2023年甘肃白银平川区4.9级地震强地面运动特征分析

Strong ground motion characteristics of the M4.9 earthquake in Baiyin Pingchuan District, Gansu Province in 2023

摘要:

中国地震预警台网在甘肃白银平川区4.9级地震中获得197组三分向地面运动加速度记录，其中仅100km范围内的就有165组，这是海原断裂带附近首次获得大量近断层强震动观测记录。本文从近场台站观测的加速度反应谱与设计谱比较、不同周期地震动与预测模型对比、地震动的空间分布方面分析了本次地震的强地面运动特征。研究结果表明：近场6个土层台的水平向谱加速度在卓越周期处大于8度多遇地震设计谱值，其中GS.D003E台EW向反应谱在峰值处甚至超过8度设防地震的设计谱值，但由于其卓越周期低于当地城乡普通建筑的自振周期，因此对附近采取了抗震措施的建筑的破坏程度较小。土层台观测的PGA、PGV、SA(0.2s)、SA(0.5s)等短周期地震动普遍大于地震动预测值，而SA(1.0s)、SA(2.0s)的中等周期地震动观测值与预测值较符合，说明本次地震的高频成分的地震动比较卓越的特点。通过对土层台和基岩台地震动衰减规律，以及土层/基岩谱比结果表明土层场地对地震动有明显的放大作用。PGA、SA(0.2s)和SA(0.5s)等短周期地震动的影响场除沿断层走向方向上的幅值较大外，在垂直于断层走向的震中西南侧的幅值也较大。而SA(1.0s)、SA(2.0s)和SA(3.0s)等中等周期的地震动在垂直于断层走向的震中西南侧幅值较大的特点更加明显，可能与震源的破裂特性及观测台站所处地区局部场地对地震动的影响有关。

Abstract:

The China Earthquake Early Warning Network obtained 197 sets of three-component ground motion acceleration records during the 4.9 magnitude earthquake in Pingchuan District, Baiyin, Gansu, among which there were 165 sets within a 100km range. This is the first time a large number of near-fault strong-motion observation records have been obtained near the Haiyuan fault zone. We investigate the characteristics of strong ground motion in terms of response spectrum, attenuation relationship and spatial distribution of ground motion. The results indicate that: the horizontal acceleration response spectrum of the 6 stations built in the soil site is greater than the design spectrum value of 8 degrees frequent earthquakes at the excellent period,and the response spectrum of GS.D003E in the EW direction even exceeds the design spectrum value of 8 degrees earthquake protection at the excellent period. However, because its excellence period is lower than the natural vibration period of local urban and rural buildings, the damage degree of nearby buildings with seismic measures is small.The observed value of PGA, PGV, SA(0.2s) and SA(0.5s) are generally greater than the predicted ground motion values, while the observed value of SA(1.0s) and SA(2.0s) are consistent with the predicted values, which indicates that the ground motion of the high frequency component of the earthquake is excellent.The attenuation relationships of ground motion at soil and bedrock stations, and the results of soil/bedrock spectrum ratio show that the soil site has an obvious amplification effect on ground motion compared with the bedrock site.The amplitudes of PGA, SA(0.2s) and SA(0.5s) are both larger along the fault strike and on the southwest side of the epicenter. However, the larger amplitude of SA(1.0s), SA(2.0s) and SA(3.0s) is more obvious only on the southwest side perpendicular to the fault strike.This phenomenon may be related to the rupture characteristics of the source and the site of the observation station in the loess hilly area.