Active tectonics of the Northern Rif (Morocco) from geomorphic and geochronological data

We present results of a geomorphological and morphotectonic analysis of the northeastern part of the Rif. We show that the present day kinematics of the Rif is characterized by active deformation along the Trougout and Nekor faults in the North-East. Digital Elevation Models of offset drainage features (streams, fluvial terraces) allow determining a normal-left-lateral motion along the Trougout fault and a left-lateral strike-slip motion along the Nekor fault. Preliminary ³He cosmogenic dates of tectonic markers yield vertical and horizontal slip rates of ∼0.9 mm/yr and ∼0.5 mm/yr, respectively along the Trougout fault. The present-day localized transtension seen in the north-eastern Rif morphology (Ras Tarf) is coeval with uplifted marine terraces near the Al Hoceima Bay. U/Th dating of shells yield an average uplift rate of ∼0.2 mm/yr during the past 500 ka. These data show that active transtension in the northeastern Rif is also associated with uplift. These new morphotectonic constraints are consistent with the GPS measurements showing southwestward overall motion of most of the Rif belt with respect to stable Africa.     

Hypocenter location accuracy and seismicity distribution in the Central Apennines (Italy)

In this paper, we analyse the seismicity distribution in the CentralApennines (Italy) using the recordings of the Rete SismometricaMarchigiana (RSM). In particular, the selected events are relocated usinga 1-D model calculated by means of an inversion procedure. The robustnessof the 1-D model and the location accuracy are tested. The capability ofthe RSM to well constrain crustal and subcrustal events in the studied areais discussed. We find that in the inner side of the chain the seismicity liesin the upper crustal layers, following the structural trend of the Apenninicbelt. A W-deepening of the events is observed in the Apenninic foredeep,where the seismicity is mainly confined in the lower crust. This evidenceimplies the deepening of the brittle to ductile transition. Some well-locatedsubcrustal events are found. Their locations seem to confirm the W-dippingsubduction of the Adriatic lithosphere beneath the Apennines.     

Paleomagnetic constraints on the Plio–Pleistocene geodynamic evolution of the external central–northern Apennines (Italy)

We report on new paleomagnetic results obtained from 27 sites sampled in the Plio–Pleistocene sequences at the external front of the central–northern Apennines. Previous analyses of Miocene (Messinian) sediments indicated that the present shape of the northern Apenninic arc is due to the oroclinal bending of an originally straight belt oriented around N320° and that vertical axis rotations accompanied the migration of the thrust fronts toward the Adriatic foreland [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. We tried to provide new paleomagnetic constraints for the timing and rates of the oroclinal bending process during the Pliocene and the Pleistocene. The results suggest that CCW rotations observed in the northern part of the studied area are possibly younger than 3 Ma. No regional rotation is recorded in the Pliocene and Pleistocene sediments from the southern part of the study area, analogously to the Messinian sediments of the ‘Acquasanta’ domain of Speranza et al. [F. Speranza et al., J. Geophys. Res. 102 (1997) 3153–3166]. A local significant CCW rotation (23°±10°) is identified in the Early Pleistocene sediments that crop out along the Adriatic coast between Ascoli and Pescara, indicating differential motion of the thrust sheets. This rotation must be younger than 1.43 Ma.     

Geodetic and geological evidence of active tectonics in south-western Sicily (Italy)

