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The initial conditions for the simulation of a seismically induced tsunami for a rapid, assumed-to-be-instantaneous vertical seafloor displacement is given by the Kajiura low-pass filter integral. This work proposes a new, efficient, and accurate approach for its numerical evaluation, valid when the seafloor displacement is discretized as a set of rectangular contributions over variable bathymetry. We compare several truncated quadrature formulae, selecting the optimal one. The reconstruction of the initial sea level perturbation as a linear combination of pre-computed elementary sea surface displacements is tested on the tsunamigenic Kuril earthquake doublet – a megathrust and an outer rise – that occurred in the central Kuril Islands in late 2006 and early 2007. We also confirm the importance of the horizontal contribution to tsunami generation, and we consider a simple model of the inelastic deformation of the wedge on realistic bathymetry. The proposed approach results are accurate and fast enough to be considered relevant for practical applications. A tool to build a tsunami source database for a specific region of interest is provided. [ABSTRACT FROM AUTHOR]

The initial condition for the simulation of a seismically-induced tsunami for a rapid, assumed instantaneous, vertical seafloor displacement is given by the Kajiura low-pass filter integral. This work proposes a new efficient and accurate approach for its numerical evaluation, valid when the sea floor displacement is discretized as a set of rectangular contributions. We compare several truncated quadrature formulae, selecting the optimal one. We verify that we can satisfactorily approximate the initial sea level perturbation as a linear combination of those induced by the elementary sea floor displacements. The methodology is tested on the tsunamigenic Kuril earthquake doublet – a megathrust and an outer-rise – occurred in the Central Kuril Islands in late 2006 and early 2007. We also confirm the importance of the horizontal contribution to the tsunami generation and we consider a simple model of the inelastic deformation of the wedge, on a realistic bathymetry. The proposed approach results accurate and fast enough to be considered relevant for practical applications, and a tool is provided to create tsunami unit source databases for a given region of interest. [ABSTRACT FROM AUTHOR]

On 12 August 2021, a >220 s lasting complex earthquake with Mw > 8.2 hit the South Sandwich Trench. Due to its remote location and short interevent times, reported earthquake parameters varied significantly between different international agencies. We studied the complex rupture by combining different seismic source characterization techniques sensitive to different frequency ranges based on teleseismic broadband recordings from 0.001 to 2 Hz, including point and finite fault inversions and the back‐projection of high‐frequency signals. We also determined moment tensor solutions for 88 aftershocks. The rupture initiated simultaneously with a rupture equivalent to a Mw 7.6 thrust earthquake in the deep part of the seismogenic zone in the central subduction interface and a shallow megathrust rupture, which propagated unilaterally to the south with a very slow rupture velocity of 1.2 km/s and varying strike following the curvature of the trench. The slow rupture covered nearly two‐thirds of the entire subduction zone length, and with Mw 8.2 released the bulk of the total moment of the whole earthquake. Tsunami modeling indicates the inferred shallow rupture can explain the tsunami records. The southern segment of the shallow rupture overlaps with another activation of the deeper part of the megathrust equivalent to Mw 7.6. The aftershock distribution confirms the extent and curvature of the rupture. Some mechanisms are consistent with the mainshocks, but many indicate also activation of secondary faults. Rupture velocities and radiated frequencies varied strongly between different stages of the rupture, which might explain the variability of published source parameters. Plain Language Summary: The earthquake of 12 August 2021 along the deep‐sea trench of the South Sandwich Islands in the South Atlantic reached a magnitude of 8.2 and triggered a tsunami. The automatic earthquake parameter determination of different agencies showed very different results shortly after the earthquake and partially underestimated the tsunami potential of the earthquake. A possible reason was the complex rupture process and that the tsunami was generated by a long and shallow slow slip rupture sandwiched between more conventional fast slip subevents at its northern and southern ends. In addition, the fault surface, which extended over 450 km, was highly curved striking 150°–220°. We investigated the different components of the seismic wavefields in different frequency ranges and with different methods. The analysis shows how even complex earthquakes can be deciphered by combining analyzing methods. The comparison with aftershocks and the triggered tsunami waves confirms our model that explains the South Sandwich rupture by four subevents in the plate boundary along the curved deep‐sea trench. Here, the depth, rupture velocities, and slip on each segment of the rupture vary considerably. The method can also be applied to other megathrust earthquakes and help to further improve tsunami warnings in the future. Key Points: A combination of multiple approaches, inversion setups, and frequency ranges deciphered the complex earthquake of 2021 South SandwichThe rupture consisted of four subevents with the largest occurring as a shallow slow rupture parallel to the South Sandwich TrenchForward modeling proves that the large, shallow thrust subevent caused the recorded tsunami [ABSTRACT FROM AUTHOR]

