2018年2月6日花莲M_W6.4地震近场地震动方向性效应

利用中国台湾省内222个强震动台站以及Palert地震预警系统520个台站所观测的三分量加速度记录,研究此次花莲M_W6.4地震近场强地震动空间分布和衰减特征,将观测结果与美国NGA-West2地震动经验预测模型进行对比,揭示此次台湾花莲地震近场地震动的长周期特点,基于回归残差分析研究地震动峰值加速度(PGA)、峰值速度(PGV)和不同周期地震动的空间分布差异,定量考察近场地震动的方向性效应.研究结果表明:(1)整体上此次地震的近场PGV观测值和周期1.0s以上的长周期加速度谱值与美国NGA-West2地震动预测模型结果接近,PGA观测值和周期小于1.0s的加速度反应谱略低于预测模型结果.从空间分布来看,周期1.0s以上的长周期地震动在断层的不同方位有系统性差异,在破裂传播前方(震中西南方位),周期大于1.0s时的反应谱明显高于美国NGA-West2地震动经验预测模型,在破裂传播后方(震中东北方位),周期大于1.0s时的反应谱低于经验预测模型,表明此次地震近场地震动具有显著的方向性效应.(2)破裂传播的方向性效应主要影响周期超过1.0s的长周期,而对PGA以及周期小于1.0s的短周期地震动影响较弱.在破裂传播前方,周期1.0～10.0s的加速度反应谱值被增强到整体观测平均水平的1.16～1.52倍;在破裂传播后方,周期1.0～10.0s的加速度反应谱值被减弱到整体观测平均水平的0.36～0.70倍.(3)此次地震破裂方向性效应的影响表现出明显的窄带效应,破裂方向性的影响(包括破裂传播前方的增强作用和破裂传播后方的减弱作用)在周期T=3.0s时达到最大,在该周期破裂传播前方的增强系数为1.52,破裂传播后方的减弱系数为0.36.从周期T=3.0s到10.0s,破裂方向性效应的影响随周期增大总体上呈减弱趋势,这与2016年日本熊本M_W7.0地震破裂方向性效应的影响特点显著不同.     

熊本MW7.0地震近场地表与井下地震动对比研究

选取日本熊本M_W7.0地震断层距小于200 km的82个近场KiK-net台站记录到的三分量记录数据进行基线校正后,获得近场地面运动水平向的峰值加速度PGA、峰值速度PGV及周期为0.2,1,2,3,5和10 s的加速度反应谱数据,并与美国NGA-West2的地震动预测模型相比较,研究熊本地震地表和井下地震动峰值及反应谱的衰减特征,通过比较KiK-net台站地表与井下记录结果,探讨浅层场地放大效应的影响。研究结果表明:① 对于井下观测结果,NGA-West2的地震动模型对PGA和短周期0.2 s的反应谱的预测值与井下观测值相比整体偏高,而PGV和较长周期地震动（如1,2和3 s的反应谱）的预测值与井下观测值较为吻合;② 地表观测记录的PGA,PGV和周期为0.2—3 s的反应谱残差整体上随v_S30对数值的增大呈线性减小的趋势,而周期为5 s和10 s的长周期部分,其场地效应的影响很小;③ 相对于井下记录,地表记录的地震动PGA,PGV和周期为0.2,1和2 s的反应谱有明显的放大,这种放大作用随浅层场地剪切波速的增大而减小;周期为3,5和10 s时长周期地震动的放大效应很小。      

