Building and Testing an <Emphasis Type="Italic">a priori</Emphasis> Geophysical Model for Western Eurasia and North Africa

We construct and evaluate a new three-dimensional model of crust and upper mantle structure in Western Eurasia and North Africa (WENA) extending to 700 km depth and having 1° parameterization. The model is compiled in an a priori fashion entirely from existing geophysical literature, specifically, combining two regionalized crustal models with a high-resolution global sediment model and a global upper mantle model. The resulting WENA1.0 model consists of 24 layers: water, three sediment layers, upper, middle, and lower crust, uppermost mantle, and 16 additional upper mantle layers. Each of the layers is specified by its depth, compressional and shear velocity, density, and attenuation (quality factors, Q _P and Q _S ). The model is tested by comparing the model predictions with geophysical observations including: crustal thickness, surface wave group and phase velocities, upper mantle _n velocities, receiver functions, P-wave travel times, waveform characteristics, regional 1-D velocities, and Bouguer gravity. We find generally good agreement between WENA1.0 model predictions and empirical observations for a wide variety of independent data sets. We believe this model is representative of our current knowledge of crust and upper mantle structure in the WENA region and can successfully be used to model the propagation characteristics of regional seismic waveform data. The WENA1.0 model will continue to evolve as new data are incorporated into future validations and any new deficiencies in the model are identified. Eventually this a priori model will serve as the initial starting model for a multiple data set tomographic inversion for structure of the Eurasian continent.     

On the <Emphasis Type="Italic">P</Emphasis> and <Emphasis Type="Italic">S</Emphasis> Receiver Functions Used for Inverting the One-Dimensional Upper Mantle Shear-Wave Velocities

The teleseismic P receiver functions are customarily inverted to attain the seismic velocities beneath a seismic station. Surface wave dispersion data are often added to reduce the effect of the non-uniqueness. The combination of P receiver function and surface wave works well in resolving the structures in the crust and uppermost mantle, but is less effective in characterizing greater (lithosphere and asthenosphere) depths due to the interference from crustal multiples. A solution to this problem is jointly to model teleseismic S receiver functions with surface wave and P receiver functions. This study adopts a fast, one-dimensional (1-D) inversion scheme. To avoid the effect of multidimensional structures away from the seismic station, we eliminate multiples that reverberate between the surface and interfaces below a restriction depth (RD), as well as S-to-P conversions below an inversion depth (ID). P-to-S conversions off the interfaces above the half-space and S-to-P conversions above the ID and multiples above the RD are properly modelled. This approach favours ray paths travelling close to stations and is, therefore, more suitable for 1-D inversions. We perform numerical experiments with and without noise and highlight the advantages of a joint receiver function and surface wave analysis.     

Attenuative Dispersion of <Emphasis Type="Italic">P</Emphasis> Waves and Crustal <Emphasis Type="Italic">Q</Emphasis> in Turkey and Germany

We have measured group delays of the spectral components of high-frequency P-waves along two portions of the North Anatolian Fault Zone (NAFZ) in Turkey and in a region of southern Germany. Assuming that the observed dispersion is associated with attenuation in the crust and that it can be described by a continuous relaxation model, we obtained Q and the high-frequency relaxation times for those waves for each of the three regions. Individual P-wave Q values exhibit large scatter, but mean values in the NAFZ increase from about 25 to 60 over the distance range 5–90 km. Mean Q values are somewhat higher in the eastern portion of the NAFZ than in the western portion for measurements made at distances between 10 and 30 km. P-wave Q values in Germany range between about 50 and 300 over the hypocentral distance range 20–130 km. In that region we separated the effects of Q for basement rock (2–10 km depth) from that of the overlying sediment (0–2 km depth) using a least-squares method. Q varies between 100 and 500 in the upper 8–10 km of basement, with mean values for most of the distance range being about 250. Q in the overlying sediments ranges between 6 and 10. Because of large scatter in the Q determinations we investigated possible effects that variations of the source-time function of the earthquakes and truncation of the waveform may have on Q determinations. All of our studies indicate that measurement errors are relatively large and suggest that useful application of the method requires many observations, and that the method will be most useful in regions where the number of oscillations following the initial P pulse is minimized. Even though there is large scatter in our Q determinations, the mean values that we obtained in Turkey are consistent with those found in earlier studies. Our conclusions that Q is significantly higher in the basement rock of Germany than in the basement rock of Turkey and that Q is lower in western Turkey than in eastern Turkey are also consistent with results of Q studies using Lg coda.     