Integrated geological, geodetic and marine geophysical data provide evidence of active deformation in south-western Sicily, in an area spatially coincident with the macroseismic zone of the destructive 1968 Belice earthquake sequence. Even though the sequence represents the strongest seismic event recorded in Western Sicily in historical times, focal solutions provided by different authors are inconclusive on possible faulting mechanism, which ranges from thrusting to transpression, and the seismogenic source is still undefined. Interferometric (DInSAR) observations reveal a differential ground motion on a SW–NE alignment between Campobello di Mazara and Castelvetrano (CCA), located just west of the maximum macroseismic sector. In addition, new GPS campaign-mode data acquired across the CCA alignment documents NW–SE contractional strain accumulation. Morphostructural analysis allowed to associate the alignment detected through geodetic measurements with a topographic offset of Pleistocene marine sediments. The on-land data were complemented by new high-resolution marine geophysical surveys, which indicate recent contraction on the offshore extension of the CCA alignment. The discovery of archaeological remains displaced by a thrust fault associated with the alignment provided the first likely surface evidence of coseismic and/or aseismic deformation related to a seismogenic source in the area. Results of the integrated study supports the contention that oblique thrusting and folding in response to NW–SE oriented contraction is still active. Although we are not able to associate the CCA alignment to the 1968 seismic sequence or to the historical earthquakes that destroyed the ancient Greek city of Selinunte, located on the nearby coastline, our result must be incorporated in the seismic hazard evaluation of this densely populated area of Sicily.     

A geological model for the Colfiorito earthquakes (September-October 1997, central Italy)

In this study, surface and subsurface geologicaldata are integrated with seismological data in orderto reconstruct a structural model for theSeptember-October 1997 Colfiorito earthquakes. Theseismic sequence is mainly controlled by two majorSW-dipping normal faults outcropping in the area (M.Pennino-M. Prefoglio and M.Civitella-Preci faults).The activated faults detach, at depth, on a commoneast-dipping low-angle normal fault, the AltotiberinaFault (AF). The AF is interpreted as the base of anactive hangingwall block which is stretching towardNE. The decrease in maximum depth of the earthquakefoci from the Colfiorito area (about 8 km) to theSellano area (about 6 km), suggested by the available seismological data, could be related to the eastward-deepening geometry of the AFdetachment. The seismic fault planes, inferred fromfocal mechanisms and aftershock distributions, arecharacterised by a moderate dip (average 40^°)toward SW, which appears to be independent from thepresence of pre-existing thrust planes.     

Geomorphology and seismotectonic elements in the giarre area,sicily

A morphostructural analysis has been performed on the eastern flank of Mt Etna, located between the towns of St. Alfio and Linera and the Ionian Sea. The research has been carried out through analysis of aerial photographs, and has allowed recognition of morphoneotectonic elements such as: some scarps with rectilinear trend, laterally becoming morphological flexures, according to the lithology; anomalies in the hydrographic network, such as rectilinear tracts of drainage, valleys with simple or double bends, hanging valleys and truncated valleys, narrow deeply engraved valleys with meanders and fluvial captures. All these elements are caused by a fault system oriented NNW–SSE, with a mainly vertical component. Seismic events with very shallow foci have been recorded in the study area; these earthquakes triggered several small landslides on the fault scarps and large series of coseismic and coaxial fractures. It is possible to show that the morphostructures examined have been reactivated during many of the seismic events that have occurred in the area. The combination of these elements verifies that the morphostructures have a real neotectonic cause, which is associated with uplifts which have occurred in the area at different times.     

Attenuation tomography of the Southern Apennines (Italy)

The aim of this study is to improve our knowledge of the attenuation structure in the Southern Apennines using a new amplitude ratio tomography method (Phillips et al., Geophys Res Lett 32(21):L21301, 2005) applied on both direct and coda envelope measurements derived from 150 events recorded by 47 stations of the Istituto Nazionale di Geofisica e Vulcanologia National Seismic Network (Rete Sismica Nazionale Centralizzata). The two-dimensional (2-D) analysis allows us to take into account lateral crustal variations and heterogeneities of this region. Using the same event and station distribution, we also applied a simple 1-D methodology, and the performance of the 1-D and 2-D path assumptions is tested by comparing the average interstation variance for the path-corrected amplitudes using coda and direct waves. In general, coda measurement results are more stable than using direct waves when the same methodology is applied. Using the 2-D approach, we observe more stable results for both waves. However, the improvement is quite small, probably because the crustal heterogeneity is weak. This means that, for this region, the 1-D path assumption is a good approximation of the attenuation characteristics of the region. A comparison between Q tomography images obtained using direct and coda amplitudes shows similar results, consistent with the geology of the region. In fact, we observe low Q along the Apennine chain toward the Tyrrhenian Sea and higher values to the east, in correspondence with the Gargano zone that is related to the Apulia Carbonate Platform. Finally, we compared our results with the coda Q values proposed by Bianco et al. (Geophys J Int 150:10–22, 2002) for the same region. The good agreement validates our results as the authors used a completely independent methodology.     

