of segments within the seismogenic zone (4–14 km depth) vary from 55 to 400 km². Empirical scaling relations show that these segments are sufficiently large to explain both, earthquakes observed in the last centuries, and the 4th century Carnuntum earthquake, for which archeo-seismological data suggest a magnitude of M ≥ 6. Based on the combination of all data (incomplete earthquake catalog, seismic slip deficits, locked segments, potential rupture areas, indications of strong pre-catalog earthquakes) we argue, that the maximum credible earthquake for the VBTF is in the range M _max = 6.0–6.8, significantly larger than the magnitude of the strongest recorded events (M = 5.7).     

Correlations between soil gas and seismic activity in the Generalized Haiyuan Fault Zone,north-central China

Radon and mercury concentrations were measured in 10 fault gas profiles in Generalized Haiyuan Fault. This paper aims to predetermine the potential seismic risk in different segments of the fault zone from the perspective of geochemistry. The background value and anomaly threshold were adopted and synthesized using the maximum value method and average method to calculate concentration intensity values of radon and mercury. Fault soil gas mercury and radon concentrations show a decreasing gradient from NW to SE indicating evident segmentation. Higher values are mostly distributed in the Maomao Mountain–Tiger Mountain fault and Jingtai area. Combined with the seismotectonic background of historical and recent earthquakes and the spatial distribution characteristics of b-values, the fault soil gas concentration intensity shows a close correlation with earthquake activity within the fault zone. Concentrations of fault gas are higher and the b-value lower in areas of strong seismic activity, and regions with weak seismic activity correspond to lower fault gas concentrations and higher b-values. It is thus considered that the Jingtai area may be more dangerous than the other areas. This paper could provide vital background information for earthquake prediction in the Generalized Haiyuan Fault Zone.     

龙首山南麓新发现的地震地表破裂带——兼论1954年山丹MS7?地震发震构造

基于详细的遥感解译和野外调查,发现龙首山南缘断裂发育有较新的地震地表破裂遗迹,包括断层坎、地震鼓包、河道的系统位错等断层地貌标志,破裂带总长度超过20 km,沿断裂走向其垂向位移介于0.35～4 m,水平位移介于0.3～1.9 m,龙首山南缘断裂主体表现为逆冲性质,仅在西端表现为局部左旋走滑的性质。通过剖面和探槽揭示,龙首山南麓地区全新世以来发生多次断层活动,最新的一次在约3.96 ka以来。经过与区域内的强震记录比对,认为此次新发现的地震地表破裂带可能是1954年山丹M_S 7地震所致。1954年山丹M_S 7地震在浅表沿两条断裂同时发生了地表破裂,表现为正花状构造的变形样式。这种同震位移分配现象以往多发现于走滑型地震中,此次在逆冲型地震中发现。龙首山南缘断裂地表破裂带的发现为揭示1954年山丹地震的震源过程和破裂样式提供了新的证据和思路。