274 research outputs found
Raised marine terraces in the Northern Calabrian Arc (Southern Italy): a ~ 600 kyr-long geological record of regional uplift
The Sibari Plain in the Northeastern Calabrian Arc displays a well-developed suite of marine terraces. This paper
deals with i) the identification and correlation of the terraces; ii) their age assignment and a tentative reconstruction
of the uplift history of the area; iii) the relationships between terraces and major faults in the study area and between uplift in the Plain and pattern of Quaternary uplift throughout the Calabrian Arc. Identifying wavecut platforms and inner-edge fragments over a linear extent of ~ 100 km was achieved by photo interpretation, 1:25 000 scale map analyses and field survey. Morphological evidence led to the correlation of the identified fragments into five complete strandlines (numbered #1 to #5 lowest to highest), at elevations ranging from 60 m to ~ 650 m.
Analysis of two parameters of the emerged platform-cliff systems, namely the platform-cliff ratio and the dissection percentage, further testifies that the two lowest terraces are strongly correlative. A 130 kyr AAR age of in situ fossil samples of Glycymeris collected at 114 m elevation within the deposit of Terrace #2 indicates a key correlation of T#2 with MIS 5.5 (the peak of the last interglacial, 124 kyr), i.e. an uplift rate of ~ 0.98 mm/yr for this strandline. The other four terraces have been tentatively associated with MIS 5.3, 7, 9 and 15. Geological observations
independent of geochronological evidence provide consistent lower age boundaries for the terraces and supply further constraints to this interpretation. Investigating the relations between setting of the terraces and location of major tectonic structures in the region is suggestive of no recent activity of two previously recognized faults, the «Sangineto Line» and the «Corigliano-Rossano Line». Instead, some limited anomalies that affect the terraces are tentatively associated with the activity of the Castrovillari Fault. Therefore, sustained uplift has been the long-term dominant process of tectonic deformation in the study area over the past 124 kyr, possibly 600 kyr. Rates and history
of uplift in the Sibari Plain are largely comparable with those observed in the whole Calabrian Arc, confirming that the uplift driving mechanism is deep-seated and closely connected to the Tyrrhenian subduction as already pointed out by several authors. Despite a dearth of Holocene raised paleoshorelines, it is suggested that similarly to what was observed only few tens of kilometres north and south of the Sibari Plain, the Late Pleistocene rise is still active today and that without Holocene uplift the Plain should have been far less developed and attractive for human settlement
Geology versus myth: the Holocene evolution of the Sybaris Plain
Historical accounts handed down the legend of the ancient Sybaris, defeated and submerged by the Crotoniates who
diverted the River Crati on the town. This paper deals with the reconstruction of the Holocene evolution of the
Sybaris Plain, through a number of geological and geomorphological observations. In particular, I found i) ∼1 m/yr
horizontal coastal progradation rate since Greek times (2.4 kyr BP), possibly since Neolithic (7.0 kyr BP), mainly
originated by active alluvial deposition and subordinately by regional uplift; ii) evidence of striking modifications
in the surface hydrography of the plain during the last 2.5 kyr, with repeated fluvial captures of the Crati and
Coscile rivers testified by ancient historians and geographers, recent maps and archeological accounts. In addition,
datings and archeological information from 7 sites in the plain provided iii) ∼0.6 mm/yr mean uplift rate during the
past 11.2 kyr, that confirms the substantial continuity of this regional process with upper Pleistocene; iv) local, high
value of subsidence (0.5÷2.0 mm/yr) affecting the Sybaris main archeological area. Subsidence is not recorded before
4000 years BP and is caused by deposition of fine, highly compressible sediments at the transition between
marine and continental environment; v) no evidence of a fault-induced contribution to the subsidence, whilst there
is the grounded possibility that man-induced subsidence prevailed in the last century; vi) widespread active continental
deposition in the area. Local rates of deposition are relatively lower (1.5 mm/yr) at sites where subsidence
is not observed, and range between 2.5 mm/yr and 3.5 mm/yr in the main archeological area. There is also evidence
of a clear decrease of the sedimentation following the Mid-Holocene flex of the fast trend of sea level rise. These
data suggest that the Holocene evolution of the Sybaris Plain is due to the progressive eastward migration of the
land-sea boundary, probably active since the Mid-Holocene (∼7.0 ka). Repeated floodings, regional uplift and relative