Areal Distribution of Ground Effects Induced by Strong Earthquakes in the Southern Apennines (Italy)

Moderate to strong crustal earthquakes are generally accompanied by a distinctivepattern of coseismic geological phenomena, ranging from surface faulting to groundcracks, landslides, liquefaction/compaction, which leave a permanent mark in thelandscape. Therefore, the repetition of surface faulting earthquakes over a geologictime interval determines a characteristic morphology closely related to seismic potential. To support this statement, the areal distribution and dimensions of effects of recent historical earthquakes in the Southern Apennines are being investigated in detail. This paper presents results concerning the 26 July 1805 earthquake in the Molise region, (I = X MCS, M = 6.8), and the 23 November 1980 earthquake in the Campania and Basilicata regions (I = X MSK, M_s = 6.9). Landslide data are also compared with two other historical earthquakes in the same region with similar macroseismic intensity. The number of significant effects (either ground deformation or hydrological anomalies) versus their minimum distance from the causative fault have been statistically analyzed, finding characteristic relationships. In particular, the decay of the number of landslides with distance from fault follows an exponential law, whereas it shows almost a rectilinear trend for liquefaction and hydrological anomalies. Most effects fall within the macroseismic area, landslides within intensity V to VI, liquefaction effects within VI and hydrologicalanomalies within IV MCS/MSK, hence at much larger distances. A possible correlation between maximum distance of effects and length of the reactivated fault zone is also noted. Maximum distances fit the envelope curves for Intensity and Magnitude based on worldwide data. These results suggest that a careful examination of coseismic geological effects can be important for a proper estimation of earthquake parameters and vulnerability of the natural environment for seismic hazard evaluation purposes.     

The Holocene paleoseismicity of the Aremogna-Cinque Miglia Fault (Central Italy)

Geomorphic and trench investigations are used toanalyze the seismic potential of the Aremogna-CinqueMiglia fault, an active N- to NW-trending, W-facingnormal fault located in Central Apennines. Wereconstructed a complex 16 km-long, as much as 6m-high, fault scarp that displaces late Holocenesediments in the Aremogna and Cinque Miglia basins.The complex surface expression of the fault, withdouble sub-parallel scarp sections, a change in strikeof about 40^° and local complexity showingimportant horizontal component, appears to becontrolled by the presence of older tectoniclineaments. We opened two trenches across the faultscarp, used a quarry exposure, and reinterpreted atrench opened by Frezzotti and Giraudi (1989), to findthe geological evidence for three Holocene surfacefaulting earthquakes on the Aremogna-Cinque Migliafault. Based on radiocarbon dating and stratigraphicand climatic considerations timing of the events isconstrained between 800 B.C. and 1030 A.D., between3735 and 2940 B.C., and between 3540 and 5000 B.C.. The most recent event is not reported in the twomillennia-long Italian Catalogues of HistoricalSeismicity. We suggest that the most recent eventcould be one of the Middle Age earthquakes of unknownorigin for which several felt reports exist in Rome.Moreover, we also consider the hypothesis that one ofthe shocks of the ambiguous September 1349 earthquakesequence could be the Aremogna-Cinque Miglia mostrecent event. Anyway, based on historicalconsideration we indicate A.D. 1349 as the youngestpossible age for this event. Finally, we suggest theAremogna-Cinque Miglia fault is part of the easternsecondary Apennines seismogenic belt. The faultparameters we obtain for this fault (i.e., recurrence interval longer than 2000 yr, verticallong-term slip rate of 0.3–0.5 mm/yr and m 6.5–6.8 forthe event) can be used as a first hand reference tocharacterize the seismic behavior of other faultsalong this section of the Apennines.     

