The Role of Frontal Thrusts in Tsunami Earthquake Generation

2021 ◽  
Author(s):  
Raquel P. Felix ◽  
Judith A. Hubbard ◽  
James D. P. Moore ◽  
Adam D. Switzer
Keyword(s):  
Subduction Zones ◽  
Generation Process ◽  
Lower Amplitude ◽  
Tsunami Earthquakes ◽  
Fault Bend ◽  
Wave Heights ◽  
Seafloor Deformation ◽  
Tsunami Earthquake ◽  
Tsunami Energy ◽  
The Impact

ABSTRACT The frontal sections of subduction zones are the source of a poorly understood hazard: “tsunami earthquakes,” which generate larger-than-expected tsunamis given their seismic shaking. Slip on frontal thrusts is considered to be the cause of increased wave heights in these earthquakes, but the impact of this mechanism has thus far not been quantified. Here, we explore how frontal thrust slip can contribute to tsunami wave generation by modeling the resulting seafloor deformation using fault-bend folding theory. We then quantify wave heights in 2D and expected tsunami energies in 3D for both thrust splays (using fault-bend folding) and down-dip décollement ruptures (modeled as elastic). We present an analytical solution for the damping effect of the water column and show that, because the narrow band of seafloor uplift produced by frontal thrust slip is damped, initial tsunami heights and resulting energies are relatively low. Although the geometry of the thrust can modify seafloor deformation, water damping reduces these differences; tsunami energy is generally insensitive to thrust ramp parameters, such as fault dip, geological evolution, sedimentation, and erosion. Tsunami energy depends primarily on three features: décollement depth below the seafloor, water depth, and coseismic slip. Because frontal ruptures of subduction zones include slip on both the frontal thrust and the down-dip décollement, we compare their tsunami energies. We find that thrust ramps generate significantly lower energies than the paired slip on the décollement. Using a case study of the 25 October 2010 Mw 7.8 Mentawai tsunami earthquake, we show that although slip on the décollement and frontal thrust together can generate the required tsunami energy, <10% was contributed by the frontal thrust. Overall, our results demonstrate that the wider, lower amplitude uplift produced by décollement slip must play a dominant role in the tsunami generation process for tsunami earthquakes.

scholarly journals Rapid estimation of tsunami earthquake magnitudes at local distance

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Akio Katsumata ◽  
Masayuki Tanaka ◽  
Takahito Nishimiya
Keyword(s):  
Magnitude Estimation ◽  
Seismic Wave ◽  
Seismic Waves ◽  
Wave Amplitude ◽  
Amplitude Distribution ◽  
Distribution Method ◽  
Finite Fault ◽  
Tsunami Earthquakes ◽  
Tsunami Earthquake ◽  
The Moment

AbstractA tsunami earthquake is an earthquake event that generates abnormally high tsunami waves considering the amplitude of the seismic waves. These abnormally high waves relative to the seismic wave amplitude are related to the longer rupture duration of such earthquakes compared with typical events. Rapid magnitude estimation is essential for the timely issuance of effective tsunami warnings for tsunami earthquakes. For local events, event magnitude estimated from the observed displacement amplitudes of the seismic waves, which can be obtained before estimation of the seismic moment, is often used for the first tsunami warning. However, because the observed displacement amplitude is approximately proportional to the moment rate, conventional magnitudes of tsunami earthquakes estimated based on the seismic wave amplitude tend to underestimate the event size. To overcome this problem, we investigated several methods of magnitude estimation, including magnitudes based on long-period displacement, integrated displacement, and multiband amplitude distribution. We tested the methods using synthetic waveforms calculated from finite fault models of tsunami earthquakes. We found that methods based on observed amplitudes could not estimate magnitude properly, but the method based on the multiband amplitude distribution gave values close to the moment magnitude for many tsunami earthquakes. In this method, peak amplitudes of bandpass filtered waveforms are compared with those of synthetic records for an assumed source duration and fault mechanism. We applied the multiband amplitude distribution method to the records of events that occurred around the Japanese Islands and to those of tsunami earthquakes, and confirmed that this method could be used to estimate event magnitudes close to the moment magnitudes.

scholarly journals Late Pleistocene Boulder Slumps Eroded from a Basalt Shoreline at El Confital Beach on Gran Canaria (Canary Islands, Spain)

