Articles de revista
http://hdl.handle.net/2117/478
2016-05-01T17:38:46ZPartial duration series distributions of the European dry spell lengths for the second half of the twentieth century
http://hdl.handle.net/2117/85539
Partial duration series distributions of the European dry spell lengths for the second half of the twentieth century
Serra de Larrocha, Carina; Lana Pons, Francisco Javier; Burgueño Rivero, August; Martínez Santafé, Maria Dolors
A spatial analysis of partial duration series, PDS, of the dry spell lengths, DSL, is applied to 267 European stations during years 1951–2000. A DSL is defined as the number of consecutive days with precipitation below 0.1 mm/day. For every station, PDS are made of DSL longer than those corresponding to 95th empirical percentile. The L-skewness and L-kurtosis diagram of the PDS distributions shows that most of the stations fit well a generalised Pareto, GP, model. Only four rain gauge records at the southeast Mediterranean coast notably depart from this model. In addition, DSL maps for return periods of 2, 5, 10, 25 and 50 years are introduced by taking into account GP parameters, which are estimated by fitting the GP distribution to empirical PDS distributions of DSL. A comparative study with those obtained in a previous paper, for the whole DSL series and the corresponding best distribution model (Pearson type III), shows that the differences of DSL for the different return periods keep within ±10 % in most of rain gauges. Moreover, a principal component analysis, PCA, is applied to the four first L-moments of the 267 rain gauges. Then, a regionalization in 11 groups is obtained after the clustering process. Finally, a regional frequency analysis is attempted, being possible to assign a GP parent distribution with different parameters to 7 out of the 11 groups.
2016-04-12T09:57:25ZSerra de Larrocha, CarinaLana Pons, Francisco JavierBurgueño Rivero, AugustMartínez Santafé, Maria DolorsA spatial analysis of partial duration series, PDS, of the dry spell lengths, DSL, is applied to 267 European stations during years 1951–2000. A DSL is defined as the number of consecutive days with precipitation below 0.1 mm/day. For every station, PDS are made of DSL longer than those corresponding to 95th empirical percentile. The L-skewness and L-kurtosis diagram of the PDS distributions shows that most of the stations fit well a generalised Pareto, GP, model. Only four rain gauge records at the southeast Mediterranean coast notably depart from this model. In addition, DSL maps for return periods of 2, 5, 10, 25 and 50 years are introduced by taking into account GP parameters, which are estimated by fitting the GP distribution to empirical PDS distributions of DSL. A comparative study with those obtained in a previous paper, for the whole DSL series and the corresponding best distribution model (Pearson type III), shows that the differences of DSL for the different return periods keep within ±10 % in most of rain gauges. Moreover, a principal component analysis, PCA, is applied to the four first L-moments of the 267 rain gauges. Then, a regionalization in 11 groups is obtained after the clustering process. Finally, a regional frequency analysis is attempted, being possible to assign a GP parent distribution with different parameters to 7 out of the 11 groups.Seismic coda attenuation after the Mw=6.2 Armenia (Colombia) earthquake of 25 January 25, 1999
http://hdl.handle.net/2117/83596
Seismic coda attenuation after the Mw=6.2 Armenia (Colombia) earthquake of 25 January 25, 1999
Ugalde, Arantza; Vargas, C A; Pujades Beneit, Lluís; Canas Torres, José Antonio
Seismic wave attenuation in the central region of the Colombian Andes is studied using coda waves. Most of the events used occurred in the region on the occasion of the Armenia 25 January 1999 earthquake. The estimation of the decay rate of coda amplitudes (called coda Q-1 or Qc-1) is performed by means of the single isotropic scattering method of Sato [1977]. The attenuation parameters Qi-1 (intrinsic absorption), Qs-1 (scattering loss), and Qt-1 (total attenuation) are also estimated using the multiple lapse time window method of Hoshiba et al. [1991]. The frequencies of interest lie between 1 and 15 Hz. Results show that scattering attenuation is predominant for the frequency bands 1.5 ± 0.5 and 13.5 ± 1.5 Hz, whereas the intrinsic absorption and scattering contribute in equal shares to total attenuation for the 3 ± 1, 5 ± 1, 7.5 ± 1.5, and 10.5 ± 1.5 Hz frequencies. A comparison among the estimated attenuation parameters indicates that Qc-1 is close to total attenuation for all the studied frequency bands. On the other hand, no evidence in support of temporal changes of Qc-1 before and after the main shock has been found. Finally, the regionalization of Qc-1 values seems to correlate well with the geotectonic characteristics of the region.
