Acta Geophysica

Published by Springer Verlag
Online ISSN: 1895-7455
Print ISSN: 1895-6572
The M w 6.2 Lefkada earthquake occurred on 14 August 2003 beneath the western coastline of Lefkada Island. The main shock was followed by an intense aftershock activity, which formed a narrow band extending over the western coast of the Island and the submarine area between Lefkada and Kefalonia Islands, whereas additional off fault aftershocks formed spatial clusters on the central and northwestern part of the Island. The aftershock spatial distribution revealed the activation of along-strike adjacent fault segment as well as of secondary faults close to the main rupture. The properties of the activated segments were illuminated by the precisely located aftershocks, fault plane solutions determination and the cross sections performed parallel and normal to their strike. The aftershock focal mechanisms exhibited mainly strike slip faulting throughout the activated area, although deviation of the dominant stress pattern is also observed. The results help to emphasize the importance of the identification of activated nearby fault segments possibly triggered by the main rupture. Because such segments are capable to produce moderate events causing appreciable damage, they should be viewed with caution in seismic hazard assessment in addition to the major regional faults. Key wordsaftershock sequence–complex faulting–Lefkada Island (Greece)–14 August 2003 Lefkada earthquake
Magnetic anomaly map of Poland with the location the survey sites along Z–W profile. Contour interval 100 nT. The map is based on a grid database with resolution of 5×5 km. Data source: Magnetic anomaly map of Poland, scale 1:500,000 (Karaczun et al. 1978). 
Relative secular variations of the geomagnetic field along the Zgorzelec–Wi ż ajny profile during 1966–2005 in selected period-times (redrawn from Bojdys et al . 2006). 1 – Relative secular variations δ ( ∆ T n ); 2 – The 6-degree polynomial approximating relative secular variations; 3 – Approximated borders of the geological units. 
Changes in time of the relative geomagnetic field values and the relative secular variations at selected secular points (s.p.) in the different geological units during 1966–2005. Curve 1 – changes of the relative geomagnetic field values ∆ T n,t = T n,t – T Belsk,t ; Curve 2 – linear approximations of changes in the relative geomagnetic field values during a selected period; Curve 3 – the third-degree polynomial approximating the changes of relative geomagnetic field values ∆ T n,t ; Curve 4 – relative secular variations of the geomagnetic field, second-degree polynomial. 
The Zgorzelec-Wiżajny profile cuts through the main European geotectonic units of the Palaeozoic Western and Central European Platform and the East European Craton, including the connecting Trans-European Suture Zone. The paper summarises 40 years of research on geomagnetic secular variations along the Zgorzelec-Wiżajny profile since 1966. It discusses methods of processing measurement records and presenting their results. The latter are presented against the background of the local geology and the crustal deep magnetic structure data. The hitherto method of variation analysis was modified to address a new trend in the geomagnetic secular variations that has emerged in the East European Craton during the last five years (2001–2005).
Recalculated raw daily doses by the SL model 501 biometer versus those by the reference biometer KZ for the period of 2005-2006. Solid line shows the regression line. Dashed line represents the 1:1 relationship. The value of line slope and intercept together with their standard errors, explained variance R 2 , and standard deviation (SD) of the differences, (SL501-KZ)/KZ × 100% are embedded into the figure.
The differences between the daily doses by RB meter and those by the model in percent of the RB doses for the period 1976-1992 as a function of the calendar day. The solid curve shows the smoothed differences by the Lowess technique.
The annual sum of the daily erythemal doses in the period of 1976-2008 from the homogenized UV data. The line shows a linear fit to the yearly data.
The differences between the monthly mean erythemal doses and their longterm (1976-2008) monthly means in percent of the long-term means after averaging over the warm subperiod months (April-October, blue points) of each year in the period of 1976-2008. The red points represent the subset for the clear-sky conditions. The pertaining solid lines (the same color as the points) represent the smoothed patterns of the differences by the Lowess technique. The dashed red curve gives smoothed pattern of the modeled UV data for clear-sky conditions derived from the ozone fractional deviations and RAF value of 1.1. The dashed blue line represents a least squares regression line fitted to all-sky differences. Colour version of this figure is available in electronic edition only.
Measurements of erythemal irradiance have been carried out continuously at Belsk since May 1975. We present a homogenization procedure of the UV time series for the period of 1976–2008. Long-term oscillations discovered in the homogenized data set agree with those extracted from the reconstructed UV data for all-sky and clear-sky conditions. The UV climatology was established and the UV variability was determined. Positive UV trends were found for the period of 1976-2008 in the annual mean (5.6±0.9% per decade), in the seasonal mean for the warm subperiod of the year (April–October, 5.5±1.0% per decade), and in monthly means (∼2–9% per decade). A satisfactory agreement between the trend extracted from the homogenized ground-based data and that found in satellite UV data for Belsk (1979–2008) supports the reliability of satellite trend analyses over wider areas during snowless periods. Key wordssurface UV radiation-homogenization-climatology-UV trends
In this study we compared contributions to polar motion excitation determined separately from each of three kinds of geophysical data: atmospheric pressure, equivalent water height estimated from hydrological models, and harmonic coefficients of the Earth gravity field obtained from Gravity Recovery and Climate Experiment (GRACE). Hydrological excitation function (Hydrological Angular Momentum — HAM) has been estimated from models of global hydrology, based on the observed distribution of surfacewater, snow, ice, and soil moisture. In our considerationwe used several global models of land hydrosphere and models ofAtmospheric Angular Momentum (AAM) and Oceanic Angular Momentum (OAM). All of themwere compared with observed Geodetic Angular Momentum (GAM). The spectra of the following excitation functions of polar motion: GAM, AAM+OAM, AAM+OAM+HAM, GAM-AAM-OAM residual geodetic excitation function, and HAM were computed too. The time variable spectra of geodetic, gravimetric, and the sum of atmospheric, oceanic, and hydrological excitation functions are also presented. Phasor diagrams of the seasonal components of polar motion excitation functions of all HAM excitation functions as well as of two GRACE solutions: Center for Space Research (CSR), Centre National d’Etudes Spatiales/Groupe de Recherche en Geodesie Spatiale (CNES/GRGS) were determined and discussed. Key wordshydrological angular momentum–geophysical excitation–polar motion
The stochastic method for finite faults is applied to simulate the ground motion of the 12 October 1992, m b = 5.9, Dahshour earthquake. The method includes discritization of the fault plane into certain number of subfaults, and a ω-squared spectrum is assigned to each of them. Contributions from all subfaults are then empirically attenuated to the observation sites, where they are summed to produce the synthetic acceleration time-history. The method is first tested against its ability of reproducing the recording at Kottamya station. The calibrated model is then applied to calculate the synthetics at a large number of grid points covering the area around the fault plane. Simulated peak values are subsequently used to produce the synthetic peak horizontal acceleration map for the area. We compare the peak horizontal acceleration with the attenuation laws proposed for Egypt as well as the macroseismic intensity map of the 1992 Dahshour earthquake. The peak horizontal acceleration contours estimated using the calibrated model are mostly consistent with the observed intensity values and evidences of strong ground motions. Our results encourage the application of the approach as a supplementary tool for site-specific strong ground motion prediction.