sea-level changes produced the eastward expansion of the plain, subsidence locally slowed it down. Therefore,
geology first allowed the creation of Sybaris, then caused its destruction
Clues for a relation between rotational effects induced by the Mw6.3 2009 L’Aquila (Central Italy) earthquake and site and source effects
The Mw6.3 2009 L’Aquila earthquake produced an impressive
number of rotational effects on vertically organized objects such as
chimneys, pillars, capitals and gravestones. We present the dataset
of such effects, that consists of 105 observations at 37 different sites
and represents a compendium of earthquake-induced istances of
rotational effects that is unprecedented in recent times. We find that
the absolute majority of the reported effects was observed in the
epicentral zone and that most of the observations are located where
the MCS intensity is between 7 and 8-9. The evident asymmetry in
the distribution of the rotational effects resembles the southeastward
directivity of the macroseismic effects and highlights a
significant convergence between rotations and damage. Finally, we
perform some qualitative analyses to recognize and evaluate which
*Manuscript
Click here to download Manuscript: revised_text.doc
2
geological and seismological parameters can be significant
contributors to local rotations. We find that surface geology and
amplification of the seismic motion at each reported location strongly
influence the occurrence and the nature of the earthquake-induced
rotational effects. Conversely, the contribution of the pattern of slip
distribution on the fault plane plays only a secondary role in
enhancing the rotational motion at each site
Clues to the identification of a seismogenic source from environmental effects. The case of the 1905 Calabria (southern Italy) earthquake
The 8 September 1905 Calabria (Southern Italy) earthquake belongs to a peculiar family of highly destructive (I0=XI) seismic events, occurred at the dawning of the instrumental seismology, for which the location, geometry and size of the causative source are still substantially unconstrained. During the century elapsed since the earthquake, previous Authors identified three different epicenters that are more than 50 km apart and proposed magnitudes ranging from M≤6.2 to M=7.9. Even larger uncertainties were found when the geometry of the earthquake source was estimated. In this study, we constrain the magnitude, location and kinematics of the 1905 earthquake through the analysis of the remarkable environmental effects produced by the event (117 reviewed observations at 73 different localities throughout Calabria). The data used in our analysis include ground effects (landslides, rock falls and lateral spreads) and hydrological changes (streamflow variations, liquefaction, rise of water temperature and turbidity). To better define the magnitude of the event we use a number of empirical relations between seismic source parameters and distribution of ground effects and hydrological changes. In order to provide constraints to the location of the event and to the geometry of the source, we reproduce the coseismic static strain associated with different possible 1905 causative faults and compare its pattern to the documented streamflow changes. From the analysis of the seismically-induced environmental changes we find that: 1) the 1905 earthquake had a minimum magnitude M=6.7; 2) the event occurred in an offshore area west of the epicenters proposed by the historical seismic Catalogs; 3) it most likely occurred along a 100° N oriented normal fault with a left-lateral component, consistently with the seismotectonic setting of the area
I terrazzi marini nell'area di Capo Vaticano (Arco Calabro): solo un record di sollevamento regionale o anche di deformazione cosismica?
In questo lavoro presentiamo uno studio di dettaglio dei terrazzi nell’area di Capo Vaticano (Calabria tirrenica), insieme ad una revisione del piano quotato del terremoto del 1905.
Il campo macrosismico rivisitato conferma che le massime intensità sono state raggiunte in un’area estesa fra Vibo Valentia e Capo Vaticano per un evento di magnitudo M=6.8±0.2; la più probabile struttura sismogenetica responsabile dell’evento è una faglia di dimensioni 36x14 km e direzione 80° (faglia “macrosismica”).
Lo studio dei terrazzi ha invece messo in evidenza che l’area in studio è in sollevamento attivo da almeno 700.000 anni, che tale processo è in lieve ma progressivo aumento nel tempo, con tassi negli ultimi 124.000 leggermente inferiori a ~1 mm/anno, e che a settentrione di Capo Vaticano i terrazzi sono chiaramente tiltati verso Nord. Inoltre, le variazioni di quota osservate nelle paleolinee di riva a cavallo di una struttura tettonica ad andamento ONO-ESE indicano che tale struttura (faglia “geologica”) è attiva da almeno 330.000 anni, con tassi verticali medi che variano negli ultimi 215.000 anni fra 0,12 e 0,16 mm/anno.
