Earthquake Tsunami Research Articles

Probabilistic Tsunami Hazard Analysis of the Pacific Coast of Mexico: Case Study Based on the 1995 Colima Earthquake Tsunami

This study develops a novel computational framework to carry out probabilistic tsunami hazard assessment for the Pacific coast of Mexico. The new approach enables the consideration of stochastic tsunami source scenarios having variable fault geometry and heterogeneous slip that are constrained by an extensive database of rupture models for historical earthquakes around the world. The assessment focuses upon the 1995 Jalisco-Colima Earthquake Tsunami from a retrospective viewpoint. Numerous source scenarios of large subduction earthquakes are generated to assess the sensitivity and variability of tsunami inundation characteristics of the target region. Analyses of nine slip models along the Mexican Pacific coast are performed and statistical characteristics of slips (e.g. coherent structures of slip spectra) are estimated. The source variability allows exploring a wide range of tsunami scenarios for a moment magnitude (Mw) 8 subduction earthquake in the Mexican Pacific region to conduct thorough sensitivity analyses and to quantify the tsunami height variability. The numerical results indicate a strong sensitivity of maximum tsunami height to major slip locations in the source, and indicate major uncertainty at the first peak of tsunami waves.

Historical tsunami earthquakes in the Southwest Pacific: an extension to Δ > 80° of the energy-to-moment parameter Θ

Historical tsunami earthquakes in the Southwest Pacific: an extension to Δ > 80° of the energy-to-moment parameter Θ

Tsunami excitation of the Ross Ice Shelf, Antarctica

The responses of the Ross Ice Shelf (RIS) to the September 16, 2015 8.3 Mw Chilean earthquake tsunami (>75 s period) and infragravity (IG) waves (50-300 s period) were recorded by a 34 element broadband seismic array deployed on the RIS for one year from November 2014. Tsunami and IG-generated signals travel from the RIS front as water-ice coupled flexural waves at gravity wave speeds (~70 m/s). Displacements across the RIS are affected by gravity wave incident direction, bathymetry under and north of RIS, and water and ice shelf thickness/properties. Horizontal displacements are about 5 times larger than vertical, producing extensional motions that may facilitate expansion of existing fractures. Excitation is continuously observed throughout the year, with horizontal displacements highest during the austral winter (>20 cm). Because flexural waves exhibit weak attenuation, significant flexural wave energy reaches the grounding zone. Flexural waves provide year-round excitation of the RIS that likely promotes iceberg calving and thus ice shelf evolution. Understanding the ocean-ice shelf mechanical interactions is important to reduce the uncertainty in the global sea level rise.

Development and verification of wall-flap-gate as tsunami inundation defence for nuclear plants

A wall-flap-gate is automatic watertight door, and it works by buoyancy without powered machineries and human operations. In the Tohoku Earthquake tsunamis, serious damages were caused by inundation from ventilators of outer walls in power plants. The wall-flap-gate is estimated to be effective in keeping sustainability of nuclear plants against extreme tsunamis. The present study examines the hydrodynamic characteristics of the wall-flap-gate by hydraulic model experiments and verifies its capability of flood prevention for nuclear plants through various prototype tests.The experimental results proved that the wall-flap-gate had sufficient strength, watertightness, and durability against tsunamis and that its motion was not disturbed by debris. The viability of the wall-flap-gate as an inundation defence structure for nuclear plants was confirmed through this study. As a result, practical wall-flap-gates are installing on Hamaoka nuclear power station in Shizuoka prefecture, Japan.

Simulated tsunami evacuation behavior of local residents and visitors in Kamakura, Japan

Currently, it is believed that evacuation is the most effective method of protecting lives from tsunamis, in particular after the events of the 2011 Tohoku Earthquake Tsunami. In many coastal areas tsunamis pose a threat not only to local residents, who know the area well, but also to visiting tourists, and thus it is important to consider both these groups when preparing evacuation plans. However, while numerous studies and simulations on tsunami evacuation have been made, research focusing on the influence of visitors on evacuation processes is limited. To clarify this the authors developed an agent-based tsunami evacuation model which considers the different behavior of local residents and visitors, which can estimate the evacuation time, number of individuals reaching each evacuation area, the location of bottlenecks and the number of casualties. The model was applied to study the case of Yuigahama Beach, Kamakura, Japan, with results indicating that the behavior and number of visitors have a significant impact on evacuation processes, especially the location of bottlenecks and the number of casualties. Results also show that heavy congestion will occur during evacuation in places where there are many visitors and thus, in such a situation, the decrease of the moving speed owing to the congestion needs to be appropriately taken into account to simulate the evacuation process. It can be concluded that reducing congestion (i.e., widening roads, guiding visitors to less congested roads) is a crucial countermeasure for a sight-seeing location to reduce the casualties that can result from a tsunami.

