1988年云南澜沧-耿马地震的烈度分布及地表破裂

1988年11月6日,在云南省西南部的澜沧-耿马断裂带上发生了两次大于7级的地震.地震造成的严重破坏和人员伤亡主要是由于极震区内抗震性能极差的毛石房、砖柱土坯房的大量倒塌所致.澜沧地震的震中基本烈度可达Ⅸ度,耿马地震极震区烈度达Ⅹ度.澜沧地震构造活动的地表证据主要是出现在极震区内的张性地裂缝带和小断层陡坎.地裂缝带和小断坎主要出现在四条相对连续的北北西走向的狭窄地带内,其长度从几百 m 到6km 不等.澜沧地震地表破裂带长约35km,宽约3km,最大垂直位移量和最大右旋水平位移量分别为1.5m 和1.4m.耿马地震地表断裂活动的明显证据包括一系列北北西走向的地裂缝带和一段长约5km的地震断层陡坎.耿马地震地表破裂带长约24km,其最大垂直位移3.5m,最大右旋水平位移为3m.两次地震形成的地表破裂带均具有右旋-正断层性质.本文讨论了这两次地震的 度分布及地表破裂特征.      

HOLOCENE PALAEOSEISMOLOGIC RECORD AND RUPTURE BEHAVIOR OF LARGE EARTHQUAKES ON THE XIANSHUIHE FAULT

The Xianshuihe Fault, the boundary of Bayan Har active tectonic block and Sichuan-Yunnan active tectonic block, is one of the most active fault zones in the world. In the past nearly 300 years, 9 historical earthquakes of magnitude ≥ 7 have been recorded. Since 2008, several catastrophic earthquakes, such as Wenchuan M_S8 earthquake, Yushu M_S7.1 earthquake and Lushan M_S7 earthquake, have occurred on the other Bayan Har block boundary fault zones. However, only the Kangding M_S6.3 earthquake in 2014 was documented on the Xianshuihe Fault. Thus, the study of surface deformation and rupture behavior of large earthquakes in the late Quaternary on the Xianshuihe Fault is of fundamental importance for understanding the future seismic risk of this fault, and even the entire western Sichuan region. On the basis of the former work, combined with our detailed geomorphic and geological survey, we excavated a combined trench on the Qianning segment of Xianshuihe fault zone which has a long elapse time. Charcoal and woods in the trench are abundant. 30 samples were dated to constrain the ages of the paleoseismic events. Five events were identified in the past 9  000 years, whose ages are:8070-6395 BC, 5445-5125 BC, 4355-4180 BC, 625-1240 AD and the Qianning earthquake in 1893. The large earthquake recurrence behavior on this segment does not follow the characteristic earthquake recurrence model. The recurrence interval is 1000~2000 years in early period and in turn there is a quiet period of about 5 000 years after 4355-4180 BC event. Then it enters the active period again. Two earthquakes with surface rupture occurred in the past 1000 years and the latest two earthquakes may have lower magnitude. The left-lateral coseismic displacement of the 1893 Qianning earthquake is about 2.9m.     

更新模型在缺少大震离逝时间的活动断裂强震发生概率计算中的应用研究

利用更新模型计算未来几十年内发生强震的条件概率需要给出上一次大震的离逝时间T, 而很多活动断裂上缺少历史大震的记载, 若采用泊松模型则可能会低估强震发生的概率.针对这种缺少大震离逝时间的活动断裂, 本文提出一种以记载完整的强震平静期长度T_s为参数的条件概率计算方法. 以东昆仑断裂带塔藏段为实例, 利用本文给出的条件概率计算方法得到该段未来50年发生强震的可能性为0.0649.      

