Seismic microzoning from synthetic ground motion earthquake scenarios parameters: The case study of the city of Catania (Italy)

The city of Catania (Italy) in the South-Eastern Sicily has been affected in past times by several destroying earthquakes with high values of estimated magnitude. The seismogenic area to the south of Volcano Etna, known as Iblean Area, is placed between the African and the Euro-Asiatic plates on the west of the Ibleo-Maltese escarpment, to the south of the Graben of the Sicilian channel and on the east of the overlapping front of Gela. Basing on the seismic history of Catania, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X-XI on MCS scale, magnitude M_W=7.41 and epicentral distance of about 13 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude M_W=6.23 and epicentral distance of about 10 km). The soil response analysis at the surface, in terms of time history and response spectra, has been obtained by 1-D equivalent linear models for about 1200 borings location available in the data-bank of the central area of Catania of about 50 km², using deterministic design scenario earthquakes as input at the conventional bedrock.Seismic microzoning maps of the city of Catania have been obtained in terms of different peak ground acceleration at the surface and in terms of amplification ratios for given values of frequency.     

Quantitative analysis of extensional joints in the southern Adriatic foreland (Italy), and the active tectonics of the Apulia region

The Adriatic foreland of the Apennines comes ashore only in Apulia (easternmost Italy). Its southern part, our study area, lacks any structural analysis devoted to define its recent-to-active tectonics. Throughout the Quaternary, this region was affected by mild brittle deformation with rare faults, characterized by small displacement, and widespread extension joints, frequently organized in sets. Therefore, we conducted a quantitative and systematic analysis of the joint sets affecting Quaternary deposits, by applying an inversion technique ad hoc to infer the orientation and ratio of the principal stress axes, R = (σ₂ ? σ₃)/(σ₁ ? σ₃). Within a general extensional regime, we recognized three deformational events of regional significance. The oldest event, constrained to the early and middle part of the Middle Pleistocene, is characterized by variable direction of extension and R between 0.64 and 0.99. The penultimate event, dated late Middle Pleistocene, is characterized by an almost uniaxial tension, with a horizontal σ₃ striking ～N43°E; R is high, between 0.85 and 0.99. The most recent event is characterized by the lowermost R values, that never exceed 0.47 and are frequently <0.30, indicating a sort of horizontal ‘radial’ extension. This event is not older than the Late Pleistocene and possibly reflects the active stress field still dominating the entire study area.     

Active tectonics of the outer northern Apennines: Adriatic vs. Po Plain seismicity and stress fields

The recent earthquake sequences of 2012 (northern Italy) and 2013 (Marche offshore) provided new, fundamental constraints to the active tectonic setting of the outer northern Apennines. In contrast to the Po Plain area, where the 2012 northern Italy earthquakes confirmed active frontal thrusting, the new focal mechanisms obtained in this study for the 2013 Marche offshore earthquakes indicate that only minor thrust fault reactivation occurs in the Adriatic domain, even for a theoretically favourably oriented maximum horizontal compression. Recent seismicity in this domain appears to be mainly controlled by transcurrent crustal faults dissecting the Apennine thrust belt. The along-strike stress field variation from the Po Plain to the Adriatic area has been quantitatively investigated by applying the multiple inverse method (MIM) to the analysis of the entire seismicity recorded from January 1976 to August 2014, from the top 12 km of the crust (fault plane solutions from 127 earthquakes with M_W ≥ 4), allowing us to obtain a comprehensive picture of the state of stress over the outer zone of the fold and thrust belt. The present-day stress field has been defined for 39 cells of 1.5° × 1.5° surface area and 12 km depth. The obtained stress field maps point out that, although the entire outer northern Apennines belt is characterized by a sub-horizontal maximum compressive axis (σ₁), the minimum compression (σ₃) is sub-vertical only in the Po Plain area, becoming sub-horizontal in the Adriatic sector, thus confirming that the latter region is dominated by an active tectonic regime of strike-slip type.     

