1,720,991 research outputs found
Sensitivity analysis for seismic source characteristics to probabilistic seismic hazard assessment in central Apennines (Abruzzo area).
No full textFault-based earthquake rupture forecast in Central Italy: remarks after the L’Aquila Mw 6.3 event.
No full textFiSH: MATLAB Tools to Turn Fault Data into Seismic-Hazard Models
No full textFaults have been increasingly integrated into seismic-hazard assessments. We have developed a package of MATLAB (http://www.mathworks.com/products/matlab, last accessed January 2016) tools (called FiSH), designed to help seismic-hazard modelers analyze fault data. These tools enable the derivation of expected earthquake rates, given common fault data, and allow researchers to test the consistency between the magnitude-frequency distributions (MFDs) assigned to a fault and some available observations. The basic assumption of FiSH is that the geometric and kinematic features of a fault are the expression of its seismogenic potential. Three tools have been designed to integrate the variable levels of information available: (1) the first tool allows users to convert fault geometry and slip rates into a global budget of the seismic moment released in a given time frame, taking uncertainties into account; (2) the second tool computes the recurrence parameters and associated uncertainties from historical and/or paleoseismological data; and (3) the third tool outputs time-independent or time-dependent earthquake rates for different MFD models. We present a test case to illustrate the capabilities of FiSH, on the Paganica normal fault in central Italy that ruptured during the 2009 L'Aquila earthquake sequence (mainshock Mw 6.3). The source codes are open, and we encourage users to handle the scripts, communicate with us regarding bugs, and/or suggest further improvements. Our intent is to distribute these tools in order to help researchers to pinpoint potential inconsistencies and obtain reliable fault-based seismic-hazard evaluations
Is a geometric-kinematic approach valid for estimating the expected seismicity rates in volcano-tectonic areas? Ideas and results from seismogenic sources at Mt. Etna (Italy)
Full text linkAbstract: At Mt. Etna (Sicily, Italy), the Timpe fault system is a structurally homogeneous domain characterized by a high seismic
potential; several considerations led us to assume that faults are, on average, constantly loaded in time, supporting the idea that
the faults behaviour is controlled by tectonic processes more than magma-induced, transient, stresses. The seismicity rates that
have been till now assigned to the fault sources are based on macroseismic and instrumental data; they can be considered
complete respectively above the damage threshold during the last two centuries, and for about ten years above ML=2. We are
now testing if these results are coherent with the seismicity rates that can be obtained using a geometric-kinematic approach,
widely used if only geological and structural data are available. The characterization of a magnitude-size scaling relationship in
volcanic environment is a key step for closing the loop, but the preliminary results are encouraging
Reply to "Comment on ‘Layered Seismogenic Source Model and Probabilistic Seismic-Hazard Analyses in Central Italy’ by B. Pace, L. Peruzza, G. Lavecchia, and P. Boncio" by W. Marzocchi
No full textSeismogenic sources in Central Italy: from causes to effects
No full textIn the last few years, Italy has been facing the problem of a new
generation of hazard maps, with the transition from standard probabilistic
seismic hazard estimates to time-dependent seismic hazard
assessments. These innovative methodologies require the detailed
knowledge of the parameters of individual sources (seismogenic
structures), so that some constraints on the seismicity characterisation,
based on independent geological evidence, can be introduced.
This work aims at analysing the methodological assumptions
that lead to assigning seismicity rates to a new zonation of the
Umbria-Marche region (Central Italy), and to exploring the consequences
in terms of seismic hazard assessment. We have used «seismogenic
boxes», that are the surface projection of active normal
master faults identified with structural geologic criteria as the sources,
entered directly into the hazard computation. The parameters
associated to the boxes (maximum magnitude, recurrence times,
seismicity model) have been evaluated in three ways: the first is a
quite traditional rating based on the earthquake catalogue; the other
two derive from the geometrical characteristics of the sources, using
the empirical relationships that correlate the energetic characteristics
to the shape and extension of the seismogenic boxes in different
ways. The seismicity model of the sources is usually of a Gutenberg-
Richter type, with the exception of two cases, for which we have
defined the seismicity rate considering the characteristic earthquake
model. The results are given in PGA hazard maps, following the
standard stationary approach, and refer to the 90% probability level
of non-exceedence in 50 years.
The results presented in this paper represent a sensitivity analysis
to appreciate how much all the geological markers may aid in
reducing the intrinsic uncertainties of estimates like the maximum
magnitude and recurrence time, first-order ingredients in the seismic
hazard assessment
The Role of Viscoelastic Stress Transfer in Long-Term Earthquake Cascades: Insights After the Central Italy 2016–2017 Seismic Sequence
No full textCentral Italy is characterized by a network of active faults that interact in a complex manner. Coseismic Coulomb stress changes have been invoked by several authors to explain the concentration of moderate-to-strong earthquakes in this region, but none has considered the time-dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale. Here starting from the 1915 Mw 6.9 ± 0.2 Fucino earthquake, we calculated the coseismic plus postseismic Coulomb failure stress changes (ΔCFS) due to eight moderate-to-strong earthquakes that have struck Central Italy in the last century and culminated with the 2016–2017 sequence. Results from this modeling coupled with some synthetic tests simulating normal fault earthquakes with different magnitudes allowed us to highlight the importance of postseismic processes. In particular, the viscoelastic stress transfer due to events of Mw ≥ 6.5 can modify the spatial distribution of ΔCFS on a centennial timescale and therefore trigger events at larger distances. In addition, using these results, we identified other earthquake clusters in the historical catalogue (last 618 years), which, like the 1915–2017 series, were potentially modulated by both coseismic and postseismic processes. Finally, considering our calculations combined with historical and paleoseismological data, we suggest that several faults in Central Italy may be at present close to failure
New seismotectonic evidence from the analysis of the 1976-1977 and 1977-1999 seismicity in Friuli (NE Italy)
No full textThe seismic sequence of Friuli 76: new seismotectonic aspects
No full textMost of the seismological data recorded during the first year of
the seismic sequence that struck Friuli in 1976 have been collected
and elaborated with a standard approach. A good quality data set of
291 hypocentral locations and 101 fault plane solutions has been
obtained and used for checking the seismogenic interpretation, and
some vertical cross-sections representing a quantity, the hypocentral
probability, which takes into account the errors in the locations have
been constructed. These sections show two high probability volumes:
one is gently north-dipping and the second is steeply southdipping.
The fault plane solutions have been projected, with the correct
space rotation, onto the sections, and their nodal planes are in
agreement with both elongations of the hypocentral probability volume.
These elaborations put under a different light the traditional
seismotectonic interpretation of the seismic sequence. On the basis
of new geological data, a 2D structural model for the frontal sector
of the Southalpine chain has been constructed. According to the
classical tectonic setting suggested for the Eastern Southalpine
chain, the cross-section shows a S-vergent thrust-belt arranged in an
embricate fan geometry. Nevertheless, at the Gemona latitude, at a
depth of 5-8 km, a N-vergent steep backthrusting system becomes
active producing a local thickening of rigid carbonatic rocks: part of
the cracks of the sequence seems to concentrate here
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