2016-03-01T11:34:12ZUgalde, ArantzaVargas, C APujades Beneit, LluísCanas Torres, José AntonioSeismic wave attenuation in the central region of the Colombian Andes is studied using coda waves. Most of the events used occurred in the region on the occasion of the Armenia 25 January 1999 earthquake. The estimation of the decay rate of coda amplitudes (called coda Q-1 or Qc-1) is performed by means of the single isotropic scattering method of Sato [1977]. The attenuation parameters Qi-1 (intrinsic absorption), Qs-1 (scattering loss), and Qt-1 (total attenuation) are also estimated using the multiple lapse time window method of Hoshiba et al. [1991]. The frequencies of interest lie between 1 and 15 Hz. Results show that scattering attenuation is predominant for the frequency bands 1.5 ± 0.5 and 13.5 ± 1.5 Hz, whereas the intrinsic absorption and scattering contribute in equal shares to total attenuation for the 3 ± 1, 5 ± 1, 7.5 ± 1.5, and 10.5 ± 1.5 Hz frequencies. A comparison among the estimated attenuation parameters indicates that Qc-1 is close to total attenuation for all the studied frequency bands. On the other hand, no evidence in support of temporal changes of Qc-1 before and after the main shock has been found. Finally, the regionalization of Qc-1 values seems to correlate well with the geotectonic characteristics of the region.Preliminary objective regionalization of the Mediterranean basin derived from surface-wave tomography
http://hdl.handle.net/2117/83388
Preliminary objective regionalization of the Mediterranean basin derived from surface-wave tomography
Martínez Santafé, Maria Dolors; Lana Pons, Francisco Javier; Badal, Jose; Canas Torres, José Antonio; Pujades Beneit, Lluís
An objective regionalization of the Mediterranean basin is derived from a tomographic study based on the fundamental mode of Rayleigh waves. The database is formed by seismic wavetrains recorded at very-broadband stations belonging to MedNet and other cooperative stations, located in the Mediterranean area. The data treatment consists of application of spectral filtering techniques aimed to determine path-averaged group velocities, computation of local group velocity maps for some periods and classification of the studied area in several homogeneous regions according to Principal Component Analysis (PCA) and Average Linkage (AL) algorithms. Finally, the group velocity dispersion curves representing each homogeneous region are compared and possible correlation between these regions and seismotectonic and structural characteristics are discussed.
2016-02-24T13:30:04ZMartínez Santafé, Maria DolorsLana Pons, Francisco JavierBadal, JoseCanas Torres, José AntonioPujades Beneit, LluísAn objective regionalization of the Mediterranean basin is derived from a tomographic study based on the fundamental mode of Rayleigh waves. The database is formed by seismic wavetrains recorded at very-broadband stations belonging to MedNet and other cooperative stations, located in the Mediterranean area. The data treatment consists of application of spectral filtering techniques aimed to determine path-averaged group velocities, computation of local group velocity maps for some periods and classification of the studied area in several homogeneous regions according to Principal Component Analysis (PCA) and Average Linkage (AL) algorithms. Finally, the group velocity dispersion curves representing each homogeneous region are compared and possible correlation between these regions and seismotectonic and structural characteristics are discussed.Statistical distribution of elapsed times and distances of seismic events: the case of the Southern Spain seismic catalogue
http://hdl.handle.net/2117/83233
Statistical distribution of elapsed times and distances of seismic events: the case of the Southern Spain seismic catalogue
Martínez Santafé, Maria Dolors; Lana Pons, Francisco Javier; Posadas, A M; Pujades Beneit, Lluís
Several empiric cumulative distributions of elapsed times and distances between seismic events occurred in the Southern Iberian Peninsula from 1985 to 2000 (data extracted from the seismic catalogue of the Andalusian Institute of Geophysics) are investigated. Elapsed times and distances between consecutive seismic events of the whole
catalogue, taking into account threshold magnitudes of 2.5, 3.0, 3.5 and 4.0, and of five seismic crises, without distinguishing magnitudes, are investigated. Additionally, the series of distances and elapsed times from the main event to every aftershock are also analysed for the five seismic crises. Even though a power law is sometimes a satisfactory model for the cumulative distribution of elapsed times and distances between seismic events, in some cases a fit with a Weibull distribution for elapsed times performs better. It is worth of mention that, in the case of the seismic crises, the fit achieved by the power law is sometimes improved when it is combined with a logarithmic law. The results derived might be a contribution to a better representation of the seismic activity by means of models that could be based on random-walk processes.
