Análise sísmica e proposta de reforço de uma estrutura do séc. XIX sujeita a uma reabilitação parcial

Trabalho final de Mestrado para a obtenção do grau de mestre em Engenharia Civil

Geodynamics of the Andaman - Sumatra - Java Trench - Arc System Based on Gravity and Seismotectonic Study

This work aims to study the variation in subduction zone geometry along and across the arc and the fault pattern within the subducting plate. Depth of penetration as well as the dip of the Benioff zone varies considerably along the arc which corresponds to the curvature of the fold- thrust belt which varies from concave to convex in different sectors of the arc. The entire arc is divided into 27 segments and depth sections thus prepared are utilized to investigate the average dip of the Benioff zone in the different parts of the entire arc, penetration depth of the subducting lithosphere, the subduction zone geometry underlying the trench, the arctrench gap, etc.The study also describes how different seismogenic sources are identified in the region, estimation of moment release rate and deformation pattern. The region is divided into broad seismogenic belts. Based on these previous studies and seismicity Pattern, we identified several broad distinct seismogenic belts/sources. These are l) the Outer arc region consisting of Andaman-Nicobar islands 2) the back-arc Andaman Sea 3)The Sumatran fault zone(SFZ)4)Java onshore region termed as Jave Fault Zone(JFZ)5)Sumatran fore arc silver plate consisting of Mentawai fault(MFZ)6) The offshore java fore arc region 7)The Sunda Strait region.As the Seismicity is variable,it is difficult to demarcate individual seismogenic sources.Hence, we employed a moving window method having a window length of 3—4° and with 50% overlapping starting from one end to the other. We succeeded in defining 4 sources each in the Andaman fore arc and Back arc region, 9 such sources (moving windows) in the Sumatran Fault zone (SFZ), 9 sources in the offshore SFZ region and 7 sources in the offshore Java region. Because of the low seismicity along JFZ, it is separated into three seismogenic sources namely West Java, Central Java and East Java. The Sunda strait is considered as a single seismogenic source.The deformation rates for each of the seismogenic zones have been computed. A detailed error analysis of velocity tensors using Monte—Carlo simulation method has been carried out in order to obtain uncertainties. The eigen values and the respective eigen vectors of the velocity tensor are computed to analyze the actual deformation pattem for different zones. The results obtained have been discussed in the light of regional tectonics, and their implications in terms of geodynamics have been enumerated.ln the light of recent major earthquakes (26th December 2004 and 28th March 2005 events) and the ongoing seismic activity, we have recalculated the variation in the crustal deformation rates prior and after these earthquakes in Andaman—Sumatra region including the data up to 2005 and the significant results has been presented.ln this chapter, the down going lithosphere along the subduction zone is modeled using the free air gravity data by taking into consideration the thickness of the crustal layer, the thickness of the subducting slab, sediment thickness, presence of volcanism, the proximity of the continental crust etc. Here a systematic and detailed gravity interpretation constrained by seismicity and seismic data in the Andaman arc and the Andaman Sea region in order to delineate the crustal structure and density heterogeneities a Io nagnd across the arc and its correlation with the seismogenic behaviour is presented.

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006. Part II: Rockfall activity and talus deformation

During many lava dome-forming eruptions, persistent rockfalls and the concurrent development of a substantial talus apron around the foot of the dome are important aspects of the observed activity. An improved understanding of internal dome structure, including the shape and internal boundaries of the talus apron, is critical for determining when a lava dome is poised for a major collapse and how this collapse might ensue. We consider a period of lava dome growth at the Soufrière Hills Volcano, Montserrat, from August 2005 to May 2006, during which a 100 × 106 m3 lava dome developed that culminated in a major dome-collapse event on 20 May 2006. We use an axi-symmetrical Finite Element Method model to simulate the growth and evolution of the lava dome, including the development of the talus apron. We first test the generic behaviour of this continuum model, which has core lava and carapace/talus components. Our model describes the generation rate of talus, including its spatial and temporal variation, as well as its post-generation deformation, which is important for an improved understanding of the internal configuration and structure of the dome. We then use our model to simulate the 2005 to 2006 Soufrière Hills dome growth using measured dome volumes and extrusion rates to drive the model and generate the evolving configuration of the dome core and carapace/talus domains. The evolution of the model is compared with the observed rockfall seismicity using event counts and seismic energy parameters, which are used here as a measure of rockfall intensity and hence a first-order proxy for volumes. The range of model-derived volume increments of talus aggraded to the talus slope per recorded rockfall event, approximately 3 × 103–13 × 103 m3 per rockfall, is high with respect to estimates based on observed events. From this, it is inferred that some of the volumetric growth of the talus apron (perhaps up to 60–70%) might have occurred in the form of aseismic deformation of the talus, forced by an internal, laterally spreading core. Talus apron growth by this mechanism has not previously been identified, and this suggests that the core, hosting hot gas-rich lava, could have a greater lateral extent than previously considered.

