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The northeastern Sunda Strait is a narrow strait separating Java and Sumatra islands. Currently, it forms a seaway between the Java Sea and the Indian Ocean. The geological setting of the region is extremely dynamic, but how the Plio-Pleistocene interplay between sea level oscillations, magmatism, and tectonics, which lead to the current setting, has not been completely understood. We analysed an important set of legacy shallow seismic data from this area to decipher these intricate relationships. Our results indicate that the tectonic extension partly dismantled the Indonesian arc since the Middle Miocene. However, volcanic products formed a barrier between the Sunda Shelf and the Indian Ocean during the Late Pliocene to the Middle Pleistocene. Marine flooding started during the Middle Pleistocene but bypassed the barrier by flooding the NW edge of Java Island. During the Late Pleistocene, high amplitudes and longer periods of the glacial-interglacial cycles ultimately connected the Java Sea with the Indian Ocean. Still, it was only during the Holocene that important erosion made this seaway efficient in transporting seawater between the two reservoirs.

The mechanism of the presence of the Sukadana basalt in the back arc of Sumatra is still an enigma, especially since the Sukadana basalt has a wide coverage area in Sumatra Island and even the Sunda Arc. In this study, we used the published research data as the main contributor to an in-depth analysis to determine the mechanism of the presence of Sukadana basalt in the back arc. This study is supported by other studies from different regions around the world. These strengthen our conclusion that the emergence of Sukadana basalt on the surface is controlled by extensional deformations associated with the northwest-southeast-trending normal fault, which are formed by the mechanism of gravitational subsidence due to the movement of the Sumatra fault. In this study we suppose that the Nishimura fracture is a sinistral strike-slip fault as it is consistent with the Riedel shear model.

The Sunda Strait region is the riskiest area between Java and Sumatra. The impact of seismic activities must be considered to reduce disaster risk. This study has answered the lack of information about detailed seismotectonic conditions in the Sunda Strait. It confirms geotectonic actions controlled by the Asymmetry Subduction of the Sunda Arc between Oblique Subduction (Sumatra) and Frontal Subduction (Java). These activities produce five main seismotectonic zones based on their respective sources: Megathrust Seismotectonic Zones, Benioff Wadati Seismotectonic Zones, Sumatra Active Fault Seismotectonic Zones, Lampung Block Seismotectonic Zone and Center Part of Sunda Strait Seismotectonic Zone. Based on these seismic source zones, the Probabilistic Seismic Hazard Analyses (PSHA) of Sunda Strait have maximum Peak Ground Acceleration (PGA)=0.465g, Pseudo Seismic Acceleration (PSA) Ss=0.2 second=1.114 g, PSA S1=1second=0.465g in Site Class SB at 7% probability in 75 years (equivalent to a mean return of 1000 years), maximum Peak Ground Acceleration (PGA)=0.484g, Pseudo Seismic Acceleration (PSA) Ss=0.2 second=1.159 g, PSA S1=1second=0.484g in Site Class SB at 2% probability in 50 years (equivalent to a mean return of 2500 years), Peak Ground Acceleration (PGA)=0.499g, Pseudo Seismic Acceleration (PSA) Ss=0.2 second=1.193g, PSA S1=1second=0.499g, in Site Class SB at 2% probability in 100 years (equivalent to a mean return of 5000 years). The results of this effort are expected to be used as the primary data for seismic risk assessment in the Sunda Strait and its surrounding area. [ABSTRACT FROM AUTHOR]

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The 2019 MW6.9 Banten Intraslab earthquake occurred at ∼100 km to the northeast of the Sunda Trench with two nodal plane models estimated by the Global Centroid-Moment-Tensor (GCMT) Project with a strike of 200° and a dip of 65°.Continuous GPS data from 11 GPS sites were used to model the source of the earthquake in three-components. The coseismic displacements and its uncertainties are obtained from the coordinates of these GPS sites from 7 days before to 7 days after the earthquake. The coseismic slip is the inversion result of those displacements based on the best fit in an elastic half-space. The maximum displacement is ∼5 cm with a large uncertainty that is comparable to the amplitude of displacement. A seismic moment of the best model (strike of 65° and dip of 54°) is 2.79 × 1019 Nm or equivalent to MW6.89. The fault model of the earthquake is highly presumed as a continuation of Sumatran Fault Zone.