Distribution of seismic intensities of the November 6, 1988, Lancang-Gengma earthquakes and their surface ruptures in Yunnan Province, China

On November 6, 1988, two earthquakes with magnitude>7 occurred on the Lancang-Gengma fault zone in south-west China. The extensive destruction and loss of lives resulted mainly from widespread collapse of unreinforced masonry and mud brick structures; the maximum preliminary intensity of the Lancang earthquakes was IX on the Chinese scale, which is similar to the Modified Mercall scale, and the highest preliminary intensity of the Gengma earthquake was probably X. The surface manifestation of tectonic activity of the Lancang earthquake was the occurrence of the earthquake-related extensional ground cracks and small fault scarps in the epicentral region. The cracks with small fault scarps occurred mainly in four relatively continuous north-northwest-trending linear zones that ranged from a few hundred meters to 6 km in length. The area within which the cracks and small scarps occurred is 35 km long by 3 km wide. The maximum net throw and the dextral horizontal offset were 1.5m and 1.4m, respectively. Clear evidence of new surface faulting caused by the Gengma earthquake includes a series of relatively continuous north-northwest-trending linear ground crack zones and a 5 km long section of fault scarps. The total length of the surface rupture zones of the Gengma earthquakes is about 24 km, with 3.5m maximum net throw and 3m maximum right-lateral slip. Both earthquakes were associated with surface faulting showing a combination of normal and right lateral motion. The distribution of seismic intensities and surface rupture characteristics of these two earthquakes are discussed in this paper. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 344–353, 1991. The research project was performed out under the direction of Professors. Xingyuan Ma and Yuntai Chen, and the field investigation was performed with help of Kui Jiang and Junchang Zhang of the Seismological Bureau of Yunnan Province. Here the authors express great appreciation.     

地震活动图像特征与强震危险区经验性预测依据的初步研究

在研究近期（10年）强震危险性判定和总结四川地区1972--2002年强震预测经验的基础上，清理了中国大陆1920--2002年47次浅源大震事件前地震活动图像特征（M≥4．7），提炼出10个方面12项经验性预测依据：主体活动区、多发时段、关联序列、大陆及地区地震异常图像、地区（带）-地段（震源区）地震增强图像（含信号震、诱发地震、地震条带）、相关地震、窗口地震、复发间隔、大陆及地区缺震、地段缺震与地段强震一缺震转折等。它们在47次震例中的综合出现率≥0．58（即依据比7／12以上）占42例；≥0．66（即8／12以上）占34例。因此，强震（M≥4．7）活动图像经验性预测依据可以作为预测有较大可能发生大地震危险区的依据之一。     

洪洞临汾大震震源断层的相互作用和地震趋势分析

山西临汾地区1303年和1695年发生了洪洞(M8)和临汾(M7 3/4)两次相距最近特大地震。地震所在区域至今仍有持续不断的小震活动。我们根据1670次中、小地震精确震源定位结果和149个小地震的震源机制。通过震源三维空间分布和震源机制解的分析,认为洪洞地震和临汾地震的强相互作用是解锁,因此导致临汾地震提前发生;此外,2者之间还存在弱相互作用,并且和随机发生的地震达到一种平衡。2次大地震对区域所积累的应变基本释放完毕,难以再形成与应力场一致的大破裂,使得临汾地区连续的地震活动以中小地震的形式体现,连续300多年都没有5级以上地震发生。估计今后临汾地区的这种低水平活动将继续下去,发展趋势是安全的。     

2015年尼泊尔M_w7.9地震破裂过程:快速反演与初步联合反演

本文介绍了2015年4月25日尼泊尔Mw7.9(MS8.1)地震发生后的破裂过程快速反演工作,以及后续开展的地震波与少量GPS资料的初步联合反演工作.两项工作得到的反演结果尽管在最大滑动量估计方面存在一些差别,但都一致地显示此次地震是发生在低倾角俯冲断裂上的一次单侧破裂事件,破裂主要朝东南方向传播;断层滑动主要发生在震中至加德满都一带.在加德满都附近区域,其下方破裂与朝东南传播的地震波的多普勒聚焦效应可能造成较强的震感和较大的破坏.对比历史大地震发现,2015年尼泊尔Mw7.9地震的浅部破裂紧邻1934年Mw8.2地震的地表破裂,余震分布与1833年M7.6地震的宏观震中基本重合,其破裂填补了前两次地震破裂以西100km左右的空区,表明此次地震是1934年Mw8.2地震与1833年M7.6地震向西继续延伸的结果.     

