Simulation of the damage to a simple RC structure in the Bhuj,India, earthquake to estimate the level of input‐motion

Analysis of a simple reinforced concrete (RC) structure damaged by the Bhuj, India, earthquake was carried out to estimate the level of shaking in the epicentral region. For this, an attempt was made to estimate the level of input motion to cause inelastic behavior to the extent observed during the field visit. To consider the inelastic effects, both yielding of steel bars as well as crushing of the concrete cover has been investigated employing the hysteretic model known as the Fiber model. The only available record at Ahmedabad of the Bhuj earthquake and four additional earthquake records from Japan and California were used in the analysis. Considering simple scaling of input motion, the level of input motion to cause crushing and spall‐off of the concrete cover as observed in the field was estimated to be of the order of 6 times the original instrumental record obtained at 240 km away from the epicenter. The methodology proposed was promising in providing a useful quantitative indication of the level of shaking when instrumental records are not available. It was also noted that the design response spectrum specified in Indian seismic code IS1893: 1984 appears inadequate compared to the extent of shaking estimated. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of the Deformation and Liquefaction of Soils in the Settlement of Korf during the Olyutor Earthquake on April 21, 2006

On April 21, 2006 an earthquake with a magnitude of M _s = 7.7 named Olyutor struck the Koryak Autonomous Region. It was the strongest earthquake for the entire period of historical and instrumental observations. The coordinates of the epicenter were 60.91° N, 166.98° E; the hypocenter’s depth was 12 km. For the efficient study of the earthquake, a team of scientists of the Institute of Volcanology and Seismology of the Far Eastern Branch of the Russian Academy of Sciences (RAS) was sent to the epicentral area. The article presents the results of studies of soil liquefaction in the settlement of Korf, which was the most affected during the Olyutor earthquake. The intensity of the earthquake in the settlement was 9 points. Numerous cracks in the soil were observed, sand volcanoes were formed, and there were numerous cases of sand and silt eruptions, subsidence, and flooding in the settlement. It was decided that the settlement was unfit for human habitation.     

Northridge, California, earthquake of 1994: density of red-tagged buildings versus peak horizontal velocity and intensity of shaking

The 1994 Northridge earthquake occurred underneath a densely populated metropolitan area, and was recorded by over 200 strong motion stations in the metropolitan area and vicinity. This rare coincidence made it an ideal case to study, in statistical sense, the correlation of damage to structures with the level of strong shaking, in particular with respect to (1) instrumental characteristics of shaking and (2) the reported site intensity scale. In this paper, statistics for the incidence of red-tagged building in 1 × 1 km² blocks in San Fernando Valley and Los Angeles is presented and analyzed, as function of the observed peak ground velocity or the local intensity of shaking. The ‘observed’ peak velocity is estimated from contour maps based on the recorded strong motion. The intensity of shaking is estimated from the published intensity map and from our modification of this map to make it more consistent with observed high damage to buildings in some localized areas. Finally, empirical scaling equations are derived which predict the average density of red-tagged buildings (per km²) as a function of peak ground velocity or site intensity of shaking. These scaling equations are specific to the region studied, and apply to Wooden Frame Construction, typical of post World War II period, which is the prevailing building type in the sample studied. These can be used to predict the density of red-tagged buildings per km² in San Fernando Valley and in Los Angeles for a scenario earthquake or for an ensemble of earthquakes during specified exposure, within the framework of probabilistic seismic hazard analysis. Such predictions will be useful to government officials for emergency planning, to the insurance industry for realistic assessment of insured losses, and to structural engineers for assessment of the overall performance of this type of buildings.     

粤西沿海震动图的生成和研究

震动图是描绘地震产生的地面运动和可能破坏情况的有效工具,主要包括峰值地面速度(PGV)等值线图、峰值地面加速度(PGA)等值线图和仪器烈度分布图等.基于华南数字地震台网记录到的2010年7月9日MS3.7级阳江地震的数据资料,利用SAC和GMT软件从记录到的地震波形数据提取地面运动参数,生成了PGV和PGA等值线图,并...     

汶川地震的面波震级测定及其多普勒效应

本文介绍了全球主要地震机构对2008年5月12日汶川地震参数的速报和修订情况,分析了美国地质调查局国家地震信息中心测定的面波震级。通过对比198个全球地震台站测定的面波震级和面波周期,得出如下结论:测定面波震级偏大的台站主要分布在震中的东北方向,测定面波震级偏小的台站主要分布在震中的西南和东南方向,面波周期偏小的台站主要分布在震中东北方向。由于此次地震破裂方向是以北东向单侧破裂为主,且地震多普勒效应导致震中东北方向振动加强,因此该方向上的面波震级偏大,地震烈度衰减慢;而震中西南方向的振动减弱,此方向面波震级偏小,地震烈度衰减快。从而造成地震烈度沿中央断裂带的北东方向衰减慢,而南西方向衰减快的特征分布。      

2021年5月21日云南漾濞MS6.4地震的快速测定与数据产品产出

2021年5月21日21时48分(北京时间)云南大理州漾濞县发生Ms6.4地震.中国地震台网中心在震后8min发布正式速报结果,随后联合多家单位启动地震相关产品的应急产出工作,共产出地震基本参数、历史地震、地震构造、震源机制、仪器地震烈度和余震精定位等9类14种数据产品.产品结果显示,本次地震发生在川滇地块滇西地区,位...     

