Time–frequency analysis of the 2012 double earthquakes records in North-West of Iran

On August 11, 2012, East-Azerbuijan province experienced moderate-size double earthquakes, approximately 60 km northeast of the city of Tabriz. The time–frequency characteristics of ground motion records during these events which caused widespread damage to the structures are investigated in detail. Wavelet transform were applied in this study as a powerful technique to detect the transient and non-stationary features associated in amplitude and frequency of ground motions. The top four PGA ground-motion records from the first and second events were used in the analysis. As a preliminary estimates, the energy contents of horizontal and vertical components of ground-motion records related to building damages were critically evaluated and discussed at different frequency level. Results of energy distribution on pseudo-period corresponding to each decomposition level show good consistency with the level of damage in the stricken area. The focus of this study on the causes of damage considering the energy content of ground motion records is helping to improve the engineering insight in design process of earthquake-resistant buildings.     

Investigation of historical earthquakes in the northeastern Fujian area

Taking the northeastern Fujian area as an example, we provide some new technological ideas and contents for the historical earthquake investigation of significant engineering construction sites. ① Make sure the integrity of earthquake materials with reference to the regional histories of culture and disasters; ② Evaluate the influence of historical earthquakes on the basis of actual records, review and identify the epicenter location and magnitude of destructive earthquakes. The research by the new technological ideas will endue the investigation of historical earthquakes with new meanings in the cultural phylogeny and credible time domain, so as to make the results of historical earthquake research more scientific. The aim of the paper is to improve the level of historical earthquake investigation for a better service to the engineering construction.     

A uniform catalog of earthquakes for seismic hazard asesment in Iran

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Magnitudes and time distribution of the swarm earthquakes August–November 2000 in NW Bohemia

During the earthquake swarm in the north-western part of the Czech Republic which happened between August and November 2000 more than 10 500 single events have been recorded at the station Wernitzgruen (WERN), located in the Vogtland (Germany) at about 13 km hypocentral distance. Most of the events were weak and followed each other so closely in time that they could not be identified at more distant stations in Middle Europe. A procedure to determine magnitudes of very small events from recordings in short distances is realized and discussed. The development over time of the seismic activity shows the typical pattern of previous earthquake swarms in this region consisting of multiple swarm episodes. For the first time, however, it is analysed using the time intervals between successive events. However, no new and reproducible patterns were found which could be useful for prognostics of future swarm activities.     

Investigation of upper crust anisotropy in Ghaen-Birjand region, east-central Iran

IntroductionWhenpropagatingthroughananisotropicmedium,ashearwavesplitsintotwo(quasi)shearwaveswithdifferentpropagationspeedsandpolarizedorthogonally.Owingtotherecentdevel-opmentofseismicobservationsystem,detectionofshearwavessplittingwithverysmalldelaytimesbetweenfasterandslowershearwavesbecameavailableandprovidedpowerfulapproachfordetectionofcrustalanisotropy.Crampin(1978)emphasizedtheroleofalignedmicrocracksasacauseofcrustalanisotropyandpointedoutthatforverticallyalignedmicrocracksthedirecti…     

Recovering relative locations of the 2005–2006 Mukacheve earthquakes from similarity of their waveforms at a single station

An algorithm was designed for inverting the set of cross-correlation coefficients between the records of recurrent earthquakes by a single station for their relative locations based on an assumption of Menke (1999) that the cross-correlation is only a function of separation between the sources and decays exponentially with it. Tested on synthetic data sets, the algorithm easily recovered the true relative locations, the initial ones seeded randomly. Inversion of the cross-correlation coefficients between the records of the two groups of the Mukacheve 2005–2006 recurrent earthquakes by the station Mukacheve steadily produced an almost flat shape of hypocenter cloud for each of the groups, final relative locations of hypocenters being almost the same for different initial seedlings. The combined set of cross-correlation coefficients for both groups was also inverted, and the shape of the combined hypocenter cloud was almost flat again. These results compare well with ones obtained earlier (Gnyp 2010) by relocating the Mukacheve earthquakes with the use of differential arrivals and source specific station terms.     

