A Note on the Correlation Between B-Value and Fractal Dimension from Synthetic Seismicity

由合成地震活動研究b值和碎形度之相關性

王錦華(Jeen-Hwa Wang)

《Terrestrial, Atmospheric and Oceanic Sciences》 2卷4期 (1991/12) Pp. 317-329

摘要

1986年5月20日花蓮地震之後數日間餘震頻繁，其中伴隨地鳴而至的地震為數甚多。王正松和溫國樑先生於24～25日間做了連續約24小時的錄音，其間發生規模大於2.0的餘震25次。經分析處理後證實其中至少有五個地震伴隨地鳴到達。本文比較這五個地鳴與對應地震的P波到達時間，並分析這些地鳴之頻譜。我們發現地鳴到達測站之時間超前地震記錄的初達P波0.2～1.1秒不等，其主頻率約在25～100 Hz之間。經過震源參數的分析比較，我們發現伴隨地鳴之地震的共同特徵是規模較大、震源較淺、至測站間之距離較近。地鳴主頻率並有隨震源深度增加而降低的趨勢，這可能與高頻波在地層中的衰減比低頻波快有關。據此推測在震源破裂過程中可能有較高頻率之地震波在一般地震儀可記錄之較低頻波產生之前即已在震源區產生。這項結果顯示，在目前使用之地震儀的頻率接收範圍之外，仍有許多與地震有關的訊息，這些訊息所代表的意義有待進一步的研究。

並列摘要

A 24-hour continuous sound recording was made after the 1986 May 20 earthquake.During the 24 hour period,25 aftershocks with a magnitude greater than 2were recorded by a temporary seismographic network.Comparing the seismogramswith the recorded sounds,we found that 5 of these aftershocks were accompaniedby earthquake sounds,and all of these sounds preceded the P-wave arrivals by 0.2to 1.1 seconds.These 5 aftershocks possessed common characteristics of greatermagnitude,shallower focus,and being closer to the recording site than other aftershocks.The predominant frequencies of the earthquake sounds ranged from 25 to100 Hz.These predominant frequencies were relatively lower when the focus wasdeeper.Based on these discoveries,we infer that,before the main faulting which resulted in the earthquakes,there were associated cracks that sent out acoustic waveswith frequencies higher than those detected by the seismographs.