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1.
Dependence of the energy released during earthquake on ambient shear stress   总被引：1，自引：0，他引：1  
Starting with dislocation model, using the result of the fracture mechanics: the slip displacement at the crack tip is proportional to the length of the crack and the applied ambient shear stressτ 0 2 , we consider the dislocation in the earthquake to be the slip displacement at the crack tip and have obtained the analysis expresses of displacement and velocity pulse for the circular crack and have calculated the seismic wave energy radiated by earthquake. The seismic wave energyE ∞M 0 τ 0 2 f(v) r , i. e.E is proportional to the seismic momentM 0 and the square of the ambient shear stressτ 0 2 and increases with the rupture velocityv r . In frequency domain, integrating the square of source velocity spectrum derived from our the scaling law model, we have also obtained the seismic wave energyE released by earthquake and earthquake radiated effficiencyη.E ∞M 0 τ 0 2 also. If takingτ 0 = 10.0 MPa, E=4.79M 0. This result is consistent with the estimate by Vassiliou and Kanamori (1982). Theη=5.26%. The distribution of the seismic wave energy is that most of the energy contains in the frequency range between the first corner frequencyf c1 and thirdf c3, amount to 92.3% the energy in the rangef<f c1 is about 3.85% and 3.85% whenf>f c3. Thef c3 is about 8Hz forM ⩾ 6, thus most of radiated energy is below 2Hz. This phenomenon had been verified by Vassiliou Kanamori. Previous results show the energy radiated by earthquake to be strongly dependent on ambient shear stress. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 146–152, 1993. This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledged. The authors are also grateful to Professor Klussmann and Mr. Hasthoff for their lots of help.  相似文献   

2.
While the hydrological balance of forest ecosystems has often been studied at the annual level, quantitative studies on the factors determining rainfall partitioning of individual rain events are less frequently reported. Therefore, the effect of the seasonal variation in canopy cover on rainfall partitioning was studied for a mature deciduous beech (Fagus sylvatica L.) tree over a 2‐year period. At the annual level, throughfall amounted to 71% of precipitation, stemflow 8%, and interception 21%. Rainfall partitioning at the event level depended strongly on the amount of rainfall and differed significantly (p < 0·001) between the leafed and the leafless period of the year. Therefore, water fluxes of individual events were described using a multiple regression analysis (ra2 > 0·85, n = 205) with foliation, rainfall characteristics and meteorological variables as predictor variables. For a given amount of rainfall, foliation significantly increased interception and decreased throughfall and stemflow amounts. In addition, rainfall duration, maximum rainfall rate, vapour pressure deficit, and wind speed significantly affected rainfall partitioning at the event level. Increasing maximum hourly rainfall rate increased throughfall and decreased stemflow generation, while higher hourly vapour pressure deficit decreased event throughfall and stemflow amounts. Wind speed decreased throughfall in the growing period only. Since foliation and the event rainfall amount largely determined interception loss, the observed net water input under the deciduous canopy was sensitive to the temporal distribution of rainfall. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
Utilizing an eigenfunction decomposition, we study the growth and spectra of energy in the vortical (geostrophic) and wave (ageostrophic) modes of a three-dimensional (3D) rotating stratified fluid as a function of ε = f/N, where f is the Coriolis parameter and N is the Brunt–Vaisala frequency. Throughout, we employ a random large-scale forcing in a unit aspect ratio domain and set these parameters such that the Froude and Rossby numbers are roughly comparable and much less than unity. Working in regimes characterized by moderate Burger numbers, i.e. Bu = 1/ε2 < 1 or Bu ≥ 1, our results indicate profound change in the character of vortical and wave mode interactions with respect to Bu = 1. Indeed, previous analytical work concerning the qualitatively different nature of these interactions has been in limiting conditions of rotation or stratification domination (i.e. when Bu ? 1 or Bu ? 1, respectively). As with the reference state of ε = 1, for ε < 1 the wave mode energy saturates quite quickly and the ensuing forward cascade continues to act as an efficient means of dissipating ageostrophic energy. Further, these saturated spectra steepen as ε decreases: we see a shift from k ?1 to k ?5/3 scaling for k f < k < k d (where k f and k d are the forcing and dissipation scales, respectively). On the other hand, when ε > 1 the wave mode energy never saturates and comes to dominate the total energy in the system. In fact, in a sense the wave modes behave in an asymmetric manner about ε = 1. With regard to the vortical modes, for ε ≤ 1, the signatures of 3D quasigeostrophy are clearly evident. Specifically, we see a k ?3 scaling for k f < k < k d and, in accord with an inverse transfer of energy, the vortical mode energy never saturates but rather increases for all k < k f . In contrast, for ε > 1 and increasing, the vortical modes contain a progressively smaller fraction of the total energy indicating that the 3D quasigeostrophic subsystem, though always present, plays an energetically smaller role in the overall dynamics. Combining the vortical and wave modes, the total energy for k > k f and ε ≤ 1 shows a transition as k increases wherein the vortical modes contain a large portion of the energy at large scales, while the wave modes dominate at smaller scales. There is no such transition when ε > 1 and the wave modes dominate the total energy for all k > k f .  相似文献   