鲁甸地震强震动记录与地震动衰减模型的对比研究

利用2014年鲁甸M_S6.5地震断层距小于300 km的32个自由场地观测台站的地震动加速度记录,分析了地震动峰值加速度(PGA)和峰值速度(PGV)的空间分布特征,并对已有地震动衰减模型中的NGA-West2四个模型和1个中国川藏区模型进行了比较分析.研究表明,地震动PGA和PGV衰减最快的方向与断层主破裂方向一致.在整个断层距(R_(rup))范围内大多数台站的地震动PGA、PGV和加速度反应谱值(Sa(T=0.1、5.0 s))均位于NGA-West2四个模型预测曲线的±1倍标准差之外.PGA、PGV和Sa(T=5.0 s)的事件内残差均值在-1.43～-0.74之间.Sa(T=0.01～5.0 s)事件内残差均值在整个距离范围内均表现出系统性偏负.NGA-West2四个模型的PGA事件内残差的空间分布特征相似,其最大正值和最大负值分布区域的震源-场地方位角约为-90°和90°,与主破裂断层方向垂直,所处地势较为平坦且台站场地V_(S30)相对较大.NGA-West2四个模型总体上会较大地高估鲁甸地震整个断层距范围内各个周期尤其是短周期(T1.0 s)的地震动加速度反应谱值.考虑本地区实际地震资料的中国川藏区地震动衰减模型也会在一定程度上高估鲁甸地震大多数台站的地震动加速度反应谱值,但是相对于NGA-West2四个模型,其预测值更接近鲁甸地震的实际观测值.     

2016年10月30日意大利MW6.6地震破裂方向性效应对地震动参数的影响

2016年10月30日意大利中部发生了M_W6.6地震,这是继8月24日M_W6.2地震后的又一次浅源破坏性地震,意大利国家强震台网在此次地震中获得了丰富的强震动三分向加速度记录。本文从工程强震动数据中心下载了三分向加速度记录,经基线校正和滤波等常规数据处理后发现,强震动体现出明显的方向性效应。根据震源机制解将强震动台站分为破裂前方区域的NW组和破裂后方区域的SE组,采用最小二乘法回归了不同分组的地震动峰值加速度、反应谱和持时的衰减规律,得出断层破裂方向性对地震动参数的幅值影响较大,在断层距相同的情况下,破裂前方区域的加速度和加速度反应谱幅值均高于破裂后方区域,而破裂前方区域的地震动持时远小于破裂后方区域,破裂方向性显著。      

2021年5月21日云南漾濞MS6.4地震随机有限断层三维地震动模拟

2021年5月21日云南省大理州漾濞县发生MS6.4 地震,震中附近遭受了强烈地震破坏.为预测此次地震的地震动影响场,利用震源运动学破裂随机模型,基于随机有限断层三维地震动模拟方法,给出了此次地震中 28个触发强震动台站的三分量加速度时程模拟记录,并结合强震动观测记录,估计了此次地震的地震应力降及震源破裂过程,进一步模拟给出了此次地震中 2823 个虚拟观测点的三分量加速度时程.结果表明,模拟记录的峰值地面加速度(PGA)、峰值地面速度(PGV)与观测值接近,并体现了地震动峰值的衰减规律、近场饱和效应和破裂方向性效应;模拟与观测记录的 5%阻尼比拟加速度反应谱(PSA)的幅值接近、谱形相似,在0.05～10 s周期段,模拟记录可以很好地预测地震动.基于三分量模拟记录给出了漾濞MS 6.4 地震的仪器测定地震烈度图,与云南省地震局发布的烈度图接近,极震区烈度最高可达Ⅷ度,震源破裂方向性导致震中 SE方向的烈度普遍高于 NW方向,受局部场地条件影响沿洱海西侧出现高烈度异常区.     

日本熊本M_W 7.0地震的长周期地震动

利用日本K-NET和KiK-net强震动台网获取的距离发震断层100 km以内136个强震动台站的三分量加速度记录,研究熊本M_W7.0地震地震动的长周期特性.基于残差分析研究不同周期地震动的空间分布差异,将观测分析结果与美国NGA经验模型、汶川和芦山地震观测结果进行对比,揭示此次熊本地震近场强震动的长周期特点及其形成机理.研究结果表明:(1)虽然总体上此次地震的近场地震动水平与美国NGA-West2经验模型的预测结果接近,但周期2 s以上地震动的分布在断层不同方位有系统性差异,在断层的北东方位,周期2.0～10.0 s的反应谱高于NGA-West2经验模型的预测结果,在西南方位,谱值低于经验预测模型.(2)我们认为此次地震2.0～10.0 s的长周期地震动的空间分布差异主要受破裂方向性的影响,在破裂传播的正前方,周期T=2.0 s,3.0 s,5.0 s,7.5 s和10.0 s的加速度谱被放大到整体观测平均水平的1 4～2.0倍.从周期T=2.0 s到10.0 s,破裂向前方向的放大作用和破裂反方向的减弱作用均有所增强,此次地震观测到的速度大脉冲记录均位于断层的东北方位,这与方向性脉冲的产生机理相吻合,速度大脉冲对加速度反应谱有显著的长周期放大作用,放大倍数值可以超过4.0,放大作用的影响主要位于脉冲的特征周期T_p附近.(3)近断层记录在建筑结构敏感的周期(0.5～2.0 s)的反应谱达到芦山地震的3～6倍,虽然与芦山地震震级接近,此次地震近断层地震动破坏力大大超过了芦山M_W6.8地震,甚至超过了汶川W_W7.9地震,这种长周期特点应该引起工程抗震设计和相关研究人员的重视.     

