ALBERT

Description: Existing evidence on the origin times of magnitude M≥7.5 earthquakes worldwide, based on authoritative earthquake catalogs, does not permit rejection of the null hypotheses of random coincidental occurrence at any time during the Earth or the Moon cycles. Specifically, the nonparametric Kuiper test statistics for cyclic variations applied to seismic evidence resulting from the empirical distributions of the M≥7.5 earthquake origin time Julian day (JD) and the Moon phase (MP) do not allow the rejection of the null hypotheses of uniform distributions within the corresponding cycles. On the other hand, the same Kuiper test permits the rejection of the null hypotheses of the same chance of occurrence on any JD or MP for strong magnitude M≥6.0 earthquakes, at least for the past four decades of presumably the best-earthquake determinations and, in particular, for earthquakes in the Northern Hemisphere (with an evident seasonal pattern). The nonparametric two-sample Kolmogorov–Smirnov test statistics suggest no preferred distances to the Moon at the occurrence of large earthquakes. All of this contributes, to the results of solid statistical testing of hypotheses, for a better understanding of the complex seismic response of the Earth’s lithosphere to periodic gravitational loading.

Description: Ischia island, in the province of Naples, is a densely populated volcanic island, in which small to moderate magnitude earthquakes occur. Due to the very shallowdepth of such events (〈 2 km), they can generate serious damage and casualties, up to the complete destruction of urban centers located within short epicentraldistance. Almost all of the earthquakes at Ischia island occur at shallow depth, beneath the Northern slopes of the Mt. Epomeo horst, which is located very close to thetown of Casamicciola. In fact, Casamicciola was completely destroyed by the 1883 earthquake (2313 victims) and experienced intensities up to XI degree on theMercalli scale. Historical records show that the background seismicity here is almost absent, but larger earthquakes tend to occur in clusters, lasting some decadesand with intervals between consecutive events on the order of years to decades. The clustering in time and the very shallow hypocentres, which cause, with respect totectonic earthquakes of similar magnitude, larger effects though limited to a relatively small area, make the seismicity in this island very peculiar. Despite suchdestructive record, till now official hazard maps strongly underestimated the seismic hazard in this area. On August 21st 2017, a very shallow earthquake with rathersmall magnitude struck the area of Casamicciola, killing two people, injuring many more and causing huge damage and partial to total collapse of edifices located justabove the earthquake fault.The maximum acceleration recorded for this earthquake exceeded by more than a factor of two the reference acceleration that should be sustained by edifices,according to official hazard maps. We propose here a complete procedure to assess and mitigate the risk, which can be rapid and economically affordable and, at thesame time, can avoid further grief due to possible occurrence of other destructive earthquakes within a short time interval. We describe the most likely buildingcollapse and casualty scenarios, in case that low-to-moderate magnitude earthquakes would occur before the edifices would be appropriately reinforced and secured.Our scenarios demonstrate the urgent need for securing operations. The proposed procedures for assessing seismic hazard and for securing urban areas provide anexample that is potentially applicable to the whole Italian peninsula. They may allow in fact the mitigation of the destructive impact of a large number of earth-quakes, which in Italy are often characterized by low or moderate magnitudes

Description: Published

Description: 105285

Description: 6T. Studi di pericolosità sismica e da maremoto

Description: JCR Journal