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1.
The observations of spread F during the nighttime hours (0000–0500 LT) have been statistically analyzed based on data of Tokyo, Akita, Wakkanai, and Yamagawa Japan vertical ionospheric sounding stations for the time intervals a month before and a month after an earthquake. The disturbances in the probability of spread F appearance before an earthquake are revealed against a background of the variations depending on season, solar activity cycle, geomagnetic and solar disturbances. The days with increased solar (Wolf number W > 100) and geomagnetic (ΣK > 30) activity are excluded from the analysis. The spread F effects are considered for more than a hundred earthquakes with magnitude M > 5 and epicenter depth h < 80 km at distances of R < 1000 km from epicenters to the vertical sounding station. An average decrease in the spread F occurrence probability one-two weeks before an earthquake has been revealed using the superposed epoch method (the probability was minimal approximately ten days before the event and then increased until the earthquake onset). Similar results are obtained for all four stations. The reliability of the effect has been estimated. The dependence of the detected effect on the magnitude and distance has been studied.  相似文献   

2.
A genetic algorithm (GA) is an artificial intelligence method used for optimization. We applied a GA to the inversion of magnetic anomalies over a thick dike. Inversion of nonlinear geophysical problems using a GA has advantages because it does not require model gradients or well-defined initial model parameters. The evolution process consists of selection, crossover, and mutation genetic operators that look for the best fit to the observed data and a solution consisting of plausible compact sources. The efficiency of a GA on both synthetic and real magnetic anomalies of dikes by estimating model parameters, such as depth to the top of the dike (H), the half-width of the dike (B), the distance from the origin to the reference point (D), the dip of the thick dike (δ), and the susceptibility contrast (k), has been shown. For the synthetic anomaly case, it has been considered for both noise-free and noisy magnetic data. In the real case, the vertical magnetic anomaly from the Pima copper mine in Arizona, USA, and the vertical magnetic anomaly in the Bayburt–Sar?han skarn zone in northeastern Turkey have been inverted and interpreted. We compared the estimated parameters with the results of conventional inversion methods used in previous studies. We can conclude that the GA method used in this study is a useful tool for evaluating magnetic anomalies for dike models.  相似文献   

3.
Based on data from ground-based vertical sounding stations, the behaviors of the ionosphere F region before a strong M 6.8 earthquake off the coast of Hokkaido, Japan, and during the moderate magnetic storm before this earthquake are compared. It was found that the critical frequency of the ionosphere F region (foF2) above the Wakkanai ground-based ionosphere vertical sounding station, which was located in the preparation zone of this earthquake, suffered a long-term disturbance of slightly more than an hour nearly half a day before the earthquake. The magnitude of earthquake-induced disturbance is comparable to that caused by a magnetic storm.  相似文献   

4.
The diurnal variations in electrical (quasistatic electric field and electrical conductivity) and meteorological (temperature, pressure, relative humidity of the atmosphere, and wind speed) parameters, measured simultaneously before strong earthquakes in Kamchatka region (November 15, 2006, М = 8.3; January 13, 2007, М = 8.1; January 30, 2016, М = 7.2), are studied for the first time in detail. It is found that a successively anomalous increase in temperature, despite the negative regular trend in these winter months, was observed in the period of six–seven days before the occurrences of earthquakes. An anomalous temperature increase led to the formation of “winter thunderstorm” conditions in the near-surface atmosphere of Kamchatka region, which was manifested in the appearance of an anomalous, type 2 electrical signal, the amplification of and intensive variations in electrical conductivity, heavy precipitation (snow showers), high relative humidity of air, storm winds, and pressure changes. With the weak flow of natural heat radiation in this season, the observed dynamics of electric and meteorological processes can likely be explained by the appearance of an additional heat source of seismic nature.  相似文献   

5.
We used CHAMP satellite vector data and the latest IGRF12 model to investigate the regional magnetic anomalies over mainland China. We assumed satellite points on the same surface (307.69 km) and constructed a spherical cap harmonic model of the satellite magnetic anomalies for elements X, Y, Z, and F over Chinese mainland for 2010.0 (SCH2010) based on selected 498 points. We removed the external field by using the CM4 model. The pole of the spherical cap is 36N° and 104°E, and its half-angle is 30°. After checking and comparing the root mean square (RMS) error of ΔX, ΔY, and ΔZ and X, Y, and Z, we established the truncation level at K max = 9. The results suggest that the created China Geomagnetic Referenced Field at the satellite level (CGRF2010) is consistent with the CM4 model. We compared the SCH2010 with other models and found that the intensities and distributions are consistent. In view of the variation of F at different altitudes, the SCH2010 model results obey the basics of the geomagnetic field. Moreover, the change rate of X, Y, and Z for SCH2010 and CM4 are consistent. The proposed model can successfully reproduce the geomagnetic data, as other data-fitting models, but the inherent sources of error have to be considered as well.  相似文献   