Ecological and genetic impact of the 2011 Tohoku Earthquake Tsunami on intertidal mud snails

Natural disturbances often destroy local populations and can considerably affect the genetic properties of these populations. The 2011 Tohoku Earthquake Tsunami greatly damaged local populations of various coastal organisms, including the mud snail Batillaria attramentaria, which was an abundant macroinvertebrate on the tidal flats in the Tohoku region. To evaluate the impact of the tsunami on the ecology and population genetic properties of these snails, we monitored the density, shell size, and microsatellite DNA variation of B. attramentaria for more than ten years (2005–2015) throughout the disturbance event. We found that the density of snails declined immediately after the tsunami. Bayesian inference of the genetically effective population size (Ne) demonstrated that the Ne declined by 60–99% at the study sites exposed to the tsunami. However, we found that their genetic diversity was not significantly reduced after the tsunami. The maintenance of genetic diversity is essential for long-term survival of local populations, and thus, the observed genetic robustness could play a key role in the persistence of snail populations in this region which has been devastated by similar tsunamis every 500–800 years. Our findings have significant implications for understanding the sustainability of populations damaged by natural disturbances.

Reconstruction of coseismic slip from the 2015 Illapel earthquake using combined geodetic and tsunami waveform data

AbstractOn 16 September 2015, a moment magnitude (Mw) 8.3 earthquake struck off the coast of central Chile, generating a large tsunami with nearby coastal wave heights observed on tide gauges in Chile and Peru of up to 4.7 m and distal observations of over 40 cm in the Kuril Islands across the Pacific Ocean. Through a transcoastal geodetic study, including tsunami time series recorded at open ocean pressure gauges, subaerial deformation observed through interferometric synthetic aperture radar from the Sentinel‐1 A satellite and continuous GPS, we identify the location and extent of coseismic slip. We find that most coseismic slip was concentrated in a patch immediately offshore, with little modeled slip near the trench. This result satisfies the tsunami waveforms measured in the deep ocean north of the rupture area, with wave heights up to 10 cm. While the event exhibits some features of a slow tsunami earthquake (moderately large tsunami and possible slow second‐stage rupture), our inversion results do not require substantial near‐trench rupture. However, the prevalence of large and shallow thrust along subduction megathrusts along central Chile raises the question of the likelihood of future such events and the implications for future hazardous tsunamigenic earthquakes.

Damage Assessment of Road Bridges Subjected to the 2011 Tohoku Pacific Earthquake Tsunami

The authors assessed the tsunami damage to a girder-type road bridge, focusing on a washed-away deck that failed during the 2011 Tohoku Pacific earthquake tsunami. The inundation depth, ratio of inundation depth to girder elevation, and flow velocity were used as the three indices of the tsunami wave load acting on a road bridge deck. A gently shaped tsunami waveform was selected at a wave-front with a water surface level increase rate of less than 2.0 m/min. The damage ratio was computed for the above three indices, as defined by the number of washed-away bridges divided by the total number of bridges exposed to the tsunami. Based on statistical analysis for the damage ratio data, damage functions using the three indices were proposed. In addition, the spatial distribution of physical wash-away damage to road bridges by the anticipated Nankai Trough earthquake tsunami was shown by applying the derived damage functions.

