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1.
Records of deep-focus Hindu Kush earthquakes in the depth ranges 70–110 and 190–230 km made by 45 digital and analogue seismic stations were analyzed to study the attenuation field of short period seismic waves in the lithosphere of central Tien Shan. The dynamic characteristics studied include the ratio of peak amplitudes in S and P waves (S/P) and the ratio of the S-wave maximum to the coda level in the range t = 400 ± 5 s, where t is the lapse time (S/c400) for 1.25 Hz. Comparatively high values of S/P are shown to prevail in most of the area, corresponding to lower S-wave attenuation. Upon this background is a band of high and intermediate attenuation in the west of the area extending along the Talas-Fergana fault in the south and afterwards turning north-northeast. The rupture areas of the two largest (M ≥ 7.0) earthquakes which have occurred in Tien Shan during the last 25 years are confined to this band. Abnormally high values of S/c400 were obtained for stations situated in the rupture zone of the August 19, 1992, magnitude 7.3 Suusamyr earthquake and around it. For two of the stations we found considerable time variations in the coda envelope before the earthquake. The effective Q was derived from compressional and shear wave data for the entire area, as well as for the band of high attenuation. Comparison with previous data shows that the attenuation field in the area has changed appreciably during 20–25 years, which can only be due to a rearrangement of the fluid field in the crust and uppermost mantle. It is hypothesized that a large earthquake is very likely to occur in the northern part of the attenuating band.  相似文献   

2.
—We analyze source parameters of microseismic events (M < ? 1) associated with high flow-rate water injections in a shale formation at a depth of 220 m. Two types of events were observed several hundred impulsive events with clear P- and S-wave arrivals, and continuous emissions with peaked spectra detected well into the experiment. For a representative collection of impulsive events, an ?2 model provided satisfactory fits to displacement spectra corrected for attenuation, and average quality factors of 34 and 15 were obtained for P and S waves. P-wave first motion analysis and E S ?/E P ratios indicated the existence of a non-double-couple component in some events, particularly early in the experiment. A clear difference was observed for estimates of stress release parameters as non-double-couple events had smaller stress drops and apparent stresses. The seismic efficiency of double-couple and non-double-couple events was limited to 0.9% and 0.05% respectively, with average values being 0.25% and 0.02%. A comparison of our results with those reported for a similar magnitude range in a hard-rock formation indicates considerably smaller estimates of stress drop and apparent stress in our case while seismic efficiencies are comparable.  相似文献   

3.
基于一维单侧有限移动震源模式,根据地震波传播过程中的多普勒效应,分别利用P波和S波拐角频率的方位变化,反演2012年7月20日江苏高邮、宝应交界MS4.9地震的发震断层面参数。P波和S波拐角频率的反演结果一致显示:本次地震的断层面破裂方向为232°左右,破裂面呈NE-SW向;地震马赫数v/c为0.2左右,平均破裂速度小于S波速度,破裂长度较短,为0.2~0.3km左右。破裂面方位与震源机制解、宏观烈度调查和余震精定位的研究结果具有一致性,结合震区周边的地质构造背景,分析认为滁河断裂很可能是高邮、宝应交界MS4.9地震的发震构造。  相似文献   

4.
Shallow strike slip earthquakes on vertical faults are modelled as two-dimensional antiplane strain ruptures in a uniformly prestressed homogeneous halfspace. Behind the rupture front, which is specified, the stress drops to a lower value. The elastodynamic boundary value problem is solved with a finite difference method. Several cases are studied, which include symmetric and one-directional rupture propagation, surface faulting, multiple events, variable rupture velocity, sticking and rebreaking of the fault plane. The time function of displacement, velocity and acceleration are interpreted as signals generated by events in the focus, namely starting, stopping and breaking through the surface of the rupture. The model explains peak velocity and peak acceleration in the near field of M5.5–6 earthquakes; which are typically about 0.2 m/s and 5 m/s2 at 10 km epicentral distance, if the rupture velocity is close to the shear wave velocity. Sticking of the fault does not alter the accelerograms significantly, but it increases the seismic moment in simple events and decreases it in multiple events.Contribution No. 226, Geophysical Institute, University of Karlsruhe.  相似文献   

