Search results for "seismic"

Tomography Application to Complex Seismic Data of the Tjornes Fracture Zone (Iceland)

2014

The Tjornes Fracture Zone (TFZ) is an active seismic zone in Northeast Iceland. It plays a key role to understand the geodynamic movement and location of tectonic plates. However the seismic experiment can not be performed close to earthquake sources, because sources are mainly located in the Greenland Sea. The unusual geological structure of TFZ and the limited conditions of an experiment lead to significant deviations between real observations and the values that are calculated in accordance with theoretical models. Consequently, there is a loss of adequacy and stability of tomography systems. Outcomes of the method, which takes into account this problem, are analyzed in the present chapt…

Diagnostics for nonparametric estimation in space-time seismic processes

2010

In this paper we propose a nonparametric method, based on locally variable bandwidths kernel estimators, to describe the space-time variation of seismic activity of a region of Southern California. The flexible estimation approach is introduced together with a diagnostic method for space-time point process, based on the interpretation of some second-order statistics, to analyze the dependence structure of observed data and suggest directions for fit improvement. In this paper we review a diagnostic method for space-time point processes based on the interpretation of the transformed version of some second-order statistics. The method is useful to analyze dependence structures of observed dat…

Polarization and high resolution parametric spectral analysis applied to the seismic signals recorded on the Marsili submarine volcano

2008

Quantification de l’ablation d’un bassin versant marno-calcaire alpin durant le Petit Age Glaciaire par l’étude d’un système lacustre (cas du lac du «…

2002

Measurements of present-day erosion may give heterogeneous results according to the methods used. This article proposes an approach to erosion during the Little Ice Age by the quantitative analysis of detritical materials trapped in a dammed lake. This infill is recognized through two drillings, and these specific observations are supplemented by a seismic reflexion survey which provided a reliable estimate of the geometry of the lake infill. The sedimentary production is calculated from three pieces of data: (1) the surface of the drainage area, (2) duration of the lake system activity and (3) the volume of trapped sediments. From the three determined variables, we propose a detritical product…

Propagation of errors due to incorrect positions of sources and detectors in wave-field tomography

2004

Tomographic data processed by 2D inversion programs can produce fairly large distortions due to incorrect source and/or detector positions. This problem is very serious in high-frequency electromagnetic tomography (GPR), due to the dimensions of the transmitter and receiver antennae. The errors can even be larger when coupled antennae are used (receiver and transmitter inside the same box) whose positions are not clearly known. Similar errors can be involved in seismic tomography, for instance when the mechanical connection between transducers and sample is defective. In this paper the problem has been studied using synthetic data which were calculated for different acquisition geometries. …

Including Covariates in the ETAS Model Triggered Seismicity

2020

The paper proposes a stochastic process that improves the assessment of seismic events in space and time, considering a contagion model (branching process) within a regression-like framework to take covariates into account. The proposed approach develops the Forward Likelihood for prediction (FLP) method for estimating the ETAS model, including covariates in the model specification of the epidemic component. A simulation study is carried out for analysing the misspecification model effect under several scenarios. Also an application to the Italian catalogue is reported, together with the reference to the developed R package.

Artificial Ground Motions and Nonlinear Response of RC Structures

2020

The selection of seismic inputs for nonlinear dynamic analysis is widely debated, mainly focusing on the advantages and disadvantages provided by the choice of natural, simulated, or artificial records. This work proves the differences in the structural behavior of RC buildings when using accelerograms with different levels of stationarity. Initially, nonlinear response under three sets of accelerograms equivalent in terms of pseudo acceleration spectrum is evaluated and compared. Then, the results of incremental dynamic analyses are compared by the statistical point of view considering different levels of irregularity for the reference structure.

Assessment of the Reliability of the SPAC Method in Urban Areas

2015

We have carried out several long-term measures of seismic noise with triangular arrays of broad-band seismic sensors, to investigate the reliability of the SPAC method in urban areas. We investigate the stationary and anisotropy of the microtremor wave field. We have found that the anisotropy of the microtremor wave field can be evaluated analyzing the HVNSR as function the azimuth. Furthermore, we showed as strong anisotropies in the microtremors are often observable in particular at high frequencies (> 1 Hz). We have verified as microtremors can be difficult to considered as ergodic processes, and for this reason time averaging, also even over a long periods of time, cannot replace an app…

On the stationarity of the horizontal to vertical noise spectral ratio

2015

The Horizontal to Vertical Noise Spectral Ratio (HVNSR) method is nowadays widely used to estimate the resonance frequencies of geological structures. In the HVNSR method, seismic noise is considered as a stationary stochastic process. However, especially in industrialized/urbanized area, this is a very strict assumption seldom occurred. Several sources of noise can generate non stationary and anisotropic microtremor fields. To investigate the stationarity of microtremor, we have carried out several long-term measures of seismic noise with broad-band seismic sensors, in areas where the main source of anthropogenic noise is well known. The signals acquired have been analyzed both in frequenc…

Wavelet correlation filter for wide-angle seismic data

2002

A new filtering technique for single-fold wide-angle reflection/refraction seismic data is presented. The technique is based on the wavelet decomposition of a set of adjacent traces followed by coherence analysis. The filtering procedure consists of three steps. In the first, a wavelet decomposition of traces into different detail levels is performed. In the second, the coherence attributes for each level are evaluated by calculating cross-correlation functions of detail portions contained in a space–time moving window. Finally, the filtered traces are obtained as a weighted reconstruction of the trace details. Each weight is obtained from the coherence-attributes distribution estimated in …