Upper-mantle seismic structure beneath SE and Central Brazil from P- and S-wave regional traveltime tomography

We present models for the upper-mantle velocity structure beneath SE and Central Brazil using independent tomographic inversions of P- and S-wave relative arrival-time residuals (including core phases) from teleseismic earthquakes. The events were recorded by a total of 92 stations deployed through different projects, institutions and time periods during the years 1992-2004. Our results show correlations with the main tectonic structures and reveal new anomalies not yet observed in previous works. All interpretations are based on robust anomalies, which appear in the different inversions for P-and S-waves. The resolution is variable through our study volume and has been analyzed through different theoretical test inversions. High-velocity anomalies are observed in the western portion of the Sao Francisco Craton, supporting the hypothesis that this Craton was part of a major Neoproterozoic plate (San Franciscan Plate). Low-velocity anomalies beneath the Tocantins Province (mainly fold belts between the Amazon and Sao Francisco Cratons) are interpreted as due to lithospheric thinning, which is consistent with the good correlation between intraplate seismicity and low-velocity anomalies in this region. Our results show that the basement of the Parana Basin is formed by several blocks, separated by suture zones, according to model of Milani & Ramos. The slab of the Nazca Plate can be observed as a high-velocity anomaly beneath the Parana Basin, between the depths of 700 and 1200 km. Further, we confirm the low-velocity anomaly in the NE area of the Parana Basin which has been interpreted by VanDecar et al. as a fossil conduct of the Tristan da Cunha Plume related to the Parana flood basalt eruptions during the opening of the South Atlantic.

Seismic activity triggered by water wells in the Parana Basin, Brazil

Triggered seismicity is commonly associated with deep water reservoirs or injection wells where water is injected at high pressure into the reservoir rock. However, earth tremors related solely to the opening of groundwater wells are extremely rare. Here we present a clear case of seismicity induced by pore-pressure changes following the drilling of water wells that exploit a confined aquifer in the intracratonic Parana Basin of southeastern Brazil. Since 2004, shallow seismic activity, with magnitudes up to 2.9 and intensities V MM, has been observed near deep wells (120-200 m) that were drilled in early 2003 near the town of Bebedouro. The wells were drilled for irrigation purposes, cross a sandstone layer about 60-80 m thick and extract water from a confined aquifer in fractured zones between basalt flow layers. Seismic activity, mainly event swarms, has occurred yearly since 2004, mostly during the rainy season when the wells are not pumped. During the dry season when the wells are pumped almost continuously, the activity is very low. A seismographic network, installed in March 2005, has located more than 2000 microearthquakes. The events are less than 1 km deep (mostly within the 0.5 km thick basalt layer) and cover an area roughly 1.5 km x 5 km across. The seismicity generally starts in a small area and expands to larger distances with an equivalent hydraulic diffusivity ranging from 0.06 to 0.6 m(2)/s. Geophysical and geothermal logging of several wells in the area showed that water from the shallow sandstone aquifer enters the well at the top and usually forms waterfalls. The waterfalls flow down the sides of the wells and feed the confined, fractured aquifer in the basalt layer at the bottom. Two seismic areas are observed: the main area surrounds several wells that are pumped continuously during the dry season, and a second area near another well (about 10 km from the first area) that is not used for irrigation and not pumped regularly. The main area displays cyclic annual activity, but the second area does not. We explain the earthquake swarms as being triggered by pore pressure diffusion in the fractured basalt layer due to additional pressure from the newly connected surface aquifer. This reaches critically prestressed areas up to a few kilometers away from the wells. During periods of continuous pumping, the reduction of pore pressure in the confined aquifer stops the seismic activity. Our study suggests that this kind of activity may be more common than previously thought and implies that many other cases of small tremors associated with the drilling of water wells may have gone unnoticed.