The April–June 2007 Trichonis Lake earthquake swarm (W. Greece): New implications toward the causative fault zone

On 10 April 2007, three moderate earthquakes with M_w = 4.9–5.1 occurred in the vicinity of Trichonis Lake (W. Greece). A local network composed of 12 three-component digital seismographs was installed in the epicentral area and recorded more than 1600 events. The double-difference algorithm HYPODD, incorporating both catalog and waveform cross-correlation differential travel-time data, was applied for the successful relocation of 1490 earthquakes. The latter led to the distinction of a main NW-SE trending and NE-dipping zone, as well as of three neighboring faults; a conjugate NW-SE striking and SW-dipping marginal fault mapped along the northeastern flanks of the lake; a E-W trending and south-dipping low-angle normal fault, possibly related to the major Agrinio Fault Zone (AFZ), parallel to the northern bank of the lake; a NE-SW striking and NW-dipping normal fault, likely related to a segment of the active Evinos fault, located south of the lake. Calculation of the Coulomb stress induced by the combination of the 1975 M_w = 6.0 event and the three largest events of 10 April 2007 on the inferred structures, reveals that most of the seismicity lies within the “stress-loaded” region, except for the westernmost activity, which probably belongs to the deep part of the AFZ. A total of 178 reliable focal mechanisms were determined by regional and local body-wave modeling (5 largest events) and P-wave first motion polarity data. The types of the obtained focal mechanisms are predominantly normal and strike-slip, however, numerous earthquakes were found to exhibit reverse faulting. Inversion of focal mechanism data showed that the prevailing principal horizontal component σ₃ is quite homogeneous throughout the activated area with a roughly NW-SE trend, parallel to the strike of the Hellenides. On the contrary, the compressional field σ₁ appears in two patterns: NE-SW trending onshore and NW-SE trending beneath the lake. This apparent rotation of σ₁ by 90° reveals a complex system enclosed by the suggested NW-SE trending antithetic faults in depths between 7 and 9 km. The calculated stress ratios beneath the lake imply that vertical forces are close to the overburden pressure. The overall inferred stress pattern is rather linked to topographic variations, locally imposing increase or decrease of the vertical forces. The presence of the water in the lake possibly plays an additional important role, penetrating through the bedrock, reducing the friction coefficient, while the pore pressure and, consequently, the effective stress increase. Thus, shearing along mature fractures is enhanced, likely yielding the observed diversity.     

Source parameters and stress release of seismic sequences occurred in the Friuli-Venezia Giulia region (Northeastern Italy) and in Western Slovenia

The source parameters of the major events of a swarm and of two seismic sequences, occurred in the Friuli area (Northeastern Italy) and in Western Slovenia, were estimated. The Claut swarm (C96) occurred since the end of January to June 1996, with a M_D 4.3 major shock and it appears composed of three sub-sequences. The two sequences are the Kobarid sequence (K98) started on April 12, 1998 with a M_D 5.6 mainshock and the M.te Sernio (S02) sequence caused by the February 14, 2002 earthquake (M_D = 4.9). Acceleration and velocity data recorded by the local seismic network of the Istituto Nazionale di Oceanografia e di Geofisica Sperimenale (OGS) and corrected for attenuation, were employed to estimate seismic moments and radiated energies. Source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the Brune stress drop, the apparent stress and the RMS stress drop. On the whole, seismic moments range from 1.7 × 10¹² to 1.1 × 10¹⁷ N m, and radiated energies are in the range 10⁶–10¹³ J. Brune stress drops are scattered and do not show any evidence of a self-similarity breakdown for sources down to 130 m radius. The radiated seismic energy scales as a function of seismic moment, with a slope of the scaling relation that decreases for increasing seismic moments.The mechanism of stress release was analyzed by computing the ɛ parameter of Zuniga [Zuniga, R., 1993. Frictional overshoot and partial stress drop. Which one? Bull. Seismol. Soc. Am. 83, 939–944]. The K98 and S02 sequences are characterized by a wide range of the ɛ parameter with stress drop mechanism varying from partial locking to overshoot cases. The ɛ values of the C96 swarm are more homogeneous and close to the Orowan's condition. The radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases. We therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences. For this purpose, we also estimated the source parameters of two other sequences occurred in the area, with mainshocks of M_D 4.1 and 5.1, respectively. We found a positive correlation between the Brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks.     

