中南美洲地区地震序列的特征

共搜集到１９６０￣１９９０年中、南美洲地区１０个地震序列。其中１个是板内地震序列。这个板内地震序列表现出的特征是：震中分布区域的长轴较短,长短轴之比低;余震震源机制和主震震源机制相比变化大。其余９个是俯冲带上的板缘地震序列,它们的共同特征是：震中分布区域的长轴较长;震源深度下限超过地壳,可以达到７０ｋｍ以下（第１０号序列例外）;主震的震源机制受俯站带的走向、倾向和倾角的控制。但是这些震序列又分为两     

中亚地区地震序列特征

共搜集到１９７０－１９８４年中亚地区８个地震序列。通过分析这些板块内部地震序列的震源分布,震源机制,归纳出它们的特征是：震中分布的长轴部比较短,震中分布长轴和短轴的比值小;长轴的方向受当地地震带的走向控制。和碰撞带走向无关。地震序列中各地震的震源深度都比较浅。其中有震源机制资料的３个地震序列表明：主震的震源机制如果是逆冲滑动,倾角则比较低;主要的震源机制如果是走向滑动,倾角则比较高。     

西南太平洋地区地震序列的特征

共搜集到１９８４￣１９９０年西南太平洋地区１２个板缘地震序列。多数地震序列的特征是：震中分布区域的长轴较长并且随主震震级和序列中强震次数而增加;震中分布区域的长、短轴长度的比值较高;地震序列的余震震源机制和主震的差异不大;震源深度下限超过地壳,可达７０ｋｍ以上。走滑型主震占的比例低,高倾角滑动面的走向既有与俯冲带走向平行的也有横切的,个别逆冲型地震的断层面走向横切俯冲带。它们显示出与板块俯冲带主体     

1982年日本茨城地震序列表现出的局部板块俯冲动态过程

板块构造的运动和动力学是地学研究的前沿课题．板块边缘强震是板块运动的直接结果．分析1982年日本茨城地震序列发现，震源断层面存在分阶段沿走向扩展、倾向调整的特殊图象．结合震源机制的走向、倾向以及滑动方向等资料，确认属于日本海沟下方的俯冲带逆冲地震．文中讨论了地震序列过程的成因，认为采用介于年尺度的空间大地测量结果与秒尺度的强震矩张量分析之间的地震序列时空分布研究，表明太平洋板块向欧亚板块局部下方俯冲的动态过程．根据地震平均错距和板块运动速度，推测近年当地可能再次发生强震．      

Dynamic subduction process of local plate revealed by Ibaraki earthquake sequence of 1982 in Japan

IntroductionIt has been brought forward in the plate tectonic theory that the global lithosphere consists of a number of active blocks floating above the asthenosphere since 1960s. And from then on, the kinematics and dynamics of lithosphere have been the frontal subjects in the contemporary geoscientific study. The Pacific Plate is the biggest one covering one fourth of the earth surface. Situated in the Eurasia Plate, our country is affected directly by the compression from the Pacific Pl…     

