| dc.description.abstract | 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. | en_US |