Attenuation characteristics of seismic ground motion in the 1995 Hyogoken-Nambu earthquake

The recorded ground motion of the 1995 Hyogoken-nambu earthquake are used to study the attenuation characteristics of near-field ground motion. The peak ground accelerations and velocities are compared to the attenuation relations derived from far-field data recorded from 76 JMA stations. Although the near-field data used include non-JMA stations, the peak ground motion data havve a relatively good fit to the far-field attenuation relations. Saturation of the peak ground motion near the fault was examined by introducing a distance saturation parameter to the attenuation relations and performing a non-linear least squares analysis on the Hyogoken-nambu earthquake data. Since the data used are from a single event, the magnitude independence of the PGA cannot be determined. However, the fit of the recorded data in the near-field is improved. The resulting attenuation relations for the Hyogoken-nambu earthquake are given by: log10 0.322+0.477Mj-log10(r+3.8)-0.00144r+0.00311h. log10PGV -1.576+0.628Mj-log10(r+7.0)-0.00130r+0.00222h where PGA(cm/s2) and PGV (cm/s) are the largest of the peak accelerations and velocities from two horizontals components, Mj is the JMA magnitude, r is the closest distance to the fault rupture, and h is the depth of the point in the fault rupture where r is measured. (AU)

Hysteretic models for cyclic behavior of deteriorating inelastic structures

The purpose of this report is to provide a theoretical basis for a range of rule-based piecewise linear hysteretic models (in Section 2), as well as differential equation-based smooth hysteric models (in Section 3). Also to provide a sound and formal reasoning for the basis of the above-mentionedmodels that are founded on the fundamentals of mechanics and the interrelationship between these various types of models (in Section 4). This research fits in with two more of MCEERïs missions: outreach to the professional user community; and to extend the fundamental knowledge base to enable a high level of computational simulation to be conducted

Africa-Eurasia kinematics in the Mediterranean : An alternative hypothesis

The post-Tortonian deformation pattern in the Central Mediterranean can be satisfactorily interpreted in the framework of a SSW-NNE to SW-NE convergence between Africa and Eurasia (Mantovani et al., 1992 and this volume). However, this hypothesis is not in line with the most widely used Africa-Eurasia kinematic models, based on the analysis of North Atlantic kinematic data, which predict a SE-NW to S-N motion between Africa and Eurasia. Here it is argued that these models might be not reliable, since are based on the assumption that Eurasia is a unique coherent block from the Atlantic ridges to the Pacific trenches, which can hardly account for the significant intraplate deformation occurring in Western Europe, and in particular, in the Iberian Peninsula and surrounding regions. This evidence would imply that the kinematic data observed along the Mid-Atlantic ridges just North of Azores and those on the Azores-Gibraltar belt cannot be used to constrain the relative motions of Eurasia with respect to North America and Africa respectively. It is shown by quantitative computations that the remaining kinematic data in the North Atlantic can be reconciled, within errors, with a NNE to NEward motion of Africa with respect to Eurasia, in the Central Mediterranean. This kinematic pattern does not involve any significant difficulty in explaining the tectonic pattern in the other sectors of the Mediterranean area and along the boundaries of the Eurasian continent

The tectonic regimes along the convergent border of the Aegean Arc from the late Miocene to the present : Southern Peloponnesus as an example

Field analysis of fault kinematics demonstrates changes in the tectonic regime on the Aegean Arc border. During the Pliocene-Early Pleistocene extensional tectonics were active; extension trended radial retreat of a high angle-dipping slab which decreased the magnitude of the push on the Aegean lithosphere. During the Mid-Late Pleistocene compression has been active in the lowlands and extension in the highlands of the arc border, the extensional directions being orthogonal to the compressional directions and parallel to the arc border. It is suggested that this has resulted from a push of a low angle-dipping slab on the Aegean lithosphere. These stress patterns are interpreted at a large wavelenght as a result of a balance between the boundary forces acting along the arc border and the body forces due to the thickening of the crust. Rotations of the paleostress directions due to rigid rotations of the material and perturbations of the stress trajectories are also considered in analysis the paleostress maps of the Aegean

Tyrrhenian Basin and Apennines : Kinematic evolution and related dynamic constraints