RELOCATION AND FOCAL MECHANISMS OF YUNNAN TONGHAI EARTHQUAKE SEQUENCE OF AUGUST 2018

The August 2018 Tonghai earthquake sequence and focal mechanisms of the two main shocks about M_S5.0 were investigated through relocation of catalog data and inversion of event waveform recordings downloaded from the China National Seismic Network. The epicenter of 2018 Tonghai earthquake locates in the southern edge of Chuandian block, where the Xiaojiang Fault separates the Chuandian block from South China block in the east, and the Red River Fault separates the Chuandian block from the Indo-China in the southwest. These two faults blocked and absorbed the continuous southward movement of Chuandian block, significant tectonic stress has been built up in the southern tip of Chuandian block. As a seismicity active zone, Tonghai has been struck by a M7.0 strong earthquake in 1970. The August 2018 Tonghai earthquake is the major earthquake occurring in Tonghai and surrounding areas since the 1970 strong earthquake. Therefore, detailed focal mechanism study for 2018 Tonghai earthquake sequence is crucial for the earthquake relief effect for the Tonghai and surrounding area. In this study, we first relocate the epicenter of earthquake sequence by using the double difference relocation method, then we inverted focal mechanism for two main earthquakes with magnitude of ~5.0 by using the W-phase method. The relocated epicentral locations of Tonghai earthquake sequence show a NE-SW trend narrow band, predominant depth range of 5~10km and near vertical seismogenic fault. The focal parameters for the August 13 earthquake are: strike of 298.2°, a dip of 45.2°, a rake of -172.9° and strike of 203.2°, a dip of 84.9°, a rake of -45.0°, respectively, and magnitude of M_W=5.07; Focal parameters for the August 14 earthquake are: strike of 297.0°, a dip of 63.6°, a rake of -161.5° and strike of 198.5°, a dip of 73.5°, a rake of -27.7°, respectively, and magnitude of M_W=4.89. Combined analysis of the relocated epicentral locations and obtained focal mechanisms suggest that the seismogenic fault of the August 2018 Tonghai earthquake sequences could be related to the NE-striking Mingxing-Erjie Fault, and the temporal and spatial distribution characteristics of the earthquake sequence is consistent with the regional seismotectonic background.     

汕头－吕宋岛岩石圈速度结构与震源构造──台湾浅滩7．3级地震构造之一

汕头－吕宋岛岩石圈速度结构剖面，划分出华南陆缘古生代陆壳、陆架区晚古生代－中生代陆壳、陆坡带中生代－早第三纪过渡壳、新生代南海海盆洋壳及吕宋岛中生代－新生代岛弧陆壳与东吕宋海槽洋壳等地壳构造组分，并确定了上述地壳构造之间的边界断裂构造及其性质。结合地震震源分布及机制，初步确定了华南陆架盆岭构造带北、南两侧地震构造的控震构造与发震构造性质及其震源力学特征；１）指出１９９４年９月１６日台湾浅滩７．３级地震属于板缘壳幔地震及造成一千公里有感范围的原因；２）马尼拉海沟的海底地堑构造与南海海盆岩石圈地幔上隆是马尼拉海沟俯冲带震源显示正断层性质的原因，且为被动的或转换俯冲带；３）东吕宋海槽仍属于菲律宾海俯冲带性质；吕宋岛东西两侧俯冲带岩石圈板片震源深度的准三层分布，可能表明俯冲带岩石圈板片存在相应的低速滑移层。     

Study on the sources of some deep focus earthquakes in Northwest Pacific region

The sources for thirteen deep focus earthquakes ofm _b≥5.5 andh>400 km in Northwest Pacific region were studied using waveform fitting and shear fracture source model. The source parameters were obtained as follows: focal depth, faulting plane, slip direction, rupture velocity, rupture length, rupture direction and scalar moment tensor. It was found that all these earthquake sources can be interpreted as shear faulting and have simple source time functions. The strike direction of faulting plane for most deep focus earthquakes coincides with that of the subduction zone, especially in the deep part of the subduction zone, it results in the tendency of reducing the dip angle of the subduction zone. The multiple point source model was also used to study the source process. The waveform fitting is better than the shear fracture model, but the general rupture direction which coincides with that from unilateral shear source model can not be obtained from the multiple point source model. This study is supported by the National Science Foundation of China and the Chinese Joint Seismological Science Foundation.     