Dispersion Measurements of <Emphasis Type="Italic">P</Emphasis> Waves and their Implications for Mantle <Emphasis Type="Italic">Q</Emphasis><Subscript><Emphasis Type="Italic">p</Emphasis></Subscript>

We analyze the anelasticity of the earth using group delays of P-body waves of deep (>200 km) events in the period range 4–32 s for epicentral distances of 5–85 degrees. We show that Time Frequency Analysis (TFA), which is usually applied to very dispersive surface waves, can be applied to the much less dispersive P-body waves to measure frequency-dependent group delays with respect to arrival times predicted from the CMT centroid location and PREM reference model. We find that the measured dispersion is due to: (1) anelasticity (described by the P-wave quality factor Q _p ), (2) ambient noise, which results in randomly distributed noise in the dispersion measurements, (3) interference with other phases (triplications, crustal reverberations, conversions at deep mantle boundaries), for which the total dispersion depends on the amplitude and time separation between the different phases, and (4) the source time function, which is dispersive when the wavelet is asymmetrical or contains subevents. These mechanisms yield dispersion ranging in the order of one to 10 seconds with anelasticity responsible for the more modest dispersion. We select 150 seismograms which all have small coda amplitudes extending to ten percent of the main arrival, minimizing the effect of interference. The main P waves have short durations, minimizing effects of the source. We construct a two-layer model of Q _p with an interface at 660 km depth and take Q _p constant with period. Our data set is too small to solve for a possible frequency dependence of Q _p . The upper mantle Q ₁ is 476 [299–1176] and the lower mantle Q ₂ is 794 [633–1064] (the bracketed numbers indicate the 68 percent confidence range of Q _p ^–1). These values are in-between the AK135 model (Kennett et al., 1995) and the PREM model (Dziewonski and Anderson, 1981) for the lower mantle and confirm results of Warren and Shearer (2000) that the upper mantle is less attenuating than PREM and AK135.     

Velocity structure of the lithosphere on the 2003 Mongolian-Baikal transect from <Emphasis Type="Italic">SV</Emphasis> waves

The S wave velocity distribution in the Earth’s crust and the first two hundred kilometers of the upper mantle is inferred from data of a seismological linear network including 18 broadband stations installed in the framework of the international teleseismic experiment carried out in 2003 in the south of Siberia and in Mongolia. Models were constructed by using P-to-S received function inversion beneath each station. Vertical cross sections of S wave velocities from the surface to depths of 65 and 270 km covering the entire 1000-km profile are constructed by the linear spline interpolation of individual velocity models. The vertical sections are also represented as anomalies relative to the standard velocity model. The most intense low velocity anomalies (from ?3 to ?6%) in the crust and upper mantle are identified beneath the Sayan, Khamar-Daban, and Khangai highlands and the Djida fold zone and agree both with other geophysical data and with the distribution of Late Cenozoic volcanic fields. The results of this work suggest that the activation of Mongolian-Siberian highlands is largely connected with uplift of the asthenosphere to the base of the crust.     

Estimating the source parameters for the M<Subscript><Emphasis Type="Italic">W</Emphasis></Subscript> 7.6 April 20, 2006 Olyutorskii earthquake from long period <Emphasis Type="Italic">P</Emphasis>-wave records made by the worldwide network

The source parameters of the M _W = 7.6 Olyutorskii earthquake were estimated using the moments of the slip rate function with degrees 1 and 2. The moments were estimated from broadband P-wave records at 52 stations of the worldwide network. The first step was to find a function S(t) for each station; this function is an apparent source time function, i.e., the P-wave slip as radiated by the source toward a station under consideration. The method of empirical Green’s functions was used to estimate S(t). The next step was to calculate the moments of S(t) of degrees 1 and 2 over time and to set up relevant equations to be solved by least squares for the unknown source moments. The horizontal linear source was used as a nonparametric model for calculating the source moments. Haskell’s parametric model was used for further interpretation of the source moments. The resulting estimates are as follows: the source centroid was 13–25 km southwest of the epicenter, the source was 105–120 km long, the source strike was 222°–228°, the rupture velocity was 2.7–3.0 km/s, and the total radiation duration was 24–27 s. These estimates indicate a bilateral rupture dominated by a southwestward sense of rupture propagation. The source characteristics are consistent with the aftershock area geometry and with the focal mechanism, as well as with surface breakage as observed by geologists in the field.     

