101 research outputs found
Non-Poissonian Earthquake Occurrence Probability through Empirical Survival Functions
Earthquake engineering normally describes earthquake activity as a Poissonian process. This approximation is simple, but not entirely satisfactory. In this paper, a method for evaluating the non-Poissonian occurrence probability of seismic events, through empirical survival probability functions, is proposed. This method takes into account the previous history of the system. It seems robust enough to be applied to scant datasets, such as the Italian historical earthquake catalog, comprising 64 events with M ≥ 6.00 since 1600. The requirements to apply this method are (1) an acceptable knowledge of the event rate, and (2) the timing of the last two events with magnitude above the required threshold. I also show that it is necessary to consider all the events available, which means that de-clustering is not acceptable. Whenever applied, the method yields a time-varying probability of occurrence in the area of interest. Real cases in Italy show that large events obviously tend to occur in periods of higher probability
The 1998-1999 Pollino (Southern Apennines, Italy) seismic crisis: tomography of a sequence
In 1998-1999 a seismic sequence occurred in the Southern Apennines, after the moderate size (mb=5.0) 9th September
1998 Pollino earthquake. It lasted about 14 months and was clearly localized to the sole north-west area
of the main shock epicenter. Its peculiarity consisted in sudden changes of activity from a series of normal faults
with Apenninic (NW-SE) trend and transfer, presumably strike slip, faults with Antiapenninic (NE-SW) and E-W
trend. The complexity of the behavior and the different orientations of the activated systems suggest that the area
acts as a hinge between the NW-SE trending Southern Apennines and the locally N-S trending Calabrian Arc
On the Long Range Clustering of Global Seismicity and its Correlation With Solar Activity: A New Perspective for Earthquake Forecasting
Large earthquakes occurring worldwide have long been recognized to be non Poisson
distributed, so involving some large scale correlation mechanism, which could be internal
or external to the Earth. We have recently demonstrated this observation can be
explained by the correlation of global seismicity with solar activity. We inferred such a
clear correlation, highly statistically significant, analyzing the ISI-GEM catalog
1996–2016, as compared to the Solar and Heliospheric Observatory satellite data,
reporting proton density and proton velocity in the same period. However, some
questions could arise that the internal correlation of global seismicity could be mainly
due to local earthquake clustering, which is a well-recognized process depending on
physical mechanisms of local stress transfer. We then apply, to the ISI-GEM catalog, a
simple and appropriate de-clustering procedure, meant to recognize and eliminate local
clustering. As a result, we again obtain a non poissonian, internally correlated catalog,
which shows the same, high level correlation with the proton density linked to solar
activity. We can hence confirm that global seismicity contains a long-range correlation,
not linked to local clustering processes, which is clearly linked to solar activity. Once we
explain in some details the proposed mechanism for such correlation, we also give
insight on how such mechanism could be used, in a near future, to help in earthquake
forecasting
Deep electrical resistivity tomography and geothermal analysis of Bradano foredeep deposits in Venosa area (Southern Italy): preliminary results
Geophysical surveys have been carried out to characterize the stratigraphical and structural setting and to better
understand the deep water circulation system in the Venosa area (Southern Italy) located in the frontal portion
of the southern Appenninic Subduction. In this area there are some deep water wells from which a water conductivity
of about 3 mS/cm and a temperature of about 35°C was measured. A deep geoelectrical tomography
with dipole-dipole array has been carried out along a profile of 10000 m and an investigation depth of about 900
m. Furthermore a broad band magnetotelluric profile consisting of six stations was performed to infer the resistivity
distribution up to some kilometres of depth. The MT profile was almost coincident with the geoelectrical
outline. The applied methods allow us to obtain a mutual control and integrated interpretation of the data. The
high resolution of the data was the key to reconstruct the structural asset of buried carbonatic horst whose top is
located at about 600 m depth. The final results coming from data wells, geothermal analysis and geophysical data,
highlighted a horst saturated with salted water and an anomalous local gradient of 60°C/km. The proposed
mechanism is that of a mixing of fossil and fresh water circulation system
Statistical properties of earthquakes clustering
International audienceOften in nature the temporal distribution of inhomogeneous stochastic point processes can be modeled as a realization of renewal Poisson processes with a variable rate. Here we investigate one of the classical examples, namely, the temporal distribution of earthquakes. We show that this process strongly departs from a Poisson statistics for both catalogue and sequence data sets. This indicate the presence of correlations in the system probably related to the stressing perturbation characterizing the seismicity in the area under analysis. As shown by this analysis, the catalogues, at variance with sequences, show common statistical properties
Integration of onshore and offshore seismic arrays to study the seismicity of the Calabrian Region: a two steps automatic procedure for the identification of the best stations geometry
We plan to deploy in the Taranto Gulf some
Ocean Bottom broadband Seismometer with Hydrophones. Our aim is to investigate the offshore seismicity of the Sibari Gulf. The seismographic network optimization consists in the identification of the optimal sites for the installation of the offshore stations, which is a crucial factor for the success of the monitoring campaign. In this paper, we propose a two steps automatic procedure for the identification of the
best stations geometry. In the first step, based on the application of a set of a priori criteria, the suitable sites to host
the ocean bottom seismic stations are identified. In the second step, the network improvement is evaluated for all the possible stations geometries by means of numerical simulation.