Tsunamis caused by large volcanic eruptions and flanks collapsing into the sea are major hazards for nearby coastal regions. They often occur with little precursory activity and are thus challenging to detect in a timely manner. This makes the pre-emptive identification of volcanoes prone to causing tsunamis particularly important, as it allows for better hazard assessment and denser monitoring in these areas. Here, we present a catalogue of potentially tsunamigenic volcanoes in Southeast Asia and rank these volcanoes by their tsunami hazard. The ranking is based on a multicriteria decision analysis (MCDA) composed of five individually weighted factors impacting flank stability and tsunami hazard. The data are sourced from geological databases, remote sensing data, historical volcano-induced tsunami records, and our topographic analyses, mainly considering the eruptive and tsunami history, elevation relative to the distance from the sea, flank steepness, hydrothermal alteration, and vegetation coverage. Out of 131 analysed volcanoes, we found 19 with particularly high tsunamigenic hazard potential in Indonesia (Anak Krakatau, Batu Tara, Iliwerung, Gamalama, Sangeang Api, Karangetang, Sirung, Wetar, Nila, Ruang, Serua) and Papua New Guinea (Kadovar, Ritter Island, Rabaul, Manam, Langila, Ulawun, Bam) but also in the Philippines (Didicas). While some of these volcanoes, such as Anak Krakatau, are well known for their deadly tsunamis, many others on this list are lesser known and monitored. We further performed tsunami travel time modelling on these high-hazard volcanoes, which indicates that future events could affect large coastal areas in a short time. This highlights the importance of individual tsunami hazard assessment for these volcanoes, the importance of dedicated volcanological monitoring, and the need for increased preparedness on the potentially affected coasts. [ABSTRACT FROM AUTHOR]

Tsunamis caused by large volcanic eruptions and flanks collapsing into the sea are major hazards for nearby coastal regions. They often occur with little precursory activity, and are thus challenging to detect in a timely manner. This makes the preemptive identification of volcanoes prone to causing tsunamis particularly important, as it allows for better hazard assessment and denser monitoring in these areas. Here, we present a catalogue of potentially tsunamigenic volcanoes in Southeast Asia and rank these volcanoes by their tsunami hazard. The ranking is based on a Multicriteria Decision Analysis (MCDA) composed of five individually weighted factors impacting flank stability and tsunami hazard. The data is sourced from geological databases, remote sensing data, historical volcano induced tsunami records and our topographic analyses, mainly considering the eruptive and tsunami history, elevation relative to the distance from the sea, flank steepness, hydrothermal alteration as well as vegetation coverage. Out of 131 analysed volcanoes, we found 19 with particularly high tsunamigenic hazard potential in Indonesia (Anak Krakatau, Batu Tara, Iliwerung, Gamalama, Sangeang Api, Karangetang, Sirung, Wetar, Nila, Ruang, Serua) and Papua New Guinea (Kadovar, Ritter Island, Rabaul, Manam, Langila, Ulawun, Bam), but also in the Philippines (Didicas). While some of these volcanoes, such as Anak Krakatau, are well-known for their deadly tsunamis, many others on this list are lesser known and monitored. We further performed tsunami travel time modelling on these high-hazard volcanoes, which indicates that future events could affect large coastal areas in a short time. This highlights the importance of individual tsunami hazard assessment for these volcanoes, dedicated volcanological monitoring, and the need for increased preparedness on the potentially affected coasts. [ABSTRACT FROM AUTHOR]

Controls on the deformation pattern (shortening mode and tectonic style) of orogenic forelands during lithospheric shortening remain poorly understood. Here, we use high‐resolution 2D thermomechanical models to demonstrate that orogenic crustal thickness and foreland lithospheric thickness significantly control the shortening mode in the foreland. Pure‐shear shortening occurs when the orogenic crust is not thicker than the foreland crust or thick, but the foreland lithosphere is thin (<70–80 km, as in the Puna foreland case). Conversely, simple‐shear shortening, characterized by foreland underthrusting beneath the orogen, arises when the orogenic crust is much thicker. This thickened crust results in high gravitational potential energy in the orogen, which triggers the migration of deformation to the foreland under further shortening. Our models present fully thick‐skinned, fully thin‐skinned, and intermediate tectonic styles in the foreland. The first tectonics forms in a pure‐shear shortening mode whereas the others require a simple‐shear mode and the presence of thick (>∼4 km) sediments that are mechanically weak (friction coefficient <∼0.05) or weakened rapidly during deformation. The formation of fully thin‐skinned tectonics in thick and weak foreland sediments, as in the Subandean Ranges, requires the strength of the orogenic upper lithosphere to be less than one‐third as strong as that of the foreland upper lithosphere. Our models successfully reproduce foreland deformation patterns in the Central and Southern Andes and the Laramide province. Key Points: Thicknesses of the orogenic crust and the foreland lithosphere control the foreland shortening mode (pure‐shear or simple‐shear)Foreland weak sediments and the upper lithosphere of the weaker orogen control the foreland tectonic style (thin‐skinned or thick‐skinned)High‐resolution geodynamic models successfully reproduce foreland deformation patterns in several natural orogen‐foreland shortening systems [ABSTRACT FROM AUTHOR]

