La scala Mercalli

Quando vi erano pochi strumenti per registrare e misurare i terremoti, alla fine dell'Ottocento, i sismologi stimavano la grandezza di un terremoto osservandone gli effetti, come ad esempio il crollo di un comignolo o la caduta di un ponte. Il sismologo Giuseppe Mercalli fu tra i primi a classificare i terremoti in base ai loro effetti definendo una scala dell’intensità o degli effetti Macrosismici

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

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

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

Le fonti sul terremoto del 10 settembre 1881 in provincia di Chieti: revisione critica e nuove conoscenze

Si e' provveduto ad una rivalutazione della distribuzione del danno legato al terremoto del 10 settembre 1881 nella provincia di Chieti, mediante una rilettura delle fonti e l'acquisizione di nuova documentazione d'archivio

Macroseismology: the lessons learnt from the 1997/98 Colfiorito seismic sequence

The seismic sequence of the Umbria-Marche Apennines was a dramatic moment for the population involved; at the same time, it provided a unique occasion for the Italian scientific community and for the national civil protection to assess their respective abilities in understanding and managing the event. Furthermore, macroseismology (including historical seismology) has knowingly confronted important methodological problems, such as the procedures for assigning macroseismic intensity, the use of the macroseismic scale, the impossibility of distinguishing the effects of earthquakes following closely in both space and time, within such a complex sequence. Starting from the analysis of the problems that were faced after the 1997/98 Umbria- Marche earthquakes, as during the following seismic crises over the last 10 years, we propose some considerations on the lessons we have learnt from that seismic sequence

The 1762 October 6 earthquake in the Middle Aterno Valley (L'Aquila, Central Italy): new constraints and new insights

The effort for reducing the uncertainties in the location and size of historical earthquakes, even moderate-size ones, is not a peripheral issue, as it plays a major role in the distribution of earthquake recurrence times that can affect the maps of seismic hazard of a territory. The L‟Aquila area (Abruzzo, Central Italy) struck by the April 6, 2009 Mw 6.3 seismic event is a typical example of an earthquake-prone region the location of whose historical seismicity needs to be better located. Thanks to a large body of geological, seismological and geodetic evidence the deep source of the 2009 mainshock has been imaged as a ~15 km-long, NW-trending, SWdipping, almost pure normal fault coinciding with the Paganica Fault accepted_Manuscript Click here to download Manuscript: accepted_source_file.doc 2 System at the surface (Fig. 1). Conversely, very few papers have addressed so far the issue of reconstructing the seismic history of the Paganica Fault, charting the relationships between this fault and the adjacent ones, and finding out the causative source for each of the earthquakes listed in the Italian earthquake Catalog (CPTI Working Group, 2004; Rovida et al., 2011)

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

The intensity attenuation of Colfiorito and other strong earthquakes: the viewpoint of forecasters and data gatherers

This article has been originated by thoughts on previous analyses related to the proba- bilistic treatment of the macroseismic attenuation, from which it turns out that in Italian territory the intensity decay I varies greatly from one region to another, depending on many factors, some of them not easily measurable. By applying a clustering algorithm we classified some macroseismic fields drawn from the Italian felt report database in three classes. Earthquakes into the same class constituted the input of a two-step procedure for the Bayesian estimation of the probability distribution of I at any distance from the epicenter, conditioned on I0, where I is considered an integer, random variable, following a binomial distribution. The estimated distributions were validated by forecasting the macroseismic field of the Colfiorito earthquake. In this article we deal with the issues left open by those statistical analyses by following two ways: on one hand we test the procedure by forecasting the macroseismic field of other strong earthquakes recorded in Italy during the last century and, on the other hand, we ask the reasons of peculiarities in the results to experts in other fields. The article is hence an introductory work, an example of the possibility and of the need of exchange of knowledge

The revision of the 30 October 1901 earthquake, west of Lake Garda (northern Italy)

On 24 November 2004 an earthquake (Mw 5.0) struck the west side of Lake Garda (northern Italy), producing moderate but widespread damage. It provided the opportunity of reviewing the seismicity of all the area over the past two centuries, whose former most significant event is the 30 October 1901 earthquake (Mw 5.5), while other minor but damaging events are the 5 January 1892 (Mw=5.0) and 16 November 1898 (Mw=4.6) earthquakes. On the reviewing we found common similarities in ground shaking distribution as recurrent damaged spots, amplification zones due to local site condition or energy radiation We believe that these findings are suitable to provide information for provisional purposes in low hazard level area hampered by the lack of knowledge about the seismic sources. New data are provided both in MCS scale and EMS. The sensitivity of a source parameters estimation technique was evaluated for the major event