昆仑山口西地震和汶川地震前中源地震活动特征研究

研究2001年昆仑山口西地震和2008年汶川地震前的中源地震活动特征,与唐山地震前的特征进行比较,发现:3次大地震前曾发生6或7次h≥60 km的中源地震,且"大震前中源地震活跃的时间跨度T"约5年或5年多。这是大震前中源地震活动最主要的两个特征,包含了孕育大地震的一些重要信息。其他特征还有:中源地震的活动—平静交替、临近大地震前的地震平静、呈条带分布和(或)地震空区等特征,这与大震前壳内地震活动性的一些特征类似。     

Ring structures of seismicity in central Tien Shan and Dzungaria: Possible precursory processes of large earthquakes

It is shown that episodes of comparative seismic quiescence that lasted about 20–25 years in the areas of study alternated with intervals of sharply increased seismicity as series of large (M ≥ 6.9) earthquakes occurred during two to three decades. Since no M ≥ 6.6 earthquake has occurred in the area for as long as 21 years after the 1992 Susamyr event, middle-term prediction would require identification of zones of imminent large earthquakes. More reliable identification of such zones rests on data relating to inhomogeneities in the field of S-wave attenuation in the lithosphere, as well as on the characteristics of ring structures of seismicity. Such structures are formed as zones of seismic quiescence that are bounded by M ? Mth earthquake epicenters, where Mth is the threshold magnitude value. Correlative relationships were previously derived, lgL(Mw) and Mth(Mw), for events with different focal mechanisms (L is the length of the longer axis of a seismicity ring and Mw is the magnitude of the associated large earthquake). These relationships were used to estimate the Mw of large events that can occur in these ring structures. The greatest earthquake with Mw ? 7.5 is probably about to occur in southern Tien Shan, east of the 1949 Khait earthquake rupture. A smaller event (Mw ～ 7.0) can occur in the Kyrgyz Range area. Still smaller earthquakes probably have their precursory areas north and east of Lake Issyk-Kul, as well as in Dzungaria.     

Seismicity before and after the two great Sumatra earthquakes of 2004 and 2005

The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast. The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.     

Major earthquakes of the southern Gornyi Altai in the Holocene

The paper describes geological and geomorphological features of ancient major earthquakes that occurred in the Holocene in the zone of the Altai earthquake of September 27, 2003 (southern Gornyi Altai). Fossil earthquakes occurred in the regions of the Northern and Southern Chuya ridges and Chuya and Kurai basins; their sources reached the surface and formed systems of coseismic ruptures oriented SE-NW or E-W. Secondary (gravitational and vibrational) paleoseismic deformations were represented by rockfalls, landslides, and gryphons in near-field zones of these paleoevents. They were spread in an area of about 2000–2500 km² coinciding, on the whole, with the position of source zones. Paleoseismogeological investigations showed that, apart from earthquakes of the 20th and 21st centuries, eight seismic events with magnitudes M = 7.0–8.0 occurred in the region over the last 8500 years. Ancient strong earthquakes that produced the observed paleoseismic ruptures occurred approximately 230–300, 1000, 1700, 2300, 3500, 4500, 5200, and 8500 years ago. Therefore, the recurrence interval averaged 1400 yr for earthquakes with a magnitude of about 7.0 and 2100 yr for events with a magnitude of about 7.5.     

东汉早期的地震活动

东汉早期(公元25—127年)的地震史料十分宝贵, 它反映了从远古零散、 不系统的地震记载转入连续记载并逐渐认识地震的过程. 这时的地震事件较多, 但研究不充分, 地震参数基本呈空白状. 史料的记载方式以“郡国地震”和“京师地震”为主; 时间上, 基本在汉和帝以后; 地点上, 以大华北为主. 本文具体分析了东汉早期的33次地震事件, 利用新的地震烈度衰减关系, 采用郡国平均地理面积和有感面积的概念, 比照地震范例的标准, 按《中国地震目录》的烈度震级表进行参数估算. 研究期间最主要的地震事件是4次震级≥6 ¹/₂ 的强震, 即公元46年10月和119年3月南阳地震、 121年10月冀南-鲁西地震和123年5月汉阳地震, 震后都有持续1—2年的余震活动. 公元118年前的地震主要分布于大华北, 震中至京师洛阳的距离多在200 km以外. 除两次5 ¹/₂ —6级地震外, 均属5—5 ¹/₂ 级中等强度地震, 少数小于4 ³/₄ 级. 京师洛阳虽经历过多次地震, 但其受影响程度并不强, 基本为有感或强有感的水平, 没有遭受过破坏性或中等强度的震害.     