We propose the use of variable resolution boundaries based on central Voronoi tessellations (CVTs) to spatially aggregate building exposure models for risk assessment to various natural hazards. Such a framework is especially beneficial when the spatial distribution of the considered hazards presents intensity measures with contrasting footprints and spatial correlations, such as in coastal environments. This work avoids the incorrect assumption that a single intensity value from hazards with low spatial correlation (e.g. tsunami) can be considered to be representative within large-sized geo-cells for physical vulnerability assessment, without, at the same time, increasing the complexity of the overall model. We present decoupled earthquake and tsunami scenario-based risk estimates for the residential building stock of Lima (Peru). We observe that earthquake loss models for far-field subduction sources are practically insensitive to the exposure resolution. Conversely, tsunami loss models and associated uncertainties depend on the spatial correlations of the hazard intensities as well as on the resolution of the exposure models. We note that for the portfolio located in the coastal area exposed to both perils in Lima, the ground shaking dominates the losses for lower-magnitude earthquakes, whilst tsunamis cause the most damage for larger-magnitude events. For the latter, two sets of existing empirical flow depth fragility models are used, resulting in large differences in the calculated losses. This study, therefore, raises awareness about the uncertainties associated with the selection of fragility models and spatial aggregation entities for exposure modelling and loss mapping. [ABSTRACT FROM AUTHOR]

Tsunami warning centres face the challenging task of rapidly forecasting tsunami threat immediately after an earthquake, when there is high uncertainty due to data deficiency. Here we introduce Probabilistic Tsunami Forecasting (PTF) for tsunami early warning. PTF explicitly treats data- and forecast-uncertainties, enabling alert level definitions according to any predefined level of conservatism, which is connected to the average balance of missed-vs-false-alarms. Impact forecasts and resulting recommendations become progressively less uncertain as new data become available. Here we report an implementation for near-source early warning and test it systematically by hindcasting the great 2010 M8.8 Maule (Chile) and the well-studied 2003 M6.8 Zemmouri-Boumerdes (Algeria) tsunamis, as well as all the Mediterranean earthquakes that triggered alert messages at the Italian Tsunami Warning Centre since its inception in 2015, demonstrating forecasting accuracy over a wide range of magnitudes and earthquake types. Probabilistic tsunami forecasting (PTF) defines an approach to tsunami early warning based on uncertainty quantification, enhancing forecast accuracy and enabling rational decision making. PTF is here developed for near-source tsunami warning, and tested in hindcasting mode over a wide range of past earthquakes. [ABSTRACT FROM AUTHOR]

We propose the use of variable resolution boundaries based on Central Voronoi Tessellations (CVT) to spatially aggregate building exposure models for risk assessment to various natural hazards. Such a framework is especially beneficial when the spatial distribution of the considered hazards present intensity measures with contrasting footprints and spatial correlations such as in coastal environments. This proposal avoids the incorrect assumption that a single intensity value from hazards with low spatial correlation (e.g. tsunami) are considered as representative within large sized geocells for physical vulnerability assessment, without, at the same time, increasing the complexity of the overall model. We present decoupled earthquake and tsunami scenario-based risk estimates for the residential building stock of Lima (Peru). We observe that earthquake loss models for far-field subduction sources are practically insensitive to the exposure resolution. Conversely, tsunami loss models and associated uncertainties depend on the spatial correlations of the hazard intensities as well as on the resolution of the exposure models. We observe that for the portfolio located in the coastal area exposed to both perils in Lima, the ground-shaking dominates the losses for lower magnitudes whilst the tsunami does for the larger ones. For the latter, two sets of existing empirical flow-depth fragility models are used, finding large differences in the losses. This study arises awareness about the uncertainties in the selection of fragility models and aggregations entities for exposure modelling and loss mapping. [ABSTRACT FROM AUTHOR]