The lack of tsunami wave warning during the Anak Krakatau collapse in 2018 resulted in devastating damage to coastal areas. The tsunami wave arrived in the coastal areas approximately half an hour after the collapse. As a tsunami wave can travel abruptly, an early warning system should warn faster. However, a warning system based on a sophisticated hydrodynamic model in real-time would take time to conduct the numerical tsunami wave simulation. Hence, this study proposes a fast and reliable estimation of tsunami wave propagation through a classic ray tracing analysis. We use two ray-tracing methods to investigate the tsunami wave propagation from Anak Krakatau to the western Banten Sea. The first method follows Snell's law, considering dispersive waves, and the second assumes non-dispersive waves based on the ray tracing equations, considering the Earth's sphericity. Both methods are quantitatively evaluated by comparing the travel time measured at Anyer and Marina Jambu. This study finds that non-dispersive wave tracing performs a shorter computational time and slightly better prediction of tsunami wave propagation than dispersive-based wave tracing, with a relative absolute difference of the travel time of 17.9–26.7% in Anyer and 3.6–5.2% in Marina Jambu. This study also confirms the importance of bathymetry validity in wave ray tracing. Two regional bathymetry datasets with a mean difference of less than 5 m result in different wave ray tracing, in which one dataset does not produce the wave ray path towards the Panaitan Island. Based on bathymetric surveys in Anyer and Marina Jambu, the national bathymetry data (BATNAS) has shown its superiority to being used as a bathymetry in the ray-tracing process, with correlations of 81% and 93% in both areas compared to other available bathymetry datasets. We summarize that reliable bathymetry data and the non-dispersive ray tracing method can be used as an initial estimation of tsunami wave propagation efficiently. • Various bathymetry data are evaluated against survey data on the Banten coast. • The national bathymetry (BATNAS) has shown its superiority. • Wave ray tracing is proposed to estimate the tsunami propagation of Anak Krakatau. • Dispersive and non-dispersive wave rays are mainly affected by bathymetry. [ABSTRACT FROM AUTHOR]

In the past years, Indonesian people put more attention to Sunda Strait located between Java and Sumatra Islands, one of the busiest straits occupied with residential, recreational, fisheries, transportation, industrial and mining activities. Previous works on numerical modelling of tidal flow hydrodynamics of the Sunda Strait have resulted in good agreement against field data; however, the calibration of the models used was not described in detail. This paper presents the process of setting up the model, extensive calibration, validation and prediction of tidal currents for the Sunda Strait. A two-dimensional tidal-driven model is constructed using Delft3D, an open-source developed by Deltares. Four different bathymetry datasets, four different boundary condition configurations, and various bed roughness values are used, and their suitability in predicting tidal water level and current are investigated. It is found that changing the bathymetry and boundary conditions improve the model validation significantly. GEBCO_2019 bathymetry dataset outperforms the Batnas, even though it has a coarser resolution. For boundary conditions, the combination of water level and current velocity results in a better validation compares to using water level or current velocity only. However, the bed roughness shows an insignificant influence in predicting tidal conditions. The averaged current velocity is lower at the Southern than the Northern side of the strait due to a larger cross-section, consequence of deeper water. High tidal currents of magnitude around 2 m.s-1 are seen at the bottleneck of the strait.

