甘肃地区地震烈度影响场评价及其与地形因子的关系

Evaluation of Seismic Intensity Influence Field in Gansu Province and its Relationship with Terrain Factors

摘要:

地震发生后，根据地震参数快速设计和显示出地震影响场，初步确定较为合理的地震烈度分布范围，对于政府及时了解灾情和损失分布非常重要。收集、整理甘肃地区实际地震等震线图，将其与现有地震烈度衰减关系生成的理论烈度图进行统计对比分析，并与研究区DEM（数字高程模型）相结合，研究地形因子对烈度影响场分布的影响。结论表明：不同震级档之间，实际与理论地震烈度分布之间规律不同；分区研究发现，除极震区外，祁连山—河西走廊地区外圈等震线理论长短轴以及面积均大于实际，甘东南地区规律则与之相反。地形因子对烈度影响场的影响是明显的，海拔越高，烈度越高；山顶点处烈度高于周围地区；相对震中而言，坡度大的地方烈度衰减快，反之则烈度衰减慢。

Abstract:

The Gansu earthquake emergency command system was founded during the Tenth Five-year Plan by the Earthquake Administration of Gansu province.It was reviewed and accepted by the China Earthquake Administration and was enacted in 2007.With this system，we can first obtain the seismic intensity distribution and influence region according to the local intensity attenuation relationship and then quickly estimate earthquake casualty loss according to the seismic intensity distribution.We can then propose emergency measures and rescue plans and assist in decision-making for earthquake relief headquarters.Damage degrees of construction and lifeline engineering，including water supply， power supply，heat supply，air supply，transportation，and communication systems，differ among affected areas.Moreover，secondary disaster influences also differ，as well as casualties and financial loss.The seismic influence field examines the influence areas by different damage intensities.After an earthquake，designing and presentation of the influence field according to the earthquake parameters and formulating a relatively reasonable seismic intensity distribution range is very important for government investigation of the situation and damage distribution.The feasibility of the earthquake influence field will directly affect the rationality and accuracy of the assessment results.The calculation results of the existing evaluation system differ significantly from the actual results；therefore，the influence of the relief results also differs.The attenuation relationship model makes use of the large scale nationwide western attenuation relationship，the Gansu attenuation relationship of seismic intensity，and modified seismic intensity affecting the field model of the Gansu area in the Gansu earthquake emergency command technology system module to make fast judgment of the seismic influence field and heavy disaster area.However，differences occur in the actual attenuation relationship among areas and magnitudes due to different source characteristics，propagation media，and site conditions.In this paper，isoseismal line maps of actual earthquakes in the Gansu region were collected and compared with theoretical intensity generated by the attenuation relationship.In addition，the influence of terrain factors on the intensity influence field in study area was analyzed by using the digital elevation model（DEM）.Conclusions show that the actual and theoretical seismic intensity distribution at each magnitude level differed. In general，the theoretical epicentral area is relatively small at the 5.0~5.2 level and shows subarea characteristics at the 5.3~5.9 level，whereas the theoretical intensity distribution is close to actual results at the 6.8~7.5 level.The subarea study shows that the outer major and minor axes and area of theoretical seismic influence field are greater than those of the actual values in the Qilian Mountains-Hexi Corridor region.However，except for the meizoseismal area，performance in the southeast region of Gansu is opposite.The impact of terrain factors on the intensity influence field is obvious.Higher altitude relates to higher intensity，and the intensity at the summit point is higher than that in the surrounding region.A greater slope to the epicenter relates to faster attenuation of the intensity and vice versa.There are obvious differences between actual and theoretical seismic influence fields，which should be considered in practical application.We should adjust the distribution of theoretical intensity by considering local terrain，landform，and site type to obtain a more reliable post earthquake assessment outcome.Furthermore, quantification of the site influence would better serve earthquake emergency response and rescue.