Tsunami Source Research Articles

Simulation of the Submarine Landslide Tsunami on 28 September 2018 in Palu Bay, Sulawesi Island, Indonesia, Using a Two-Layer Model

The strike-slip earthquake on 28 September 2018 (Mw 7.5) along the Palu-Koro fault on Sulawesi Island has raised concerns about the potential impact of tsunamis generated by submarine landslides in Palu Bay, Indonesia. The horizontal displacement of the Palu-Koro fault generated landslide tsunamis that covered Palu Bay, creating wave-related hazards along the coastal area. Based on the unusual amount of information on this tsunami, this study investigated possible sources using the available preliminary data. The generation of comparatively small tsunamis by coseismic seafloor deformation is omitted, and only tsunamis generated by submarine/subaerial landslides are analyzed in this study. Two-layer modeling (soil and water) based on the shallow-water equation was used to simulate the tsunami propagation in the bay with severe, moderate, and minor impacts. The accuracy of the model was validated based on the waveform at the Pantoloan tidal gauge and trace data. The tsunami heights from a combination of small to large submarine landslides could reach up to 3.0–7.0 m along the Palu shores. This model focused on studying the effects of the tidal level on coastal inundation in Palu Bay, using the 2018 Palu tsunami event as a benchmark scenario, to demonstrate the capabilities of the model. One result shows that, regardless of the tidal level, the 2018 Palu tsunami, which occurred during high tide, will always result in flooding, with a maximum tsunami height of up to 7.0 m above mean sea level. The main results suggest two causes for this tsunami event: the tsunami source and the topography. First, the model requires one large source at the bay entrance to reproduce the arrival time (approximately 5 min) and the large wave observed at the Pantoloan gauge. To reproduce the later waves, small sources in the bay (S1–S6) and minor large sources (L2 and L3) are needed. Second, the datum correction for the terrain is changed to improve the accuracy of the water level. Additionally, the removal of buildings from the topography is important to achieve highly accurate flow depths and to obtain an inundation area close to the real situation. The impacts along the coastline of Palu Bay from peak waves can be used to identify tsunami hazards in the area in the future.

Postseismic fluid discharge chemically recorded in altered pseudotachylyte discovered from an ancient megasplay fault: an example from the Nobeoka Thrust in the Shimanto accretionary complex, SW Japan

Megasplay fault branching from plate boundaries of subduction zones is thought to be important sources of earthquakes and tsunamis. In this study, we performed structural and geochemical analyses on a fossilized megasplay fault (the Nobeoka Thrust of the Shimanto accretionary complex) to understand fluid-rock interaction and how the splay fault plays a role in fluid flow in the seismogenic zone. As a result of structural observations, we report that the principal slip zone (PSZ) of the Nobeoka Thrust is composed of foliated cataclasite originating from a sandstone-shale mélange and includes a thin (~ 1.5 mm thick) pseudotachylyte layer. Major and trace element composition analysis and EPMA element mapping revealed that the pseudotachylyte is enriched in Li and Cs within the PSZ, as well as in the slip zone of a minor fault in the footwall. Li and Cs enrichment in pseudotachylyte is interpreted as a result of fluid-rock interaction in the postseismic stage, because such an anomaly only results from a large fluid/rock ratio (R > 512–24 at 250–350 °C) under the influence of Li- and Cs-enriched fluids. The amount of fluid that reacted with the pseudotachylyte is estimated to be 1.78 × 100 to 7.61 × 103 m3.

Tsunamigenic Splay Faults Imply a Long‐Term Asperity in Southern Prince William Sound, Alaska

AbstractCoseismic slip partitioning and uplift over multiple earthquake cycles is critical to understanding upper‐plate fault development. Bathymetric and seismic reflection data from the 1964 Mw9.2 Great Alaska earthquake rupture area reveal sea floor scarps along the tsunamigenic Patton Bay/Cape Cleare/Middleton Island fault system. The faults splay from a megathrust where duplexing and underplating produced rapid exhumation. Trenchward of the duplex region, the faults produce a complex deformation pattern from oblique, south‐directed shortening at the Yakutat‐Pacific plate boundary. Spatial and temporal fault patterns suggest that Holocene megathrust earthquakes had similar relative motions and thus similar tsunami sources as in 1964. Tsunamis during future earthquakes will likely produce similar run‐up patterns and travel times. Splay fault surface expressions thus relate to plate boundary conditions, indicating millennial‐scale persistence of this asperity. We suggest structure of the subducted slab directly influences splay fault and tsunami generation landward of the frontal subduction zone prism.