芦山7.0级地震强震动记录及其震害相关性

2013年4月20日芦山地震中的强震动记录是我国自2008年汶川地震后再一次比较全面地获得的高质量的数字强震动记录。国家数字强震动台网共获得3分量自由场记录114组,成都地震烈度速报台网获得63组。文章对强震动记录进行了常规处理,统计了强震动记录随断层距的数量分布情况,绘制了空间地震动加速度等值线图。结合芦山地震震源机制解和破裂过程研究成果,选取典型记录,分析加速度、速度时程的波形、振幅等特征,识别了此次地震滑冲现象,估算了竖向最大永久位移。通过利用观测数据与国外的地震动预测公式对比,分析了不同周期反应谱地震动幅值及加速度反应谱衰减规律,阐明了此次地震的地震动在近场高频成分较卓越的特点。震后现场考察了3个典型强震动台站附近建筑物震害,分析了地震动与工程震害的相关性,地震烈度的评定反映了地震破坏的程度。     

2016年8月24日意大利佩鲁贾M_W 6.2地震动特性

2016年8月24日在意大利佩鲁贾地区发生M_W 6.2地震,截至北京时间2016年8月25日8时,共获得强震记录192组,分析地震动PGA、反应谱以及能量参数的衰减特征。研究结果表明:(1)峰值。此次地震PGA100 cm/s~2记录的水平平均反应谱在短周期明显大于欧洲的设计谱。两水平方向平均反应谱谱比小于1.5,并且在短周期(T0.5 s)谱比差值变化较大,说明此次地震EW向地震动对短周期结构物影响较大;(2)衰减特性。整体看来,此次地震中的PGA值均不同程度低于中国第五代区划图中的中强地震区、中国西部地区、美国西部地区以及欧洲中小地震衰减模型的预测值,且衰减快。Arias强度的衰减变化趋势与Travasarou等的理论模型基本一致,但均小于理论模型值;(3)持时。此次地震的相对持时随震中距增大有逐渐增大趋势,持时均大于Kempton及McQuire的理论模型,表明此次地震的能量释放时间较长。此次意大利地震的地震动参数特征研究表明,该地震具有能量衰减快、持续时间长、对短周期结构物影响较大等特点,验证了此次地震破坏集中在近场、远场震害相对较轻的结论,这也是造成本次地震灾害严重的主要原因。     

云南漾濞6.4级地震强地面运动三要素基本特征分析

2021年5月21日云南漾濞发生6.4级地震,中国数字化强震动观测网络在主震中捕获28组加速度数据。对84条三分向加速度记录进行常规处理,计算出对应的地震动参数,并绘制震中附近水平向PGA和PGV等值线图,结果显示其走向和形态与震后烈度调查结果相近。将实际观测的相对持时进行曲线回归,求得相关系数,并据此计算出T_d(5%～95%)持时对应的震源持续时间在10.22～13.06 s间,与震源破裂过程反演结果基本一致。再通过分析近场6个台站记录的加速度反应谱,并与抗震设计谱比较,总结此次地震的频谱特性,为该区域抗震设防提供参考依据。     