6.
The seismological data on the destructive Taiwan earthquake of February 5, 2016, (MS = 6.5) are analyzed. The source rupture length is estimated by different techniques using P-waves spectra at teleseismic distances, azimuthal hodograph, and distribution of mb magnitude. The obtained results agree with each other.  相似文献   

7.
The temperature variations of the near-surface atmosphere in Kamchatka at Paratunka observatory and fluxes of outgoing infrared radiation prior to strong Kuril earthquakes (November 15, 2006, M = 8.3; January 13, 2007, M = 8.1) have been analyzed. It is shown that the radiation fluxes at ground level, as measured on satellites above the epicenter of earthquakes and above a remote observatory, coincide with each other, both in magnitude and in the feature of their time variations. The temperature measured directly at the observatory and the temperature at surface level estimated from satellite observations differ in magnitude, but they coincide in the feature of their time variations. The detected temperature increase (despite the negative regular trend at this time of year) is caused by the appearance of an additional heat source entering in the nearsurface atmosphere. This result, together with the studies of variations of various geophysical data before strong earthquakes performed earlier in Kamchatka, led to the conclusion that the additional heat source is in the Earth’s crust.  相似文献   

8.
In this study, pre-seismic and post-seismic total electron content (TEC) anomalies of 63 Mw?≥?5.0 earthquakes in Turkey (36°–42°N, 26°–45°E) were statistically investigated. The largest earthquake that occurred in Turkey during 2003–2016 is the Mw 7.1 Van earthquake on October 23, 2011. The TEC data of epicenters is obtained from CODE-GIM using a simple 4-point bivariate interpolation. The anomalies of TEC variations were determined by using a quartile-based running median process. In order to validate GIM results, we used the GPS-TEC data of available four IGS stations within the size of the Van earthquake preparation area. The anomalies that are detected by GIM and GPS-TEC show a similar pattern. Accordingly, the results obtained with CODE-GIM are reliable. The statistical results show that there are not prominent earthquake precursors for Mw?≤?6.0 earthquakes in Turkey.  相似文献   

9.
Simultaneous observations of high-latitude long-period irregular pulsations at frequencies of 2.0–6.0 mHz (ipcl) and magnetic field disturbances in the solar wind plasma at low geomagnetic activity (Kp ~ 0) have been studied. The 1-s data on the magnetic field registration at Godhavn (GDH) high-latitude observatory and the 1-min data on the solar wind plasma and IMF parameters for 2011–2013 were used in an analysis. Ipcl (irregular pulsations continuous, long), which were observed against a background of the IMF Bz reorientation from northward to southward, have been analyzed. In this case other solar wind plasma and IMF parameters, such as velocity V, density n, solar wind dynamic pressure P = ρV2 (ρ is plasma density), and strength magnitude B, were relatively stable. The effect of the IMF Bz variation rate on the ipcl spectral composition and intensity has been studied. It was established that the ipcl spectral density reaches its maximum (~10–20 min) after IMF Bz sign reversal in a predominant number of cases. It was detected that the ipcl average frequency (f) is linearly related to the IMF Bz variation rate (ΔBz/Δt). It was shown that the dependence of f on ΔBz/Δt is controlled by the α = arctan(By/Bx) angle value responsible for the MHD discontinuity type at the front boundary of magnetosphere. The results made it possible to assume that the formation of the observed ipcl spectrum, which is related to the IMF Bz reorientation, is caused by solar wind plasma turbulence, which promotes the development of current sheet instability and surface wave amplification at the magnetopause.  相似文献   

10.
Tectonic activities, electrical structures, and electromagnetic environments are major factors that affect the stability of spontaneous fields. The method of correlating regional synchronization contrasts(CRSC) can determine the reliability of multi-site data trends or shortimpending anomalies. From 2008 to 2013, there were three strong earthquake cluster periods in the North–South seismic belt that lasted for 8–12 months. By applying the CRSC method to analyze the spontaneous field E_(SP) at 25 sites of the region in the past 6 years, it was discovered that for each strong earthquake cluster period, the E_(SP) strength of credible anomalous trends was present at minimum 30%of the stations. In the southern section of the Tan-Lu fault zone, the E_(SP) at four main geoelectric field stations showed significant anomalous trends after June 2015, which could be associated with the major earthquakes of the East China Sea waters(MS7.2) in November 2015 and Japan's Kyushu island(MS7.3) in April 2016.  相似文献   

