1,720,967 research outputs found
Direct P-Wave Seismic Noise Interferometry for Groundwater Monitoring: A Modelling Study
No full textIn this study, we monitor the depth variation of an unconfined aquifer by applying seismic noise interferometry to synthetic data modelled with a 2D finite-difference software. We consider two models with the same subsurface geological structure, but with different water table levels representing two monitoring periods. The receivers are placed at the topographic surface and collect the seismic signals generated by a source located at the bottom of the aquifer to simulate a pumping system. First, cross-correlation of seismic traces with a reference one is used to produce interferograms (i.e., virtual surveys) for both the tested models. Then, direct P-wave arrivals identified in the two interferograms are compared through the stretching technique in order to estimate the relative velocity changes (dv/v). Finally, the estimated dv/v values are related to theoretical ones obtained using a reference subsurface model to produce the water level depth in the considered monitoring period.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Applied Geophysics and Petrophysic
Seismic Noise Azimuthal Spectral Ratios to Monitor Landslide Kinematics
No full textIn this work, we explore the potential of seismic noise as a monitoring tool for landslide kinematic behavior. We monitored an earth slide with low-frequency seismometers and we collected ambient vibrations during two following stages characterized by different displacement rates and stress states of the involved media. Spectral ratios between signals collected on the sliding body and at stable locations suggest that polarization of seismic noise in the azimuthal plane is sensitive to the direction of joint sets and deformation areas created by slope accelerations and differential movements. As a consequence, the analysis of seismic noise polarization could be of valuable help for monitoring the landslide kinematics
Groundwater level monitoring tests with seismic interferometry
No full textThe objective of this work is to evaluate whether the seismic passive interferometry technique can be used to monitor undeground water variations in both unconfined and confined aquifers that present different hydrogeological characteristics. We collected ambient vibrations in two different water catchment fields where the water level has been artificially modified by activating a pre-existing pumping system. We first estimated the seismic velocity variations by means of Stretching technique and then compared the obtained curve with the water table level monitored by the pumping system. For both the analysed case studies, the dV/V curves showed a clear correlation with the water table variations. Moreover, this experiment reveals that different time windows of the correlogram may infer a different composition of the seismic wavefield. Provided that the absolute groundwater depth can be retrieved, the ambient noise interferometry could be employed to develop a continuous water monitoring system with dense networks for better management of the water resource
Monitoring ca lita landslide by means of the ambient seismic noise
No full textThis study presents the analysis of the ambient seismic noise recorded on the Ca Lita landslide. In this perspective, we coupled the cross-correlation and polarization techniques with the objective of investigating the variations of the unstable slope's characteristics at two different époques. The results of this study revealed that both methods provide useful information to characterize the dynamic conditions of the active landslide. In particular, the combination of the cross-correlation and polarization techniques allow studying the wavefield evolution over time which seems to be a reliable precursor of the landslide's occurrence. Therefore, the obtained results confirm the potential of ambient seismic noise analysis as a reliable tool to improve our capabilities of slopes failure forecasting
Lab and Field Tests of a Low-Cost 3-Component Seismometer for Shallow Passive Seismic Applications
Full text linkWe performed laboratory tests and field surveys to evaluate the performance of a low-cost 3-component seismometer, consisting of three passive electromagnetic spring-mass sensors, whose 4.5 Hz natural frequency is extended down to 0.5 Hz thanks to hyper damping. Both lab and field datasets show that the −3 dB band of the seismometer ranges approximately from 0.7 to 39 Hz, in agreement with the nominal specifications. Median magnitude frequency response curves obtained from processing field data indicate that lower corner of the −3 dB band could be extended down to 0.55 Hz and the nominal sensitivity may be overestimated. Lab results confirm the non-linear behavior of the passive spring-mass sensor expected for high-level input signals (a few to tens of mm/s) and field data confirm relative timing accuracy is ±10 ms (1 sample). We found that absolute timing of data collected with USB GPS antennas can be affected by lag as large as +0.5 s. By testing two identical units, we noticed that there could be differences around 0.5 dB (i.e., about 6%) between the components of the same unit as well as between the same component of the two units. Considering shallow passive seismic applications and mainly focusing on unstable slope monitoring, our findings show that the tested seismometer is able to identify resonance frequencies of unstable rock pillars and to generate interferograms that can be processed to estimate subsurface velocity variations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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