2016-02-22T11:49:01ZMartínez Santafé, Maria DolorsLana Pons, Francisco JavierPosadas, A MPujades Beneit, LluísSeveral empiric cumulative distributions of elapsed times and distances between seismic events occurred in the Southern Iberian Peninsula from 1985 to 2000 (data extracted from the seismic catalogue of the Andalusian Institute of Geophysics) are investigated. Elapsed times and distances between consecutive seismic events of the whole
catalogue, taking into account threshold magnitudes of 2.5, 3.0, 3.5 and 4.0, and of five seismic crises, without distinguishing magnitudes, are investigated. Additionally, the series of distances and elapsed times from the main event to every aftershock are also analysed for the five seismic crises. Even though a power law is sometimes a satisfactory model for the cumulative distribution of elapsed times and distances between seismic events, in some cases a fit with a Weibull distribution for elapsed times performs better. It is worth of mention that, in the case of the seismic crises, the fit achieved by the power law is sometimes improved when it is combined with a logarithmic law. The results derived might be a contribution to a better representation of the seismic activity by means of models that could be based on random-walk processes.Urban non-engineered buildings in Merida, Venezuela. Seismic performance and proposals for retrofit and for new construction
http://hdl.handle.net/2117/78991
Urban non-engineered buildings in Merida, Venezuela. Seismic performance and proposals for retrofit and for new construction
López Almansa, Francisco; Pujades Beneit, Lluís; Castillo, A.
The seismic risk for an informal settlement in Mérida (“La Milagrosa”) is qualitatively assessed and retrofit strategies are
proposed. The buildings in the settlement are thoroughly examined and four prototype buildings are chosen to represent
the vast majority of houses in “La Milagrosa”. The structural behavior of these buildings under gravity loads and seismic
actions is deeply analyzed; this study shows that the prototype buildings are unsafe for gravity loads, and that the seismic
demands largely exceed their capacity. Based on these conclusions, feasible retrofit strategies are proposed, together with
draft recommendations for new similar constructions. Earlier quantitative estimative appraisals show that the proposed
seismic strengthening measures can be very effective in reducing fatalities and economical losses, and are significantly
more cost-efficient than reconstruction-based approaches. These conclusions might be generalized to many non-engineered
urban areas in earthquake-prone regions of the developing world.
2015-11-10T19:03:43ZLópez Almansa, FranciscoPujades Beneit, LluísCastillo, A.The seismic risk for an informal settlement in Mérida (“La Milagrosa”) is qualitatively assessed and retrofit strategies are
proposed. The buildings in the settlement are thoroughly examined and four prototype buildings are chosen to represent
the vast majority of houses in “La Milagrosa”. The structural behavior of these buildings under gravity loads and seismic
actions is deeply analyzed; this study shows that the prototype buildings are unsafe for gravity loads, and that the seismic
demands largely exceed their capacity. Based on these conclusions, feasible retrofit strategies are proposed, together with
draft recommendations for new similar constructions. Earlier quantitative estimative appraisals show that the proposed
seismic strengthening measures can be very effective in reducing fatalities and economical losses, and are significantly
more cost-efficient than reconstruction-based approaches. These conclusions might be generalized to many non-engineered
urban areas in earthquake-prone regions of the developing world.Fractal structure and predictive strategy of the daily extreme temperature residuals at Fabra Observatory (NE Spain, years 1917-2005)
http://hdl.handle.net/2117/78472
Fractal structure and predictive strategy of the daily extreme temperature residuals at Fabra Observatory (NE Spain, years 1917-2005)
Lana Pons, Francisco Javier; Burgueño, August; Serra de Larrocha, Carina; Martínez Santafé, Maria Dolors
A compilation of daily extreme temperatures recorded at the Fabra Observatory (Catalonia, NE Spain) since 1917 up to 2005 has permitted an exhaustive analysis of the fractal behaviour of the daily extreme temperature residuals, DTR, defined as the difference between the observed daily extreme temperature and the daily average value. The lacunarity characterises the lag distribution on the residual series for several thresholds. Hurst, H, and Hausdorff, Ha, exponents, together with the exponent beta of the decaying power law, describing the evolution of power spectral density with frequency, permit to characterise the persistence, antipersistence or randomness of the residual series. The self-affine character of DTR series is verified, and additionally, they are simulated by means of fractional Gaussian noise, fGn. The