2020年7月12日唐山古冶MS5.1地震的强震动特征

首都圈强震动观测台相对密集,区域强震动观测能力较强。2020年7月12日6时38分在河北省唐山市古冶区发生M_S5.1地震,强震动台和烈度台共收集到三分量强震动记录363组。通过强震动记录数据处理绘制了PGA和PGV的空间分布图,初步认识到此次地震强烈的地震动主要集中于震中附近区域,远离震中的天津塘沽—宁河—宝坻三角区域也观测到“异常增大趋势”的地震动,这与1976年唐山地震的宏观烈度异常区较为一致。同时分析了强震动记录PGA、PGV随距离的衰减规律,通过与为第五代区划图编制建立的东部强震区衰减关系的计算值对比,可以看出与此次地震中PGA、PGV的衰减具有一致的趋势。      

Archeoseismological investigation of the Kurmenty medieval settlement site,northeastern Issyk-Kul region,Kyrgyzstan

Archeoseismological studies of the Kurmenty settlement have proved the seismogenic origin of the deformation in the walls at this site. The radiocarbon age of the first seismic event damaged the walls of the settlement is 7th century AD. The second seismic event occurred a few centuries later, probably in the late Middle Ages. The strongest seismic events of North Tien Shan occurred in the late 19th–early 20th century as the Chilik (1889, M = 8.4) and Kebin (1911, M = 7.9) also damaged the walls of the Kurmenty settlement. The local shaking intensity during these seismic events was I ≥ VII on MSK-64 scale.     

Seismotectonic position of the Kaliningrad September 21, 2004, earthquake

The paper presents an alternative consistent seismotectonic model of the Kaliningrad (Russia) September 21, 2004, earthquake according to which source zones of the two strongest shocks were confined to a N-S fault off the Sambiiskii Peninsula in the Kaliningrad region. A left-lateral deformation fractured a local crustal zone between the town of Yantarnyi and the settlement of Bakalino. The model was constructed with the use of a method developed by the authors for structural analysis of gravity and magnetic data. Initial materials are revised in terms of the EMS-98 macroseismic scale, and modified maps showing the shaking intensity in the NW part of the Sambiiskii Peninsula are compiled.     

公元180年甘肃表氏地震考

根据史料记载,各种地震目录均将东汉灵帝光和三年秋(公元180年)表氏地震震中定在甘肃省高台县西(39.4°N,99.5°E),震中烈度Ⅹ度,震级7(1/2).本文通过对历史地震资料的重新考证和表氏新旧县城遗址的实地考察,对公元180年表氏地震的震中位置作了如下修正:震前的表氏县城位于甘肃省肃南县明花区新墩子城,也应是震中所在地,其地理位置为39.6°N、99.3°E,精度2类;震后重建的县城在今骆驼城或草沟井城.通过对史料震害的认真分析,并将本次地震与两汉时期8次6(1/2)级以上地震及高台附近地区9次地震的地震参数、震害和波及范围进行对照,最终将震中烈度修正为Ⅸ—Ⅹ度,震级修正为7级.     

The Shaking Table Test on the Performance of Cement-mixed Piles in Liquefiable Railway Foundations

Cement-mixed piles, as countermeasure against liquefaction of silt and sand ground, can improve the shear strength and bearing capacity of foundation soil, meaning cement-mixed piles are capable of resisting displacement when an earthquake happens. However, investigations of cement-mixed piles by experimental methods such as the shaking table test is few and far between. It is especially true for the seismic performance of cement-mixed piles in liquefiable railway foundations in high seismic intensity regions. To this end, a cross-section of the Yuxi-Mengzi railway was selected as the prototype and studied by the shaking table test in this study. The results showed that composite foundation of cement-mixed piles was not liquefied when the seismic acceleration was lower than 0.30g. In the process of acceleration increasing from 0.30g at 2Hz to 0.60g at 3Hz, the upper middle silt outside slope toe was partly liquefied. The foundation soil under the shoulders and center of subgrade was far from the initial liquefaction criterion during the test. Cement-mixed piles can effectively reduce the embankment settlement and differential settlement. It can be concluded that, the design of cement-mixed piles can ensure the seismic performance of the subgrade, and satisfy the seismic design requirements of the Yuxi-Mengzi railway in areas of VⅢ degrees seismic fortification intensity.     