4.
In order to empirically obtain the scaling relationships for the high-frequency ground motion in the Western Alps (NW Italy), regressions are carried out on more than 7500 seismograms from 957 regional earthquakes. The waveforms were selected from the database of 6 three-component stations of the RSNI (Regional Seismic network of Northwestern Italy). The events, M W ranging between 1.2 and 4.8, were recorded within a hypocentral distance of 200 km during the time period: 1996–2001. The peak ground velocities are measured in selected narrow-frequency bands, between 0.5 and 14 Hz. Results are presented in terms of a regional attenuation function for the vertical ground motion, a set of vertical excitation terms at the reference station STV2 (hard-rock), and a set of site terms (vertical and horizontal), all relative to the vertical component of station STV2.The regional propagation of the ground motion is modeled after quantifying the expected duration of the seismic motion as a function of frequency and hypocentral distance. A simple functional form is used to take into account both the geometrical and the anelastic attenuation: a multi-variable grid search yielded a quality factor Q(f) = 310f 0.20, together with a quadri-linear geometrical spreading at low frequency. A simpler, bi-linear geometrical spreading seems to be more appropriate at higher frequencies (f > 1.0 Hz). Excitation terms are matched by using a Brune spectral model with variable, magnitude-dependent stress drop: at M w 4.8, we used Δσ = 50 MPa. A regional distance-independent attenuation parameter is obtained (κ0 = 0.012 s) by modelling the average spectral decay at high frequency of small earthquakes.In order to predict the absolute levels of ground shaking in the region, the excitation/attenuation model is used through the Random Vibration Theory (RVT) with a stochastic point-source model. The expected peak-ground accelerations (PGA) are compared with the ones derived by Ambraseys et al. (1996) for the Mediterranean region and by Sabetta and Pugliese (1996) for the Italian territory.  相似文献   

5.
Ｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆａｍｂｉｅｎｔｓｔｒｅｓｓｖａｌｕｅｓｆｏｒｍｉｃｒｏ－ｅａｒｔｈｑｕａｋｅｓｅｑｕｅｎｃｅｓｉｎＷｅｓｔｅｒｎＹｕｎｎａｎ　Ｅａｒｔｈｑｕａｋｅ　Ｐｒｅｄｉｃｔｉｏｎ　Ｅｘｐｅｒｉｍｅｎｔａｌ　ＦｉｅｌｄＪｉａ－Ｚ...  相似文献   

