MeMoVolc report on classification and dynamics of volcanic explosive eruptions

Classifications of volcanic eruptions were first introduced in the early twentieth century mostly based on qualitative observations of eruptive activity, and over time, they have gradually been developed to incorporate more quantitative descriptions of the eruptive products from both deposits and observations of active volcanoes. Progress in physical volcanology, and increased capability in monitoring, measuring and modelling of explosive eruptions, has highlighted shortcomings in the way we classify eruptions and triggered a debate around the need for eruption classification and the advantages and disadvantages of existing classification schemes. Here, we (i) review and assess existing classification schemes, focussing on subaerial eruptions; (ii) summarize the fundamental processes that drive and parameters that characterize explosive volcanism; (iii) identify and prioritize the main research that will improve the understanding, characterization and classification of volcanic eruptions and (iv) provide a roadmap for producing a rational and comprehensive classification scheme. In particular, classification schemes need to be objective-driven and simple enough to permit scientific exchange and promote transfer of knowledge beyond the scientific community. Schemes should be comprehensive and encompass a variety of products, eruptive styles and processes, including for example, lava flows, pyroclastic density currents, gas emissions and cinder cone or caldera formation. Open questions, processes and parameters that need to be addressed and better characterized in order to develop more comprehensive classification schemes and to advance our understanding of volcanic eruptions include conduit processes and dynamics, abrupt transitions in eruption regime, unsteadiness, eruption energy and energy balance

Suggestion for a new classification of earthquakes according to the focal depth

In this paper the Author suggests to regard the lowerlimit of the category of the so-called shallow earthquakes identical with thelevel of the regional isostatic compensation and the upper limit of theso-called deep shocks identical with the Byerly-discontinuity

Volcanism and seismicity in the Indo-Australian seismic belt: manifestations of intraplate tectonics

Disregarding the mid-oceanic ridges, the oceanic part of the Indo-Australian Seismic Belt is the longest, seismically active zone in theworld-ocean. It begins west of Ceylon and runs towards Australia. Theoceanic part does not show any correlation with seismologically importantsubmarine features, such as transform faults, rift valleys or oceanictrenches. On the basis of the distribution of earthquake-epicenters theauthor supposes that the belt does not end at the westernmost coast ofAustralia but penetrates the continent and can be detected as far assouth of Tasmania (Fig. 1). The length of the belt as a whole thus issome 11800 km out of which the length of its oceanic part measures about6500 km, which is much longer than an oceanic trench area or the islandarc, associated with it. The medium width of the belt is 1300 km. Allthe shocks are of shallow origin.The belt is characterized by a very mild volcanism; three submarineeruptions are known from the volcanological literature and two furthe

Some characteristics of the seismicity of the Tyrrhenian Sea Region

In the first p a r t of the paper the seismic strain release
 of the T y r r h e n i a n Sea Region (including Italy), as the function of time,
 is examined on the basis of t h e d a t a of the e a r t h q u a k e s t h a t took place
 f r om 1901.01.01 to 1970.12.31, between the northern l a t i t u d e s of 34° and
 44° and between the eastern longitudes of 8° and 18.5°, respectively. All
 registered shocks with a R i c h t e r - m a g n i t u d e of 5.5 or over it were considered,
 i n d e p e n d e n t l y f r om t h e focal d e p t h . Three periods were recognized in the
 a c t i v i t y ; t h e lengths of which are not t h e same, however.
 I n the second p a r t the elastic strain release in accordance with the
 focal d e p t h of t h e same e a r t h q u a k e s is t r e a t e d briefly. It was found t h at
 t h e t o t a l strain-release had a maximum value in t h e depth between 0 and
 74 kms and there was a minimum between the depth of 300 and 524 kins
 with an interval between 375 and 449 kms within which no earthquakes
 occurred at all. The general p a t t e r n of the d i s t r i b u t i o n of seismicity as
 t h e f u n c t i o n of hypocentral d e p t h reminds to the well-known picture, one
 can experience in other regions where i n t e r m e d i a t e and deep shocks occur.
 This s t a t e m e n t is consistent w i t h t h e idea, according to which t h e seismicity
 of t h e Tyrrhenian Sea Region can be discussed and explained in t h e light
 of t h e theory of new global tectonics.
 F i n a l l y , in the t h i r d p a r t of the study, the authors have s t a t e d t h at
 in some cases multiple events occurred b e n e a t h t h e Tyrrhenian Sea Region.
 Such multiple seismic events were detected in the case of other areas, such
 as the Fiji-Tonga-Kermadec Region, the seismic belt of South America
 etc., — but, according to the knowledge of t h e authors, this is t h e first occasion
 when multiple seismic events are demonstrated in the Tyrrhenian
 Sea Region