Bachelor's thesis. / Format: PDF. Bibl.

Master's thesis. / Format: PDF. Bibl.

Several laterally extensive candidate tsunami deposits are preserved along coastlines facing the eastern Java Trench, indicating it has experienced mega-thrust earthquakes in the past. We investigated 37 coastal sites in Bali, Lombok, Sumba and Timor islands, many of which preserve course sand and pebble layers that overlie sharp basal contacts with scour marks into the mud, fine upward in grain size, and have bimodal grain size distributions. Other unique features are the common occurrence of marine fossils and concentrations of heavy minerals. The occurrence of these high-energy deposits interlayered with clay-rich units indicates the coarse clastics are anomalous because they were deposited in what is normally a very low-energy depositional environment. The lateral extent and paucity of thin, coarse clastic layers with marine organisms are inconsistent with local stream flood event, and the proximity to the equator of the sites diminishes the possibility of marine flood events from cyclones. The sparse, but consistent, the occurrence of at least two candidate tsunami deposits at depths of 1 and 2 meters over 950 km along the strike of the Java Trench may reveal that mega-thrust earthquakes have occurred there and generated giant tsunamis in the recent past. Five widely scattered imbricated boulder deposits are also found on Bali, Lombok, and Sumba. The boulders consist of slabs of hardpan up to 2.5 m in length and 80 cm thick that was torn from a near-shore seabed and stacked on top of one another. Some of the boulders were carried over the erosional coastal bank and deposited up to 100 meters inland. Comparisons with imbricated boulder ridges formed during the 1994 tsunami in east Java indicate that these deposits are from one or multiple tsunamis sourced by the Java Trench. Experiments in effective ways to communicate and implement tsunami disaster mitigation strategies have led us to train local communities about the 20-20-20 rule. If coastal communities experience more than 20 seconds of shaking from an earthquake, even if it is not intense, they should evacuate the coast. The time delay between the earthquake and arrival of tsunami waves is around 20 minutes, which is the time window for evacuation. Some tsunami waves may be as high as 20 meters, which is the target elevation for evacuation. Adopting the 20-20-20 rule could save thousands of lives throughout the region, especially in Bali where nearly 1 million people inhabit likely tsunami inundation zones.

京都大学 / 新制・課程博士 / 博士(地球環境学) / 甲第24064号 / 地環博第227号 / 新制||地環||43(附属図書館) / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)准教授 西川 完途, 教授 瀬戸口 浩彰, 教授 本川 雅治 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DGAM

Doctoral dissertation. / Format: PDF. Bibl.

Campaign GPS measurements during 2001-2003 in the transition between subduction and collision of the Banda arc reveal how strain is partitioned away from the trench and distributed to other parts of the arc-trench system. Genrich, et. al. (1996) conducted a GPS campaign (1992-1994) throughout the Eastern Sunda and Banda arcs that demonstrated partial accretion of the arc to the Australian plate. We reoccupied many of the sites from this earlier study and 7 additional stations, 3 of which are new benchmarks. Our study shortened many baselines and extended the observation epoch to ten years for many key stations. The resulting GPS velocity field for the active Banda arc-continent collision reveals: 1) several mostly rigid crustal blocks exist in the transition from subduction to collision, 2) relative to an Asian reference frame, most of these blocks move in the same direction as the Australian lower plate, but at different rates, 3) block boundaries may exist between the islands of Lombok and Komodo, Flores and Sumba, Savu and West Timor, and between Timor and Darwin, 4) the Timor Trough may account for at least 20 mm/yr of motion between Timor and Darwin, 5) a major transverse fault off the coast of West Timor separates the Savu/Flores/Sumba block from the Timor/Wetar Block and may account for variations in movement in Rote, 6) the Flores thrust moves the eastern Sunda arc north relative to Asia by decreasing amounts to the west, 7) the back-arc Wetar Thrust system takes up the majority of plate convergence between Australia and Asia, and 8) fault boundaries are not found between many blocks, such as various islands of the Sunda arc and forearc with different amounts of motion.