6.
By linear regression and orthogonal regression methods, comparisons are made between different magnitudes (lo-cal magnitude ML, surface wave magnitudes MS and MS7, long-period body wave magnitude mB and short-period body wave magnitude mb) determined by Institute of Geophysics, China Earthquake Administration, on the basis of observation data collected by China Seismograph Network between 1983 and 2004. Empirical relations between different magnitudes have been obtained. The result shows that: 1 As different magnitude scales reflect radiated energy by seismic waves within different periods, earthquake magnitudes can be described more objectively by using different scales for earthquakes of different magnitudes. When the epicentral distance is less than 1 000 km, local magnitude ML can be a preferable scale; In case M<4.5, there is little difference between the magnitude scales; In case 4.5MS, i.e., MS underestimates magnitudes of such events, therefore, mB can be a better choice; In case M>6.0, MS>mB>mb, both mB and mb underestimate the magnitudes, so MS is a preferable scale for deter-mining magnitudes of such events (6.08.5, a saturation phenomenon appears in MS, which cannot give an accurate reflection of the magnitudes of such large events; 2 In China, when the epicentral distance is less than 1 000 km, there is almost no difference between ML and MS, and thus there is no need to convert be-tween the two magnitudes in practice; 3 Although MS and MS7 are both surface wave magnitudes, MS is in general greater than MS7 by 0.2~0.3 magnitude, because different instruments and calculation formulae are used; 4 mB is almost equal to mb for earthquakes around mB4.0, but mB is larger than mb for those of mB≥4.5, because the periods of seismic waves used for measuring mB and mb are different though the calculation formulae are the same.  相似文献   

7.
Although we know that rainfall interception (the rain caught, stored, and evaporated from aboveground vegetative surfaces and ground litter) is affected by rain and throughfall drop size, what was unknown until now is the relative proportion of each throughfall type (free throughfall, splash throughfall, canopy drip) beneath coniferous and broadleaved trees. Based on a multinational data set of >120 million throughfall drops, we found that the type, number, and volume of throughfall drops are different between coniferous and broadleaved tree species, leaf states, and timing within rain events. Compared with leafed broadleaved trees, conifers had a lower percentage of canopy drip (51% vs. 69% with respect to total throughfall volume) and slightly smaller diameter splash throughfall and canopy drip. Canopy drip from leafless broadleaved trees consisted of fewer and smaller diameter drops (D50_DR, 50th cumulative drop volume percentile for canopy drip, of 2.24 mm) than leafed broadleaved trees (D50_DR of 4.32 mm). Canopy drip was much larger in diameter under woody drip points (D50_DR of 5.92 mm) than leafed broadleaved trees. Based on throughfall volume, the percentage of canopy drip was significantly different between conifers, leafed broadleaved trees, leafless broadleaved trees, and woody surface drip points (p ranged from <0.001 to 0.005). These findings are partly attributable to differences in canopy structure and plant surface characteristics between plant functional types and canopy state (leaf, leafless), among other factors. Hence, our results demonstrating the importance of drop‐size‐dependent partitioning between coniferous and broadleaved tree species could be useful to those requiring more detailed information on throughfall fluxes to the forest floor.  相似文献   