2021 ◽  
Vol 9 (2) ◽  
pp. 138
Author(s):  
Inés Galindo ◽  
Markes E. Johnson ◽  
Esther Martín-González ◽  
Carmen Romero ◽  
Juana Vegas ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Historical Record ◽  
Three Dimensions ◽  
Marine Biota ◽  
Gran Canaria ◽  
Basaltic Rocks ◽  
Individual Wave ◽  
Wave Heights ◽  
Scientific Value ◽  
The Impact

This study examines the role of North Atlantic storms degrading a Late Pleistocene rocky shoreline formed by basaltic rocks overlying hyaloclastite rocks on a small volcanic peninsula connected to Gran Canaria in the central region of the Canary Archipelago. A conglomerate dominated by large, ellipsoidal to angular boulders eroded from an adjacent basalt flow was canvassed at six stations distributed along 800 m of the modern shore at El Confital, on the outskirts of Las Palmas de Gran Canaria. A total of 166 individual basalt cobbles and boulders were systematically measured in three dimensions, providing the database for analyses of variations in clast shape and size. The goal of this study was to apply mathematical equations elaborated after Nott (2003) and subsequent refinements in order to estimate individual wave heights necessary to lift basalt blocks from the layered and joint-bound sea cliffs at El Confital. On average, wave heights in the order of 4.2 to 4.5 m are calculated as having impacted the Late Pleistocene rocky coastline at El Confital, although the largest boulders in excess of 2 m in diameter would have required larger waves for extraction. A review of the fossil marine biota associated with the boulder beds confirms a littoral to very shallow water setting correlated in time with Marine Isotope Stage 5e (Eemian Stage) approximately 125,000 years ago. The historical record of major storms in the regions of the Canary and Azorean islands indicates that events of hurricane strength were likely to have struck El Confital in earlier times. Due to its high scientific value, the outcrop area featured in this study is included in the Spanish Inventory of Geosites and must be properly protected and managed to ensure conservation against the impact of climate change foreseen in coming years.

Numerical Research on FPSOs With Green Water Occurrence

2009 ◽  
Vol 53 (01) ◽  
pp. 7-18
Author(s):  
Renchuan Zhu ◽  
Guoping Miao ◽  
Zhaowei Lin
Keyword(s):  
Three Dimensional ◽  
Green Water ◽  
Floating Body ◽  
Incoming Wave ◽  
Model Case ◽  
Floating Structures ◽  
Design And Optimization ◽  
Head Waves ◽  
Wave Heights ◽  
The Impact

Green water loads on sailing ships or floating structures occur when an incoming wave significantly exceeds freeboard and water runs onto the deck. In this paper, numerical programs developed based on the platform of the commercial software Fluent were used to numerically model green water occurrence on floating structures exposed to waves. The phenomena of the fixed floating production, storage, and offloading unit (FPSO) model and oscillating vessels in head waves have been simulated and analyzed. For the oscillating floating body case, a combination idea is presented in which the motions of the FPSO are calculated by the potential theory in advance and computional fluid dynamics (CFD) tools are used to investigate the details of green water. A technique of dynamic mesh is introduced in a numerical wave tank to simulate the green water occurrence on the oscillating vessels in waves. Numerical results agree well with the corresponding experimental results regarding the wave heights on deck and green water impact loads; the two-dimensional fixed FPSO model case conducted by Greco (2001), and the three-dimensional oscillating vessel cases by Buchner (2002), respectively. The research presented here indicates that the present numerical scheme and method can be used to actually simulate the phenomenon of green water on deck, and to predict and analyze the impact forces on floating structures due to green water. This can be of great significance in further guiding ship design and optimization, especially in the strength design of ship bows.

What Is Tsunami Earthquake?

2021 ◽  
Author(s):  
Toshikazu Ebisuzaki
Keyword(s):  
Surface Waves ◽  
Seismic Waves ◽  
Submarine Landslides ◽  
Lower Efficiency ◽  
Tsunami Waves ◽  
Tsunami Earthquakes ◽  
Seismic Surface Waves ◽  
Tsunami Earthquake ◽  
Volcanic Islands ◽  
2004 Tsunami

