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Statistical analysis of earthquake occurrences and implications for earthquake forecasting and seismichazard assessment
No full textThis dissertation is organized in three chapters:
1. Chapter I: Empirical evaluation of the magnitude-independence assumption;
2. Chapter II: Features of seismic sequences are similar in different crustal tectonic regions;
3. Chapter III: On the b-value estimation and its variability.
Chapter I and Chapter II consist of manuscripts presently in press on Geophysical Journal
International and submitted to Bulletin of the Seismological Society of America journals,
respectively. Chapter III is a document - including contributions from Ilaria Spassiani and
Matteo Taroni - that will be converted soon into a manuscript for publication.
In Chapter I, we focus on the magnitude-independence assumption (the magnitude of any
earthquake is independent from the past), which stands behind the most common earthquake
forecasting models. The reliability of this assumption, which severely limits the capability
to forecast large earthquakes with high probabilities, has been questioned by several authors,
who found evidence for correlated magnitudes and/or different seismicity patterns
before earthquakes of different magnitudes. Our goal is to contribute to this discussion by
empirically investigating the validity of the magnitude-independence assumption through a
comprehensive and rigorous analysis. Specifically: i) we implement a metric-based correlation
(inspired by the nearest-neighbor method proposed by Baiesi and Paczuski (2004)
and elaborated by Zaliapin et al. (2008)) to identify the precursory seismicity, avoiding the
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use of space-time-magnitude windows for the identification of foreshocks, mainshocks and
aftershocks; ii) we consider different instrumental catalogs and multiple synthetic (ETAS)
catalogs; iii) we carefully consider spatiotemporal variations of the magnitude of completeness
when statistically comparing the frequency-magnitude distribution of background and
triggered earthquakes; iv) we statistically analyze different space-time-magnitude features
of the seismicity which anticipates a triggered event. Our findings are in agreement with
the magnitude-independence assumption which stands behind the most common earthquake
forecast models. We find only one departure from the expected model: larger events tend
to nucleate at a higher distance from the ongoing sequence. This result, which confirms the
findings of a previous independent study, could be hopefully used to improve the current
forecasting models. We also notice that the reliability of the magnitude-independence assumption
may depend on the spatial scale considered, as we identify possible departures in
small areas, which could reflect different ways to release locally seismic energy. Finally, we
show that some significant departures from the magnitude-independence assumption do not
survive when considering spatiotemporal variations of the magnitude of completeness.
In Chapter II, we contribute to answer the following question: do earthquake cluster
properties change depending on the tectonic environment under consideration? The common
answer to this question is positive, and it is generally based on discrepancies observed
among a limited number of seismic sequences pertaining different tectonic environments.
We contribute to this discussion analyzing the clustering properties in three areas related
to distinct tectonic regimes: Italy, Southern California and Japan. Specifically, we investigate
on this aspect by i) adopting the nearest-neighbor method [Baiesi and Paczuski (2004);
Zaliapin et al. (2008)] to identify all the sequences of triggered events; ii) implementing a
comprehensive statistical analysis of several features of the seismicity recorded in different
instrumental catalogs. We demonstrate that sequences of triggered events are characterized
by comparable distributions through the three regions, though the latter are characterized
by a different dominant fault type (compressional, extensional or strike-slip). We conclude
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that, at least for active seismic crustal regions, the tectonic regime does not seem to play a
key role in affecting the spatiotemporal clustering properties. These findings have two important
implications: first, they suggest that calibrating earthquake forecast models based
on the specific tectonic regime may not be necessary, at least in the case of active seismic
crustal regions; second, they support the use of common declustering models, avoiding the
need to re-calibrate them according to the tectonic environment. As regards the background
seismicity, it shows some significant departures from the hypothesis of a stationary Poisson
process when looking at short time scales (1-year time intervals). This could suggest
transient perturbations of the background seismicity rate due to undetected seismicity or to
localized physical processes, whose effects seem to decrease on longer time scales.
