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1.
The 26th April 1986 Dharamsala earthquake (mb 5.5) occurred in the Kangra region of Himachal Himalaya, which lies in the rupture zone of great Kangra earthquake of 1905. This was the first moderate sized earthquake to be recorded at a few sites of the strong ground motion array in the NW Himalaya. The accelerograms of this earthquake have been used to estimate its source parameters, site amplification functions and to estimate the effective shear wave attenuation factor Qβ in the frontal region of Himachal Himalaya. A double couple fault plane solution for the earthquake has been obtained based on the spectra of the transverse component of the accelerograms. The estimated values of the source parameters are seismic moment: 2.1×1024 dyne-cm, static stress drop (Δσ): 36 bars, source radius (r): 2.8 km and moment magnitude (Mw): 5.4. The estimated average values of effective shear wave attenuation factor Qβ for various sites are in the range of 125 to 300 with an overall spatial average of 239. The influence of local site effects on the observed PGA values have been examined on the basis of site amplification functions.  相似文献   

2.
On July 25, 1969, anM s 5.9 earthquake shook the Kwangtung Province near Yangjiang, China. Casualties and extensive damage were reported in the epicentral area. The Yangjiang earthquake occurred within the passive margin located along China's southeast coast. This stable continental setting is seismically one of the most quiet regions of China; historic records indicate this earthquake to have been the first devastating one in the area. A remarkable feature of this earthquake sequence is that its foreshocks and aftershocks are relatively small in terms of number and magnitude despite the relatively large main shock.Waveforms of long-and short-period teleseismicP and long-period teleseismicSH waves have been modeled to estimate the source parameters for this earthquake. The focal mechanism determined is predominately strike-slip with a small normal component (strike=263°, dip=79°, rake=194°) and is in good agreement with observations in the epicentral area regarding dislocation direction of fissures, distribution of aftershocks, and isoseismals. The average seismic moment is 5.15×1024 dyne-cm and the focal depth is estimated to be 9 km. The earthquake is characterized by a rather short source-time function and a high stress drop of approximately 380 bars. The observed pattern of the foreshock-main shock-aftershock sequence is interpreted in terms of the large stress drop associated with the main shock and the material properties at and near the source. TheP-axis orientation lies roughly NW-SE and is consistent with the maximum compressive stress observed along the coast of southeast China. This stress orientation is consistent with the NW subducting Philippine Sea plate and the SE ward push from central China due to the convergence between Indian and Eurasian subcontinents.  相似文献   

3.
This paper presents the results of a modified two-step inversion algorithm approach to find S wave quality factor Q β(f) given by Joshi (Bull Seis Soc Am 96:2165–2180, 2006). Seismic moment is calculated from the source displacement spectra of the S wave using both horizontal components. Average value of seismic moment computed from two horizontal components recorded at several stations is used as an input to the first part of inversion together with the spectra of S phase in the acceleration record. Several values of the corner frequency have been selected iteratively and are used as inputs to the inversion algorithm. Solution corresponding to minimum root mean square error (RMSE) is used for obtaining the final estimate of Q β(f) relation. The estimates of seismic moment, corner frequency and Q β(f) from the first part of inversion are further used for obtaining the residual of theoretical and observed source spectra which are treated as site amplification terms. The acceleration record corrected for the site amplification term is used for determination of seismic moment from source spectra by using Q β(f) obtained from first part of inversion. Corrected acceleration record and new estimate of seismic moment are used as inputs to the second part of the inversion scheme which is similar to the first part except for use of input data. The final outcome from this part of inversion is a new Q β(f) relation together with known values of seismic moment and corner frequency of each input. The process of two-step inversion is repeated for this new estimate of seismic moment and goes on until minimum RMSE is obtained which gives final estimate of Q β(f) at each station and corner frequency of input events. The Pithoragarh district in the state of Uttarakhand in India lies in the border region of India and Nepal and is part of the seismically active Kumaon Himalaya zone. A network of eight strong motion recorders has been installed in this region since March, 2006. In this study we have analyzed data from 18 local events recorded between March, 2006 and October, 2010 at various stations. These events have been located using HYPO71 and data has been used to obtain frequency-dependent shear-wave attenuation. The Q β(f) at each station is calculated by using both the north-south (NS) and east-west (EW) components of acceleration records as inputs to the developed inversion algorithm. The average Q β(f) values obtained from Q β(f) values at different stations from both NS and EW components have been used to compute a regional average relationship for the Pithoragarh region of Kumaon Himalaya of form Q β(f)?=?(29?±?1.2)f (1.1 ± 0.06).  相似文献   