Double-difference relocation of earthquakes in central-western China, 1992–1999

The double-difference earthquake location algorithm was applied to the relocation of 10,057 earthquakes that occurred in central-western China (21^∘N to 36^∘N, 98^∘E to 111^∘E) during the period from 1992 to 1999. In total, 79,706 readings for P waves and 72,169 readings for S waves were used in the relocation. The relocated seismicity (6,496 earthquakes) images fault structures at seismogenic depths that are in close correlation with the tectonic structure of major fault systems expressed at the surface. The new focal depths confirm that most earthquakes (91%) in this region occur at depths less than 20 km.     

Viscoelastic deformations after the 2006–2007 Simushir earthquakes

Continuous measurements at the Kuril GPS network since 2006 have revealed anomalous coseismic and postseismic displacements of the Earth’s crust, which accompanied the great 2006–2007 earthquake doublet in the central Kuriles and were observed during 2.5 years after the events. Prior to the earthquakes, all observation sites of the Kuril network were moving towards the continent due to the subduction deformation of the continental margin. After the events, the direction of displacement had changed to the opposite direction at the stations located on the Matua, Ketoy, and Kharimkotan Islands, which were the nearest to the seismic events, and experienced a significant turn on the Urup Island nearby. Modeling of postseismic viscoelastic relaxation of strains in the asthenosphere suggested an acceptable explanation for the long-term anomalous offsets revealed. By solving the corresponding inverse problems, we estimated the viscosity of the upper mantle and constrained the slip distribution of the 2006 Simushir earthquake.     

Historical earthquakes and a tsunami in Bohai Sea

Quantitative analysis on seismicity showed that there are several seismic dense zones in Bohai Sea. These seismic dense zones of modern small earthquakes behave prominent NE orientation, although a seismic dense zone with NW direction exists actually. Taking 39°N as a boundary, seismicity in the south is different from that in north of Bohai Sea. Almost all strong earthquakes and seismic dense zones are concentrated in the southern part. Based on archives and seismic dense characteristics, we amended the epicenter of strong earthquakes in 1548 and discussed about magnitude of the earthquake in 1888. Possibility of the event in 173 as a tsunami was discussed. The event in 1597 was doubted as a strong earthquake in Bohai Sea.     

Application of a time-magnitude prediction model for earthquakes

In this paper we discuss the physical meaning of the magnitude-time model parameters for earthquake prediction. The gestation process for strong earthquake in all eleven seismic zones in China can be described by the magnitude-time prediction model using the computations of the parameters of the model. The average model parameter values for China are： b = 0.383, c=0.154, d = 0.035, B = 0.844, C = -0.209, and D = 0.188. The robustness of the model parameters is estimated from the variation in the minimum magnitude of the transformed data, the spatial extent, and the temporal period. Analysis of the spatial and temporal suitability of the model indicates that the computation unit size should be at least 4°× 4°for seismic zones in North China, at least 3° × 3° in Southwest and Northwest China, and the time period should be as long as possible.     

Statistical analysis on temporal-spatial correlativity within temporal doublets of strong earthquakes in North China and its vicinity

Introduction Being the important evidence of seismic trend prediction, the characters of spatial-temporal distribution of strong earthquakes can, to some extent, reflect the gestation mechanism and the migration law of strong quakes. From temporal point of view, a number of scholars consider the occurrence of strong earthquakes as the independent events, i.e., Poisson process. Based on this assumption, various predicted models are brought forward, such as stationary Poisson model, subsection …     

Seismicity in Major Seismotectonic Provinces of Iran

Seismicity parameters,i.e.,seismic activity rate,X,the so-called Gutenberg-Richter b value(orβ),and maximum possible magnitude,Mmax,for major seismotectonic provinces of Iran are estimated through the application of Kijko and SellevolPs uncertainty models.The uncertainty models facilitated the estimation of seismic activity parameters from incomplete and uncertain data files in the catalog of earthquakes in major seismotectonic provinces of Iran.Zagros has the highest seismic activity rate,and is characterized by the occurrence of mainly small-and mid-sized earthquakes.Kopeh Dagh has the lowest activity rate but is characterized by a greater occurrence of major earthquakes.However,the Makran and Alborz-Azarbayejan seismotectonic provinces are most likely the regions which are capable of generating great earthquakes.     