On a possible origin of the anomalous effects that were observed during the May 24, 2013 earthquake in the Sea of Okhotsk

The deep-focus Sea of Okhotsk earthquake that occurred on May 24, 2013 (h = 630 km, M _w = 8.3) was accompanied by anomalous effects that were unknown previously. A combined analysis of published data concerning the source rupture evolution and some features of the deep structure provided an explanation of some anomalous effects, such as the large number of aftershocks and the low level of ground shaking in the epicentral area. However, GPS observations revealed high coseismic vertical displacements in the area. The seafloor uplift in the Sea of Okhotsk and the adjacent coasts was 3–12 mm, peaking at the approximate center of the sea, while Kamchatka and the North Kuril Islands subsided by 3–18 mm, peaking at the Apacha station 190 km east of the earthquake epicenter. These maximum estimates are 1.2–1.8 times the analogous values (10 mm) for the Chile mega-earthquake of May 20, 1960 (M _w ~ 9.5). It is known that the large distances at which ground shaking is felt during deep-focus earthquakes are due to the fact that the body waves travel through the high-Q lower mantle. However, this does not explain the paradox of the present earthquake in the Sea of Okhotsk, viz., a constant intensity of shaking (two grades) in the range of epicentral distances between 1300 and 9500 km. The explanation requires consideration of the earth’s free oscillations excited by the earthquake.     

A note on an instrumental comparison of the modified mercalli (MMI) and the Japanese meteorological agency (JMA) intensity scales,based on computed peak accelerations

In many parts of the world, subjectively based earthquake intensity scales similar to those of the Modified Mercalli Intensity (MMI) are applied regularly. Although the characteristics of these scales are quite similar, it is often difficult to convert an estimate of strong ground shaking measured by the MMI scale into its equivalent on other scales. In this paper, an instrumental correlation of the Japanese Intensity scale (JMA) with the MMI scale is described. Currently, one common yardstick that is available for both Japan and the United States is the statistic of peak accelerations. The correlation is done by comparing the JMA for sites where the ‘peak acceleration’ is known in Japan with the MMI for sites in the United States where the peak acceleration is also known. To ensure a direct correspondence of peak accelerations in these two countries, the peak values recorded in the U.S. are corrected by determining the peak acceleration as recorded by the Japanese accelerograph, the SMAC, while it is subjected to the excitation recorded in the United States.     

2018年1月20日乌鲁木齐县M_S4.8地震强震动观测记录初步分析

2018年1月20日乌鲁木齐县发生MS4.8地震,乌鲁木齐市区多处震感强烈。此次地震新疆强震台网共获取36条地震动加速度记录,距离震中21.8km的草原工作站烈度速报台记录到本次地震最大峰值加速度97.1×10^-2m/s^2(NS向),距离震中最近的永丰镇峰值加速度70.8×10^-2m/s^2(NS向)。经计算永丰镇仪器烈度为5.5度,与现场工作队考察结果基本一致。对获取到的地震动加速度进行频谱分析,卓越频率集中在2~8Hz范围内,这可能是造成永丰镇建筑物出现轻微破坏的原因之一。将峰值加速度与经验性衰减关系进行对比,震中距小于33km时,水平峰值加速度普遍高于经验性衰减关系。     

1997年9月三水地震震相特征与发震构造

１９９７年９月广东省三水市发生的ＭＬ３．７、４．４级地震因震中烈度比同等震级的其它震例偏高许多,而且多个台站均记录到长周期振动规则的正弦形面波而特别引人注目。精确测定了这组地震的震源位置,得到震源深度约等于１ｋｍ;对比分析了震相记录特征、震区周围的历史地震活动及地质构造背景,认为这是一组罕见的低震级高烈度震例,其发生可能与震中附近的Ｆ７断层活动有关。     

1985年8月23日新疆乌恰地震6.7级强余震频谱分析

在1985年8月23日新疆乌恰7.4级地震后二十天,即9月12日04点45分53秒发生了一次6.7级的强余震,在距微观震中约4公里处获得了强震记录。其最大水平向加速度值为123.8伽,是最大竖向加速度值的四倍。这次地震的反应谱峰值周期比海城、唐山、松潘地震都长。因此,虽然在微观震中处地震动强度相当于烈度7°,但震害却仅是6°。     

Source Parameters of the ML 3.8 Earthquake on January 20, 2000 near Meckenheim, Germany