Forecasting and early warning systems are important investments to protect lives, properties, and livelihood. While early warning systems are frequently used to predict the magnitude, location, and timing of potentially damaging events, these systems rarely provide impact estimates, such as the expected amount and distribution of physical damage, human consequences, disruption of services, or financial loss. Complementing early warning systems with impact forecasts has a twofold advantage: It would provide decision makers with richer information to take informed decisions about emergency measures and focus the attention of different disciplines on a common target. This would allow capitalizing on synergies between different disciplines and boosting the development of multihazard early warning systems. This review discusses the state of the art in impact forecasting for a wide range of natural hazards. We outline the added value of impact-based warnings compared to hazard forecasting for the emergency phase, indicate challenges and pitfalls, and synthesize the review results across hazard types most relevant for Europe. Plain Language Summary Forecasting and early warning systems are important investments to protect lives, properties and livelihood. While such systems are frequently used to predict the magnitude, location, and timing of potentially damaging events, they rarely provide impact estimates, such as the expected physical damage, human consequences, disruption of services, or financial loss. Extending hazard forecast systems to include impact estimates promises many benefits for the emergency phase, for instance, for organizing evacuations. We review and compare the state of the art of impact forecasting across a wide range of natural hazards and outline opportunities and key challenges for research and development of impact forecasting. [ABSTRACT FROM AUTHOR]

Historical data indicate that the Middle America subduction zone represents the primary tsunamigenic source that affects the Central American coastal areas. In recent years, the tsunami potential in the region has mainly been assessed using maximum credible earthquakes or historical events showing moderate tsunami potential. However, such deterministic scenarios are not provided with their adequate probability of occurrence. In this study, earthquake rates have been combined with tsunami numerical modeling in order to assess probabilistic tsunami hazard posed by local and regional seismic sources. The common conceptual framework for the probabilistic seismic hazard assessment has been adapted to estimate the probabilities of exceeding certain tsunami amplitudes along the Central American Pacific coast. The study area encompasses seismic sources related to the Central America, Colombia and Ecuador subduction zones. In addition to the classical subduction inter-plate events, this study also incorporates sources at the outer rise, within the Caribbean crust as well as intra-slab sources. The study yields conclusive remarks showing that the highest hazard is posed to northwestern Costa Rica, El Salvador and the Nicaraguan coast, southern Colombia and northern Ecuador. In most of the region it is 50 to 80% likely that the tsunami heights will exceed 2 m for the 500 year time exposure (T). The lowest hazard appears to be in the inner part of the Fonseca Gulf, Honduras. We also show the large dependence of PTHA on model assumptions. While the approach taken in this study represents a thorough step forward in tsunami hazard assessment in the region, we also highlight that the integration of all possible uncertainties will be necessary to generate rigorous hazard models required for risk planning. [ABSTRACT FROM AUTHOR]

This study reports on recent developments of the Indonesia Tsunami Early Warning System (InaTEWS), specifically the tsunami modeling components used in the system. It is a dual system: firstly, InaTEWS operates a high-resolution scenario database pre-computed with the finite element model TsunAWI; running in parallel, the system also contains a supra real-time modeling component based on the GPU-parallelized linear long-wave model easyWave, capable of dealing with events outside the database coverage. The evolution of the tsunami scenario database over time is covered in the first sections also touching on the involved capacity building efforts. Starting with a coverage of just the Sunda Arc region, the database now includes scenarios for 15 fault zones. The study is augmented by an investigation of warning products used for early warning; the estimated wave height (EWH) and the estimated time of arrival (ETA). These parameters are determined by easyWave and TsunAWI with model specific approaches. Since the numerical setup of the two models is very different, the extent of variations in warning products is investigated for a number of scenarios, where both pure database scenarios and applications to real events are considered. Finally, the performance of the system in past tsunami events is reviewed to point out major system updates. [ABSTRACT FROM AUTHOR]

The complexity of coseismic slip distributions influences the tsunami hazard posed by local and, to a certain extent, distant tsunami sources. Large slip concentrated in shallow patches was observed in recent tsunamigenic earthquakes, possibly due to dynamic amplification near the free surface, variable frictional conditions or other factors. We propose a method for incorporating enhanced shallow slip for subduction earthquakes while preventing systematic slip excess at shallow depths over one or more seismic cycles. The method uses the classic k−2 stochastic slip distributions, augmented by shallow slip amplification. It is necessary for deep events with lower slip to occur more often than shallow ones with amplified slip to balance the long-term cumulative slip. We evaluate the impact of this approach on tsunami hazard in the central and eastern Mediterranean Sea adopting a realistic 3D geometry for three subduction zones, by using it to model ~ 150,000 earthquakes with M w from 6.0 to 9.0. We combine earthquake rates, depth-dependent slip distributions, tsunami modeling, and epistemic uncertainty through an ensemble modeling technique. We found that the mean hazard curves obtained with our method show enhanced probabilities for larger inundation heights as compared to the curves derived from depth-independent slip distributions. Our approach is completely general and can be applied to any subduction zone in the world. [ABSTRACT FROM AUTHOR]

Tsunami forecast possibilities for areas with a small base of historical tsunamis have been discussed using the Probabilistic Tsunami Hazard Assessment (PTHA) method, which is based on a statistical analysis of a sufficiently large number of real and predictive earthquakes with a subsequent calculation of possible tsunami waves. This method has been used for a long-term tsunami hazard assessment on the Mediterranean coast of Egypt. The predicted wave heights have been shown to vary along the coastline due to the inhomogeneity of the coastal topography and specific features of the tsunami radiation pattern in the sea. The predicted wave heights for 1000 years vary in the range between 0.8 and 3.4 m. [ABSTRACT FROM AUTHOR]