8.
Partitioning resistance to overland flow on rough mobile beds   总被引：1，自引：0，他引：1  
For overland flows transporting predominantly bed load over rough mobile beds without rainfall, resistance to flow f may be divided into four components: surface resistance fs, form resistance ff, wave resistance fw, and bed‐mobility resistance fm. In this study it is assumed that f = fs + ff + fw + fm, and an equation is developed for each component. The equations for fs and ff are borrowed from the literature, while those for fw and fm are developed from two series of flume experiments in which the beds are covered with various concentrations of large‐scale roughness elements. The first series consists of 65 experiments on fixed beds, while the second series contains 194 experiments on mobile beds. All experiments were performed on the same slope (S = 0·114) and with the same size of sediment (D = 0·00074 m). The equations for fw and fm are derived by a combination of dimensional analysis and regression analysis. The analyses reveal that the major controls of fw and fm are the Froude number F and the concentration of the roughness elements Cr. When the equations for fw and fm are summed, the Cr terms cancel out, leaving fw+m = 0·63F?2. An equation is developed that predicts total f, and the contributions of fs, ff, fw and fm to f are computed from the series 1 and 2 experiments. An analysis of the first series reveals that in clear‐water flows over fixed beds, fw accounts for 52 per cent of f. A similar analysis of the second series indicates that in sediment‐laden flows over mobile beds fw comprises 37 per cent and fm 32 per cent of f, so that together fw and fm account for almost 70 per cent of f. Finally, regression analyses indicate that where F > 0·5, fw and fm each vary with F?2 and fw/fm = 1·18. The equation developed here for predicting total f applies only to the range of hydraulic, sediment, and bed roughness conditions represented by the experimental data. With additional data from a broader range of conditions the same methodology as employed here could be used to develop a more general equation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

9.
选取2009~2014年发生在云南地区、每个地震均在10个以上台站有记录的7412个地震数据,作走时曲线。同时为提高精度,重点对其中每个地震均在80%以上台站有记录的、ML≥3.0的83个地震数据,再作线性分析、折合走时曲线和区间稳定性分析,结合前人研究成果得到了研究区的初始地壳速度模型。选取2010~2014年云南省内M≥3.0的200次地震,采用Hyposat批处理方法迭代初始速度模型,以及对S波作分层速度拟合,得到云南地区的地壳速度模型,即2015云南模型:v_(P1)=6.01km/s,v_(P2)=6.60km/s,v_(Pn)=7.89km/s,H_1=20km,H_2=21km,v_(S1)=3.52km/s,v_(S2)=3.86km/s,v_(sn)=4.43km/s。基于新模型的地震重定位分析表明,云南地区地震事件大多发生于20km内的上地壳;对2011年3月10日盈江M5.8和2014年8月3日鲁甸M6.5典型地震进行重定位,得出震源深度分别与精定位结果和震中强震台震源距接近,表明新的一维速度模型能更好地反映研究区平均速度结构。  相似文献   

10.
In order to estimate the recurrence intervals for large earthquakes occurring in eastern Anatolia, this region enclosed within the coordinates of 36∘–42∘N, 35∘–45∘E has been separated into nine seismogenic sources on the basis of certain seismological and geomorphological criteria, and a regional time- and magnitude-predictable model has been applied for these sources. This model implies that the magnitude of the preceding main shock which is the largest earthquake during a seismic excitation in a seismogenic source governs the time of occurrence and the magnitude of the expected main shock in this source. The data belonging to both the instrumental period (MS≥ 5.5) until 2003 and the historical period (I0≥ 9.0 corresponding to MS≥ 7.0) before 1900 have been used in the analysis. The interevent time between successive main shocks with magnitude equal to or larger than a certain minimum magnitude threshold were considered in each of the nine source regions within the study area. These interevent times as well as the magnitudes of the main shocks have been used to determine the following relations:
fwawhere Tt is the interevent time measured in years, Mmin is the surface wave magnitude of the smallest main shock considered, Mp is the magnitude of the preceding main shock, Mf is magnitude of the following main shock, and M0 is the released seismic moment per year in each source. Multiple correlation coefficient and standard deviation have been computed as 0.50 and 0.28, respectively for the first relation. The corresponding values for the second relation are 0.64 and 0.32, respectively. It was found that the magnitude of the following main shock Mf does not depend on the preceding interevent time Tt. This case is an interesting property for earthquake prediction since it provides the ability to predict the time of occurrence of the next strong earthquake. On the other hand, a strong negative dependence of Mf on Mp was found. This result indicates that a large main shock is followed by a smaller magnitude one and vice versa. On the basis of the first one of the relations above and taking into account the occurrence time and magnitude of the last main shock, the probabilities of occurrence P(Δ t) of main shocks in each seismogenic source of the east Anatolia during the next 10, 20, 30, 40 and 50 years for earthquakes with magnitudes equal 6.0 and 7.0 were determined. The second of these relations has been used to estimate the magnitude of the expected main shock. According to the time- and magnitude-predictable model, it is expected that a strong and a large earthquake can occur in seismogenic Source 2 (Erzincan) with the highest probabilities of P10 = 66% (Mf = 6.9 and Tt = 12 years) and P10 = 44% (Mf = 7.3 and Tt = 24 years) during the future decade, respectively.  相似文献   