4.
In this paper a heterogeneous fault model of the Tangshan earthquake is suggested, which consists of two southern sub-faults striking N30°E and two northern sub-faults striking N50°E. Total length of the main shock fault is 114 km and seismic moment is about 1.4 × 1020 N·m. The epicentre of the main shock is located at the southern part, near the intersection of the two bands. Accelerations of two aftershocks (M L 5.5, M S 6.9) were used as empirical Green’s functions to synthesize the accelerations of the main shock in near and far field. A method that small events and main shock are considered not satisfying the similarity relationship in the improved empirical Green’s function is also applied in this paper. Peak values, duration and response spectra of synthesized accelerations in far field are in agreement with the observed records. The synthesized results in near field are also in agreement with the epicentral intensity distribution of the main shock. The results show that the peak acceleration of Tangshan earthquake in epicentral region exceeds 1.1 g. It is consistent with the peak accelerations recorded in some large earthquakes occurred in recent years. The research is supported by the National Science Foundation of China.  相似文献   

5.
The source parameters for 213 Bhuj aftershocks of moment magnitude varying from 2.16 to 5.74 have been estimated using the spectral analysis of the SH- waveform on the transverse component of the three-componnet digital seismograms as well as accelerograms. The estimated stress drop values for Bhuj aftershocks show more scatter (Mo0.5 to 1 ∞ Δσ) toward the larger seismic moment values (log Mo ≥ 1014.5 N-m, larger aftershocks), whereas, they show a more systematic nature (Mo3 ∞ Δσ) for smaller seismic moment (log Mo < 1014.5 N-m, smaller aftershocks) values. This size dependency of stress drop has also been seen from the relation between our estimated seismic moment and source radius, however, this size-dependent stress drop is not observed for the source parameter estimates for the other stable continental region earthquakes in India and around the world. The estimated seismic moment (Mo), source radius (r) and stress drop (Δσ) for aftershocks of moment magnitude 2.16 to 5.74 range from 1.95 × 1012 to 4.5 × 1017 N-m, 239 to 2835 m and 0.63 to 20.7 MPa, respectively. The near-surface attenuation factor (k) is found to be large of the order of 0.03 for the Kachchh region, suggesting thick low velocity sediments beneath the region. The estimated stress drop values show an increasing trend with the depth indicating the base of seismogenic layer (as characterized by larger stress drop values (>15 MPa)) lying in 22–26km depth range beneath the region. We suggest that the concentration of large stress drop values at 10–36km depth may be related to the large stress/strain associvated with a brittle, competent intrusive body of mafic nature.  相似文献   

6.
— On 28 March, 1999 (19:05:10.09, UT) a significant earthquake of M w 6.4 occurred in the Garhwal Himalaya (30.555°N, 79.424°E). One hundred and ten well-recorded aftershocks show a WNW-ESE trending northeasterly dipping seismic zone extending from a depth of 2 to 20?km. As the main shock hypocenter occurred at the northern end of this seismic zone and aftershocks extended updip, it is inferred that the main-shock rupture nucleated on the detachment plane at a depth of 15?km and then propagated updip along a NE-dipping thrust plane. Further, the epicentral distribution of aftershocks defines a marked concentration near a zone where main central thrust (MCT) takes a significant turn towards the north, which might be acting as an asperity in response to the NNE compression due to the underthrusting of Himalayan orogenic process prevalent in the entire region. Presence of high seismicity including five earthquakes of magnitude exceeding 6 and twelve earthquakes of magnitude exceeding 5 in the 20th century is presumed to have caused a higher level of shallow crustal heterogeneity in the Garhwal Himalaya, a site lying in the central gap zone of the Himalayan frontal arc. Attenuation property of the medium around the epicentral area of the 1999 Chamoli earthquake, covering a circular area of 61,500?km2 with a radius of 140?km, is studied by estimating the coda Q c from 48 local earthquakes of magnitudes varying from 2.5–4.8. These earthquakes were recorded at nine 24-bit REFTEK digital stations; two of which were equipped with three-component CMG40T broadband seismometers and others with three-component L4-3D short-period seismometers. The estimated Q o values at different stations suggest on average a low value of the order of (30?±?0.8), indicating an attenuating crust beneath the entire region. The frequency-dependent relation indicates a relatively low Q c at lower frequencies (1–3?Hz) that can be attributed to the loss of energy due to scattering on heterogeneities and/or the presence of faults and cracks. The large Q c at higher frequencies may be related to the propagation of backscattered body waves through deeper parts of the lithosphere where less heterogeneities are expected. An important observation is that the region north of MCT (more rigid highly metamorphosed crystalline rocks) is less attenuative in comparison to the region south of MCT (less rigid slightly metamorphosed rocks (sedimentary wedge)). The acceleration decays to 50% at 20?km distance and to 7% at 100?km. Hence, even 1g acceleration at the source may not cause significant damage beyond 100?km in this region.  相似文献   