Intraplate earthquake swarm in Belo Jardim, NE Brazil: reactivation of a major Neoproterozoic shear zone (Pernambuco Lineament)

Intraplate earthquakes in stable continental areas have been explained basically by reactivation of pre-existing zones of weakness, stress concentration, or both. Zones of weakness are usually identified as sites of the last major orogeny, provinces of recent alkaline intrusions, or stretched crust in ancient rifts. However, it is difficult to identify specific zones of weakness and intraplate fault zones are not always easily correlated with known geological features. Although Northeastern Brazil is one of the most seismically active areas in the country (magnitudes 5 roughly every 5 yr), with hypocentral depths shallower than similar to 10 km and seismic zones as long as 30-40 km, no clear relationship with the known surface geology can be usually established with confidence, and a clear identification of zones of weakness has not yet been possible. Here we present the first clear case of seismic activity occurring as reactivation of an old structure in Brazil: the Pernambuco Lineament, a major Neoproterozoic shear zone. The 2004 earthquake swarm of Belo Jardim (magnitudes up to 3.1) and the recurrent activities in the nearby towns of Sao Caetano and Caruaru (magnitudes up to 4.0 and 3.8), show that the Pernambuco Lineament is a weak zone. A local seismic network showed that the Belo Jardim swarm of 2004 November occurred by normal faulting on a North dipping, E-W oriented fault plane in close agreement with the E-W trending structures within the Pernambuco Lineament. The Belo Jardim activity was concentrated in a 1.5 km (E-W) by 2 km (downdip) fault area, and average depth of 4.5 km. The nearby Caruaru activity occurs as both strike-slip and normal faulting, also consistent with local structures of the Pernambuco Lineament. The focal mechanisms of Belo Jardim, Caruaru and S. Caetano, indicate E-W compressional and N-S extensional principal stresses. The NS extension of this stress field is larger than that predicted by numerical models such as those of Coblentz & Richardson and we propose that additional factors such as flexural stresses from the nearby Sergipe-Alagoas marginal basin could also affect the current stress field in the Pernambuco Lineament.

The intracratonic Caraibas-Itacarambi earthquake of December 09, 2007 (4.9 m(b)), Minas Gerais State, Brazil

On December 9, 2007, a 4.9 m(b) earthquake occurred in the middle of the Sao Francisco Craton, in a region with no known previous activity larger than 4 m(b). This event reached intensity VII MM (Modified Mercalli) causing the first fatal victim in Brazil. The activity had started in May 25, 2007 with a 3.5 magnitude event and continued for several months, motivating the deployment of a local 6-station network. A three week seismic quiescence was observed before the mainshock. Initial absolute hypocenters were calculated with best fitting velocity models and then relative locations were determined with hypoDD. The aftershock distribution indicates a 3 km long rupture for the mainshock. The fault plane solution, based on P-wave polarities and hypocentral trend, indicates a reverse faulting mechanism on a N30 degrees E striking plane dipping about 40 degrees to the SE. The rupture depth extends from about 0.3 to 1.2 km only. Despite the shallow depth of the mainshock, no surface feature could be correlated with the fault plane. Aeromagnetic data in the epicentral area show short-wavelength lineaments trending NNE-SSW to NE-SW which we interpret as faults and fractures in the craton basement beneath the surface limestone layer. We propose that the Caraibas-Itacarambi seismicity is probably associated with reactivation of these basement fractures and faults under the present E-W compressional stress field in this region of the South American Plate. (c) 2009 Elsevier B.V. All rights reserved.