Regional and global tsunami hazard analysis requires simplified and efficient methods for estimating the tsunami inundation height and its related uncertainty. One such approach is the amplification factor (AF) method. Amplification factors describe the relation between offshore wave height and the maximum inundation height, as predicted by linearized plane wave models employed for incident waves with different wave characteristics. In this study, a new amplification factor method is developed that takes into account the offshore bathymetry proximal to the coastal site. The present AFs cover the North-Eastern Atlantic and Mediterranean (NEAM) region. The model is the first general approximate model that quantifies inundation height uncertainty. Uncertainty quantification is carried out by analyzing the inundation height variability in more than 500 high-resolution inundation simulations at six different coastal sites. The inundation simulations are undertaken with different earthquake sources in order to produce different wave period and polarity. We show that the probability density of the maximum inundation height can be modeled with a log-normal distribution, whose median is quite well predicted by the AF. It is further demonstrated that the associated maximum inundation height uncertainties are significant and must be accounted for in tsunami hazard analysis. The application to the recently developed TSUMAPS-NEAM probabilistic tsunami hazard analysis (PTHA) is presented as a use case. [ABSTRACT FROM AUTHOR]

Abstract: Applying probabilistic methods to infrequent but devastating natural events is intrinsically challenging. For tsunami analyses, a suite of geophysical assessments should be in principle evaluated because of the different causes generating tsunamis (earthquakes, landslides, volcanic activity, meteorological events, and asteroid impacts) with varying mean recurrence rates. Probabilistic Tsunami Hazard Analyses (PTHAs) are conducted in different areas of the world at global, regional, and local scales with the aim of understanding tsunami hazard to inform tsunami risk reduction activities. PTHAs enhance knowledge of the potential tsunamigenic threat by estimating the probability of exceeding specific levels of tsunami intensity metrics (e.g., run‐up or maximum inundation heights) within a certain period of time (exposure time) at given locations (target sites); these estimates can be summarized in hazard maps or hazard curves. This discussion presents a broad overview of PTHA, including (i) sources and mechanisms of tsunami generation, emphasizing the variety and complexity of the tsunami sources and their generation mechanisms, (ii) developments in modeling the propagation and impact of tsunami waves, and (iii) statistical procedures for tsunami hazard estimates that include the associated epistemic and aleatoric uncertainties. Key elements in understanding the potential tsunami hazard are discussed, in light of the rapid development of PTHA methods during the last decade and the globally distributed applications, including the importance of considering multiple sources, their relative intensities, probabilities of occurrence, and uncertainties in an integrated and consistent probabilistic framework. [ABSTRACT FROM AUTHOR]

Compared with a single GPS system, GPS/GLONASS observations can improve the satellite visibility, optimize the spatial geometry and improve the precise positioning performance. Although the advantage over GPS-only methods in terms of positioning is clear, the potential contributions of GPS/GLONASS to co-seismic displacement determination and the subsequent seismic source inversion still require extensive study and validation. In this paper, we first extended a temporal point positioning model from GPS-only to GPS/GLONASS observations. Using this new model, the performance of the GPS/GLONASS method for obtaining coseismic displacementswas then validated via eight outdoor experiments on a shaking table. Our result reveals that the GPS/GLONASS method provides more accurate and robust co-seismic displacements than the GPS-only observations in a non-optimal observation environment. Furthermore, as a case study, observation data recorded during the September 2015 Mw 8.3 Illapel earthquake in Chile were re-processed. At some stations, obvious biases were found between the co-seismic displacements derived from GPS-only and GPS/GLONASS observations. The subsequent slip distribution inversion on a curved fault confirms that the differences in the co-seismic displacements causes differences in the inversion results and that the slip distributions of the Illapel earthquake inferred from the GPS/GLONASS observations tend to be shallower and larger. [ABSTRACT FROM AUTHOR]

Despite having been rather seismically quiescent for the last decades, the Makran subduction zone is capable of hosting destructive earthquakes and tsunami. In particular, the well-known thrust event in 1945 (Balochistan earthquake) led to about 4000 casualties. Nowadays, the coastal regions are more densely populated and vulnerable to similar events. Furthermore, some recent publications discuss rare but significantly larger events at the Makran subduction zone as possible scenarios. We analyze the instrumental and historical seismicity at the subduction plate interface and generate various synthetic earthquake catalogs spanning 300 000 years with varying magnitude-frequency relations. For every event in the catalogs we compute estimated tsunami heights and present the resulting tsunami hazard along the coasts of Pakistan, Iran and Oman in the form of probabilistic tsunami hazard curves. We show how the hazard results depend on variation of the Gutenberg-Richter parameters and especially maximum magnitude assumption. [ABSTRACT FROM AUTHOR]

