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    Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/66811


    Title: 利用人工震源進行地震定位之評估;Evaluation of Earthquake Location Uncertainty in Taiwan : Earthquake Relocation with Explosions by JHD
    Authors: 洪肇謙;Chau-cien,Hong
    Contributors: 地球科學學系
    Keywords: 地震定位;JHD;人工震源
    Date: 2015-01-21
    Issue Date: 2015-03-16 15:35:31 (UTC+8)
    Publisher: 國立中央大學
    Abstract: 地震定位是利用地震發生時,各個地震站所接收到的地震波到時、能量大小等,利用逆推計算式推算出該地震之震源,也就是利用接收到的資料利用地震站之間相對位置去推定未知地震的震源位置。本研究反過來利用人工震源百分之百正確的震源位置,去修正各個地震站所得到的相對地震定位震源結果,以求得更好的資料準確性。
      本研究所用地震資料是由氣象局(CWBSN)自2001年1月到2013年9月間的全台地震站所觀測到的地震資料作為初始定位結果,再加入TAIGER計畫中共10個炸孔資料,使用聯合地震定位(Joint hypocenter determination,JHD),挑選周圍20Km內地震站資料,執行地震定位,和氣象局初始定位結果做比較,得到修正量值和偏移方向5值,為往後研究提供參考。聯合地震定位特色在於做相對地震定位的同時執行地震站修正,以地震站的修正來彌補地震站覆蓋率不足和地層側向變化可能造成的結果誤差,但模型本身可能造成的結果誤差、地震資料的品質差異和定位範圍過大,都可能影響定位結果的品質。
      討論各個區域分別重新定位後的結果,並和初始定位的結果做比較。各個區域的地震群集更加密集,近海區域的初始定位結果皆受到地震站位置影響偏向內陸,重新定位後皆向海域偏移。在相對地震站覆蓋率較大的區域,重新定位結果偏移方向並無一定趨勢,以此可知地震站位置和覆蓋率為主要造成誤差之原因。在北線地震重新定位結果大多偏北;在南線之地震定位結果大多偏南,可能是台灣北部和南部構造差異,一維速度構造模型無法完整呈現,故在重新定位結果上,定位偏移方向有偏北和偏南的差異。在南線由於地震事件較多,可藉由地震事件震源分步看出台灣近地表地層變化:S1到S3、S3P之間可見震源分布越往西越趨向表層,可知表層沉積物向西往中部山區(中央山脈)逐漸減少的趨勢。在S4地震事件則是明顯地分布在中央山脈和海岸山脈,中間條帶狀無地震分部處為花東縱谷區。
      已知炸孔可提供相對地震定位上更好的定位結果,但仍要注意選定區域的範圍大小和地震站的分布位置,若要進行更詳盡的構造討論,需要更精密的速度構造模型執行定位,方能提升定位結果的品質。此次重新定位同時計算定位結果偏移量和偏移角度,為往後研究提供重要參考。
    ;The young Taiwan orogen is situated on the plate boundary between the Eurasian and Philippine sea plates. Owing to the high convergent rate between these two plates, the crustal structure in Taiwan is complicated and three-dimensional. As a consequence, earthquake locations routinely determined by 1D velocity structure from Central Weather Bureau (CWB) is not sufficient for the seismogenic studies. Although several 3D velocity structures have been published and were used for the earthquake relocations, it is great to provide other methods to estimate the uncertainty of the earthquake locations from the routine. In 2008, the TAIGER project has conducted an active source experiment, which provides 10 explosions as known source locations to calibrate the earthquake locations from 1D model. In this study, we use Joint Hypocentral Determination (JHD) with explosions as master events to relocate earthquakes between Jan. 2001 and Sep. 2013 from CWB catalogue to estimate the uncertainties.
    As a result, the earthquake location by 1D model is highly influenced by the 3D crustal structure, which was revealed by the station corrections from JHD. The station corrections in the mountains can be up to -2.3 sec and those in the plain area are around 2.2 sec and the magnitudes of station corrections are slightly different between the northern and southern Taiwan. The horizontal and vertical shifts of earthquake locations are around 1.0~4.9 km and -1.8~0.9 km, respectively. One of the largest shifts among those shot regions is in northwestern Taiwan (N2 shot) with 4.9±1.4 km in horizontal and -1.2±1.4 km in vertical and the shift direction is 306±16.1°. On the other hand, the region with the smallest shift is in southwestern Taiwan (S2 shot) with with 1.0±0.8 km in horizontal and 0.9±1.4 km in vertical and the shift direction is 176±54.5°.
    Appears in Collections:[地球物理研究所] 博碩士論文

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