The role of the seismic trigger in the Calitri landslide (Italy): historical reconstruction and dynamic analysis

The study covered by this paper was focused on the historical case of the Calitri landslide, which was repeatedly reactivated by earthquakes, as reported since 1694. The town of Calitri (Southern Italy) is located on a ridge whose southern slope, from its top to the Ofanto river valley floor, has been historically affected by major landsliding. The last record of recurrence of the Calitri landslide leads back to the 1980 Irpinia earthquake, which caused significant damage to the town and had pervasive and visible ground effects. Based on a detailed historical reconstruction of landsliding and seismicity at Calitri, the study analysed the current static and dynamic stability of the landsliding slope by means of a finite-difference numerical analysis, taking into account the various factors of landslide initiation and kinematics. The results of the numerical analysis: (i) were consistent with the roto-translational mechanism observed upon the latest reactivation of the landslide; (ii) demonstrated that excess pore pressure redistribution caused a lag between the seismic trigger and the initiation of landsliding; and (iii) showed the impact of seismic input frequency on propagation and depth of slope instability.     

The 1997 Umbria-Marche (Italy) earthquake sequence: Tomographic images obtained from data of the GNDT-SSN temporary network

We present some preliminary images of the 3-D P-wavevelocity model and of the relocated seismicityobtained from the data collected by the GNDT-SSNtemporary network installed in the epicentral area ofthe earthquake sequence that followed the 26September, 1997, Central Italy main shock(M_w = 6.0). This network consisted of a total of 15stations, was deployed in the southern part of thearea affected by the earthquake sequence and operatedfor a total of 17 days starting on 10/18/97.Our results indicate that 1) the P-velocity structuredisplays a pattern of lateral variations consistentwith the general NW-SE trend of the Apennines in thearea; 2) the aftershock foci distribute, in thesouthern part of the sequence, on distinct and welldefined SW dipping planes which surface intersectionsmatch previously recognized active normal faults; 3)a distinct zone of aftershock quiescence is observedin correspondence of the 10/12 (M_L = 5.3) and10/14/97 (M_L = 5.7) hypocenters near Sellano; 4)the seismicity at the southern end is very shallow andit is unclear the relationship between the 1997 andthe 1979 Norcia sequences.     

Determining and modeling tectonic movements along the central part of the North Anatolian Fault (Turkey) using geodetic measurements

The North Anatolian Fault (NAF), which extends from Karl?ova in Eastern Turkey to the Gulf of Saros in the Northern Aegean Sea, is one of the longest active strike-slip faults in the world with a length of about 1500 km. Within the North Anatolian Shear Zone (NASZ) there are long splays off the main trunk of the NAF veering towards the interior parts of Anatolia. Although the whole shear zone is still seismically active, the major seismicity is concentrated along the main branch of the NAF. Splays of the NAF dissect the shear zone into different continental blocks. The largest splay of the NAF was selected to analyze the distribution of movements between the faults delimiting these blocks. Four years of GPS measurements and modeling results indicate that the differential motion between the Anatolian collage and the Eurasian plate along the central part of the NAF is partitioned between fault splays and varies between 18.7 ± 1.6 and 21.5 ± 2.1 mm/yr with the main branch taking ∼90% of the motion.     

The 1997 Umbria-Marche (Italy) earthquake sequence: analysis of the data recorded by the local and temporary networks

