Recent activity and seismotectonics of the Eastern Pyrenees

Results from a recent earthquake in the Eastern Pyrenees are presented and the seismotectonics of the region is analyzed from the presently available data. On 26 September 1984 an earthquake (M_L = 4.4) took place in the area of the historical destructive earthquake of 1428. Several portable stations installed in the epicentral area to record aftershocks permitted of defining a precise location at 42°19.2′N, 2°10.2′E and 5 km depth. A maximum felt intensity of V (MSK) is obtained from macroseismic data. The epicentral location lies within a block bounded by E-W-trending structures and the focal solution shows right-lateral shearing with a NW-SE pressure axis.The seismicity in the Eastern Pyrenees shows a complex pattern which can be associated with both E-W fractures and NE-SW fault systems. Focal solutions of another two recent earthquakes of M_L ~ 4, with differences in horizontal pressure axis, are also discussed.     

The April 2007 earthquake swarm near Lake Trichonis and implications for active tectonics in western Greece

We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the vicinity of Lake Trichonis (western Greece). First we relocated the earthquakes, using P- and S-wave arrivals to the stations of the Hellenic Unified Seismic Network (HUSN), and then we applied moment tensor inversion to regional broad-band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm. The relocated epicentres, cluster along the eastern banks of the lake, and follow a distinct NNW–ESE trend. The previous strong sequence close to Lake Trichonis occurred in June–December 1975. We applied teleseismic body waveform inversion, to obtain the focal mechanism solution of the strongest earthquake of this sequence, i.e. the 31 December 1975 (Mw 6.0) event. Our results indicate that: a) the 31 December 1975 Mw 6.0 event was produced by a NW–SE normal fault, dipping to the NE, with considerable sinistral strike-slip component; we relocated its epicentre: i) using phase data reported to ISC and its coordinates are 38.486°N, 21.661°E; ii) using the available macroseismic data, and the coordinates of the macroseismic epicentre are 38.49°N, 21.63°E, close to the strongly affected village of Kato Makrinou; b) the earthquakes of the 2007 swarm indicate a NNW–SSE strike for the activated main structure, parallel to the eastern banks of Lake Trichonis, dipping to the NE and characterized by mainly normal faulting, occasionally combined with sinistral strike-slip component. The 2007 earthquake swarm did not rupture the well documented E–W striking Trichonis normal fault that bounds the southern flank of the lake, but on the contrary it is due to rupture of a NW–SE normal fault that strikes at a  45° angle to the Trichonis fault. The left-lateral component of faulting is mapped for the first time to the north of the Gulf of Patras which was previously regarded as the boundary for strike-slip motions in western Greece. This result signifies the importance of further investigations to unravel in detail the tectonics of this region.     

Complex geometry and segmentation of the surface rupture associated with the 14 November 2001 great Kunlun earthquake, northern Tibet, China

The 14 November 2001 Kunlun, China, earthquake with a moment magnitude (M_w) 7.8 occurred along the Kusai Lake–Kunlun Pass fault of the Kunlun fault system. We document the spatial distribution and geometry of surface rupture zone produced by this earthquake, based on high-resolution satellite (Landsat ETM, ASTER, SPOT and IKONOS) images combined with field measurements. Our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture, including the Sun Lake, Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments from west to east. These segments, each 55 to 130 km long, are separated by step-overs. The Sun Lake segment extends about 65 km with a strike of N45° 75°W (between 90°05′E 90°50′E) along the previously unrecognized West Sun Lake fault. A gap of about 30 km long exists between the Sun Lake and Buka Daban Peak where no obvious surface ruptures can be observed either from the satellite images or field observations. The Buka Daban–Hongshui River, Kusai Lake, Hubei Peak and Kunlun Pass segments run about 365 km striking N75° 85°W along the southern slope of the Kunlun Mountains (between 91°07′E 94°58′E). This segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field. Detailed mapping suggest that these five first-order segments can be further separated into over 20 second-order segments with a length of 10–30 km, linked by smaller scale step-overs or bends.Our result also shows that the total coseismic surface rupture length produced by the 2001 Kunlun earthquake is about 430 km (excluding the 30-km-long gap), which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded.Finally, we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 M_w 7.8 earthquake is complex. It consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes.     