The Middle America convergent margin is capable of generating tsunamigenic earthquakes as portrayed through historical data. However, historical tsunamigenic sources appear to be unevenly distributed along the Middle America convergent margin. The last significant tsunami generated along the southern segments of this convergent margin occurred in 1992 causing 10-m run-up in Nicaragua. In particular, the Costa Rican Pacific coast has not clear evidences of significant wave heights or local tsunami events. Partly this could be explained by the lack of historical data since paleotsunami information is not available; thus, no tsunami data beyond 500 years could be found. Nevertheless, large rupture areas or shallow ruptures offshore Costa Rica cannot be neglected. We hereby present the results of numerical simulations aimed to assess the tsunamigenic potential of seismic sources offshore southern Central America. Our approach follows the deterministic method where earthquake maximum credible scenarios are assessed. We assumed hundreds of fault ruptures to obtain surface displacement and tsunami wave heights at the shoreline to assess the tsunami threat along south Nicaragua and Costa Rica. These fault scenarios are based on historical earthquakes as well as on the newest geodetic studies that provided slip deficit. Shallow part of locked segments in this region could release accumulated stress in the near future and may generate tsunamis similar to the 1992 Nicaragua M 7.6 and 2012 El Salvador M 7.4 tsunami earthquakes. The numerical simulations presented in this study show that maximum wave heights up to 2-6 m could affect the southern Pacific coast of Central America even when moderate-to-large M 7.0-8.0 interplate or outer rise earthquakes occur. [ABSTRACT FROM AUTHOR]

Global Positioning System (GPS) has been proved to be a powerful tool for measuring co-seismic ground displacements with an application to seismic source inversion. Whereas most of the tsunamis are triggered by large earthquakes, GPS can contribute to the tsunami early warning system (TEWS) by helping to obtain tsunami source parameters in near real-time. Toward the end of 2012, the second phase of the BeiDou Navigation Satellite System (BDS) constellation was accomplished, and BDS has been providing regional positioning service since then. Numerical results indicate that precision of BDS nowadays is equivalent to that of the GPS. Compared with a single Global Satellite Navigation System (GNSS), combined BDS/GPS real-time processing can improve accuracy and especially reliability of retrieved co-seismic displacements. In the present study, we investigate the potential of BDS to serve for the early warning system of tsunamis in the South China Sea region. To facilitate early warnings of tsunamis and forecasting capabilities in this region, we propose to distribute an array of BDS-stations along the Luzon Island (Philippines). By simulating an earthquake with Mw = 8 at the Manila trench as an example, we demonstrate that such an array will be able to detect earthquake parameters in real time with a high degree of accuracy and, hence, contribute to the fast and reliable tsunami early warning system in this region. [ABSTRACT FROM AUTHOR]

Despite having been rather seismically quiescent for the last decades, the Makran subduction zone is capable of hosting destructive earthquakes and tsunami. In particular, the well-known thrust event in 1945 (Balochistan earthquake) led to about 4000 ca- sualties. Nowadays, the coastal regions are more densely populated and vulnerable to similar events. Furthermore, some recent publications discuss rare but significantly larger events at the Makran subduction zone as possible scenarios. We analyze the instrumental and historical seismicity at the subduction plate interface and generate various synthetic earthquake catalogs spanning 300 000 years with varying magnitude- frequency relations. For every event in the catalogs we compute estimated tsunami heights and present the resulting tsunami hazard along the coasts of Pakistan, Iran and Oman in the form of probabilistic tsunami hazard curves. We show how the hazard results depend on variation of the Gutenberg-Richter parameters and especially maximum magnitude assumption. [ABSTRACT FROM AUTHOR]

Fostered by and embedded in the general development of information and communications technology (ICT), the evolution of tsunami warning systems (TWS) shows a significant development from seismic-centred to multisensor system architectures using additional sensors (e.g. tide gauges and buoys) for the detection of tsunami waves in the ocean. Currently, the beginning implementation of regional tsunami warning infrastructures indicates a new phase in the development of TWS. A new generation of TWS should not only be able to realise multi-sensor monitoring for tsunami detection. Moreover, these systems have to be capable to form a collaborative communication infrastructure of distributed tsunami warning systems in order to implement regional, ocean-wide monitoring and warning strategies. In the context of the development of the German Indonesian Tsunami Early Warning System (GITEWS) and in the EU-funded FP6 project Distant Early Warning System (DEWS), a service platform for both sensor integration and warning dissemination has been newly developed and demonstrated. In particular, standards of the Open Geospatial Consortium (OGC) and the Organization for the Advancement of Structured Information Standards (OASIS) have been successfully incorporated. In the FP7 project Collaborative, Complex and Critical Decision-Support in Evolving Crises (TRIDEC), new developments in ICT (e.g. complex event processing (CEP) and event-driven architecture (EDA)) are used to extend the existing platform to realise a component-based technology framework for building distributed tsunami warning systems. [ABSTRACT FROM AUTHOR]

