1,721,091 research outputs found
Seismicity of central Italy in the context of the geological history of the Umbria-Marche Apennines
No full textIn the Umbria-Marche Apennines, direct evidence of earthquakes (including data from geodetic, geophysical, historical, and paleoseismological research) is not older than 20–10 ka, but the events themselves are influenced by the whole ~250 m.y. geo- logical history of the region. For seismic sequences that have occurred in the past few decades, seismological data of increasing quality provide detailed images of the active NNW-SSE–trending normal fault systems in the upper 10 km of the crust. Major historical earthquakes and sparse paleoseismological data are also aligned parallel to the same lineaments, which clearly define the distribution of the major seismogenic sources of the region. The close connection between active tectonics and older Quater- nary faults that border a series of extensional intramountain basins is demonstrated by the fact that seismogenic and Quaternary faults are distributed along the same alignments, formed within similarly oriented stress fields, and accommodate WSW- ENE extension coherently with the active strain field. The Quaternary to present tec- tonics form part of a long-lived extensional process, active over 15–20 m.y., which is migrating eastward through time across the Italian peninsula, superimposed on the previous compressional phase that created the Apennines. The older Umbria-Marche geological history, recorded in the Triassic to Paleogene stratigraphic succession of the region, also influences the present-day distribution of seismicity. Specifically, the complex mechanical stratigraphy of the region determines the superposition of rocks with different rheological behaviors and overall thickness of the seismogenic layer. Almost all of the earthquakes occur within the sedimentary cover, with main shocks located close to the basal contact with the underlying Paleozoic basement
Hypothesis for the mechanics and seismic behaviour of low-angle normal faults: the example of the Altotiberina fault Northern Apennines
No full textWidespread mapping of low-angle normal faults in areas of former continental extension continues to prompt debate as to whether such structures may be seismically active at very low dips ( 3 (i.e. v >0.93).The short-lived attainment of P f > 3 along small fault portions,in an area characterised by large amounts of CO2,account for the microseismic activity located along the ATF,which occurs on rupture surfaces in the range of 10 10 3 km 2..PublishedJCR Journalope
Slow-to-fast transition of giant creeping rockslides modulated by undrained loading in basal shear zones
Full text linkGiant rockslides are widespread and sensitive to hydrological forcing, especially in climate change scenarios. They creep slowly for centuries and then can fail catastrophically posing major threats to society. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse remain elusive. We couple laboratory experiments on natural rockslide shear zone material and in situ observations to provide a scale-independent demonstration that short-term pore fluid pressure variations originate a full spectrum of creep styles, modulated by slip-induced undrained conditions. Shear zones respond to pore pressure increments by impulsive acceleration and dilatancy, causing spontaneous deceleration followed by sustained steady-rate creep. Increasing pore pressure results in high creep rates and eventual collapse. Laboratory experiments quantitatively capture the in situ behavior of giant rockslides and lay physically-based foundations to understand the collapse of giant rockslides
Fault architecture and deformation mechanisms in exhumed analogues of seismogenic carbonate-bearing thrusts
No full textMechanical heterogeneities in Umbria-Marche Apennines Thrusts: A field and experimental perspective
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Growth and deformation mechanisms of talc along a natural fault: a micro/nanostructural investigation
No full textThis paper documents the occurrence of large
amounts of talc within a continental normal fault. The
talc-in reaction is deformation-enhanced and occurs by the
interaction between dolostones and silica-rich hydrothermal
fluids. In the high-strain, foliated fault core, talc forms
an interconnected network of oriented (001) lamellae,
200–300 nm thick, locally associated with minor tremolite
fibres, up to 300 nm in diameter. The talc structure is
affected by several strain-induced defects, among which
(001) interlayer delamination that produces talc ‘‘sublamellae’’
down to 10–30 nm thick. Micro/nanostructural
observations definitely point to a predominant deformation
mechanism of (001) frictional sliding, further enhanced by
pervasive delamination that gives rise to an almost infinite
number of possible sliding surfaces. These effects have
fundamental implications in fault mechanics, resulting in
significant fault weakening
A large fault partially reactivated during two contiguous seismic sequences in Central Italy. The role of geometrical and frictional heterogeneities
Full text linkEarthquakes can rupture multiple fault segments as well as faults with complex geometry, or heterogeneous pre-stress and frictional properties. These observations have been documented mainly for moderate-to-large earthquakes by inverting geodetic and seismic data and by studying the influence of fault orientation and rheology within the regional stress field.
In this work we have studied the Gorzano fault, GF, a large normal fault within the active fault system of Central Italy that during the last two largest Italian seismic sequences, L'Aquila (2009) and Amatrice-Visso-Norcia (2016–2017), was reactivated via a series of 5.0 < Mw < 6.0 events. We calculated moment tensor solutions for 134 M > 3 events and evaluated their normalized slip-tendency. Merging these results with high resolution earthquake catalogs, available M > 5 earthquake slip distributions, and frictional properties characterizing the activated fault, we develop a mechanical model and discuss potential earthquake rupture scenarios.
The GF is an optimally oriented fault within the regional stress field and from, the reactivation via aftershock or mainshock slip of complementary fault portions from 2009 to 2017 indicates that the fault behaves as a single fault structure. The geometrical and mechanical heterogeneities suggest that the most likely slip behavior of GF is the reactivation of different fault portions with M > 5.0. However, due to favorable initial stress conditions, we suggest that a seismic rupture can produce the complete reactivation of the fault, resulting in a M 6.5–6.6 earthquake as documented in paleoseismological data
Frictional strength and deformation microstructures of mineralogically controlled Serpentinites
No full textSismicità profonda e geometria delle deformazioni intra-litosferiche in Italia centrale.
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