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The Banda Arc in eastern Indonesia has a complex tectonic history involving oceanic and continental subduction, arc‐continent collision and slab rollback. Among these the subduction rollback that began at 16 Ma shaped the regional tectonic configuration, causing notable upper plate extension evidenced by the Banda Sea and Weber Deep. However, the effects of subduction rollback on the lower plate remain less understood. The Aru Trough, part of subducting Australian continental margin, shows strong deformation and high seismicity, making it ideal for studying these effects. Utilizing multibeam bathymetry, seismic reflection profiles, GPS observations, seismicity and focal mechanisms, we investigate the crustal deformation, driving mechanisms and seismic risks in the Aru Trough under the background of Banda slab rollback. The Aru Trough shaped like an inverted triangle narrows from 160 to 40 km southward. It has a fast 53.8 mm/yr extensional rate at present, when combined with its maximum width suggesting a 3 Ma age. High‐angle faults (>60°) are present at its margins and interior. The trough has a high density of seismicity up to 5.9 events per 25 km2, with dominant normal and strike‐slip events, consistent with observed deformational patterns. The low seismic b‐value of 0.82 ± 0.01 suggests a high‐stress state with potential for strong earthquakes (Mw ≥ 6.5). Our findings indicate that lower plate deformation is profoundly influenced by subduction rollback, oblique arc‐continent collision and regional strike‐slip faulting. Understanding deformation in the Aru Trough is crucial for grasping the broader tectonic evolution of the Banda Arc and assessing seismic risks. Key Points: The Aru Trough is deformed by extension as evidenced by high‐angle normal faults and fast present‐day extensional rate of 53.8 mm/yrThe Aru Trough was initiated by slab rollback at 3 Ma with subsequent evolution affected by arc‐continent collision and strike‐slip faultingSeismicity in the Aru Trough shows a high density and low seismic b‐value, indicating high stress and a potential for strong earthquakes [ABSTRACT FROM AUTHOR]

The seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude M ≥ 4.6 and focal mechanisms for earthquakes of magnitude M ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude M ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths <70 km and 70% having magnitudes M < 5.0. Approximately 88 earthquakes of magnitude M ≥ 5.0 occur per year, with 12 events of magnitude M ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths >70 km trace the Wadati‐Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths >70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike‐slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia. Plain Language Summary: The Philippines‐Taiwan region is tectonically active with frequent earthquakes. We summarize the geographical distribution, sources, and frequency of earthquakes in the region over 21 years, compare distributions to proposed tectonic models, and investigate earthquake hazards. This region experiences on average 88 earthquakes per year of magnitudes ≥5.0. Twelve events of magnitudes ≥7.0 occurred between January 2000 and March 2021. Most earthquake activity is shallow and occurs at depths ≤70 km. In some regions, such as Southern Mindanao in the Philippines, seismicity extends to depths >600 km. Shallow earthquakes are generated by various faulting sources, and seismic hazards are abundant and seismic risk is high, as several population centers are located near active faults. Key Points: We summarize seismotectonics of the Philippines‐Taiwan region using hypocenters, focal mechanisms, seafloor age, and tectonic modelsShallow seismicity is abundant, consisting of thrust, strike‐slip, and normal faulting, which all pose serious seismic hazardsSubduction zone seismicity occurs at depths ∼100–250 km for young (20–40 Ma) oceanic lithosphere, and up to 680 km for older (60–80 Ma) [ABSTRACT FROM AUTHOR]

We present an overview of tsunami occurrences based on an analysis of a global database of tsunamis for the period 1900–2020. We evaluate the geographic and statistical distribution of various tsunami source mechanisms, high-fatality tsunamis, maximum water heights (MWHs) of tsunamis, and possible biases in the observation and recording of tsunami events. We enhance a global statistical overview with case studies from Indonesia, where tsunamis are generated from a diverse range of sources, including subduction zones, crustal faults, landslides, and volcanic islands. While 80% of global recorded tsunamis during 1900–2020 have been attributed to earthquake sources, the median MWH of earthquake tsunamis is just 0.4 m. In contrast, the median water height of landslide tsunamis is 4 m. Landslides have caused or contributed to 24% of fatal tsunamis. During 1900–2020, more tsunamis with water heights > 1 m occurred in Indonesia than in any other country. In this region fatal tsunamis are caused by subduction zone earthquakes, landslides, volcanos, and intraplate crustal earthquakes. Landslide and volcano tsunami sources, as well as coastal landforms such as narrow embayments have caused high local maximum water heights and numerous fatalities in Indonesia. Tsunami hazards are increased in this region due to the densely populated and extensive coastal zones, as well as sea level rise from polar ice melt and local subsidence. Interrelated and often extreme natural hazards in this region present both an opportunity and a need to better understand a broader range of tsunami processes. [ABSTRACT FROM AUTHOR]