Bottom Displacement Research Articles

Effects of Friction at Movable Supports on Elasto-Plastic Seismic Responses of Continuous Girder Bridges

The effect of friction on movable supports on the elasto-plastic seismic responses of continuous girder bridges was analyzed on the basis of three aspects including stiffness contribution, friction energy dissipation of the movable supports, and kinetic interaction between the girders and movable piers. Finite element models were established, which considered the friction non-linearity of the movable supports and the material nonlinearity of the reinforced concrete piers. In addition, nonlinear time history analysis was performed to analyze the effects of friction at the movable supports on the pier bottom curvature, girder displacement, velocity, and acceleration. The results indicated that the frictional effect at movable supports is not always favorable. In some cases, the friction at these points must be considered. For the nonlinear time history analysis, the effect of natural vibration characteristics of the bridge and the response spectrum of the ground should also be considered. For some complicated continuous bridges, particularly those with the heights and stiffness of the fixed and movable piers, the friction at movable supports should be considered in seismic analysis.

Wooden window frames with structural sealants: manufacturing improvements and experimental validation of a finite element model

This paper proposes a finite element (FE) model of a novel wooden window frame typology and validates it by experimental tests on window frames and corner joint specimens. The innovation consists of the application of the structural silicone sealant only at the interface between wood and one of the thin glass layers of the double-glazing glass, so achieving a low application depth. This technique reduces the sealant quantity and allows the disassembly and substitution of the glass from the frame in case of breakage. In order to inform the FE model of the whole frame, the dowelled butt corner joint strength is measured by specific experimental tests. The results show a good correlation between the FE model and the experimental results in the range of small frame deformations, which are of interest for the proposed application. In particular, the FE curve overestimates the bottom corner displacement of about 17% at 1000 N load, 7% at 2000 N and less than 5% at higher applied force on the upper corner. The model is then applied to various wooden frame geometries in order to evaluate if the proposed silicone application mode and dowelled corner joints type allow an acceptable stiffness of the frame, and, in particular, low deformations of the bottom corner joint, in order to maintain the wooden frame functionality when subject to external loads. The approach could be useful when assessing optimal sealing application modes, wood-sealant-glass joint geometries, corner joint geometries and window frame geometries to limit the bottom corner joint deformation within the required technical specifications.

Tsunami and acoustic-gravity waves in water of constant depth

A study of wave radiation by a rather general bottom displacement, in a compressible ocean of otherwise constant depth, is carried out within the framework of a three-dimensional linear theory. Simple analytic expressions for the flow field, at large distance from the disturbance, are derived. Realistic numerical examples indicate that the Acoustic-Gravity waves, which significantly precede the Tsunami, are expected to leave a measurable signature on bottom-pressure records that should be considered for early detection of Tsunami.

Depth-integrated equation for large-scale modelling of low-frequency hydroacoustic waves

AbstractWe present a depth-integrated equation for the mechanics of propagation of low-frequency hydroacoustic waves due to a sudden bottom displacement associated with earthquakes. The model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of three-dimensional models and so creating a solid base for tsunami early warning systems.

