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1.
The modified Weibull spectrum is utilized to calculate the zeroth spectral moment (mo) using Monte Carlo integration methods. Then significant wave height (Hs) is calculated using the formula This is validated with observed buoy data and numerical wave model (WAM) predicted significant wave heights. The Weibull parameters have been calculated using energy densities from observed spectra recorded by DS5 buoy (13.80° N, 82.52° E, depth 3355.48 m) by the method of maximum likelihood (MLE).The relative root mean square error (RRMS) and relative bias error criteria show that modified Weibull spectrum estimated significant wave heights are better than those predicted by WAM model. The monthly averaged observed wave power spectra for the year 2005 recorded by deep water buoy DS5 is considered in this work. The spectra exhibit bimodal sea states for several months of the year.  相似文献   

2.
It is well accepted that the parent distribution for individual ocean wave heights follows the Weibull model. However this model does not simulate significant wave height which is the average of the highest one-third of some ‘n’ (n- varies) wave heights in a wave record. It is now proposed to redefine significant wave height as average of the highest one-third of a constant number (n-constant, say,n = 100) of consecutive individual wave heights. The Weibull model is suggested for simulating redefined significant wave height distribution by the method of characteristic function. An empirical support of 100.00% is established by Χ2-test at 0.05 level of significance for 3 sets of data at 0900, 1200 and 1500 hrs at Valiathura, Kerala coast. Parametric relations have been derived for the redefined significant wave height parameters such as mean, maximum one-third average, extreme wave heights, return periods of an extreme wave height and the probability of realising an extreme wave height in a time less than the designated return period.  相似文献   

3.
A 97-day-long record on waves and currents was obtained using wave rider buoy and current meter moored at 2.5 km off Gopalpur from 19 May to 23 August 2008 representing southwest monsoon months. A Valeport tide gauge was used to record water level at Gopalpur port. Simultaneously, beach profiles at 4 transects were monitored using real-time kinematic (RTK) global positioning system (GPS). A total of 636,167 waves were analyzed for the period; a range of 3,200–9,700 waves approach the coast in an individual day. During the study, unusual characteristics of wave were observed on July 29, 2008, with a magnitude of significant wave height, Hs = 2.85 m, maximum wave height, Hmax = 5.22 m, and peak wave period, Tp = 10.2 s, and on August 11, 2008, with Hs = 2.28 m, Hmax = 5.37 m, and Tp = 11.1 s. Significant beach loss was noticed during these periods, and severe erosion was recorded on August 1, 2008. Beach profile data indicates that 18–58 cu. m/m sediment was lost during the study period. The paper provides an overview of the statistical analysis of wave heights, periods, direction, and spectral energy density and explains the cause of coastal erosion and loss of sediment.  相似文献   

4.
The spatial distribution of soil shear-wave velocity and the fundamental period of vibration were selected as input parameters for the determination of potential seismic site effects in the Saguenay region, Canada. The methodology used in this study involved three clear steps. First, a 3D geological model of the surficial deposits was built taking into consideration the type, spatial distribution and thickness of the deposits. Second, representative average Vs values were determined for each of the major soil units. Finally, the average shear-wave velocity from the ground surface to bedrock (Vsav), the shear-wave velocity of the upper 30 m (Vs30) and the fundamental site resonance period (T0) were calculated over a regular grid for the study area. The results include the spatial distribution of the fundamental site resonance period, the average shear-wave velocity in the first 30 m of the ground and the spatial distribution of National Building Code of Canada seismic soil classes for the Saguenay region.  相似文献   

5.
人工神经网络在海浪数值预报中的应用   总被引：6，自引：0，他引：6       下载免费PDF全文
探讨将人工神经网络技术和传统的数值模式相结合,以期得到一个更有效的海浪预报方法.以第3代海浪模式的模拟结果作为输入,浮标观测资料作为输出,采用人工神经网络进行训练,训练的初步结果显示,人工神经网络可以改进海浪数值模式的预报精度,但在波高比较大时,改进的效果并不令人满意.为此,对观测值大于1.5m时的有效波高进行再训练,从而结果有了进一步的改善.研究结果证明人工神经网络技术可以提高海浪数值预报的精度.  相似文献   