2021年青海玛多MS7.4地震序列精定位与震源机制研究

利用双差定位法对2021年5月22日玛多M_S7.4地震序列中1 434个地震进行重新定位,使用TDMT矩张量反演方法求解玛多地震序列M≥4.5地震的震源机制解,综合分析得到如下结论:(1)玛多地震序列震中整体走向为NWW-SEE向,与昆仑山口—江错断裂展布方向相吻合,序列总长度170 km,呈NWW向和SEE向双侧破裂,主震西北侧存在NW向条带,可能是此次地震的分支断裂活动,在南东侧存在余震稀疏段以及横穿玛多—甘德断裂的余震分布带,推测可能是地下速度结构差异所致;(2)主震附近地震序列以左旋走滑型地震为主,优势走向为NWW向,倾向NE,倾角较高,与昆仑山口—江错断裂性质基本一致,结合余震定位结果推断昆仑山口—江错断裂为本次地震的发震断层;(3)主震附近地震序列P轴平均方位角为237°,P轴,T轴平均倾角分别为15°、16°,N轴平均倾角为65°,结合研究区构造特征推断,本次地震是由NEE-SWW向水平挤压应力推动NWW-SEE向断裂发生左旋走滑错动所致。     

日本海-鄂霍次克海下俯冲带的应力状态及其深部形变

通过地震分布及地震机制解所反映的日本海-鄂霍次克海俯冲带的形态及应力状态,研究了俯冲带深部形变及650km间断面的穿透问题.日本海Benioff带较直,连续性较好;鄂霍次克海Benioff带弯度稍大,220-320km深度之间地震很少.两俯冲带在浅部及深部地震密集,100-200km深度之间有双地震层.应力状态随深度变化,200km深度以下P,T轴方向相对集中,P轴接近俯冲方向,在约100-200km深度附近,P,T轴均接近俯冲方向.观测和理论地震图拟合分析表明,地震断层面走向接近俯冲带走向,断裂的结果使俯冲带在深部倾角变小.     

2008年5月12日四川汶川8.0级地震与部分余震的震源机制解

采用区域和远台Pn或Pg初至波初动符号, 利用下半球等面积投影, 求解了2008年5月12日四川汶川8.0级地震和截止到2008年12月10日发生的部分4级以上余震的震源机制解。 汶川8.0级地震的震源机制为: 节面Ⅰ的走向为5°, 倾角为48°, 滑动角为39°; 节面Ⅱ的走向为247°, 倾角为62°, 滑动角为131°。 P轴方位角为309°, 仰角为8°, T轴方位角为208°, 仰角为54 °, B轴方位角为44°, 仰角为35°。 结合地质构造和余震空间分布, 可以确定节面Ⅱ为发震断层面。 根据震源机制解, 引发本次地震的断层活动主要表现为逆冲, 主破裂面为S67°W与该地震所在断层的走向基本一致(断裂总体走向N45°E)^[1]; 主压应力轴P轴为N51 °W, 主压应力轴P轴方位与该区域构造应力场方向基本一致。 根据余震震源机制解结果, 龙门山断裂带南段发生的余震与北段发生的余震的震源机制都具有优势分布, 且两者差异明显。 早期发生在南段的余震的破裂是以逆倾滑动为主, 兼有走向滑动; 而随着时间的推移, 余震向北段迁移, 在龙门山构造的北段地震震源的破裂方式以走向滑动为主, 兼有一定的逆倾滑动; 龙门构造带南段震源应力场受主震应力场的控制, 而龙门构造带北段震源应力场不仅受区域应力场的影响, 还受主震应力场的影响。     

Fault plane parameters of Sanhe-Pinggu M8 earthquake in 1679 determined using present-day small earthquakes

The great Sanhe-Pinggu M8 earthquake occurred in 1679 was the largest surface rupture event recorded in history in the northern part of North China plain. This study determines the fault geometry of this earthquake by inverting seismological data of present-day moderate-small earthquakes in the focal area. We relocated those earthquakes with the double-difference method. Based on the assumption that clustered small earthquakes often occur in the vicinity of fault plane of large earthquake, and referring to the morphology of the long axis of the isoseismal line obtained by the predecessors, we selected a strip-shaped zone from the relocated earthquake catalog in the period from 1980 to 2009 to invert fault plane parameters of this earthquake. The inversion results are as follows: the strike is 38.23°, the dip angle is 82.54°, the slip angle is -156.08°, the fault length is about 80 km, the lower-boundary depth is about 23 km and the buried depth of upper boundary is about 3 km. This shows that the seismogenic fault is a NNE-trending normal dip-slip fault, southeast wall downward and northwest wall uplift, with the right-lateral strike-slip component. Moreover, the surface rupture zone, intensity distribution of the earthquake and seismic-wave velocity profile in the focal area all verified our study result.     