7.
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8.
The attenuation properties of the crust in the Chamoli region of Himalaya have been examined by estimating the frequency-dependent relationships of quality factors for P waves (Qα) and for S waves (Qβ) in the frequency range 1.5–24 Hz. The extended coda normalization method has been applied on the waveforms of 25 aftershocks of the 1999 Chamoli earthquake (M 6.4) recorded at five stations. The average value of Qα is found to be varied from 68 at 1.5 Hz to 588 at 24 Hz while it varies from 126 at 1.5 Hz to 868 at 24 Hz for Qβ. The estimated frequency-dependent relations for quality factors are Qα = (44 ± 1)f(0.82±.04) and Qβ = (87 ± 3)f(0.71±.03). The rate of increase of Q(f) for P and S waves in the Chamoli region is comparable with the other regions of the world. The ratio Qβ/Qα is greater than one in the region which along with the frequency dependence of quality factors indicates that scattering is an important factor contributing to the attenuation of body waves in the region. A comparison of attenuation relation for S wave estimated here (Qβ = 87f0.71) with that of coda waves (Qc = 30f1.21) obtained by Mandal et al. (2001) for the same region shows that Qc > Qβ for higher frequencies (>8 Hz) in the region. This indicates a possible high frequency coda enrichment which suggests that the scattering attenuation significantly influences the attenuation of S waves at frequencies >8 Hz. This observation may be further investigated using multiple scattering models. The attenuation relations for quality factors obtained here may be used for the estimation of source parameters and near-source simulation of earthquake ground motion of the earthquakes, which in turn are required for the assessment of seismic hazard in the region.  相似文献   

9.
Spectral parameters have been estimated for 214 Petatlan aftershocks recorded at stations between Petatlan and Mexico City and between Petatlan and Acapulco. The spectral parameters were used to obtain empirical relations for the estimation of seismic moment from coda length and fromM L . Stress drops, using Brune's model, were calculated for these aftershocks. Six events with large stress drop are located within a previously suggested asperity, and seven more suggest a boundary zone at the intersection of the Petatlan and Zihuatanejo aftershock rupture volumes. Stress drops increase with increasing seismic moment up to 1020 dyne-cm but appear to be constant at greater moment values. The peak horizontal velocity times distance of aftershocks recorded near the coast and between the coast and Mexico City (30 to 270 km away), scales linearly with seismic moment, and predicts well the peak horizontal values of large (M s 7.0) coastal thrust events recorded on rock sites at Mexico City. Peak horizontal velocity is a straightforward measurement, thus this relation allows us to evaluate expected ground motion between the Pacific coast and Mexico City from the seismic moment of subduction related earthquakes along the coast.  相似文献   

10.
A moderate Mw 4.9 earthquake struck the Beni Haoua (Algeria) coastal area on April 25, 2012. The mainshock was largely recorded by the accelerograph network of the Centre National de Recherche Appliquée en Génie Parasismique (CGS). The same day the earthquake occurred, eight mobile short period stations were deployed through the epicentral area. In this study, we use accelerogram and seismogram data recorded by these two networks. We combined the focal mechanism built from the first motion of P waves and from waveform inversion, and the distribution of aftershocks to well constrain the source parameters. The mainshock is located with a shallow focal depth, ～9 km, and the focal mechanism shows a nearly pure left lateral strike slip motion, with total seismic moment of 2.8?×?1016 N.m (Mw?=?4.9). The aftershocks mainly cluster on a narrow NS strip, starting at the coast up to 3–4 km inland. This cluster, almost vertical, is concentrated between 6 and 10 km depth. The second part of this work concerns the damage distribution and estimated intensity in the epicentral area. The damage distribution is discussed in connection with the observed maximum strong motion. The acceleration response spectrum with 5 % damping of the mainshock and aftershocks give the maximum amplitude in high frequency which directly affects the performance of the high-frequency structures. Finally, we tie this earthquake with the seismotectonic of the region, leading to conclude that it occurred on a N–S transform zone between two major compressional fault zones oriented NE–SW.  相似文献   