Bayesian spatio-temporal analysis of stomach cancer incidence in Iran, 2003–2010

Stomach cancer is the second most common cancer in Iranian men and the fourth most common cancer in Iranian women. The incidence rate of this cancer in Iranian men is almost 2.5 times that in women. The objective of this study was to investigate the trend of stomach cancer incidence rate in Iran in an 8-year time period (2003–2010) and also update the incidence estimates of stomach cancer. Data from a total number of 41,830 patients diagnosed with stomach cancer according to the International Classification of Diseases (C16) in 2003–2010 were analyzed. We used Bayesian spatial and Bayesian spatio-temporal models to study the relative risk and trend of stomach cancer incidence rate in Iran. Out of 41,830 stomach cancer registered patients, 72% were male. The average smoothed SIRs were 0.79, 0.82 and 0.78 for the general, female and male population, respectively. This shows a nearly stable incidence rate. The northwest of Iran had the highest incidence rate of stomach cancer. The trend of this rate was declining to the lowest rate in the southeast of the country. The estimated values of coefficient of the trend term for general, female and male population in this model were 0.0085, ? 0.018 and 0.0041, which indicate almost a stable fixed trend. The map of temporal trends also showed that although the incidence rate of this cancer is to some extent stable, in general, in the central and in the east of the country the incidence relative risk has increased over time. The prevalence of Helicobacter pylori infection, Lower socioeconomic status and Iodine deficiency were speculated to be relevant factors for the high incidence rates of stomach cancer in the northwest of Iran. Preventive measures in the north and northwest of Iran could have an effect on controlling this cancer in these areas.     

Multi—scale expression of spatial activity anomalies of earthquakes and its indicative significance on the space and time attributes of strong earthquakes

The noise model based on a trous wavelet algorithm produces a multi-scale expression of image through the combination of wavelet transform and a testing model of statistical significance.This kind of expression not only gives the formation and location of image structure on different scales,but also eliminates the influence of noise Since the algorithm does not need any priori hypotheses,it is suitable for the data with complex structure.The research line is employed in this paper to analyze the spatial activity of earthquake.The method of how to recognize and describe the multi-scale space activity of earthquake is emphatically discussed in this paper.Taking typical sequences in Southwest China as research cases,we systematically study the structure characters of spatial activity of earthquake on different scales.Results show that multi-scale space structure to some extent possesses indicative effect on strong epicenters.And the foreshock anomalies of Songpan seismic sequence also reveal interesting pattem during the spatial-temporal evolvement.     

Temporal migration of earthquakes in Koyna–Warna (India) region by pore-fluid diffusion

Continuous occurrences of several thousands of earthquakes in Koyna–Warna region since the initial impoundment (1962) of the Koyna reservoir has attracted the attention of seismologists all over the world to know the exact earthquake physical processes involved. The area has been a site for reservoir-triggered earthquakes for the last four and half decades. Major bursts of seismic activity occurred during 1967, 1973, 1980, 1993, and 2000 and recently in 2005 with magnitudes exceeding 5.0 in the region. A notable southward migration of seismicity has been observed following the impoundment of another reservoir, the nearby Warna reservoir. All the mainshocks suggest that the significant southward migration might be due to pore-pressure diffusion. We have divided the entire period from 1967 to 2007 in several sequences starting by a mainshock of M >5. Each sequence is critically analyzed in terms of triggering by the diffusion process through the fractured medium. The pore-fluid diffusion tensor D for each sequence is estimated based on Darcy’s law. The direction of temporal migration of seismicity of each sequence except 1980 is correlated well with the eigenvectors of diffusion. The fluid flow eigenvectors are constrained with one of the strike directions of the focal mechanisms. The frequency magnitude distribution shows the b value to vary from 0.5 to 1.2. Spatial distribution of the b value further indicates that the area along the major faults is more prone to future earthquake.     