El-Fayoum New City represents one of the new urban settlements that are recently erected all over Egypt. Because seismic recordings are not available, I used the stochastic method to simulate the largest damaging earthquake from the closest seismic source to the proposed area of the city. To verify the method and its computed results in Egypt, a study termed “method verification” was performed. I found that the October 12, 1992, earthquake (M b = 5.8) that occurred southwest of Cairo in the vicinity of the Dahshour region, at the coordinates 29.77°N, 31.07°E, is a significant earthquake to the city. The parameters of the path from the hypocenter of the event to the city were taken into consideration. To determine the site parameters, a shallow seismic refraction survey was carried out in the studied area. Accordingly, I simulated time-histories and pseudo-spectral accelerations from the October 12, 1992, earthquake at the location of seismic profiles. Finally, it is demonstrated that the site is characterized by high ground motion amplification factors, producing a high ground motion acceleration value.
In this work we estimated the source process and the source parameters of the 1993 and 1995 Gulf of Aqaba earthquakes. To investigate the source process of both events, we inverted the teleseismic P- and SH-waveform data using an iterative technique in which the rupture is modeled as a series of point source subevents with varying mechanisms. The main source process of the 1993 event can be explained by two subevents with essentially the same mechanism. These two subevents had different focal depths. The second subevent was about 5 s later than the first one and about 70% of the moment rate released with the second one. The total rupture duration time was about 12 s. Our solution for the 1995 Gulf of Aqaba earthquake indicated that the event consists of three subevents with various fault geometries and about 60% of the moment released by the second subevent. The first subevent occurred at a depth of 13 km, and was followed after 9 s by the second one at a depth of 11 km; the third subevent, at a depth of 9 km occurred 19 s after the second one. The total duration of the earthquake rupture process was about 18.7 s. The obtained mechanisms for the 1993 and 1995 Gulf of Aqaba earthquakes are well correlated with the structural setting of the Gulf of Aqaba.
Seismicity in the northernmost part of the Red Sea has been studied using data from Hurghada Seismological Network in addition to readings from the existing neighbouring networks. Relocated events in addition to data from national centers are used to obtain a complete and true picture for the seismicity of the area. The spatial distribution of earthquakes defines three earthquake zones in the Gulf of Aqaba and three zones at the entrance of the Gulf of Suez and southern tip of Sinai Peninsula. The thermal activity and the triple junction nature control the activity in this area. The activity defines also an active trend extending from the southern tip of Sinai Peninsula to the median zone of the Red Sea. The seismicity of this trend is probably related to the active spreading zone associated with the opening of the Red Sea. The b-values are derived for the entrance areas of the two gulfs and for Gulf of Aqaba. Values of b are 1.35 for the triple junction region, 1.13 for the activity before the 22 November 1995 Gulf of Aqaba mainshock and 1.25 for the aftershocks of this event.
All CMT fault plane solutions for the 13 earthquakes of M W ≥ 5 listed in Table 1, from 1 Jan. 1995 to 20 Aug. 2007 in the area: 19-24°E, 36-41°N. Small solid circles show the epicenters of the 13 earthquakes and triangles denote the position of SES stations. A lower hemisphere projection is used with black and white quadrants for compression and dilatation respectively. Numbers attached refer to the events in Table 1. Bold dark color numbers mark CMT solutions of the earthquakes sensed at PIR station, italic red color numbers those at IOA station while underlined blue color numbers denote the earthquakes detected at PAT station. The hatched area denote the current selectivity map of IOA station. See color version of this figure in electronic edition.
A 12-year period experimental data, from 1 January 1995, to 20 August 2007, have been examined for possible correlations between Seismic Electric Signals (SES) of the VAN method and source parameters of the corresponding earthquakes in Western Greece. During that period 13 earthquakes of magnitude M W ≥ 5 with epicenters in the area 19–24°E, 36–41°N and available the CMT solutions (Centroid Moment Tensor focal mechanism solutions) have been found to be preceded by a SES each time at one of the three VAN stations of IOA, PIR or PAT. The results of IOA and PIR stations are compared to those reported by Uyeda et al. 1999, for the previous period 1983–1994. The IOA station seems to be sensitive to earthquakes with thrust type mechanisms being mainly consistent to its past behavior. The PIR station, which is moved from its previous position by few kilometers, exhibits some changes. It detects now both strike slip and thrust type earthquakes and becomes sensitive to new areas indicating probably the strong dependence of the SES station detection ability upon its location.
The paper presents 2D density and magnetic models of the crust and upper mantle along the DSS line profile of the CELEBRATION 2000 project that crosses the most important geological units in Central Europe. These are the Alps-Carpathians-Pannonian (ALCAPA) region, the SE part of the Paleozoic Platform (PLZ), the Trans-European Suture Zone (TESZ) and a fragment of the SW portion of the East European Craton (EEC). The density and magnetic models were constructed on the basis of a 2D model of P-wave velocity converted into density model, geological data as well as geothermal data and the results of integrated geophysical modelling for the lithosphere-asthenosphere boundary. This allowed us to construct a comprehensive geophysical 2D model of the crust and enlargement the geophysical-geological characteristics of the lithosphere in the Pannonian basins, the Carpathian orogen, and in the transitional zone between the ALCAPA plate and the East European Craton (passing through the Paleozoic Platform). As a result, we have provided evidence for the heterogeneity of the density in the lithospheric mantle, terrane concept of the East European Craton foreland, and confirmed the possibility of rift events along the SW boundary of the Precambrian craton in SE Poland.
Composition of interplanetary and geomagnetic observations for November 20-21, 2003: (a) IMF B z component in the GSM coordinate, (b) proton number density N sw , (c) solar wind flow speed V sw , (d) solar wind dynamic pressure P sw , and (e) interplanetary electric field E y .
A study of the geomagnetic storm of November 20–21, 2003, is presented using Solar X-rays data, solar wind parameters and magnetic index, Dst. The results suggest that very large X class flares may not cause very intense geomagnetic storms, as flares of M importance would do. Furthermore, the results suggest that the solar wind structure that was responsible for this storm is of the shock-driver gas configuration in which the sheath is the most geoeffective element. Presently it is shown that an intense storm can be driven by two successive southward B z structures without a resultant “double dip” at the boundary of these structures within the corresponding interval of the main phase. Furthermore, this study confirms earlier results that show that pressure enhancement does not cause the direct injection of new particles into the ring current region; rather it causes a local adiabatic energization of the particles already within the ring current region.
Frequency analysis of the Sumatra-Andaman earthquake of 2004, one of the most significant and best-recorded earthquakes, is based on spectral seismograms obtained from their broadband seismograms. The Sumatra-Andaman earthquake is found to have a wide-range frequency content of P-wave radiation during the rupturing process. On the basis of stacking spectral seismograms we distinguished four time events of the rupturing process of a total length of about 540 s. The frequency, f max, is the highest for the first event (0.163 Hz in time interval 0–88 s), lowest for the second — which is the strongest (0.075 Hz in time interval 88–204 s). For third and fourth events frequencies are similar (0.089 and 0.082 Hz in time intervals 204–452 and 452–537 s, respectively). The frequency also shows an azimuthal dependence (±0.02 Hz). Azimuths for which the frequency, f max, has maximum and minimum values are 203–222° and 23–42°, respectively. These observations are discussed in relation to previously published papers on this topic.