The various uncertainties in the earthquake-triggered tsunami threat assessment are difficult to quantify and/or integrate into the tsunami early warning process. Uncertainties in the (seismic) input parameters and the lack of knowledge about the earthquake slip distribution contribute most to the total uncertainty in real-time evaluated tsunami assessment. We present a method how to integrate and quantify these uncertainties in the warning process by evaluating a tsunami warning level probability distribution with a Bayesian network (BN) approach. As soon as an earthquake is detected, the seismic source parameter estimates are evaluated and a probabilistic overview on different tsunami warning levels is provided, feasible to support a decision maker at a warning center with important additional data. A BN system has been developed exemplarily for the region Sumatra. In this paper, we describe the method of BN generation by ancestral sampling, we critically analyse the assumptions made and weight the pro and cons of the BN approach. A case study demonstrates the workflow of the BN system in real-time and reveals the promising power of a BN analysis in the framework of early warning. [ABSTRACT FROM AUTHOR]

Our analysis of new bathymetric data reveals six submarine landslides at the eastern Sunda margin between central Java and Sumba Island, Indonesia. Their volumes range between 1 km³ in the Java fore-arc basin up to 20 km³ at the trench off Sumba and Sumbawa. We estimate the potential hazard of each event by modeling the corresponding tsunami and its run-up on nearby coasts. Four slides are situated remarkably close to the epicenter of the 1977 tsunamigenic Sumba M w = 8.3 earthquake. However, comparison of documented tsunami run-up heights and arrival times with our modeling results neither allows us to confirm nor can we falsify the hypothesis that the earthquake triggered these submarine landslides. [ABSTRACT FROM AUTHOR]

We present the GITEWS approach to source modeling for the tsunami early warning in Indonesia. Near-field tsunami implies special requirements to both warning time and details of source characterization. To meet these requirements, we employ geophysical and geological information to predefine a maximum number of rupture parameters. We discretize the tsunamigenic Sunda plate interface into an ordered grid of patches (150×25) and employ the concept of Green's functions for forward and inverse rupture modeling. Rupture Generator, a forward modeling tool, additionally employs different scaling laws and slip shape functions to construct physically reasonable source models using basic seismic information only (magnitude and epicenter location). GITEWS runs a library of semi- and fully-synthetic scenarios to be extensively employed by system testing as well as by warning center personnel teaching and training. Near realtime GPS observations are a very valuable complement to the local tsunami warning system. Their inversion provides quick (within a few minutes on an event) estimation of the earthquake magnitude, rupture position and, in case of sufficient station coverage, details of slip distribution. [ABSTRACT FROM AUTHOR]

A new tsunami forecasting method for near-field tsunami warning is presented. This method is applied in the German-Indonesian Tsunami Early Warning System, as part of the Indonesian Tsunami Warning Center in Jakarta, Indonesia. The method employs a rigorous approach to minimize uncertainty in the assessment of tsunami hazard in the near-field. Multiple independent sensors are evaluated simultaneously in order to achieve an accurate estimation of coastal arrival times and wave heights within very short time after a submarine earthquake event. The method is validated employing a synthetic (simulated) tsunami event, and in hindcasting the minor tsunami following the Padang 30 September 2009 earthquake. [ABSTRACT FROM AUTHOR]

Submarine landslides can generate local tsunamis with high run-ups, posing a hazard to human lives and coastal facilities. Both ancient (giant Storegga slide off Norwegian coast, 8200 B. P.) and recent (Papua New Guinea, 1998) events show high potential danger of tsunamigenic landslides and the importance of mitigation efforts. This contribution presents newly discovered landslides 70 km off Padang (Western Sumatra, Indonesia) based on recent bathymetry measurements. This highly populated city with over 750,000 inhabitants exhibits high tsunami vulnerability due to its very low elevation. We model tsunamis that might have been induced by the detected landslide events. Estimations of run-up heights extrapolated from offshore tsunami amplitudes for Padang and other locations in the northern Mentawai fore-arc basin yield maximum values of about 3 m. We also provide a systematic parametric study of landslide-induced tsunamis, which allows us to distinguish potentially dangerous scenarios for Padang. Inside the fore-arc basin, scenarios involving volumes of 0.5–25 km³ could endanger Padang. Apart from slide volume, the hazard distribution mainly depends on three landslide parameters: distance to Padang, water depth in the generation region, and slide direction. [ABSTRACT FROM AUTHOR]

