Relative frequencies of seismic main shocks after strong shocks in Italy

We analysed a catalogue of Italian earthquakes, covering 55 yr of data from 1960 to 2014 with magnitudes homogeneously converted to Mw, to compute the time-dependent relative frequencies with which strong seismic shocks (4.0 ≤ Mw < 5.0), widely felt by the population, have been followed by main shocks (Mw ≥ 5.0) that threatened the health and the properties of the persons living in the epicentral area. Assuming the stationarity of the seismic release properties, such frequencies are estimates of the probabilities of potentially destructive shocks after the occurrence of future strong shocks. We compared them with the time-independent relative frequencies of random occurrence in terms of the frequency gain that is the ratio between the time-dependent and time-independent relative frequencies. The time-dependent relative frequencies vary from less than 1 per cent to about 20 per cent, depending on the magnitudes of the shocks and the time windows considered (ranging from minutes to years). They remain almost constant for a few hours after the strong shock and then decrease with time logarithmically. Strong earthquakes (with Mw ≥ 6.0) mainly occurred within two or three months of the strong shock. The frequency gains vary from about 10 000 for very short time intervals to less than 10 for a time interval of 2 yr. Only about 1/3 of main shocks were preceded by at least a strong shock in the previous day and about 1/2 in the previous month

Evoluzione Biologica: La nascita dell' organizzazione del vivente

Saggio sul concetto e sull' evoluzione storico/scientifica di organizzazione dei sistemi vivent

Recalibration of the Intensity Prediction Equation in Italy Using the Macroseismic Dataset DBMI15 Version 2.0

We re-compute the coefficients of the intensity prediction equation (IPE) in Italy using the data of the DBMI15 V2.0 intensity database and the instrumental and combined (instrumental plus macroseismic) magnitudes reported by the CPTI15 V2.0 catalog. We follow the same procedure described in a previous article, consisting of a first step in which the attenuation of intensity I with respect to the distance D from macroseismic hypocenter is referred to the expected intensity at the epicenter IE and a second step in which IE is related to the instrumental magnitude Mi, the combined magnitude Mc, the epicentral intensity I0 and the maximum intensity Imax, using error-in-variable (EIV) regression methods. The main methodological difference with respect to the original article concerns the estimation of the uncertainty of IE to be used for EIV regressions, which is empirically derived from the standard deviation of regression between IE and Mi and also used for the regressions of IE with Mc, I0 and Imax. In summary, the new IPE determined from DBMI15 V2.0 is I=I_E-0.0081(D-h)-1.072[ln(D)-ln(h)] where D=√(R^2+h^2 ), h=4.49 km and IE can be calculated from the intensity data distribution of the earthquake. If the intensity data distribution is not available, IE can be calculated from the following relationships I_E=-2.578+1.867M_w I_E=I_

Harmonic Fluctuation of the Slope of the Frequency\u2013Magnitude Distribution (b\u2010Value) as a Function of the Angle of Rake

Previous works suggested that the slope (b-value) of the frequency\u2013magnitude distribution of earthquakes might significantly vary as a function of the style of faulting. In this work, we resume such hypothesis using improved datasets and procedures and by testing a simple harmonic functional form of the b-value as a function of the angle of rake \u3bb. Using the Global Centroid Moment Tensor (CMT) catalog updated to the middle of 2016, we reliably compute the b-value over 12 nonoverlapping rake windows with width \u3b3 30\ub0 showing a clear oscillating behavior with highs for normal and lows for reverse mechanisms. We also test the existence of a spatial link between variations of the style of faulting and of the b-value by determining the rake and the b-value separately from the Global CMT catalog and from a magnitude homogenized version of the bulletin of the International Seismological Centre, respectively, based on a spatial tessellation of the Earth\u2019s surface. For both approaches, we verify, using two statistical methods, that the b-values computed from earthquakes with different tectonic styles are actually different from each other for many combinations of rakes and particularly for all combinations of almost pure tectonic styles. We find that the fitted harmonic function has zero phase and unit frequency, thus indicating that b-value modulation is about proportional to 12sin \u3bb. Because the latter corresponds to the dot product between the unit versors of the coseismic displacement and of the gravity force component along the fault plane, b-value modulation appears to be about proportional to the work done by the gravity force during the fault slip

Earthquakes Parameters from Citizen Testimonies: A Retrospective Analysis of EMSC Database

We aim to compute macroseismic parameters (location and magnitude) using the BOXER code for the first time on the citizen testimonies, that is, individual intensity data points (IDPs) at the global scale collected and made available by the LastQuake system of the European-Mediterranean Seismological Centre (EMSC). IDPs available for different earthquakes are selected to eliminate those that are geographically inconsistent with most data; then they are clustered spatially based on various methods. For each cluster with at least three IDPs, a macroseismic data point (MDP), corresponding to an intensity value assessed for given localities as in classical macroseismic studies, is computed by various central tendency estimators (average, median, and trimmed averages). Finally, macroseismic parameters are obtained by MDP distribution using two location methods of BOXER code. For each earthquake, we used raw and corrected intensities and 132 different combinations of grouping methods, estimators, and BOXER methods. We assigned a ranking to the combinations that best reproduce instrumental parameters and used such a ranking to select preferred combinations for each earthquake. We analyzed retrospectively the reliability of the parameters as a function of time and space. The results are essentially identical using original and corrected intensities and show higher reliability for BOXER’s method 1 than for method 0; they are dependent on the geographical area, and generally improve over time and with the number of IDPs collected. These findings are useful for the future real-time analyses, and for evaluating the location and magnitude of earthquakes whenever a sufficient number of IDPs are available and with a distribution such that MDPs can be derived and the BOXER method applied

Automated assessment of macroseismic intensity from written sources using the fuzzy sets

We apply a computer-aided methodology to assess macroseismic intensity from the descriptions reported by documentary material available for eight Italian earthquakes occurred around the beginning of the instrumental era. The procedure consists of three phases: (i) the identification of significant macroseismic effects on the sources and their archiving in a georeferenced database, (ii) the association between the effects and the degrees of the intensity scale by the comparison with traditional estimates made by macroseismic experts, (iii) the assessment of intensities using a multi-attribute decision-making algorithm based on the Fuzzy Sets logic. This work represents a substantial improvement of our previous efforts as we completely redesigned the three phases of the procedure in the light of the experience of the last 10 years and analyzed six further Italian earthquakes so that our database now includes more than 19,000 encoded effects. Our formalized procedure allows to tracing all of the steps of intensity assessment process so that to identify discrepancies with respect to the expert evaluations that might be possibly due to mistakes or to the incomplete account of the available information. Hence, this approach may be useful for providing a systematic and reproducible intensity assessment as well as for supporting standard manmade assessments. The database of effects we have built could also be employed for testing the internal consistency of the macroseismic scale as well as for designing an improved macroseismic scale, based on consistent statistical criteria