11.
Selecting three half orbits near the epicenter of Pu’er earthquake, we analyzed the Ne data recorded in their revisited orbits during a year before this earthquake, and extracted Ne precursors. The results show that: ① There are significant seasonal variations of ionospheric Ne in night time, which exhibit different shapes respectively in four seasons; ② There are three main shapes of Ne: single-peak, saddle-shaped and even-shaped, all of which may occur in four seasons, but each season with its typical shape relatively; ③ Spatial images of Ne showed high values near the epicenter in 30 days before the earthquake, and there is a good correlation between anomaly and distribution of earthquake in space and time, which reflects that these spatial anomalies were indeed concerned with the earthquake; ④ There shows a certain similarity of the Ne curves among revisited orbits, which can provide background information for distinguishing and identification of seismic anomaly.  相似文献   

12.
An attempt has been made to study the behavior of nailed vertical excavations in medium dense to dense cohesionless soil under seismic conditions using a pseudo-dynamic approach. The effect of several parameters such as angle of internal friction of soil(Φ), horizontal(k_h) and vertical(k_v) earthquake acceleration coefficients, amplification factor(f_a), length of nails(L), angle of nail inclination(α) and vertical spacing of nails(S_v) on the stability of nailed vertical excavations has been explored. The limit equilibrium method along with a planar failure surface is used to derive the formulation involved with the pseudo-dynamic approach, considering axial pullout of the installed nails. A comparison of the pseudo-static and pseudo-dynamic approaches has been established in order to explore the effectiveness of the pseudo-dynamic approach over pseudo-static analysis, since most of the seismic stability studies on nailed vertical excavations are based on the latter. The results are expressed in terms of the global factor of safety(FOS). Seismic stability, i.e., the FOS of nailed vertical excavations is found to decrease with increase in the horizontal and vertical earthquake forces. The present values of FOS are compared with those available in the literature.  相似文献   

13.
Aftershock hazard maps contain the essential information for search and rescue process, and re-occupation after a main-shock. Accordingly, the main purposes of this article are to study the aftershock decay parameters and to estimate the expected high-frequency ground motions (i.e., Peak Ground Acceleration (PGA)) for recent large earthquakes in the Iranian plateau. For this aim, the Ahar-Varzaghan doublet earthquake (August 11, 2012; M N =6.5, M N =6.3), and the Ilam (Murmuri) earthquake (August 18, 2014 ; M N =6.2) have been selected. The earthquake catalogue has been collected based on the Gardner and Knopoff (Bull Seismol Soc Am 64(5), 1363-1367, 1974) temporal and spatial windowing technique. The magnitude of completeness and the seismicity parameters (a,??b) and the modified Omori law parameters (P,??K,??C) have been determined for these two earthquakes in the 14, 30, and 60 days after the mainshocks. Also, the temporal changes of parameters (a,??b,??P,??K,??C) have been studied. The aftershock hazard maps for the probability of exceedance (33%) have been computed in the time periods of 14, 30, and 60 days after the Ahar-Varzaghan and Ilam (Murmuri) earthquakes. For calculating the expected PGA of aftershocks, the regional and global ground motion prediction equations have been utilized. Amplification factor based on the site classes has also been implied in the calculation of PGA. These aftershock hazard maps show an agreement between the PGAs of large aftershocks and the forecasted PGAs. Also, the significant role of b parameter in the Ilam (Murmuri) probabilistic aftershock hazard maps has been investigated.  相似文献   

14.
The degree of closeness of ionospheric parameters during one magnetic storm and of the same parameters during another, similar, storm is estimated. Overall, four storms—two pairs of storms close in structure and appearance according to recording of the magnetic field Х-component—were analyzed. The examination was based on data from Sodankyla observatory (Finland). The f-graphs of the ionospheric vertical sounding, magnetometer data, and riometer data on absorption were used. The main results are as follows. The values of the critical frequencies foF2, foF1, and foE for different but similar magnetic storms differ insignificantly. In the daytime, the difference is on average 6% (from 0 to 11.1%) for all ionospheric layers. In the nighttime conditions, the difference for foF2 is 4%. The nighttime values of foEs differ on average by 20%. These estimates potentially make it possible to forecast ionospheric parameters for a particular storm.  相似文献   

15.
In this study a new method is presented to determine model parameters from magnetic anomalies caused by dipping dikes. The proposed method is applied by employing only the even component of the anomaly. First, the maximum of the even component is divided to its value at any distance x in order to obtain S1. Then, theoretical even component values are computed for the minimal depth (h) and half-width (b) values. S2 is obtained by dividing their maximum to the value computed for the same distance x. A set of S2 values is calculated by slowly increasing the half-width, and h and b for the S2 closest to S1 are determined. The same procedure is repeated by increasing the depth. The determined b values are plotted against the corresponding values of h. After repeating the process and plotting curves for different distances, it is possible to determine the actual depth and half-width values.  相似文献   

