基于汶川主震及余震的预警参数与震级相关性研究

Research on correlation between early-warning parameters and magnitude for the Wenchuan Earthquake and its aftershocks

地震预警作为一种能够有效减轻地震灾害的手段已经被世界上越来越多的国家和地区所研究,并在实际应用中取得了显著的减灾实效.利用汶川主震及其余震P波和S波初期部分的信息,研究了最终地震震级与4个预警参数的相关性.考察的4个参数是位移幅值(Pd)、速度平方积分(IV2)、P波卓越周期和特征周期(τp和τc).使用的数据集时间跨度从2008年5月12日至2008年10月4日,共计218次震级大于等于4级的地震事件,包括主震8.0、最大余震6.5和7次大于等于6.0级的事件.Pd、IV2和τc在震级小于等于6.5级时与最终震级具有较好的相关性,没有出现震级饱和现象,验证了前人的统计结果.但是在估算主震震级时,都存在不同程度的低估现象,IV2参数尤其明显.另外,Pd和IV2统计曲线在M6级附近存在着一个斜率变化,并且Pd结果与前人统计结果相差较大.τp的统计结果表明该参数不适合应用到汶川地区的地震预警系统中.

As one of the effective ways to mitigate earthquake hazards, earthquake early warning （EEW） has been studied by many countries and regions in the world. They have achieved significant mitigation practical effectiveness during operations. We studied the correlation between the final event magnitude and four early-warning parameters obtained from the early portion of P and S phases for the Wenchuan mainshock and its aftershocks. The investigated parameters are the peak displacement （Pa）, the integral of the velocity squared （IV2）, and the predominant and characteristic periods （rp and r0）. The used dataset spans from 12 May 2008 to 4 October 2008 and includes 218 events with magnitude greater than or equal to 4, including the main event （MS. 0）, the largest aftershock of M6.5, and 7 events with magnitude greater than 6. Pd, IV2 and rc are well correlated with the final magnitude and no saturation effect is observed when magnitudes are less than or equal to 6. 5, confirming previous results. However, when estimating the mainshock, these parameters have different degrees of underestimated phenomenon, especially IV2 parameter. In addition , there are slope changes in the Pa and IV2regression curves around M6, and Pa result is quite different from the previous results, rp result shows that this parameter is not suitable for the EEW system in the Wenchuan area.