5.
The characteristics of the attenuation field of short-period shear waves in the region of Nevada nuclear test site (NNTS) are studied. The seismograms of underground nuclear explosions (UNEs) and earthquakes recorded by three seismic stations in 1975–2012 at the epicentral distances of up to 1000 km are processed by the methods based on the analysis of the amplitude ratios of Sn to Pn and Lg to Pg waves, as well as the S-coda envelopes for close events. It is shown that the structure of the attenuation field in the Earth’s crust and upper mantle in the NNTS region experienced significant temporal variations during the interval of nuclear operations. The strongest variations were associated with UNEs conducted in the Pahute Mesa area, which held about two-thirds of the most intense explosions. Our data indicate that temporal variations in the structure of the attenuation field are related to the migration of deep fluids. A comparison of the general characteristics of the attenuation field in the regions of the three large nuclear test sites is presented.  相似文献   

6.
Effects of Rock Damage on Seismic Waves Generated by Explosions   总被引：1，自引：0，他引：1  
—?In studying the physical processes involved in the generation of seismic waves by explosions, it is important to understand what happens in the region of high stresses immediately surrounding the explosion. This paper examines one of the processes that takes place in this region, the growth of pre-existing cracks, which is described quantitatively as an increase in rock damage. An equivalent elastic method is used to approximate the stress field surrounding the explosion and a micro-mechanical model of damage is used to calculate the increase in damage. Simulations for a 1?kt explosion reveal that the region of increased damage can be quite large, up to ten times the cavity radius. The damage is initiated on a damage front that propagates outward behind the explosive stress wave with a velocity intermediate between that of P and S waves. Calculations suggest that the amount of increased damage is controlled primarily by the initial damage and the extent of the region of increased damage is controlled primarily by the initial crack radius. The motions that occur on individual cracks when damage increases are converted to seismic moment tensors which are then used to calculate secondary elastic waves which radiate into the far field. It is found that, while the contribution from an individual crack is small, the combined effect of many cracks in a large region of increased damage can generate secondary waves that are comparable in amplitude to the primary waves generated by the explosion. Provided that there is asymmetry in the damage pattern, this process is quite effective in generating S waves, thus providing a quantitative explanation of how S waves can be generated by an explosion. Two types of asymmetry are investigated, a shear pre-stress and a preferred orientation of cracks, and it is found that both produce similar effects.  相似文献   

7.
—Studies of seismic anisotropy in situ can help to discriminate between different rock types for the lower crust. In this context we investigate the sensitivity of an iterative linearized 3-D travel-time inversion scheme for transversely isotropic media with respect to two types of systematic errors wrong velocities and interface topography of the hanging wall of the lower crust. The computations simulate realistic field conditions such as found for the Variscan crust at the Urach geothermal anomaly. The study focusses on the possible information content of split S M ?S arrivals observed along two orthogonal expanding spread profiles. It ensues that an imperfect knowledge of the layer geometry is of minor importance compared to errors in the velocities of the hanging wall. In particular, upper crust anisotropy has to be considered carefully. Generally, the anisotropy of transversely polarized shear waves (SH waves) was recovered with higher accuracy than the anisotropy of vertically polarized shear waves (SV waves).  相似文献   

8.
Seismicity and Casing Failures Due to Steam Stimulation in Oil Sands   总被引：1，自引：0，他引：1  
—This paper describes observations of seismicity and casing failures associated with steam stimulation operations at Imperial Oil Ltd.’s Cold Lake oil field in Alberta, Canada. A total of 11 oil-producing pads were monitored over a 1–2 year period using 3-component geophones cemented at depths ranging from 160 m to 400 m and data acquisition systems with a flat frequency response up to 1.5 kHz. Most of the seismicity was detected during the steaming operations and was located in the formation overlying the oil-bearing layer. Some activity was observed in the shales above, however, the reservoir itself showed almost no evidence of seismicity. The estimated seismic moment of the observed events was in the range 105–107 N·m (?2.7 < M < ?1.3). According to a theoretical model (Talebi et al., 1998) and in situ observations, the seismic source corresponding to casing failure events should be well described by a dipole registering seismic moment in the order of 2 · 106 N·m. Seismic signals of a total of four observed casing failures were analyzed. The partial failures produced seismic moments slightly lower than this value while total failures were stronger by about one order of magnitude. The use of the SV/SH amplitude ratio, in conjunction with accurate source locations, provided a robust technique for the detection of casing failures.  相似文献   