11.
Phosphorus (P) export from agricultural lands above known threshold levels can result in adverse impacts to receiving water quality. Phosphorus loss occurs in dissolved and sediment‐bound, or particulate phosphorous (PP), forms, with the latter often dominating losses from row‐cropped systems. To target practices, land managers need good computer models and model developers need good monitoring data. Sediment monitoring data (e.g. radiometric finger printing and sediment P sorption capacity) can help identify sediment source areas and improve models, but require more sediment mass than is typically obtained by automatic sampling. This study compares a simple suspended sediment sampler developed at the University of Exeter (UE) with automatic sampling in intermittent channels draining corn and alfalfa fields. The corn field had a greater runoff coefficient (27%) than alfalfa (11%). No differences were found in enrichment ratios (sediment constituent/soil constituent) in PP (PPER) or percent loss on ignition (LOIER) between paired UE samplers on corn. The median LOIER for the UE samplers (1·9%) did not differ significantly (p > 0·13) from the automatic sampler (2·0%). The PPER from the UE samplers was on average 20% lower than the automatic samplers. A correlation (r2 = 0·75) was found between sediment PP and % LOI from automatic samplers and UE samplers for particles < 50 µm, while for > 50 µm PP concentration did not change with changes in % LOI. Sediment ammonium‐oxalate extractable metals were similarly related to LOI, with the strongest correlation for iron (r2 = 0·71) and magnesium (r2 = 0·70). Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

12.
介绍了“中国大陆构造环境监测网络”（简称“陆态网络”）重力观测体系。从分形几何学角度研究了陆态网络重力测网的分形特征,计算得到测网分维数Df=1.5598、最佳网格化间距r=139km。综合测网分维数与重力时变距、重力异常范围、测网范围等量化指标,对陆态网络重力测网的地震监测能力进行分析,结果表明,测网最佳网格化间距等特征值与MS6.0地震引发的重力场变化区域的特征异常区半径等统计量化指标接近,具备监测我国除边界及藏北无人区以外大陆区域的MS6.0及以上地震的能力。  相似文献   

13.
An eigenfunction solution is presented for the dynamic response of vertical circular cylinders to earthquake excitation in a compressible fluid of finite depth. This single eigenseries expansion eliminates the need for a double summation over both the eigenfunctions and the trial functions as required by Rayleigh-Ritz methods. Revised definitions for the added mass and hydrodynamic radiation damping coefficients per unit length are derived from the hydrodynamic fluid pressures. Based on comparisons between these newly defined coefficients, the compressibility of the fluid is found to be relatively more important at dimensionless frequencies greater than unity (ω > 1.0) when analysing both rigid and flexible cylinders having relatively large diameter to water depth ratios,r0/h > 0.25 (squatty type). This conclusion regarding the relative importance of the fluid compressibility is derived from a comparison between the relative magnitudes and the vertical distributions over depth of both the added mass and radiation damping coefficients per unit length for both rigid and flexible squatty cylinders. From additional comparisons with Rayleigh-Ritz solutions that require trial functions, the results for totally immersed flexible slender cylinders (r0/h< 0.10) are shown to be equivalent; but the results for totally immersed flexible squatty cylinders (r0/h > 0.25) are not. The reason for this difference appears to be in the truncation of the trial function series in the Rayleigh-Ritz methods, which excludes the higher mode shapes, and in the definitions of the added mass coefficients. Comparisons with laboratory data for both rigid and flexible cylinders confirm the accuracy of the solutions obtained by the eigenseries in the limited frequency interval above the highest frequency for surface gravity waves (f > 1.0 Hz) and below the first dimensionless cut-off frequency for acoustic waves (ω< 1.0).  相似文献   