The Impact of Post-tsunami Surveys on the NCEI/WDS Global Historical Tsunami Database

Since the late nineteenth century, post-tsunami survey teams have been collecting water height data (e.g. maximum inundation, runup, flow depth) as well as other types of data, including geologic and socio-economic effects. The NOAA National Centers for Environmental Information (NCEI) and co-located World Data Service (WDS) for Geophysics provide data management and access to global tsunami data. NCEI’s Global Historical Tsunami Database includes information on over 2200 tsunami sources and over 26,000 runup points. The tsunami database has adapted to capture the advancements of post-tsunami survey data collection and distribution methods. The first International Tsunami Survey Team (ITST), which surveyed the impacts of the 02 September 1992 Nicaragua tsunami, spurred the formalization of standards and guidance for post-tsunami surveys. The post-tsunami survey data analyzed are a significant contribution, in quality and quantity, to the runup database. The 26 December 2004 Indonesia and 11 March 2011 Japan events alone account for over 25% of the total number of runup points in the database. Further, the analysis indicates that post-tsunami survey data capture a more complete representation of the tsunami that is being documented, not just the highest runup measurements. This range in post-tsunami survey runup heights for events, in the NCEI/WDS tsunami database, provides a more reliable historical tsunami dataset to test tsunami models against. This study also provides readers an understanding of the evolution of the tsunami database, particularly regarding the ongoing need to adapt to emerging scientific advances and standards.

Revealing the Source of the 27 August 1810 Loreto, Baja California, Tsunami from Historical Evidence and Numerical Modelling

Historical documents revealed that on 27 August 1810 an earthquake affected the Loreto town and the surrounding region, along 200 km of the coast of Baja California, Mexico, and damage was considerable due to strong ground motions. However, the 1810 Loreto earthquake, unlike other earthquakes of the nineteenth and twentieth centuries, produced an extensive tsunami flooding on the eastern coast of Baja California, from Loreto to La Paz. We report here the historical account of this event and analyse the source of the related tsunami. Based on the historical record and the tectonic setting, we infer that this earthquake was produced along a transform fault, right-lateral strike slip fault, Farallon fault, on the Baja California Gulf. However, the associated tsunami was disproportionally large if compared with the earthquake intensity (IX) and approximate magnitude (7.4 Mw), fault style, and the relatively late tsunami arrival, i.e. an hour after the earthquake, suggesting that a submarine landslide, triggered by this earthquake, was the suspect source for the Loreto tsunami. We present here historical data and a numerical model of the Loreto 1810 tsunami to elucidate the source, using both the 1810 earthquake and a submarine landslide, and confirm that a submarine landslide is most likely the tsunami-triggering mechanism that followed the 1810 earthquake.

Tsunami hazard assessment for atoll islands inside the South China Sea: A case study of the Xisha Archipelago

The potential tsunami hazard for atoll islands inside the South China Sea (SCS) has not been investigated previously. In this study, we assess the tsunami hazard for the Xisha Archipelago using a deterministic approach. The tsunami source considered in this study is hypothesized earthquakes in the Manila subduction zone. We employ COMCOT (COrnell Multi-grid Coupled Tsunami model) for tsunami simulations. Different with previous deterministic assessments, our study investigates the uncertainties caused by bathymetric resolution and rupture complexities (here refers to rupture speed and direction variations related to fault geometry complexity). Comparison between results of different resolution suggests that coarser grids may over/underestimate tsunami hazards around mid-ocean atoll islands and this depends on the surrounding bathymetry. But results of different datasets show that GEBCO may lead to a lower result than the multibeam data. We also investigate the uncertainties caused by different rupture speed and direction, which are highly affected by subducting seamounts/ridge. Different rupture direction will shift the hardest hit locations to areas, which are possibly underestimated in cases of instantaneous ruptures. Also, the distribution of slip and location of the rupture zone can affect the local tsunami wave height significantly. We suggest that near-island high-resolution bathymetric data and dynamic rupture process should be considered in future tsunami hazard assessment in locations with similar geological structures.