9.
—Imperial Oil Resources Limited uses cyclic steam stimulation to recover oil from their Cold Lake oil field in Alberta. This operation, in particular situations, can be associated with the failure of well casings in the Colorado shales above the oil-bearing formation. A number of fluid injection operations was undertaken at this site and the associated microseismicity was detected using two three-component geophones and fifteen hydrophones. The purpose of this experiment was to simulate the occurrence of a casing failure, determine the feasibility of monitoring in a shallow environment, and characterize the microseismic activity. A calibration survey provided values of 1786 ± 108 m/s for P-wave velocity, 643 ± 56 m/s for S-wave velocity and 0.428 ± 0.017 for Poisson’s ratio in the shale formation. Estimates of the quality factor Q P were 15 for the horizontal direction and 38 for the vertical direction, corroborating the evidence of velocity anisotropy. Calibration shots were located to within 10 m of the actual shot points using triangulation and polarization techniques. Several hundred microseis mic events were recorded and 135 events were located. The results showed that microseismic activity was confined to depths within 10 meters of the injection depth. The experiment clearly established the feasibility of detecting microseismicity induced by fluid injection rates typical of casing failures in shales at distances over 100 m.  相似文献   

10.
Large, shallow, thrust earthquakes in the Solomon Islands region tend to occur in closely related pairs. Two recent sequences are July 14, 1971 (MS = 7.9) and July 26, 1971 M(S = 7.9) and 14h37m, July 20, 1975 (MS = 7.9) and 19h54m, July 20, 1975 (MS = 7.7). The mechanism of these seismic doublets has important bearing on the triggering mechanism of earthquakes in subduction zones. Detailed analysis of the seismic body waves and surface waves were performed on the 1971, 1974, and 1975 doublets, providing a better understanding of: (1) the mechanics of seismic triggering, (2) the state of stress on the fault plane, and (3) the nature of subduction between the Pacific and Indian plates. The results indicate that although the geometry of the subduction zone in the Solomon Islands is complicated by the presence of several sub-plates, the slip direction of the Indian plate with respect to the Pacific plate is relatively uniform over the entire region. The large seismic moments of the 1971 sequence (1.2 · 1028 and 1.8 · 1028 dyne cm) indicate that these events directly represent the underthrusting of the Indian and Solomon plates beneath the Pacific plate. The body waves from these doublets, recorded on the WWSSN long-period seismograms, are remarkably impulsive and simple compared with those from events of comparable seismic moment in other subduction zones. In addition, the source dimensions of the body waves are 30–70 km in length, substantially smaller than the overall rupture surfaces radiating the surface waves which are 100–300 km in length. These facts suggest the existence of relatively large, isolated high-stress zones on the fault plane. This type of stress distribution is distinct from other regions which have more heterogeneous stress distribution on the fault plane, and this is proposed as the principal characteristic of this region responsible for the occurrence of the doublets and for the apparent efficiency of triggering in the Solomon trench. Prior to the 1971 sequence, similar sequences have occurred in the same area in 1919–1920 and 1945–1946. From the amount of slip (1.3 m) determined for the 1971 sequence and the apparent recurrence interval of 25 years, a seismic slip rate of 5 cm yr?1 is determined. This value is a significant portion of the convergence rate between the Indian and Pacific plates indicating that the plate motion here is taken up largely by seismic slip.  相似文献   

11.
—Anisotropy in the subcontinental lithosphere becomes increasingly important, because it is observed in many seismic studies especially for P n -waves. Typical rocks of the uppermost mantle are peridotites, which predominantly exhibit a pronounced elastic anisotropy. This anisotropy is mainly caused by the anisotropic elastic properties and the lattice preferred orientation (here referred to as texture) of olivine. To evaluate the elastic anisotropy of peridotites from the subcontinental lithosphere, specimens of the Northern Hessian Depression (Germany) and the Balmuccia Ultramafic Massif (Northern Italy) have been used. They comprise four olivine texture types, which are characteristic for olivine textures observed worldwide. The bulk rock elastic properties have been calculated using olivine and orthopyroxene textures, their single-crystal elastic constants at ambient pressure/temperature conditions and their volume fraction. Clinopyroxene and spinel are assumed to be randomly distributed. The effect of four different orientations of the foliation within the uppermost mantle has been evaluated, since this orientation is usually unknown.¶Two of the olivine textures have a pronounced azimuthal dependence of compressional waves when a horizontal foliation within the uppermost mantle is presumed. These variations cause significant azimuthal variations of the P-wave reflections coefficients at the Moho. Primarily, we predict a significant azimuthal dependence of the critical points where the reflected amplitude increases from approximately 15% to 95%. Possibly, these azimuthal variations can be detected by seismic reflection measurements carried out at earth surface.¶The remaining two texture types only manifest a small directional dependence. When anisotropy of compressional waves is observed in seismic studies, these latter types can only be of subordinate importance. However, all of the peridotites investigated are able to explain the seismically observed azimuthal variations of compressional waves when a vertical foliation is proposed. This ambiguity can be substantially reduced when shear waves (S-waves) are considered. The directional distribution of S-wave velocities and of the S-wave splitting exhibits characteristic patterns for the different olivine texture types. This could be used to discriminate between different texture types and orientations of the foliation within the uppermost mantle. A fundamental requirement for a more comprehensive interpretation is the availability of detailed S-wave observations. The maximum S-wave splitting in the peridotites investigated coincides with the maximum of the faster (leading) S-wave. This may be of importance to detect S-wave splitting in future seismic studies.  相似文献   

