An earthquake-triggered submarine mass failure mechanism for the 1994 Mindoro tsunami in the Philippines : Constraints from numerical modeling and submarine geomorphology

Tsunamis have been known to result from a wide range of phenomena, such as earthquakes, volcanic eruptions, submarine mass failures, and meteorite impacts. Of earthquake-generated tsunamis, those arising from strike-slip mechanisms are less common, with the 1994 Mindoro tsunami in the Philippines among the few known examples. The 1994 Mindoro tsunami followed a Mw 7.1 earthquake along the right-lateral Aglubang River Fault. The tsunami affected the coasts surrounding the Verde Island Passage, one of the Philippines’ insular seas located between the islands of Luzon and Mindoro, and east of the West Philippine Sea margin. A total of 78 lives were lost due to the earthquake and tsunami, with 41 being directly attributed to the tsunami alone. Despite the close spatial and temporal association between the 1994 Mindoro earthquake and tsunami, previous numerical modeling suggests the need for other contributing mechanisms for the 1994 tsunami. In this study, we conducted submarine geomorphological mapping of the South Pass within the Verde Island Passage, with particular focus on identifying possible submarine mass failures. Identification of submarine features were based on Red Relief Image Map (RIMM), Topographic Position Index (topographic position index)-based landform classification, and profile and plan curvatures derived from high-resolution bathymetry data. Among the important submarine features mapped include the San Andres submarine mass failure (SASMF). The San Andres submarine mass failure has an estimated volume of 0.0483 km3 and is located within the Malaylay Submarine Canyon System in the Verde Island Passage, ∼1 km offshore of San Andres in Baco, Oriental Mindoro. We also explored two tsunami models (EQ-only and EQ+SMF) for the 1994 Mindoro tsunami using JAGURS. The source mechanisms for both models included an earthquake component based on the Mw 7.1 earthquake, while the EQ+SMF also included an additional submarine mass failure component based on the mapped San Andres submarine mass failure. Modeled wave heights from the EQ-only model drastically underestimates the observed wave heights for the 1994 Mindoro tsunami. In contrast, the EQ+SMF model tsunami wave height estimates were closer to the observed data. As such, we propose an earthquake-triggered, submarine mass failure source mechanism for the 1994 Mindoro tsunami

Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex (Philippines) : A review

New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age. Radiometric dating of its plutonic and volcanic-hypabyssal rocks yielded middle Eocene ages. On the other hand, the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge – island arc affiliated Coto block of the ophiolite complex, together with isotopic age datings of its dikes and mafic cumulate rocks, also yielded Eocene ages. This offers the possibility that the Zambales Ophiolite Complex could have: (1) evolved from a Mesozoic arc (Acoje block) that split to form a Cenozoic back-arc basin (Coto block), (2) through faulting, structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or (3) through the interplay of slab rollback, slab break-off and, at a later time, collision with a microcontinent fragment, caused the formation of an island arc-related ophiolite block (Acoje) that migrated trench-ward resulting into the generation of a back-arc basin (Coto block) with a limited subduction signature. This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation

フィリピン共和国マニラ海溝とフィリピン海溝沿いに分布する完新世海成段丘のテクトニックな解釈

京都大学0048新制・課程博士博士(理学)甲第15882号理博第3623号新制||理||1527(附属図書館)28461京都大学大学院理学研究科地球惑星科学専攻(主査)准教授 堤 浩之, 教授 竹村 惠二, 教授 飯尾 能久学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDA

GIS-based spatial analysis of sinkholes in Cebu City, Philippines: Insights on sinkhole genesis and development

In 2017, at least 770 sinkholes were reported to occur in Cebu City, a populated town in the Philippines dominantly underlain by karstic formations. In this study, the genesis and development of these sinkholes were related to various geomorphologic, geologic, and hydrologic factors in order to determine their influence on sinkhole distribution in the area using GIS-based spatial analyses. Results show that the sinkhole frequency varies with respect to the relative age of the underlying karstic formation, slope, and elevation. Most sinkholes occur on younger bedrock, low slope, and low elevation areas. However, sinkholes that occur on younger bedrock are significantly smaller in area than those in older bedrock; in terms of total area, the sum of the areas of sinkholes are greater on relatively older bedrock. Other factors found to influence sinkhole occurrence were lineaments and streams. GIS-based analyses of sinkholes such as those presented in this study are useful for sinkhole susceptibility prediction and disaster risk reduction management efforts of communities

Occurrence of 1 ka-old corals on an uplifted reef terrace in west Luzon, Philippines: Implications for a prehistoric extreme wave event in the South China Sea region