In the past years, Indonesian people put more attention to Sunda Strait located between Java and Sumatra Islands, one of the busiest straits occupied with residential, recreational, fisheries, transportation, industrial and mining activities. Previous works on numerical modelling of tidal flow hydrodynamics of the Sunda Strait have resulted in good agreement against field data; however, the calibration of the models used was not described in detail. This paper presents the process of setting up the model, extensive calibration, validation and prediction of tidal currents for the Sunda Strait. A two-dimensional tidal-driven model is constructed using Delft3D, an opensource developed by Deltares. Four different bathymetry datasets, four different boundary condition configurations, and various bed roughness values are used, and their suitability in predicting tidal water level and current are investigated. It is found that changing the bathymetry and boundary conditions improve the model validation significantly. GEBCO_2019 bathymetry dataset outperforms the Batnas, even though it has a coarser resolution. For boundary conditions, the combination of water level and current velocity results in a better validation compares to using water level or current velocity only. However, the bed roughness shows an insignificant influence in predicting tidal conditions. The averaged current velocity is lower at the Southern than the Northern side of the strait due to a larger cross-section, consequence of deeper water. High tidal currents of magnitude around 2 m.s-1 are seen at the bottleneck of the strait. [ABSTRACT FROM AUTHOR]

Nowadays, satellite technology has developed significantly. Geodesy satellites such as Grace and Grace-FO can be used for subsurface mapping. The mapping is in the form of detection of the plate details, faults, and regional geodynamic conditions. This study aims to detect plate and faults from space geodesy using the gravity disturbance and Bouguer gravity anomaly parameter. The study area is in the Sunda Strait. Gravity disturbance is one of the gravity model parameters. Gravity disturbance is the gravitational potential of the topography expressed by the spherical harmonic model and the topographic effect by Barthelmes's calculations. Gravity disturbance can visualize subsurface conditions. Bouguer gravity anomaly is needed to get the condition on subsurface objects. This parameter visualizes subsurface conditions in the form of rocks and non-rocks. These conditions can distinguish oceanic crust and continental crust. Gravity contours are needed to obtain plate and faults predictions. The results obtained are validated patterns and shapes with plate and faults secondary data. The tolerance used in this validation is 80%. The gravity disturbance parameter obtained a value of 83% in verifying the accuracy of assessment in plate and faults detection. The Bouguer gravity disturbance parameter obtained a verification value of accuracy assessment in plate detection but 65% in faults detection. This accuracy assessment uses pattern and texture parameters in detecting the similarity of two or more images. This plate and faults detection results are more detailed and can be used for geophysical, geological, earthquake, and earth dynamics applications.

The 22 December 2018 Anak Karakatau tsunami in Indonesia was a rare event in that few instrumental records existed of tsunamis generated by volcanic sources before this event. The tsunami, which left a death toll of 437, is of global importance as it provides opportunities to develop knowledge on generation, propagation and coastal effects of volcanic tsunamis. Here, we report results of field surveys along the coast of the Sunda Strait, Indonesia to study tsunami wave heights and coastal damage. We surveyed 29 locations and measured ranges of tsunami runup from 0.9 to 5.2 m, tsunami heights from 1.4 to 6.3 m, flow depths from 0.2 m to 3.0 m and inundation distances from 18 to 212 m. The largest tsunami heights and concentration of damage and fatalities occurred on the western shore of Java from Tanjung Lesung to Sumur. The largest cluster of fatalities occurred at Tanjung Lesung, where more than 50 people died while attending an outdoor music being held at the shoreline. The tsunami runup and tsunami height in Tanjung Lesung were 4.0 and 2.9–3.8 m, respectively. We believe this tragedy could have been avoided if the event organizers were more aware of the hazard posed by the Anak Krakatau volcano, as it had been actively erupting for several months prior to the tsunami, and simply moved the concert stage 100 m inland. Many of the locations surveyed demonstrated a similar pattern where the majority of casualties and destruction occurred within 100 m of the coast; in several locations, lives were saved where buildings were located at least this distance inland. The significant damage and numerous deaths which occurred in Sumur, despite the moderate tsunami height of 2.3–2.5 m, can be attributed to the extremely low-lying coastal land there. Flow depth in Sumur was 0.9–2.0 m. During our field surveys, nearly one year after the event, we noted that some of the damaged buildings were being rebuilt in the same locations just 10–30 m from the shoreline. We question this practice since the new buildings could be at the same tsunami risk as those damaged in the 2018 event. [ABSTRACT FROM AUTHOR]