12.
In the summer of 1984, a three-dimensional, high-resolution microearthquake network was operated in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau, Utah. During a six-week period, approximately 3,000 seismic events were observed of which the majority were impulsive, higher frequency (>10 Hz), short duration (<2–3 sec) events probably associated with the caving of the roof from a longwall operation. In contrast, 234 of the largest located events appeared to occur predominantlybeneath the mines to a depth of 2 to 3 km consistent with previous studies. The magnitudes of these events ranged from less thanM c 0 to 1.6. In addition to the unusual depths of these latter events, an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non-double-couple, possibly implosional source. Implosional events have been observed in other studies of mine seismicity; however, the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms. Previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse, and a shear-implosional displacement mechanism. Shear failure must be involved in the failure process of the Gentry Mountain implosional events as evidenced by well-defined shear waves in the observed seismograms. Simultaneous monitoring in the East Mountain coal mining area to the south by the University of Utah revealed typical shear failure events mixed with implosional events. The observed double-couple, reverse focal mechanisms at East Mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas. This suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field. Thus in addition to the seismic events associated with caving of the roof from the longwall operation, there appear to be at least two other types of mining-induced seismic events occurring in the eastern Wasatch Plateau, both submine in origin: (1) events characterized by apparent non-double-couple possibly implosional focal mechanisms and well-defined shear waves; and (2) shear events, which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes. The small mining-induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed, pre-existing zones of weakness. Topography, overburden, method of mining, and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events.  相似文献   

13.
Scaling relations for seismic events induced by mining   总被引：1，自引：0，他引：1  
The values of seismic moment andS-wave corner frequency from 1575 seismic events induced in South African, Canadian, Polish, and German underground mines were collected to study their scaling relations. The values ofP-wave corner frequency from 649 events were also available. Seismic moments of these events range from 5*103 to 2*1015 N·m (moment magnitude is from –3.6 to 4.1), theS-wave corner frequency ranges from 0.7 to 4438 Hz, and theP-wave corner frequency is between 5 and 4010 Hz. The slope of a regression line between the logarithm ofS- andP-wave corner frequencies is equal to one, and the corner frequencies ofP waves are higher than those ofS waves on the average by about 25 percent. In studies of large and moderate earthquakes it has been found that stress drop is approximately independent of the seismic moment, which means that seismic moment is inversely proportional to the third power of corner frequency. Such a behavior was confirmed for most of the data considered here. A breakdown in the similarity betwen large and small events seems to occur for the events with moment magnitude below –2.5. The average values of seismic moment referred to the same range of corner frequency, however, are vastly different in various mining areas.  相似文献   

14.
Parameters of seismic waves from clusters of local weak earthquakes that occurred at the upper boundary of the seismofocal zone in depth intervals of 40–60 and 70–90 km along eastern Hokkaido are investigated for the period 1998–2003, including the strong (M = 8.0) Tokachi-Oki earthquake of September 26, 2003. Analysis of data indicates that the distribution of anisotropic properties along Hokkaido is inhomogeneous and parameters of split waves (the azimuth of the fast S wave and the time delay between split S waves) are sensitive to variations in the stress-strain state of the medium. Unstable behavior of split wave parameters and increased values of the ratio V P /V S for clusters of events in the areas of the Hidaka Mountains and Nemuro Peninsula imply that the medium is in a mechanically weakened state (in the regime of intense dilatant deformation). On the contrary, the regions beneath the Tokachi and Kushiro plains are more rigid and are characterized by lower V P /V S values and comparatively stable behavior of wave parameters. Anomalous parameters of split waves from events of clusters in areas of different stations correlate with each other and are related to occurrence times of large earthquakes around Hokkaido, which may point to a redistribution of stresses and strains and fluid migration in the subduction zone.  相似文献   