11.
Fifty earthquakes that occurred in Hungary (central part of the Pannonian basin) with local magnitude $M_\textrm{L}$ ranging from 0.8 to 4.5 have been analyzed. The digital seismograms used in this study were recorded by six permanent broadband stations and 20 short-period ones at hypocentral distances between 10 and 327 km. The displacement spectra for P- and SH-waves were analyzed according to Brune’s source model. Observed spectra were corrected for path-dependent attenuation effects using an independent regional estimate of the quality factor Q S . To correct spectra for near-surface attenuation, the κ parameter was calculated, obtaining it from waveforms recorded at short epicentral distances. The values of the κ parameter vary between 0.01 and 0.06 s with a mean of 0.03 s for P-waves and between 0.01 and 0.09 s with a mean of 0.04 s for SH-waves. After correction for attenuation effects, spectral parameters (corner frequency and low-frequency spectral level) were estimated by a grid search algorithm. The obtained seismic moments range from 4.21×1011 to 3.41×1015 Nm (1.7?≤?M w ?≤?4.3). The source radii are between 125 and 1,343 m. Stress drop values vary between 0.14 and 32.4 bars with a logarithmic mean of 2.59 bars (1 bar = 105 Pa). From the results, a linear relationship between local and moment magnitudes has been established. The obtained scaling relations show slight evidence of self-similarity violation. However, due to the high scatter of our data, the existence of self-similarity cannot be excluded.  相似文献   

12.
Based on the scattering coda model by which local and regional earthquakes are interpreted (K. Aki, 1969), and using observational coda data of 68 aftershocks of the 1985 Luquan, Yunnan earthquake registered by the VGK seismographs installed at 12 stations in the Yunnan regional short-period network, theQ-values of coda waves are calculated respectively for 6 time intervals. It is observed that within the frequency range of 0.40–1.65 Hz of the observed data, theQ-values are closely related with the frequencies and the calculated codaQ ranges between 80–240 with the coefficient of frequency dependence η=0.45. The calculated source factorsB(f> p) of the coda waves which indicate the scattering strength are mostly within the order 10?23–10?24. Areas with lowQ-values present high scattering. It should be noted that by comparing data obtained before and after the Luquan earthquake, clear changes can be detected in theQ-values measured at stations close to the epicentral region, and that theQ-values of the aftershock coda are less than about one half of the pre-shock values. It may be mentioned that the time-dependent regional variations of theQ-values might possibly bring about practical significance in earthquake prediction. Moreover, aftershock focal parameters are determined. Through discussions on the quantitative relations between the focal parameters, we get: 1gE=1.59M L+ 11.335;E=(2.10 × 10?5)M 0; length of focal rupturea=0.40?0.80 km for 3.0≤M L<5.0 events; stress drop Δσ=(6.0–130) ×105 Pa. Through interpretation of the data, we have also learned the important characteristics that there is no linear relation between the stress drops and the earthquake magnitudes.  相似文献   

13.
We investigate the scaling relationships among earthquake source parameters using more than 300 good quality broad band seismograms from 30 small earthquakes in the Kumaon Himalaya from the spectral analysis of P and S waves. The average ratio of P/S wave corner frequency is found to be 1.13, which is suggestive of shift in the corner frequency. The estimated seismic moment range from 1.6?×?1013–5.8?×?1015 N?m, while the stress drop varies from 0.6 to 16 bars with 80 % of the events below 10 bars. An analysis of stress drop and apparent stress drop indicates the partial stress drop mechanism in the region. The source radii are between 0.17 and 0.88 km. The total seismic energy varies from 1.79?×?108 to 7.30?×?1011 J. We also observe the variation in seismic energy for a given seismic moment. The scaling relation between the seismic moment and stress drop suggests the breakdown of constant stress drop scaling for the range of seismic moments obtained here for the region. This shows the anomalous behavior of small earthquakes in the region. The study indicates that the stress drop is the dominant scaling factor for the moments studied here.  相似文献   