16.
The estimation of the quality factor Q plays a fundamental role in enhancing seismic resolution via absorption compensation in the near-surface layer. We present a new geometry that can be used to acquire field data by combining surface and cross-hole surveys to decrease the effect of geophone coupling on Q estimation. In this study, we drilled number of receiver holes around the source hole, each hole has different depth and each geophone is placed geophones into the bottom of each receiver hole to avoid the effect of geophone coupling with the borehole wall on Q estimation in conventional cross-hole seismic surveys. We also propose a novel tomographic inversion of the Q factor without the effect of the source signature, and examine its stability and reliability using synthetic data. We estimate the Q factors of the near-surface layer in two different frequency bands using field data acquired in the Dagang Oilfield. The results show that seismic absorption in the near-surface layer is much greater than that in the subsurface strata. Thus, it is of critical practical importance to enhance the seismic solution by compensating for near-surface absorption. In addition, we derive different Q factors from two frequency bands, which can be treated, to some extent, as evidence of a frequency-dependent Q.  相似文献   

17.
An earthquake withM=6.5 happened on January 15, 2000 in Yao’an of Yunnan Province. After the earthquake, a temporary digital network with 6 detectors around the epicenter area was set up. 402 aftershocks were located more precisely. According to coda short recording observed, the coda averaging quality factor has been acquired via Sato’s single scattering model analyses,Q c(f)=49f 0.95,f=1.5～20.0 Hz, which has the attenuation characteristics of high structural active region.  相似文献   

18.
Spatial and time variations in the critical frequencies foF2 before the strong earthquake of August 15, 1963, with the magnitude M = 7.75 are analyzed. The epicenter of the earthquake was located in the vicinity of the magnetic equator in the American longitudinal sector. The data of the topside ionosonde on board Alouette-1 and of the series of ground-based ionosondes has been used for this purpose. The ground-based ionosondes made it possible to detect an insignificant anomalous decrease in foF2 within the zone of earthquake preparation a few days prior to the earthquake. This result confirms the conclusion drawn earlier on the basis of the satellite data. The modification of the ionosphere at the F-region level is more evident in the satellite than in the ground-based data. It is also noted that the character of the time variations in foF2 a day before the earthquake is similar to the so called “quiet time” Q-disturbances in the ionosphere, when the electron concentration at the F region maximum differs from the median values by more than 20% under undisturbed geophysical conditions.  相似文献   

19.
An important task in seismic hazard assessment is estimation of the intensity and frequency of extremely strong earthquake effects, in particular, peak ground velocities (PGV). Earlier, a method was proposed to evaluate PGV values based on the magnitude of displacements of rock blocks (Rodkin et al., 2012). In this study, this method is used to analyze field data on the source zones of the August 19, 1992, MS = 7.3 Susamyr earthquake and the January 3, 1911, Mw = 7.9 Kemin earthquake, and estimate maximum ground shaking at the upper construction site of the Upper Naryn series of hydropower plants, Kyrgyz Republic. It is shown that the resulting estimates are consistent with data obtained through other techniques. Therefore, the new approach can be recommended to estimate earthquake effects.  相似文献   

20.
We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake (m max) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from 1907 to 2012. Five seismogenic zones were delineated, viz. Hazara-Kashmir Syntaxis, Karakorum Seismic Zone, Kohistan Seismic Zone, Nanga Parbat Syntaxis, and SE-Kashmir Seismic Zone. Then, the seismicity analysis and maximum credible earthquake estimation were carried out for each zone. The low b value (<1.0) indicates a higher stress regime in all the zones except Nanga Parbat Syntaxis Seismic Zone and SE-Kashmir Seismic Zone. The m max was estimated following three different methodologies, the fault parameter approach, convergence rates using geodetic measurements, and the probabilistic approach using the earthquake catalogue and is estimated to be M w 7.7, M w 8.5, and M w 8.1, respectively. The maximum credible earthquake (m max) estimated for each zone shows that Hazara Kashmir Syntaxis Seismic Zone has the highest m max of M w 8.1 (±0.36), which is espoused by the historical 1555 Kashmir earthquake of M w 7.6 as well as the recent 8 October 2005 Kashmir earthquake of M w 7.6. The variation in the estimated m max by the above discussed methodologies is obvious, as the definition and interpretation of the m max change with the method. Interestingly, historical archives (～900 years) do not speak of a great earthquake in this region, which is attributed to the complex and unique tectonic and geologic setup of the Kashmir Himalaya. The convergence is this part of the Himalaya is distributed not only along the main boundary faults but also along the various active out-of-sequence faults as compared to the Central Himalaya, where it is mainly adjusted along the main boundary fault.  相似文献   

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