We present some preliminary results obtained from thejoined analysis of the data collected by the permanentand the temporary networks operating in the area ofthe earthquake sequence that followed (andanticipated) the 26 September, Central Italy, mainshocks. In particular, these earthquake data haveallowed us to determine a well constrainedwave-velocity model (both P and S) with stationcorrections which demonstrated to produce robusthypocentral locations. These velocity modelswith station corrections have been used forre-locating the whole September 1997–July 1998subset of data of the permanent network, and theprevious background seismicity, starting from May1996. The focal mechanisms of the largest events werealso obtained from an analysis of the first-motionpolarities.Our results indicate that 1) the seismic activityaligns on a SE-NW trend for a total length of about50 km of extension; 2) the focal depth of theseevents is restricted to the range 0–9 km; 3) mostevents can be related to sub-parallel SW dipping faultplanes; 4) focal mechanisms of the largest shocks(M_L > 4) show a coherent behaviour, withnormal fault solution on SSE-NNW striking, SW dippingplanes; 5) the space-time evolution of the activitydisplays a discontinuous mode of energy release, withdifferent episodes of activation and an apparentclustering of aftershocks at the edges of the areaswhich presumably ruptured in the main shocks.     

Morphological,sedimentological and tectonic features of diamante-m. Carpinoso Marine terrace flight (tyrrhenian coast of northern Calabria,Italy)

Marine terrace flights resulting from the interaction of Quaternary glacio-eustatic fluctuations and tectonic uplift are a typical feature of the Tyrrhenian coast of Calabria in Southern Italy; in particular a térrace flight with four orders of terraces is evident in the Diamante area. The lowest terrace levels (fourth order: Diamante-Cirella terrace) are typified by a calcarenitic deposit with Cladocora caespitosa which give a Th/U age > 300,000 years. The third order terrace has a sedimentary cover formed of a basal discontinuous level of well rounded pebbles which underlies a deeply weathered coarse-grained sand horizon. The deposit ends with a paleosol locally cut by erosional scours filled by yellowish tuff deposits. The formation of this terrace dates from the Middle Pleistocene. The second order terrace presents a sedimentary cover composed of two generations of soils and is attributed to Middle Pleistocene age. The first order terrace (M. Carpinoso terrace) presents a wave-cut platform covered by a clastic deposit of marine and continental origin; this deposit consists of superimposed depositional events separated by unconformities, bounded by two diachronous surfaces. The formation of the wave-cut platform could be related to several sea-level stands during a long-lasting slow subsidence phase of the coastal area during the Lower Pleistocene. The uplift following terrace formation displaced the first order terrace most markedly; tectonic lineations controlled the hydrographic pattern and erosion of the surfaces.     

西藏中部的发震构造

西藏中部的发震构造是晚第四纪以来强烈活动的北东、北西和近南北向的活动断层及受其控制的地堑半地堑型盆地和拉分盆地，东西向缝合线和断层晚第四纪以来的运动性不明显，对地震活动没有明显的控制作用，活动断层的规模和晚第四纪以来的运动性质对地震的震级和数量有明显的的控制作用。８级地震的发生与拉分盆地内部张剪切断层与盆地一侧新活动幅度大的次级走滑断层的相互作用密切相关。     

Structural evolution of the Pleistocene Cimini trachytic volcanic complex (Central Italy)

Structural, geomorphological, geophysical and volcanological data have been processed for the implementation of a dedicated GIS through which the structural evolution of the Pleistocene trachytic Cimini volcano (central Italy) has been reconstructed. The evolution of the Cimini complex includes three main close-in time phases: (1) intrusion of a shallow laccolith, rising along NW and NE trending faults and stagnating at the contact between the Mesozoic-Cenozoic and the Pliocene-Pleistocene sedimentary units constituting the bedrock of the volcano; (2) emplacement of lava domes along radial and tangential fractures formed by the swelling induced by the laccolith growth; (3) ignimbrite eruptions and final effusion of olivine-latitic lavas. Domes are both of Pelean and low lava dome type and their morphology was controlled by the location on the inclined surface of the swelled area. Some domes show to have uplifted upper Pliocene thermally metamorphosed clay sediments, suggesting a cryptodome-like growth. Comparison of the top of the Mesozoic-Cenozoic units with the top of the upper Pliocene-Pleistocene sedimentary complex, suggests that the laccolith emplaced in a graben of the Mesozoic-Cenozoic sedimentary complex filled by the Pliocene–Pleistocene sediments uplifted by the shallow intrusion. Stress patterns acting on the Cimini area have been deduced analysing the drainage network and the morphotectonic lineaments. Rose diagrams show a large dispersion of the lineaments reflecting the local presence of radial and tangential fractures. The most frequent extensional NW and NE trending lineaments have regional significance and controlled the magma uprise leading to the laccolith emplacement.     