14.
In this study, continuous wavelet transform is applied to estimate the frequency-dependent quality factor of shear waves, Q S , in northwestern Iran. The dataset used in this study includes velocigrams of more than 50 events with magnitudes between 4.0 and 6.5, which have occurred in the study area. The CWT-based method shows a high-resolution technique for the estimation of S-wave frequency-dependent attenuation. The quality factor values are determined in the form of a power law as Q S (f)?=?(147?±?16)f 0.71?±?0.02 and (126?±?12)f 0.73?±?0.02 for vertical and horizontal components, respectively, where f is between 0.9 and 12 Hz. Furthermore, in order to verify the reliability of the suggested Q S estimator method, an additional test is performed by using accelerograms of Ahar-Varzaghan dual earthquakes on August 11, 2012, of moment magnitudes 6.4 and 6.3 and their aftershocks. Results indicate that the estimated Q S values from CWT-based method are not very sensitive to the numbers and types of waveforms used (velocity or acceleration).  相似文献   

15.
Based on the three component accelerograms, recorded at near-field distance by a temporary seismic network consisting of digital cassette tape recording accelerographs, the focal mechanisms of three aftershocks of the April 18, 1985, Luquan, Yunnan Province, China, earthquake ofM S=6.1, are calculated using seismic moment tensor inversion technique. The phases of direct P, S and converted SP waves in the displacement seismograms, produced by twice integrations of the observed accelerograms, are identified via forward calculation using Green’s functions for homogeneous semi-infinite elastic medium, and used in the inversion. The results of inversion show that a better fit of synthetic to the observed seismograms of direct as well as converted phases can be achieved if appropriate weighting functions are used in solving the over definite linear equations. While these aftershocks are of different magnitudes (M L=4.8, 3.2 and 3.5, respectively) and hypocentral locations, their focal mechanisms are very similar and consistent with that of the main shock. This feature demonstrates the intrinsic correlation between the occurrence of aftershocks and the seismogenic fault of main shock. Our experimentations show that using the near field accelerogram obtained from the digital seismic network with appropriate azimuthal coverage on the focal sphere, with the aid of even simple medium model, not only the shear dislocation source, but also the isotropic part and CLVD (compensated linear vector dipole) can be retrieved by the technique of moment tensor inversion. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13, 412–419, 1991. This work is supported by the Chinese Joint Seismological Sciences Foundation and the Western Yunnan Earthquake Prediction Test Site (WYEPTS), State Seismological Bureau.  相似文献   

16.
In this study, source parameters of the September 18, 2011 M w 6.9, Sikkim earthquake were determined using acceleration records. These parameters were then used to generate strong motion at a number of sites using the stochastic finite fault modeling technique to constrain the causative fault plane for this earthquake. The average values of corner frequency, seismic moment, stress drop and source radius were 0.12 Hz, 3.07 × 1026 dyne-cm, 115 bars and 9.68 km, respectively. The fault plane solution showed strike-slip movement with two nodal planes oriented along two prominent lineaments in the region, the NE-oriented Kanchendzonga and NW-oriented Tista lineaments. The ground motions were estimated considering both the nodal planes as causative faults and the results in terms of the peak ground accelerations (PGA) and Fourier spectra were then compared with the actual recordings. We found that the NW–SE striking nodal plane along the Tista lineament may have been the causative fault for the Sikkim earthquake, as PGA estimates are comparable with the observed recordings. We also observed that the Fourier spectrum is not a good parameter in deciding the causative fault plane.  相似文献   

17.
A point source seismological model is used in this study to model the available strong motion accelerograms recorded by 17 events and to calculate three seismological model parameters, the source, path, and quality factor. Due to the paucity of recorded events, this is the first time these model parameters have been obtained for the northeastern and its surrounding region of India. The quality factors of the horizontal and vertical components of recorded events with corresponding standard deviations are QH(f) = 188.55f0.94, σ1 value (25, 0.025) and QV(f) = 169.76f0.93, σ1 value (20, 0.03), respectively. The source parameter stress drop values (μσ) vary within 124–180 bars for the subduction region and 80–169 bars for the active region. The Kappa factors for the horizontal and vertical components of recorded events on the soft rock site are 0.06 and 0.05, respectively. These seismological model parameters obtained in this study will be useful for future work deriving a ground motion attenuation relation based on a spectral model. Finally, these results are useful for seismic hazard assessment of a region having sparsely recorded events.  相似文献   