Research on the 1879 South Wudu M8. 0 Earthquake and Its Co-Seismic Fracture

INTRODUCTIONAstrong earthquake struck between Wudu and Wenxian in Gansu Province on July1,1879,another catastrophic earthquake hittingthe southeastern mountainous area of the province ever sincethe1654TianshuiM8.0earthquake.After an elapse of126years,this massive earthquake has fadedfrommemoryastime goes onandthe humanand natural environment changes.However,the historicaldocumentation about the earthquake is abundant,including official documents of the Qing Dynasty,local newspapers and…     

俯冲带上特大地震静态库仑应力变化对后续余震触发效果的研究

地震静态触发研究在全世界范围内广泛开展,并取得显著成效;但是否所有的大地震,地震静态触发都有很好的效果,对此目前还不甚清楚.本文通过计算最近发生在俯冲带上的三次特大地震(2011年日本东北地震(M_w=9.1)、2010年智利地震(M_w=8.8)与2004年苏门答腊—安达曼地震(M_w=9.0))所产生的静态库仑应力变化,考察主震库仑应力变化对其后续余震空间分布的影响,从而研究俯冲带上特大地震对地震的触发效果.计算结果显示:对于2011年日本东北地震,仅有47%的后续余震发生在库仑应力增加的区域;2010年智利地震也只有47.6%的余震位置处于库仑应力变化的正值区;2004年苏门答腊地震触发了49.8%的后续余震.文中通过进一步改变模型参数(如:采用不同的有效摩擦系数,使用不同作者给出的震源模型等)进行计算,结果表明这三大地震对后续余震的触发比例仍然不高(最好情况下,触发比例也不超过60%).但对于板内地震(如:2008年汶川地震,1999年集集地震),主震对后续余震的触发比例超过85%.由此可以推知,对于俯冲带上的特大地震,地震静态触发效果不显著.因此,对于俯冲带上大地震的触发问题,还需深入研究.     

利用FOCMEC方法反演2011年江西瑞昌与湖北阳新交界M_S4.6地震的震源机制解

利用FOCMEC方法反演了2011年9月10日江西瑞昌与湖北阳新交界MS4.6地震的震源机制解。反演结果为:节面I的走向304°,倾角76°,滑动角4°;节面Ⅱ的走向213°,倾角86°,滑动角165°;P轴的方位角、倾角分别为260°、7°;T轴的方位角、倾角分别为168°、13°;B轴的方位角、倾角分别为19°、75°。其中节面Ⅱ的走向和活动性质与震中附近的郯庐断裂带的分支断裂——池河—西山驿断裂较为接近。分析认为NNE向的池河—西山驿断裂可能是瑞昌—阳新MS4.6地震的发震构造。     

Earthquake swarms in the Kamchatka subduction zone and estimation of possible tsunami generation locations

An analysis of the space-time locations of earthquake swarms in the Kamchatka subduction zone showed that the source zones of these earthquake swarms, as well as of the epicenters of most tsunami-generating earthquakes, are confined to the seamounts in the barrier ridge between Kamchatka and the deep-sea trench. The ??dot clouds?? of hypocenters of practically all earthquake swarms dip toward the trench on seismic sections that are oriented across the subduction zone trend; this fits the auxiliary focal solution of tsunami-generating earthquakes as was first noticed by L.M. Balakina and is in agreement with the model experiment carried out by L.I. Lobkovskii et al. We discuss a likely scenario for the generation of reverse-thrust blocks whose movements are accompanied by earthquake swarms and by tsunami-generating earthquakes. We estimate the locations of the most probable tsunami generation.     