The post-Oligocene kinematic evolution of the central Mediterranean region is synthetically described. The proposed reconstruction is based on a comparative study of tectonically-controlled sedimentary sequences and of coeval tectonic features in areas experiencing stretching (Algero-Provencal Basin, Tyrrhenian Basin) and shortening (Appenines). The derived step by step palinspastic reconstruction at Langhian times states a number of constraints for the geodynamic processes that affected the area during Neogene and Quaternary times. Both continental (often thinned) and oceanic lithosphere were involved in subduction processes. The former prevailed in the northern sector, while both oceanic and continental lithosphere were present in the southern area. The long duration of the subduction processes in the southern sectors may be related to the existence of large portions of sinking oceanic lithosphere which dragged down intervening portions of continental lithosphere

P-wave teleseismic tomography : Contribution to the delineation of the upper mantle structure of Italy

In recent years seismic tomography has emerged as a powerful tool to study the crustal and upper mantle structure and to constrain kinematic models of tectonic evolution in regions of plate margins. We applied a well established and robust inversion technique ("ACH" technique) to compute a three-dimensional model of the compressional wave velocity in the lithosphere-asthenosphere system beneath Italy. We used a high quality dataset of about 4700 selected arrival times of teleseismic events digitally recorded at the National Seismic Network. The results show a substantial improvement, in terms of variance reduction, model resolution, and standard errors, with respect to similar inversions (same technique, same starting model, same station and event distribution) performed with data derived directly from bulletins. Our interpretation of the computed velocity model, mainly based on the observation of regions of positive velocity anomalies (up to about 5 percent), substantiates the hypothesis that a complex subduction system has developed beneath the Italian peninsula. The most prominent high velocity regions are the Alps, the northern Apennines, and the southern Tyrrhenian sea. Low velocity regions are found in the upper mantle of the Adriatic microplate and beneath Sicily. Some of the high velocity regions are also characterized by intermediate and deep seismicity, whereas some others are apparently aseismic (like the Alps), mainly depending on the age of subduction. In the southern Tyrrhenian sea, where the subduction is still active, a high velocity zone as deep as about 500 km is associated with the well known seismicity related to the Wadati-Benioff zone. In the northwestern portion of the Apennines, a strong high velocity anomaly is observed in the upper 200-250 km. We found that well located subcrustal earthquakes as deep as 90 km occur in the same region, gently dipping to the southwest. We propose that they delineate the upper portion of the Adriatic lithosphere sinking beneath the Tuscany-Corsica block, whose deepest part is depicted by the high velocity anomaly. The high velocity becomes weaker and deeper moving southeastward along the Apenninic chain, suggesting that the subducted slab in no continuous at depth. The complex geometry of the subducted lithosphere may be due to the stretching of the downgoing slab in response to arc migration, and/or to an irregular geometry of the two converging plates

Geological and seismological evidence of strike-slip displacement along the E-W Adriatic-Central Apennine belt

New geological, geophysical and seismological data produced in the last decade allow an improved definition of the kinematics of the Tyrrhenian Sea-central Apennines-Adriatic Sea system. The integration of these different types of dataset outlines a complex E-W deformational belt running from the Adriatic Sea, at Gargano latitudes, to the Latium-Abruzzi Platform domain (central Apennines). Its possible prosecution in the Tyrrhenian Sea is discussed. This belt has its own seismotectonic characteristics, and divides the Apennines into two zones with different seismotectonic behaviour. All these data were integrated into a multidisciplinary model that results in the introduction of a strike-slip displacement sometimes in Pliocene to recent times along the central Apennines-Adriatic Sea E-W belt. This relative motion can take for the strike-slip block tectonics observed in the central Apennines as well as for the uplift of Gargano and Tremiti Islands areas, including their seismicity. The displacement is related to a differing behaviour of the chain, foreland systems across this bend and can be justified either by assuming a partially active sinking of the southern Adriatic lithosphere or a slower sinking processes in the northern Adriatic one

