Research on the Characteristics and Site Influencing Factors of Strong Ground Motion in the Minxian-Zhangxian Earthquake
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摘要: 岷漳地震强地震动加速度峰值较小,然而震害却相对严重,局部黄土场地震害及地震动放大效应显著。基于岷漳地震强地震动记录,开展幅值、频谱和持时三要素特征分析,探讨震中距、场地类别、土层条件等对地震动特征参数的影响规律,从地震动特征角度分析此次地震震害相对较重的原因及对震害的潜在影响。结果表明:(1)Ⅲ类场地与Ⅰ类场地相比,峰值加速度放大2.1~4.6倍,持时延长10~43 s,反应谱在周期0.18~0.86 s时,谱值较大;(2)黄土场地与非黄土场地相比,峰值加速度及峰值速度分别放大1.5~3.7倍和1.55~1.8倍,持时延长8~35 s,反应谱在周期大于0.32 s时,谱值明显较大,存在显著的黄土场地地震动放大效应;(3)设计地震分组为第二组的Ⅱ类黄土场地,加速度反应谱的平均曲线、拟合曲线在周期0.8~3.0 s时与规范设计谱的谱值差大于20%。Abstract: The field investigations of the Minxian-Zhangxian Earthquake (MZE) indicated that amplification effects of site conditions and topography on ground motion were very obvious in loess regions. There is a common question why the small peak ground acceleration (PGA) cause relatively serious damage of loess area in MZE. Based on the strong motion records of the MZE, this paper analyzes the amplitude, spectrum and duration characteristics of ground motion, discusses the influence of propagation distance and site conditions on the characteristic parameters of ground motion. From the perspective of ground motion characteristics, the reasons for the relatively heavy earthquake damage and the potential impact on the earthquake damage are analyzed. The results show that: (1)Compared with Class I site, the PGA of Class III site is increased by 2.1~4.6 times, the duration is prolonged by 10~43 s, and the response spectrum value is larger in the period of 0.18~0.86s. (2) Compared with non-loess site, the PGA of loess site is increased by 1.5~3.7 times, the peak ground velocity of loess site is increased by 1.55~1.8 times, the duration is prolonged by 8~35 s, and the response spectrum value is obviously larger when the period is greater than 0.32s. There is a significant loess site ground motion amplification effect. (3) The pseudo-acceleration spectrum of design earthquake-2nd group and site-class II significantly larger than Chinese design spectra in period 0.8~0.3 s.
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表 1 强地震记录按震中距和场地条件分组统计表
Table 1. Statistics of strong motion records grouped in terms of epicentral distance and site condition
