This study conducted experimental tests on the undisturbed Nanjing Yangtze River floodplain soft soil using the bender element instrument to determine the maximum dynamic shear modulus of the Yangtze River floodplain overconsolidated soft soil. The Gmax of floodplain soft soil with different overconsolidated ratio OCR, initial effective confining pressure σ3c′, and void ratio e are discussed. The results indicated that Gmax reduced as e rose for given σ3c′ and OCR. In addition, an increase in OCR contributed to a gradual decrease in the decay rate of Gmax, while the Gmax decay rate is insensitive to the change of σ3c′. The void ratio-normalized maximum shear modulus Gmax/F(e) improved with the increase in the stress-normalized initial effective confining pressure σ3c′/Pa, whereas the growth rate gradually drops, and a power relationship is then obtained between Gmax/F(e) and σ3c′/Pa. Based on the regression analysis, a Gmax prediction method is established for reasonably characterizing Yangtze River floodplain soft soils with various over-consolidation states, initial stress conditions, and compactness levels, with a prediction error of less than 10%.
Tunnels crossing inactive faults may suffer from severe damage during earthquakes. Fault sites have a significant hanging wall effect during earthquakes, but this effect on the tunnel seismic response has not been specifically quantified. In this study, shaking table tests were conducted to investigate the fault site effect and seismic response of fault-crossing tunnels. The hanging wall effect is the results of the geometric effect due to the asymmetric distribution of inclined fault. This geometric effect will lead to the reflection of seismic waves between the ground surface and fault interface and exacerbating the acceleration of the hanging wall. The acceleration of the tunnel located in the hanging wall is significantly greater than that located in the footwall, which is not only attributed to the dynamic characteristic of the site, but also the interaction between the dynamic characteristics of different areas of the site. For the tunnel sections located in the hanging wall, the influence range of the fault is approximately twice the tunnel diameter, for those located in the footwall, the fault has limited effect.
2016年8月至2016年10月唐山余震区小震活动增强,尤其是8月21日至9月22日期间,其中9月10日发生震级最大地震为唐山开平ML4.7地震.为了解中强地震发震特征及地震序列变化,基于模板匹配定位识别技术,利用2016年8月1日至2016年10月31日连续波形进行唐山开平地震前后微震检测和定位.从研究区域内中国地震台网目录中选择283个地震事件作为模板事件,基于连续波形共检测识别出878个地震事件,其数量约为模板事件的3倍,约为中国地震台网目录的1.4倍,检测后的地震目录完备震级由原来的ML0.2提升至ML-0.1.利用双差定位方法对847个地震事件进行重定位,结果显示震中附近小震活动频繁,且在唐山开平地震震中周边分布较集中.分析震群分布特征认为唐山开平地震属于唐山老震区正常地震活动,发震断层为唐山-古冶断裂的可能性较大.
2022年9月5日12时52分四川甘孜州泸定县发生Ms6.8地震,造成重大人员伤亡和财产损失.本文利用此次地震中距离发震断层80 km以内获得的92个三分量加速度记录,研究此次地震近断层地震动峰值加速度(PGA)、峰值速度(PGV)和不同周期加速度反应谱(Sa)的空间分布与衰减特征,探讨了近断层地震动的脉冲特征及其对地震动反应谱的影响.研究结果表明:(1)此次地震近断层地震动表现出随观测方向变化的较强极性特征,其中51LDJ记录的南北分量约达到东西分量的3倍,这主要受地震的走滑破裂特征影响.(2)近场地震动强度的空间分布主要受此次地震发震断层的走向控制,峰值加速度、速度和加速度反应谱值的分布与断层走向特点一致.较强的观测值多位于烈度Ⅶ度以上的区域,与震害分布相符,地震动强度分布从一定程度决定了震害分布.(3)从实际观测结果与地震动经验模型的对比来看,经验模型对本次地震PGA和0.2 s的短周期地震动有较好的预测;对于PGV和周期0.5 s以上的地震动反应谱,本文考察的6个经验模型均有不同程度的高估.(4)本次泸定地震有2条典型脉冲记录,均位于距离发震断层15km以内,脉冲记录波形具有明显的双向脉冲特征,记录的PGV分别达到56.0cm/s和37.0cm/s.速度脉冲在其脉冲特征周期附近,对加速度反应谱有显著放大作用.受此影响,距离断层最近的T2471台站记录的东西向和南北向反应谱在周期0.6～1.5 s范围均显著高于Ⅷ度罕遇地震设计谱.此外,局部地形对地震动短周期成分有重要影响,T2471记录东西向反应谱在0.1～0.2 s,也远远超过了 Ⅷ度罕遇地震设计谱.
2023年2月6日土耳其发生2次Ms7.8地震,造成了严重的人员伤亡和经济损失,土耳其1999年建立的地震保险体系在本次地震中一定程度上达到了减轻地震灾害损失的目的.本文首先对土耳其地震保险制度体系进行介绍,并结合本次地震受灾地区建筑物震害数据和当地投保信息,深入分析了土耳其地震保险在分散地震风险中发挥的重要作用;最后针对我国地震保险现状及存在的问题提出建议.
