1,721,105 research outputs found
Earthquake occurrence models in the short and long term for the Italian seismicity
No full textThe ETES, ERS and LTST models have been submitted to the CSEP (Collaboratory
for the study of Earthquake Predictability) forecast testing for Italy (ETH-Zurich) and locked down
to test their validity on real data in a forward way starting from August 1, 2009.This work describes three earthquake occurrence models, two in the short-(24 hour) and one in
long-term (5- and 10 year), applied to the whole Italian territory in order to assess the occurrence
probability of future (M≥5.0) earthquakes. The first model for short-term forecasts is a purely
stochastic Epidemic Type Earthquake Sequence model (ETES). The second short-term epidemic
forecast is based on a model physically constrained by the application of Dieterich rate-state
constitutive law to the earthquake clustering (ERS). The third forecast is based on a Long Term
model that considers the perturbation of earthquake probability for interacting faults by static
Coulomb stress changes (LTST). These models have been submitted to the CSEP (Collaboratory
for the study of Earthquake Predictability) forecast testing for Italy (ETH-Zurich) and locked down
to test their validity on real data in a forward way starting from August 1, 2009.CSEP testing center for ItalySubmitted1-233.1. Fisica dei terremotiJCR Journalope
An algorithm for doble difference joint hypocenter determination: application to the 2002 Molise (Central Italy) earthquake sequence
No full textWe have developed an original computer code for double difference hypocenter
determination including an independent routine for the cross-correlation estimate of the time
difference between two waveform segments, relative to different events recorded by the same
stations. This computer code has been tested relocating a set of 26 events recorded by the seismic
stations of the telemetered Italian national network operated by the INGV. The hypocentral
solutions so obtained are characterized by standard deviations typically of the order of magnitude
of 50 m, in comparison with the errors of a few kilometers characterizing the performance of the
INGV bulletins. The proximity of hypocenters in several groups of events closely separated in time
shows that our relocations are the result of an accurate analysis, rather than that of random errors.
The method developed in this study is suitable for rapid and accurate hypocentral determination
carried out by a permanent sparsely distributed network of stations, even before that mobile
equipment installed in the area affected by new seismic activity allows higher resolution locations.JCR Journalope
Matlab software for the analysis of seismic waves recorded by three-element arrays
No full textWe develop and implement an algorithm for inverting three-element array data on a Matlab platform. The algorithm allows reliable estimation of back-azimuth and apparent velocity from seismic records under low signal-to-noise conditions. We start with a cubic-spline interpolation of the waveforms and determine the differences between arrival times at pairs of array elements. The time differences are directly computed from cross-correlation functions. The advantages of this technique are: (a) manual picking of the onset of each arrival is not necessary at each array element; (b) interpolation makes it possible to estimate time differences at a higher resolution than the sampling rate of the digital waveforms; (c) consistency among three independent determinations provides a reliability check; and (d) the value of apparent velocity indicates the nature of the recorded wavelet and physically checks the results. The algorithm was tested on data collected by a tri-partite array (with an aperture of ~250 m) deployed in 1998 by the National Data Center of Israel, during a field experiment in southern Israel, 20 km southwest of the Dead Sea. The data include shallow explosions and natural earthquakes under both high and low signal-to-noise conditions. The procedure developed in this study is considered suitable for searching of small aftershocks subsequent to an underground explosion, in the context of On-Site Inspections according to the Comprehensive Nuclear-Test-Ban Treaty (CTBT).In press3.8. Geofisica per l'ambienteJCR Journalope
Short-range forecasting model in Italy
No full textA stochastic triggering (epidemic) model
incorporating short-term clustering was fitted
to the instrumental earthquake catalog of Italy
for event with local magnitudes 2.6 and greater
to optimize its ability to retrospectively forecast
33 target events of magnitude 5.0 and greater that
occurred in the period 1990–2006.A stochastic triggering (epidemic) model
incorporating short-term clustering was fitted
to the instrumental earthquake catalog of Italy
for event with local magnitudes 2.6 and greater
to optimize its ability to retrospectively forecast
33 target events of magnitude 5.0 and greater that
occurred in the period 1990–2006. To obtain an
unbiased evaluation of the information value of
the model, forecasts of each event use parameter
values obtained from data up to the end of the
year preceding the target event. The results of the
test are given in terms of the probability gain of
the epidemic-type aftershock sequence (ETAS)
model relative to a time-invariant Poisson model
for each of the 33 target events. These probability
gains range from 0.93 to 32000, with ten of the target
events yielding a probability gain of at least 10.
As the forecasting capability of the ETAS model
is based on seismic activity recorded prior to the
target earthquakes, the highest probability gains
are associated with the occurrence of secondary mainshocks during seismic sequences. However,
in nine of these cases, the largest mainshock of
the sequence was marked by a probability gain
larger than 50, having been preceded by previous
smaller magnitude earthquakes. The overall evaluation
of the performance of the epidemic model
has been carried out by means of four popular
statistical criteria: the relative operating characteristic
diagram, the R score, the probability gain,
and the log-likelihood ratio. These tests confirm
the superior performance of the method with respect
to a spatially varying, time-invariant Poisson
model. Nevertheless, this method is characterized
by a high false alarm rate, which would make its
application in real circumstances problematic.This work was partially supported
for the years 2005–2007 by the Project S2—Assessing
the seismogenic potential and the probability of strong
earthquakes in Italy (Slejko and Valensise coord.)—S2
Project has benefited from funding provided by the Italian
Presidenza del Consiglio dei Ministri—Dipartimento della
Protezione Civile (DPC). Scientific papers funded by DPC
do not represent its official opinion and policies. The
authors are grateful to the Editors, Laura Peruzza, and
David Perkins, and to two anonymous reviewers, for their
comments and suggestions that contributed to a significant
improvement of the paper.Published9-263.1. Fisica dei terremotiJCR Journalreserve
A rate-state model for aftershocks triggered by dislocation on a rectangular fault: a review and new insights
No full textWe compute the static displacement, stress, strain and the Coulomb failure stress produced in
an elastic medium by a finite size rectangular fault after its dislocation with uniform stress drop
but a non uniform dislocation on the source. The time-dependent rate of triggered earthquakes
is estimated by a rate-state model applied to a uniformly distributed population of faults whose
equilibrium is perturbated by a stress change caused only by the first dislocation. The rate of
triggered events in our simulations is exponentially proportional to the shear stress change, but
the time at which the maximum rate begins to decrease is variable from fractions of hour for
positive stress changes of the order of some MPa, up to more than a year for smaller stress
changes. As a consequence, the final number of triggered events is proportional to the shear
stress change. The model predicts that the total number of events triggered on a plane containing
the fault is proportional to the 2/3 power of the seismic moment. Indeed, the total
number of aftershocks produced on the fault plane scales in magnitude, M, as 10M. Including
the negative contribution of the stress drop inside the source, we observe that the number of
events inhibited on the fault is, at long term, nearly identical to the number of those induced
outside, representing a sort of conservative natural rule. Considering its behavior in time, our
model does not completely match the popular Omori law; in fact it has been shown that the
seismicity induced closely to the fault edges is intense but of short duration, while that expected
at large distances (up to some tens times the fault dimensions) exhibits a much slower decay.Published1259-1273JCR Journalope
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
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