Changes in Tsunami Risk to Residential Buildings at Omaha Beach, New Zealand

Coastal settlements worldwide have suffered significant damage and loss to tsunami hazards in the last few decades. This period coincides with socio-economic changes that have heightened spatio-temporal risk through increased coastal development and infrastructure. In this study, we apply a spatio-temporal loss model to quantify the changes in direct economic losses to residential buildings from tsunami hazards over a 20-year period in Omaha Beach, New Zealand. The approach reconstructed temporal urban settlement patterns (1992, 1996, 2006 and 2012) for an area potentially exposed to regional source tsunami inundation hazard. Synthetic depth–damage functions for specific building classes were applied to estimate temporal damage and loss from tsunami inundation exposure at each building location. Temporal loss estimates were reported for a range of risk metrics, including probable maximum loss, loss exceedance and average annual loss. The results showed that an increase in the number of buildings and changes to building design (i.e., storeys, floor area, foundations) influenced the increasing risk to direct economic loss over the study period. These increases were driven by conversion from rural to urban land use since 1996. The spatio-temporal method presented in this study can be adapted to analyse changing risk patterns and trends for coastal settlements to inform future tsunami mitigation measures and manage direct economic losses.

Development and Utilization of Real-Time Tsunami Inundation Forecast System Using S-net Data

It is important to advance preparation for a tsunami disaster, one of the great concerns in Japan. Forecasting tsunami inundation is one such solution, which contributes to perceiving the danger of the tsunami, as the inundation is directly linked with the damage. Therefore, we developed a new real-time tsunami forecast system, aimed at rapidly and accurately forecasting tsunami inundation on land, based on offshore tsunami data observed by the seafloor observation network along the Japan Trench, S-net. The developed system takes a database approach. A database called a tsunami scenario bank was constructed by assuming all the possible tsunami sources affecting the target region and simulating offshore pressure data, coastal tsunami heights, and tsunami inundation. The forecast system searches for suitable tsunami scenarios whose offshore pressure data explain the observed data, based on the multi-index method. The multi-index method can evaluate the resemblance of offshore pressure data by using three indices, which are sensitive to different aspects of the pressure change distribution. When tsunami scenarios meet the criteria of the multi-index method, the system provides forecast information generated from coastal tsunami heights and tsunami inundation of the selected scenarios. A prototype system was constructed for the Pacific coastal region of Chiba prefecture as a target region and has been updated through a test operation. We also investigated the comprehensible visualization and effective disaster response using tsunami forecast information. Through workshops and tabletop exercises with local government officers using the forecast system, timelines and local disaster management plans for tsunamis were tested and revised. This led to the establishment of a standard operating procedure for tsunami disaster response through the use of tsunami observation and forecast information.

The September 28th, 2018, Tsunami In Palu-Sulawesi, Indonesia: A Post-Event Field Survey

On September 28th, 2018, a powerful earthquake (Mw 7.5) struck the Island of Sulawesi in Indonesia. The earthquake was followed by a destructive and deadly tsunami that hit the Bay of Palu. A UNESCO international tsunami survey team responded to the disaster and surveyed 125 km of coastline along the Palu Bay up to the earthquake epicentre region. The team performed 78 tsunami runup and inundation height measurements throughout the surveyed coastline. Measured values reached 9.1 m for the runup height and 8.7 m for the inundation height, both at Benteng village. The survey team also identified ten large coastal sectors that collapsed into the sea of Palu Bay after the earthquake. The distribution of the measured tsunami data within Palu Bay exhibits a clear localised impact suggesting the contribution of secondary non-seismic local sources to the generation of the tsunami. Findings of the field reconnaissance are discussed to provide an insight into the remaining debated source of the Palu tsunami.

Tsunami Data Assimilation Without a Dense Observation Network

AbstractThe tsunami data assimilation method enables tsunami forecasting directly from observations, without the need of estimating tsunami sources. However, it requires a dense observation network to produce desirable results. Here we propose a modified method of tsunami data assimilation for regions with a sparse observation network. The method utilizes interpolated waveforms at virtual stations. The tsunami waveforms at the virtual stations between two existing observation stations are estimated by shifting arrival times with the linear interpolation of observed arrival times and by correcting the amplitudes for their water depths. In our new data assimilation approach, we employ the Optimal Interpolation algorithm to both the real observations and virtual stations, in order to construct a complete wavefront of tsunami propagation. The application to the 2004 Sumatra‐Andaman earthquake and the 2009 Dusky Sound, New Zealand, earthquake reveals that addition of virtual stations greatly helps improve the tsunami forecasting accuracy.

