- 學位論文
中央山脈南段地震偵測與分析：利用山區臨時地震偵測網
Monitoring of seismicity using newly deployed, local seismic network in southern Central Range
摘要
中央山脈南段的地震活動由近幾年的研究結果可以發現，該區域不僅是群震頻繁發生的地點，亦在孕震帶更深部( > 20公里)發現有長微震的存在，而這些快、慢地震除了空間相近、其時間的演化也具高度相關。因此這個區域的地震觀測，可能可以解答：不同滑移型態的地震特性為何？其對應到的構造特性是什麼？受什麼物理過程所控制？然而，過去對此區的深部構造和地震物理行為的理解，卻局限於較為稀疏的地震網。 因此，為進一步理解淺部地震活動和深部長微震活動的關係，本研究擬透過利用本研究室與中央大學顏宏元老師、臺灣大學陳勁吾老師一起布設的中央山脈南段臨時地震網（資料時間為2015/12/28至2016/08/18），佐以台灣寬頻地震觀測網(BATS)進行整合地震偵測，期望能建立該區域較為完整的微震目錄，並對其進行時空特徵之分析和討論。利用架設期間的資料，我們以STA/LTA初步篩選可能地震、續以目視確認，一共偵測出4229個地震，其中有648未被由氣象局所記錄。以雙差分地震定位法重新定位後，可發現美濃地震過後，地震數量及地震發生率明顯的增加，且震前震後半年內的地震數量變化指示可能的地震靜止期。在空間上，美濃地震前近主震震源的地震數量稀少且較分散，震後多數餘震發生在中央山脈南段的長微震震源位置上方，並在震後一個月內有明顯向東、北方向遷移的情況，與速度剖面結合能推測地震成因與含水量的多寡有關。此外在地震偵測時亦有發現一明顯的地震空區的存在，推測與此區高熱的板塊擠壓環境有關。而長微震及地震間於研究期間內的相依性低，但在俯視圖上兩者高度重疊分布緊密，且在深度15公里有明顯的分界，兩者不同的孕震構造說明此區控制淺部地殼地震和孕震帶下方長微震的主應力方向並不同。
並列摘要
Southern Central Range of Taiwan is a place not only hosting earthquake swarm in shallow depth but also tectonic tremors in the deeper crust. Both phenomena are closely located in space and often correlated in time, which provides a rare opportunity towards the understanding of physical mechanisms governing different styles of slip. The better detection of small earthquakes in this area may help us answer the questions below: what is the deep fault structures in this area? what is the spatio-temporal association between tremors and earthquakes in this area? and what is the different characteristics of different faulting styles (fast slip events at shallow vs. slow slip events at deeper part)? However, there are only few seismic stations in this mountain area, limiting our understanding of regional seismotectonics. By cooperating with Prof. Horng-Yuan Yen in NCU and prof. Chin-Wu Chen in NTU, we deployed 6 new seismic stations on the top the tremor source during the study period of 2015/12/28 to 2016/08/18. Combining with BATS operated by Academia Sinica, STA/LTA method was applied with manually check to identify earthquakes. Out of 4229 events, 648 events are not included in the CWB earthquake catalog. We find that after ML 6.4 Meinong earthquake, the occurrence rate of daily earthquakes increases dramatically from 9.4 to 19.4. Until the end of the study period, the seismicity rate hasn’t been back to the pre-Meinong event level. The double-difference locations reveal that before the mainshock, the earthquakes near the mainshock are sparse distributed. The aftershock concentrated however, not only near the source zone but also propagated to southern Central Range where the tectonic tremors are distributed at the greater depth. An aseismic zone was also found in the study area, coinciding with high-temperature and dry environment. Although the tremors and mainshock are closely located, the correlation between the mainshock and tremors is found to be low using static Coulomb stress change model.
參考文獻
延伸閱讀
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