Tangkil and Rajabasa Volcanoes are neighbouring subduction-zone volcanoes located on the southeast tip of Sumatra Island (Sunda Strait, Indonesia). Stratigraphic correlation of lavas in Tangkil-Rajabasa volcanic area was established from field observations, morphological analysis, and K-Ar dating analysis. Detailed petrography and geochemical data of two and eleven lava units from Tangkil and Rajabasa, respectively, were then integrated with the stratigraphy to show the temporal variations. Early stage (> 4.3 Ma) effusives of Tangkil Volcano are dacitic to rhyolitic (67-71 wt. % SiO2; Tklf), whereas the later (c. 4.3 Ma) rocks are basalt to basaltic andesite (c. 52 wt. % SiO2; Tklm). Tangkil shows bimodal magmatism, of which the felsic endmember is > 71 wt. % SiO2 and < 0.1 wt. % MgO. Lavas of Rajabasa Volcano are comparatively younger (c. 0.3 to 0.1 Ma) with compositions ranging from basalt to andesite (51-62 wt. % SiO2; Rbs). Chemical variations of Rajabasa accounts for the interactions of at least three endmembers: Mg-rich medium-K basalt magma, low-Mg medium-K basalt magma, and high-K andesitic magma. During the long evolution of Rbs magma system, the temporal chemistry shows rising-falling variation in SiO2 and MgO indicating the three magmas were active. The felsic endmember magma of Rajabasa is fixed in composition (at ~62 wt. % SiO2; ~2.2 wt. % MgO). The rocks from the last Tklf and Rbs indicate open system processes by containing plagioclase and pyroxene phenocrysts that show resorption of evolved core and overgrowth of less evolved mantle. The multiple zones of dissolution-overgrowth in plagioclase crystals and the fluctuating trend in temporal whole-rock variation suggest that the changes of magmatic condition in temperature, H2O, or chemical composition were repetitive. [ABSTRACT FROM AUTHOR]

This study aims to simulate tsunami wave heights and their travel time toward the West Kalimantan coastal area. A Nuclear Power Plant (NPP) will be developed in a coastal area in the West Kalimantan Province, Indonesia. The two scenarios of events that may trigger the tsunami waves are volcanic events caused by Mount Krakatau located in the Sunda Strait and tectonic subduction located at the Indian Ocean on the west side of the Sunda Strait. Modeling the tsunami propagation using a finite-element-based hydrodynamic model developed by the US Army Corps of Engineer, namely the Surface-water Modeling System (SMS), is carried out. The model simulates tsunami wave propagation for six alternative locations at the proposed site of NPP. The model domains consist of Sunda Strait and Karimata Strait domains. The Sunda Strait domain model is validated by the observed historical tsunami heights reaching the 12 locations in Lampung, Banten, West Java, and Jakarta of Indonesia. The model validations show a good agreement. The validated hydrodynamic model results of the Sunda Strait model are used as the boundary conditions for the Karimata Strait domain model. The Karimata Strait model results show that the peaks of tsunami wave heights that reach the western Kalimantan coast are between 12 cm and 116 cm. The minimum wave height peak that reaches the six prospective locations is 12 cm, which is located in Sambas Regency. [ABSTRACT FROM AUTHOR]

A joint Indonesia-Singapore Deep Sea Expedition (SJADES 2018) focusing on the benthic fauna of the little sampled, western region of the Indonesian Archipelago has resulted in an extensive collection of sea stars (Asteroidea). Of these, two new species, an astropectinid and pterasterid, are herein described from mesopelagic depths in the Sunda Strait. [ABSTRACT FROM AUTHOR]