Abstract A tsunami earthquake is defined as an earthquake which induces abnormally strong tsunami waves compared with its seismic magnitude (Kanamori 1972; Kanamori and Anderson 1975; Tanioka and Seno 2001). We investigate the possibility that the surface waves (Rayleigh, Love, and tsunami waves) in tsunami earthquakes are amplified by secondly submarine landslides, induced by the liquefaction of the sea floor due to the strong vibrations of the earthquakes. As pointed by Kanamori (2004), tsunami earthquakes are significantly stronger in longer waves than 100 s and low in radiation efficiencies of seismic waves by one or two order of magnitudes. These natures are in favor of a significant contribution of landslides. The landslides can generate seismic waves with longer period with lower efficiency than the tectonic fault motions (Kanamori et al 1980; Eissler and Kanamori 1987; Hasegawa and Kanamori 1987). We further investigate the distribution of the tsunami earthquakes and found that most of their epicenters are located at the steep slopes in the landward side of the trenches or around volcanic islands, where the soft sediments layers from the landmass are nearly critical against slope failures. This distribution suggests that the secondly landslides may contribute to the tsunami earthquakes. In the present paper, we will investigate the rapture processes determined by the inversion analysis of seismic surface waves of tsunami earthquakes can be explained by massive landslides, simultaneously triggered by earthquakes in the tsunami earthquakes which took place near the trenches.

scholarly journals Effect of Girder Spacing and Depth on the Solitary Wave Impact on Coastal Bridge Deck for Different Airgaps

2019 ◽  
Vol 7 (5) ◽  
pp. 140 ◽  
Author(s):  
Rameeza Moideen ◽  
Manasa Ranjan Behera ◽  
Arun Kamath ◽  
Hans Bihs
Keyword(s):  
Solitary Wave ◽  
Bridge Deck ◽  
Impact Force ◽  
Storm Surges ◽  
Wave Impact ◽  
Wave Condition ◽  
Bridge Damage ◽  
Wave Heights ◽  
The Impact ◽  
Vertical Impact

Coastal bridge damage has become a severe issue of concern in the recent past with the destruction of a considerable number of bridges under the impact of waves during tsunami and storm surges. These events have become more frequent, with waves reaching the bridge deck and causing upliftment and destruction. Past studies have demonstrated the establishment of various theoretical equations which works well for the submerged deck and regular wave types but show much scatter and uncertainty in case of a deck that is above still water level (SWL). The present study aims to generate a solitary wave to represent an extreme wave condition like a tsunami in the numerical wave tank modeled using the open source computational fluid dynamics (CFD) model REEF3D and to study the vertical impact force on the coastal bridge deck. A parametric study is carried out for increasing wave heights, girders spacing and depth for varying airgaps to analyze the effect of these parameters on the peak vertical impact force. It is observed that increasing the girder spacing and girder depth is effective in reducing the peak vertical impact force for the cases considered.

A Numerical Study of Electrode Arrangements for Precise Microdrop Generation in an Electrowetting-Based Digital Microfluidic Platform

2019 ◽  
Author(s):  
Yin Guan ◽  
Baiyun Li ◽  
Mengnan Zhu ◽  
Shengjie Cheng ◽  
Jiyue Tu ◽  
...  
Keyword(s):  
Free Surface ◽  
Cell Model ◽  
Numerical Study ◽  
Digital Microfluidics ◽  
Surface Force ◽  
Viscous Force ◽  
Generation Process ◽  
Parallel Plates ◽  
Digital Microfluidic ◽  
The Impact

Abstract Owing to the wide applications in a large variety of multi-disciplinary areas, electrowetting-based digital microfluidics (DMF) has received considerable attention in the last decade. However, because of the complexity involved in the droplet generation process, the techniques and configurations for precise and controllable microdrop generation are still unclear. In this paper, a numerical study has been performed to investigate the impact of electrode arrangements on microdrop generation in an electrowetting-based DMF Platform proposed by a previously published experimental work. The governing equations for the microfluidic flow are solved by a finite volume formulation with a two-step projection method on a fixed numerical domain. The free surface of the microdrop is tracked by a coupled level-set and volume-of-fluid (CLSVOF) method, and the surface tension at the free surface is computed by the continuum surface force (CSF) scheme. A simplified viscous force scheme based on the ‘Hele-Shaw cell’ model is adopted to evaluate the viscous force exerted by the parallel plates. The generation process has been simulated with three different electrode arrangements, namely, ‘SL’, ‘SW’, and ‘SQ’. The effect of electrode arrangement on microdrop volume has been investigated. Besides, the influences of the initial microdrop location and volume on the generation process for the ‘SL’ design have been studied. The results can be used to advance microdrop generation techniques for various electrowetting-based DMF applications.