In Chapter III, we focus on the b-value, one of the parameters of the well known magnitudefrequency
Gutenberg-Richter law. The main motivation is that its variability has often been
used to advocate its use as an earthquake precursor, and/or as a stress indicator. As a matter
of fact, many studies claim that a decrease of the b-value occurs before large earthquakes, a
feature which is generally explained in terms of increased stress. We argue that several factors,
which are very often neglected in seismology, may induce bias in the b-value estimation
and lead to apparent variations that do not have any real physical meaning. To show that,
we: i) analyze three theoretical biases: the Jensen inequality, the normal approximation
for the b-value error estimate, and the correlation between the b-value and the maximum
foreshock magnitude in the sequence; ii) we quantify (by numerical simulations) the bias
induced by an improper magnitude of completeness selection, which affects the analysis of
real seismic catalogs. We show that: i) the Jensen inequality and the normal approximation
for the b-value error estimate influence, at different degree, the b-value and its uncertainty for
catalogs with less than 100 data; ii) the maximum magnitude in the dataset may introduce
a bias in the b-value estimate, by yielding a systematic underestimation of the b-value when
a large earthquake is included; this bias is particularly severe for small datasets (N 500);
iii) it is very likely to estimate a significantly low b-value only as a consequence of the incom-
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pleteness of the catalog and goodness-of-fits test, such as the Lilliefors test, could fail to spot
an incomplete recording for small datasets, making this bias very difficult to be recognized:
iv) assuming, for any space-time subset of a catalog, the same completeness threshold as for
the whole catalog could induce strong errors
[Archivio Rai Teche: Presidente Aden Abdulla Osman visita Papa Paolo VI]
No full textIncontro ufficiale del Presidente Somalo Aden Abdulla Osman a Roma con Papa Paolo VI. Presenti il Cardinale Amleto Cicognani, il Ministro degli Esteri somalo Abdullahi Issa Mohamud, On. Mohamed Scek Dahir. Saluti e scambio di doni.Madaxweynaha Soomaaliyeed, Aadan Cabdulle Cusmaan iyo wafdigiisi waxay si rasmi ah ula kula kulmeen Roma Boobka Paolo VI. Waxaana goobjoog ka ahaa Cardinale Amleto Cicognani, Wasiirka arrimaha dibadda ee Soomaalia Cabdullaahi Ciise, mudane Maxamed Sh. Daahir. Salaan iyo haddiyado ayaa lays dhaafsaday.Official visit of Somali President Aden Adbullah Osman Daar in Rome to Pope Paul VI. At the presence of Italian cardinal Amleto Cicognani, the Somali Minister of Foreign Affairs Abdullahi Issa, Hon. Mohamed Sheikh Dahir. Greetings and gifts exchange.Link:http://www.teche.rai.it/techecustomer/somalia-filmati/fmt/iframe3/Materiale video messo a disposizione del Centro Studi Somali da Rai Teche.Vido-wyo ay Xarunta Cilmibaarista Soomaaliyeed ka heshay Rai Teche.Video made available by Rai Teche
Clothing and furnishings
No full textImage taken from the website "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) and included in the Somali Archive with the permission of the owner of the collection, Mr. Davies.Sawir laga soo qaatay mareegta: "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) oo lagu biiriyay Kaydka Soomaaliya, kaddib markii laga helay ruqsad milkiilaha Mr. Davies.Immagine tratta dal sito "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) e inclusa nell'Archivio Somalia con il consenso del curatore della collezione Rick Davies
Map of Somalia coast circa 1750
No full textImmagine tratta dal sito "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) e inclusa nell'Archivio Somalia con il consenso del curatore della collezione Rick Davies.Sawir laga soo qaatay mareegta "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) oo lagu biiriyay Kayda Soomaaliya, kaddib markii laga helay ruqsad milkiilaha sawwirrada, Rick Davies.Image taken from the website "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) and included in the Somali Archive with the permission of the owner of the collection, Mr. Davies
Bimal elders on board the Marco Polo, in 1907
No full textImage taken from the website "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) and included in the Somali Archive with the permission of the owner of the collection, Mr. Davies.Sawir laga soo qaatay mareegta "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/), waxaana lagu biiriyay Kaydka Soomaaliya, kaddib markii oggolaasho laga helay qofka diyaariyay oo ah Rick Davies.Immagine tratta dal sito "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) e inclusa nell'Archivio Somalia con il consenso del curatore della collezione Rick Davies
Maacluumaad hab waxbarid
No full textMacluumaad loogu talaggaly in wax lagu baro, gaar ahaan, caruurta Soomaaliyeed, oo ka kooban: heeso xul ah, magacyada midabbada iyo cilmiga oogada dhulka oo kooban.Materiali didattici destinati all'insegnamento prevalentemente a bambini somali: Heeso (Canzoni), Midabbada (I colori), Oogada Dhulka (Superficie Terrestre).Teaching material meant especially for Somali children: Heeso (Songs), Midabbada (The colours), Oogada Dhulka (Earth's Surface)
Afka iyo Dhaqanka Soomaaliyeed. Maxaa inaga khaldan?