The Influence of Path Corrections and a Three-dimensional Global <Emphasis Type="Italic">P</Emphasis>-wave Velocity Model on Seismic Event Location in Kazakhstan

We relocate 81 large nuclear explosions that were detonated at the Balapan and Degelen Mountain subregions of the Semipalatinsk test site in Kazakhstan during the years 1978 to 1989. The absolute locations of these explosions are available, as well as very accurate estimates of their origin times. This ground truth information allows us to perform a detailed analysis of location capability. We use a sparse network of stations with highly accurate first arrival picks measured using a waveform cross-correlation method. These high quality data facilitate very accurate location estimates with only a few phases per event. We contrast two different approaches: 1) a calibration-based approach, where we achieve improved locations by using path corrections, and 2) a model-based approach, where we achieve improved locations by relocating in a recently published global 3-D P-velocity model. Both methods result in large improvements in accuracy of the obtained absolute locations, compared to locations obtained in a 1-D reference earth model (ak135). The calibration-based approach gives superior results for this test site, in particular when arrival times from regional stations are included. Estimated locations remain well within a 1000 km² region surrounding the ground truth locations when the path corrections for the Balapan and Degelen Mountain subregions are interchanged, but even for the short separation between these two regions, we find variations in the path corrections that cause systematic mislocations. The model-based approach also results in substantially reduced mislocation distances and has the distinct advantage that it is, in principle, transportable to other source regions around the world.     

Numerical simulation of the <Emphasis Type="Italic">F</Emphasis>2-layer stratification and appearance of the <Emphasis Type="Italic">F</Emphasis>3 and <Emphasis Type="Italic">G</Emphasis> layers in the equatorial ionosphere: The morphology of the phenomena

This work is devoted to a numerical simulation of the equatorial ionosphere, performed using the GSM TIP model completed with a new block for calculating the electric field. It has been indicated that the usage of the wind system calculated according to the MSIS-90 model makes it possible to reproduce the electromagnetic drift velocities at the equator, the effect of the F2-layer stratification, and the appearance of the F3 layer in the equatorial ionosphere. The calculations performed using the modified GSM TIP model made it possible to detect a maximum in the electron density vertical profile at an altitude of ∼1000 km, formed by H⁺ ions, which we called the G layer. If this layer actually exists, it can be observed during sounding the low-latitude ionosphere from satellites during dark time of day.     

Region-specific <Emphasis Type="Italic">S</Emphasis>-wave attenuation for earthquakes in northwestern Iran

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).     

The moment magnitude <Emphasis Type="Italic">M</Emphasis><Subscript>w</Subscript> and the energy magnitude <Emphasis Type="Italic">M</Emphasis><Subscript>e</Subscript>: common roots and differences