1985年新疆乌恰地震烈度与发震构造

１９８５年乌恰地震发生在新疆乌恰县城东南４０ｋｍ的克孜勒苏河谷中。震中烈度为Ⅸ度,地震类型为主震－余震型,余震具有波伏衰减的特征。乌恰县城和乌帕尔镇大多数房屋倒塌或遭到破坏。主震在极震区内克孜勒苏河谷阶地上产生了一条地表破裂带,其长为１５ｋｍ,宽为１００￣８００ｍ,由地震断层、挤压脊和地震裂缝组成。１９９５年乌恰地震的发震构造是卡兹克阿尔特逆掩断裂。该地震应属褶皱类型地震,这类地震产生的震害具有上     

汶川8.0级与昆仑山口西8.1级地震前地震活动异常特征与启示

两次特大地震前在不同时段、 不同范围出现了多项相似的地震活动性异常, 它们对预测特大地震具有一定意义: ① 两次大震前10余年, 青藏块体同期出现了两个规模巨大的中强以上地震增强区, 两次大地震发生在增强区内的空区里; ② 两次巨大地震前数年, 形成规模巨大的中强地震活动带, 地震发生在两个条带间的平静区里; 同期形成中等以上地震活动环, 其内部的地震频度、 加卸载响应比及非均匀度等参数甚高, 且随时间而变化, 这可作为孕震进入中期的信号; ③ 两次大震前的震群、 震丛均很显著, 昆仑山口西地震前四个显著震丛环绕震中四周分布, 汶川地震前震群在震中周围形成包围圈, 它们应视为大震孕育进入后期的显示; ④ 大震前数月, 靠近发震断裂带发生少量中小地震或少见的震群。 汶川地震前10个月, 龙门山断裂带北部发生两次青川4级多地震和松潘4.3级地震, 南部康定附近发生3次4级以上地震。 紫坪铺水库区小震群于震前3个月活动十分强烈。 昆仑山口西地震前约1年青海兴海发生6.6级地震, 昆仑山口西发生5.1级地震, 该地震距离8.1级地震约30 km。这些特征给我们的重要启示是: ① 特大地震前出现的前兆时空特征与常见的中强地震差异很大, 现行的监测预报体制(分省分片负责)与特大地震前兆不相适应; ② 特大地震的预测预报不能单纯依靠地震前兆, 必须与地质构造及深部探测紧密结合起来; ③ 特大地震的预测预报应有新的预报战略、 观测系统与组织机构相适应。     

Variations in short-period shear-wave attenuation in the Baikal Rift Zone and their relationship to seismicity

This paper presents results from a study of variations in short-period shear-wave attenuation in the lithosphere of the Baikal Rift Zone (BRZ). We used earthquake records made at the Ulan-Bator station (ULN) at epicentral distances of ～400–1300 km. The ratios of maximum amplitudes in the Sn and Pn waves were considered. We show that these ratios are on the whole considerably higher than those in other areas of Central Asia. It was found that zones of low shear wave attenuation coincide with the rupture zones of large earthquakes that occurred during the 19th and 20th centuries. We identified zones of high attenuation where no large (M～ > 7.0) seismic events have occurred during at least 180 years. The hypothesis we propose is that precursory processes before future large earthquakes may be occurring in these zones. We discuss the question of whether wave attenuation characteristics may be related to seismicity.     

Discrimination of earthquakes and quarry blasts in the eastern Black Sea region of Turkey

