Historical earthquakes and a tsunami in Bohai Sea

Quantitative analysis on seismicity showed that there are several seismic dense zones in Bohai Sea. These seismic dense zones of modern small earthquakes behave prominent NE orientation, although a seismic dense zone with NW direction exists actually. Taking 39°N as a boundary, seismicity in the south is different from that in north of Bohai Sea. Almost all strong earthquakes and seismic dense zones are concentrated in the southern part. Based on archives and seismic dense characteristics, we amended the epicenter of strong earthquakes in 1548 and discussed about magnitude of the earthquake in 1888. Possibility of the event in 173 as a tsunami was discussed. The event in 1597 was doubted as a strong earthquake in Bohai Sea.     

Automatic detection,location and quantification of earthquakes: Application to tsunami warning

We describe a fully automated seismic event detection and location system, providing for real-time estimates of the epicentral parameters of both local and distant earthquakes. The system uses 12 telemetered short-period stations, with a regional aperture of 350 km, as well as two 3-component broad-band stations. Detection and location of teleseismic events is achieved independently and concurrently on the short-period and long-period channels. The long-period data is then used to obtain an estimate of the seismic momentM ₀ of the earthquake through the mantle magnitudeM _m, as introduced byOkal andTalandier (1989). In turn, this estimate ofM ₀ is used to infer the expected tsunami amplitude at Papeete, within 15 minutes of the recording of Rayleigh waves. The performance of the method is discussed in terms of the accuracy of the epicentral parameters and seismic moment obtained in real time, as compared to the values later published by the reporting agencies. Our estimates are usually within 3 degrees of the reported epicenter, and the standard deviation on the seismic moment only 0.19 unit of magnitude for a population of 154 teleseismic events.     

冲绳海槽地区地震潜在海啸对中国东南沿海的影响研究

采用球坐标系下非线性浅水波方程, 研究日本本州M9.0大地震引发的海啸对中国东南沿海的影响, 并计算了冲绳海槽构造带上3个不同段落可能发生潜在地震引发的海啸, 分析这些海啸与日本大海啸的浪高和走时关系. 结果表明, 日本地震海啸模拟结果与日本当地报道及中国东南沿海7个验潮站的报道结果相符. 冲绳海槽构造带中段可能发生的3次不同震级（M7.0, M7.5, M8.0）潜在地震引发的海啸到达中国东南沿海的时间比日本海啸提前约4个小时, 从震源区传播3个多小时即可到达华东沿海部分验潮站. 冲绳海槽M7.5潜在地震海啸在验潮站上计算的波高与日本海啸相当, 中冲绳海槽M8.0潜在地震海啸在大陈站的波高将超过0.9 m, 在坎门站波高将超过1.8 m. 北冲绳海槽的潜在地震海啸威胁主要集中在江苏盐城、 上海一带, 南冲绳海啸主要对台湾东北部和浙江沿海产生威胁. 本文对冲绳海槽构造带上潜在地震引发海啸的模拟结果, 可为中国东南沿海地区的防震减灾、 海啸预警提供有意义的参考.      

A note on differences in tsunami source parameters for submarine slides and earthquakes

The nature of tsunami sources is reviewed, including source duration, displacement amplitudes, and areas and volumes of selected past earthquakes, slumps and slides that have or may have generated a tsunami. This review shows that the velocity of spreading of submarine slides and slumps (1–100 m/s) can be comparable to the long wavelength tsunami velocity (30–140 m/s for water depth 100<h<2000 m). In contrast, typical velocities of spreading dislocations during most earthquakes are one order of magnitude larger (2–3 km/s). Other significant differences between earthquake and slide and slump sources are that the balance of the total uplifted material in the case of slides is essentially zero, while for earthquakes it can be considerable, and that the vertical displacements for slides and slumps, per unit area of their horizontal projection, can be orders of magnitude larger than during earthquakes. This can result in high concentrations of the total change in the potential energy of fluid, above the source, over much smaller areas than during earthquakes.     

海底地震有限断层破裂模型对近场海啸数值预报的影响

快速准确的海啸源模型是近场海啸精确预警的关键.尽管目前还没有办法直接对其进行正演定量计算,但是可以通过多源地震、海啸观测数据进行反演或联合反演推算.不同的海啸源可能导致不同的预警结论,了解不同类型海啸源适用性、评估海啸源特征差异对近场海啸的影响,无论对于海啸预警还是海啸模拟研究尤为重要.本文评估分析了6种不同同震断层模型对2011年3月11日日本东北地震海啸近场数值预报的影响,重点对比分析了有限断层模型与均一滑动场模型对近场海啸产生、传播、淹没特征的影响及各自的误差.研究表明:近场海啸波能量分布主要取决于海啸源分布特征,特别是走向角的差异对海啸能量分布影响较大;有限断层模型对海啸灾害最为严重的39°N以南沿岸地区的最大海啸爬坡高度明显优于均一滑动场模型结果;综合对比DART浮标、GPS浮标及近岸潮位站共32个站次的海啸波幅序列结果发现有限断层模型整体平均绝对/相对误差比均一滑动场模型平均误差要低,其中Fujii海啸源的平均绝对/相对误差最小,分别是0.56 m和26.71%.UCSB海啸源的平均绝对/相对误差次之.3个均一滑动场模型中USGSCMT海啸源模拟精度最高.相对于深海、浅海观测站,有限断层模型比均一滑动场模型对近岸观测站计算精度更高.海啸源误差具有显著的方向性,可能与反演所采用的波形数据的代表性有关;谱分析结果表明Fujii海啸源对在12至60 min主频波谱的模拟要优于UCSB海啸源.海啸源中很难真实反映海底地震破裂过程,然而通过联合反演海啸波形数据推算海啸源的方法可以快速确定海啸源,并且最大限度的降低地震破裂过程与海啸产生的不确定性带来的误差.     