18.
We consider the results of reconstructing the stress-strain state of the Earth’s crust in South Baikal from the focal mechanism data for the Kultuk earthquake of August 27, 2008 (M w = 6.3) and its aftershocks. The source parameters of the main shock were determined by calculating the seismic moment tensor. The focal mechanism solutions of 32 aftershocks (M w ≥ 2.3) were obtained through the deployment of a local seismic network at South Baikal. It is found that the main shock and first aftershocks (August–September) gave rise to the activation of latitudinal fragments of the segmented near-edge fault, and the sources of the consequent aftershocks were dominated by the NW-striking planes related to the small intrabasin structures. The calculations of seismotectonic deformations based on the data on the focal mechanisms of the earthquakes show that the area of activation is dominated by the transtension regime (with deformation in the form of extension with shear). The epicentral and hypocentral fields of the aftershocks and the mechanisms of their sources reflect the complex tectonic structure of the source zone of the Kultuk earthquake, which exhibits a clear subvertical zonality of the local seismically active volume and a wedge-shaped area of crustal destruction.  相似文献   

19.
We exploit S-wave spectral amplitudes from 112 aftershocks (3.0 ≤ ML ≤ 5.3) of the L’Aquila 2009 seismic sequence recorded at 23 temporary stations in the epicentral area to estimate the source parameters of these events, the seismic attenuation characteristics and the site amplification effects at the recording sites. The spectral attenuation curves exhibit a very fast decay in the first few kilometers that could be attributed to the large attenuation of waves traveling trough the highly heterogeneous and fractured crust in the fault zone of the L’Aquila mainshock. The S-waves total attenuation in the first 30 km can be parameterized by a quality factor QS(f) = 23f 0.58 obtained by fixing the geometrical spreading to 1/R. The source spectra can be satisfactorily modeled using the omega-square model that provides stress drops between 0.3 and 60 MPa with a mean value of 3.3±2.8 MPa. The site responses show a large variability over the study area and significant amplification peaks are visible in the frequency range from 1 to more than 10 Hz. Finally, the vertical component of the motion is amplified at a number of sites where, as a consequence, the horizontal-to-vertical spectral ratios (HVSR) method fails in detecting the amplitude levels and in few cases the resonance frequencies.  相似文献   

20.
During the last six years, National Geophysical Research Institute, Hyderabad has established a semi-permanent seismological network of 5–8 broadband seismographs and 10–20 accelerographs in the Kachchh seismic zone, Gujarat with a prime objective to monitor the continued aftershock activity of the 2001 Mw 7.7 Bhuj mainshock. The reliable and accurate broadband data for the 8 October Mw 7.6 2005 Kashmir earthquake and its aftershocks from this network as well as Hyderabad Geoscope station enabled us to estimate the group velocity dispersion characteristics and one-dimensional regional shear velocity structure of the Peninsular India. Firstly, we measure Rayleigh-and Love-wave group velocity dispersion curves in the period range of 8 to 35 sec and invert these curves to estimate the crustal and upper mantle structure below the western part of Peninsular India. Our best model suggests a two-layered crust: The upper crust is 13.8 km thick with a shear velocity (Vs) of 3.2 km/s; the corresponding values for the lower crust are 24.9 km and 3.7 km/sec. The shear velocity for the upper mantle is found to be 4.65 km/sec. Based on this structure, we perform a moment tensor (MT) inversion of the bandpass (0.05–0.02 Hz) filtered seismograms of the Kashmir earthquake. The best fit is obtained for a source located at a depth of 30 km, with a seismic moment, Mo, of 1.6 × 1027 dyne-cm, and a focal mechanism with strike 19.5°, dip 42°, and rake 167°. The long-period magnitude (MA ~ Mw) of this earthquake is estimated to be 7.31. An analysis of well-developed sPn and sSn regional crustal phases from the bandpassed (0.02–0.25 Hz) seismograms of this earthquake at four stations in Kachchh suggests a focal depth of 30.8 km.  相似文献   

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