The application of this procedure allows us to identify the best stations geometry to be achieved in the monitoring campaign
The clustering of polarity reversals of the geomagnetic field
Often in nature the temporal distribution of inhomogeneous stochastic point
processes can be modeled as a realization of renewal Poisson processes with a
variable rate. Here we investigate one of the classical examples, namely the
temporal distribution of polarity reversals of the geomagnetic field. In spite
of the commonly used underlying hypothesis, we show that this process strongly
departs from a Poisson statistics, the origin of this failure stemming from the
presence of temporal clustering. We find that a Levy statistics is able to
reproduce paleomagnetic data, thus suggesting the presence of long-range
correlations in the underlying dynamo process.Comment: 4 pages, in press on PRL (31 march 2006?
Evaluation of site effects in the Aterno river valley (Central Italy) from aftershocks of the 2009 L'Aquila earthquake
A temporary network of 33 seismic stations was deployed in the area struck by the 6th April 2009, Mw 6.3, L’Aquila earthquake (central Italy), with the aim to investigate the site amplification within the Aterno river Valley. The seismograms of 18 earthquakes recorded by 14 of the 33 stations were used to evaluate the average horizontal to vertical spectral ratio (HVSR) for each site and the standard horizontal spectral ratio (SSR) between a site and a reference station. The obtained results have been compared to the geological and geophysical information in order to explain the resonance frequencies and the amplification levels with respect to surface geology of the valley.
The result indicate that there is no uniform pattern of amplification, due to the complex geologic setting, as the thickness and degree of cementation of the deposits is highly variable. As consequence, a large number of the local site response is observed, therefore it is very difficult to elaborate a unique model that can explain such a variability of the amplification.Published697-7154.1. Metodologie sismologiche per l'ingegneria sismicaJCR Journalpartially_ope
Evaluation of the local site effects in the upper and middle Aterno valley
In the months following the April 6th, 2009, L’Aquila earthquake, several Italian and foreign research institutions installed dozens of seismic stations to monitor more than 100 localities with the aim of studying the local site effects in the epicentral area (upper and middle Aterno valley).
The stations (accelerometers and velocimeters) have been deployed inside or very close to the inhabited areas. Among the investigated sites there are Onna, where almost the totality of the buildings collapsed, and the historic centre of L’Aquila, both towns suffering many casualties. The preliminary results for the examined sites show an extreme variability of ground motion and significant amplification for the most damaged localities.In press4.1. Metodologie sismologiche per l'ingegneria sismicaN/A or not JCRope
Low frequency characteristics of twelve large earthquakes
A global survey of the low-frequency (1-21 mHz) source characteristics of large events are studied. We are particularly interested in events unusually enriched in low-frequency and in events with a short-term precursor. We model the source time function of 12 large earthquakes using teleseismic data at low frequency. For each event we retrieve the source amplitude spectrum in the frequency range between 1 and 21 mHz with the Silver and Jordan method and the phase-shift spectrum in the frequency range between 1 and 11 mHz with the Riedesel and Jordan method. We then model the source time function by fitting the two spectra. Two of these events, the 1980 Irpinia, Italy, and the 1983 Akita-Oki, Japan, are shallow-depth complex events that took place on multiple faults. In both cases the source time function has a length of about 100 seconds. By comparison Westaway and Jackson find 45 seconds for the Irpinia event and Houston and Kanamori about 50 seconds for the Akita-Oki earthquake. The three deep events and four of the seven intermediate-depth events are fast rupturing earthquakes. A single pulse is sufficient to model the source spectra in the frequency range of our interest. Two other intermediate-depth events have slower rupturing processes, characterized by a continuous energy release lasting for about 40 seconds. The last event is the intermediate-depth 1983 Peru-Ecuador earthquake. It was first recognized as a precursive event by Jordan. We model it with a smooth rupturing process starting about 2 minutes before the high frequency origin time superimposed to an impulsive source
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