Historical records suggest that the coastlines of the British Virgin Islands (BVI) and the Sultanate of Oman have been subjected to catastrophic storm and tsunami events throughout recorded history. In 1945, a 7.8 magnitude earthquake -100 km south of Karachi, Pakistan generated a tsunami that impacted the coast of Oman and resulted in over 4000 deaths. Although the 1945 tsunami deposit has been documented, no other paleo-tsunami deposits have been identified despite the fact that historical and paleo-seismic records suggest the contrary. Similarly, the north-eastern islands of the Caribbean, particularly Anegada, BVI, have been subjected to intense hurricane strikes over the past 300 years. Due to its position relative to the Atlantic Ocean and the Puerto Rico Trench, Anegada is a potential recorder of local (e.g. 1690, 1867) and trans-oceanic tsunami events (e.g. 1755 Lisbon) as well. Potential tsunami overwash events at both locations are expected to be intermingled with marine incursions resulting from major storms and Holocene sea level change. Discerning between storm and tsunami overwash is problematic and usually favours a storm interpretation due to their frequency in the geologic record. This bias and lack of properly constrained geologic evidence has hindered the accuracy of tsunami prediction models, and subsequently, the assessment of seismic and tsunami hazards at both locations. Several studies employ the use of foraminifera to distinguish between storm and tsunami deposition; however, they are traditionally conducted in contrasting settings where differences between the terrestrial and marine realms are easily detected. Marine influenced settings lack the same degree of contrast; therefore, microfossil analysis alone is not effective. This dissertation investigates the use of foraminiferal taphonomy as an overwash indicator in two types of coastal settings: 1. a silisiclastic arid system lagoon (Sur, Sultanate of Oman), and 2. semi-tropical carbonate marine ponds (Anegada, British Virgin Islands). Although traditional microfossil taphonomic characteristics have been reported in some overwash studies, no multi-variate investigation into their usefulness as tsunami or storm indicators has previously been conducted. This dissertation shows that the surface condition (e.g. angularity, color, size, fragmentation, etc.) of foraminifera provides important information regarding the origin of overwash deposits and is useful in detecting older deposits at both locations when combined with other proxies. Several important contributions have resulted from this research: 1. Taphofacies analysis helped to constrain sediment provenance and modern nearshore hydrodynamics in an arid system lagoon that could not be achieved with traditional foraminiferal analysis alone. 2. The combined use of foraminiferal provenance and taphonomy was effective in identifying the 1945 Makran Trench tsunami at Sur Lagoon and will be a good indicator of older events at this location; a point which is particularly significant since no geologic evidence of previous tsunami events has ever been recorded. High abundances of predominantly marine taxa coupled with high abundances of large test sizes, fragments and fossil specimens were found to be indicators of tsunami deposition in contrast to lagoon deposition which was characterized by smaller test sizes and less robust lagoon taxa. 3. The preservation of the reefal dwelling Homotrema rubrum, a common encrusting foraminifer in Caribbean reef settings, provided the direction of origin of an overwash event deposited in marine ponds at Anegada and constrained the list of potential overwash candidates. Large and highly preserved Homotrema fragments that are typical of modem reef and storm wrack sediment were found in high abundances within Sand and Shell Sheet in three marine ponds at Anegada. A decrease in the abundance of highly preserved specimens from north to south throughout the ponds, coupled with mollusc taphonomic data strengthens a tsunami interpretation for the deposit. This dissertation shows that taphofacies analysis has broad application to event stratigraphy in a variety of coastal systems. Although the application of taphonomic analysis between the two contrasting environments was widely different, in both cases, taphonomic data provided indicative information regarding the origin of deposition of overwash units at Anegada, BVI and Sur, Sultanate of Oman. / Thesis / Doctor of Philosophy (PhD)

Samples from 13 different sites along the south coast of West Java yield 7 candidate paleo-tsunami sands, which may represent 4 different paleo-tsunami events. Ages obtained from one deposit may document a tsunami and coastal subsidence from an earthquake in 1,053 AD. The tsunami deposit from this event is preserved in an uplifted marine terrace exposed at Panto Cape, Banten Province. We speculated that the terrace has been uplifted about 4.6 m to the present height of 2 m above sea level, since the 1053 AD event at a rate of 4.8 mm/a. This uplift is strong evidence that strain is accumulating at the Java Trench and enough has already accumulated to generate a megathrust earthquake event.Numerical models using ComMIT of possible megathrust earthquake scenarios were constructed using the 2004 Sumatra earthquake, 30-m fault slip, and the 2011 Japan earthquake as proxies. These three scenarios yield earthquakes of Mw 9.3, 9.5 and 8.9, respectively. The worst case scenario is used to estimate the extent of tsunami inundation of the SW coast of Java, which totals 643 km2. The total number of people who inhabit the inundation area is around 451,000. Some coastal configurations cause a no escape situation where the modeled tsunami arrives in less than 20 minutes, which is not enough time for those near the coast to escape far enough inland or to a sufficient elevation to avoid the tsunami. These areas include the coastlines of Sukabumi, Cianjur and west Garut Regencies and the Pameungpeuk area.