6.
ZAI-JIN YOU  †  BAOSHU YIN† 《Sedimentology》2006,53(5):1181-1190
A unified criterion is developed for initiation of non‐cohesive sediment motion and inception of sheet flow under water waves over a horizontal bed of sediment based on presently available experimental data. The unified threshold criterion is of the single form, Uo = 2πC[1 + 5(TR/T)2]?1/4, where Uo is the onset velocity of sediment motion or sheet flow, T is wave period, and C and TR are the coefficients. It is found that for a given sediment, Uo initially increases sharply with wave period, then gradually approaches the maximum onset velocity Uo = 2πC and becomes independent of T when T is larger. The unified criterion can also be extended to define sediment initial motion and sheet flow under irregular waves provided the significant wave orbital velocity and period of irregular waves are introduced in this unified criterion.  相似文献   

7.
Studying seismic wave propagation across rock masses and the induced ground motion is an important topic, which receives considerable attention in design and construction of underground cavern/tunnel constructions and mining activities. The current study investigates wave propagation across a rock mass with one fault and the induced ground motion using a recursive approach. The rocks beside the fault are assumed as viscoelastic media with seismic quality factors, Qp and Qs. Two kinds of interactions between stress waves and a discontinuity and between stress waves and a free surface are analyzed, respectively. As the result of the wave superposition, the mathematical expressions for induced ground vibration are deduced. The proposed approach is then compared with the existing analysis for special cases. Finally, parametric studies are carried out, which includes the influences of fault stiffness, incident angle, and frequency of incident waves on the peak particle velocities of the ground motions.  相似文献   

8.
Shear wave velocity (V s) and the fundamental site period of the subsurface condition are the primary parameters that affect seismic soil amplification in particular sites. Within the topmost layer of the soil, which measures 30 m, the average shear wave velocity V s30 is commonly used to build codes for site classification for the design of earthquake-resistant structures and to conduct microzonation studies. In this study, the development of a microzonation map for V s30 distribution, National Earthquake Hazard Reduction Program V s30 site classification, and a fundamental site period for Penang are presented. The multichannel analysis of surface wave (MASW) test was conducted for more than 50 sites with available borehole data to develop the microzonation maps. The ten selected V s profiles measured by MASW show a good correlation with the data obtained using empirical correlations in a previous study. The highest V s values were identified at the northeastern and southeastern parts of Penang Island, corresponding to the shallow bedrock and the outcrop zone. Conversely, the lowest V s values were found in the northwestern and southwestern parts of the Penang mainland owing to the thick layer of soft clay and silt deposits. The site period map shows the variation in site periods, with the highest value of 1.03 s at the western part of the Penang mainland and the lowest value of 0.02 s at the eastern part of the Penang Island. The microzonation maps developed in this study are vital to studies on seismic hazard and earthquake mitigation programs in Malaysia.  相似文献   

9.
Thirty‐three samples, including 22 eclogites, collected from the Dabie ultrahigh‐pressure (UHP) metamorphic belt in eastern China, have been studied for seismic properties. Compressional (Vp) and shear wave (Vs) velocities in three mutually perpendicular directions under hydrostatic pressures up to 1.0 GPa were measured for each sample. At 1.0 GPa, Vp (7.5–8.4 km s?1), Vs (4.2–4.8 km s?1), and densities (3.2–3.6 g cm?3) in the UHP eclogites are higher than those of UHP orthopyroxenite (7.3–7.5 km s?1, 4.1–4.3 km s?1, 3.2–3.3 g cm?3, respectively) and HP eclogites (7.1–7.9 km s?1, 4.0–4.5 km s?1, 3.1–3.5 g cm?3, respectively). Kyanitites (with 99.5% kyanite) show extremely high velocities and density (9.37 km s?1, 5.437 km s?1, 3.581 g cm?3, respectively). The eclogites show variation of Vp‐ and Vs‐anisotropy up to 9.70% and 9.17%, respectively. Poisson’s ratio (σ) ranges from 0.218 to 0.278 (with a mean of 0.255) for eclogites, 0.281–0.298 for granulites and 0.248 to 0.255 for amphibolites. The σ values for serpentinite (0.341) and marble (0.321) are higher than for other lithologies. The elastic moduli K, G, E of kyanitite were obtained as 163, 102 and 253 GPa, respectively. The Vp and density of representative UHP metamorphic rocks (eclogite & kyanitite) were extrapolated to mantle depth (15 GPa) following a reasonable geotherm, and compared to the one dimension mantle velocity and density model. The comparison shows that Vp and density in eclogite and kyanitite are greater than those of the ambient mantle, with differences of up to ΔVp > 0.3 km s?1 and Δρ > 0.3–0.4 g cm?3, respectively. This result favours the density‐induced delamination model and also provides evidence in support of distinguishing subducted high velocity materials in the upper mantle by means of seismic tomography. Such ultra‐deep subduction and delamination processes have been recognized by seismic tomography and geochemical tracing in the postcollisional magmatism in the Dabie region.  相似文献   