14.
Summary The relations of the defining parameters of a geodetic system to the deflections of the vertical in this system given byVening Meinesz have been used in the computation of a best fitting ellipsoid. The data was that used byHayford in the computation of the resulting International Ellipsoid. Assuming the undulation (N 0) at Meades Ranch to be zero, the results are: a=6,378,194 m and l/f=299.9. This a is much nearer to modern values than that of the Internaitonal Ellipsoid. If a flattening of 1/298.24 is fixed andN 0=+3m,a=6,378,164 m which differs by one meter from a recent determination given byKaula.  相似文献   

15.
The 2010 Yushu MS7.1 earthquake occurred in Ganzi-Yushu fault, which is the south boundary of Bayan Har block. In this study, by using double difference algorithm, the locations of mainshock (33.13°N, 96.59°E, focal depth 10.22 km) and more than 600 aftershocks were obtained. The focal mechanisms of the mainshock and some aftershocks with MS>3.5 were estimated by jointly using broadband velocity waveforms from Global Seismic Network (GSN) and Qinghai Seismic Network as well. The focal mechanisms and relocation show that the strike of the fault plane is about 125° (WNW-ESE), and the mainshock is left-laterally strikeslip. The parameters of shear-wave splitting were obtained at seismic stations of YUS and L6304 by systematic analysis method of shear-wave splitting (SAM) method. Based on the parameters of shear-wave splitting and focal mechanism, the characteristics of stress field in seismic source zone were analyzed. The directions of polarization at stations YUS and L6304 are different. It is concluded that after the mainshock and the MS6.3 aftershock on April 14, the stress-field was changed.  相似文献   

16.
In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered respectively at the 4 short period stations installed near the foci shortly after theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and northern areas. The southern area presents a faster attenuation (Q c=114), whereas the northern area shows a slower attenuation (Q c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear relation between the coda source factorA o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM 0=lgA 0(f)+17.6,M D=0.67lgA 0(f)+1.21 and logM 0=1.5M D+15.79. In addition, the rates of amplitude attenuationβ s andβ m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ s/βm=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations which can distinguish between the inherentQ i and scatteringQ s, testify to this areas having lowQ-values correspond to stronger scatterings. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 71–82, 1992. This study is partly supported by the Seismological Science Foundation of the State Seismological Bureau of China, and the present English version of the paper is translated from its Chinese original by Wenyi Xia, Seismological Bureau of Yunnan Province.  相似文献   

17.
The M w=9.3 megathrust earthquake of December 26, 2004 off the coast of Sumatra in the Indian Ocean generated a catastrophic tsunami that caused widespread damage in coastal areas and left more than 226,000 people dead or missing. The Sumatra tsunami was accurately recorded by a large number of tide gauges throughout the world's oceans. This paper examines the amplitudes, frequencies and wave train structure of tsunami waves recorded by tide gauges located more than 20,000 km from the source area along the Pacific and Atlantic coasts of North America.  相似文献   