Diurnal variations of TEC over Europe at different latitudes (from 35ºN to 70ºN) around a longitude of 20ºE during the storm of November 6-12, 2004.
Diurnal variations of TEC over North America at different latitudes (from 29ºN to 64ºN) around a longitude of-19ºE during the storm of November 6-12, 2004.
Variations of AE index between November 6 and 11, 2004.
The occurrence of the auroral oval at 22 UT on Nov. 7 (a) and Nov. 9, 2004 (b), respectively.
GPS data from the International GNSS Service (IGS) network were used to study the development of the severe geomagnetic storm of November 7–12, 2004, in the total electron content (TEC) on a global scale. The TEC maps were produced for analyzing the storm. For producing the maps over European and North American sectors, GPS measurements from more than 100 stations were used. The dense network of GPS stations provided TEC measurements with a high temporal and spatial resolution. To present the temporal and spatial variation of TEC during the storm, differential TEC maps relative to a quiet day (November 6, 2004) were created. The features of geomagnetic storm attributed to the complex development of ionospheric storm depend on latitude, longitude and local time. The positive, as well as negative effects were detected in TEC variations as a consequence of the evolution of the geomagnetic storm. The maximal effect was registered in the subauroral/auroral ionosphere during substorm activity in the evening and night period. The latitudinal profiles obtained from TEC maps for Europe gave rise to the storm-time dynamic of the ionospheric trough, which was detected on November 7 and 9 at latitudes below 50°N. In the report, features of the response of TEC to the storm for European and North American sectors are analyzed.
Earthquake of November 30, 2004, in Podhale region, southern Poland, was of unexpectedly big size in this area of weak seismicity. As Poland is considered a country of low seismicity, the earthquake has caused concern about seismic hazard in Poland, especially since it took place shortly after the even more unexpected Kaliningrad Region, Russia, earthquakes of September 21, 2004, that inflicted minor damage in northern Poland. The paper presents the findings on the Podhale earthquake which reached macroseismic intensity up to 7 and magnitude 4.7 (m b; ISC). The event was felt up to a distance of about 100 km and inflicted slight damage to buildings in its narrow epicentral area, thus evidencing its relatively shallow depth. The quake has been located near the village of Skrzypne, about 15 km west-southwest of the district capital Nowy Targ. The source mechanism has been found to be of dip slip normal fault type, although a problem remains of association of this mechanism with known tectonic dislocations in the region. The earthquake has been followed by a long series of aftershocks. Their distribution in time is also studied and the biggest aftershocks have been located.
Variations of Kp (a), Ap (b) and Dst (c) indexes in September 2004.
Geographic map of GPS stations used for retrieving TEC over Europe. The circle indicates the area of monitoring of ionosphere by GPS satellites from the single LAMA station. 
Variations ∆TEC = TEC − TEC non-perturbed over Riga, Lamkowo and Borowiec stations from 17 to 22 September 2004.
GPS observations of the European permanent network were used to identify seismo-ionospheric precursors of Baltic Sea earthquake of 21 September 2004. It is a very rare event for this region of Europe (magnitude of about 5.0). This value is the threshold for the occurrence of seismic effects in the ionosphere. In total electron content (TEC) data over the region of the earthquake, a specific ionospheric anomaly appeared one day before the earthquake was detected. The ionospheric variability had a positive sign with an enhancement of about 4–5 TECU (1 TECU = 1016 electrons/m2) relative to the non-disturbed state of the ionosphere. The anomaly had a duration of 4–5 hours in the day time. The special size of this anomaly was about 1000 km. The characteristic parameters of the anomaly show that it can be associated with ionospheric precursors of an earthquake.
The Harvard CMT catalogue contains 481 shallow earthquakes that occurred between 1 January 1977 and 30 November 2005 within a broad region defined by the geographical latitude from 3°S to 14°N and by the longitude from 91°E to 102°E. There are 230 events that occurred before the great earthquake of 26 December 2004. Their surface distribution is not uniform and the source area of the 2004 great event appears as an area of seismic quiescence with a radius of about 100 km. There are 186 events that occurred between the two great earthquakes of 26 December 2004 and 28 March 2005. Practically all of them are located to the northwest from the great earthquake of 2005, that in turn was followed by 63 events, mostly located to the southeast. The cumulative seismic moment from earthquakes before the occurrence of the great event of 2004 increased rather regularly with time, with sudden increase about twenty years and two years before the occurrence of the great event. The seismic moment of earthquakes between the two great events increased rapidly during the first ten-fifteen days, then flattened out and increased slowly with time. After the great event of 2005 the seismic moment shows quiet increase during some 115 days, then sudden jump, followed by very small activity till the end of our observations. From the spatial distribution of seismic moment of earthquakes that occurred before the great event of 2004 it follows that its largest release appeared to the southeast from the great event, around the rupture area of the great earthquake of 2005. The largest release of seismic moment from earthquakes between the two great events is observed in the vicinity of the 2004 event and further up to the north. The seismic moment from earthquakes that occurred after the great event of 2005 was mostly released in its vicinity and further down to the south.
The average value of the intrinsic shear wave quality factor, Q β , for the 15 km of the upper crust in the NW Himalaya is estimated. Thirty-two teleseismic broadband SH and sSH waveforms of 8 October 2005 South Asian earthquake (Mw = 7.6), from sixteen Global Seismographic Network stations of the National Earthquake Information Center network have been used. The selected windows of the direct and depth phases have been Fourier transformed and smoothed using the Hamming and Tuckey technique. Ratio of the smoothed spectra of depth and direct phases are obtained in the frequency range 0.2–1.5 Hz. A straight line is fitted in the least-square sense to the spectral ratio versus frequency. The value of Q β is estimated from the slope of the line. The frequency independent average value of Q β is estimated to be 218±56. Key wordsseismic hazard-shear wave analysis-intrinsic attenuation-NW Himalaya-8 October 2005 South Asian earthquake
Epicenters of the 2005 Mukacheve earthquakes relocated with application of adjusted arrivals (the hollow squares and the diamond, same as in Fig. 4), with application of adjusted arrivals and the arrival residuals CM1 (Tables 7, 8) (the crosses, along with the epicenter of the reference earthquake), as well as adjusted arrivals and station terms CM3 (Tables 7, 8) (the circles, along with the epicenter of the reference earthquake). In the background: the thick dashed line-the Mukacheve fault in the pre-Neogenic basement (Khomenko 1971, 1987).
Based on the results of application of correlation analysis to records of the 2005 Mukacheve group of recurrent events and their subsequent relocation relative to the reference event of 7 July 2005, a conclusion has been drawn that all the events had most likely occurred on the same rup-ture plane. Station terms have been estimated for seismic stations of the Transcarpathians, accounting for variation of seismic velocities beneath their locations as compared to the travel time tables used in the study. In methodical aspect, potentials and usefulness of correlation analysis of seismic records for a more detailed study of seismic processes, tectonics and geodynamics of the Carpathian region have been demonstrated.