The coastal and offshore areas around the Sunda Strait will be developed to be a submarine cable corridor connecting between Java and Sumatra Islands. There are some requirements that should be considered before laying the underwater cables. One of these considerations is to understand the seafloor morphology of the Sunda Strait. The study was conducted based on six of track lines with 1 km line spacing and 4 Cross lines. The water depth obtained then was corrected to the depth of water from the Lowest Water Level (LWL). The seabed condition in the near shore area of Sumatra side is very flat and is influenced by 2 km offshore tide activity. The coast line is characterized by mangrove and fine fraction of sediments (mud and clay). At the Java side, the coastal morphology is characterized by the very steep slope and most of the area is occupied by the industrial activities.

The biogenic silica of sediment samples from Core CJ01-185 which is collected from the eastern India Ocean off the Sunda Strait is analyzed to evaluate the impact of the opening of the Sunda Strait on a paleoproductivity evolution. The new results indicate that the biogenic silica mass values of Core CJ01-185 show the lowest 0.86% in the last glacial period, and reach its maxima of 1.89% in the late Holocene. Furthermore, the biogenic silica mass accumulation rate (MARBSi) values also vary with much higher during the late Holocene than during the last glaciation. The input of additional terrigenous materials from the Java Sea has enhanced the paleoproductivity and increased the biogenic silica mass and MARBSi values after the opening of the Sunda Strait. It is suggested that the paleoproductivity in the study area is mainly influenced by the southeast monsoon and upwelling before the opening of the Sunda Strait. However, the paleoproductivity is dominated by the terrigenous materials input other than by the southeast monsoon or upwelling in the Holocene. [ABSTRACT FROM AUTHOR]

Sunda Strait is the outflow strait of the South China Sea branch of the Pacific to Indian Ocean Throughflow. The annual mean volume transport through the Sunda Strait is around 0.25 Sv from the Java Sea to the eastern Indian Ocean, only 2.5% of the IndonesianThroughflow, and thus has been ignored by previous investigations. However, the Nutrient concentrations in the Sunda Strait and its vicinity are found highly related to the water transport through the Sunda Strait. Particularly, our observation shows significant intraseasonal variability (ISV) of currents at period around 25–45 days in the Sunda Strait. Both remote and local wind forcing contribute to the ISVs in the Sunda Strait. The intraseasonal oscillation of sea surface wind in the central Indian Ocean drives upwelling/downwelling equatorial Kelvin waves to propagate along the equator and subsequently along the Sumatra-Java coasts, resulting in negative/positive sea level anomalies in the south of the Sunda Strait. The local intraseasonal sea surface wind anomalies also tend to induce negative/positive sea level anomalies in the south of the Sunda Strait by offshore/onshore Ekman transport while there are upwelling/downwelling events. The ensuring sea level gradient associated with the sea level anomalies in the south of the Sunda Strait induces intraseasonal outflow (from Indian Ocean to Java Sea) and inflow (from Java Sea to Indian Ocean) through the strait. Analyses also show that the chlorophyll-a concentrations in the south of the Sunda Strait are lower/higher during the inflow/outflow period of the ISV events in March through May. The mechanism attributes to both the nutrient-rich water transported by the intraseasonal flow in the Sunda Strait and by the upwelling and Ekman transport driven by the local sea surface wind anomalies. [ABSTRACT FROM AUTHOR]