The Dibra (Albania) earthquake of November 30, 1967

On November 30, 1967, a strong earthquake of magnitude M = 6.6 struck the Dibra region, eastern Albania, causing considerable loss of human life and grave material damage both in the territory of Albania and that of Yugoslavia.The object of this study is to describe the effects of this earthquake on landscape and buildings, as well as to define its macroseismic field. The study further deals with some features of the aftershocks of M 4.0 distributed in time and space, the aftershock activity and the focal-mechanism solution of the main event.From the study of the macroseismic field of this earthquake and its fault, which extends over 10 km in a 40° northeasterly direction, from the distribution of aftershocks in space and the focal-mechanism solution of this earthquake, the conclusion has been reached that this event is connected with the Vlora—Dibra seismogenic belt.The authors have mentioned the existence of this traverse belt as early as 1969 (Sulstarova and Koçiaj, 1969). The existence of this belt is also shown by the chronological and geographical distribution of some strong earthquakes in Albania in the period 1800–1967 (their macroseismic field and the position of their epicentres), and by the focal-mechanism solutions of some of these earthquakes. The Vlora—Elbasan—Dibra transverse seismogenic belt continues for several hundred kilometres northeast and southwest beyond the territory of Albania.     

The determination of the epicentre by a vectorial modelling of macroseismic intensity distribution

A vectorial modelling of observed macroseismic intensity aimed at the analytical determination of the epicentre is proposed here. The methodology is based on the determination of a plane system of vectors which characterises the macroseismic intensity distribution. The epicentre of each seismic event considered is determined as the centre of this vector system by an analytical expression which is independent from all possible directions of seismic energy propagation. The analysis of the intensity distribution is carried out by a new model called a macroseismic plane, different from the one known as macroseismic field, formed by a set of small areas built around the observed intensity points; hence its name.With the proposed methodology, some earthquakes in southern Italy and eastern Sicily are analysed calculating their epicentres, also for distributions of observed intensity which are particularly complex.     

Spatial relationships between natural seismicity and faults, southeastern Ontario and north-central New York state

A statistical analysis was carried out to investigate spatial associations between natural seismicity and faults in southeastern Ontario and north-central New York State (between 73°18′ and 77°00′W and 43°30′ and 45°18′N). The study area is situated to the west of the seismically active St. Lawrence fault zone, and to the east of the Lake Ontario basin where recently documented geological and geophysical evidence points to possible neotectonic faulting. The weights of evidence method was used to judge the spatial associations between seismic events and populations of faults in eight arbitrarily defined orientation groups. Spatial analysis of data sets for seismic events in the periods 1930–1970 and post-1970 suggest stronger spatial associations between earthquake epicentres and faults with strikes that lie in the NW–SE quadrants, and weaker spatial associations of epicentres with faults that have strikes in the NE–SW quadrants. The strongest spatial associations were determined for groups of faults with strikes between 101° and 146°. The results suggest that faults striking broadly NW–SE, at high angles to the regional maximum horizontal compressive stress, are statistically more likely to be spatially associated with seismic events than faults striking broadly NE–SW. If the positive spatial associations can be interpreted as indicating genetic relationships between earthquakes and mapped faults, then the results may suggest that, as a population, NW–SE trending faults are more likely to be seismically active than NE–SW striking faults. Detailed geological studies of faults in the study area would be required to determine possible neotectonic displacements and the kinematics of the displacements.     

The pyrenean earthquake of february 29, 1980: An example of complex faulting

An M_b = 5.1 earthquake occurred on February, 29, 1980, in the Western Pyrenees near Arudy (France). The telemetred network of the I.P.G.P., operating in this area since 1978, allowed a good localization of this earthquake (43°4.21′N, 0°24.59′W, depth 4km). During the two years preceding this earthquake the seismic activity exhibited a gradual decrease. A foreshock of magnitude 1.6 was recorded three hours before the main shock.A temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence. Fifty fault-plane solutions for earthquakes ranging from magnitude 1.5-4 were obtained. A complex pattern of faulting was revealed, with both strike-slip and normal faulting. However, a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence. This stress tensor is in agreement with previous results in this area.     