Dating Holocene lavas on Stromboli,Italy using cosmogenic He

In-situ cosmogenic ³He exposure ages of pyroxene phenocrysts from basalts from the Upper Neostromboli formation in southwest Stromboli date its eruption at 7.0 ± 0.3 ka (1σ, n = 3, Ginostra site) and 6.8 ± 0.2 ka (1σ, n = 10, Timpone del Fuoco site) respectively. Correlation of our new data to previous K/Ar and palaeomagnetic ages from the northwestern Neostromboli phase suggests that it erupted within a confined period between roughly 6 and 14 ka. The low uncertainty on the ³He_cos ages as well as on individual exposure ages (4.4–8.7%) demonstrates that ³He_cos exposure dating is a viable tool for dating Holocene basalt lavas. The ages compare favourably to uncertainties obtained for radiocarbon dating of similar rocks.     

Coda-Q and its lapse time dependence analysis in the interaction zone of the Dinarides,the Alps and the Pannonian basin

The single backscattering model was used to estimate total attenuation of coda waves (Q_c) of local earthquakes recorded on eight seismological stations in the complex area of the western continental Croatia. We estimated Q₀ and n, parameters of the frequency dependent coda-Q using the relation Q_c = Q₀fⁿ. Lapse time dependence of these parameters was studied using a constant 30 s long time window that was slid along the coda of seismograms. Obtained Q_c were distributed into classes according to their lapse time, t_L. For t_L = 20–50 s we estimated Q₀ = 45–184 and n = 0.49–0.94, and for t_L = 60–100 s we obtained Q₀ = 119–316 and n = 0.37–0.82. There is a tendency of decrease of parameter n with increasing Q₀, and vice versa. The rates of change of both Q₀ and n seem to decrease for lapse times larger than 50–80 s, indicating an alteration in rock properties controlling coda attenuation at depths of about 100–160 km. A very good correlation was found between the frequency dependence parameter n and the Moho depths for lapse times of 50, 60 and 70 s.     

Crustal deformation before the 2008 Wenchuan MS8.0 earthquake studied using GPS data

We used GPS velocities from approximately 700 stations in western China to study the crustal deformation before the Wenchuan M_S8.0 earthquake. The processing methods included analyses of the strain rate field, inversion of fault locking and the GPS velocity profiles. The GPS strain rate in the E-W direction in the Qinghai-Tibet block shows that extensional deformation was dominant in the western region of the block (west of 92.5° E), while compressive deformation predominated in the eastern region of the block (from 92.5° E to 100° E). On a regional scale, the hypocentral region of the Wenchuan earthquake was located at the edge of an intense compression deformation zone of about 1.9 × 10⁻⁸/a in an east-west direction. The characteristic deformation in the seismogenic fault was compressive with a dextral component. The compression deformation rate was greater in the fault's western region than in its eastern region, and the strain accumulation was very slow on the fault scale. The results of a fault locking inversion show that the locking fraction and slip deficit was greater in the middle-northern section of the seismogenic fault than in the southern section. The GPS velocity profile before the Wenchuan earthquake shows that the compression deformation was smaller than the dextral deformation, which is asymmetrical with respect to the distribution of co-seismic displacement. These deformation characteristics should provide some clues to the Wenchuan earthquake which occurred in the later period of the earthquake cycle.     

The Himalayan foreland basin crust and upper mantle

Modeling of multimode surface wave group velocity dispersion data sampling the eastern and the western Ganga basins, reveals a three layer crust with an average V_s of 3.7 km s^?1, draped by ～2.5 km foreland sediments. The Moho is at a depth of 43 ± 2 km and 41 ± 2 km beneath the eastern and the western Ganga basins respectively. Crustal V_p/V_s shows a felsic upper and middle crust beneath the eastern Ganga basin (1.70) compared to a more mafic western Ganga basin crust (1.77). Due to higher radiogenic heat production in felsic than mafic rocks, a lateral thermal heterogeneity will be present in the foreland basin crust. This heterogeneity had been previously observed in the north Indian Shield immediately south of the foreland basin and must also continue northward below the Himalaya. The high heat producing felsic crust, underthrust below the Himalayas could be an important cause for melting of midcrustal rocks and emplacement of leucogranites. This is a plausible explanation for abundance of leucogranites in the east-central Himalaya compared to the west. The uppermost mantle V_s is also significantly lower beneath the eastern Ganga basin (4.30 km s^?1) compared to the west (4.44 km s^?1).     