组别 震中距 场地类型 场地类别 台站个数 记录条数 1 近场 基岩 Ⅰ 1 3 2 近场 土层 — — — 3 中远场 基岩 Ⅰ 2 6 4 中远场 土层 (Ⅱ) 6(4) 18(12) 5 远场 基岩 Ⅰ 3 9 6 远场 土层 (Ⅱ/Ⅲ) 51(20/3) 153(60/9) 注:括号外的数量代表各组别对应的台站个数或记录条数;括号中的数量代表Ⅱ类/Ⅲ类场地对应的台站个数或记录条数。 表 2 典型台站的地震记录相关参数
Table 2. Parameters of seismic records at typical stations
序号 台站名称 台站编号 震中距/km 场地类别 合成PGA/(cm·s−2) 合成PGV/(cm·s−1) 合成PGV/合成PGA 卓越周期/s 特征周期/s 1 青川桥楼 51 QCQ 235.97 Ⅰ类 4.76 0.44 0.09 0.16 0.36 2 长安台 61 CHA 435.66 Ⅰ类 1.83 0.25 0.14 0.28 0.61 3 汤峪台 61 TAY 342.85 Ⅰ类 2.76 0.50 0.18 0.61 0.79 4 临潭 62 LTA 76.22 Ⅰ类 8.36 0.78 0.09 0.32 0.34 5 五竹镇 62 WZZ 52.18 Ⅰ类 17.71 1.94 0.11 0.20 0.68 6 舟曲 62 ZHQ 33.72 Ⅰ类 18.30 1.43 0.08 0.25 0.29 7 安县地办 51 AXD 327.76 Ⅱ类 2.83 0.55 0.19 0.87 0.70 8 广元曾家 51 GYZ 278.22 Ⅱ类 14.18 0.89 0.06 0.19 0.21 9 江油专业 51 JYT 308.52 Ⅱ类 4.22 0.65 0.15 0.47 0.60 10 九寨勿角 51 JZW 171.43 Ⅱ类 8.96 0.67 0.08 0.21 0.33 11 九寨永丰 51 JZY 149.40 Ⅱ类 17.86 1.36 0.08 0.19 0.26 12 九寨章扎 51 JZZ 141.06 Ⅱ类 15.20 1.06 0.07 0.12 0.26 13 理县木卡 51 LXK 338.07 Ⅱ类 2.38 0.13 0.05 0.33 0.25 14 平武木座 51 PWM 217.75 Ⅱ类 12.21 0.65 0.05 0.25 0.21 15 高陵台 61 GAL 448.48 Ⅱ类 4.84 0.85 0.18 0.53 0.75 16 华阴台 61 HUY 539.86 Ⅱ类 2.18 0.48 0.22 0.98 0.92 17 蓝田台 61 LAT 469.25 Ⅱ类 4.88 0.65 0.13 0.65 0.69 18 八松 62 BAS 106.42 Ⅱ类 9.61 1.06 0.11 0.17 0.57 19 皋兰 62 GLA 197.80 Ⅱ类 13.31 1.62 0.12 0.34 0.54 20 观象台 62 GXT 200.98 Ⅱ类 6.25 0.60 0.10 0.20 0.45 21 金崖 62 JIA 162.83 Ⅱ类 9.48 0.64 0.07 0.25 0.25 22 康乐 62 KLE 106.44 Ⅱ类 8.09 1.58 0.20 0.10 0.80 23 刘家堡 62 LJB 179.62 Ⅱ类 10.42 1.29 0.12 0.18 0.51 24 平安 62 PAN 202.37 Ⅱ类 11.84 0.68 0.06 0.35 0.31 25 沙湾 62 SHW 97.28 Ⅱ类 14.56 0.89 0.06 0.07 0.26 26 宕昌 62 TCH 62.63 Ⅱ类 95.64 4.64 0.05 0.13 0.19 27 天水 62 TSH 155.16 Ⅱ类 34.50 1.98 0.06 0.14 0.26 28 冶力关 62 YLG 69.26 Ⅱ类 43.82 1.79 0.04 0.13 0.17 29 卓尼 62 ZNI 65.32 Ⅱ类 6.67 0.10 0.01 0.08 0.07 30 中铺 62 ZPU 147.63 Ⅱ类 8.00 0.78 0.10 0.22 0.36 31 草滩台 61 CAT 439.92 Ⅲ类 3.95 0.63 0.16 0.20 0.63 32 吝店台 61 LID 494.02 Ⅲ类 3.61 0.52 0.14 0.60 0.69 33 和平 62 HEP 163.63 Ⅲ类 17.58 1.67 0.10 0.21 0.47 表 3 由拟合式算出的不同类型场地峰值加速度
Table 3. PGA for various site types computed from fitted formula
场地类型 峰值加速度/(cm·s−2) 50 km 100 km 200 km 300 km 400 km 基岩/Ⅰ类场地 14.13 7.94 4.22 2.95 2.29 土层场地 47.52(3.4) 21.67(2.7) 10.07(2.4) 6.39(2.2) 4.63(2.0) Ⅱ类场地 37.41(2.7) 18.20(2.3) 8.85(2.1) 5.81(2.0) 4.31(1.9) Ⅲ类场地 — 36.31(4.6) 13.18(3.1) 7.30(2.5) 4.79(2.1) 注:括号内数值表示针对基岩场地(Ⅰ类场地)峰值加速度的放大系数。 表 4 由拟合式算出的黄土与非黄土场地峰值加速度