reconstruction theorem leads to the quantification of the complexity (correlation dimension, mu*, and Kolmogorov entropy, kappa.) and predictive instability (Lyapunov exponents, lambda, and Kaplan-Yorke dimension, D-KY) of the residual series. All fractal parameters are computed for consecutive and independent segments of 5-year lengths. This strategy permits to obtain a high enough number of fractal parameter samples to estimate time trends, including their statistical significance. Comparisons are made between results of predictive algorithms based on fGn models and an autoregressive autoregressive integrated moving average (ARIMA) process, with the latter leading to slightly better results than the former. Several dynamic atmospheric mechanisms and local effects, such as local topography and vicinity to the Mediterranean coast, are proposed to explain the complex and instable predictability of DTR series. The memory of the physical system (Kolmogorov entropy) would be attributed to the interaction with the Mediterranean Sea.
2015-10-29T10:50:38ZLana Pons, Francisco JavierBurgueño, AugustSerra de Larrocha, CarinaMartínez Santafé, Maria DolorsA compilation of daily extreme temperatures recorded at the Fabra Observatory (Catalonia, NE Spain) since 1917 up to 2005 has permitted an exhaustive analysis of the fractal behaviour of the daily extreme temperature residuals, DTR, defined as the difference between the observed daily extreme temperature and the daily average value. The lacunarity characterises the lag distribution on the residual series for several thresholds. Hurst, H, and Hausdorff, Ha, exponents, together with the exponent beta of the decaying power law, describing the evolution of power spectral density with frequency, permit to characterise the persistence, antipersistence or randomness of the residual series. The self-affine character of DTR series is verified, and additionally, they are simulated by means of fractional Gaussian noise, fGn. The reconstruction theorem leads to the quantification of the complexity (correlation dimension, mu*, and Kolmogorov entropy, kappa.) and predictive instability (Lyapunov exponents, lambda, and Kaplan-Yorke dimension, D-KY) of the residual series. All fractal parameters are computed for consecutive and independent segments of 5-year lengths. This strategy permits to obtain a high enough number of fractal parameter samples to estimate time trends, including their statistical significance. Comparisons are made between results of predictive algorithms based on fGn models and an autoregressive autoregressive integrated moving average (ARIMA) process, with the latter leading to slightly better results than the former. Several dynamic atmospheric mechanisms and local effects, such as local topography and vicinity to the Mediterranean coast, are proposed to explain the complex and instable predictability of DTR series. The memory of the physical system (Kolmogorov entropy) would be attributed to the interaction with the Mediterranean Sea.Aftershock sequences of three seismic crises at southern California, USA, simulated by a cellular automata model based on self-organized criticality
http://hdl.handle.net/2117/78319
Aftershock sequences of three seismic crises at southern California, USA, simulated by a cellular automata model based on self-organized criticality
Monterrubio Velasco, Marisol; Lana Pons, Francisco Javier; Martínez Santafé, Maria Dolors
Several properties of aftershock series related to the main shocks of Landers, Northridge and Hector Mine (southern California, USA) are reproduced by the Dynamic Fiber Bundle Model, DFBM. Optimum values for the three parameters governing DFBM are determined by searching for the best agreement of real aftershock series properties and those of synthetic sequences generated by this model. The analysis of the model parameter values provides details on the underlying physical mechanism of the aftershock sequence generation. First, the ratio of seismic energy radiated as seismic waves and transferred as stress-strain to adjacent faults; second, the degree of stress heterogeneity reproducing the complex behavior of real aftershock series. Additionally, the results of simulations support the coexistence of two types of relaxation processes. One of them is associated with the well-known modified Omori's (MO) law, which involves elapsed times between consecutive aftershocks monotonically increasing; the other is manifested by episodes of sudden stress release, with inter-event times much shorter than those predicted by MO law. These episodes are assumed to be a consequence of the complex distribution of tectonic stresses and fault geometry. The first process is associated to events designed as leading aftershocks, LA. The second process generates series of events which are designed as cascades, CA. It is worth of mention that several properties concerning CAs can be reasonably related to critical changes on stress field along the simulation process.