The intraplate Porto dos Gauchos seismic zone in the Amazon craton - Brazil

The largest earthquake observed in the stable continental interior of the South American plate occurred in Serra do Tombador, Mato Grosso state - Brazil, on January 31,1955 with a magnitude of 6.2 m(b). Since then no other earthquake has been located near the 1955 epicentre. However, in Porto dos Gauchos, 100 km northeast of Serra do Tombador, a recurrent seismicity has been observed since 1959. Both Serra do Tombador and Porto dos Gauchos are located in the Phanerozoic Parecis basin. Two magnitude 5 earthquakes occurred in Porto dos Gauchos, in 1998 and 2005, with intensities up to VI and V, respectively. These two main shocks were followed by aftershock sequences lasting more than three years each. Local seismic stations have been deployed by the Seismological Observatory of the University of Brasilia since 1998 to study the ""Porto dos Gauchos"" seismic zone (PGSZ). A local seismic refraction survey was carried out with two explosions to help define the seismic velocity model. Both the 1998 and 2005 earthquake sequences occurred in the same WSW-ENE oriented fault zone with right-lateral strike-slip mechanisms. The epicentral zone is in the Parecis basin, near its northern border where there are buried grabens, generally trending WNW-ESE, such as the deep Mesoproterozoic Caiabis graben which lies partly beneath the Parecis basin. However, the epicentral distribution indicates that the 1998 and 2005 sequences are related to a N60 degrees E fault which probably crosses the entire Caiabis graben. The 1955 earthquake, despite the uncertainty in its epicentre, does not seem to be directly related to any buried graben either. The seismicity in the Porto dos Gauchos seismic zone, therefore, is not directly related to rifted crust. The probable direction of the maximum horizontal stress near Porto dos Gauchos is roughly E-W, consistent with other focal mechanisms further south in the Pantanal basin and Paraguay. but seems to be different from the NW-SE direction observed further north in the Amazon basin. The recurrent seismicity observed in Porto dos Gauchos, and the large 1955 earthquake nearby, make this area of the Parecis basin one of the most important seismic zones of Brazil. (C) 2009 Elsevier B.V. All rights reserved.

Basement depths in the Parecis Basin (Amazon) with receiver functions from small local earthquakes in the Porto dos Gauchos seismic zone

Receiver functions from small local earthquakes were used to determine sediment thicknesses in Porto dos Gauchos seismic zone (PGSZ), Parecis basin, Amazonian craton, Brazil. The high velocity contrast between basement and sediments (P-wave velocities of 6.1 and 3.0 km/s, respectively) favors the generation of clear P-to-S converted phases (Ps) seen in the radial component, and also S-to-P conversions (Sp) seen in the vertical component. A reference 10 velocity model determined with shallow refraction experiment in PGSZ helped to convert Ps P time differences to basement depths at 15 stations deployed for aftershocks studies. The results of receiver function integrated with the shallow refraction reveal that the basement depths in the PGSZ increases from the basin border in the north up to about 600 m depth in the south. The basement topography, however, does not vary smoothly and a basement high with a steep topography was detected near the epicentral area. A 400 m elevation difference within 1.7 km distance suggests a possible border fault of a buried graben. This feature seems to be oriented roughly WSW-ENE and could indicate basement structures related to the seismicity of the Porto dos Gauchos Seismic Zone. (C) 2011 Elsevier Ltd. All rights reserved.

Coda wave attenuation in the Parecis Basin, Amazon Craton, Brazil: sensitivity to basement depth

Small local earthquakes from two aftershock sequences in Porto dos GaA(0)chos, Amazon craton-Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor (Q (c)) of coda waves modeled usingwhere Q (0) is the coda quality factor at frequency of 1 Hz and eta is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239-252, 2008), based in the temporal attenuation coefficient, chi(f) instead of Q(f), given by the equation for the calculation of the geometrical attenuation (gamma) and effective attenuation Q (c) values have been computed at central frequencies (and band) of 1.5 (1-2), 3.0 (2-4), 6.0 (4-8), 9.0 (6-12), 12 (8-16), and 18 (12-24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin for the surrounding shield and for the whole region of Porto dos GaA(0)chos Using the independent frequency model, we found: for the cratonic zone, gamma = 0.014 s (-aEuro parts per thousand 1), nu a parts per thousand 1.12; for the basin zone with sediments of similar to 500 m, gamma = 0.031 s (-aEuro parts per thousand 1), nu a parts per thousand 1.27; and for the Parecis basin with sediments of similar to 1,000 m, gamma = 0.047 s (-aEuro parts per thousand 1), nu a parts per thousand 1.42. Analysis of the attenuation factor (Q (c)) for different values of the geometrical spreading parameter (nu) indicated that an increase of nu generally causes an increase in Q (c), both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, (in the deepest part of the basin), than in the basement, (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.