10.
Mo  H. M.  Ye  W.  Hong  H. P. 《Natural Hazards》2022,111(3):2459-2485

The estimation of snow hazard and load faces the small sample size effect because of the short snow depth record at a station. To reduce such an effect, we propose to estimate the return period value of the annual maximum ground snow depth S, sT, for Canada sites by applying the regional frequency analysis (RFA) and the region of influence approach (ROIA). The use of RFA and ROIA to map Canadian snow hazard is new. The comparison of their performance for snow hazard mapping has not been explored in the literature. We also consider the at-site analysis approach (ASA) for estimating sT by using three often used probability distributions for S. A comparison of the estimated sT by using the three approaches (ASA, RFA, ROIA) indicates that there is considerable scatter between the estimated sT value although the identified overall spatial trends of sT are similar. It is shown that the two-parameter lognormal distribution for S at most Canadian sites, based on the at-site analysis, is preferred; this differs from the Gumbel distribution used to develop the design snow load in Canadian structural design code. The new findings indicate that it is valuable to consider the lognormal distribution for developing design snow load for Canadian sites.

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11.
In the early stages of wave growth it is seen that wave heights are underestimated by presently available models especially in a low wind regime. Parametric wind-sea relationships of significant wave height (H2) and zero-crossing period (T 2) for slight to moderate sea-states were proposed earlier on an analysis of wind and wave data. This model is based on the concept of time delay between the wind speed (U) and wave evolution process. It is simple and requires less computational effort compared to the spectral method. The present paper attempts to test and evaluate the performance of the proposed model with additional field data of wind and waves measured off the Indian coast. MeasuredU,H 2, andT 2 ranged between 1 and 15 m/s, 0·5 and 2·7 m and 4 and 10 s respectively. By and large, the comparison between model output and field observations are encouraging. A hindcast study was carried out earlier using a spectral wave prediction model (TOHOKU) for Indian Seas using field measurements which include the data sets utilized in this study. Comparison between these two models reveals a good agreement.  相似文献   

12.

The detrimental effects of an earthquake are strongly influenced by the response of soils subjected to dynamic loading. The behavior of soils under dynamic loading is governed by the dynamic soil properties such as shear wave velocity, damping characteristics and shear modulus. Worldwide, it is a common practice to obtain shear wave velocity (V s in m/s) using the correlation with field standard penetration test (SPT) N values in the absence of sophisticated dynamic field test data. In this paper, a similar but modified advanced approach has been proposed for a major metro city of eastern India, i.e., Kolkata city (latitudes 22°20′N–23°00′N and longitudes 88°04′E–88°33′E), to obtain shear wave velocity profile and soil site classification using regression and sensitivity analyses. Extensive geotechnical borehole data from 434 boreholes located across 75 sites in the city area of 185 km2 and laboratory test data providing information on the thickness of subsoil strata, SPT N values, consistency indices and percentage of fines are collected and analyzed thoroughly. A correlation between shear wave velocity (V s) and SPT N value for various soil profiles of Kolkata city has been established by using power model of nonlinear regression analysis and compared with existing correlations for other Indian cities. The present correlations, having regression coefficients (R 2) in excess of 0.96, indicated good prediction capability. Sensitivity analysis predicts that significant influence of soil type exists in determining V s values, for example, typical silty sand shows 30.4 % increase in magnitude of V s as compared to silt of Kolkata city. Moreover, the soil site classification shows Class D and Class E category of soil that exists typically in Kolkata city as per NEHRP (Recommended provisions for seismic regulations for new buildings and other structures—Part 1: Provisions. Prepared by the Building Seismic Safety Council for the Federal Emergency Management Agency (Report FEMA 450), Washington, DC, 2003) guidelines and thereby highlighting the seismic vulnerability of the city. The results presented in this study can be utilized for seismic microzonation, ground response analysis and hazard assessment for Kolkata city.