Starting from the classical empirical magnitude-energy relationships, in this article, the derivation of the modern scales for moment magnitude M _w and energy magnitude M _e is outlined and critically discussed. The formulas for M _w and M _e calculation are presented in a way that reveals, besides the contributions of the physically defined measurement parameters seismic moment M ₀ and radiated seismic energy E _S, the role of the constants in the classical Gutenberg–Richter magnitude–energy relationship. Further, it is shown that M _w and M _e are linked via the parameter Θ = log(E _S/M ₀), and the formula for M _e can be written as M _e = M _w + (Θ + 4.7)/1.5. This relationship directly links M _e with M _w via their common scaling to classical magnitudes and, at the same time, highlights the reason why M _w and M _e can significantly differ. In fact, Θ is assumed to be constant when calculating M _w. However, variations over three to four orders of magnitude in stress drop Δσ (as well as related variations in rupture velocity V _R and seismic wave radiation efficiency η _R) are responsible for the large variability of actual Θ values of earthquakes. As a result, for the same earthquake, M _e may sometimes differ by more than one magnitude unit from M _w. Such a difference is highly relevant when assessing the actual damage potential associated with a given earthquake, because it expresses rather different static and dynamic source properties. While M _w is most appropriate for estimating the earthquake size (i.e., the product of rupture area times average displacement) and thus the potential tsunami hazard posed by strong and great earthquakes in marine environs, M _e is more suitable than M _w for assessing the potential hazard of damage due to strong ground shaking, i.e., the earthquake strength. Therefore, whenever possible, these two magnitudes should be both independently determined and jointly considered. Usually, only M _w is taken as a unified magnitude in many seismological applications (ShakeMap, seismic hazard studies, etc.) since procedures to calculate it are well developed and accepted to be stable with small uncertainty. For many reasons, procedures for E _S and M _e calculation are affected by a larger uncertainty and are currently not yet available for all global earthquakes. Thus, despite the physical importance of E _S in characterizing the seismic source, the use of M _e has been limited so far to the detriment of quicker and more complete rough estimates of both earthquake size and strength and their causal relationships. Further studies are needed to improve E _S estimations in order to allow M _e to be extensively used as an important complement to M _w in common seismological practice and its applications.     

Upper lithospheric structure in the central Fennoscandian shield: Constraints from P- and S-wave velocity models and V<Subscript>P</Subscript>/V<Subscript>S</Subscript> ratio distribution of the BALTIC wide-angle seismic profile

The paper presents an analysis of the crust and upper mantle structure in the central Fennoscandian shield based on new P- and S-wave 2D velocity models of the BALTIC wide-angle reflection and refraction profiles. Using reprocessing of the old data, new P- and S-wave velocity models and V _P /V _S ratio distribution were developed. Moving from SW to NE, the thickness of the crust varies strongly, from ∼36 km to extremely thick, 58–64 km, crossing Wiborg rapakivi massif, Saimaa and Outokumpu areas, and Eastern Finland complex. Based on the lateral variations of V _P , V _P /V _S and thickness of the crust, three main blocks of the crust and upper mantle were distinguished from SW to NE: southwestern, associated with Wiborg rapakivi massif; the central, having the highest thickness of the crust; and the northeastern, not well documented, with Archaean basement.     

Linear transformations of anomalous potential fields using <Emphasis Type="Italic">S</Emphasis> and <Emphasis Type="Italic">R</Emphasis> approximations

Methods for linear transformations of anomalous physical fields based on R and S approximations of the elements of the initial field are described. The results of the numerical experiment and analytical extension of the gravity field measured in a detailed gravity survey in two regions of Russia are presented.     

The 20-second regional magnitude <Emphasis Type="Italic">M</Emphasis><Subscript><Emphasis Type="Italic">S</Emphasis></Subscript>(20R) for the Russian Far East

A new modified magnitude scale M _S (20R) is elaborated. It permits us to extend the teleseismic magnitude scale M _S (20) to the regional epicenter distances. The data set used in this study contains digital records at 12 seismic stations of 392 earthquakes that occured in the northwest Pacific Ocean in the period of 1993–2008. The new scale is based on amplitudes of surface waves of a narrow range of the periods (16–25 s) close to the period of 20 s, for distances of 80–3000 km. The digital Butterworth filter is used for processing. On the basis of the found regional features concerning distance dependence for seismic wave attenuation, all the stations of the region have been subdivided into two groups, namely, “continental” and “island-arc.” For each group of stations, its own calibration function is proposed. Individual station corrections are used to compensate for the local features.     