Sediment deformation in Miocene and post-Miocene strata, Northeastern Brazil: Evidence for paleoseismicity in a passive margin

Stratigraphic intervals characterized by varied and complex styles of soft-sediment deformation structures are well preserved in Miocene and Late Pleistocene to Holocene deposits of a sedimentary basin located in Northeastern Brazil. The Miocene strata, represented by the Barreiras Formation, record only brittle structures, including numerous faults and fractures with straight and high angle-dipping planes that are often filled with sands derived from overlying beds. Folds consisting of broad anticlines and synclines are also present in this unit. The late Pleistocene to Holocene deposits, named Post-Barreiras Sediments, contain an indurated sandy package with a large variety of ductile and brittle deformation structures (i.e., massive sandstones with isolated sand fragments and breccias, undulatory strata, sand dykes and diapirs, sinks and bowls, pebbly pockets, plunged sediment mixtures, fitted sand masses, cone-shaped cracks, fault grading and sedimentary enclaves). These features, confined to sharp-based stratigraphic horizons that progressively grade downward into undisturbed deposits, are related to seismic shocks of high surface-wave magnitude (i.e., Ms>5 or 6). Amalgamated seismites suggest that previously formed seismites were affected by subsequent seismic-wave propagation. Seismic waves caused by activity along one, or most likely, several tectonic structures would have propagated throughout the depositional environment, producing laterally extensive seismites. The close proximity to earthquake epicenters would have promoted pervasive re-sedimentation due to pore overpressure, resulting high volumes of massive sandstones and breccia. The similarity between deposits with correlatable strata from many other areas along the Brazilian coast allows raise the hypothesis that the seismic episodes might have affected sedimentation patterns in a large (i.e., extension of several hundreds of kilometers) geographic area. Thus, the modern seismicity recorded along Northeastern Brazil was recurrent during the Quaternary and, perhaps, also in the Pliocene. The estimated high magnitude of the seismic events and the great regional extent of the affected area demonstrate that the Brazilian coast experienced tectonic stress through the last geological episodes of its evolution, which would have favored sediment accumulation and penecontemporaneous re-sedimentation. This geological context is unexpected in a passive margin, inducing to revisit the debate on how active is a passive margin. (C) 2010 Elsevier B.V. All rights reserved.

Técnicas de suavização aplicadas à caracterização de fontes sísmicas e à análise probabilística de ameaça sísmica

A avaliação de risco sísmico, fundamental para as decisões sobre as estruturas de obras de engenharia e mitigação de perdas, envolve fundamentalmente a análise de ameaça sísmica. Calcular a ameaça sísmica é o mesmo que calcular a probabilidade de que certo nível de determinada medida de intensidade em certo local durante um certo tempo seja excedido. Dependendo da complexidade da atividade geológica essas estimativas podem ser bas- tante sofisticadas. Em locais com baixa sismicidade, como é o caso do Brasil, o pouco tempo (geológico) de observação e a pouca quantidade de informação são fontes de muitas incer- tezas e dificuldade de análise pelos métodos mais clássicos e conhecidos que geralmente consideram, através de opiniões de especialistas, determinadas zonas sísmicas. Serão discutidas algumas técnicas de suavização e seus fundamentos como métodos al- ternativos ao zoneamento, em seguida se exemplifica suas aplicações no caso brasileiro.

Sismicidade e correlação com feições geológicas: o caso do lineamento Pernambuco e seu entorno