Per verificare quanto ognuna di queste due strutture fosse congruente con gli elementi geologici, topografici e macrosismici a disposizione, abbiamo calcolato il campo di deformazione indotto in superficie dall’azione della faglia “macrosismica” rispetto a quello della faglia “geologica”. Il confronto qualitativo fra le deformazioni aspettate evidenzia una buona congruenza nella risposta della faglia “geologica” e rafforza l’ipotesi che a tale struttura possa essere associato l’evento del 1905, anche alla luce di recenti localizzazioni ipocentrali ottenute da inversione di registrazioni storiche.
The area of Capo Vaticano in western Calabria displays a well-developed suite of marine terraces. This same region was hit in 1905 by one of the strongest – and still poorly cleared – earthquakes of the instrumental era.
Our revision of the intensity map of the event confirms the location of the most damaged area (between Vibo Valentia and Capo Vaticano) and indicates that the most likely source is a N80°-trending, 36(L) x 14(W) km structure with a macroseismic magnitude M=6.8±0.2.
A detailed study of the marine terraces shows that sustained uplift has been the long-term dominant process of tectonic deformation in this area over the past 700 kyr, with an average long-term uplift rate slightly less than 1.0 mm/yr, and that terraces are tilted northward. Moreover, the four lowest paleoshorelines are displaced by a WNW-ESE trending fault, that indicates that the fault is active in the last 215,000 years with mean vertical slip rates of 0.12-0.16 mm/yr.
Finally, we perform a qualitative comparison between the set of geological, topographic and macroseismic data available and the expected deformation fileds induced by each of the afore-mentioned faults. It is therefore suggested that the good response of the WNW-trending fault strenghtens the hypothesis of this structure as the source of the 1905 earthquake
Rotational Effects associated with ground motion during the Mw 6.3 2009 L’Aquila (Central Italy) Earthquake
The Mw 6.3 2009 L’Aquila (Central Italy) earthquake produced more than one hundred rotational effects on chimneys, pillars, capitals and gravestones. In this paper we focus on the 37 objects that can be more reliably considered as representative of pure rotational ground motion, and find a relation between the distribution of the observed rotations, the epicentral distance, the macroseismic intensities and the directivity effects that characterize the L’Aquila event. We also find sound relationships between the type of observed rotations and the geophysical, geotechnical and geomorphological characteristics of the site of observation. In downtown L’Aquila we find 1) a remarkable convergence between distribution of the rotations and of the damage; 2) 100% of the rotations occurred at sites characterized by high factors of amplification and poor geological setting; 3) the ground rotations are not strongly dependent on topographic effects. Finally, from quantitative analyses of GPS data we find that the effect of the seismic arrival on an individual vertical object retrieved rotated is an overall rotation with a substantially unpredictable directio
Performances of the Italian Seismic Network, 1985-2002: the hidden thing
Abstract
Seismic data users and people managing a seismic network take a great interest in the
potentiality of the data, with the difference that the former look at stability, the latter at
improvements. In this work, we measure the performances of the Italian Telemetered Seismic
Network in the years 1985-2002 by defining basic significant parameters and studying their
evolution during those years. Then, we deal with the geological methods used to characterise
or to plan seismic station deployments in a few cases. Last, we define the gain of the network
as the percentage of well-located earthquakes with respect to the total recorded earthquakes.
By analysing the distribution of non-located (“missed”) earthquakes, we suggest possible
actions to take in order to increase the gain.
Results show that completeness magnitude is 2.4 in the average over the analysed period,
and it can be as low as 2.2 when we consider non-located earthquakes as well. Parameters
such as the minimum recording distance and the RMS of the location decrease with time,
reflecting improvements in the location quality. Methods for geologic and seismological
characterisation of a possible station site also resulted to be effective. Finally, we represent
the number of missed earthquakes at each station, showing that nine stations control more
than 50% of all missed earthquakes, and suggesting areas in Italy where the network might be
easily improved
- …