Seismic velocity and Poisson’s ratio tomography of the crust beneath southwest Anatolia: an insight into the occurrence of large earthquakes

The western part of Anatolia is one of the most seismically and tectonically active continental regions in the world, and much of it has been undergoing NS-directed extensional deformation since the Early Miocene. In this study, we determine 3-D tomographic images of the crust under the southwestern part of the North Anatolian Fault Zone by inverting a large number of arrival time data of P and S waves. From the obtained P- and S-wave velocity models, we estimated the Poisson’s ratio structures for a more reliable interpretation of the obtained anomalies. Our tomographic results confirmed the major tectonic features detected by previous studies and revealed new structural heterogeneities related to the active seismotectonics of the studied area. High P-wave velocity anomalies are recognized near the surface, while at deeper crustal layers, low P-wave velocities are widely distributed. The crustal S-wave velocity and Poisson’s ratio exhibit more structural heterogeneities compared to the P-wave velocity structure. Microearthquake activity is intense along highly heterogeneous zones in the southwestern part, which is characterized by low to high P-wave velocity, low S-wave velocity, and high Poisson’s ratio anomalies. Large earthquakes are also concentrated in zones dominated by low velocities and low to high Poisson’s ratios. Results of the checkerboard and synthetic tests indicate that the imaged anomalies are reliable features down to a depth of 25 km. Moreover, they are consistent with many geological and geophysical results obtained by other researchers along the southwestern part of the North Anatolian Fault Zone. An erratum to this article can be found at     

Simultaneous inversion of velocity structures and hypocentral locations: Application to the Friuli seismic area NE Italy

A layeredP- andS-wave velocity model is obtained for the Friuli seismic area using the arrival time data ofP- andS-waves from local earthquakes. A damped least-squares method is applied in the inversion.The data used are 994P-wave arrival times for 177 events which have epicenters in the region covered by the Friuli seismic network operated by Osservatorio Geofisico sperimentale (OGS) di Trieste, which are jointly inverted for the earthquake hypocenters andP-wave velocity model. TheS-wave velocity model is estimated on the basis of 978S-wave arrival times and the hypocenters obtained from theP-wave arrival time inversion. We also applied an approach thatP- andS-wave arrival time data are jointly used in the inversion (Roecker, 1982). The results show thatS-wave velocity structures obtained from the two methods are quite consistent, butP-wave velocity structures have obvious differences. This is apparent becauseP-waves are more sensitive to the hypocentral location thanS-waves, and the reading errors ofS-wave arrival times, which are much larger than those ofP-waves, bring large location errors in the joint inversion ofP- andS-wave arrival time. The synthetic data tests indicated that when the reading errors ofS-wave arrivals are larger than four times that ofP-wave arrivals, the method proposed in this paper seems more valid thanP- andS-wave data joint inversion. Most of the relocated events occurred in the depth range between 7 and 11 km, just above the biggest jump in velocity. This jump might be related to the detachment line hypothesized byCarulli et al. (1982). From the invertedP- andS-wave velocities, we obtain an average value 1.82 forV _p /V _s in the first 16 km depth.     

3D <Emphasis Type="Italic">v</Emphasis><Subscript>P</Subscript> and <Emphasis Type="Italic">v</Emphasis><Subscript>S</Subscript> models of southeastern margin of the Tibetan plateau from joint inversion of body-wave arrival times and surface-wave dispersion data

A new 3D velocity model of the crust and upper mantle in the southeastern (SE) margin of the Tibetan plateau was obtained by joint inversion of body- and surface-wave data. For the body-wave data, we used 7190 events recorded by 102 stations in the SE margin of the Tibetan plateau. The surface-wave data consist of Rayleigh wave phase velocity dispersion curves obtained from ambient noise cross-correlation analysis recorded by a dense array in the SE margin of the Tibetan plateau. The joint inversion clearly improves the v _S model because it is constrained by both data types. The results show that at around 10 km depth there are two low-velocity anomalies embedded within three high-velocity bodies along the Longmenshan fault system. These high-velocity bodies correspond well with the Precambrian massifs, and the two located to the northeast of 2013 M _S 7.0 Lushan earthquake are associated with high fault slip areas during the 2008 Wenchuan earthquake. The aftershock gap between 2013 Lushan earthquake and 2008 Wenchuan earthquake is associated with low-velocity anomalies, which also acts as a barrier zone for ruptures of two earthquakes. Generally large earthquakes (M ≥ 5) in the region occurring from 2008 to 2015 are located around the high-velocity zones, indicating that they may act as asperities for these large earthquakes. Joint inversion results also clearly show that there exist low-velocity or weak zones in the mid-lower crust, which are not evenly distributed beneath the SE margin of Tibetan plateau.     