海底変位の計算方法が津波評価に与える影響～３次元海底地殻変動解析～

海底変位の計算方法が津波評価に与える影響～３次元海底地殻変動解析～

Wave-Field Decomposition of Ocean Bottom Seismograms

Seismograms recorded on the seafloor are affected by reverberations in the overlying ocean layer. We examine the feasibility of removing these reverberations through a 1D wave‐field decomposition based on a reflection–transmission formulation of the problem. Two decomposition schemes are presented. The first scheme involves a simple manipulation of the fundamental matrix relating stress and displacement of plane harmonic waves to upgoing and downgoing wavevector coefficients and requires measurement of both ocean bottom displacement and pressure. The second approach involves only displacement recordings and knowledge of the water column depth. This latter quantity will generally be known a priori from deployment logs, or, alternatively, it may be estimated using vertical displacement and pressure seismograms in a preprocessing step. Both approaches require prior information on seabed properties. In the case of P ‐wave incidence, the decomposition depends primarily on the seabed S velocity β . This quantity can be determined by examining trial decompositions over a range of β ’s and selecting the value that minimizes the energy of the upgoing S ‐wave component at the arrival time of the incident wave. We apply this approach to synthetic seismograms for a simple Earth structure and to recordings of two large events from the Central Oregon Locked Zone Array (COLZA) on the continental margin of Oregon. The real data indicate that the wave‐field decompositions are largely successful at lower frequencies (<0.1 Hz) but that 3D scattering, likely originating near the sediment–basement contact, is manifested at higher frequencies.

The Deformation Character of Retaining Wall under Horizontal Earthquake

The soil pressure can be influenced by the deformation of retaining wall because of the interaction of wall and soil. The dynamic soil pressure and plastic bottom displacement induced by earthquake action will subsequently result the deformation of the wall. The dynamic soil pressure will vary with the wall deformation and, on the other hand, change the deformation of the wall. The wall under lateral earthquake is assumed to be a single freedom system, thus only one deformation mode is considered in this paper. Based on this assumption, the differential equation of wall-soil dynamic interaction system is proposed.

Static Wind Load and Gravity Coupling Effect of Tall Structure

The cantilever beam model of tall building structure which includes lateral wind load and vertical gravity coupling has been established in the paper. The form of finite difference has been concluded from equations of the model acted on static wind load. Amplified coefficients of bottom moment and top displacement are calculated and analyzed. The result shows that gravity second order effect of tall buildings will be enhanced when ratio of gravity rigidity or ratio of bending and shearing rigidity increase.

Tsunamis and acoustic-gravity waves from underwater earthquakes

A study of wave radiation by a piston bottom displacement, in a compressible ocean of constant depth, is carried out within the framework of a two-dimensional linear theory. Simple analytic expressions for the flow field, at a large distance from the disturbance, are derived. A realistic numerical example indicates that the Acoustic-Gravity waves, which significantly precede the tsunami, are expected to leave a significant signature on bottom-pressure records that should be considered for early detection of tsunamis.

Contribution of nonlinearity in tsunami generated by submarine earthquake

Abstract. Rapid co-seismic bottom displacements during strong submarine earthquake give rise to intensive low-frequency elastic oscillations of water layer. Nonlinear energy transfer from the elastic oscillations to long gravitational waves may provide an additional contribution to tsunami. The nonlinear tsunami generation mechanism is examined analytically. Finiteness of bottom elasticity is taken into account. General parameters responsible for amplitude and energy of the nonlinear contribution to tsunami wave are revealed.

The source of the 1722 Algarve earthquake: evidence from MCS and Tsunami data

The 27 December 1722 Algarve earthquake destroyed a large area in southern Portugal generating a local tsunami that inundated the shallow areas of Tavira. It is unclear whether its source was located onshore or offshore and, in any case, what was the tectonic source responsible for the event. We analyze available historical information concerning macroseismicity and the tsunami to discuss the most probable location of the source. We also review available seismotectonic knowledge of the offshore region close to the probable epicenter, selecting a set of four candidate sources. We simulate tsunamis produced by these candidate sources assuming that the sea bottom displacement is caused by a compressive dislocation over a rectangular fault, as given by the half-space homogeneous elastic approach, and we use numerical modeling to study wave propagation and run-up. We conclude that the 27 December 1722 Tavira earthquake and tsunami was probably generated offshore, close to 37°01′N, 7°49′W.