THE SOURCE PARAMETERS AND RUPTURE PROCESS OF THE MW7.0 EARTHQUAKE IN ALASKA,USA ON DECEMBER 1, 2018

A magnitude M_W7.0 earthquake struck north of Anchorage, Alaska, USA on 1 December 2018. This earthquake occurred in the Alaska-Aleutian subduction zone, on a fault within the subducting Pacific slab rather than on the shallower boundary between the Pacific and North American plates. In order to better understand the earthquake source characteristics and slip distribution of source rupture process as well as to explore the effect of tectonic environment on dynamic triggering of earthquake, the faulting geometry, slip distribution, seismic moment, source time function are estimated from broadband waveforms downloaded from IRIS Data Management Center. We use the regional broadband waveforms to infer the source parameters with ISOLA package and the teleseismic body wave recorded by stations of the Global Seismic Network is employed to conduct slip distribution inversion with iterative deconvolution method. The focal mechanism solution indicates that the Alaska earthquake occurred as the result of tensile-type normal faulting, the estimated centroid depth from waveform inversion shows that the earthquake occurred at the depth of 56.5km, and the centroid location is 10km far away in northeast direction relative to the location of initial epicenter. We use the aftershock distribution to constrain the fault-plane strike of a normal fault to set up the finite fault model, the finite fault inversion shows that the earthquake slip distribution is concentrated mainly on a rectangular area with 30km×20km, and the maximum slip is up to 3.6m. In addition, the slip distribution shows an asymmetrical distribution and the range of possible rupture direction, the direction of rupture extends to the northeast direction, which is same as that of aftershock distribution for a period of ten days after the mainshock. It is interesting to note that a seismic gap appears in the southwest of the seismogenic fault, we initially determined that the earthquake was a typical normal fault-type earthquake that occurred in the back-arc extensional environment of the subduction collision zone between the Pacific plate and the North American plate, this earthquake was not related to tectonic movement of faults near the Earth's surface. Due to the influence of high temperature and pressure during the subduction of the Pacific plate toward to the north, the subduction angle of the Pacific plate becomes steep, causing consequently the backward bending deformation, thus forming to a tensile environment at the trailing edge of the collision zone and generating the M_W7.0 earthquake in Alaska.     