<Emphasis Type="Italic">R/S</Emphasis> analysis of the <Emphasis Type="Italic">Dst</Emphasis> index

The paper addresses estimation of the Hurst exponent for time series of the hourly values of the Dst index for the period from 1957 to 2011. It is found that the Hurst exponent is 0.79–0.94 for yearly intervals and 0.8–1.0 for monthly intervals. Based on R/S graphs, the Dst cycles are identified; they range from 3–4 months to 2.2 years and from 8.5 to 22 years in length. It is shown that a Dst time series can be quite satisfactorily described by an α-stable Levy process.     

Origination of <Emphasis Type="Italic">G</Emphasis> conditions in the ionospheric <Emphasis Type="Italic">F</Emphasis> region depending on solar and geomagnetic activity

The dependence of the origination of G conditions in the ionospheric F region on solar and geomagnetic activity has been determined based on numerical simulation of the ionosphere over points 50° N, 105° E and 70° N, 105° E for summer conditions at noon. It has been found that the threshold value of the Kp geomagnetic activity index (Kp _S ), beginning from which a G condition can originate, is minimal for a low solar activity level at relatively high latitudes during the recovery phase of a geomagnetic storm. On average, Kp _S increases with increasing solar activity, but G conditions can originate at high solar activity levels and be absent at moderate ones for certain Kp values, which was apparently predicted for the first time. These properties of the origination of G conditions do not contradict the known results of a G-condition statistical analysis performed based on the data from the global network of ionospheric stations.     

Dayside auroras during unusually large positive values of the IMF <Emphasis Type="Italic">B</Emphasis><Subscript><Emphasis Type="Italic">z</Emphasis></Subscript> component

The characteristics of dayside auroras during the large (16–24 nT) positive values of the IMF B _z component, observed on January 14, 1988, during the interaction between the Earth’s magnetosphere and the body of the interplanetary magnetic cloud, have been studied based on the optical observations on Heiss Island. A wide band of diffuse red luminosity with an intensity of 1–2 kilorayleigh (kR) was observed during 6 h in the interval 1030–1630 MLT at latitudes higher than 75° CGL. Rayed auroral arcs, the brightness of which in the 557.7 nm emission sharply increased to 3–7 kR in the postnoon sector immediately after the polarity reversal of the IMF B _y component from positive to negative, were continuously registered within the band. Bright auroral arcs were observed at the equatorward edge of red luminosity. It has been found out that the red auroral intensity increases and the band equatorward boundary shifts to lower latitudes with increasing solar wind dynamic pressure. However, a direct proportional dependence of the variations in the auroral features on the dynamic pressure variations has not been found. It has been concluded that the source of bright discrete auroras is located in the region of the low-latitude boundary layer (LLBL) on closed geomagnetic field lines. The estimated LLBL thickness is ∼3 R _e . It has been concluded that the intensity of the dayside red band depends on the solar wind plasma density, whereas the position of the position equatorward boundary depends on the dynamic pressure value and its variations.     

Stable carbon isotope evidence for tracing the diet of the host <Emphasis Type="Italic">Hepialus</Emphasis> larva of <Emphasis Type="Italic">Cordyceps sinensis</Emphasis> in the Tibetan Plateau

Two types of Hepialus larvae with different diets were distinguished in the Sejila Mountain, Tibetan Plateau based on the stable carbon isotope data of the host Hepialus larva of Cordyceps sinensis and its closely adjacent tender plant roots and humus fractions. Type I is the larva chiefly fed by soil humus, and characterized by the δ ¹³C values of −22.6‰ to −23.4‰, and more than −23.4‰ in its heads. Type II is the larva chiefly fed by tender plant roots, and characterized by the δ ¹³C values of −24.6‰ to −27.6‰, and less than −24.6‰ in its heads. Our result has exceeded the traditional understanding that their food sources only come from the tender plant roots, and may provide evidence for choosing cheap and high-quality foods and further establishing artificial habitats in their large-scale reproduction. Supported by the National Key Technology R & D Program (Grant No. 2007BAI32B05)