InSAR-DEM analyses integrated with geologic field methods for the study of long-term seismogenic fault behavior: Applications in the axial zone of the central Apennines (Italy)

The integration of terrain computer modeling with field methods may provide a powerful mechanism for understanding active faults geometry, kinematics and long-term fault behavior. Radar interferometry was used on ERS tandem images to create a geocoded DEM (InSAR-DEM) with a nominal 20-m spatial-resolution of the central Apennines axial zone, a seismically active area characterized by historical destructive earthquakes with M 7. The potential was tested of InSAR-DEM application to the Fucino and Sulmona basin boundary faults, which have well-defined seismological, paleoseismological and/or geological evidence for their having seismogenic sources. In particular, slope maps extracted from the InSAR-DEM were used for fault scarps detection, whether on carbonate bedrock (fault scarp type 2) or affecting continental deposits within the basin (fault scarp type 1), and compared with the available geological and new field data. In order to assess the DEM accuracy and to evaluate morphometric parameters related to the long-term slip-rates of the faults, a set of topographic profiles was extracted from the InSAR-DEM and compared with analogous profiles derived from the available topographic map (i.e., 1/25,000, with 25 m contour interval). In particular, the use of InSAR-DEM analyses showed its better results, with respect to the standard topography, for urban/agricultural gently sloped areas where fault scarps affected unconsolidated and particularly soft sediments (e.g., Fucino basin fault systems), while in severely sloped carbonate ridge and forested areas low coherences and layover effects made InSAR-DEM application problematic. A maximum value of 1.1 ± 0.2 mm yr^–1 slip-rate was obtained for the Fucino boundary fault. Finally, the recognized en-échelon pattern of the Sulmona basin boundary fault, provided a segmentation model for this structure corroborated by geological-structural field data.     

Regional stress field in the area of Stromboli (Italy): insights into structural data and crustal tectonic earthquakes

Crustal tectonic seismicity on Stromboli is here discussed along with the regional tectonic and geodynamic context of the Aeolian archipelago, Italy. The aim of this paper is to contribute to the reduction of the crucial gap in information concerning the tectonic activity originating at the volcano Stromboli in the last decade. It is indeed well known that Strombolian eruptions, related to the persistent state of activity on this volcano, allow a fast collection of seismic data which are mainly represented by explosion quakes and tremor. However, only some sporadic information concerns tectonic earthquakes due to their low occurrence rate. A catalog of 150 crustal tectonic earthquakes recorded at Stromboli from 1985 to 1996 is presented here. The analyses of the seismograms were carried out on the basis of the records of the station STR, located in the southwestern part of the island. The magnitude considered ranged from 1.5 to 3.7. Hypocentral location indicates foci at less than 12 km, although for the majority of the earthquakes, which are not recorded at the seismic stations deployed on the other islands of the Aeolian archipelago, a shallower (within a few kilometers) depth can be hypothesized. The strain release associated with the 150 tectonic earthquakes of our catalog was also evaluated. The low levels of occurrence and seismic energy release reached throughout the ca. twelve years analyzed here confirm the minor role played by processes of brittle failure of rocks. This aspect of seismic activity is nevertheless important as it can provide a contribution to the knowledge of the dynamics of this volcano. The focal mechanisms available, integrated with data from the literature, show the T-axes oriented about NE–SW and NW–SE. These findings are consistent with the deformative and tectonic characteristics of this volcanic edifice and of the Aeolian archipelago, which shows the same two directions of extension. This is in agreement with subduction, which is very old or which passively evolves towards the final stages, and is controlled by the transform activity of the Aeolian–Tindari–Giardini fault system.