Our paleotsunami surveys of the southern Java coast led to the discovery of five imbricate coastal boulder fields near Pacitan, Indonesia that may date to the mid-to-late 19th century or prior and two similar fields at Pantai Papuma and Pantai Pasir Putih that were tsunami-emplaced during the 1994 7.9 Mw event in East Java. Estimated ages for the fields near Pacitan are based on historical records and radiocarbon analyses of coral boulders. The largest imbricated boulders in fields near Pacitan and in East Java are similar in size (approximately 3 m^3) and are primarily composed of platy beachrock dislodged from the intertidal platform during one or several unusually powerful wave impactions. Hydrodynamic wave height reconstructions of the accumulations near Pacitan indicate the boulders were likely tsunami rather than storm-wave emplaced, as the size of the storm waves needed to do so is not viable. We evaluate the boulders as an inverse problem, using their reconstructed wave heights and ComMIT tsunami modeling to suggest a minimum 8.4 Mw earthquake necessary to dislodge and emplace the largest boulders near Pacitan assuming they were all deposited during the same tsunami event and that the rupture source was located along the Java Trench south of Pacitan. A combined analysis of historical records of Java earthquakes and plate motion measurements indicates a seismic gap with >25 m of slip deficit along the Java Trench. A 1000-1500 km rupture along the subduction interface of this segment is capable of producing a 9.0-9.3 Mw megathrust earthquake and a giant tsunami. However, evidence for past megathrust earthquake events along the this trench remains elusive. We use epicenter independent tsunami modelling to estimate wave heights and inundation along East Java in the event that the trench were to fully rupture. By translocating ComMIT slip parameters of Japan's 2011 9.1 Mw event along the trench offshore East Java, we demonstrate possible wave heights in excess of 20 m at various locations along its southern coasts. Approximately 300,000-500,000 people in low-lying coastal communities on the southern coasts of East Java could be directly affected. We recommend at-risk communities practice the "20/20/20 principle" of tsunami hazard awareness and evacuation.

The focus of this work is magma-crust interaction processes and associated crustal volatile release in subduction zone volcanoes, drawing on rock, mineral, and gas geochemistry as well as experimental petrology. Understanding the multitude of differentiation processes that modify an original magma during ascent to the surface is vital to unravel the contributions of the various sources that contribute to the final magmas erupted at volcanoes. In particular, magma-crust interaction (MCI) processes have been investigated at a variety of scales, from a local scale in the Vesuvius, Merapi, and Kelut studies, to a regional scale, in the Java to Bali segment of the Sunda Arc.  The role of crustal influences is still not well constrained in subduction systems, particulary in terms of the compositional impact of direct magma crust interplay. To address this shortcoming, we studied marble and calc-silicate (skarn) xenoliths, and used high resolution short timescale experimental petrology at Vesuvius volcano. The marbles and calc-silicates help to identify different mechanisms of magma-carbonate and magma-xenolith interaction, and the subsequent effects of volatile release on potential eruptive behaviour, while sequential short-duration experiments simulate the actual processes of carbonate assimilation employing natural materials and controlled magmatic conditions. The experiments highlight the efficiency of carbonate assimilation and associated carbonate-derived CO2 liberated over short timescales. The findings at Merapi and Kelut demonstrate a complex magmatic plumbing system underneath these volcanoes with magma residing at different depths, spanning from the mantle-crust boundary to the upper crust. The erupted products and volcanic gas emissions enable us to shed light on MCI-processes and associated volatile release in these systems. The knowledge gained from studying individual volcanoes (e.g., Merapi and Kelut) is then tested on a regional scale and applied to the entire Java and Bali arc segment. An attempt is presented to distinguish the extent of source versus crustal influences and establish a quantitative model of late stage crustal influence in this arc segment. This thesis therefore hopes to contribute to our knowledge of magma genesis and magma-crust interaction (MCI) processes that likely operate in subduction zone systems worldwide.

This project is a diplomatic transcription and English translation of a passage from an 18-century manuscript that chronicles a remarkable Portuguese embassy to China (Macau). The embassy embarked from Lisbon in February 1752, sailing in a luxuriously outfitted ship (Nossa Senhora da Conceição e Lusitânia Grande), in convoy with a warship (Nossa Senhora das Brotas). The English translation is important because it makes the account accessible to scholars who lack familiarity with Portuguese.This voyage to China is remarkable in light of the long history of maritime loss by the Portuguese. Although the normal projected loss of life on this route was 20%, this journey was made without one death. Some of the most fascinating aspects of the journey include the following: a) how the intrepid crew of the Nossa Senhora (most of whom were novices) and the passengers dealt with bad weather at sea; b) the religious rites conducted during the voyage by Jesuit priests en route to the Far East missions, which the passengers firmly believed mitigated the dangers and were thus responsible for their safe journey; c) the intriguing political maneuvering between the Portuguese and Chinese in Macau; and d) the meticulous descriptions of the different cultures, peoples and places encountered on the journey.