Table 4. The peak acceleration of loess and non-loess sites computed from fitting formula
场地类型 峰值加速度/(cm·s−2) 50 km 100 km 200 km 300 km 400 km 南向非黄土 93.33 23.99 6.17 2.79 1.59 北向黄土 59.70(0.6) 23.44(1.0) 9.21(1.5) — — 东向黄土 — 89.13(3.7) 21.98(3.6) 9.68(3.5) 5.42(3.4) 注:括号内数值表示针对非黄土场地峰值加速度的放大倍数。 表 5 峰值速度与峰值加速度的比值
Table 5. The ratio of PGV to PGA
场地类型 峰值速度与峰值加速度的比值/(cm·s−1·g−1) ≤50 km 50~100 km >100 km 基岩 77 100 133 黄土 — 29 130 非黄土 — 51 84 注:PGV单位为cm·s−1,PGA单位为g,两者比值的单位为/(cm·s−1·g−1)。 表 6 统计谱拟合曲线的特征值
Table 6. The characteristic values of pseudo-acceleration spectrum
设计地震分组 台站数/个 Tg/s βmax γ Ⅱ类-第二组 15 0.42 2.04 0.70 Ⅱ类-第三组 9 0.49 2.08 0.63 Ⅱ类-第二组黄土场地 5 0.45 1.88 0.43 Ⅱ类-第三组黄土场地 8 0.51 2.09 0.63 表 7 基岩场地相对持时及能量持时的平均值(单位:秒)
Table 7. The average value of the relative duration and energy duration of the soil site(Unit: s)
震中距/km Td(≥Amax/2) Td(≥Amax/3) Td(5%~95%) Td(5%~75%) NS EW UD NS EW UD NS EW UD NS EW UD 50~100 40.19 43.16 43.17 43.14 43.22 43.32 20.94 23.88 23.32 9.13 12.59 13.18 >100 69.01 69.05 69.01 69.02 69.05 69.05 29.59 39.77 36.85 14.83 25.82 22.16 表 8 不同类别场地相对持时及能量持时的平均值(单位:秒)
Table 8. The average value of the relative duration and energy duration of the different sites(Unit: s)
场地类别 台站个数 Td(≥Amax/2) Td(≥Amax/3) Td(5%~95%) Td(5%~75%) NS EW UD NS EW UD NS EW UD NS EW UD Ⅰ类 3 69.01 69.05 69.01 69.02 69.05 69.05 29.59 39.77 36.85 14.83 25.82 22.16 Ⅱ类 20 69.81 68.90 70.76 72.55 71.70 72.53 37.47 36.05 45.26 21.65 20.50 28.44 Ⅲ类 3 111.52 111.88 112.04 112.03 112.15 112.38 58.87 62.57 82.02 35.40 35.69 60.05 表 9 黄土场地与非黄土场地相对持时及能量持时的平均值(单位:秒)
Table 9. The average value of the relative duration and energy duration of loess and non-loess sites(Unit: s)
震中距/km 土层条件 台站个数 Td(≥Amax/2) Td(≥Amax/3) Td(5%~95%) Td(5%~75%) NS EW UD NS EW UD NS EW UD NS EW UD 100~300 非黄土 6 63.44 62.95 64.81 64.65 64.85 65.57 33.24 32.95 36.94 20.63 21.04 23.97 黄土 8 67.62 67.27 68.26 72.92 70.75 72.03 36.96 37.16 44.19 21.82 21.33 26.43 >300 非黄土 3 59.68 54.38 60.11 60.06 59.73 60.35 29.52 20.81 32.53 15.89 7.41 19.05 黄土 3 98.51 99.69 99.95 99.87 99.88 99.97 55.24 54.55 77.52 28.97 30.27 52.11 -
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