2015-10-27T11:12:24ZMonterrubio Velasco, MarisolLana Pons, Francisco JavierMartínez Santafé, Maria DolorsSeveral properties of aftershock series related to the main shocks of Landers, Northridge and Hector Mine (southern California, USA) are reproduced by the Dynamic Fiber Bundle Model, DFBM. Optimum values for the three parameters governing DFBM are determined by searching for the best agreement of real aftershock series properties and those of synthetic sequences generated by this model. The analysis of the model parameter values provides details on the underlying physical mechanism of the aftershock sequence generation. First, the ratio of seismic energy radiated as seismic waves and transferred as stress-strain to adjacent faults; second, the degree of stress heterogeneity reproducing the complex behavior of real aftershock series. Additionally, the results of simulations support the coexistence of two types of relaxation processes. One of them is associated with the well-known modified Omori's (MO) law, which involves elapsed times between consecutive aftershocks monotonically increasing; the other is manifested by episodes of sudden stress release, with inter-event times much shorter than those predicted by MO law. These episodes are assumed to be a consequence of the complex distribution of tectonic stresses and fault geometry. The first process is associated to events designed as leading aftershocks, LA. The second process generates series of events which are designed as cascades, CA. It is worth of mention that several properties concerning CAs can be reasonably related to critical changes on stress field along the simulation process.Evaluation of the GPR frequency spectra in asphalt pavement assessment
http://hdl.handle.net/2117/76524
Evaluation of the GPR frequency spectra in asphalt pavement assessment
Pedret Rodés, Josep; Pérez Gracia, María de la Vega; Martínez Reguero, Adriana Haydée
Ground penetrating radar (GPR) is frequently used in pavement assessments, mainly using the evaluation of wave travel times. However, GPR data provide further information that could be used in order to determine the inner conditions and characteristics about materials. In this paper, the possible analysis of the frequency spectrum of GPR signals is analysed and discussed. Several tests were carried out in a portion of a highway in two different stages of its service life. Results highlight the relationship between the shape of the spectrum and the frequency signature with the structure and conditions of the pavement.
2015-08-26T11:49:36ZPedret Rodés, JosepPérez Gracia, María de la VegaMartínez Reguero, Adriana HaydéeGround penetrating radar (GPR) is frequently used in pavement assessments, mainly using the evaluation of wave travel times. However, GPR data provide further information that could be used in order to determine the inner conditions and characteristics about materials. In this paper, the possible analysis of the frequency spectrum of GPR signals is analysed and discussed. Several tests were carried out in a portion of a highway in two different stages of its service life. Results highlight the relationship between the shape of the spectrum and the frequency signature with the structure and conditions of the pavement.Application of particle motion technique to structural modal identification of heritage buildings
http://hdl.handle.net/2117/28420
Application of particle motion technique to structural modal identification of heritage buildings
Caselles Magallón, Josep Oriol; Martínez, Guillermo; Clapes Boixader, Jaime; Roca Fabregat, Pedro; Pérez Gracia, María de la Vega
Determining the behavior of a structure estimated by means of finite elements analysis requires not only an in-depth knowledge of its geometry and dynamic properties but also an experimental validation to corroborate the adequacy of the characteristics of the structure. Most of the current structural identification techniques are based on linear methods that call for many measurement points
and/or a relative simple structure. Complex structures are somewhat still an unexplored field due to the difficulties with the finite element method and the experimental corroboration of its results. This study presents the use of particle motion computation applied to each structural vibration mode to improve the identification of its dynamic properties, and its application to the Gothic Cathedral of Palma de Majorca (Spain).