The Indonesian archipelago is known for the occurrence of catastrophic earthquake-generated tsunamis along the Sunda Arc. The tsunami hazard associated with submarine landslides however has not been fully addressed. In this paper, we compile the known tsunamigenic events where landslide involvement is certain and summarize the properties of published landslides that were identified with geophysical methods. We depict novel mass movements, found in newly available bathymetry, and determine their key parameters. Using numerical modeling, we compute possible tsunami scenarios. Furthermore, we propose a way of identifying landslide tsunamis using an array of few buoys with bottom pressure units. [ABSTRACT FROM AUTHOR]

To address one of the central questions of plate tectonics—How do large transform systems work and what are their typical features?—seismic investigations across the Dead Sea Transform (DST), the boundary between the African and Arabian plates in the Middle East, were conducted for the first time. A major component of these investigations was a combined reflection/refraction survey across the territories of Palestine, Israel and Jordan. The main results of this study are: (1) The seismic basement is offset by 3–5 km under the DST, (2) The DST cuts through the entire crust, broadening in the lower crust, (3) Strong lower crustal reflectors are imaged only on one side of the DST, (4) The seismic velocity sections show a steady increase in the depth of the crust-mantle transition (Moho) from ∼26 km at the Mediterranean to ∼39 km under the Jordan highlands, with only a small but visible, asymmetric topography of the Moho under the DST. These observations can be linked to the left-lateral movement of 105 km of the two plates in the last 17 Myr, accompanied by strong deformation within a narrow zone cutting through the entire crust. Comparing the DST and the San Andreas Fault (SAF) system, a strong asymmetry in subhorizontal lower crustal reflectors and a deep reaching deformation zone both occur around the DST and the SAF. The fact that such lower crustal reflectors and deep deformation zones are observed in such different transform systems suggests that these structures are possibly fundamental features of large transform plate boundaries. [ABSTRACT FROM AUTHOR]

Due to the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic, a large number of elective knee replacement procedures had to be postponed in both early and late 2020 in most western countries including Germany and the UK. It is unknown how public interest and demand for total knee arthroplasties was affected. Public interest in knee pain, knee osteoarthritis and knee arthroplasty in Germany and the UK was investigated using Google Trend Analysis. In addition, we monitored for changes in patient composition in our outpatient department. As of early March in Germany and of late March in the UK, until the lockdown measures, a 50 to 60% decrease in relative search frequency was observed in all categories investigated compared to the beginning of the year. While public interest for knee pain rapidly recovered, decreased interest for knee osteoarthritis and replacement lasted until the easing of measures. Shortly prior to and during the first lockdown mean search frequency for knee replacement was significantly decreased from 39.7% and 36.6 to 26.9% in Germany and from 47.7% and 50.9 to 23.7% in the UK (Germany: p = 0.022 prior to lockdown, p < 0.001 during lockdown; UK: p < 0.0001 prior to and during lockdown). In contrast, mean search frequencies did not differ significantly from each other for any of the investigated time frames during the second half of 2020 in both countries. Similarly, during the first lockdown, the proportion of patients presenting themselves to receive primary knee arthroplasty compared to patients that had already undergone knee replacement declined markedly from 64.7% to 46.9%. In contrast, patient composition changed only marginally during the lockdown measures in late 2020 in both Germany and the UK. We observed a high level of public interest in knee arthroplasty despite the ongoing pandemic. The absence of a lasting decline in interest in primary knee arthroplasty suggests that sufficient symptom reduction cannot be achieved without surgical care for a substantial number of patients. [ABSTRACT FROM AUTHOR]

Flank instability and sector collapses, which pose major threats, are common on volcanic islands. On 22 Dec 2018, a sector collapse event occurred at Anak Krakatau volcano in the Sunda Strait, triggering a deadly tsunami. Here we use multiparametric ground-based and space-borne data to show that prior to its collapse, the volcano exhibited an elevated state of activity, including precursory thermal anomalies, an increase in the island's surface area, and a gradual seaward motion of its southwestern flank on a dipping décollement. Two minutes after a small earthquake, seismic signals characterize the collapse of the volcano's flank at 13:55 UTC. This sector collapse decapitated the cone-shaped edifice and triggered a tsunami that caused 430 fatalities. We discuss the nature of the precursor processes underpinning the collapse that culminated in a complex hazard cascade with important implications for the early detection of potential flank instability at other volcanoes. On 22 December 2018, the western flank of Anak Krakatau collapsed into the sea of the Sunda Strait triggering a tsunami which killed approximately 430 people and displaced 33,000. Here, the authors show that Anak Krakatau exhibited an elevated state of activity several months prior to the collapse, including precursory thermal anomalies, an increase in the island's surface area, and a gradual seaward motion of the southwestern flank. [ABSTRACT FROM AUTHOR]