Development and Application of a Building Group Destruction Probability Model Based on the Great East Japan Earthquake Tsunami Experience

Development and Application of a Building Group Destruction Probability Model Based on the Great East Japan Earthquake Tsunami Experience

東日本大震災における津波観測および港内係留船の被災実態調査に基づく係留限界津波高さの推定

After the 2011 Great east Japan earthquake disaster, many reports on the tsunami profile at ports and disaster surveys on vessels moored in ports along the Pacific Ocean have been published. We also conducted surveys on the sea disasters of several large vessels such as crude oil and coal carriers by reproducing the moored vessel's behavior through a numerical simulation method on ship motions and tsunami. In a judgement of ship refuge action from ports, it is important for ship onboard and fleet management to grasp tsunami information after huge earthquake. In this paper, we have tried to find out a threshold of tsunami wave height for ship-mooring based on surveys on the observed tsunami data and the ship status in the ports during the 2011 Tohoku earthquake tsunami.

A Review of Source Models of the 2015 Illapel, Chile Earthquake and Insights from Tsunami Data

The 16 September 2015 Illapel, Chile, earthquake and associated tsunami have been studied by many researchers from various aspects. This paper reviews studies on the source model of the earthquake and examines tsunami data. The Illapel earthquake occurred in the source region of previous earthquakes in 1943 and 1880. The earthquake source was studied using various geophysical data, such as near-field seismograms, teleseismic waveform and backprojection, GPS and InSAR data, and tsunami waveforms. Most seismological analyses show a duration of ~100 s with a peak at ~50 s. The spatial distribution has some variety, but they all have the largest slip varying from 5 to 16 m located at 31°S, 72°W, which is ~70 km NW of the epicenter. The shallow slip seems to be extended to the trench axis. A deeper slip patch was proposed from high-frequency seismic data. A tsunami earthquake model with a total duration of 250 s and a third asperity south of the epicenter is also proposed, but we show that the tsunami data do not support this model.

Regional long-period magnitude scales and their capabilities for tsunami warning

The tsunami warning system in the Russian Far East employs the medium-period magnitude MS (BB) by Vaniek–Soloviev. However, its use may lead to inadequacies and underestimates for the tsunamigenic potential of an earthquake. Specifically, this can happen in the case of a so-called tsunami–earthquake. This kind of earthquakes with a nonstandard spectrum was revealed by H. Kanamori in 1972. This problem can be overcome by using a magnitude scale that deals with longer period seismic waves. This study develops a technique for determining the magnitudes at regional distances (from 70 to 4500 km) using the amplitudes of surface seismic waves of periods of 40 and 80 s. At distances of 70–250 km, the amplitude of the joint group of shear and surface waves is used. For the new magnitudes designated M S(40) and M S(80), experimental calibration curves are constructed using more than 1250 three-component records at 12 stations of the region. The magnitudes are calibrated so as to produce an unbiased estimate of the moment magnitude M w in the critical range 7.5–8.8. The rms error of the single-station estimate M w is around 0.27. At distances below 250 km and M w ≥ 8.3, the estimate of M w obtained by the proposed technique becomes saturated at the level of M w ~ 8.3, which is acceptable for operative analysis because no missed alarms arise. The technique can be used in operational tsunami warning based on seismological data. This can markedly decrease the number of false alarms.

Study on the Evaluation of Temporal Change in Horizontal and Vertical Tsunami Forces Acting on a Bridge Superstructure

Bridge superstructures were washed away in the 2011 Tohoku earthquake tsunami. To determine whether and when bridge superstructures are washed away, it is essential to evaluate the temporal change in horizontal and vertical tsuneimi forces. In this study, tsunami force acting on bridge superstructures and its estimation formulae are investigated from hydraulic model experiments and numerical simulations. Prom experimented results, it is found that it can be determined from a comparison between the temporal change in horizontal tsuneimi force and that in static friction force taking into account vertical tsunami force whether and when a bridge superstructure move. Furthermore, a drag force equation with the projection area taking into account water surface elevation and a Morison equation in which inertia force is added to the drag force equation are proposed for horizontal tsunami force, and an estimation formula composed of buoyancy force and downward lift force is proposed for vertical tsunami force. From a comparison with numerical results, it was revealed that the estimation formulae can predict the temporal change in the horizontal and vertical tsunami forces except for short wave period, suggesting that it can be evaluated using the estimation formulae whether and when a bridge superstructures moves.

