当涂地震站震级偏差分析

Analysis of magnitude deviation at Dangtu Seismic Station

选取当涂地震站2015年12月至2020年4月记录的120个1.2<ML<5.3近震(均为浅源地震),其中省外地震震级为ML≥2.0。重新计算单台震级ML台,与安徽省测震台网中心所测地方性震级ML省进行对比,得出二者的震级偏差,分析在不同震中距和台站方位角范围内震级偏差的分布规律。结果如下:①按震中距分析,可知:Δ<70 km,M_(L)台偏小。70 km≤Δ<180 km,单台震级大部分偏小,在反射波临界范围内,部分地震震级偏差较小,多在±0.2内摆动,偏差可忽略。Δ≥180 km,震级普遍偏大;②按台站方位角分析,结果如下:方位角≤66°,震级偏差多大于0,震中大部分位于郯庐断裂带以东;方位角大于66°,震级偏差多小于0,大部分地震位于郯庐断裂带以西和长江以北。综合分析认为:量规函数、反射波、断裂带和震源机制均会对震级偏差产生影响,且震级偏差大小能在一定程度上反映地质结构差异。

One hundred and twenty 1.2<M_(L)<5.3 near earthquakes recorded at Dangtu Seismic Station from December 2015 to April 2020 are selected(all of them are shallow earthquakes).Among them,the magnitude of earthquakes in other provinces is M_(L)≥2.0.The single station ML magnitude is recalculated for each event.The magnitude deviations from that measured by the Anhui Seismological Network Center are calculated and their distribution with epicenter distance(Δ)and azimuth are analyzed.The following results are obtained:①WhenΔ≤70 km,the recalculated single station ML magnitude is smaller;②When 70 km<Δ<180 km,most of the recalculated single station M_(L)magnitude is smaller;the magnitude deviation for some earthquakes within the critical range of reflected waves is within±0.2,which is negligible;③WhenΔ≥180 km,most of the recalculated single station ML magnitude is larger.The distribution of magnitude deviation with azimuth has the following characteristics:when the azimuth is smaller than 66°,the magnitude deviation is mostly greater than 0,the earthquakes are located to the east of the Tanlu fault zone.When the azimuth is larger than 66°,the magnitude deviation is mostly less than 0,most of the earthquakes are located to the west of the Tanlu fault zone and north of the Yangtze River.Based on the analysis of the magnitude deviation with respect to epicenter distance and azimuth angle,it is concluded that the magnitude deviation is affected by calibration function,reflected wave,fault zone,and focal mechanism.The difference of magnitude deviation can reflect the difference of geological structure to some extent.