A numerical study on nearshore behavior of Japan Sea tsunamis using Green’s functions for Gaussian sources based on linear Boussinesq theory

ABSTRACT The aim of this study is to estimate how and what kinds of tsunamis are generated near shorelines in the Japan Sea, using earthquake tsunami sources proposed by the Japanese government. Tsunami propagation based on these sources was first simulated based on the linear Boussinesq theory for Miho Bay, where a historical tsunami inundated the shoreline. The results indicate that tsunami sources not only near the bay but also farther from the bay could generate significant tsunami fluctuations. Thus, the amplification of the latter tsunamis was examined using Fourier analysis. Tsunami waveforms in the bay periodically fluctuate with large amplitudes after the first wave. The Fourier analysis specified these periods to be 13–16 min, consistent with the estimated resonance periods of the bay. Therefore, it can be concluded that one of the factors responsible for the amplification of tsunamis in Miho Bay is the bay-scale resonance. To investigate why resonance occurs during tsunamis, a relationship between the tsunami source geometry and the generated tsunami was examined. This analysis indicates that specific tsunami sources located in critical areas could enhance the resonance in Miho Bay.

Modeling the large runup along a narrow segment of the Kaikoura coast, New Zealand following the November 2016 tsunami from a potential landslide

The 2016 Mw 7.8 Kaikoura earthquake and consequent tsunami have been controversial because of uncertainty over whether and where the plate interface ruptured and the incapability of the proposed source models to reproduce the near-field runup of 7 m. Existing models identify a wide range of locations for the interface rupture, from on land to offshore, and fail to reproduce runup of 7 m near Kaikoura. To generate the large tsunami peak in Kaikoura tide gauge record and the observed runup height, offshore seafloor movement is necessary, but the offshore extension of the plate-interface rupture and its type, either seismic rupture or a landslide, is uncertain. Here, we propose a submarine landslide in addition to the earthquake source, with the landslide delayed 10–20 min after the earthquake rupture. The landslide volume is 4.5–5.2 km3, located within 173.7–174.3oE (longitude) and 42.6–42.15oS (latitude). Our proposed dual tsunami source successfully reproduces near-field tide gauge records as well as observed near-field runup height of 7 m. We showed that more accurate source models of earthquakes can be achieved by considering observed runup data through runup inversions in addition to waveform inversions.

Tsunamigenic potential of a Holocene submarine landslide along the North Anatolian Fault (northern Aegean Sea, off Thasos island): insights from numerical modelling

Abstract. The North Anatolian Fault in the northern Aegean Sea triggers frequent earthquakes of magnitudes up to Mw∼7. This seismicity can be a source of modest tsunamis for the surrounding coastlines with less than 50 cm height according to numerical modelling and analysis of tsunami deposits. However, other tsunami sources may be involved, like submarine landslides. We assess the severity of this potential hazard by performing numerical simulations of tsunami generation and propagation from a Holocene landslide (1.85 km3 in volume) identified off Thasos. We use a model coupling the simulation of the submarine landslide, assimilated to a granular flow, to the propagation of the tsunami wave. The results of these simulations show that a tsunami wave of water height between 1.10 and 1.65 m reaches the coastline at Alexandroupoli (58 000 inhabitants) 1 h after the triggering of the landslide. In the same way, tsunami waves of water height between 0.80 and 2.00 m reach the coastline of the Athos peninsula 9 min after the triggering of the landslide. Despite numerous earthquakes of Mw>7 and strong detrital input (on the order of 30 cm ka−1), only a few Holocene landslides have been recognized so far, asking for tsunami recurrence in this area.

Ionospheric GNSS Imagery of Seismic Source: Possibilities, Difficulties, and Challenges.