Vertical components of the 0.02 s MUKU velocity records windowed around the Pg arrival times adjusted relative to the times in the reference earthquakes of 07.07.2005-1 and 31.03.2006-1. Note a gradual 'compression' of successive traces in group B. The time interval between the circles in the right panel is 0.1 s. Records are shown normalized relative to their largest amplitudes within a window. component Z of the group A earthquakes component Z of the groups B and C earthquakes
Three groups of recurrent events have been identified within the 2005–2006 Mukacheve series of about forty M SH0.3–1.8 near-surface earthquakes. After a cross-correlation analysis of their waveforms and subsequent relocation with application of the adjusted arrivals and station terms it turned out that they most likely belong to at least two distinct crustal layers separated by an interface at about 4 km; the seismic activation started deeper and progressed upwards. As concerns polarities of first arrivals, the same source mechanism was inferred within individual groups, indicating a normal faulting along the Az ≈ 120° with a slight component of right lateral slip; this finding is consistent with data available on some other local sources, as well as with an ambient field of extensional stresses in the local crust and a significant horizontal gradient of vertical movements across the epicenter area of the Mukacheve series.
In this paper, optical measurements of aerosol properties made during a ship cruise from Poland to Antarctic Station in September and October 2006, and during the cruise back to Gdynia in April and May 2007 are described. A large gradient of pollution between the clear South Atlantic and the dusty North Atlantic was observed. The maximum of aerosol optical thickness at a wavelength of 500 nm reached 0.4 at 20°N in September 2006 and 0.3 at 40°N in May 2007, respectively. Strong Saharan dust transport is suggested as an explanation for the small values of Ångström exponent observed (values of 0.2 and 0.4 on these respective dates). On the Southern Hemisphere the aerosol optical thickness at 500 nm ranged from 0.05 to 0.2. Significant increases of the aerosol optical thickness were associated with strong wind and sea salt production. Good agreement was found when the in situ measurements of aerosol optical thickness were compared to satellite retrievals and modelling results.
Geographical position of epicenter (triangle) and nearest GPS-IGS stations.
In this paper we present specific features of TEC (total electron content of the ionosphere) behavior as possible precursors of Kythira (Southern Greece) earthquake of January 8, 2006 (M6.8). For this purpose, we used both the TEC data of GPS-IGS stations nearest to the epicenter, and TEC maps over Europe. The favorable circumstance for this analysis was the quiet geomagnetic situation during the period prior to the earthquake. One day before the earthquake, a characteristic anomaly was found out as the day-time significant increase of TEC at the nearest stations, up to the value of 50% relative to the background condition. To estimate the spatial dimensions of seismo-ionospheric anomaly, the differential mapping method was used. The ionosphere modification as a cloud-like increase of electron concentration situated in the immediate vicinity of the forthcoming earthquake epicenter has been revealed. The amplitude of modification reached the value of 50% relative to the non-disturbed condition and was in existence from 10:00 till 22:00 UT. The area of significant TEC enhancement had a size of about 4000 km in longitude and 1500 km in latitude.
This paper presents preliminary results from a study considering the parameterisation of coarse-grid 2D flood models to take into account sub-grid scale flow patterns occurring in the urban area. A simulation of a severe flood in an urbanized coastal floodplain is first run using a fine grid that can resolve the flow around and between buildings. Next, the same model is run again using the same underlying topography, although stripped from any buildings, and a set of 7 values of the roughness parameter (Manning’s n), all larger than (or equal to) the value used in the original run. A further set of simulations is carried out using a five-fold increased grid cell size. It is found that while it may be possible to model the overall effects of the buildings using strongly increased roughness parameter values, using a coarse grid otherwise has implications related to the loss of information about the site topography that results in flood flow routes being incorrectly modelled.
This paper presents a neural network approach to determine 2D inverse modeling of a buried structure from gravity anomaly profile. The results of the applied neural network method are compared with the results of two other methods, least-squares minimization and the simple method. Sphere, horizontal cylinder and vertical cylinder and their gravity effects are considered as the synthetic models and the synthetic data, respectively. The synthetic data are also corrupted with noise to evaluate the capability of the methods. Then the Dehloran bitumen map in Iran is chosen as a real data application. Anomaly value of the cross-section, which is taken from the gravity anomaly map of Dehloran bitumen, is very close to those obtained from these methods.
An M8.3 earthquake struck the southwestern part of the Hellenic Arc, near the Island of Crete, in AD 365, generating a tsunami that affected almost the entire eastern Mediterranean region. Taking into account that the time history of seismicity in this region is fairly complete for such earthquakes in the historical catalog, which can be dated as back as the 5th century B.C., there is no indication that this segment of plate boundary has been fully ruptured again. The seismic hazard associated with this part of the Hellenic Arc necessitates the evaluation of the rupture characteristics of this great event. The constraint of the faulting geometry was initially achieved by using information from seismicity, and the focal mechanisms of earthquakes that occurred during the instrumental period. A rupture model for this great earthquake is constructed by assuming an elastic medium and calculating the theoretical surface displacements for various fault models that are matched with the observed surface deformation gleaned from historical reports. The resulted fault model concerns thrust faulting with a rupture length of 160 km and a seismic moment of 5.7 × 1028 dyn·cm, an average slip of 8.9 m and a corresponding moment magnitude equal to 8.4, in excellent agreement with the macroseismic estimation. The absence of such events recurrence is an indication of the lack of complete seismic coupling that is common in subduction zones, which is in accordance with the back arc spreading of the Aegean microplate and with previous results showing low coupling for extensional strain of the upper plate.
Earthquake activity and regional tectonics in the Eastern Mediterranen (after Riad et al . 1996). Colour version of this figure is available in electronic edition only. 
The morphological and structure scheme of the Eastern Mediterranean. On the right is the submenu of the second level operation (Loubrieu et al . 2001). Colour version of this figure is available in electronic edition only. 
An offshore open boundary and characteristics when a simple harmonic wave propagates in the x direction. 
Contour of uplift predicted for the fault (Stiros and Drakos 2006). 
Computed tsunami waveforms at reference locations (over 120 min). 
The historical tsunamigenic event of 21 July AD 365 destroyed several coastal locations in the Eastern Mediterranean region. The foremost destructive impacts were recorded in Crete and Egypt. The present study re-examines the effect of location, direction, height and time of travel of the tsunami towards the Egyptian coast. Evidently, this tsunamigenic event is related to an earthquake which is identified with a Hellenic Arc subduction-zone event of great magnitude, M > 8, as manifested by up to 9 m uplift in western Crete. The maximum run-up height distribution in the front of the Nile Delta was about 9.5 m in Alexandria, while those of the neighboring cities were 7.1 m, 4.9 m, and 1.9 m at Rashid, Damietta and El-Arish, respectively. Data obtained from this study is essential to evaluate the tsunami hazards along the Egyptian coast. Key wordsAD 365 tsunami-tsunami magnitude-tsunami intensity-Eastern Mediterranean region
Side view and dimensions of the experimetal basin. 
Velocity field in the bottom layer. 
Comparison of the experimental and calculated horizontal velocity profiles.
New three-dimensional numerical non-hydrostatic model with a free surface that was designed for modelling the bottom and bank stability subjected by ship propeller jets is presented. Unlike all known models, it describes three-dimensional fields of velocities generated by ship propellers, turbulence intensity and length scale in the given domain of arbitrary bottom and coastal topography. Results of simulations are compared with the laboratory experiments.