With sea level rise in the early Holocene, the warm and low-salinity sea water from the Java Sea was transported into the eastern Indian Ocean after the opening of the Sunda Strait. However, the impact of this process on sediment provenance and paleoproductivity is rarely known. In this study, we analyzed the grain size, Sr-Nd-Pb isotopic compositions and biogenic elements of core CJ01-185 (1538 m water depth) in the eastern Indian Ocean off the Sunda Strait. Our new results reveal a large volcanic eruption in the west of Java at 2.1 ka, and the Krakatau eruption at 1883 CE. On the basis of the Pb isotopic compositions, 87 Sr/ 86 Sr ratios, and ε Nd values, we infer that sediments from core CJ01-185 were derived primarily from Java Island. There is a distinct change in Sr-Nd-Pb isotopic compositions of the sediments from the last glacial period to the Holocene, indicating less radiogenic Nd isotopes from the Java Sea into the eastern Indian Ocean after the opening of the Sunda Strait at ∼10 ka. Moreover, the sedimentation rate increased significantly from 6.5 cm kyr −1 during the last glacial period to 20 cm kyr −1 in the Holocene. The input of additional terrigenous nutrients from the Java Sea induced paleoproductivity with higher TOC and TN concentrations after the opening of the Sunda Strait. Our results thus suggest that the paleoproductivity was mainly influenced by terrigenous materials input in the Holocene, other than southeast monsoon or upwelling in the last glacial period. [ABSTRACT FROM AUTHOR]

Sunda Strait is an area of strait that has potential for enormous natural wealth. However, this potential is threatened by oil spills that occurred due to the activities of transportation and storage of crude oil. A study of ecological risk assessment of oil spills was conducted to measure the magnitude of the threat of oil spills and to have preemptive strategies to minimize the impact if a large-scale oil spills occur in the future. From the analysis of the trajectory, it can be concluded that the areas that are vulnerable to the impact of the oil spill were Panimbang Beach, Wells Island, Coastal Cigeulis, Cimanggu, Selat Panaitan, Cilegon, Anyer, Mediation, and Jabung Sragi. The applicability of the trajectory final data can be used as a reference in determining the risk level of oil particles which expose to ecosystems around the Sunda Strait and the foremost result was that it would be used to minimize the impact of the oil spills in the future.

In this paper, development on a coastal surveillance radar network, which is called ISRA (Indonesian Sea Radar), is presented. This radar network was developed for surveillance at the Sunda strait. The radar network monitors the sea traffics and activities at the Sunda strait, which an international shipping route. There were three radars installed for this network. All these radars in this research use FMCW (Frequency Modulated Continuous Wave) technology. This FMCW has an advantage of low power consumption, low cost of operational, longer life time and high reliability. Another important feature of this radar is the LPI (Low Probability of Intercept) capability, where the signal transmission of this radar cannot be easily detected by a radar detector (Electronic Support Measure) so that this radar can be used for a covert operation. Detected targets by radars are shown on the display and on the web based display for the radar network. These three radars on the remote sites can be monitored and controlled via an internet connection from the control room in our Bandung office, which is 300 KMs away. The results of this research and development show the Indonesian capability to build a complex system such as a chain of coastal surveillance radar network. The knowledge obtained from this research will be used to develop more advanced radars for different applications. [ABSTRACT FROM AUTHOR]

The male of Pseudomacrochiron parvum (A. Scott, 1909), which is unknown so far, is described and fi gured on specimenscollected off Labuan, Sunda Strait (06 º10'S 105 º45'E), westward of the type locality in Indonesian waters, and expand the descriptionof the female.

The study is aimed at proposing a solution for preventing ship accidents, ship collisions in particular, in Indonesia's busiest ferry crossing lane between Merak on Java Island and Bakauheni on Sumatera Island on the Sunda Strait, which intersects with the Indonesian Archipelagic Sea Lane. The Indonesian Archipelagic Sea Lane is provided by the Government of Indonesia, an archipelagic country, as an international passageway for ships sailing through Indonesian waters from the Indian Ocean to the South China Sea and the Pacific Ocean, by implementing a traffic separation scheme that regulates traffic proceeding in opposite or nearly opposite directions by means of a separation zone or line, traffic lane, etc. The study is motivated by records of fatal accidents that have taken place in the strait, and a portrait of the congested crossing lane is provided. The concept of a traffic separation scheme and its implementation in the Sunda Strait is simulated, with the conclusion that the scheme could minimize potential collisions between ships sailing through the strait. Therefore, it is urgent for the government to implement the scheme. [ABSTRACT FROM AUTHOR]