Elastic oscillations of water column in the 2003 Tokachi-oki tsunami source: in-situ measurements and 3-D numerical modelling

Abstract. During the 2003 Tokachi-Oki tsunamigenic earthquake the real-time JAMSTEC observatory obtained records which provided a unique opportunity to have a look deep inside the tsunami source. Considering water column as a compressible medium we processed the bottom pressure records in order to estimate amplitude, duration and velocity of bottom displacement. Spectral analysis of the records revealed a clear manifestation of the low-frequency elastic oscillations of water column. We also presented 3-D finite-difference numerical model developed in the framework of linear potential theory of ideal compressible fluid to better understand dynamical processes in the tsunami source. The model reproduces position of the main spectral maximum rather correctly. However, due to neglecting of crust elasticity and to lack of exact knowledge of spatiotemporal laws of bottom motion, there is an essential difference between in-situ observed and computed spectra.

Discharge determination by Acoustic Doppler Current Profilers (ADCP): a moving bottom error correction method and its application on the River Amazon at Óbidos

Since 1995, hydrologists of the HiBAm (Hydrology and Geochemistry of the Amazon Basin) Research Program carried out several hundred discharge measurements in the Amazon basin. Implementation of modern discharge measurement techniques using ultrasonic devices (ADCP), give evidence of a systematic error linked to the displacement of the river bottom due to high water velocity close to the bottom. This error leads to an underestimation of discharge value. It was possible to establish a correlation between the water velocity close to the river bottom and the error between real position and position computed by ADCP when the boat returns to its starting point after a two-way crossing of the river. When there is no bottom displacement, i.e. during low flow period, this return position error is weak (less than 50 m). This has allowed quantification of river bed load speed, or bottom displacement speed. A correction method was developed on the basis of this correlation. This method, systematically applied to ADCP discharge measurements obtained at Óbidos hydrometric station, allowed all measured discharges to be corrected, especially for 1997 and 1999 floods. Another method, based on the analysis of real trajectory of the boat (obtained from topographic measurement or GPS positioning) compared with the ADCP computed trajectory, is under study.

Tsunami generation in compressible ocean

Most of the tsunami modelling studies have been carried out within the framework of incompressible fluid theory. Estimations we made show that this approach quite appropriately describes the stages of tsunami propagation and run-up, whereas incompressible fluid theory fails to describe the process of tsunami generation properly. Comparative studies of wave generation by piston bottom displacements in compressible and incompressible fluids have been carried out within the framework of linear potential theory. The analysis of exact analytical solutions to the problem has shown that a substantial difference exists between the behaviour of compressible and incompressible fluids under typical tsunami source conditions. It was also shown that bottom displacements of seismic origin must give rise to standing acoustic waves in the source region. As a result each tsunami should have its own “voice”, the characteristics of which depend on bottom topography, sediment features and on the time history and spatial structure of the bottom displacement. This “voice” may serve as an additional important tool for tsunami forecasting.

Influence of Inside Fluid Motion on Tension Variation of a Deep Sea Drilling Riser in Disconnected Mode

Influence of inside fluid mass which exists inside the riser pipe on tension variation of the deep sea drilling riser in disconnected mode is investigated. A simple calculation method of the tension variation is proposed taking the inside mass motion into account based on the lumped mass method. This method is verified through the comparison with the tension variation and the riser bottom displacement measured in a basin test using a riser model. The influence of the inside mass on the tension variation is numerically investigated for deep sea drilling risers with 3 different length using the calculation method. For the deep sea riser over 2, 000 m length, the mass corresponding to about 50% of the total inside mass acts on the riser top as the additional tension variation.

Three‐dimensional modeling of pull‐apart basins: Implications for the tectonics of the Dead Sea Basin