Resolving every detail of the three-dimensional canopy morphology and its underlying topography remains untenable when modeling high Reynolds number geophysical flows. How to represent the effects of such a complex morphological variability and any concomittant topographic variability into one-dimensional bulk flow representation remains a fundamental challenge to be confronted in canopy turbulence research. Theoretically, planar averaging to the scale of interest should be applied to the time-averaged mean momentum balance; however, such averaging gives rise to covariance or dispersive terms produced by spatial correlations of time-averaged quantities that remain ‘unclosed’ or require parameterization. When the averaging scale is commensurate with few canopy heights, these covariances can be labeled as ‘micro-dispersive’ stresses. When averaging is intended to eliminate low-wavenumber topographic variations, we refer to these covariances as ‘macro-dispersive’ terms. Two flume experiments were used to explore the magnitude and sign of both micro- and macro-dispersive fluxes relative to their conventional Reynolds stresses counterparts: a rod-canopy with variable roughness density and a dense rod canopy situated on gentle hilly terrain. When compared to the conventional momentum flux, the micro-dispersive fluxes in the lowest layers of sparse canopies can be significant (∼50%). For dense canopies, the dispersive terms remain negligible when compared to the conventional momentum fluxes throughout. For the macro-dispersive fluxes, model calculations suggest that these terms can be neglected relative to the Reynolds stresses for a deep canopy situated on a narrow hill. For the region in which topographic variations can interact with the pressure, both model calculations and flume experiments suggest that the macro-dispersive fluxes cannot be neglected, and their value can be 20% of the typical Reynolds stresses.
Macroscopic flow above and within porous medium. (a) Definition of flow layers within porous medium. Conceptual models of (b) sharp interface, (c) gradual transition, between free-fluid and porous medium flow.  
This paper explores the concept of a macroscopic boundary between turbulent flows above and within rough permeable walls. The macroscopic boundary and the associated conditions for macroscopic flow variables have been thoroughly investigated for laminar, but not for turbulent flows. The literature on laminar flows follows two main conceptual models of the boundary: sharp boundary with step changes in macroscopic variables and gradual boundary with smooth changes of variables. The former approach is usually associated with the two-domain simulation models and the latter one with the single-domain models. This paper presents the derivation of the step conditions for velocity and shear stress at the macroscopic boundary between turbulent boundary layer and turbulent porous media flows. The physical meaning of the main terms in the shear stress condition is discussed in order to clarify the relationship between two-domain and single-domain simulation models.
Double averaged equations for atmospheric boundary layer flows are introduced as natural extensions of single averaged Reynolds equations. We show that in circumstances where double averaged equations are needed, the two fundamental properties of Reynolds averaging are violated. First, we consider double-averaging in free air turbulence, where the aim is to separate coherent motions from background turbulence. We illustrate the different properties of the main operators that have been used and the physical meaning of the terms that result. Second, in canopy flows, the multiply connected nature of the canopy airspace leads to a different set of departures from the standard Reynolds equations. We establish the physical meaning of the extra terms that arise. Finally we briefly discuss the problems, both practical and theoretical, that arise when we use double averaged equations to interpret real data.
The required fictitious nodes for the application of Clayton and Engquist (1977) absorbing boundary condition for the fourth-order special accuracy on the left (a), right (b) and bottom (c) edges of the model (ix and lz denote the maximum number of grid points in the x-and z-directions, respectively).
This article presents the implementation of two well known absorbing boundary conditions in a fourth-order accurate staggered grid SH-wave finite difference (FD) algorithm with variable grid size, in a very simplified manner. Based on simulated results, it was confirmed that the Clayton and Engquist absorbing boundary condition causes edge-reflections in case of larger angle of incidence of body waves on the model edges. The results of various numerical experiments revealed that the Israeli and Orszag sponge boundary condition is efficient enough to avoid edge-reflections for any angle of incidence of the body. We recommend the use of both the Clayton and Engquist and Israeli and Orszag absorbing boundary conditions simultaneously to avoid any edge-reflections.
The crustal structure of North Abu-Simbel area was studied using spectral ratios of short-period P waves. Three-component short period seismograms from the Masmas seismic station of the Egyptian National Seismic Network Stations were used. The Thomson-Haskell matrix formulation was applied for linearly elastic, homogeneous crustal layers. The obtained model suggests that the crust under the study region consists of a thin (0.8 km) superficial top layer with a P-wave velocity of 3.8±0.7 km/s and three distinct layers with a mean P-wave velocity of 6.6 km/s, overlaying the upper mantle with a P-wave velocity of 8.3 km/s (fixed). The results were obtained for 14 different earthquakes. The P-wave velocities of the three layers are: 5.8±0.6 km/s, 6.5±0.4 km/s and 7.2±0.3 km/s. The total depth to the Moho interface is 32±2 km. The crustal velocity model estimated using observations is relatively simple, being characterized by smooth velocity variations through the middle and lower crust and normal crustal thickness. The resultant crustal model is consistent with the model obtained from previous deep seismic soundings along the northern part of Aswan lake zone.
b. The tectonic map of the region of investigation (see a for location). The recently active, major regional faults (see text), the Lut (or Dasht-e-Lut; Dasht meaning “desert”) block and the Afghan block are identified. The epicentres of all large earthquakes, with M w > 7.0, that occurred since1960, in the eastern section of the Plateau of Iran, between 27° and 37°N latitude, 55° to 65°E longitude are 
a. A generalized geologic and tectonic map of the region in and around the Sistan Suture Zone (adapted from Tirrul et al. 1983). The two adjoining major continental blocks, the Lut and Afghan blocks are identified. The dashed square marks the broad area of investigation and also the location of b. The symbols denote: 1. The Maastrichtian-Paleogene volcanic rocks; 2. Neo-Tethyan accretionary complex; 3. Oceanic crust; 4. Cimmerian continent; 5. Paleo-Tethyan suture; 6. NeoTethyan suture; 7. Active trench; 8. Active major strike-slip fault; 9. Spreading rift; 10. The Sistan Suture zone. The geographic locations are: Alborz (A), Birjand (B), Bitlus (Bi), Esfandageh (E), Kabul (Kb), Kandahar (Kh), Karachi (Kr), Mashad (M), Makran (Ma), Nain (N), Pontides (P), Sabsevar (Sa). Epicentral locations of large, historical and recent earthquakes are marked: the January 10, 1493, Nauzad event (M S = 7.0); the February 15, 1549, Qa'en event (M S = 6.7); the 1838, Nosratabad event (M S = 7.0) (Berbarian et al. 1999); and the February 16, 1941, Mohammadabad event (M = ?) (Walker et al. 2004).
The cumulative Benioff strain (eq. 1) released before the September 16, 1978 earthquake by intermediate events of the test episode, 1968-1978, within a radius of: (a) 150 km, (b) 300 km, and (c) 650 km from the 1978 earthquake epicentre is plotted versus time. Note that, of the three graphs, the power law fits the seismicity significantly better than the linear law in (b). (d) The curvature parameter C is plotted versus the circular region radius. The smallest values of C reflect a better power law fit. The estimated critical region for this event is around 300 km (see text).
