A τ_c magnitude estimation of the 20 April 2013 Lushan earthquake,Sichuan, China

A crucial part of proposed earthquake early warning systems is a rapid estimate for earthquake magnitude.Most of these methods are focused on the first part of the P-wave train,the earlier and less destructive part of the ground motion that follows an earthquake.A method has been proposed by using the period of the P-wave to determine the magnitude of a large earthquake at local distance,and a specific relation for the Sichuan region was calibrated according to acceleration records of Wenchuan earthquake.The Mw 6.6 earthquake hit Lushan County,Sichuan,on April 20,2013 and the largest aftershocks provide a useful dataset to validate the proposed relation and discuss the risks connected to the extrapolation of magnitude relations with a poor dataset of large earthquake waveforms.A discrepancy between the local magnitude(ML)estimated by means ofτc evaluation and the standard ML(6.4 vs.7.0)suggests using caution when ML vs.τc calibrations do not include a relevant dataset of large earthquakes.Effects from large residuals could be mitigated or removed by introducing selection rules onτc function,by regionalizing the ML vs.τc function in the presence of significant tectonic or geological heterogeneity,and by using probabilistic and evolutionary methods.     

Temporal vP/vS variation characteristics in different zones of China’s Capital Circle area before and after Wen’an earthquake

On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of r...     

Temporal vP/vS variation characteristics in different zones of China’s Capital Circle area before and after Wen’an earthquake

On July 4, 2006, an earthquake of MS5.1 took place in Wen’an, Hebei Province, just at the south center of China’s Capital Circle area digital seismograph network. It is the strongest event recorded ever since the network went into operation in 2002. We processed the vast amounts of phase data yielded by the 107 digital seismic stations between 2002~2007 using Wadati method. In order to improve the precision and stability of shear and compressional wave velocities (vP/vS) calculation, we impose a number of restrictions on the computation environment and condition, e.g., the earthquakes are densely concentrated, selected stations are limited in range, the number of stations in- volved in the computation is larger than 5 and linear fitting features high precision and small error. Under these restrictions, the study shows that vP/vS in and around Wen’an and Tangshan underwent a normal-low-normal proc- ess one year before Wen’an earthquake, vP/vS became obviously low and the low ratio lasted for about one year, meanwhile, little variation of vP/vS was seen in Xingtai, northwest of Beijing, southwest of Beijing, Beijing-Tianjin and Beijing; after the quake, the vP/vS returned normal in Wen’an and Tangshan. Error and stability analysis of the calculated result for vP/vS shows it is convincible that anomaly appeared in and around Wen’an and Tangshan be- fore Wen’an earthquake.     

华东地区未来中强震的概率预测

利用概率统计方法 ,对华东地区 1 999～ 2 0 0 5年发生不同震级的地震概率进行预测 ,结果表明 ,该地区仍处于地震活跃时段 ,发生 5级地震的概率不断增加 ,到 2 0 0 0年发生 5级以上地震的平均概率为 0 .5左右 ,但近 1～ 2年内发生 6级以上地震的可能性不大 ,发震概率仅为0 .1 5。     

Application test of matter element analysis in earthquake forecast

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1993年1月北京“震级问题研讨会”述评

1993年1月在北京举行了震级问题研讨会,本文对会议涉及到的我国地震台网测定的大震速报震级,与国际台网测定结果存在系统偏差的问题,从事实、原因、改进方法、消除可能带来的影响以及今后的改进意见等方面,进行了全面评述。     

Research on completeness of earthquake data in the Chinese mainland (II) — The regional distribution of the beginning years of basically complete earthquake data

Based on the concrete conditions of earthquake data in the west of China, East China and South China, we studied the completeness of data in these regions by suitable methods to local conditions. Otherwise, we roughly estimated monitoring capability of local networks in China since 1970 and some outlying regions where the data is lack. Finally, we gave the regional distribution of the beginning years since which the data for different magntiude intervals are largely complete in the Chinese mainland. Contribution No. 94A0050, Institute of Geophysics, SSB, China.     

震级离散下的震级频度关系

运用最大熵原理,研究震级离散条件下震级频度关系,得到震级离散条件下震级概率分布函数,结果表明:(1)震级大于等于某一震级的地震次数应通过离散求和的方式得到,而不应通过积分的方式得到;(2) 震级上限取为∞的情况下,古登堡意义和里克特意义两种震级频度关系式的b值相等;震级上限有限的情况下,里克特意义震级频度关系式可能不是直线.     

1992兰德斯地震震源处应力量值的研究

给出了根据地震前后应力轴偏转、地震应力降和地震前后相对主应力大小,计算震源处应力量值的方法.并将该方法运用于兰德斯地震的霍姆斯特德谷断层段,获得了该子断层10 km深度处震前最大、中间和最小主应力的量值分别为271,266 MPa和259 MPa;震前断层面上的正应力和剪切应力分别为265MPa和6.2 MPa;震后断...     

日本近年来关于地震预测研究的科学计划和科学理念

尽管日本国土面积只占世界陆地的1%,但发生的地震却占全球地震总数的10%左右。尤其是致灾型大地震的发生率很高。为应对这一问题,日本政府自1965年开始推进地震预测研究计划,并经历了多个阶段的计划和修订。近年来,随着信息科学领域的快速发展,日本政府将信息科学引入到了地震科学研究,开展了《利用信息科学的地震研究》计划,旨在促进面向新地震预测科学的创新性研究。目前,日本地震调查本部对地震预测的总体观点“一定程度上可预测板间地震的发生时间,但现有研究仍无法预测未来地震,当前工作的重点是预测未来地震的震动规模”。地震预测的科学研究理念正从原先的“灾害发生的预测”向“灾害发展过程的预测”转变。

     

在2004年12月26日印尼9级地震前收到特大临震信息

2004年12月26日印尼发生9级大地震.震前于2004年12月19日3点22分,中国北京工业大学地震研究所收到声压为16.8Pa的特大次声异常信号.为了预测将发生地震的震级,对比2001年11月14日在中国青海Ms8.1级地震前收到声压为12.88Pa的次声波异常信号.为此做出临震预测:2004年12月19日至28日在全球范围内将发生大于Ms8.1级地震甚至会发生大于Ms8.5级地震.     

河南地区地震目录最小完整性震级探讨

以河南地区(31°-37°N,110°-117°E)1970-2020年11月地震目录作为研究资料,采用G—R关系法、震级—序号法和最大曲率法测定不同时段最小完整性震级Mc.结果 显示,1970-1979年由于研究区内台站数量少,Mc约为ML2.5;1980-2001年为稳定的模拟观测时期,地震监测能力有所提升,Mc约...     

琼中地震台计算震级与中国地震台网中心测算震级差异的探讨

震级是大震速报中最重要的参数之一,震级差异的大小直接影响到资料的使用及台站的速报质量。本文根据琼中地震台近8年的记录资料中260例地震进行精确分析,与中国地震台网中心所发布的地震震级进行对比,对震级差异形成的原因进行探讨,初步得出琼中地震台的震级校正值,有利于提高琼中地震台速报地震震级的准确性。