Correlation between movement of tectonicblocks and earthquakes in groups

Introduction ZHANG and ZHONG (1977), ZHANG, et al (1978) and ZHANG (1984) pointed out that Chinese mainland is divided into two parts by the NS-trending tectonic belt, i.e., the eastern area and the western area, and each area is divided into tectonic blocks by faults. In the eastern area, the faults are trending NNE and NNW, mainly NNE, and the long axis strike of blocks is nearly trending NS. In the western area, faults are trending NEE and NWW, mainly NWW, long axis strike …     

Hydrochemical Characteristics of the Aral Sea in 2012–2013

The decrease in Aral Sea area, which started in the 1960s, caused considerable changes in the hydrological, chemical, and biological structure of sea water. Regular observations of Aral water chemistry ceased in the early 1990s. There were no observations of the concentrations of biogenic element compounds in water (the so-called “first-day analyses”). During expeditions of the Institute of Oceanology, RAS, in September 2012 and October 2013, integrated hydrochemical observations were carried out, including measuring the concentrations of biogenic element compounds, dissolved oxygen, hydrogen sulfide, and carbonate equilibrium components. An objective of this study was to develop methods of hydrochemical studies under high water salinity (mineralization). In addition to the standard hydrochemical complex, water samples were taken to determine total water mineralization and the concentration of dissolved and suspended metal forms. The results of these studies are given.     

Investigation of the SA evolution by using the CHAOS-4 model over 1997–2013

The temporal and spatial evolution characteristics of the geomagnetic secular acceleration(SA) are investigated, based on CHAOS-4 core field model during the period of 1997–2013. The SA evolution on a short time scale is associated with the phenomenon of the geomagnetic jerk. More details of the global extent and the occurrence time of the successive jerks(the 1999, 2003, 2007, and 2011 jerks) are obtained. The location, size and reversed polarity pattern for the 1999 jerk are similar to those for the 2003 jerk in the Asian-Indian sector. While the 2007 and 2011 jerks mainly take place in the Atlantic sector. The direction and speed of the shift for the four jerks are different, identified by the occurrence time of the jerks. The zonal motions of the SA patches exhibit an oscillation pattern in the Asian-Indian sector, whereas a purely westward drifting pattern is along the equator in the Atlantic sector. It is believed that the shift of the jerks is related to the motion of SA-B_r patches observed at the core-mantle boundary(CMB).     

Memory effect in M ≥ 7 earthquakes of Taiwan

The M?≥?7 earthquakes that occurred in the Taiwan region during 1906–2006 are taken to study the possibility of memory effect existing in the sequence of those large earthquakes. Those events are all mainshocks. The fluctuation analysis technique is applied to analyze two sequences in terms of earthquake magnitude and inter-event time represented in the natural time domain. For both magnitude and inter-event time, the calculations are made for three data sets, i.e., the original order data, the reverse-order data, and that of the mean values. Calculated results show that the exponents of scaling law of fluctuation versus window length are less than 0.5 for the sequences of both magnitude and inter-event time data. In addition, the phase portraits of two sequent magnitudes and two sequent inter-event times are also applied to explore if large (or small) earthquakes are followed by large (or small) events. Results lead to a negative answer. Together with all types of information in study, we make a conclusion that the earthquake sequence in study is short-term corrected and thus the short-term memory effect would be operative.     

Long-range dependence in the time series of Taiţa River discharges

ABSTRACT

The aim of this article is to offer an insight into the hydrology of southeast Romanian catchments, which have not been studied systematically. The complex behaviour of the Tai?a, one of the most important rivers situated in the northern part of Dobrogea, is demonstrated. Long-range dependence (LRD) in the time series of its streamflow, including the presence of trends, is supported by an estimated Hurst exponent of approximately 0.8, as well as statistical tests.

Editor D. Koutsoyiannis; GUEST editor S. Weijs