We investigated whether accelerated seismic strain release precedes large earthquakes occurring in and around the Sistan Suture Zone, Eastern Iran. Online catalogs of teleseismic events occurring post-1960 within the region 27.0°–37.0°N, 55.0°–65.0°E, report five M w > 7.0 earthquakes, namely, 1968 Dasht-e-Bayaz, 1978 Tabas, 1979 Khuli-Buniabad, 1981 Sirch and 1997 Zirkuh-e-Q’aenat events. We defined four earthquake test episodes, 1968–1978, 1978–1981, 1979–1981, and 1981–1997, with all catalogued intermediate events having magnitudes within 2.0 units that of the final large event. Using the 1968 event as the starting point, we investigated possible increased moderate earthquake activity patterns prior to the large events of 1978, 1981 and 1997 by examining if the cumulative Benioff strain released from such preceding events followed a power law time-to-failure. Our investigation seem to suggest that the 1978, 1981 and 1997 events (i) followed a period of accelerated moderate earthquake activity and (ii) the radius of their optimal critical region, R, scaled with their magnitude, M, according to the scaling law log R ∝ 0.36 M. Our suggestions conform to those proposed by similar investigations in varied seismotectonic regimes.
AE energy rate distribution (a) and temporal changes of D 2 during CO 2 desorption on tested coal (b).
AE energy rate distribution (a) and temporal changes of D 2 during CH 4 desorption on tested coal (b).
Multifractal spectra D q (q) of AE generated in coal during CO 2 desorption and/or CH 4 desorption.
Multifractal spectra D q (q) of AE generated in coal during sorption of CO 2 .
This paper presents study of non-linear dynamics of acoustic emission (AE) generated in coal samples subjected to gas sorption-desorption. Carbon-dioxide and methane were used as sorbats. Experimental facilities used in high pressure sorption of CO2 and/or CH4 on coal comprised a pressure vessel and associated pressurisation and monitoring systems. Tests were conducted on medium-rank coal obtained from the Upper Silesia Basin. Several approaches to the treatment of experimental results are proposed in order to detect and characterize deterministic chaos: (1) analysis of fractal/multifractal character of AE energy rate, using fractal generalised dimensions D q(q); (2) analysis of temporal changes of AE energy rate and its fractal correlation dimension D 2; and (3) evaluation of attractor dimension within the reconstructed phase space from experimental time series. It was shown that AE generated during CO2 sorption on medium-rank coal is a more heterogeneous and lower dimensional process in comparison with AE induced by CO2 desorption. Yet, the AE associated with desorption of CO2 exhibits higher heterogeneity than the AE generated during desorption of CH4. There are certain similarities between changes of D2 during desorption of CO2 as well desorption of CH4. However, dynamics of these changes and character of time distributions of D2 differ, depending on a sorbate. We do not know the precise reason for observed differences, but we presume that the carbon-dioxide molecules dissimilarity to methane molecules can account for them.
The results of laboratory experimental studies of the DC-induced acoustic emission (AE) in saturated sand models of sedimentary rock are presented. It is shown that direct current acting on a geological medium generates acoustic vibrations in it. The experimental methodology is based on recording acoustic pulses generated by the rock model (sample) when the electric field is applied. The amplitude-frequency parameters of the AE signals depend on petrophysical properties of the solid phase, on the salinity of porous medium, and the electric field (current intensity and voltage). The above research is the first step towards the full identification of the characteristics of the AE signals generated by rocks in a DC electric field.
Simultaneous measurements of acoustic emission (AE) and expansion/contraction of coal samples subjected to gas sorption-desorption processes were conducted on high-and medium-rank coal. The aim of this study was to examine the influence of the coal rank and type of sorbate on measured AE and strain characteristics. The experimental equipment employed in this study consisted of a pressure vessel and associated pressurisation and monitoring units. The arrangement of pressure-vacuum valves permitted the coal sample to be pressurised and depressurised. Carbon-dioxide and methane were used as sorbats. Acoustic emission and strains were recorded continuously for a period of 50 hours during sorption and for at least 12 hours during the desorption process. Tests were conducted on cylindrical coal samples at 298 K. The experimental data were presented as plots of AE basic parameters versus time and in strain diagrams. These studies lead to the following conclusions: 1. There are significant differences in AE and strain characteristics for the two systems (coal-CO2 and coal-CH4); 2. There is a direct influence of rank and type of coal on its behaviour during the sorption-desorption of gas. An attempt has been made to interpret the results obtained on the grounds of the copolymer model of coal structure. More research is needed into this topic in order to get a quantitative description of the observed facts.
The Nevada Seismic Array (NVAR) is a small-aperture seismic array designed for monitoring an eventual nuclear test ban treaty. In spite of the 4 km aperture, large amplitude variations are recorded due to the complicated local geology. This study takes advantage of the collocated infrasound and seismic sensors to discuss the use of air-to-ground coupled waves to characterize the shallow geological structure existing beneath the array. Complex transfer functions between the infrasound and the corresponding seismic signals are computed as the quotient of the cross-spectrum of the infrasound signal and the seismic signal and the power spectrum of the infrasound signal. Then the median of the transfer functions for the sites where shallow geologic information is available is compared to a theoretical model. In the theoretical approach, the signals are modeled as instantaneous pressure loads propagating at sound speed velocities (330 m/s). Both theory and observations are in agreement which suggests that inverting the transfer functions to determine elastic properties of the medium, and eventually computing site effects, is possible.
The paper deals with the application of time-frequency methods, Continuous Wavelet Transform (CWT) and Matching Pursuit algorithm (MP), to acoustic full waveform processing. The goal of the research is to present possible ways of application of these methods, particularly for the precise identification of selected acoustic waves, waveform decomposition into separate waves, and determination of zones of different elastic parameters in the geological profiles. The simulations, developed methodology, and results of each method are discussed in detail. The Continuous Wavelet Transform is used to improve qualitative interpretation. Time-depth-frequency plots for a given frequency are constructed to distinguish the waves and identify gas-bearing zones. The Matching Pursuit has a better resolution in time-frequency space than CWT; thus, it is used to extract individual waves from the whole acoustic waveform, i.e., decompose the signal. For the extracted waves, the slowness is calculated. Results from MP methods are compared with their counterpart parameters obtained from the original waveforms. Additionally, time-frequency decompositions are used for the determination of the frequency content of each wave packet to get unique information about formation in situ.
Development of AE rate and strains (ε L , ε T , ε V ) as a function of time and gas pressure for sample A during CH 4 presorption-sorption of mixture (a) and during gradual desorption of gas mixture (b). Correlation between cumulative activity and volumetric strain during CH 4 presorption-sorption of mixture (c) (↑ gas injection, ↓ reduction of gas pressure).
Plots of volumetric strain for A and B samples during displacement sorption.
The aim of this study was to assess whether acoustic emission (AE) could carry information on preferential sorption/desorption of CH4 or CO2 in coal. AE and expansion/contraction of two nearly identical cylindrical coal samples were continuously monitored during displacement sorption experiments. One sample was subjected to presorption of CH4, followed by sorption of CH4/CO2 mixture. With the other one, presorption of CO2 preceded sorption of the mixture. The results obtained are the following: first, AE and stain kinetics show that the affinity of the coal tested is higher for CO2 than for CH4; second, methane is preferentially desorbed after presorption of CH4 — sorption of mixture of CH4 and CO2; third, during displacement sorption, kinetics of AE and sample swelling/shrinkage bring out the importance of presorption and the sorbate used. It matters whether the coal is first exposed to CH4 or to CO2. The present study has demonstrated that injection of CO2 into the coal previously exposed to CH4 causes considerable swelling of the coal. On desorption after CH4/CO2 exchange sorption, initial shrinkage is followed by swelling of the coal. These results could have implications for the sequestration of CO2 in coal seams and CH4 recovery from coalbeds (ECBM). Swelling/shrinkage of the coal matrix should be included in models used to predict coal permeability and gas flow rates. They also show that the AE technique can give more insights into coal matrix-gas interactions.
