基于地震学的强地震动衰减关系

Ground motion attenuation relationships based on seismology

世界上大多数国家或地区缺少足够的强地震动观测数据,难以直接用统计方法建立区域强地震动衰减关系.为克服这一瓶颈,本文讨论了在这些地区建立基于地震学的强地震动衰减关系的进展,强调了震源谱中的应力降Δσ、品质因子中的Q0和η以及几何衰减项的两个分段点距离R1和R2等区域性参数取值的重要性,提出了借助区域数字地震监测台网的小地震记录(Mw=3.5~4.5、震源深度≤30 km)联合反演这5个区域参数的思路和方法.将其作为输入,建立区域强地震动衰减关系,用区域强地震动观测数据(Mw≥4.5、震源深度≤30 km)检验,结果表明:在日本东北地区,本文方法建立的衰减关系与强震记录符合很好;在中国四川和云南地区,检验数据相对有限,5、6级的衰减关系与相应的强震数据(4.5≤Mw<5.5、5.5≤Mw<6.5)符合不错,7级的衰减在大于100 km处偏慢.通过3个地区的例子,说明了建立基于地震学强地震动衰减关系方法的适用性.

In most countries or regions of the world, observed strong ground motion data is not enough, which makes it difficult to develop empirical attenuation relations statistically.To overcome this bottleneck, this paper discussed the progresses to build seismology based regional ground motion attenuation relationship there, the importance of estimating the values of regional parameters, stress drop Δσ in source spectrum, Q0 and η in quality factor, and two distances R1 and R2 in geometric attenuation term were emphasized, and the idea and approach to acquire these five values were presented by means of an joint inversion of small earthquake records （Mw=3.5-4.5, focal depth≤30 km） from regional digital monitoring network.Based on these parameters, regional attenuation relations were built and examined by the strong ground motion data （Mw≥4.5, focal depth≤30 km）.The result matches the observed strong ground motion data well for the northeastern region of Japan and it is also good for earthquakes with magnitude 5 and 6 in Sichuan and Yunnan regions of China where there are not enough data for checking, but it is larger than the observed data for earthquakes with magnitude 7 and distance further than 100 km.The feasibility of the proposed method is shown through three cases.