Macroseismic field of the March 4, 1977 Vrancea earthquake

The macroseismic field of the Vrancea earthquake of March 4, 1977, characterized by the following parameters : H = 19h 21m 56s, ø = 45.8°N, γ = 26.8° E, h = 95 Km, M = 7.2, I = VIIIMSK has been analyzed. The following problems were studied : area and shape of the isoseismals of intensity III–VIII ; elongation of the isoseismal ellipses and decrease of intensity with distance. The results confirm our previous studies (Radu and Apopei, 1978) of strong intermediate earthquakes, but render evidence for some peculiarities in the seismic intensity attenuation as well.     

The influence of tectonically derived relief and climate on the extent of the last Glaciation east of the Patagonian ice fields (Argentina, Chile)

Two large ice fields between 46°30′ and 51°30′S cover the Patagonian Andes. The North and South Patagonian Ice Fields are separated by the transandine depth line at 47°45′ to 48°15′S. Canal and Río Baker run through this depression. The two ice fields are generally considered relics of a continuous ice cap, which covered the entire Patagonian Andes from 39° to 52°S and extended far into the eastern foreland of the Andes. This assumption is not correct for the 200-km-long section of the Andes between Lago Pueyrredón (Lago Cochrane in Chile) (47°15′S) and Lago San Martín (Lago O'Higgins in Chile) (48°45′S). The lack of a continuous ice cap extending far into the east is caused by the transandine depth line, playing a crucial role in the fluvial erosion and the glacial scouring of this tectonic zone. This depression formed a river system (e.g. Río Baker, Río Bravo and Río Mayer) that drains towards the west. Reconstruction of the maximum glacial advance of the last ice age shows that the eastern outlet glaciers of the two ice fields between Lago San Martín and Lago Pueyrredón did not drain towards the east, but rather followed the general gradient of the transandine depth line. In this area the eastern flank of the Andes between Monte San Lorenzo (3770 m) and Sa. de Sangra (2155 m) supported valley glaciers, which were independent of the expanding ice fields. Only a few valley glaciers advanced towards the Patagonian Meseta. The terminal moraines of these glaciers were erroneously interpreted as the eastern edge of a continuous ice cap. North of 47°30′S the outlet glaciers of the NPI advanced 200 km during the LGM and the late glacial advances nearly reached to 71°W. In contrast, south of 49°S glacier expansion was comparatively less: The LGM is situated only 85–115 km east of the present margins of the large outlet glaciers (O'Higgins, Viedma, and Upsala), and no late glacial advance reached 72°W. These considerable differences of glacier expansion were influenced by the northward migration of the westerly precipitation belt during glacial cycles. There is tentative evidence that the glaciers advanced three times in the period from 14 000 to 9 500 ¹⁴C years BP.     

The stress field near the sites of the Meckering (1968) and Calingiri (1970) earthquakes, Western Australia

A comparison of three methods of stress determination using overcoring tests, earthquake focal-mechanism solutions, and fault-displacement analysis, was carried out near the epicentres of the 1968 Meckering and the 1970 Calingiri earthquakes, Western Australia. Shallow overcoring measurements (3–10 m) were made at seven sites in competent granite, along a 200-km north—south traverse through the location of the Meckering earthquake. The in situ measurements indicate a high regional compressive stress, acting about N77°E. This compares with the direction of the P-axes from the Meckering and Calingiri earthquakes of N91°E and N102°E, respectively, and east-west orientation of major principal stress deduced from observations of surface faulting. The highest maximum principal stress, 23 MPa, was measured at the site farthest north from the Meckering epicentre (~ 90 km), and the lowest, 4 MPa, was measured near the epicentre. The magnitude of the stress increases with distance away from the epicentral area at about 0.2 kPa/m. The results were corrected for drilling water temperature, thermal rock stresses, and suction pore pressure. The total correction was less than 2 MPa at most sites.Estimates of shear stress release from the fault-scarp displacements for Meckering and Calingiri were of similar magnitude (~10 MPa) to the difference between observed shear stress at sites close to and sites remote from the Meckering earthquake.As a cause of the earthquake it is proposed that the fault plane is progressively weakened by alteration or weathering, and that a small long-term fluctuation of head of ground water was the trigger.The high stress at shallow depths, the growing evidence of east—west major principal stress in most of the Australian continent, and the existence of horizontal stress higher than gravity lithostatic stress may have a common explanation, in terms of the driving forces of plate tectonics. The Australian results do not agree with the north—south orientation suggested by crude plate-drift theories in which the major stress is in the direction of the drift, and do not appear to fit with orientations from other continents, in the Richardson et al. (1976) interacting plate model which assumes a velocity-dependent plate driving force. An analysis of driving forces at diverging plate boundaries was carried out and suggests no dominant force-velocity relationship, thus forces independent of plate velocity may control the stress orientation in the plate.     

