ABSTRACT

We present attenuation relations for peak ground velocity (PGV) and acceleration (PGA) for northeastern Mexico, where seismic activity has been underestimated over the years. We tested four models derived from a parametrical form previously proposed for intraplate earthquakes in Central Mexico but using regional data recorded by the Mexican National Seismological Service (Servicio Sismológico Nacional de Mexico, SSN). For comparison and as a selection criteria, we used the decaying trend of the models, the ratio between the observed and the predicted data (logarithmic) as a function of the distance and its standard deviation, and we determined the following attenuation relations: $logPGV=-4.36+0.8Mw-0.00015R-0.97log\left(R\right)-0.0041H+{\sigma }_A+{\sigma }_E$ $logPGA=0.31+0.23Mw+0.0011R-1.48log\left(R\right)-0.0022H+{\sigma }_A+{\sigma }_E$

Where M_W is the moment magnitude, R the hypocentral distance, and H the focal depth (both in km). ${\sigma }_A$ and ${\sigma }_E$ correspond to the intra-event and inter-event standard deviations. For PGV ${\sigma }_{A}and{\sigma }_E\hspace{0.17em}$ are 0.18 and 0.004, while for PGA ${\sigma }_A$ and ${\sigma }_E$ are 0.25 and 0.30, respectively. We found that by using the original distance definition R, (dependent on the hypocentral distance and on the magnitude altogether), the results are basically the same as when using the hypocentral distance directly. We also tried to incorporate an independent variable to characterize the local soil conditions of the recording stations. Despite the fact of finding a good residual behavior with that incorporation, the empirical functions of acceleration (PGA) stopped decaying around 250 km, implying a physical impasse and making the models inadequate for greater distances, situation that did not occur with velocities (PGV). The obtained constants found for the local site conditions on both PGA and PGV were similar between stations, showing no strong impact on the site effects on the predictive equations. The proposed models fulfill the purposes of having small residual fitting and simple attenuation relations that depend only on magnitude, hypocentral distance and focal depth, making them practical and easy to apply for engineering or seismic risk assessment purposes with the available data from local or regional networks.

摘要

我们展示了墨西哥东北部峰值地面速度 ( PGV ) 和加速度 ( PGA ) 的衰减关系，多年来那里的地震活动一直被低估。我们测试了四种模型，这些模型源自先前针对墨西哥中部板内地震提出的参数形式，但使用了墨西哥国家地震局 ( Servicio Sismológico Nacional de Mexico, SSN ) 记录的区域数据。为了比较和作为选择标准，我们使用模型的衰减趋势，观察数据和预测数据之间的比率（对数）作为距离及其标准差的函数，我们确定了以下衰减关系：$日志PGV=-4.36+0.8米w-0.00015R-0.97日志\left(R\right)-0.0041H+{\sigma }_{\mathrm{一种}}+{\sigma }_{乙}$ $日志PG\mathrm{一种}=0.31+0.23米w+0.0011R-1.48日志\left(R\right)-0.0022H+{\sigma }_{\mathrm{一种}}+{\sigma }_{乙}$

其中M _W是矩量级，R是震源距离，H是焦深（均以 km 为单位）。${\sigma }_{\mathrm{一种}}$和${\sigma }_{乙}$对应于事件内和事件间的标准偏差。对于PGV ${\sigma }_{\mathrm{一种}}\mathrm{一种}nd{\sigma }_{乙}\hspace{0.17em}$分别为 0.18 和 0.004，而对于PGA ${\sigma }_{\mathrm{一种}}$和${\sigma }_{乙}$分别为 0.25 和 0.30。我们发现，通过使用原始距离定义R，（取决于震源距离和震级），结果与直接使用震源距离时基本相同。我们还尝试加入一个自变量来描述记录站的当地土壤条件。尽管通过该合并发现了良好的剩余行为，但加速度的经验函数 ( PGA ) 在 250 公里左右停止衰减，这意味着物理僵局并使模型不适用于更远的距离，速度 ( PGV )不会出现这种情况. 在PGA和站点之间的PG​​V相似，表明站点对预测方程的影响没有很大影响。所提出的模型实现了具有小残差拟合和仅取决于震级、震源距离和焦深的简单衰减关系的目的，使它们实用且易于应用来自本地或区域网络的可用数据的工程或地震风险评估目的.