15.
Several independent indicators imply a high probability of a great (M > 8) earthquake rupture of the subduction megathrust under the Mentawai Islands of West Sumatra. The human consequences of such an event depend crucially on its tsunamigenic potential, which in turn depends on unpredictable details of slip distribution on the megathrust and how resulting seafloor movements and the propagating tsunami waves interact with bathymetry. Here we address the forward problem by modelling about 1000 possible complex earthquake ruptures and calculating the seafloor displacements and tsunami wave height distributions that would result from the most likely 100 or so, as judged by reference to paleogeodetic data. Additionally we carry out a systematic study of the importance of the location of maximum slip with respect to the morphology of the fore-arc complex. Our results indicate a generally smaller regional tsunami hazard than was realised in Aceh during the December 2004 event, though more than 20% of simulations result in tsunami wave heights of more than 5 m for the southern Sumatran cities of Padang and Bengkulu. The extreme events in these simulations produce results which are consistent with recent deterministic studies. The study confirms the sensitivity of predicted wave heights to the distribution of slip even for events with similar moment and reproduces Plafker's rule of thumb. Additionally we show that the maximum wave height observed at a single location scales with the magnitude though data for all magnitudes exhibit extreme variability. Finally, we show that for any coastal location in the near field of the earthquake, despite the complexity of the earthquake rupture simulations and the large range of magnitudes modelled, the timing of inundation is constant to first order and the maximum height of the modelled waves is directly proportional to the vertical coseismic displacement experienced at that point. These results may assist in developing tsunami preparedness strategies around the Indian Ocean and in particular along the coasts of western Sumatra.  相似文献   

16.
Love waves from five earthquakes in southwest Germany, Italy, Yugoslavia, Greece and Algeria, as recorded at the broadband Gräfenberg array in eastern Bavaria, are modelled in detail using an extended reflectivity method. The focal mechanisms are taken from the literature or determined from long-period WWNSS data. The theoretical double-couple moment function used for modelling increases smoothly during the risetime T from zero to the seismic moment M0. T and M0 are determined by matching the observed and theoretical Love-wave seismograms in the long-period WWNSS frequency band. T is approximately equal to the rupture duration; values from 1.4 to 20 s are found. Seismic moments generally agree within a factor of about two with those found by other authors from larger data sets. The earthquakes in southwest Germany and Greece were simple events and can be modelled very well by one double couple. In the case of the other earthquakes, the theoretical Love-wave seismograms are too short. For these earthquakes there is some independent evidence for a multiple-event nature. This evidence is condensed into source models consisting of two or three double couples representing separate and complete sub-earthquakes, which then explain the observations quite well. In the case of the Algerian earthquake, the long Love-wave duration may also be due to complications in structure along the wavepath across the Mediterranean and the Alps. The present results show that accurate Love-wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration. Use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied. The Gräfenberg array is well suited for such an investigation of European and North African earthquakes.  相似文献   

17.
—We determined the response to P- and S-wave incidence of the permanent stations of the seismic network of Baja California (RESNOM) using two independent methods. We selected 65 events with magnitudes between 2.2 and 4.8 and hypocentral distances ranging between 5 and 330 km. The site response of the ten stations analyzed was first estimated using average spectral ratios between the horizontal and the vertical components of motion (H/V ratios). As a second approach we performed a simultaneous inversion for source and site. In order to invert the spectral records to determine the site response, we made an independent estimate of the attenuation for two different source-station path regions. Then we corrected the spectral records for the attenuation effect before we made the inversion. Although the average H/V ratio of many sites is inside the error bars of the site response estimated with the spectral inversion, the spectral inversion tends to give higher values. For the S wave some sites show similar frequency of predominant peak when comparing the responses obtained with both methods. In contrast, for the P waves the H/V ratios disagree with the results of the inversion. In general, the site response of the stations is strongly frequency dependent for both P and S waves. We also found that the natural frequency of resonance of the sites is near 0.5 Hz for P and near 0.8 Hz for the S waves.  相似文献   