In recent years, a large number of quarry blasts have been detonated in the eastern Black Sea region. When these blasts are recorded by seismic stations, they contaminate the regional earthquake catalog. It is necessary to discriminate quarry blast records from the earthquake catalogs in order to determine the real seismicity of the region. Earthquakes and quarry blasts can be separated through different methods. These methods should be applied concurrently in order to safely distinguish these events. In this study, we discriminated quarry blasts from earthquakes in the eastern Black Sea region of Turkey. We used 186 seismic events recorded by the Karadeniz Technical University and Bogaziçi University Kandilli Observatory Earthquake Research Institute stations which are Trabzon, Espiye, Pazar, Borçka, Ayd?ntepe, and Gümü?hane between years of 2002 and 2010. For the discrimination of quarry blasts from earthquakes, we used both, statistical methods (calculation of the maximum ratio of S to P waves (S/P), complexity (C)) and spectral methods (spectrogram calculation). These methods included measuring the maximum amplitude S/P, C, spectral ratio, and time-frequency analysis. We especially relied on two-dimensional time-frequency analysis methods to discriminate quarry blasts from earthquakes in Turkey. As a result of this study, 68 % of the examined seismic events were determined to be quarry blasts and 32 % to be earthquakes. The earthquakes occurring on land are related to small faults and the blasts are concentrated in large quarries. Nearly 40 % of the earthquakes occurred in the Black Sea, most of them are related to the Black Sea thrust belt, where the largest earthquake was observed in the time period studied. The areas with the largest earthquake potential in the eastern Black Sea region are in the sea.     

2013年8月河北蔚县小震群遗漏地震检测与发震构造分析

华北地区近年来小震群活动频繁, 在有数字波形记录的中强地震相对缺乏的背景下, 小震群发震构造精细研究可为华北地区地震危险性分析和地震趋势判断提供重要依据. 本文利用匹配滤波技术对2013年8月22—25日河北蔚县小震群遗漏地震事件进行检测, 并通过地震精定位和震源机制求解分析此次震群的发震构造. 计算结果显示, 通过互相关扫描检测到18次被地震台网常规分析遗漏的地震, 约为地震目录给出的13次地震事件的1.38倍. 该震群发震构造有北东向和北西向两组断裂, 震群活动前期以北东向构造活动为主, 后期地震主要发生在北西向构造, 北西向构造在此次震群活动中地震频度和强度均高于北东向构造. 震源机制计算结果显示北西向构造发震机制以正断拉张为主.      

A slow earthquake

Anomalous earthquakes such as creep events, tsunami earthquakes and silent earthquakes have been reported in the recent literature. In this paper we discuss an anomalous “slow earthquake” that occurred on June 6, 1960 in southern Chile. Although the surface-wave magnitude of this event is only 6.9, it excited anomalously large long-period multiple surface waves with a seismic moment of 5.6 · 10²⁷ dyn cm. The Benioff long-period seismogram of this earthquake recorded at Pasadena shows an extremely long, about 1.5–2 h coda of Rayleigh waves, with a period of 10–25 s. The coda length for other events with a comparable magnitude which occurred in the same region is about 10 min. This observation suggests that the long coda length is due to a long source rupture process which lasted at least 1 h. Although at least 15 distinct events can be identified in the coda, no short-period body waves were recorded corresponding to these, except for the first one. These results suggest that a relatively small (M_s ? 6.9) earthquake triggered a series of slow events; the duration of the whole sequence being longer than 1 h. This event probably occurred on a transform fault on the extension of the Chile Rise and provides important information regarding the nature of the transform fault.     

两次巨震的天文影响

讨论了1960年智利Ms8．9和2004年印度洋Ms8．7地震的天文影响，它们的影响方式虽有不同，但都是在天文大事件的背景下发生的。     

天山中段地区重复地震时空特征研究

基于2009—2017年新疆区域数字地震台网记录的地震波形数据,利用波形互相关技术及主事件定位方法识别并重新定位了新疆天山中段及其周缘的重复地震。以波形互相关系数0.9作为阈值来确定研究区的重复地震事件,统计结果显示3万零181个事件中的1万1 618个为重复地震事件,这些重复地震事件组成了2395组重复地震对和重复地震丛,占总事件数的38.5%。根据重复地震重定位前后地震对之间距离的统计结果推测,该区域的系统定位误差约为5—10 km。进一步结合该区域最新的震源分类结果对不同震源类型重复地震的时空分布特征予以分析,结果显示:重复矿山爆破事件在空间上呈丛集性分布,且其中的93.6%发生于白天,同时呈现季节性发生模式,即爆破多发生于夏季,而冬季较少;而重复构造地震在空间上大多沿断层分布,24小时内呈随机分布的特征,且研究时段内每个月的活动水平相对平稳;重复诱发地震成丛分布于靠近油气田和水库的区域,但其中部分诱发地震的位置与构造地震重叠,发震时间特征与构造地震相似,为随机分布。