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
Key wordsaftershock sequence–complex faulting–Lefkada Island (Greece)–14 August 2003 Lefkada earthquake
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).
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.
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
≥ 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.
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
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.
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.
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
, 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
is estimated from the slope of the line. The frequency independent average value of Q
is estimated to be 218±56.
Key wordsseismic hazard-shear wave analysis-intrinsic attenuation-NW Himalaya-8 October 2005 South Asian earthquake
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.
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.
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
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.
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
Key wordsaerosol-optical properties-pollution transport model