Evapotranspiration in the Pampean Region using field measurements and satellite data

Evapotranspiration (LE) is an important factor for monitoring crops, water requirements, and water consumption at local and regional scale. In this paper, we applied the semi-empirical model to estimate the daily latent heat flux (LE_d = Rn_d + A − B(Ts − Ta)). LE_d has been estimated using satellite images (Thematic Mapper sensor) and a local dataset (incoming and outgoing short- and long-wave radiation) measured during three years. We first estimated the daily net Radiation (Rn_d) from a linear equation derived from the instantaneous net Radiation (Rn_d = CRn_i + D). Subsequently, coefficients A and B have been estimated for two different cover vegetations (pasture and soybean). For each vegetation cover, an error analysis combining Rn_d, A, B, and surface and air temperatures has been calculated. Results showed that Rn_d had good performance (nonbias and low RMSE). LE_d errors for pasture and soybean were ±28 W m⁻² and ±40 W m⁻² respectively.     

Time-Domain Moment Tensors for shallow (h ≤ 40 km) earthquakes in the broader Aegean Sea for the years 2006 and 2007: The database of the Aristotle University of Thessaloniki

We present a catalog of moment tensor (MT) solutions and moment magnitudes, M_w, for 119 shallow (h ≤ 40 km) earthquakes in Greece and its surrounding lands (34°N–42°N, 19°E–30°E) for the years 2006 and 2007, computed with the 1D Time-Domain Moment Tensor inversion method (TDMT_INV code of Dreger, 2003). Magnitudes range from 3.2 ≤ M_w ≤ 5.7. Green's functions (GF) have been pre-computed to build a library, for a number of velocity profiles applicable to the broader Aegean Sea region, to be used in the inversion of observed broad band waveforms (10–50 s). All MT solutions are the outcome of a long series of tests of different reported source locations and hypocenter depths. Quality factors have been assigned to each MT solution based on the number of stations used in the inversion and the goodness of fit between observed and synthetic waveforms. In general, the focal mechanisms are compatible with previous knowledge on the seismotectonics of the Aegean area. The new data provide evidence for strike-slip faulting along NW–SE trending structures at the lower part of Axios basin, close to the heavily industrialized, and presently subsiding, region of the city of Thessaloniki. Normal faulting along E–W trending planes is observed at the Strimon basin, and in Orfanou Gulf in northern Greece. A sequence of events in the east Aegean Sea close to the coastline with western Anatolia sheds light on an active structure bounding the north coastline of Psara–Chios Islands about 20–25 km in length exhibiting right lateral strike-slip faulting.     

Inferred fault geometry and slip distribution of the 2010 Jiashian,Taiwan, earthquake is consistent with a thick-skinned deformation model

We invert measurements of coseismic displacements from 139 continuously recorded GPS sites from the 2010, Jiashian, Taiwan earthquake to solve for fault geometry and slip distribution using an elastic uniform stress drop inversion. The earthquake occurred at a depth of ~ 23 km in an area between the Western Foothills fold-and-thrust belt and the crystalline high mountains of the Central Range, providing an opportunity to examine the deep fault structure under Taiwan. The inferred rupture plane is oblique to the prominent orientation of thrust faults and parallel to several previously recognized NW-striking transfer zones that appear to connect stepping thrusts. We find that a fault striking 318°–344° with dip of 26°–41° fits the observations well with oblique reverse-sinistral slip under a low stress drop of about 0.5 MPa. The derived geodetic moment of 2.92 × 10¹⁸ N-m is equivalent to a M_w = 6.24 earthquake. Coseismic slip is largely concentrated within a circular patch with a 10-km radius at the depth between 10 and 24 km and maximum slip of 190 mm. We suggest this earthquake ruptured the NW-striking Chishan transfer fault zone, which we interpret as a listric NE-dipping lateral ramp with oblique slip connecting stepping thrust faults (ramps). The inferred slip on the lateral ramp is considerably deeper than the 7–15 km deep detachment identified in previous studies of western Taiwan. We infer an active basal detachment under western Taiwan at a depth of at least ~ 20–23 km based on these inversion results. The earthquake may have nucleated at the base of the lateral ramp near the intersection with the basal detachment. Coulomb stress change calculations suggest that this earthquake moved several NE-striking active thrust faults in western Taiwan nearer to failure.     