Stable fault sliding and earthquake nucleation

The process of earthquake nucleation is studied assuming that faults are rupture surfaces on which sliding is controlled by friction. Earthquakes are assumed to arise through an instability of frictional sliding. Empirical slip laws indicate that, under constant ambient conditions, friction depends on time, slip rate and slip history. Regular stick-slip behaviour is induced by velocity weakening, a negative dependence of friction on slip rate. Velocity weakening is introduced into a model for a propagating Somigliana dislocation under slowly increasing ambient shear stress. The instability occurs when the rate at which friction decreases becomes greater than the rate at which the applied stress must increase to produce an advance of fault slip. The possibility that this condition is fullfilled depends on the velocity dependence and on the spatial distribution of friction on the fault. A critical nucleation width of the dislocation is associated with the instability and is controlled by the friction distribution, which determines the size of the initial slipping patch. Depending on the stress drop and the characteristics slip distance, the critical nucleation width may be greater for small earthquakes than for large earthquakes, with respect to the initial slipping patch

Análisis de estructuras indeterminadas de sección variable, (marcos de varios pisos con retícula ortogonal) por el método de distribución de momentos

Estudio de los orígenes de la Distribución de Momentos y sus aplicaciones a casos especiales, donde se puede obtener una convergencia de un ciclo, a través de la preparación de soluciones directas por medio de fórmulas algebráicas de los momentos finales, debidos a cargas verticales para estructuras de un piso sin movimiento lateral. Se resuelve al final del texto un problema típico que aparece en la referencia #1, páginas 201 y 202 (viga continua de sección variable parabólica - tres luces).(AU)

Les tremblements de terre au Mexique en 1985 leurs repercussions psychologiques et l'intervention des psychanalystes / 1985 Earthquake in Mexico: Its psychological impacts

Starting with a real event, the Mexican earthquake of 1985, this article describes a certain number of practices of Mexican psychoanalysts and their theoretical reflections which grew out of the experience of helping a disasterstruck population during a crisis period

Amenazas volcánicas en Costa Rica : Una estrategia de prevención

Costa Rica al igual que otros países centroamericanos, presenta un claro carácter volcánico, lo que le ha brindado un importante atractivo turístico, así como un componente de amenaza. Este artículo presenta una metodología de estudio para analizar, evaluar y minimizar los riesgos en la zona basada en varios enfoques complementarios: a) datos históricos de erupciones de el Arenal, b)datos históricos de erupciones en volcanes considerados similares c)análisis de simulación de la dispersión de contaminantes químicos y su efecto en la salud, d)valoración toxicológica y epidemiológica del impacto de los contaminantes y e)influencia de los factores meteorológicos en la distribución y concentración de los contaminantes. Los resultados se basan principalmente en la simulación numérica de la dispersión de dióxido de azufre utilizando el modelo de Pluma Gaussiana para una fuente de emisión y velocidad de vientos constantes, para lo que se utilizarón las distintas condiciones meteorológicas que se presentan en la zona. Los estudios muestran que en una erupción intensa, aún a treinta kilómetros del Arenal, dependiendo de las condiciones meteorológicas, podría darse una concentración de dióxido de azufre superior a la inmediatamente peligrosa para la vida y salud, equivalente a 266 mg/m3. La metodología utilizada muestra que la simulación numérica es un recurso de bajo costo, y con un potencial de beneficio relativo muy alto, por lo que se recomienda que Costa Rica y los demás países de la Región, inviertan en minimizar el riesgo recurriendo a ésta, tomando en consideración la influencia de las condiciones atmosféricas y su afectación por la topografía. La simulación de dispersión de contaminantes puede utilizarse para la planificación territorial y para la planificación, prevención y resolución médico-asistencial. Igualmente la simulación numérica puede utilizarse para determinar los puntos de monitoreo atmosférico tomando en cuanta la escala de los fenómenos meteorológicos (microescala, mesoescala, escala sinoptica y global). Es imprescindible, para lograr una solución global al problema de la mitigación, la cooperación entre diversas instituciones y pobladores para monitorear los volcanes y sus efectos en forma idónea (medición de gases atmosféricos, monitoreo geológico, vigilancia epidemiológica de la salud, monitoreo de efectos ambientales y mediciones meteorológicas). Este marco intersectorial y participativo permite una mejor utilización de recursos por su efecto sinérgico. (AU)