Late quaternary evolution of a subantarctic paleofjord, Tierra del Fuego

Lago Roca-Lapataia valley (54°50′S, 68°34′W) is a paleofjord that was occupied by a valley-glacier system during the glacial maximum of the late Pleistocene (estimated ca. 18–20 ka BP). Deglaciation began before 10,080 ± 270 BP. The marine fauna in several marine terraces found in the area shows that early-middle Holocene climatic conditions were basically the same as at present. Species found are characteristic of cold and shallow waters, although minor temperature fluctuations cannot be ruled out for this period. A recent radiocarbon date of 7518 ± 58 BP on Chlamys patagonica (NZ # 7730) confirms that Lago Roca was transformed into a fjord ca. 7500–8000 BP. The sea reached its maximum level of 8–10 m a.s.l. around 6000 BP and at 4000–4500 BP was at least above 6 ± 1 m a.s.l. Later, when sea level fell, Lago Roca was occupied by fresh water and was no longer tidal. The relative land-sea positions during this period are a consequence of combined eustatic and neotectonic processes.     

Macroseismic Surveys in Theory and Practice

Macroseismology is the part of seismology that collects and evaluates non-instrumental data on earthquakes, i.e., effects on people, objects, buildings and nature. The methods that seismologists use for collecting and evaluating the macroseismic data are often based on long (trial-and-error) experience more than on some formal procedure. Until very recently manuals or guidelines on how to do a macroseismic survey were rare and often superficial. After an earthquake is felt in some region, the data are usually collected by means of questionnaires. Field survey is an obligatory tool that complements the questionnaires in the case of a damaging earthquake. An overview of the approaches to deriving the earthquake parameters (epicentre and barycentre, epicentral intensity, magnitude, depth, source parametres) from macroseismic data, as well as a review of some existing practices is given.     

Hazard mapping based on macroseismic data considering the influence of geological conditions

The object of this study is to consider directly the influence of regional geological conditions on the assessment of seismic hazard. It is assumed that macroseismic data at individual locations contain, in an average way, the influence of geological conditions.A Data Base referring to 199 historical (5) and instrumental (194, in the 1947–1993 period) events with macroseismic information in 1195 locations of Portugal was built. For any given seismic event, whenever macroseismic information was available at a location (town, village, etc.), an EMS-92 intensity value was estimated. To each one of those locations a geological unit, representing the most common type of soil, was assigned, based on the Geological Portuguese Map at a scale 1:500 000; the geological units were grouped into three categories: soft, intermediate and hard soils.The Data Base was used to determine the attenuation laws in terms of macroseismic intensity for the three different geological site conditions, using multiple linear regression analysis. The reasonability of the laws was tested by (i) checking residual distributions and (ii) comparing the map of isoseismals of important earthquakes with the isoseismals generated by the attenuation curves derived for each one of the three different soil classes, taking into consideration the soil class of each site. The main results of attenuation modeling are: high dispersion on macroseismic intensity data; all the models predict intensity values, for short hypocentral distances, lower than the ones observed; and for some important analyzed earthquakes and for the observed range of distances, the models confirm the expectancy that macroseismic intensity increases from hard to soft soil.The approach to obtain the hazard assessment at each location consisted in the use of the attenuation law specifically derived for the class of soil of that particular location. This method, which considers the influence of the regional geology, was illustrated with the mapping of hazard for the country for several return periods. Comparison with previous maps not taking into consideration the regional geological conditions emphasizes the importance of this new parameter. It can be concluded that (i) soil segmentation is clearly the cause for hazard increase in the region to the north of Lisbon, especially at sites with soft and intermediate soils as the ones in lower Tagus valley; the maximum increase on hazard is, in any case, less than one degree; (ii) when geological conditions are disregarded in the attenuation regression analysis, hazard pattern is similar to the one obtained for the case of hard soil everywhere.     

