Search results for " seismicity"
showing 10 items of 49 documents
Monochromatic Long-Period Seismicity Prior to the 2012 Earthquake Swarm at Little Sitkin Volcano, Alaska
2021
Detection of the earliest stages of unrest is one of the most challenging and yet critically needed aspects of volcano monitoring. We investigate a sequence of five unusual long-period (LP) earthquakes that occurred in the days prior to the onset of a months-long volcano-tectonic (VT) earthquake swarm beneath Little Sitkin volcano in the Aleutian Islands during late 2012. The long-period earthquakes had two distinctive characteristics: their signals were dominated by a monochromatic spectral peak at approximately 0.57 Hz and they had impulsive P and S-wave arrivals on a seismometer located on Amchitka Island 80 km to the southeast of the volcano. In each case, the monochromatic earthquakes …
The Palermo (Sicily) seismic cluster of September 2002, in the seismotectonic framework of the Tyrrhenian Sea-Sicily border area
2009
The northern coast of Sicily and its offshore area represent a hinge zone between a sector of the Tyrrhenian Basin, characterized by the strongest crustal thinning, and the sector of the Sicilian belt which has emerged. This hinge zone is part of a wider W-E trending right-lateral shear zone, which has been affecting the Maghrebian Chain units since the Pliocene. Seismological and structural data have been used to evaluate the seismotectonic behavior of the area investigated here. Seismological analysis was performed on a data set of about 2100 seismic events which occurred between January 1988 and October 2002 in the Southern Tyrrhenian Sea. This paper focuses…
ETAS Space–Time Modeling of Chile Triggered Seismicity Using Covariates: Some Preliminary Results
2021
Chilean seismic activity is one of the strongest in the world. As already shown in previous papers, seismic activity can be usefully described by a space–time branching process, such as the ETAS (Epidemic Type Aftershock Sequences) model, which is a semiparametric model with a large time-scale component for the background seismicity and a small time-scale component for the triggered seismicity. The use of covariates can improve the description of triggered seismicity in the ETAS model, so in this paper, we study the Chilean seismicity separately for the North and South area, using some GPS-related data observed together with ordinary catalog data. Our results show evidence that the use of s…
Interaction between seismicity and deformation on different time scales in volcanic areas: Campi Flegrei and Stromboli
2019
We study oscillations recorded at Stromboli and Campi Flegrei by different sensors: seismometers, strainmeters and tiltmeters. We examine both the high-frequency (>0.5 Hz) portion of the spectrum and very long period signals up to tidal scales. In this context, seismicity and deformation are investigated on different time scales (from minutes to days/years) in order to identify the basic elements of their interaction, whose understanding should provide new insights on the predictive models. In this work, the strict relation of tides and volcanic processes is shown. At Stromboli, indeed the transition from the stationary phase to the non-stationary phase seems to have a tidal precu…
Significance of earthquake-related anomalies in fluids of Val D'Agri (southern Italy)
2001
Geochemical investigations carried out at the Campano–Lucano Apennine (Southern Italy) revealed the presence of fluids composed of a mixing between components of shallow and deep origin, where mantle-derived helium is also detectable. For the gas phase, the deep component is represented by both CH4 and CO2-rich gases, while the shallow one is N2-dominated. Coinciding with the 3 April 1996 ML=4.9 earthquake, the CH4-rich component mixed with the shallow, N2-dominated one at the Tramutola well (Val d’Agri), displaying wide variations in mixing proportions. In contrast, no significant modifications occurred in relation to the 1998 ML=5.5 event. According to the collected data, an earthquake-re…
Seismotectonics in the North-Western Sicily Continental Margin: implications for Geohazard assessment
2017
Active processes in the Northern Sicily Continental Margin (NSCM) have been analysed to produce a seismotectonic map, in order to obtain a useful tool for the assessment of the seismic hazard of the sea-land region. The seismotectonic map is composed of overlapping layers that represent the distribution of different features, such as lithostratigraphy, tectonic elements, seismicity, heat flow, gravimetry, magnetometry, Moho depth, horizontal and vertical movements, submarine landslides, fluid emissions, outlining the mutual relationship and the active structures. The NSCM is suitable to test this approach because it’s located in a transitional area between the Sicilian-Maghrebian chain to t…
Active north-vergent thrusting in the northern Sicily continental margin in the frame of the quaternary evolution of the Sicilian collisional system
2021
Abstract A three-stage evolution has characterized the Sicilian Fold and Thrust Belt (SFTB) during the last 15 My: two main thin-skinned shortening events involving mainly Meso-Cenozoic carbonate units, followed by thick-skinned thrusting involving Plio-Pleistocene deposits in the frontal area as well as the crystalline basement in the inner and deeper sector of the chain. We investigated the northern Sicily continental margin, by using differently-penetrative seismic reflection data and new field surveys, which revealed, both offshore and onshore, north-vergent compressional structures that affected the tectonic edifice during Quaternary time. These structures, correlated with the kinemati…
Mixed Non-Parametric and Parametric Estimation Techniques in R Package etasFLP for Earthquakes’ Description
2017
etasFLP is an R package which fits an epidemic type aftershock sequence (ETAS) model to an earthquake catalog; non-parametric background seismicity can be estimated through a forward predictive likelihood approach, while parametric components of triggered seismicity are estimated through maximum likelihood; estimation steps are alternated until convergence is obtained and for each event the probability of being a background event is estimated. The package includes options which allow its wide use. Methods for plot, summary and profile are defined for the main output class object. The paper provides examples of the package's use with description of the underlying R and Fortran routines.
Hydrothermal pressure-temperature control on CO2 emissions and seismicity at Campi Flegrei (Italy)
2021
Fluids supplied by stored magma at depth are causal factors of volcanic unrest, as they can cause pressurization/heating of hydrothermal systems. However, evidence for links between hydrothermal pressurization, CO2 emission and volcano seismicity have remained elusive. Here, we use recent (2010−2020) observations at Campi Flegrei caldera (CFc) to show hydrothermal pressure, gas emission and seismicity at CFc share common source areas and well-matching temporal evolutions. We interpret the recent escalation in seismicity and surface gas emissions as caused by pressure-temperature increase at the top of a vertically elongated (0.3–2 km deep) gas front. Using mass (steam) balance consideration…
Windowed Etas Models With Application To The Chilean Seismic Catalogs
2015
Abstract The seismicity in Chile is estimated using an ETAS (Epidemic Type Aftershock sequences) space–time point process through a semi-parametric technique to account for the estimation of parametric and nonparametric components simultaneously. The two components account for triggered and background seismicity respectively, and are estimated by alternating a ML estimation for the parametric part and a forward predictive likelihood technique for the nonparametric one. Given the geographic and seismological characteristics of Chile, the sensitivity of the technique with respect to different geographical areas is examined in overlapping successive windows with varying latitude. A different b…