Numerical investigations on one-dimensional nonlinear acoustic wave with third and fourth order nonlinearities are presented using high-order finite-difference (HFD) operators with a simple flux-limiter (SFL) algorithm. As shown by our numerical tests, the HFDSFL method is able to produce more stable, accurate and conservative solutions to the nonlinear acoustic waves than those computed by finite-difference combined with the flux-corrected-transport algorithm. Unlike the linear acoustic waves, the nonlinear acoustic waves have variable phase velocity and waveform both in time-space (t-x) domain and frequency-wavenumber (f-k) domain; of our special interest is the behaviour during the propagation of nonlinear acoustic waves: the waveforms are strongly linked to the type of medium nonlinearities, generation of harmonics, frequency and wavenumber peak shifts. In seismic sense, these characteristics of nonlinear wave will introduce new issues during such seismic processing as Normal Moveout and f-k filter. Moreover, as shown by our numerical experiment for a four-layer model, the nonlinearities of media will introduce extra velocity errors in seismic velocity inversion.
Seismic refraction survey and DC resistivity measurements were made across the margin of the Lake Ngami. The structure and stratigraphy at the lake were determined. High resolution aeromagnetic data showed a prominent anomaly coinciding with the Kunyere Fault. Estimated depths to magnetic sources are increasing towards the lake. Two velocity layers were mapped. The top layer (500 m/s) is thin outside the lake and thicker inside the lake. The underlying layer (3125 m/s) has undeterminable thickness. Resistivity sounding results inside the lake showed that the low velocity layer has four sub-units: dry hard clays; diatomaceous earth; soft clays interlayered with silts; and wet whitish clays interlayered with silts. Normal faults were mapped along the profile with a total displacement up to 50 m. The results of the study indicate that the formation of the Lake Ngami basin was structurally controlled and probably initiated by the tectonics of the Okavango Rift Zone.
Snapshot of cloud water mixing ratio (light shaded isosurface) of q c = 0.05 g kg −1 and the activation tendency larger than 1 (mg s) −1 (a patchy dark shaded areas). Top/bottom panel is for suppressed/active in-cloud activation.
Percentile distribution of space and time averaged activation tendency in areas where q c > 0.01 g kg −1 for the pristine case. The light shading represents values for 10-40% and 60-90% ranges; the dark shading is for 40-60% range. The black line is the mean value. Left/right panel is for simulations without/with in-cloud activation.
As Figure 2, but for the cloud droplet concentration in the pristine case.
As Figure 3, but for the polluted case.
CFADs of the effective radius for each pristine simulation in areas where q c > 
This paper describes implementation of the warm-rain bin microphysics in a LES model based on the EULAG fluid flow solver. The binmicrophysics EULAG is applied to the case of shallow nonprecipitating tropical convection to investigate the impact of the secondary activation of cloud droplets above the cloud base. In a previous study applying the EULAG model with the double-moment bulk warm-rain microphysics scheme, the in-cloud activation was shown to have significant implications for the mean microphysical and optical characteristics of the cloud field. By contrasting the simulations with and without in-cloud activation as in the previous study, we show that the in-cloud activation has qualitatively similar but quantitatively smaller effect. In particular, the concentration of cloud droplets in the bin simulation without in-cloud activation decreases with height not as strongly as in corresponding simulations applying the double-moment bulk scheme. Key wordsshallow convection–cloud physics–bin microphysics–droplet activation
Quite recently two intense Seismic Electric Signals activities were recorded at Pirgos station in western Greece. They have been followed by two strong earth-quakes with magnitudes 6.1 and 6.9 that occurred in western Greece and southern Greece; the latter is the strongest earthquake that occurred in Greece during the last two decades. The compatibility of these results with some relationship between selectivity and earthquake focal mechanism suggested by Uyeda et al. (1999) is discussed.
Description of layers.
One of the primary scientific and technical goals of Space Weather investigations is to produce data in order to study the Sun impact on the Earth and its environment. Studies based on data mining philosophy increase our knowledge of the physical properties of Space Weather, modelling capabilities, and gain applications of various procedures in Space Weather monitoring and forecasting. The paper focuses on an analysis of the availability on the Internet of near-real time and historical collections of the European ground-based and satellite observations, operational indices and parameters. A detailed description of data delivered is included. The following issues are discussed: (1) raw observations, and/or corrected/updated data, (2) resolution and availability of real-time and historical data, (3) products resulting from models and theory including maps, forecasts and alerts, (4) platforms for data delivery.
Record and spectral composition of vibrations on the soil surface.
Typical diagram of deformation growing under the dynamic loading.
Dynamic stability of soils under the foundation in conditions of natural moisture content.
Accumulation of soil foundation deformations under the dynamic loading.
Response of different soils to dynamic loading is of fundamental interest in many engineering, geophysical and environmental studies. Many methods have been proposed to estimate dynamic stability of soils. One more approach, based on laboratory cyclic testing, is discussed in this paper. In our tests, not only the specific features of examined soils, but also different conditions of static and dynamic loading have been taken into account. An analysis of the obtained experimental data explicitly supports the hypothesis of a logarithmic relationship between the axial deformation of soil in cyclic triaxial compression and the number of loading cycles. Evaluation of soil deformation under vibrodynamic loads can also be based on energy approach. The use of critical amount of energy dissipated by soil per its unit volume has been proved to be reliable even in a low dynamic stress range. Convergence of the proposed solution was proved using field measurements and observations. The proposed approach has been applied to evaluate additional settlements of structures founded on the basis of different soil profiles and under various static and dynamic loading conditions.
Soil particle-size distributions (PSD) have been used to estimate soil hydraulic properties. Various parametric PSD models have been proposed to describe the soil PSD from sparse experimental data. It is important to determine which PSD model best represents specific soils. Fourteen PSD models were examined in order to determine the best model for representing the deposited soils adjacent to dams in the China Loess Plateau; these were: Skaggs (S-1, S-2, and S-3), fractal (FR), Jaky (J), Lima and Silva (LS), Morgan (M), Gompertz (G), logarithm (L), exponential (E), log-exponential (LE), Weibull (W), van Genuchten type (VG) as well as Fredlund (F) models. Four-hundred and eighty samples were obtained from soils deposited in the Liudaogou catchment. The coefficient of determination (R 2), the Akaike’s information criterion (AIC), and the modified AIC (mAIC) were used. Based upon R 2 and AIC, the three- and four-parameter models were both good at describing the PSDs of deposited soils, and the LE, FR, and E models were the poorest. However, the mAIC in conjunction with R 2 and AIC results indicated that the W model was optimum for describing PSD of the deposited soils for emphasizing the effect of parameter number. This analysis was also helpful for finding out which model is the best one. Our results are applicable to the China Loess Plateau.