18.
M TSU : Recovering Seismic Moments from Tsunameter Records   总被引：1，自引：0，他引：1  
We define a new magnitude scale, MTSU, allowing the quantification of the seismic moment M0 of an earthquake based on recordings of its tsunami in the far field by ocean-bottom pressure sensors (``tsunameters') deployed in ocean basins, far from continental or island shores which are known to affect profoundly and in a nonlinear fashion the amplitude of the tsunami wave. The formula for MTSU, MTSU = log10 M0 − 20 = log10 X (ω) + CDTSU + CSTSU + C0, where X (ω) is the spectral amplitude of the tsunami, CDTSU a distance correction and CSTSU a source correction, is directly adapted from the mantle magnitude Mm introduced for seismic surface waves by Okal and Talandier. Like Mm, its corrections are fully justified theoretically based on the representation of a tsunami wave as a branch of the Earth's normal modes. Even the locking constant C0, which may depend on the nature of the recording (surface amplitude of the tsunami or overpressure at the ocean floor) and its units, is predicted theoretically. MTSU combines the power of a theoretically developed algorithm, with the robustness of a magnitude measurement that does not take into account such parameters as focal geometry and exact depth, which may not be available under operational conditions in the framework of tsunami warning. We verify the performance of the concept on simulations of the great 1946 Aleutian tsunami at two virtual gauges, and then apply the algorithm to 24 records of 7 tsunamis at DART tsunameters during the years 1994–2003. We find that MTSU generally recovers the seismic moment M0 within 0.2 logarithmic units, even under unfavorable conditions such as excessive focal depth and refraction of the tsunami wave around continental masses. Finally, we apply the algorithm to the JASON satellite trace obtained over the Bay of Bengal during the 2004 Sumatra tsunami, after transforming the trace into a time series through a simple ad hoc procedure. Results are surprisingly good, with most estimates of the moment being over 1029 dyn-cm, and thus identifying the source as an exceptionally large earthquake.  相似文献   

19.
Taipei, the capital of Taiwan, suffered from destructive earthquakes four times during the 20th century (M L = 7.3 on April 15, 1909; M L = 6.8 on November 15, 1986; the Chi–Chi M L = 7.3 earthquake on September 21, 1999; and M L = 6.8 on March 31, 2002). Analysis of recorded data shows a strong dependence of spectral amplification in the Taipei Basin on earthquake depth and azimuth. At low frequencies (f < 3 Hz) significant larger amplifications are observed for shallow earthquakes as compared to intermediate depth events. The former ones also display strong azimuthal dependence. As structures with large response periods such as bridges and tall buildings are sensitive to these low frequencies the understanding of the associated wave effects within the basin and their role for site effect amplification is critical. The tool we employ is 3D finite-difference modeling of wave propagation of incident wave fronts. The available detailed model of the basin allows studying the wave effects. Modeling clearly reveals that basin edge effects as observed in data are related to surface wave generation at the basin edges with a high degree of azimuthal dependency. The reproduced site amplification effects are in qualitative agreement with the observations from strong motion data.  相似文献   

20.
The Central Apennines, Italy, are characterized by moderate seismic activity on normal faults, oriented in directions parallel to the Apenninic chain. The subject of this study is the Umbria-Marche Apennines, a segment approximately 200-km long, where three main seismic events occurred in the last three decades. The 1979 Norcia earthquake was a Mw = 5.8 event, taking place at the south end of the considered segment. The 1984 Gubbio earthquake was a Mw = 5.6 event which took place at the north end. The 1997-1998 Colfiorito sequence constituted 8 main shocks with magnitudes Mw between 5 and 6 and epicenters located between the Gubbio and the Norcia earthquake areas. A model made of an elastic half-space is considered, in which the seismic sources are represented by rectangular dislocations which have the appropriate values of source parameters, and in which the static stress field produced by each event is calculated. The analysis of the Coulomb stress change (ΔC) as a function of time shows that the coseismic stress transfer and fault interaction played an important role in the region during the past three decades: 7 earthquakes of the 9 considered took place where ΔC>0. Such an interaction has been confirmed by the analysis of the aftershocks in the Colfiorito zone post September 26, 1997: about the 61% of the aftershocks considered took place where ΔC>0. The comparison between the ΔCs due to the coseismic stress transfer and the rate ΔĊt due to the tectonic stress allows us to quantify the time advance of the earthquakes. The ΔCs pattern shows positive values in two areas that can be regarded as historical seismic gaps.  相似文献   

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