Abstract: The energy from marine environment has not been explored to the fullest, while the needs of energy in Indonesia have increased. Therefore, studying the potential of wind, currents, tides and wave energy might be the solution for building new power plants in Indonesia. This study focused around the area of Sunda Strait and the measurements that are taken from the secondary data of satellite images. From the satellite data processing and references based on energy potential of marine power plants it can be concluded that wave and wind energies are the two energies that are potential to be used. [Copyright &y& Elsevier]

Abstract: The Sunda Strait lies between the islands of Java and Sumatra and separates the nearly orthogonal subduction along the south of Java and oblique subduction beneath Sumatra. The Sumatra fault accommodating most of the trench parallel shear of the oblique subduction initiates in the Sunda Strait. This setting implies that the Sunda Strait is an attractive area to study the geodynamic evolution of the western Indonesian region. Thirteen multichannel seismic lines acquired in the Sunda Strait have allowed a detailed study of the structure, sedimentation patterns and volcanic activities that occurred in the Sunda Strait. The Sunda Strait evolution has been strongly tied with the development of the Sumatra fault in this area. The opening of the Sunda Strait initiated in the early Late Miocene following the commencement of the Sumatra fault system in the Middle Miocene. Since then, three major graben systems have been evolved, which are referred to as the West and East Semangko Grabens, and the Krakatau Graben. These graben systems can be regarded as pull-apart basins developed within the releasing fault overstep area in between the main strand of the Sumatra fault and its relay faults south off Ujung Kulon. Prior to the Late Miocene most of the Sunda Strait and the surroundings probably developed in a non-marine environment. In Late Miocene the Sunda Strait started to open and volcanism began and has been the main source of clastics. Three major sedimentary units can be identified which represent Late Miocene, Pliocene and Pleistocene sediments respectively. The Late Miocene unit has been developed in the shelfal area on top of the Middle Miocene unconformity following a relative rapid sea level rise, and a subsequent highstand prior to the sea level fall at the end of Miocene. Its lower part has syn-structurally been deposited into the Late Miocene basement block faulting. The early deposition of the Pliocene unit was in response to the Pliocene sea level rise and abundant clastic supply. The deposition became very rapid due to graben formation combined with stronger volcanism. However, its lateral distribution was confined by uplift of ridges within the grabens. [Copyright &y& Elsevier]

The occurrence of bottom simulating reflections (BSRs) along the Sunda margin off Indonesia is investigated for the first time using seismic reflection data from three surveys conducted across the subduction zone and the forearc domain off southern Sumatra to central Java. BSRs commonly concur with the base of the thermodynamically stable hydrate zone and are thus an important indicator for gas hydrates. Along the Sunda Arc, BSR occurrence is restricted to the forearc domain in regions likely to represent a focussing of fluid flow, such as the forearc basin slopes or anticline structures. Dissociation of gas hydrates due to uplift along anticline structures may be an important secondary cause of BSR formation. The absence of BSRs in the forearc basin center despite continuous sedimentation to ensure carbon supply may be related to the very high sedimentation rate (>0.4 km/Ma) which causes unused carbon to pass through the stability zone even for a high rate constant of methanogenesis. In addition, the interbedding of low- and high-permeability layers renders fluid flow across layering ineffective. No BSR phases could be detected along the accretionary prism or the outer high, although the P–T regime would allow a potential BSR to lie within the accretionary sedimentary column. [Copyright &y& Elsevier]