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13.
Simultaneous measurements of compressional and shear wave velocities, Vp and Vs, in acidic and basic igneous rocks and volcanic glasses, were made up to 900°C and at 10–20 kbar.The effects of pressure and temperature on Vp and Vs in glasses and glassy rocks change at about 600°C, presumably the glass transition temperature. These effects are directly related to the silica content in the samples. and for obsidian are negative at room temperature and 245°C, but are positive at 655°C. The velocity—pressure relations for obsidian display an obvious hysteresis phenomena. for basalt glass is slightly negative, but is positive for usual substances at room temperature, and for obsidian and glassy andesite are positive up to about 600°C but are negative above that temperature. However, for basalt glass as well as other crystalline rocks, and are negative at all temperatures. Glass once heated above the glass transition temperature Tg under pressure P1 retains the memory of pressure P1 after it is cooled down below Tg and while subjected to another pressure P2. An abrupt shift of the velocities correlating to pressure P2 occurs when the glass is again heated to Tg. Vp−T and Vs−T relations for obsidian, glassy andesite, and basalt glass clearly exhibit this pressure memory.  相似文献   

14.
The surface-wavemagnitudes Ms are determined for 30 great shallow earthquakes that occurred during the period from 1953 to 1977. The determination is based on the amplitude and period data from all available station bulletins, and the same procedure as that employed in Gutenberg and Richter's “Seismicity of the Earth” is used. During this period, the Chilean earthquake of 1960 has the largest Ms, 8.5. The surface-wave magnitudes listed in “Earthquake Data Reports” are found to be higher than Ms on the average. By using the same method as that used by Gutenberg, the broad-band body-wave magnitudes mB are determined for great shallow shocks for the period from 1953 to 1974. mB is based on the amplitudes of P, PP and S waves which are measured on broadband instruments at periods of about 4–20 s. The 1-s body-wave magnitudes listed in “Bulletin of International Seismological Center” and “Earthquake Data Reports” are found to be much smaller than mB on the average. Through the examination of Gutenberg and Richter's original worksheets, the relation between mB and Msis revised to mB = 0.65 Ms+ 2.5 which well satisfies the mg and Msdata for Msbetween 5.2 and  相似文献   

15.
The study area lies between latitude 18–26°N and longitude 73–83°E, and mainly covers the Central India Tectonic Zone (CITZ). The frequency-dependent shear wave quality factor (Qs) has been estimated over the CITZ and its surroundings using Double Spectral Ratio (DSR) method. We have considered 25 local earthquakes with magnitude (ML) varies from 3.0 to 4.7 recorded at 11 stations running under national seismic network. The Fast Fourier Transformed (FFT) spectra were computed from the recorded waveform having time-window from onset of S-phase to 1.0 s and for a frequency-band of 0.1–10 Hz. Three different shear wave velocities (i.e., 3.87, 3.39 and 3.96 km/s) were obtained over the study area based on a pair of earthquakes recorded at a pair of stations. The low Qs values of 51–96 at 1 Hz (i.e., Qs = 51f0.49; Qs = 90f0.488 and Qs = 96f0.53) were found in the area covering the Son–Narmada–Tapti (SONATA) lineament, CITZ, eastern part of the Satpura fold belt, Vindhyan and Gondwana basins, Godavari and Mahanadi grabens, and southern part of Gangetic plain. Intermediate Qs values of the order of 204–277 (i.e., Qs = 204f0.56 and Qs = 277f0.55) were noted in the cartonic areas, namely, Bundelkhand, Dharwar-Bhandara and Bastar. While the higher Qs values of 391–628 at 1 Hz (i.e., Qs = 391f0.49, Qs = 409f0.48, Qs = 417f0.48, Qs = 500f0.66, Qs = 585f0.65 and Qs = 628f0.69) were found in the eastern part of the SONATA, CITZ, and the northeastern part of the Satpura fold belt. The low Qs values might be attributing to the more heterogeneous SONATA rift system. Low Qs values further may presumably be associated with lower-level of seismicity and apparently account for higher tectonic stress accumulation over long duration. The long-term accumulated stress is generally released through occasional triggering of moderate magnitude earthquakes in the SONATA zone. Surrounding the SONATA region, the higher Qs values possibly accounts for a more homogeneous subsurface structure along the SONATA zone.  相似文献   