This thesis presents and discusses the results of the various seismic areas in the State of Pernambuco, with the aim of having a vision of regional seismicity and its causes. To the papers published in journals were added two new original works submitted to international journals, dealing with seismic areas located in the counties of São Caetano, Cupira, and Agrestina. All seismic areas mentioned in this thesis are located on the Pernambuco Lineament and its surroundings (both in branches or single faults within 40 km of it). The Pernambuco Lineament is a Neoproterozoic shear zone of continental-scale that deformed the Borborema Province, and presents as branches, shear zones with NE-SW direction. The new submitted papers are from the analysis of data collected by three local networks of stations that operated in the following areas: network SO07 (seismicity in the district of Santa Luzia - São Caetano, 2007), network BM10 (data from seismic areas of Serra Verde ( Cupira) and Barra do Chata (Agrestina), in 2010), network SO10 (seismicity near the urban center of São Caetano in 2010). These data were used for determining the hypocenters and focal mechanisms in order to discuss the relationship between the seismicity and geological features of the area. The new mechanisms obtained, as well as the previously published allowed the determination of the direction of the average stress in the region. The direction of stress in the region involving the various seismic areas, now or previously studied, is quite stable and approximate EW direction (SHmax). The correlation between seismicity and geological features is observed on the lineament and north of it. In the south (Cupira and Agrestina), in seismic areas nearby shear zones NE-SW, there is no correlation and seismogenic EW normal faults are active and its motion is compatible with regional stresses. It is probable that these active faults are more recent than the Neoproterozoic, probably of the Cretaceous period, when the last great movement of the Pernambuco Lineament occurred

Estudo da atividade sísmica em São Caetano-PE em 2007

In this dissertation we studied the seismic activity in the São Caetano county, Pernambuco State, Northeastern Brazil, located near the Pernambuco Lineament. The Pernambuco Lineament is a one of Neoproterozoic continental-scale shear zones that deforms the Borborema province. The seismicity estudied occurred in a NE trending branch of Pernambuco Lineament. The seismic activity in São Caetano started in 2006 and in May 20th, 2006 a 4,0 mb earthquake hit there. This was the largest earthquake ever reported in Pernambuco State. This dissertation is the result of a campaign done in the period from Februay 1th 2007 to July 31 th 2007. In this campaign up to nine three-component digital seismographic stations were deployed and the collected data was used to determine hypocenters and focal mechanism. A total of 214 earthquakes, recorded at least by three stations, were analyzed. To determine hypocenters and time origin the HYPO71 program was used assuming a half-space model with parameters : VP (P-wave velocity) equal to 5.90 km/s and the ratio VP/VS 1.70, where VS is the S-wave velocity. The earthquakes hypocentral distribution was approximately 4 km long and agrees with the NE-SW direction of the Pernambuco Lineamento branch. Hypocentres depth range from 2 to 8 km. The composed focal mechanism was made from a group of 14 selected earthquakes. We try firstly to find the fault plane solution matching the polarity distribution at stations, using the FPFIT program. The result was 43 deg ± 15 deg for strike, 59 deg ± 9 deg for dip and -142 deg ± 15 deg for rake. We also fitted a plane using the hypocentral distribution to obtain the dip and azimuth of the hypocentral distribution. The results obtained by this fit were 58 deg for the azimuth, 55 deg for the dip and -155 deg for rake. This result shows a mechanism of a strike-slip dextral fault with a normal component. This dissertation shows, once more, that there is a good correlation between the seismic activity and geological features in the region near the Pernambuco Lineament and its NE branches

Estudo sísmico no açude Tucunduba, Senador Sá, CE

The Tucunduba Dam, is west of Fortaleza, Ceará State. The seismic monitoring of the area, with an analogical station and seven digital stations, had beginning on June 11, 1997. The digital stations, operated from June to November 1997. The data collected in the period of digital monitoring was analyzed for determination of hypocenters, focal mechanisms, and shear-wave anisotropy analysis. For determination of hypocenters, it was possible to find an active zone of nearly 1 km in length, with depth between 4.5 and 5.2 km. A 60AZ/88SE fault plane was determined using the least-squares method and hypocenters of a selected set of 16 earthquakes recorded. Focal mechanisms were determined, in the composite fault plane solution, a strike-slip fault, trending nearly E-W, was found. Single fault plane solutions were obteined to some earthquakes presented mean values of 65 (azimuth), and 80 (dip). Shear-wave anisotropy was found in the data. Polarization directions and travel time delays, between S spliting waves, were determined. It was not possible to obtain any conclusion on the cause of the observed anisotropy. It is not clear if there is correlation between seismicity and mapped faults in the area, although the directions obtained starting from the hipocentros and focal mechanism are they are consistent with directions, observed in the area, photo, topographic and fractures directions observed in the area