Onshore tsunami deposits caused by the 1993 Southwest Hokkaido and 1983 Japan Sea earthquakes

Onshore tsunami deposits resulting from the 1993 Southwest Hokkaido and 1983 Japan Sea earthquakes were described to evaluate the feasibility of tsunami deposits for inferring paleoseismic events along submarine faults. Tsunami deposits were divided into three types, based on their composition and aerial distribution: (A) deposits consisting only of floating materials, (B) locally distributed siliclastic deposits, and (C) widespread siliclastic deposits. The most widely distributed tsunami deposits consist of the first two types. Type C deposits are mostly limited to areas where the higher tsunami runup was observed. The scale of tsunami represented by vertical tsunami runup is an important factor controlling the volume of tsunami deposits. The thickest deposits, about 10 cm, occur behind coastal dunes. To produce thick siliclastic tsunami deposits, a suitable source area, such as sand bar or dune, must be available in addition to sufficient vertical tsunami runup. Estimation of the amounts of erosion and deposition indicates that tsunami deposits were derived from both onshore and shoreface regions. The composition and grain size of the tsunami deposits strongly reflect the nature of the sedimentary materials of their source area. Sedimentary structures of the tsunami deposits suggest both low and high flow régimes. Consequently, it seems very difficult to identify tsunami deposits based only on grain size distribution or sedimentary structure of a single site in ancient successions.     

Automatic real time parameter determination of tsunami earthquakes in the Far East of Russia: Algorithms and software

A system of algorithms and software modules is described for automatic real time determination of epicenters and magnitudes of potential tsunami earthquakes. Modules are compiled into a single software system called Tsunami Source Quick Location (SS TSQL). The TSQL complex was successfully tested on dozens of real digital recordings. Currently, the TSQL complex is continuously operated in a test mode within the first phase of the seismic subsystem of the Tsunami Warning System (SS TWS) in the Far East of Russia.     

Mechanism of volcanic earthquakes of the Sheveluch volcano,Kamchatka

Determinations of the local mechanisms of three volcanic earthquakes are given connected with the eruption of the Sheveluch volcano (November, 1964). As initial material the data on first arrivals of P-waves are used. The local mechanism of all three earthquakes is close to a strike-slip type of faulting and similar to the focal mechanism of tectonic earthquakes of Kamchatka. One nodal surface of all the volcanic earthquakes strikes in the same direction as the outbursts of the directed volcano explosions.     

浅俯冲带缓慢动力变形与地震及海啸发生的自洽机理

2012年6月9日出版的《地球物理学研究通讯》(Geophysical Research Letters)发表了美国圣地亚哥州立大学地质学系有关板块俯冲带地震及海啸发生机理研究的最新成果.该研究提出了浅俯冲带地震及其所引发海啸的"自洽"机制.     

2007年甘肃部分地震的震源参数反演

2007年甘肃测震台网记录到M_L>3.0的地震43次,本文选取了其中17例,利用垂直向PG波初动波形进行了地震矩张量反演,给出了最佳双力偶解,并对一些地震发震背景和发震机理进行了分析讨论.对地震机理研究及未来地震预报提供了参考依据.     

地震与海啸

海啸是严重的地震次生灾害之一,简要介绍了海啸的成因、分布、量度、传播特征及对我国的影响;并就国际及我国如何加强海啸监测,联合建设预警预报系统提出建议。     

Probability-consistent earthquakes and probability-consistent conservative earthquakes

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抚顺老虎台煤矿矿震震源机制的研究

利用１９８８－１９９５年６月间抚顺考虑台煤矿１００个矿震记录的５３４个Ｐ波初动方向数据和抚顺及周围地区１２０个天然地震记录的５２６个Ｐ波初动方向数据,用格点深度法分别计算出它们的综合断层面解的Ｐ、Ｂ、Ｔ轴并对其进行了对比分析。     

2011年云南腾冲5.2级双震发震机理

本研究联合使用观测震相到时和波形互相关数据,采用双差法对2011年6月20日与8月9日发生在云南腾冲的5.2级双震及其余震序列进行重定位,并采用gCAP(generalized Cut and Paste)方法反演了该双震全矩张量解.结果显示,双震震中位于龙川江断裂的西侧,余震序列在深度上为一个倾斜的柱状体,且倾向腾冲火山区;6月20日和8月9日5.2级地震均表现为体积缩小的闭合型破裂,包含有显著的非双力偶成分,但后者包含的非双力偶成分相对明显减小.这些结果表明,云南腾冲5.2级双震及余震活动可能与火山下方的地壳岩浆作用密切相关,龙川江断裂为热物质向上运移提供了通道,而双震型地震的发生可能与首次地震的破裂体积缩小挤出的流体作用于断裂密切相关.     

Undead earthquakes

This short communication deals with the problem of fake earthquakes that keep returning into circulation. The particular events discussed are some very early earthquakes supposed to have occurred in the U.K., which all originate from a single enigmatic 18th century source.     

唐山与通海两大地震的强余震的差别及其原因探讨

1970年通海地震序列与1976年唐山地震序列的对比表明,两次地震的余震衰减,余震强度和频度,余震分布区的形状等有区别.对此提出了一种解释：若余震分布区域的长轴长度a与短轴长度b之比a/b越大,则震源体越接近于一个面,在一个面上进行的调整过程应当比较简单,余震的衰减比较快,强余震比较少而小;反之则震源体越表现出一个体的形态,在一个体内进行的调整过程应当比较复杂,余震衰减比较慢,强余震比较多而大.对于那些在主震后能够很快进行定位并勾画出余震区域轮廓的情况,可以尝试利用a/b快速判断后面强余震的多少以及余震衰减的快慢.