16.
North-east India is seismically very active and has experienced many widelydistributed shallow, large earthquakes. Earthquake generation model for the region was studied using seismicity data [(1906–1984) prepared by National Geophysical Data Centre (NGDC), Boulder Colorado, USA]. For establishing statistical relations surface wave magnitudes (M s≥5·5) have been considered. In the region four seismogenic sources have been identified which show the occurrences of atleast three earthquakes of magnitude 5·5≤M s≤7·5 giving two repeat times. It is observed that the time interval between the two consecutive main shock depends on the preceding main shock magnitude (M p) and not on the following main shock magnitude (M f) revealing the validity of time predictable model for the region. Linear relation between logarithm of repeat time (T) and preceding main shock magnitude (M p) is established in the form of logT=cM p+a. The values ofc anda are estimated to be 0–36 and 1–23, respectively. The relation may be used for seismic hazard evaluation in the region.  相似文献   

17.
A geotechnical information system (GTIS) was constructed within a spatial geographic information system (GIS) framework to reliably predict geotechnical information and accurately estimate site effects at Gyeongju, an urban area in South Korea. The system was built based on both collected and performed site investigation data in addition to acquired geo-knowledge data. Seismic zoning maps were constructed using the site period (T G) and mean shear wave velocity to a depth of 30 m (V S30), and these maps were presented as a regional strategy to mitigate earthquake-induced risks in the study area. In particular, the T G distribution map indicated the susceptibility to ground motion resonance in periods ranging from 0.2 to 0.5 s and the corresponding seismic vulnerability of buildings with two to five stories. Seismic zonation of site classification according to V S30 values was also performed to determine the site amplification coefficients for seismic design and seismic performance evaluation at any site and administrative subunit in the study area. In addition, we investigated the site effects according to subsurface and surface ground irregularities at Gyeongju by seismic response analyses in time domains based on both two- and three-dimensional spatial finite element models, which were generated using spatial interface coordinates between geotechnical subsurface layers predicted by the GTIS. This practical study verified that spatial GIS-based geotechnical information can be a very useful resource in determining how to best mitigate seismic hazards, particularly in urban areas.  相似文献   

18.
Assessment of the wave climate at near coast is vital for estimation of morphological changes, such as growth of sand spit and associated siltation of tidal inlets. Vellar (bar-built) estuary is one of the prominent estuaries along the southeast coast of India, located at 11°30′N and 79°46′E, less studied in terms of its morphological features. The inlet of Vellar is exposed to high energetic waves, inducing large sediment transport rates and shoreline changes. Local wave characteristics are not accurately defined and the available wave information at near coast is limited (point based observations). In the present study, three decoupled numerical models are employed to derive the monthly nearshore wave climate at Vellar by transforming waves from deep water to nearshore. These models are independently validated with buoy observations in deep water and wave gauge data at nearshore. Based on the nearshore wave data, littoral drift along the coast was estimated and compared with the spit growth at Vellar inlet. The estimated average littoral drift along this coast from February to October is 1.93 × 106 m3 toward north and from November to January it is 1.52 × 106 m3 toward south, resulting in a net northerly drift. Results indicated that increase in the wave energy during the period of July to September is responsible for the maximum growth of the sand spit observed in the field.  相似文献   

19.
平直沙坝海岸叠加波浪的裂流试验   总被引：1，自引：0，他引：1       下载免费PDF全文
王彦  邹志利 《水科学进展》2015,26(1):123-129
为研究叠加波浪场的裂流特征,在平直沙坝海岸地形进行了叠加波浪形成的沿岸波高周期性变化的裂流试验研究。试验中叠加波浪是由波浪在垂直岸线的丁坝反射所形成的两列交叉波浪叠加产生,交叉波浪是具有等频率但入射角相反的两波列。通过对叠加波浪节腹点垂直岸线位置浪高的测量和沙坝范围内沿岸布置的声学多普勒测速仪流速测量结果来分析沙坝海岸丁坝反射波形成的裂流特性,讨论了波浪节腹点对裂流位置和裂流空间尺度的影响。对不同周期情况在x=5 m沙坝顶处的速度剖面对比,分析了不同周期对裂流的影响。  相似文献   

20.
Directional wave data collected during an experiment at a location on the continental shelf of the south west coast of India using a WAVEC buoy, have been analysed based on the technique of Kuiket al (1988). The observed wave spectra indicate that the wave field is composed of sea waves (with peaks around 0·18 and 0·23 Hz) travelling nearly in the wind direction (WNW-N), and lower frequency (0·09 Hz) swell waves from the South. The parameterization of the wave directional spread shows that both local wind conditions and nonlinear wave-wave interactions control the shape of the directional distribution. The directional distribution is generally bimodal in the transition region between sea and swell and at higher frequencies when rapid changes in wind speed and direction occur.  相似文献   

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