No full textWaxaa Prof. Cabdalla Mansuur muxaadaradan ku falanqaynayaa dhibaatooyin la xiriira dhaqanka Soomaaliyeed: 1) wuxuu aaminsan yahay in Soomaalidu ay ku fashashay ama kari la’dahay in ay is waafajiso saddex nidaam oo ay ku dhaqanto, kuwaasoo kala ah: nidaam dowladeed, nidaam diimeed iyo nidaam dhaqameed, isla markiina middoodna si fiican uma haysato Soomaalidu; 2) Sidoo kale wuxuu falanqaynayaa jahawareer ka taagan haybta shakhsiga (ID) Soomaaliyeed oo aan xasillayn.Il Prof. Cabdalla Mansuur, nella sua conferenza, analizza alcuni problemi connessi alla cultura somala. 1. Egli ritiene che i somali abbiano fallito nel conciliare i tre seguenti sistemi: sistema governativo, sistema religioso e sistema tradizionale, e allo stesso momento non praticano bene nessuno dei tre; 2) analizza poi le cause dell'attuale confusione nell'uso scritto della lingua relativamente all'identità personale (ID) che non è stabile.Prof. Cabdalla Mansuur analyzes here some problems linked to Somali culture. 1. He affirms that Somalis have failed in conciliating the three following systems: government, religious and traditional system, while practicing righteously neither of them; 2. He analyzes the causes behind the confusion in the use of the written language relating to the personal identity (ID) which isn't fixed yet.Link: https://www.youtube.com/watch?v=eANVUvwowEs&feature=youtu.beSi aad u eegto videyahan samay download-ka faylkan kaddib guji link-iga ama u guuri link-iga bog cusub ee internet.Scaricare il file per accedere al link, oppure copiare il link in una nuova pagina internet.Download the file to access the link, or copy the link in a new page
Djibouti – Poste de Police – Place Menelick
No full textSawirkan waxaa laga soo qaatay mareegta "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) waxaana lagu biiriyay Kaydka Soomaaliya, kaddib markii ruqsad laga helay milkiilaha, Mr. Davies.Immagine tratta dal sito "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) e inclusa nell'Archivio Somalia con il consenso del curatore della collezione Rick Davies.Image taken from the website "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) and included in the Somali Archive with the permission of the owner of the collection, Mr. Davies
Somalia – Mogadiscio – Le Officine Boero
No full textImmagine tratta dal sito "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) e inclusa nell'Archivio Somalia con il consenso del curatore della collezione Rick Davies.Sawir laga soo qaatay mareegta "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/), waxaana lagu biiriyay Kaydka Soomaaliya, kaddib markii oggolaasho laga helay qofka diyaariyay oo ah Rick Davies.Image taken from the website "Mogadishu: Images from the past" (https://mogadishuimages.wordpress.com/) and included in the Somali Archive with the permission of the owner of the collection, Mr. Davies