The examination of currents by merging model results and radial velocity High-Frequency (HF) radar data has been undertaken in the Sunda Strait, which links Sumatera Island and Java Island, involving two coastal sites (Anyer and Labuan) and using the Ensemble Transform Kalman Filter (ETKF). Dependent validation involved the data used during model analysis while independent validation utilised observations from a different site. These validations are needed to obtain an optimal representativity error, which has the lowest averaged root mean square (RMS) value over time and is appropriate for all sites. Moreover, the optimal representativity error was evaluated using the relative error reduction and the associated skill score metric. The results show that the model analysis for both independent and dependent validation has better results than the model with no blending. Interestingly, independent validation has a smaller RMS value than the model with no blending, although it is still greater than the dependent validation. The best results were obtained from model analysis of all sites, with the representativity error value being 0.2704 m / s for Anyer and 0.4459 m / s for Labuan. However, they have a pattern in the RMS error over time series. It is necessary to consider the factor such as winds that would modulate the magnitude of radial velocity. • Model accuracy is improved by blending HF radial velocity using the ETKF. • The representativity error is optimized by using independent validation. • Every site has a different optimal representativity error. • Improved model analysis can be obtained from either the original HF radar data or the HF radar data obtained at a different site. • Every site has a different optimal representativity error. • The root mean square error values of the currents are modulated by the strength of the winds. [ABSTRACT FROM AUTHOR]

This article is an exploratory report study of the disaster risk reduction (DRR) of the 2018 Sunda Strait volcanic tsunami, using the Digital Weberianism Bureaucracy (DWB) concept introduced by Muellerleile and Robertson. The actors of DRR, including their contributions according to their role in disaster management immediately after the drastic calamity, were mapped by the measurements of Social Network Analysis (SNA) using the Gephi Software and Correspondence Analysis (CA) using SPSS. Field data were obtained from 150 individuals who were directly affected by the volcanic tsunami by using digital questionnaires designed at an Open Data Kit (ODK) platform as part of a partially mixed sequential dominant status design research method. Centrality measurement in SNA shows a number of dominant actors in DRR observed from the three aspects of DWB, namely intelligent efficiency, sizing-up objectivity, and remotely rationality. Qualitative data were collected to further explore the roles of each actor in DRR. This research illustrates the weak integration of early warning and rapid information system applications developed by national disaster agencies, resulting in the failure to achieve DRR. This study also provides a theoretical contribution by expanding and enriching the DWB concept as a reframing of Weberian bureaucracy in the digital era. [ABSTRACT FROM AUTHOR]

The eruption of the Anak Krakatoa volcano (Indonesia) in December 2018 produced a destructive tsunami with maximum runup of 13 m killing 437 people. Since the occurrence of this rare tsunami, it has been a challenge as how to model this tsunami and to reconstruct the network of coastal observations. Here, we apply a combination of qualitative physical modeling and wavelet analyses of the tsunami as well as numerical modeling to propose a source model. Physical modeling of a volcano flank collapse showed that the initial tsunami wave mostly involves a pure-elevation wave. We identified initial tsunami period of 6.3–8.9 min through Wavelet analysis, leading to an initial tsunami dimension of 1.8–7.4 km. Twelve source models were numerically modelled with source dimensions of 1.5–4 km and initial tsunami amplitudes of 10–200 m. Based on the qualities of spectral and amplitude fits between observations and simulations, we constrained the tsunami source dimension and initial amplitude in the ranges of 1.5–2.5 km and 100–150 m, respectively. Our best source model involves potential energy of 7.14 × 1013–1.05 × 1014 J equivalent to an earthquake of magnitude 6.0–6.1. The amplitude of the final source model is consistent with the predictions obtained from published empirical equations. • Initial tsunami wave is a pure-elevation wave based on our physical modeling. • The dominant tsunami period is 6.3–8.9 min giving tsunami length of 1.8–7.4 km. • Final tsunami source has a length of 1.5–2.5 km and amplitude of 100–150 m. • Our model has energy of 7.14 × 1013–1.05 × 1014 J equivalent to M 6.0 earthquake. [ABSTRACT FROM AUTHOR]