In the early morning hours on January 20,2000 at 03:03:17 (UTC) an M_L = 3.8earthquake occurred east of the city ofMeckenheim. It awakened many people in theMeckenheim-Bonn-Siegburg area. At least 200people called the police or fire brigade inBonn. The earthquake was felt as far asLimburg (Westerwald) and east Belgium. Themaximum intensity (EMS) in theMeckenheim-Adendorf area was 5. Theinstrumental epicenter was located at50.60^° N latitude and 7.08^° Elongitude. Source depth was 9.5 km. Localmagnitude M_L was 3.8 ± 0.3 andseismic moment was 1.86*10¹⁴ Nm,corresponding to a momentmagnitude M_W of 3.4± 0.2.Following the Brune model, the sourceradius was 0.45 km with an averagedislocation of 1.0 cm and a 0.8 MPa stressdrop. The source mechanism from a firstmotion fault plane solution shows a normalfault mechanism with a significant strikeslip contribution. Trend and plunge of themajor and minor principal axes P/T are168^°/54^° and275^°/12^°, respectively. Aninversion of the moment tensor fromamplitudes of direct waves reveals a doublecouple mechanism with a smaller strike slipcontribution than the first motion faultplane solution, but also shows asignificant 16% non-double couplecomponent of the total moment. Theintensity epicenter was determined by agrid search algorithm and was found to be14 km east from the instrumental epicenter.The macroseismic magnitude was 3.6.     

Main Factors Affecting the Distribution of the Macroscopic Destruction Field of Earthquake

It is proposed that some possible macroseismic epicenters can be determined quickly from the relationship that the microseismic epicenters located by instruments bear with faults.Based on these so-called macroseismic epicenters,we can make fast seismic hazard estimation after a shock by use of the empirical distribution model of seismic intensity.In comparison with the method that uses the microseismic epicenters directly,this approach can increase the preccision of fast seismic hazard estimation.Statistical analysis of 133 main earthquakes in China was made.The result shows that the deviation distance between the microseismic epicenter and macroseismic epicenter falls within the range of 35km for 88% earthquakes of the total and within the range of 35to 75km for the remaining ones.Then,we can take the area that has the microseismic epicenter as its center and is 35km in radius as the area for emphatic analysis,and take the area within 75km around the microseismic epicenter as the area for general analysis.The relation between the 66 earthquake cases on the N-S Seismic Belt in China and the spatial distribution characteristics of faults and the results of focal mechanism solution were analyzed in detail.We know from the analysis that the error of instrumental epicenter determination is not the only factor that gives effects to the deviation of the macroseismic epicenter.In addiditon to it,the fault size,fault distribution,fault activity,fault intersection types,earthquake magnitude,etc,are also main affecting factors.By sorting out ,processing and analyzing these affecting factors,the principle and procedures for quickly determining the possible position of the macroseismic epicenter were set up.Taking these as a basis and establishing a nationwide database of faults that contains relevant factors,it is possible to apply this method in practical fast estimation of seismic hazard.     

The August 27, 2008, <Emphasis Type="Italic">M</Emphasis><Subscript>W</Subscript> = 6.3, Kultuk earthquake effects in the Nearepicenter zone: Macroseismic survey results

In this work, the macroseismic effects of the Kultuk earthquake (M _W = 6.3), which took place on August 27, 2008 in the southwestern closure of the Baikal Lake, are under consideration. The intensity of shocks in inhabited localities located in the epicentral zone reached 7–8 points on the MSK-64 scale. The earthquake was named after the local settlement of Kultuk, which was the mostly damaged area by the earthquake. The considered seismic event caused significant material damage (about 250 million rubles according to preliminary estimates). In inhabited localities of Southern Pribaikalie thousands of cases of damaged ovens and chimneys were registered. Some buildings were highly damaged and, accordingly, they are unfit for further use. The earthquake was the cause of numerous rockslides, rockfalls, and landslides on steep natural and artificial slopes. A macroseismic survey allowed us to establish the asymmetrical distribution of the intensity of shocks relative to the epicenter.     

Localized changes in geomagnetic total intensity values prior to the 1995 Hyogo-ken Nanbu (Kobe) earthquake

Changes in total geomagnetic field intensity, of 2–3 nT, were observed prior to the 1995 Hyogo-ken Nanbu (Kobe) earthquake at the Amagase (AMG) site, located approximately 70 km from the epicenter. We examined whether the observed variations are local signals arising from the Earth's crust, or global variations that are unlikely to originate from the crust. To remove global-scale variations in total geomagnetic intensity data, we employed a regional geomagnetic field model. Using data recorded at five reference sites in Japan, we estimated global-scale variations in total geomagnetic intensity, and removed them from the observed total geomagnetic intensity at the AMG site. The reminder still showed variations during the period prior to the Kobe earthquake. In addition, these pre-seismic variations include two of the largest shifts recorded during the entire observation period at the AMG site, raising the possibility that these variations were indeed related to the earthquake. These variations cannot be interpreted as signals arising from the area close to the seismic source because of the large distance between the epicenter and the site. Therefore, our results raise the possibility that the physical state of the Earth's crust shows marked changes over a wide region in the lead-up to a seismic event.