We model the three‐dimensional (3‐D) crustal deformation in a deep pull‐apart basin as a result of relative plate motion along a transform system and compare the results to the tectonics of the Dead Sea Basin. The brittle upper crust is modeled by a boundary element technique as an elastic block, broken by two en echelon semi‐infinite vertical faults. The deformation is caused by a horizontal displacement that is imposed everywhere at the bottom of the block except in a stress‐free “shear zone” in the vicinity of the fault zone. The bottom displacement represents the regional relative plate motion. Results show that the basin deformation depends critically on the width of the shear zone and on the amount of overlap between basin‐bounding faults. As the width of the shear zone increases, the depth of the basin decreases, the rotation around a vertical axis near the fault tips decreases, and the basin shape (the distribution of subsidence normalized by the maximum subsidence) becomes broader. In contrast, two‐dimensional plane stress modeling predicts a basin shape that is independent of the width of the shear zone. Our models also predict full‐graben profiles within the overlapped region between bounding faults and half‐graben shapes elsewhere. Increasing overlap also decreases uplift near the fault tips and rotation of blocks within the basin. We suggest that the observed structure of the Dead Sea Basin can be described by a 3‐D model having a large overlap (more than 30 km) that probably increased as the basin evolved as a result of a stable shear motion that was distributed laterally over 20 to 40 km.

Numerical modelling of the tsunami generation process by the moving sea bottom displacement

The process of tsunami generation by the moving horizontal bottom displacement is studied numerically. The influence produced by the displacement rate and the range of the run on the parameters of the wave generated is studied. A comparison with the results derived using the linear theory of long waves is made.

Analysis and modeling of the results of ECONOMEX

ECONOMEX was a study of ULF/VLF noise along an eastern US continental shelf/slope region, conducted between January and April 1991. Concurrent measurements of surface wave directional spectra and meteorological parameters were collected as a part of the SWADE experiment. Extended time series of pressure and bottom displacement have now been analyzed, plotted, and compared with predictions based on the local wave spectra. In most cases, the contribution from local sources appears far more significant than distant sources, such as storms. D. H. Cato’s dipole source mechanism [J. Acoust. Soc. Am. 57, 1076–1095 (1975)] agrees well with data from sensors ranging in depth between 450 and 2500 m, but the monopole mechanism is also significant at the shallowest sensor (100 m). A new method for evaluating Cato’s theory is also discussed. The method, since it involves direct evaluation of the dipole source convolution integral, does not require separability of the magnitude and directional dependence of the surface wave spectrum.

On the spectra shape of seismic noise and earthquakes recorded in the ocean

The shape of the spectra of ocean bottom noise and earthquakes recorded in the course of seismological observations in the ocean is analysed. The generalized spectra of bottom seismic noise are suggested as reference curves for comparison with new data. The comparison showed a similarity in the shape and level of the generalized spectra to the noise spectra obtained recently both on the bottom and under the bottom by seismographs placed in holes drilled by the Deep-sea Drilling Project. The spectral analysis of the earthquakes recorded on the bottom of the North-west Pacific basin has shown clear maxima at frequencies of 7–17 Hz formed both by site effects and by absorption of seismic energy in the lithosphere. The frequency of spectral maxima decrease with increasing epicentral distance. Comparison of the earthquake spectra with generalized spectra of bottom noise revealed (probably) incidental coincidence in the frequencies of the minimum for noise spectra (10 Hz) and the average maximum of earthquake record spectra. The sharp mechanical impacts on a bottom seismograph, usually induced by bottom displacements under the instrument, are suggested as rough analogues of the impulses for the bottom instrument system transient calibration. Test measurements have shown that in many cases this method makes it possible to distinguish spectral peaks characterising earthquakes and seismic noise wave trains from those which are caused by coupling resonances of the OBS-sediment interface.

The estimation of ocean bottom seismographs' coupling characteristics by means of microshock recordings

A transient technique was used for estimating the bottom-instrument response function in experiments with bottom seismographs (OBS) in deep ocean. The sharp mechanical impacts on bottom seismograph usually induced by bottom displacements under the instrument (microshocks) are suggested as rough analogues of the impulses for the bottom-instrument system transient calibration. It has been found that microshocks has usually sufficiently small duration to be used for coupling characteristics estimates. Test measurements have shown that in many cases this method makes it possible to distinguish spectral features characterising earthquakes and seismic noise wavetrains from those which are caused by coupling resonances of the OBS-sediment inter-face.