Expansion of Magellanic Moorland during the late Pleistocene: Palynological evidence from northern Isla de Chiloé, Chile

The late Quaternary vegetation of northern Isla de Chiloé is inferred from palynological analysis of a section in the Río Negro drainage (42°03′S, 73°50′W). At ca. 30,500 yr B.P., maxima of Astelia and Donatia occurred, suggesting wetland development. From that time until ca. 27,000 yr B.P., steppe indicators such as Compositae/Gramineae dominated, suggesting drier conditions. After 27,000 yr B.P., the moorland shrub Dacrydium gradually increased, reaching a maximum by 18,000 yr B.P. At this time Astelia increased again, suggesting development of cushion bog during cold and wet conditions. The glacial-postglacial transition is characterized by a marked change from peaty sediments to clays, a decrease in the cushion bog flora, and the prevalence of Gramineae/ Compositae and swamp taxa. This vegetation prevailed until ca.7000 yr B.P. when forest taxa became dominant. The floristic pattern inferred from the pollen spectra of the Rio Negro section suggests that the late Pleistocene vegetation of Chiloé resembled modern Magellanic Moorland vegetation (52°–56°lat S). Based on climatic conditions presently associated with Magellanic Moorland, its occurrence in Chiloé at low elevations during the late Pleistocene implies a decrease in average temperature of at least 4°C and an increase in annual precipitation of at least 1500 mm.     

Petrology, structure and tectonic significance of the Tuclame banded schists in the Sierras Pampeanas of Córdoba and its relationship with the metamorphic basement of northwestern Argentina

In the northwest of the Sierras Pampeanas of Córdoba (Central Argentina), in the Tuclame area, rocks called ‘banded schists’ are recognized. They are known since 120 years ago and are one of the most important lithologies of the metamorphic complex in this region. The compositional banding is the most conspicuous structural mesoscopic feature, composed of quartz-rich and mica-rich layers. It is a tectonic banding produced by pressure solution during a compressive event. P–T conditions of 557 ± 25 °C and 3.9 ± 1 kb were obtained for the main metamorphic event. A detailed field checking allowed recognition of the banded schists as decimetric or centimetric xenoliths isolated within the regional migmatites and the anatectic granitoids and as kilometric-scale belts within Sierras de Córdoba and San Luis. The authors have also identified banded schists in the Sierras de Aconquija, Ambato, Ancasti and Guasayán. Other workers recognized them in the Puna, Cumbres Calchaquíes, Sierras de Quilmes and Fiambalá, among the most well known outcrops. The banded schists have systematic petrological features and a distinctive mesoscopic structure that allow their identification and correlation with the other outcrops, which are arranged as a huge belt 2000 km long and 150 km wide, between 64°00′–66°30′W and 25°00′–41°34′S. In this work, all these rocks are proposed to be integrated into the Puncoviscana Basin, since field evidence indicated that the banded schists transitionally pass by transposition to phyllitic rocks typical of this metamorphosed basin, which would cover a region of about 300,000 km². At present, there is no accurate geochronology available for the metamorphic and deformation events proposed in this work for the Tuclame banded schists. However, considering the regional geological evidence, the great spread of the petrostructural process forming these rocks, the transition between the Puncoviscana Formation and the banded schists, and the earlier idea that the Puncoviscana Formation is the shallowest equivalent of deeper structural levels in the Sierras Pampeanas, we favor for the moment the hypothesis that the banded schists could be part of the oldest evolution of the Pampean orogeny (early Pampean stage) and could represent different structural levels of the same orogen, probably a late Precambrian–early Palaeozoic orogen. The events of migmatization and emplacement of anatectic granitoids could represent a late Pampean stage of early Palaeozoic age. Thus, the Pampean orogeny could have lasted around 30–40 Ma (570–530 Ma).     