18.
—A temporary network has been used to study the seismic activity in the central-northern part of the Tendaho Rift (Afar Triangle, Ethiopia). Small size earthquakes (M < 2.5) characterize the seismicity during the time interval 1993–1994 when the seismic array was operating. Shocks are mainly located in the central part of the Tendaho rift and their epicentral distribution highlights a remarkable coincidence with NW-SE trending tectonically active structures. Focal depths are confined in the range of 3–8?km. ? The few acceptable fault plane solutions suggest the occurrence of both strike-slip and dip-slip rupture mechanisms, which are often characterized by a nodal plane oriented approximately NW-SE. ?A detailed study of earthquake waveforms using polarization analysis showed the occurrence of splitting phenomena for the S waves. Despite the differences in focal mechanisms, the similarity of the faster S-wave directions (NW-SE to NNW-SSE) suggests that the direction of geological structures and/or the systems of fractures adjacent to the faults could bias shear-wave propagation. The splitting time between fast and slow shear waves shows no systematic relationship with either hypocentral distance or focal depth, suggesting that the anisotropic volume is constrained to depths shallower than 3?km.  相似文献   

19.
Surface-wave amplitudes in the period range 50–100 s at eight European and North American stations, horizontal slip profiles along the rupture zone and the timing of certain events along the fault during rupture time are all engaged in unison to reconstruct the motion at the source. A modified source model is used to accommodate a moving rupture with variable dislocation in the direction of propagation.It is inferred that the rupture started at about 13 h 11 m 55 s GMT near San Juan Bautista and propagated unilaterally northwestward along N35°W over 400 km with an average rupture velocity of 3.5 km/s. At 13 h 12 m 12 s, the dynamic shear front, moving with the rupture speed, hit the Lick Observatory. Then, at 13 h 12 m 18 s, the rupture arrived to the vicinity of the epicenter in the Santa Cruz Mountains given by B. Bolt. There the slip changed sharply from an average of 0.5 m to a high value of 3 m causing extensive landslides and avalanches. At 13 h 12 m 32.5 s two railroad clocks at San Rafael were stopped. Finally, at 13 h 12 m 36 s the offset front hit the Naval Observatory at Mare Island and stopped the astronomical clocks there. Conspicuous surface waves, visible on Wiechert seismograms in Europe in the period range 55–65 s, reflect the true rupture time.The seismic data inversion yields an effective radiation source some 240 km long with an average vertical extent of some 34 km over a total fault length of 400 km (UdS ? 29,000 m km2or μUdS ? 9 · 1027dyn cm). It began at the Santa Cruz Mountains and ended some 20 km off coast Point Arena. Thus, due to the nonuniform slip profile, only 35 of the total fracture length contributed to the far radiation field.Although the product of the average source displacement (over the entire fault) and the vertical extent appears to be fairly well determined from the surface-wave spectrums, the separate values of these entities cannot be uniquely determined. If the average surface displacements (～ 3.2 m) are diagnostic of the entire fault, a vertical extent of H = 34 km is required.Finally, a new analysis of surface waves from the Alaska earthquake of July 10, 1958, the Queen Charlotte Islands earthquake of August 22, 1949 and the Kern County shock of July 21, 1952, enables us to draw parallels between the three biggest major events which occurred along the NE Pacific coast during 1906–1958. A common feature of all of these earthquakes is that vertical failure extents of 30–40 km are implied.  相似文献   

20.
为优化处于长周期地震动输入下的大型建筑剪力墙结构,进行了振动台试验。分析普通地震动与长周期地震动波的区别,证明了长周期地震波具有显著长周期分量的特性。将某一高层酒店剪力墙作为研究案例,设计模拟实验台的构建流程与传感器布局,将建筑模型缩尺比例设置为1∶10。选择CA波、RG波、EL波作为实验用地震波,从位移与结构周期、层间剪力与位移比、易损性以及损失评估等方面对大型建筑剪力墙的抗震性能进行了评估。振动台试验结果表明,在位移相同的情况下,长周期地震波下的建筑极限承载力最小;在经历CA波、RG波、EL波后,模型的自振周期均发生变化,而EL波作用下模型的自振周期始终比基本周期略长;不同地震波下,X、Y向层间剪力变化基本趋于一致;CA波、EL波作用下,X向位移比较为接近,而剪力墙Y向上位移比在三种地震波作用下具有较大差异性;在长周期地震波作用下,大型建筑剪力墙损伤最为严重。  相似文献   

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