Travel time and trajectory moments of conservative solutes in three dimensional heterogeneous porous media under mean uniform flow

We present expressions satisfied by the first statistical moments (mean and variance–covariance) of travel time and trajectory of conservative solute particles advected in a three-dimensional heterogeneous aquifer under uniform in the mean flow conditions. Closure of the model is obtained by means of a consistent second-order expansion in σ_Y (standard deviation of the log hydraulic conductivity) of (statistical) moments of quantities of interest. As such, the results obtained are nominally limited to mildly non-uniform fields, with σ_Y < 1. Resulting mean and variance of particles travel time and trajectory are functions of first and second moments and cross-moments of trajectory and velocity components. Our solution is applicable to infinite domains and is free of distributional assumptions. As an important application of the methodology we obtain closed-form expressions for the unconditional mean and variance of travel time and particle trajectory for isotropic log-conductivity domain characterized by an exponential variogram. This allows us to recover the non linear behavior of mean travel time versus distance, in agreement with numerical results published in the literature, as well as a non-linear effect in the mean trajectory. The analysis of trajectory variance allows recovering some known results regarding transverse macro-dispersion, evidencing some limitations typical of perturbation theory.     

Multidecadal changes in moisture condition during climatic growing period of crops in Northeast China

Investigating the spatiotemporal dynamics of agricultural water status during crop growth season can provide scientific evidences for more efficient use of water resources and sustainable development of agricultural production under climate change. In this study, the following were used to evaluate the multidecadal changes in moisture condition during climatic growth period of crops in Northeast China from 1961 to 2010: (1) the daily climate variables gathered from 101 meteorological stations in Northeast China for 1961–2010; (2) FAO (Food and Agriculture Organization) Penman–Monteith equation; (3) 80% guaranteed probability for agro-climatic indicators; and (4) the daily average temperature stably passing 0 °C, which is the threshold temperature of climatic growth period for crops. Reference crop evapotranspiration (ET₀) and relative moisture index were further calculated. The results showed that Northeast China’s climate in the main agricultural areas over the past 50 years was warmer and drier in general, with a growing range and intensity of drought. From 1961 to 2010, when the daily average temperature stably passed 0 °C, the average annual total precipitation (P) and ET₀ with 80% guaranteed probability in Northeast China both emerged as decreasing trends with averages of 555.0 mm and 993.7 mm, respectively. However, the decline in P was greater than that of annual total ET₀. As a result, the annual relative moisture indices sharply decreased with an average of −0.44, mostly fluctuating from −0.59 to −0.25. As far as spatial distributions were concerned, the inter-regional reductions in P and relative moisture index over the past 50 years were conspicuous, especially in some agricultural areas of central Heilongjiang Province, northeastern Jilin Province and northeastern Liaoning Province. On the contrary, ET₀ obviously increased in some agricultural areas of central and northwestern Heilongjiang Province (eg. Qiqiha’er, Shuangyashan, Hegang, Suihua, etc.), and northeastern Jilin Province (eg. Baicheng). This indicated that drought existed and was unfavorable for crop growth and development, especially during the period of 2001–2010. This finding revealed that drought was still one of the most important agricultural meteorological disasters in Northeast China. Some countermeasures should be formulated to adapt to climate change. Our findings have important implications for improving climate change impact studies, for breeding scientists to breed higher yielding cultivars, and for agricultural production to cope with ongoing climate change.     