Magnetotelluric method is widely applied to study the Russian part of the East-European Craton, as well as the Caucasus and the Urals: several thousand soundings were performed during the last few years. Their periods range is approximately from 0.003 to 3000 seconds, which allows to study the sedimentary cover and the consolidated crust. Resistivity cross-sections along several regional profiles which run across the tectonic structures of the East-European Craton and the adjacent folded systems were obtained, mainly using 1D and 2D interpretational tools. MT investigations provided important information about the structure and reservoir properties of sedimentary complexes, the state of active geodynamic regions, the graphitization and fluid regime of the consolidated crust, and the permeable and fluid-saturated crustal zones.
The simulation of solute transport in rivers is frequently based on numerical models of the Advection-Dispersion Equation. The construction of reliable computational schemes, however, is not necessarily easy. The paper reviews some of the most important issues in this regard, taking the finite volume method as the basis of the simulation, and compares the performance of several types of scheme for a simple case of the transport of a patch of solute along a uniform river. The results illustrate some typical (and well known) deficiencies of explicit schemes and compare the contrasting performance of implicit and semi-Lagrangian versions of the same schemes. It is concluded that the latter have several benefits over the other types of scheme.
Rectangular discretisation grid. 
Analytical solution and simulation results with use of UP and CN schemes after 750 s with parameters: v x = v y = 0.106 m/s, D xx = D yy = 0.425 m 2 /s, D xy = D yx = 0.325 m 2 /s, ∆x = ∆y = 1 m and ∆t = 0.5 s. Mass (M = 10 arbitral units) has been injected instantaneously at a point x 0 = 50 m, y 0 = 50 m and time t 0 = 0 s. Note different scales for concentration.
The spread of a passive contaminant in an open-channel reach is considered with use of a two-dimensional advection-diffusion equation with the included off-diagonal dispersion coefficients. This paper presents the calculation of truncation errors, namely numerical diffusion and numerical dispersion for various finite difference schemes. The accuracy of the considered finite-difference approximations is analysed by deriving and studying the relevant modified partial differential equation.
AE 60 (thin line), F 60 (dashed line) and NewF 60 (thick line) plotted against time from 00 UT on 07 September 1995 to 12 UT on 08 September 1995 (see text for de- tails).  
AE 05 (thin line), F 05 (dashed line) and NewF 05 (thick line) plotted against time from 06 UT to 18 UT on 07 September 1995 (see text for details).  
AE 60 (thin line) and NewF 60 (thick line) plotted against time from 00 UT on 14 October to 00 UT on 23 October 1995 (see text for details).  
AE 60 (thin line) and NewF 60 (thick line) plotted against time from 00 UT on 23 October to 24 UT on 31 October 1995 (see text for details).  
The AE index has two components: one driven by the solar wind and one related to the magnetotail unloading process. We recall some past findings on this issue and present a new ANN algorithm for the AE forecasting at 5 and 60 min time scales, built by adding to a previous algorithm a further layer with a hyperbolic tangent transfer function and two more inputs, the output at time t and the difference between the input at time t and the output at time t - 1. We show that, at the 60 min time scale and for AE > 400 nT, the new algorithm performs better than the former one, while no improvement is obtained at the 5 min time scale. This result confirms that the AE component driven by the solar wind can be forecast, at least partially, while the unloading component may not be reproduced from solar wind inputs.
Comparison of the total optical thickness derived from NAAPS and measured by AERONET station at: (a) Belsk, (b) Leipzig, and (c) during SAWA experiment. Panel (d) shows variability of the correlation coefficient as a function of the threshold AOT below which the correlation coefficient was derived. Data sets from Belsk, Leipzig, and SAWA measurements are presented. Figure 2d presents variability of the correlation coefficient as a function of the AOT cutoff value. For a given cutoff threshold the correlation coefficient was calculated based on dataset limited to AOT's smaller than this threshold. In all cases the correlation coefficient increases with growing AOT threshold. This indicates that model predictions improve for higher aerosol events and also that the model has difficulties in representing low continental aerosol concentrations, as denoted by small correlation values for AOT's below 0.3. Those relatively clean continental conditions are often affected by anthropogenic emissions which are not fully resolved in NAAPS.  
Annual average aerosol optical thickness (AOT) distribution over Europe.  
Monthly values of the aerosol optical thickness over Central Poland averaged over the period 1998-2004.  
Seasonal contribution to AOT (in percents) of each of the modeled aerosol components over Central Poland in spring (a), summer (b), autumn (c), and winter (d). aerosol drops below 5%. These values are somehow smaller than GOCART results; Chin et al. (2002) showed contribution of organic and black carbon between 20-40%. The last, sea salt aerosol class contributes from 15% during polluted springs up to 38% during clean winters to the total AOT modeled over Central Poland. In all cases it is caused by advection of air masses loaded with sea salt particles from Northern Atlantic and North Sea. It is expected that the actual sea salt concentrations over Central Poland would be somehow smaller due to chemical reactions and transformation of those particles during transport in the continental boundary layer. Many of such microphysical and chemical mechanisms affecting aerosol life-time are not included in the NAAPS model. The results of NAAPS simulations show frequent occurrence of mineral dust over Poland. Saharan dust events were observed during the SAWA experiment in 2005 (Markowicz et al. 2008). Results of more than two months of lidar and sun-photometer observations confirm several dust events over Warsaw. During those episodes the total AOT raised over 0.7 at 500 nm wavelength. In order to assess the frequency of dust transport over Poland we defined a mineral dust AOT threshold, equal to 0.1 and analyzed the NAAPS output in terms of this threshold value. Figure 8 shows monthly averaged percentage of days with dust AOT exceeding the threshold over Central Poland. One can distinguish two dust seasons (spring and autumn) in  
Average number of days (%) with mineral dust aerosol inflow over Central Poland with the optical thickness exceeding 0.10.  
This study contains a comparative analysis of aerosol optical thickness (AOT) between numerical calculations obtained from the Navy Aerosol Analysis and Prediction System (NAAPS) model and direct observations from the AERONET robotic network and the Saharan Aerosol over WArsaw (SAWA) field campaign. AOT was calculated for 500 nm wavelength. The comparison shows underestimation of the total aerosol optical thickness simulated by NAAPS. The correlation coefficients between model and observation oscillates between 0.57 and 0.72. Results of seven-year (1998–2004) NAAPS simulation of aerosol components (sea salt, mineral dust, sulphate, and smoke) show large temporal and spatial variability of the aerosol optical thickness over Europe. The least polluted region is the Iberian Peninsula, while the highest aerosol burdens occurred in Central Europe, mostly due to anthropogenic sulphate particles. Finally, the analysis of mineral dust transport shows frequent episodes of Saharan dust inflow over Central Europe. There are about 20 days a year (4 days in May) when instantaneous AOT associated with mineral dust aerosol increases over 0.1. Key wordsaerosol-optical properties-pollution transport model
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Alban Kuriqi
  • University of Lisbon
A.F. Moene
  • Wageningen University & Research
Bert Holtslag
  • Wageningen University & Research
Sukanta Basu
  • Delft University of Technology
Gert-Jan Steeneveld
  • Wageningen University & Research