| 摘要: | 印度尼西亞爪哇島是全球地震活躍度最高的地區之一，經常發生具破壞性和災害性的地震。而中深層地震（深度約60到300公里）已被證實具有很大的破壞性。然而，儘管已知其可能造成的地震災害，在爪哇島南部，對於中深層地震破壞行為的了解仍然甚少。此外，具第二大破壞性災害的地震就發生在此區域，為2006年5月27日地震矩規模6.4的爪哇地震，僅次於2004年位於蘇門答臘的大型逆衝地震。爪哇地震發生於淺層地殼，被稱為是印度尼西亞最具致命性的地震。在本篇論文中，我們的研究主要針對位於爪哇島地區及其鄰近區域的中深層地震和發生於2006年5月27日地震矩規模6.4的淺層地殼地震。
本研究使用有限斷層逆推，探討於1998年到2017年在爪哇島南部及其鄰近地區，5個地震矩規模大於6.1的中層地震(深度60至300公里)，其破裂過程和震源特徵。利用遠震體波和表面波，進行小波域震波逆推。首先，利用GCMT (Global Centroid Moment Tensor)資料庫決定最佳的斷層面方向作為初步反演的震源機制解（走向和傾角），以用於分析滑移分佈和震源時間函數（source time functions, STFs）。我們的研究結果顯示，除了1998年的地震以外，大多數地震都表現出較簡單的破裂過程，具有單一且集中的滑移區，以及簡單的三角形震源時間函數。結果指出，除了發生在2014年的地震以外，地震破裂方向主要為沿著傾角方向向下。我們更使用了方向性證實此破裂行為。有三起的地震事件顯示破裂面傾向於近垂直（傾角向下）方向，而有兩起地震事件則表現出近水平方向（傾角向下和圓形）的傾向。考慮到不易證實破裂面與隱沒板塊有關，我們期望藉由密集部署於爪哇島的地震觀測網，將有助於我們深入了解隱沒帶動力學。
我們也對於2006年5月27日，發生於爪哇島南部地震矩規模6.4的左移走向滑移地震，進行了有限斷層逆推。同樣從GCMT決定最佳斷層面方向，作為初步反演的震源機制解（走向和傾角）。結果顯示，東北-西南走向西傾的斷層破裂面逆推結果較好，因為其與Tsuji et al. (2009) 重新定位的餘震分布和干涉合成孔徑雷達 (InSAR) 圖像的結果更一致。震源時間函數顯示了共21秒複雜的地震破裂過程。滑移量分布顯示了三個主要滑移區及非平滑的破裂過程，即破裂是由初始破裂點(震源)沿斷層傾角向上。為增強對地震危害的準備，本研究中，討論了四個地震動預估式 (ground-motion prediction equations, GMPEs)，用來預測地震的地震動，並以PGA表示。視覺上比較顯示，BSSA14 地震動預測模型是最合適的模型，因為此模型比其他三個模型更符合觀察。更進一步分析對地震破裂模式與其所造成的地震災害間的關係，有助於對地震災害的評估，特別是在人口密集的印度尼西亞爪哇島。;Java (Indonesia) is one of the most seismically active regions in the world, often hosting in several destructive and damaging earthquakes. The intermediate-depth earthquakes (~60 to 300 km depth) have been shown to be destructive, however, the rupture behavior of these earthquakes in southern Java remains poorly understood despite their potential seismic hazard. In addition, the second largest destructive disaster after the 2004 Sumatra-like megathrust earthquake also occurred in this region, namely the 27 May 2006 Mw 6.4 Java earthquake. This earthquake was the shallow crustal event which was claimed as the deadliest earthquake in the country. In this thesis, my study mainly focuses on the intermediate-depth earthquakes and the 27 May 2006 Mw 6.4 shallow crustal earthquake in the Java region and its surrounding areas.
Finite-fault inversions were performed to investigate the rupture processes and source characteristics of five intermediate-depth earthquakes (60 to 300 km depth) with moment magnitudes (Mw) ≥ 6.1 from 1998 to 2017 in the southern region of Java and its surrounding areas. A wavelet-based seismic inversion technique was employed using teleseismic body waves and surface waves. Initially, preliminary inversions of the focal mechanisms (strike and dip) were conducted using the Global Centroid Moment Tensor (GCMT) database to determine the optimal fault plane orientation for slip distributions and source time functions (STFs). Our findings reveal that most of the earthquakes exhibited a simple rupture process characterized by a single and compact asperity with a single triangular STF, except for the 1998 earthquake. The results indicate that the ruptures primarily propagated unilaterally along the down-dip direction, except for the 2014 earthquake. Further analysis using directivity confirmed the rupture behavior. The preferred rupture planes for the three events were near-vertical (down-dip), while two events exhibited subhorizontal orientations (down-dip and circular). Considering the challenges in determining the rupture plane associated with the subducting slab, the densely deployed national seismic networks in Java are expected to provide valuable insights into the dynamics of the subduction zone.
Finite-fault inversion was also performed on the 27 May 2006 Mw 6.4 left lateral strike-slip earthquake, a moderate shallow crustal earthquake that occurred in southern Java. Preliminary inversions of the focal mechanism (strike and dip) from the GCMT were also conducted to obtain the optimal fault plane orientation. The results show that the southwest-northeast trending west-dipping fault is our preferred rupture plane as it is more consistent with the relocated aftershock distribution and the InSAR image of Tsuji et al. (2009). The STF shows a complicated moment release history, with a total rupture duration of about 21 s. The slip distribution exhibits complex slip patches with three major asperities and rough propagation, dominantly propagated up-dip from the initial rupture break (hypocenter). To improve seismic risk preparation, four candidate ground-motion prediction equations (GMPEs) were discussed in this study to predict ground motion of the earthquake in terms of peak ground acceleration (PGA). The visual comparison revealed that the BSSA14 ground-motion prediction model shows a better fit than the other three models, indicating the most appropriate ground-motion model among the candidates. The rupture pattern in the relationship to the resulted damage was further analyzed to have a better understanding of further seismic hazard assessment, especially for populated region in Java Island, Indonesia. |