Samples from 13 different sites along the south coast of West Java yield 7 candidate paleo-tsunami sands, which may represent 4 different paleo-tsunami events. Ages obtained from one deposit may document a tsunami and coastal subsidence from an earthquake in 1,053 AD. The tsunami deposit from this event is preserved in an uplifted marine terrace exposed at Panto Cape, Banten Province. We speculated that the terrace has been uplifted about 4.6 m to the present height of 2 m above sea level, since the 1053 AD event at a rate of 4.8 mm/a. This uplift is strong evidence that strain is accumulating at the Java Trench and enough has already accumulated to generate a megathrust earthquake event.Numerical models using ComMIT of possible megathrust earthquake scenarios were constructed using the 2004 Sumatra earthquake, 30-m fault slip, and the 2011 Japan earthquake as proxies. These three scenarios yield earthquakes of Mw 9.3, 9.5 and 8.9, respectively. The worst case scenario is used to estimate the extent of tsunami inundation of the SW coast of Java, which totals 643 km2. The total number of people who inhabit the inundation area is around 451,000. Some coastal configurations cause a no escape situation where the modeled tsunami arrives in less than 20 minutes, which is not enough time for those near the coast to escape far enough inland or to a sufficient elevation to avoid the tsunami. These areas include the coastlines of Sukabumi, Cianjur and west Garut Regencies and the Pameungpeuk area.

En tant qu'événement parmi les plus puissants de l'histoire éruptive récente de Lombok, les matériaux volcaniques expulsés par le volcan Samalas en 1257 couvrent toute l'île de Lombok et sont largement répandus dans sa partie est. Près de 800 ans après l'éruption, l'impact géomorphologique de cette éruption sur l'île reste inconnu, alors que ses conséquences climatiques et sociétales globales sont désomais mieux comprises. Une combinaison des informations stratigraphiques, des topographies actuelles, des mesures géophysiques, des sources écrites locales, analyse de laboratoire et informatique ont été utilisées pour obtenir des informations détaillées sur les impacts géomorphologiques de l'éruption du volcan Samalas sur la zone côtière le long du détroit d' Alas, Nusa Tenggara Ouest, Indonésie. Cette étude fournit de nouvelles informations relatives à l'impact géomorphologique d'une éruption volcanique majeure dans des zones côtières, dans ce cas-ci, dans la partie est de Lombok, ainsi que sur la côte ouest de Sumbawa. En premier lieu, les résultats de l'étude montrent que le paysage de la partie est de Lombok est encore évolué jusqu'à présent. Le volume de matière volcanique de l'éruption des Samalas reste à environ 14% du volume initial. Deuxièmement, la découverte de Babad Suwung fournit une description supplémentaire de l'éruption des Samalas sur l'île de Sumbawa et pourraient être la plus ancienne observation visuelle de déferlantes pyroclastiques après celles de Pline Ie Jeune en 79 pour le Vésuve. Enfin, l'éruption du volcan Samalas en 1257 a prouvé avoir déclenché un tsunami mineur qui a frappé l'île de Belang, sur la côte ouest de Sumbawa. / As the most powerful event in Lombok’s recent eruptive history, volcanic materials thatwere expelled by the Samalas volcano in 1257 CE covered the entire of Lombok Islandand are widespread in its eastern part. Almost 800 years after the eruption, the geomorphological impact of this eruption on the island of Lombok remains unknown,whereas its overall climatic and societal consequences are now better understood. Acombination of stratigraphic information, present-day topography, geophysical measurement with two-dimensional resistivity profiling technique, local written sources,as well as laboratory and computational analysis, were used to obtain detailed information concerning geomorphic impacts of the 1257 CE eruption of Samalas volcano on the coastal area along the Alas Strait in West Nusa Tenggara Province, Indonesia. This study provides new information related to the geomorphic impact of amajor eruption volcanic in coastal areas, in this case, on the eastern part of Lombok and the western coast of Sumbawa. In the first place, the study result shows that since the 1257 CE eruption, the landscape on the eastern part of Lombok is still evolved untilthe present time. The volume of the 1257 CE volcanic material remains about 14% from the initial volume. Secondly, the discovery of Babad Suwung provides additional explanation of Samalas eruption and may become the oldest visual observation of pyroclastic surges and volcanic fallout, following those by Pliny the Younger in 79 CE. Finally, the 1257 CE eruption of Samalas volcano has proven triggered a minor tsunami that hit Belang Island, on the west coast of Sumbawa.