scholarly journals A COMPARISON OF NATURE WAVES AND MODEL WAVES WITH SPECIAL REFERENCE TO WAVE GROUPING

1980 ◽  
Vol 1 (17) ◽  
pp. 177 ◽  
Author(s):  
Hans F. Burcharth
Keyword(s):  
Phase Distribution ◽  
Random Phase ◽  
Power Spectra ◽  
Height Distribution ◽  
Wave Group ◽  
Storm Waves ◽  
Wave Height Distribution ◽  
Storm Wave ◽  
Wave Heights ◽  
The Impact

This paper represents a comparative analysis of the occurrence of wave grouping in field storm waves and laboratory waves with similar power spectra and wave height distribution. Two wave patterns - runs of waves and jumps in wave heights - which have significant influence on the impact on coastal structures were included in the analysis of storm wave records off the coasts of Cornwall, U.K. and Jutland, Denmark. Two different laboratory wave generator systems, based on random phase distribution of component waves, were used. Within the limitations given by the relatively small number of analysed records it is shown that wave group statistics can be satisfactorily reproduced by random phase generators that are not based on a limited number of component waves, but for example based on filtering of white noise. It is also shown that the statistics of large waves and wave groups containing large waves depend on whether the waves are defined from zero-upcrossings or zero-downcrossings. Although very similar seas were chosen for the analysis it was found that significant differences in the wave group statistics from the two locations existed. Also a considerable scatter in the wave group statistics throughout the storms was found.

scholarly journals Impact of interseismic deformation on phase transformations and rock properties in subduction zones

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sebastian Cionoiu ◽  
Evangelos Moulas ◽  
Lucie Tajčmanová
Keyword(s):  
Phase Transformations ◽  
Subduction Zones ◽  
Systematic Investigation ◽  
Rock Properties ◽  
Principal Stresses ◽  
High Deformation ◽  
Alumina Inclusion ◽  
Rock Heterogeneity ◽  
Slow Earthquakes ◽  
The Impact

AbstractPhase transformations greatly affect physical properties of rocks and impose a first-order control on geodynamic processes. Under high deformation rates, rheological heterogeneities cause large spatial variations of stress in materials. Until now, the impact of higher deformation rates, rock heterogeneity and stress build up on phase transformations and material properties is not well understood. Here we show, that phase transitions are controlled by the stress build-up during fast deformation. In a deformation experiment (600 °C, 1.47 GPa), rock heterogeneity was simulated by a strong elliptical alumina inclusion in a weak calcite matrix. Under deformation rates comparable to slow earthquakes, calcite transformed locally to aragonite matching the distribution of maximum principal stresses and pressure (mean stress) from mechanical models. This first systematic investigation documents that phase transformations occur in a dynamic system during deformation. The ability of rocks to react during fast deformation rates may have serious consequences on rock rheology and thus provide unique information on the processes leading to giant ruptures in subduction zones.

How to be fooled searching for significant variations of the b-value

2019 ◽  
Vol 220 (3) ◽  
pp. 1845-1856 ◽  
Author(s):  
W Marzocchi ◽  
I Spassiani ◽  
A Stallone ◽  
M Taroni
Keyword(s):  
B Value ◽  
Earthquake Forecasting ◽  
Unbiased Estimation ◽  
Maximum Magnitude ◽  
Generation Process ◽  
Data Set ◽  
Potential Sources ◽  
Value Estimation ◽  
Earthquake Generation ◽  
The Impact

SUMMARY An unbiased estimation of the b-value and of its variability is essential to verify empirically its physical contribution to the earthquake generation process, and the capability to improve earthquake forecasting and seismic hazard. Notwithstanding the vast literature on the b-value estimation, we note that some potential sources of bias that may lead to non-physical b-value variations are too often ignored in seismological common practice. The aim of this paper is to discuss some of them in detail, when the b-value is estimated through the popular Aki’s formula. Specifically, we describe how a finite data set can lead to biased evaluations of the b-value and its uncertainty, which are caused by the correlation between the b-value and the maximum magnitude of the data set; we quantify analytically the bias on the b-value caused by the magnitude binning; we show how departures from the exponential distribution of the magnitude, caused by a truncated Gutenberg–Richter law and by catalogue incompleteness, can affect the b-value estimation and the search for statistically significant variations; we derive explicitly the statistical distribution of the magnitude affected by random symmetrical error, showing that the magnitude error does not induce any further significant bias, at least for reasonable amplitude of the measurement error. Finally, we provide some recipes to minimize the impact of these potential sources of bias.

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