FOCAL FAULTS AND STRESS FIELD CHARACTERISTICS OF M7.0 JIUZHAIGOU EARTHQUAKE SEQUENCE IN 2017

On August 8, 2017, Beijing time, an earthquake of M7.0 occurred in Jiuzhaigou County, Aba Prefecture, Sichuan Province, with the epicenter located at 33.20°N 103.82°E. The earthquake caused 25 people dead, 525 people injured, 6 people missing and 170000 people affected. Many houses were damaged to various degrees. Up to October 15, 2017, a total of 7679 aftershocks were recorded, including 2099 earthquakes of M ≥ 1.0. The M7.0 Jiuzhaigou earthquake occurred in the northeastern boundary belt of the Bayan Har block on the Qinghai-Tibet Plateau, where many active faults are developed, including the Tazhong Fault(the eastern segment of the East Kunlun Fault), the Minjiang fault zone, the Xueshan fault zone, the Huya fault zone, the Wenxian fault zone, the Guanggaishan-Daishan Fault, the Bailongjiang Fault, the Longriuba Fault and the Longmenshan Fault. As one of the important passages for the eastward extrusion movement of the Qinghai-Tibet Plateau(Tapponnier et al., 2001), the East Kunlun fault zone has a crucial influence on the tectonic activities of the northeastern boundary belt of Bayan Kala. Meanwhile, the Coulomb stress, fault strain and other research results show that the eastern boundary of the Bayan Har block still has a high risk of strong earthquakes in the future. So the study of the M7.0 Jiuzhaigou earthquake' seismogenic faults and stress fields is of great significance for scientific understanding of the seismogenic environment and geodynamics of the eastern boundary of Bayan Har block. In this paper, the epicenter of the main shock and its aftershocks were relocated by the double-difference relocation method and the spatial distribution of the aftershock sequence was obtained. Then we determined the focal mechanism solutions of 24 aftershocks(M ≥ 3.0)by using the CAP algorithm with the waveform records of China Digital Seismic Network. After that, we applied the sliding fitting algorithm to invert the stress field of the earthquake area based on the previous results of the mechanism solutions. Combining with the previous research results of seismogeology in this area, we discussed the seismogenic fault structure and dynamic characteristics of the M7.0 Jiuzhaigou earthquake. Our research results indicated that:1)The epicenters of the M7.0 Jiuzhaigou earthquake sequence distribute along NW-SE in a stripe pattern with a long axis of about 35km and a short axis of about 8km, and with high inclination and dipping to the southwest, the focal depths are mainly concentrated in the range of 2~25km, gradually deepening from northwest to southeast along the fault, but the dip angle does not change remarkably on the whole fault. 2)The focal mechanism solution of the M7.0 Jiuzhaigou earthquake is:strike 151°, dip 69° and rake 12° for nodal plane Ⅰ, and 245°, 78° and -158° for nodal plane Ⅱ, the main shock type is pure strike-slip and the centroid depth of the earthquake is about 5km. Most of the focal mechanism of the aftershock sequence is strike-slip type, which is consistent with the main shock's focal mechanism solution; 3)In the earthquake source area, the principal compressive stress and the principal tensile stress are both near horizontal, and the principal compressive stress is near east-west direction, while the principal tensile stress is near north-south direction. The Jiuzhaigou earthquake is a strike-slip event that occurs under the horizontal compressive stress.     

An integrated geodynamic model of the Nankai subduction zone and neighboring regions from geophysical inversion and modeling

I investigate large-scale deep crustal structures of the Nankai subduction zone and neighboring region using regional magnetic and gravity anomalies, heat flow measurements, and earthquake hypocenters. It is found that ages, dip angles, and geothermal states of the subducting slab have direct influences on mantle wedge serpentinization. The weakest serpentinization observed in the Nankai forearc region is associated with the youngest downgoing plate of the Shikoku Basin. Conspicuous gravity anomalies identified in the forearc region are coincidental spatially with magnetic anomalies after the reduction to the pole, a mathematical procedure that helps relocate magnetic sources and boundaries, and allows us to more easily interpret magnetic data. It is argued that these patches of magnetic and gravity anomalies are caused by the same sources of anomalous density and magnetization, and are linked directly to preexisting structures such as magnetic anomalies and their boundaries in the subducting oceanic crust. Since the gravity and magnetic anomaly patches are found to be closely related to interplate seismogenic behaviors in the Nankai subduction zone, I suggest that major magnetic boundaries in the Shikoku Basin are likely weak places for slab tears that trigger seismic segmentations along the subduction zone.     

2021年美国阿拉斯加半岛MW8.2地震震源特征分析

采用远场地震波资料和有限断层反演方法获得2021年7月29日6时15分(UTC)美国阿拉斯加州以南海域MW8.2地震的震源破裂过程模型,探讨此次地震发生的动力学背景。破裂过程反演的结果显示这次地震的滑动量分布比较集中,破裂长度约为160km,地震主体破裂发生在20～40km深度范围内,破裂由深部向浅部发展,表明此次地震释放了俯冲带浅部的应变能,破裂持续时间近120s,破裂面上最大滑移量达5m。此外,主震破裂区域中的余震分布较小,大部分余震发生在主震南部,出现这种现象表明震源区的破裂较为彻底并触发了俯冲带浅部位置的地震,本次地震的有限断层反演结果和余震分布均显示破裂向东发展,但未破裂至震中以西的舒马金空区,表明舒马金空区东部的地震危险性仍然存在。