Abstract Recent 230Th dating of fossil corals in west Luzon has provided new insights on the emergence of late Quaternary marine terraces that fringe west Luzon Island facing the Manila Trench. Apart from regional sea level changes, accumulated uplift from aseismic and seismic processes may have influenced the emergence of sea level indicators such as coral terraces and notches. Varied elevations of middle-to-late Holocene coral terraces along the west Luzon coasts reveal the differential uplift that is probably associated with the movement of local onland faults or upper-plate structures across the Manila Trench forearc basin. In Badoc Island, offshore west of Luzon mainland, we found notably young fossil corals, dated at 945.1 ± 4.6 years BP and 903.1 ± 3.9 years BP, on top of a ~5-m-high reef platform. To constrain the mechanism of emergence or emplacement of these fossil corals, we use field geomorphic data and wave inundation models to constrain an extreme wave event that affected west Luzon about 1000 years ago. Our preliminary tectonic and tsunami models show that a megathrust rupture will likely lead to subsidence of a large part of the west Luzon coast, while permanent coastal uplift is attributed to an offshore upper-plate rupture in the northern Manila Trench forearc region. The modeled source fault ruptures and tsunami lead to a maximum wave height of more than 3 m and inundation distance as far as 2 km along the coasts of western and northern Luzon. While emplacement of coral boulders by an unusually strong typhoon is also likely, modeled storm surge heights along west Luzon do not exceed 2 m even with Typhoon Haiyan characteristics. Whether tsunami or unusually strong typhoon, the occurrence of a prehistoric extreme wave event in west Luzon remains an important issue in future studies of coastal hazards in the South China Sea region

DataSheet1_An earthquake-triggered submarine mass failure mechanism for the 1994 Mindoro tsunami in the Philippines: Constraints from numerical modeling and submarine geomorphology.docx

Tsunamis have been known to result from a wide range of phenomena, such as earthquakes, volcanic eruptions, submarine mass failures, and meteorite impacts. Of earthquake-generated tsunamis, those arising from strike-slip mechanisms are less common, with the 1994 Mindoro tsunami in the Philippines among the few known examples. The 1994 Mindoro tsunami followed a Mw 7.1 earthquake along the right-lateral Aglubang River Fault. The tsunami affected the coasts surrounding the Verde Island Passage, one of the Philippines’ insular seas located between the islands of Luzon and Mindoro, and east of the West Philippine Sea margin. A total of 78 lives were lost due to the earthquake and tsunami, with 41 being directly attributed to the tsunami alone. Despite the close spatial and temporal association between the 1994 Mindoro earthquake and tsunami, previous numerical modeling suggests the need for other contributing mechanisms for the 1994 tsunami. In this study, we conducted submarine geomorphological mapping of the South Pass within the Verde Island Passage, with particular focus on identifying possible submarine mass failures. Identification of submarine features were based on Red Relief Image Map (RIMM), Topographic Position Index (topographic position index)-based landform classification, and profile and plan curvatures derived from high-resolution bathymetry data. Among the important submarine features mapped include the San Andres submarine mass failure (SASMF). The San Andres submarine mass failure has an estimated volume of 0.0483 km3 and is located within the Malaylay Submarine Canyon System in the Verde Island Passage, ∼1 km offshore of San Andres in Baco, Oriental Mindoro. We also explored two tsunami models (EQ-only and EQ+SMF) for the 1994 Mindoro tsunami using JAGURS. The source mechanisms for both models included an earthquake component based on the Mw 7.1 earthquake, while the EQ+SMF also included an additional submarine mass failure component based on the mapped San Andres submarine mass failure. Modeled wave heights from the EQ-only model drastically underestimates the observed wave heights for the 1994 Mindoro tsunami. In contrast, the EQ+SMF model tsunami wave height estimates were closer to the observed data. As such, we propose an earthquake-triggered, submarine mass failure source mechanism for the 1994 Mindoro tsunami.</p

Slab rollback and microcontinent subduction in the evolution of the Zambales Ophiolite Complex (Philippines): A review

New radiolarian ages show that the island arc-related Acoje block of the Zambales Ophiolite Complex is possibly of Late Jurassic to Early Cretaceous age. Radiometric dating of its plutonic and volcanic-hypabyssal rocks yielded middle Eocene ages. On the other hand, the paleontological dating of the sedimentary carapace of the transitional mid-ocean ridge – island arc affiliated Coto block of the ophiolite complex, together with isotopic age datings of its dikes and mafic cumulate rocks, also yielded Eocene ages. This offers the possibility that the Zambales Ophiolite Complex could have: (1) evolved from a Mesozoic arc (Acoje block) that split to form a Cenozoic back-arc basin (Coto block), (2) through faulting, structurally juxtaposed a Mesozoic oceanic crust with a younger Cenozoic lithospheric fragment or (3) through the interplay of slab rollback, slab break-off and, at a later time, collision with a microcontinent fragment, caused the formation of an island arc-related ophiolite block (Acoje) that migrated trench-ward resulting into the generation of a back-arc basin (Coto block) with a limited subduction signature. This Meso-Cenozoic ophiolite complex is compared with the other oceanic lithosphere fragments along the western seaboard of the Philippines in the context of their evolution in terms of their recognized environments of generation