苏鲁交界及南黄海地区地震波速比的变化特征

VARIATION CHARACTERISTICS OF SEISMIC V_P/V_S RATIO AT JIANGSU-SHANDONG BORDER AND SOUTH YELLOW SEA REGION

本文主要应用多台波速比和单台波速比的方法,计算了苏鲁交界及南黄海(北纬33°30′至36°00′,东经117°00′至121°00′)范围内,1984至1991年7月发生在该区域的163次M_L>1.7地震的波速比值,并对波速比结果进行t检验和模糊数学分析识别。分析结果发现,1985年1月至11月出现了不连续的波速比低值异常时段,模糊数学识别的异常从属函数在这段时间也呈现高值。异常恢复后,1987年2月17日发生了射阳M_S5.1地震。初步认为1985年的波速比低值异常与射阳5.1级地震有关。单台波速比1984—1991年7月变化正常,在射阳5.1级地震前变化不明显。

This paper mainly computed the VP / Vsratio value of 163 earthquakes with M≥1.7 occurred in the range og Jiangsu-Shandong border and South Yellow Sea (33 ?33 '-36?00' N, 117?00' -121 ?00' E) from 1984 to July 1991 using methods of multistation VP / Vs ratio and single station VP / Vs ratio.The author also carried out t examination and fuzzy mathematics analysis and recognization on the VP / Vs results. It is found from the analytical results that there apeared an abnormal time interval with discontinuous low VP/ Vs ratio value from January to November, 1985 and the anomalous subordinate function recognized by the fuzzy mathematics also showed a high value during this time interval. After the anomaly recovery, an earthquake with Ms of 5.1 occurred in Sheyang on 17 February, 1987. The author considered preliminarily that the anomaly of low VP/ Vs ratio value in 1985 is related to the Sheyang earthquake of Ms = 5.1. The monthly variation of single-station VP/ Vs ratio from 1984 to July 1991 were normal, and the Variations were not obvious before Sheyang earthquake with Ms of 5.1.