abstract: Shallow earthquakes in the upper part of the overriding plate of subduction zones can be devastating due to their proximity to population centers despite the smaller rupture extents than commonly occur on subduction megathrusts that produce the largest earthquakes. Damaging effects can be greater in volcanic arcs like Java because ground shaking is amplified by surficial deposits of uncompacted volcaniclastic sediments. Identifying the upper-plate structures and their potential hazards is key for minimizing the dangers they pose. In particular, the knowledge of the regional stress field and deformation pattern in this region will help us to better understand how subduction and collision affects deformation in this part of the overriding plate. The majority of the upper plate deformation studies have been focused on the deformation in the main thrusts of the fore-arc region. Study of deformation within volcanic arc is limited despite the associated earthquake hazards. In this study, I use maps of active upper-plate structures, earthquake moment tensor data and stress orientation deduced from volcano morphology analysis to characterize the strain field of Java arc. In addition, I use sandbox analog modeling to evaluate the mechanical factors that may be important in controlling deformation. My field- and remotely-based mapping of active faults and folds, supplemented by results from my paleoseismic studies and physical models of the system, suggest that Java’s deformation is distributed over broad areas along small-scale structures. Java is segmented into three main zones based on their distinctive structural patterns and stress orientation. East Java is characterized by NW-SE normal and strike-slip faults, Central Java has E-W folds and thrust faults, and NE-SW strike-slip faults dominate West Java. The sandbox analog models indicate that the strain in response to collision is partitioned into thrusting and strike-slip faulting, with the dominance of margin-normal thrust faulting. My models test the effects of convergence obliquity, geometry, preexisting weaknesses, asperities, and lateral strength contrast. The result suggest that slight variations in convergence obliquity do not affect the deformation pattern significantly, while the margin shape, lateral strength contrast, and perturbation of deformation from asperities each have a greater impact on deformation. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

東部インドネシアには，太平洋プレートとオーストラリアプレートの相対運動に起因する大規模な左横ずれ断層帯が発達する．この断層帯の地震地質学的な情報は限られており，地震災害軽減の大きな障壁となっていた．本研究では，スラウェシ島やバンダ弧の島々において，変動地形調査・古地震調査・物理探査を行った．各調査地域で詳細な活断層分布図を作成し，断層の変位速度や平均活動間隔，最近の大地震の時期を明らかにした．その結果，将来起こりうる地震の規模が推定され，また近い将来に地震が発生する可能性の高い地域が見いだされた． / In eastern Indonesia, the relative motion between the Pacific and Australian plates is accommodated by a large left-lateral strike-slip fault system. The lack of geologic information on the fault system has been a significant barrier to understanding the seismic hazard posed by this fault system. This study integrates tectonic geomorphic, paleoseismic, and shallow geophysics investigations to uncover the faulting and seismic behavior of the fault system, focusing on central Sulawesi and the northern Banda Arc. This study provides detailed active fault map of each investigated area and clarifies slip rates, average recurrence interval, and timing of the recent large earthquakes. This study also estimates the seismic potential of the active faults and highlights the areas with a high possibility of hosting large earthquakes in the future. / 博士(理学) / Doctor of Philosophy in Science / 同志社大学 / Doshisha University