山西断陷带太原—临汾部分的强地震平均复发间隔与未来危险段落研究

AVERAGE RECURRENCE INTERVALS OF STRONG EARTHQUAKES AND POTENTIAL RISKY SEGMENTS ALONG THE TAIYUAN-LINFEN PORTION OF THE SHANXI GRABEN SYSTEM

130 3年山西洪洞M8大地震距今已 70 0年 .为了分析长期地震危险性 ,本文将山西断陷带太原—临汾部分划分为 5个震源段 ,根据历史地震和GPS观测资料 ,估算出各段的平均地震矩率与强地震平均复发间隔 ,进而根据最近 30多年的台网地震资料计算获得的b值图象 ,分析不同段落现今应力积累的相对水平 .主要结果表明 :临汾盆地段的平均地震矩率为2 .2 1× 10 16 ～ 3.0 3× 10 16 N·m/a ,M7.5地震的平均复发间隔估值为 15 6 0～ 2 14 0a .灵石—洪洞段M8地震的平均复发间隔估值在 4 30 0～ 5 10 0a之间 ,相当于平均矩率为 2 .5 8× 10 16 ～ 3.10× 10 16 N·m/a .b值图象显示灵石—洪洞段与临汾盆地段现今处于低或较低的应力水平 ,可能反映自 130 3年M8和 16 95年M7.5大地震破裂后 ,这两段的断面强度至今仍未恢复 .候马段和介休—汾阳段具有相对较高的应力水平 ,并结合平均复发间隔估值 ,判定这两个段落可能是未来强震的潜在危险段 .

Since the great 1303 Hongtong,Shanxi,earthquake of magnitude 8,700 years have elapsed. To analyze the long-term seismic potential,this paper divides the Taiyuan-Linfen portion of the Shanxi graben system into 5 seismogenic segments. Based on data of historical earthquakes and GPS observation,the authors estimate mean seismic-moment rates and average recurrence intervals of strong earthquakes for the individual segments,and further analyze relative levels of current stress cumulation on the segments based on mapping b -values along the graben system by using the network seismic data for the recent over 30 years. The main result shows that the Linfen basin segment has an estimated mean seismic-moment rate of 2.21×10 16 ～3.03×10 16 N·m/a,and its average recurrence interval for M =7.5 earthquake is estimated to be between 1 560 and 2 140 years. For the Lingshi-Hongtong segment,the estimated average recurrence interval for M =8 earthquakes is between 4 300 and 5 100 years,equivalent to having a mean moment-rate of 2.58×10 16 ～3.10×10 16 N·m/a. The contour map of b -values shows that the two segments of Lingshi-Hongtong and Linfen basin have been being at low or relatively low stress levels,reflecting that since the 1303 M =8 and the 1695 M =7.5 earthquake ruptures,the fault-plane′s strengths of the both segments have not been resumed yet. And the other two segments,the Houma and the Jiexiu-Fenyang,have relatively high stress levels,and have been already identified as potential risky segments for the coming earthquakes from the analysis combining with the estimated average recurrence intervals of earthquakes on the both segments.