2022年9月5日四川泸定MS6.8地震近断层地震动特征

2022年9月5日12时52分四川甘孜州泸定县发生M_S6.8地震,造成重大人员伤亡和财产损失。本文利用此次地震中距离发震断层80 km以内获得的92个三分量加速度记录,研究此次地震近断层地震动峰值加速度(PGA)、峰值速度(PGV)和不同周期加速度反应谱(S_a)的空间分布与衰减特征,探讨了近断层地震动的脉冲特征及其对地震动反应谱的影响。研究结果表明：(1)此次地震近断层地震动表现出随观测方向变化的较强极性特征,其中51LDJ记录的南北分量约达到东西分量的3倍,这主要受地震的走滑破裂特征影响。(2)近场地震动强度的空间分布主要受此次地震发震断层的走向控制,峰值加速度、速度和加速度反应谱值的分布与断层走向特点一致。较强的观测值多位于烈度VII度以上的区域,与震害分布相符,地震动强度分布从一定程度决定了震害分布。(3)从实际观测结果与地震动经验模型的对比来看,经验模型对本次地震PGA和0.2 s的短周期地震动有较好的预测;对于PGV和周期0.5 s以上的地震动反应谱,本文考察的6个经验模型均有不同程度的高估。(4)本次泸定地震有2条典型脉冲记录,均...     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.     

On the maintenance of the axisymmetric part of the flow in the atmosphere

Summary The maintenance of the axisymmetric component of the flow in the atmosphere is investigated by means of a steady-state, quasi-geostrophic formulation of the meteorological equations. It is shown that the meridional variations in the time-averaged axisymmetric variables can be expressed as the sum of three contributions, one being due to the eddy heat transport, another to the eddy momentum transport, and a third to the convective-radiative equilibrium temperature which enters the problem through the specification of a Newtonian form of diabatic heating. The contributions by the large scale eddies are evaluated through the use of observed values for the eddy heat and momentum transports.The contributions from each of the three forcing mechanisms to the temperature and zonal wind fields are invstigated individually and found to be of about equal importance. The sum of the three contributions are also presented for the temperature, the zonal wind, the stream function associated with the mean meridional circulation and the corresponding vertical motion. Although the results fail to reproduce the main observed features of the lower stratosphere, they are found to be in good agreement with observations in the middle latitude troposphere. At any pressure level, for example, the computed mean zonal wind has a jet-like profile and the axis of the jet is found to slope to the south with height, as observed in the atmosphere.Based in part on a thesis submitted by the first author as partial fulfillment of the requirements for the Ph.D. degree at the University of Michigan. — Publication No. 194 from the Department of Meteorology and Oceanography, The University of Michigan.     

On the gravimetric undulations of the geoid and the deflections of the vertical

Summary The author mentions the aims of the World-wide gravity project he established in the Ohio State University in Columbus, in 1950. He outlines the practical procedure of the gravimetric computations of the undulationsN and the vertical deflection components and and emphasizes that only by the global international cooperation and additional gravity observations at sea carried out during the last decade it has been possible to gather to Columbus the needed gravity material. Since there exist still large gravimetrically unsurveyed areas it is of vital significance to study what gravity anomalies are best to be used for these regions. The given figures concerning the accuracy of theN, and , estimated theoretically and obtained in practice, indicate that in the gravimetrically well surveyed parts of the world like in Europe and the United States we can get gravimetrically on basis of existing gravity material theN-values with accuracy of about 5–10 meters, and and with the accuracy of about 1. The geoid undulationsN are already computed in Columbus for more than 6000 points of the northern hemisphere. The sample maps show the interesting geoid of Europe and vicinity between the latitudes 60° and 30° and longitude 5° W and 30° E, drafted on basis of more than 1000N-values computed at the corners of 1°×1° squares. It is interesting to realize that the geoid undulations in all this area are positive, the extreme values being between 40 and 50 meters. The geophysical significance of the geoid maps of this kind is pointed out.     