Coastal Morphology Change Before and After 2011 Off the Pacific Coast of Tohoku Earthquake Tsunami at Rikuzen-Takata Coast

This study investigates the changes in coastal topography of the Rikuzen-Takata Coast in Iwate Prefecture, Japan before and after the 2011 off the Pacific coast of Tohoku Earthquake Tsunami and the effects of coastal structures on these changes. The changes in coastal topography were analyzed using bathymetry data and aerial photographs before and after the tsunami in addition to aerial video during the tsunami. The bathymetry data were obtained from 1989 to 2002 during the construction of three submerged breakwaters and from after the 2011 tsunami until 2013. The aerial photographs were acquired from 1947 to 2015, and the aerial videos were acquired during the tsunami run-up and backwash. The results demonstrated that the coast was eroded mainly due to the tsunami backwash, and the submerged breakwaters trapped the seaward transport of sediment from the coast. Erosion was partly prevented in locations where the seawall was not washed away. The coastal structures had significant effects on the behavior of the coastal tsunami and on sediment transport. We also found that the coast did not recover naturally at the desired speed after the tsunami because the coast had been stable before the tsunami. Coastal restoration five years after the 2011 tsunami are also summarized in the Appendix to illustrate the future reconstruction plan for the study coast.

Innovation for Resilient Coastal Structures to Reduce Tsunami Disaster

The Great East Japan Earthquake Tsunami on March 11, 2011, caused unprecedented damage mainly in northeast Japan. This paper introduces the characteristics of the tsunami and resultant damage. The mechanism of the breaching of coastal structures and the effect of surviving structures on damage reduction in land are discussed. Then, a two-level tsunami mitigation concept, proposed and adopted by a committee hosted by the Government for recovery and reconstruction, is introduced. Within this framework, coastal structures are required to be resilient to external forces exceeding the design level. Various technologies that have been developed based on experience and research after the tsunami are introduced.

Numerical Simulations of Large-Scale Sediment Transport Caused by the 2011 Tohoku Earthquake Tsunami in Hirota Bay, Southern Sanriku Coast

A numerical sediment transport model (STM) was used to investigate coastal geomorphic changes that resulted from the 2011 Tohoku earthquake tsunami in Rikuzentakata City and Hirota Bay on the southern Sanriku Coast of Japan. The simulation was verified using observed inundation processes and heights, measured topographic changes and sediment deposition. Aerial video footage recorded by the Iwate Prefectural Police was also used. The results show that the numerical model was able to predict the spatial distribution and volume of erosion and deposition in Hirota Bay, as well as sediment transport processes. The effects of sediment transport on tsuneimi inundation were also investigated. Numerical results revealed that the majority of the sand dunes were eroded by the first wave, especially during the strong return flow of the receding wave. Large flows and sand dune erosions can occur elsewhere if tsunamis inundate a plain with a limited shore-normal width. These events could cause large-scale morphological changes comparable to those that occurred in Rikuzentakata City.

Experimental Study on Embankment Reinforcement by Steel Sheet Pile Structure Against Tsunami Overflow

This study proposes a new embankment reinforcement using steel sheet piles against tsunami overflow, which has been known as the main cause of the failures of the embankments by the 2011 Tohoku Earthquake Tsunami. Effectiveness of the proposed technique was discussed through a hydraulic experiment. A model of embankment was set in a horizontal open channel, and one or two steel plates are installed into the embankment from the top as vertical walls inside. Temporal variations of the shapes of the embankment and the sheet pile structures were obtained from video images. In most of the cases, the sheet pile structures started to rotate after the erosion of the landward slope of the embankment. However the rotation stopped at about 30° and 10° from the initial location with the single- and double-wall cases. Height of the embankment after overflow was less than 20% with no reinforcement, while more than 70% and 95% of the height were kept with the single- and double-wall structures, respectively. The performance of the embankment with the reinforcement was also discussed in terms of tsunami energy reduction with an additional fixed-bed experiment.