Origin and evolution of the Steamboat Springs siliceous sinter deposit, Nevada, U.S.A.

Siliceous hot spring deposits from Steamboat Springs, Nevada, U.S.A., record a complex interplay of multiple, changing, primary environmental conditions, fluid overprinting and diagenesis. Consequently these deposits reflect dynamic geologic and geothermal processes. Two surface sinters were examined—the high terrace, and the distal apron-slope, as well as 13.11 m (43 ft) of core material from drill hole SNLG 87-29. The high terrace sinter consists of vitreous and massive-mottled silica horizons, while the distal deposit and core comprise dominantly porous, indurated fragmental sinters. Collectively, the three sinter deposits archive a complete sequence of silica phase diagenetic minerals from opal-A to quartz. X-ray powder diffraction analyses and infrared spectroscopy of the sinters indicate that the distal apron-slope consists of opal-A and opal-A/CT mineralogy; the core yielded opal-A/CT and opal-CT with minor opal-A; and the high terrace constitutes opal-C, moganite, and quartz. Mineralogical maturation of the deposit produced alternating nano–micro–nano-sized silica particle changes. Based on filament diameters of microbial fossils preserved within the sinter, discharging thermal outflows fluctuated between low-temperatures (< 35 °C, coarse filaments) and mid-temperatures ( 35–60 °C, fine filaments). Despite transformation to quartz, primary coarse and fine filaments were preserved in the high terrace sinter. AMS ¹⁴C dating of pollen from three horizons within core SNLG 87-29, from depths of 8.13 to 8.21 m (26′8″ to 26′11″), 10.13 to 10.21 m (33′3″ to 33′6″), and 14.81 to 14.88 m (48′7″ to 48′10″), yielded dates of 8684 ± 64 years, 11,493 ± 70 years and 6283 ±60 years, respectively. In the upper section of the core, the stratigraphically out-of-sequence age likely reflects physical mixing of younger sinter with quartzose sinter fragments derived from the high terrace. Within single horizons, mineralogical and morphological components of the sinter matrix were spatially patchy. Overall, the deposit was modified by sub-surface flow of alkali-chloride thermal fluids depositing a second generation of silica, and periodically, by acidic steam condensate formed during periods when the water table was low. Local faulting produced considerable fracturing of the sinter. Hence, the Steamboat Springs sinter experienced a complex history of primary and secondary hydrothermal, geologic and diagenetic events, and their inter-relationships and effects are locked within the physical, chemical and biological signatures of the deposit.     

Earthquake recurrence on the Calaveras fault east of San Jose, California

Occurrence of small (3 M_L < 4) earthquakes on two 10-km segments of the Calaveras fault between Calaveras and Anderson reservoirs follows a simple linear pattern of elastic strain accumulation and release. The centers of these independent patches of earthquake activity are 20 km apart. Each region is characterized by a constant rate of seismic slip as computed from earthquake magnitudes, and is assumed to be an isolated locked patch on a creeping fault surface. By calculating seismic slip rates and the amount of seismic slip since the time of the last significant (M 3) earthquake, it is possible to estimate the most likely date of the next (M - 3) event on each patch. The larger the last significant event, the longer the time until the next one. The recurrence time also appears to be increased according to the moment of smaller (2 < M_L < 3) events in the interim. The anticipated times of future larger events on each patch, on the basis of preliminary location data through May 1977 and estimates of interim activity, are tabulated below with standard errors. The occurrence time for the southern zone is based on eight recurrent events since 1969, the northern zone on only three. The 95% confidence limits can be estimated as twice the standard error of the projected least-squares line. Events of M 3 should not occur in the specified zones at times outside these limits. The central region between the two zones was the locus of two events (M = 3.6, 3.3) on July 3, 1977. These events occurred prior to a window based on the three point, post-1969 slip-time line for the central region.