太平洋中部地磁台11年周期变化的研究

综合APIA、HONOLULU、PAMATAI 3个地磁台三分量的11年周期变化的形态后,可定性地提出该变化源于内场。如内源为核幔边界的电涡流,则其中心点应位于3台之间。     

Magnetic stratigraphy of the Ordovician in the lower reach of the Kotuy River: the age of the Bysy-Yuryakh stratum and the rate of geomagnetic reversals on the eve of the superchron

Until recently, the existing data prevented the geophysicists from accurately dating the Bysy-Yuryakh stratum, which outcrops in the middle reach of the Kotuy River, constraining the time of its formation to a wide interval from the end of the Late Cambrian to the beginning of the Silurian. The obtained paleomagnetic data unambiguously correlate the Bysy-Yuryakh stratum to the Nyaian regional stage and constrain its formation, at least a considerable part of it, by the Tremadocian. This result perfectly agrees with the data on the Bysy-Yuryakh conodonts studied in this work and yields a spectacular example of the successful application of paleomagnetic studies in solving important tasks of stratigraphy and, correspondingly, petroleum geology. Within the Bysy-Yuryakh stratum, we revealed a large normal-polarity interval corresponding to the long (>1 Ma) period when the geomagnetic reversals were absent. This result, in combination with the data for the Tremadocian and Middle–Upper Cambrian sequences of the other regions, indicates that (1) the rate of occurrence of the geomagnetic reversals on the eve of the Ordovician Moyero superchron of reversed polarity was at most one reversal per Ma; (2) the superchron does not switch on instantaneously but is preceded by a certain gradual change in the operation conditions of the dynamo mechanism which, inter alia, manifests itself by the reduction of the frequency of geomagnetic reversals with the approach of the superchron. This finding supports the views according to which a process preparing the establishment of the superchrons takes place at the core–mantle boundary.     

On the variation in the geomagnetic dipole over the geological history of the Earth

The global database on the paleointensity, containing determinations of the virtual dipole moment (VDM) for a stable (normal) regime of the geomagnetic field in a time interval of up to 3.5 Ga, is supplemented by new VDM determinations and analyzed. The field generation process started no later than 3–3.5 Ga (earlier data are absent) at the stage of the Earth’s core formation. Since that time, the dipole value has differed from its present value by no more than an order of magnitude, and the deviations that have already been detected tend toward smaller values. The distribution of VDM values in the time interval 0–400 Ma is bimodal, which apparently reflects the presence of two different generation levels of the geomagnetic field distinguished by a relatively large value (close to the present field value) and a relatively small value (approximately half as large as the present value). The total duration of decreased VDM values appreciably exceeds that of increased VDM values (179.1 and 28.6 Myr, respectively). On the whole, data on the paleointensity do not contradict the hypothesis about the dipole nature of the field over the last 400 Myr; however, the number of determinations at high paleolatitudes is too small to draw decisive conclusions on the validity (or invalidity) of the dipole field approximation based solely on paleointensity data.     

Comparison Between the Nutations of the Planet Mars and the Nutations of the Earth

The nutations of the planets Mars andEarth are investigated and compared. Alarge number of interior structureparameters are involved in the nutationcomputations. The comparison between the observations and the computationsprovides several constraints on these parmeters andtherefore allows a better understanding of the physics of the interior of theplanet. For the Earth, the high precision of the observations of the nutationshas led to a very good determination of interior properties of the planet. ForMars, observations of nutations are not yet available, and we review how theamplitude of the Martian nutations depends on the hypotheses consideredfor its interior. Although Mars is very similar to the Earth, its interior is not well known;for example, we don't knowif its core is liquid or solid. Only if the core is liquid,the Free Core Nutation (FCN) normal mode exists and can alter the nutationswhich are close to the resonance. From the observed geoids, it is known thatboth planets are not in hydrostatic equilibrium. The departure is larger forMars than for the Earth, and consequently, the implication of considering a convective mantle instead of a mantle in hydrostatic equilibrium described byClairaut's equation for the initial equilibrium state of the planet is largeron the Martian nutations than on the Earth nutations. The consequences of theuncertainty in the core dimensions are also examined and shown to be of a veryhigh influence for Mars if the core is liquid, due to the potential changes inthe FCN resonance. The influence of the presence of an inner core, which isknown to exist for the Earth, could be more important for Mars than for theEarth if the inner core is large. Due to the presence of Tharsis on Mars, thetriaxiality of this planet has, additionally, larger effects than on Earth.     

Evolutionary Changes in the Configuration of the Magnetic Field of the Solar Corona in the Epoch of the Minimum

Geomagnetism and Aeronomy - The evolution of the magnetic configuration in the solar corona is studied. The curvature of the K-corona helmets obtained from an analytical approximation of the...