Mercury emissions and stable isotopic compositions at Vulcano Island (Italy)

Sampling and analyses methods for determining the stable isotopic compositions of Hg in an active volcanic system were tested and optimized at the volcanic complex of Vulcano (Aeolian Islands, Italy). Condensed gaseous fumarole Hg_(fum)^T, plume gaseous elemental Hg_(g)⁰ and plume particulate Hg_(p)^II were obtained at fumaroles F0, F5, F11, and FA. The average total Hg emissions, based on Hg^T/SO₂ in condensed fumarolic gases and plumes, range from 2.5 to 10.1 kg y^? 1, in agreement with published values [Ferrara, R., Mazzolai, B., Lanzillotta, E., Nucaro, E., Pirrone, N., 2000. Volcanoes as emission sources of atmospheric mercury in the Mediterranean Basin. Sci. Total Environ. 259(1–3), 115–121; Aiuppa, A., Bagnato, E., Witt, M.L.I., Mather, T.A., Parello, F., Pyle, D.M., Martin, R.S., 2007. Real-time simultaneous detection of volcanic Hg and SO₂ at La Fossa Crater, Vulcano (Aeolian Islands, Sicily). Geophys. Res. Lett. 34(L21307).]. Plume Hg_(p)^II increases with distance from the fumarole vent, at the expense of Hg_(g)⁰ and indicates significant in-plume oxidation and condensation of fumarole Hg_(fum)^T.Relative to the NIST SRM 3133 Hg standard, the stable isotopic compositions of Hg are δ²⁰²Hg_(fum)^T = ? 0.74‰ ± 0.18 (2SD, n = 4) for condensed gaseous fumarole Hg_(fum)^T, δ²⁰²Hg_(g)⁰ = ? 1.74‰ ± 0.36 (2SD, n = 1) for plume gaseous elemental Hg_(g)⁰ at the F0 fumarole, and δ²⁰²Hg_(p)^II = ? 0.11‰ ± 0.18 (2SD, n = 4) for plume particulate Hg_(p)^II. The enrichment of Hg_(p)^II in the heavy isotopes and Hg_(g)⁰ in the light isotopes relative to the total condensed fumarolic Hg_(fum)^T gas complements the speciation data and demonstrates a gas-particle fractionation occurring after the gas expulsion in ambient T° atmosphere. A first order Rayleigh equilibrium condensation isotope fractionation model yields a fractionation factor α_cond-gas of 1.00135 ± 0.00058.     

New insights in the geodynamics of the Lipari–Vulcano area (Aeolian Archipelago,southern Italy) from geological,geodetic and seismological data

Geological, geodetic and seismological data have been analyzed in order to frame the Lipari–Vulcano complex (Aeolian archipelago, southern Italy) into the geodynamic context of the southeastern Tyrrhenian Sea. It is located at the northern end of a major NNW–SSE trending right-lateral strike-slip fault system named “Aeolian–Tindari–Letojanni” which has been interpreted as a lithospheric discontinuity extending from the Aeolian Islands to the Ionian coast of Sicily and separating two different tectonic domains: a contractional one to the west and an extensional one to the north-east. Structural field data consist of structural measurements performed on well-exposed fault planes and fractures. The mesostructures are mostly represented by NW–SE striking normal faults with a dextral-oblique component of motion. Minor structures are represented by N–S oriented joints and tension gashes widespread over the whole analyzed area and particularly along fumarolized sectors. The analyzed seismological dataset (from 1994 to 2013) is based on earthquakes with magnitude ranging between 1.0 and 4.8. The hypocenter distribution depicts two major alignments corresponding to the NNW–SSE trending Aeolian–Tindari–Letojanni fault system and to the WNW–ESE oriented Sisifo–Alicudi fault system. GPS data analysis displays ∼3.0 mm/yr of active shortening between the two islands, with a maximum shortening rate of about 1.0 × 10⁻¹³ s⁻¹, between La Fossa Caldera and south of Vulcanello. This region is bounded to the north by an area where the maximum values of shear strain rates, of about 0.7 × 10⁻¹³ s⁻¹ are observed. This major change occurs in the area south of Vulcanello that is also characterized by a transition in the way of the vertical axis rotation. Moreover, both the islands show a clear subsidence process, as suggested by negative vertical velocities of all GPS stations which exhibit a decrease from about −15 to −7 mm/yr from north to south. New data suggest that the current kinematics of the Lipari–Vulcano complex can be framed in the tectonic context of the eastward migrating Sisifo–Alicudi fault system. This is dominated by transpressive tectonics in which contractional and minor extensional structures can coexist with strike-slip motion.     