Up to now, the possibility to obtain images of seismic source from ionospheric Global Navigation Satellite Systems (GNSS) measurements (seismo‐ionospheric imagery) has only been demonstrated for giant earthquakes with moment magnitude Mw ≥ 9.0. In this work, we discuss difficulties and restrictions of this method, and we apply for the first time the seismo‐ionospheric imagery for smaller earthquakes. The latter is done on the example of the Mw7.4 Sanriku‐oki earthquake of 9 March 2011. Analysis of 1‐Hz data of total electron content (TEC) shows that the first coseismic ionospheric disturbances (CID) occur ~470–480 s after the earthquake as TEC enhancement on the east‐northeast from the epicenter. The location of these first CID arrivals corresponds to the location of the coseismic uplift that is known as the source of tsunamis. Our results confirm that despite several difficulties and limitations, high‐rate ionospheric GNSS data can be used for determining the seismic source parameters for both giant and smaller/moderate earthquakes. In addition to these seismo‐ionospheric applications, we raise several fundamental questions on CID nature and evolution, namely, one of the most challenging queries—can moderate earthquake generate shock‐acoustic waves?

Re-examination of the Tsunami Source Model of the 2011 off Pacific coast of Tohoku Earthquake

Re-examination of the Tsunami Source Model of the 2011 off Pacific coast of Tohoku Earthquake

Tsunami source estimation for the 2011 off the Pacific coast of Tohoku Earthquake using thickness distribution of tsunami deposits in a wide area

Tsunami source estimation for the 2011 off the Pacific coast of Tohoku Earthquake using thickness distribution of tsunami deposits in a wide area

日本海東縁部における広域的地殻構造境界の津波波源の設定

日本海東縁部における広域的地殻構造境界の津波波源の設定

New map of tsunami-hazard for the south Kuril Islands

The tsunami-zoning map (possible tsunami heights of a frequency of 1 event within 50 and 100 years) for the coast of the South Kuril Islands have been updated (former map have been developed in 2006). The update is based on the development of the tsunami-activity model, mainly due to the increase of the number of basic coastal locations (from 18 to 62) for which the parameters of the recurrence function were estimated, as well as on the modernization of the numerical model. Serious progress in simulations was achieved in setting the initial conditions, using the seismic tsunami source model. Field surveys on the coast to search for traces of historical and paleotsunami, as well as qualitative documentation of the Tohoku tsunami manifestations allowed to clarify the model of tsunami-activity in Southern Kuril Islands. The sufficiently large amount of data in this case (which is generally untypical for the tsunami) allowed authors, to apply the statistical approach for evaluation of the tsunami hazard distribution along the coast. Estimates of tsunami heights were spread from the basic coastal locations to adjacent parts of the coast using detailed simulation of all significant tsunamis and calculating wave heights at the shoreline. The detailed maps of tsunami-hazard at scale 1:100,000 have been made for the settlements of Yuzhno-Kurilsk, Kurilsk, Malokurilskoe, and Krabozavodskoe.

SUBMARINE MASS FAILURE: WAVE GENERATION BY GRANULAR SLIDES

Submarine mass failures (SMF) are a potential source of hazardous tsunamis. While the link between seismic events and the magnitude of tsunami waves has been extensively studied and corresponding approaches are included in numerical tsunami warning models, the basic implementation of SMF generated waves is subject to ongoing research. In this context, laboratory experiments are essential for the validation of numerical schemes. Most experimental studies apply rigid slide models whereas only few include granular slides (e.g. Watts 1997, Ataie-Ashtiani & Najafi-Jilani 2008, Grilli et al. 2017). The objective of this study is to gain a better insight into the hydraulic processes related to wave generation by submarine granular slides based on experiments as well as establishing a comprehensive data set for the validation of numerical models.

DEVELOPMENT OF MULTISCALE MULTIPHYSICS INTEGRATED SIMULATOR FOR TSUNAMI RUNUP CALCULATION COUPLED WITH STRUCTURE ANALYSIS

The 2011 Great East Japan Earthquake (GEJE) has shown that Tsunami disasters not only cause flooding damage but also can be a phenomenon accompanied by many damage of structures. In order to evaluate the damage of the building due to the tsunami, a three dimensional numerical tank with structure analysis is required, but the calculation cost is very high to calculate from the tsunami source of the tsunami to the inundation zone. Therefore, the purpose of this research is to develop a system that can calculate the destruction of buildings from a wave source of the tsunami in a series and confirm its validity. Specifically, the stability of Tsunami breakwaters in Kamaishi Bay and the seawalls in Otsuchi Bay was investigated.