2015-06-26T08:12:41ZCaselles Magallón, Josep OriolMartínez, GuillermoClapes Boixader, JaimeRoca Fabregat, PedroPérez Gracia, María de la VegaDetermining the behavior of a structure estimated by means of finite elements analysis requires not only an in-depth knowledge of its geometry and dynamic properties but also an experimental validation to corroborate the adequacy of the characteristics of the structure. Most of the current structural identification techniques are based on linear methods that call for many measurement points
and/or a relative simple structure. Complex structures are somewhat still an unexplored field due to the difficulties with the finite element method and the experimental corroboration of its results. This study presents the use of particle motion computation applied to each structural vibration mode to improve the identification of its dynamic properties, and its application to the Gothic Cathedral of Palma de Majorca (Spain).Nanozonation in dense cities : testing a combined methodology in Barcelona City (Spain)
http://hdl.handle.net/2117/28414
Nanozonation in dense cities : testing a combined methodology in Barcelona City (Spain)
Salinas Naval, Víctor; Caselles Magallón, Josep Oriol; Pérez Gracia, María de la Vega; Santos Assunçao, Sonia; Clapes Boixader, Jaime; Pujades Beneit, Lluís; González Drigo, José Ramón; Canas Torres, José Antonio; Martínez Sánchez, Joan
Microzonation is widely used in seismic risk evaluations to define the predominant period values, which are usually associated with extended areas of a few hundred meters. However, the representative values corresponding to these areas are obtained from few measurements in each area. Thereby, results are accurate only in the case of depth-dependent soils. However, not detected narrow and sharp lateral changes in soil are potentially the cause of imprecision and could be a source of specific errors. This article aims to present several tests conducted in order to emphasise the importance of accurate selection of points, to underscore the necessity of more precise and detailed evaluations, and to suggest a possible methodology to select the most appropriate data acquisition points. Results highlight the need to divide microzonation areas into smaller zones for a precise evaluation in locations where sudden changes in soil characteristics exist. Therefore, in such sites the requirement of nanozonation appears; defining zones with the same soil response. Distance between vibration measurements could be the main problem for nanozonation; data acquisition in areas with irregular geology can be time consuming when a precise analysis is required. In the most complicated environments or in dense cities, it could even be unfeasible. Consequently, it is necessary to establish a functional methodology to adequately distribute the measurement points throughout the area. On this occasion, three sites in Barcelona city were studied. This city is surrounded by mountains at NW, W, and S, and by the Mediterranean Sea at N and E. As a consequence, the shallow geology is characterized by many paleochannels and streams that are currently buried. These geological structures most likely affect the soil response maps, including nanozonation.
2015-06-26T06:19:38ZSalinas Naval, VíctorCaselles Magallón, Josep OriolPérez Gracia, María de la VegaSantos Assunçao, SoniaClapes Boixader, JaimePujades Beneit, LluísGonzález Drigo, José RamónCanas Torres, José AntonioMartínez Sánchez, JoanMicrozonation is widely used in seismic risk evaluations to define the predominant period values, which are usually associated with extended areas of a few hundred meters. However, the representative values corresponding to these areas are obtained from few measurements in each area. Thereby, results are accurate only in the case of depth-dependent soils. However, not detected narrow and sharp lateral changes in soil are potentially the cause of imprecision and could be a source of specific errors. This article aims to present several tests conducted in order to emphasise the importance of accurate selection of points, to underscore the necessity of more precise and detailed evaluations, and to suggest a possible methodology to select the most appropriate data acquisition points. Results highlight the need to divide microzonation areas into smaller zones for a precise evaluation in locations where sudden changes in soil characteristics exist. Therefore, in such sites the requirement of nanozonation appears; defining zones with the same soil response. Distance between vibration measurements could be the main problem for nanozonation; data acquisition in areas with irregular geology can be time consuming when a precise analysis is required. In the most complicated environments or in dense cities, it could even be unfeasible. Consequently, it is necessary to establish a functional methodology to adequately distribute the measurement points throughout the area. On this occasion, three sites in Barcelona city were studied. This city is surrounded by mountains at NW, W, and S, and by the Mediterranean Sea at N and E. As a consequence, the shallow geology is characterized by many paleochannels and streams that are currently buried. These geological structures most likely affect the soil response maps, including nanozonation.