OSL chronology of Quaternary terraced deposits outcropping between Mt. Etna volcano and the Catania Plain (Sicily,southern Italy)

In this paper we tested the applicability of the Optically Stimulated Luminescence (OSL) technique through Single-Aliquot Regenerative-dose (SAR) protocol, on single grain quartz extracted from alluvial–coastal sediments. Five samples were collected from deposits belonging to a flight of seven orders of coastal–alluvial terraces outcropping in the area between Mt. Etna volcano and the Catania Plain (Sicily, southern Italy), at the front of the Sicilian fold and thrust system. After various performance tests, we obtained OSL ages ranging between 240 ± 12 and 80 ± 4 ka, consistent with the normal evolutionary model of a terraced sequence, moving from the highest to the lowest elevation. Obtained data allowed us to determine a mean uplift rate of 1.2 mm/year during the last 240 ka, mostly related to regional uplift processes coupled with sea-level changes. Moreover, terraces belonging to the two highest orders are folded, forming a large anticline. According to our results, the frontal thrust of the Sicilian chain was active between 236 and 197 ka ago, even though seismological and geodetic data suggest current activity to the back.     

Seismic microzonation studies for the city of Ragusa (Italy)

The seismic history of the city of Ragusa (Italy), the geotechnical characterisation of the subsoil and the site response analysis should be correctly evaluated for the definition of the Seismic Geotechnical Hazard of the city of Ragusa, through geo-settled seismic microzoning maps. Basing on the seismic history of the city of Ragusa, the following earthquake scenarios have been considered: the “Val di Noto” earthquake of January 11, 1693 (with intensity X–XI on MCS scale, magnitude M_W=7.41 and epicentral distance of about 53 km); the “Etna” earthquake of February 20, 1818 (with intensity IX on MCS scale, magnitude M_W=6.23 and epicentral distance of about 64 km); the Vizzini earthquake of April 13, 1895 (with intensity I=VII–VIII on MCS scale, magnitude M_W=5.86 and epicentral distance of about 26 km); the “Modica” earthquake of January 23, 1980 (with intensity I=V–VI on MCS scale, magnitude M_W=4.58 and epicentral distance of about 10 km); the “Sicilian” earthquake of December 13, 1990 (with intensity I=VII on MCS scale, magnitude M_W=5.64 and epicentral distance of about 50 km). Geotechnical characterisation has been performed by in situ and laboratory tests, with the definition of shear wave velocity profiles in the upper 30 m of soil. Soil response analyses have been evaluated for about 120 borings location by some non-linear 1-D models. Finally the seismic microzonation of the city of Ragusa has been obtained in terms of maps with different peak ground acceleration at the surface; shaking maps for the central area of the city of Ragusa were generated via GIS for the earthquake scenarios.     

Nonlinear geodynamics of the Baikal rift system: An evolution scenario with triple equilibrium bifurcation

This is an attempt to analyze the current lithospheric stress pattern in the Baikal rift in terms of nonlinear dynamics as an open self-organizing system in order to gain more insights into the general laws of regional seismicity. According to the suggested approach, the stress pattern inferred from seismic moments of 70,000 M_LH ≥ 2.0 events that occurred in the region between 1968 and 1994 is presented as a phase portrait in the phase spaces of the seismic moments. The obtained phase portrait of the system evolution fits well a scenario with triple equilibrium bifurcation where stress bifurcations account for the frequency of M > 5.5 earthquakes. Extrapolation of the results into the nearest future indicates probability of such a bifurcation (a catastrophe of stress), i.e., there is growing risk that M ≈ 7 events may happen in the region within a few years.