Latitude	Longitude	Depth	Mag.	Target date	Standard error (days)
37°17′± 2′N	121°39′±2′W	5.0 ±2 km	3.0–4.0	7-22-77	22.3
37°26′± 2′N	121°47′±2′W	6.0 ± 2 km	3.0–4.0	9-02-77	8.0

Full-size table

     

Seismogeological effects on rocks during the 12 April 1998 upper So a Territory earthquake (NW Slovenia)

On 12 April 1998, the strongest earthquake (M_L 5.7), with an epicentre in Slovenia, in the last 100 years shook the upper So a Territory (NW Slovenia). Its maximum intensity was between VII and VIII according to the European Macroseismic Scale (EMS-98). Its epicentre is located in the area SE of the town of Bovec in the Krn mountain range (Julian Alps). Apart from substantial material damage to nearby settlements, the earthquake caused considerable changes to the landscape through many rockfalls and landslides. In this paper, we try to assess the effects of this event on the natural surroundings. The presented results are useful to understand the relation between “seismogeological” effects and the intensity scale EMS-98 for this particular event, but might also be a first step towards a future statistically meaningful assessment of the intensity scale on the basis of “seismogeological” effects.     

The 2003 Lefkada earthquake: Field observations and preliminary microzonation map based on liquefaction potential index for the town of Lefkada

A strong earthquake (Mw = 6.2) occurred offshore the island of Lefkada (or Lefkas) on August 14, 2003. The maximum intensity has been evaluated Io = VIII (EMS) at Lefkada municipality, while VI to VII+ intensities were evaluated at many other villages of the island. The offshore NNE-SSW oriented strike-slip right-lateral fault was activated by the main shock. This fault is the northern termination of the Cephalonia transform fault. The most characteristic macroseismic effects were extensive typical ground failures like rock falls, soil liquefactions, subsidence, densification, ground cracks and landslides. These macroseismic effects are remarkably similar to those reported from some historical Lefkada shocks, e.g. 1704, 1914 (Ms = 6.3) and 1948 (Ms = 6.5). Sand boils and ground fissures with ejection of mud were observed at the seaside of the town of Lefkada, and in the villages of Nydri and Vassiliki.In situ soil profiles are obtained based mainly on borings after the earthquake. Boreholes records with SPT values (standard penetration test) are obtained and the “simplified procedure” originally developed by Seed and Idriss was employed to evaluate the liquefaction resistance of soils. The results indicated that the silty sandy layer, which lies beneath the artificial fill in the coastal zone in Lefkada town, had liquefied during the 14 August Earthquake. An attempt was also made to establish a preliminary microzonation map for Lefkada town using the data from Liquefaction Potential Index analyses. Our map was validated by the occurrence of liquefaction phenomena inside the town.     

Presence of Hippidion at two sites of western Argentina: Diet composition and contribution to the study of the extinction of Pleistocene megafauna

The composition of Hippidion diet, and possible changes that could relate to its extinction, were evaluated in the Argentinean-Chilean Central Andes, a Neotropical environment characterized by arid to semiarid conditions (Andean hot and cold deserts). Microhistological analyses were made on feces of Hippidion found at Los Morrillos (31°43′S–68°42′W, 3000 m a.s.l.) and Gruta del Indio (34°35′S, 68°22′W, 660 m a.s.l.). At Gruta del Indio the diet of Hippidion was based mainly on woody species. At Los Morrillos, it was based on herbaceous species.This flexibility in diet composition could be a relative adaptive advantage allowing a longer permanence of this species in comparison to others recorded in the region (such as Megatheriumand Mylodon). Nevertheless, this advantage was not enough to guarantee its survival during the Holocene. Extinction could have been affected by diverse agents, such as growing aridification of the area, increasing competition with other species (mainly Lama guanicoe), and human presence, along with a relatively low population density (as expected from the limited presence of Hippidion at the archaeological and palaeontological sites of South America. At Gruta del Indio significant changes in the diet of Hippidion corresponding to different intervals of the period 31,000–9000 ¹⁴C BP are not evident. Given this evidence for similar diets for Hippidion throughout the late Quaternary, other factors need to be considered to explain the extinction of this horse.