The effect of compliant prisms on subduction zone earthquakes and tsunamis

Earthquakes generate tsunamis by coseismically deforming the seafloor, and that deformation is largely controlled by the shallow rupture process. Therefore, in order to better understand how earthquakes generate tsunamis, one must consider the material structure and frictional properties of the shallowest part of the subduction zone, where ruptures often encounter compliant sedimentary prisms. Compliant prisms have been associated with enhanced shallow slip, seafloor deformation, and tsunami heights, particularly in the context of tsunami earthquakes. To rigorously quantify the role compliant prisms play in generating tsunamis, we perform a series of numerical simulations that directly couple dynamic rupture on a dipping thrust fault to the elastodynamic response of the Earth and the acoustic response of the ocean. Gravity is included in our simulations in the context of a linearized Eulerian description of the ocean, which allows us to model tsunami generation and propagation, including dispersion and related nonhydrostatic effects. Our simulations span a three-dimensional parameter space of prism size, prism compliance, and sub-prism friction – specifically, the rate-and-state parameter b−a that determines velocity-weakening or velocity-strengthening behavior. We find that compliant prisms generally slow rupture velocity and, for larger prisms, generate tsunamis more efficiently than subduction zones without prisms. In most but not all cases, larger, more compliant prisms cause greater amounts of shallow slip and larger tsunamis. Furthermore, shallow friction is also quite important in determining overall slip; increasing sub-prism b−a enhances slip everywhere along the fault. Counterintuitively, we find that in simulations with large prisms and velocity-strengthening friction at the base of the prism, increasing prism compliance reduces rather than enhances shallow slip and tsunami wave height.

The kinematics of crustal deformation in Java from GPS observations: Implications for fault slip partitioning

Our understanding of seismic risk in Java has been focused primarily on the subduction zone, where the seismic records during the last century have shown the occurrence of a number of tsunami earthquakes. However, the potential of the existence of active crustal structures within the island of Java itself is less well known. Historical archives show the occurrence of several devastating earthquake ruptures north of the volcanic arc in west Java during the 18th and the 19th centuries, suggesting the existence of active faults that need to be identified in order to guide seismic hazard assessment. Here we use geodetic constraints from the Global Positioning System (GPS) to quantify the present day crustal deformation in Java. The GPS velocities reveal a homogeneous counterclockwise rotation of the Java Block independent of Sunda Block, consistent with a NE–SW convergence between the Australian Plate and southeast Asia. Continuous GPS observations show a time-dependent change in the linear rate of surface motion in west Java, which we interpret as an ongoing long-term post-seismic deformation following the 2006 Mw 7.7 Java earthquake. We use an elastic block model in combination with a viscoelastic model to correct for this post-seismic transient and derive the long-term inter-seismic velocity, which we interpret as a combination of tectonic block motions and crustal faults strain related deformation. There is a north–south gradient in the resulting velocity field with a decrease in the magnitude towards the North across the Kendeng Thrust in the east and the Baribis Thrust in the west. We suggest that the Baribis Thrust is active and accommodating a slow relative motion between Java and the Sunda Block at about 5±0.2 mm/yr. We propose a kinematic model of convergence of the Australian Plate and the Sunda Block, involving a slip partitioning between the Java Trench and a left-lateral structure extending E–W along Java with most of the convergence being accommodated by the Java megathrust, and a much smaller parallel motion accommodated along the Baribis (∼5±0.2 mm/yr) and Kendeng (∼2.3±0.7 mm/yr) Thrusts. Our study highlights a correlation between the geodetically inferred active faults and historical seismic catalogs, emphasizing the importance of considering crustal fault activity within Java in future seismic assessments.

Effects of dispersion in tsunami Green's functions and implications for joint inversion with seismic and geodetic data: A case study of the 2010 Mentawai Mw 7.8 earthquake

AbstractTsunami observations play an important role in resolving offshore earthquake slip distributions. Nondispersive shallow‐water models are often used with a static initial sea surface pulse derived from seafloor deformation in computation of tsunami Green's functions. We compare this conventional approach with more advanced techniques based on a dispersive model with a static initial sea surface pulse and with the surface waves generated from kinematic seafloor deformation. These three sets of tsunami Green's functions are implemented in finite‐fault inversions with and without seismic and geodetic data for the 2010 Mentawai Mw 7.8 tsunami earthquake. Seafloor excitation and wave dispersion produce more spread‐out waveforms in the Green's functions leading to larger slip with more compact distribution through the inversions. The fit to the recorded tsunami and the deduced seismic moment, which reflects the displaced water volume, are relatively insensitive to the approach used for computing Green's functions.