How strong will be the following earthquake?

<p>In this study, we have applied to northeastern Italy and western Slovenia medium-low seismicity an algorithm for strong aftershock forecasting we originally developed for medium-high seismicity in Italy (Gentili and Di Giovambattista, 2017). The method, called NESTORE (Next STrOng Related Earthquake), analyzes the seismicity after medium and strong earthquakes, in order to forecast if a subsequent large earthquake (SLE) will follow. A SLE following a main shock can cause significant damages to already weakened buildings and infrastructures, therefore a timely advisory information to the civil protection is of great interest for effective decision-making. We performed the analysis on different time-spans after the mainshock, in order to simulate the increase of information available as time passes during the seismic clusters. NESTORE subdivides the clusters of seismicity into two classes: “A” if the difference in magnitude between the mainshock and the strongest aftershock is lower than 1, and B otherwise. Several statistical features based on time-space and energy evolution of seismicity are analyzed separately and, if they are sufficiently informative for SLE forecasting, they are used for independent decision trees training. The results are merged together by a Bayesian approach, obtaining a time-dependent probability Prob(A) to have an A cluster, i.e. to have at least one SLE. This study is possible thanks to the OGS bulletins, an accurate local catalogue, characterized by low completeness magnitude, compiled by the National Institute of Oceanography and Experimental Geophysics. We tested the method on 1976 highly destructive Friuli cluster (mainshock magnitude 6.5 — the strongest in the last 80 years in the region) and on two small clusters of seismicity in NE Italy in 2019, obtaining encouraging results: 6 hours after the mainshock, for two A clusters NESTORE supplies Prob(A)=98% while for the B one Prob(A)=2%.</p>

The Influence of the Strong Aftershocks on Seismic Performance on Long-Span Arch Bridges Based on the Energy Method

Equivalent seismic wave can be formed by a main wave and two strong aftershock waves on the basis of energy equivalent principle. With a long-span arch bridge as a research object, the hysteretic energy distribution of the pier and arch were got by the action of the main wave and equivalent seismic wave based on energy method. And then the situation of bridge damage was assessed by Seismic Ditao Niu damage index, the regular pattern of structure damage affected by strong aftershock was revealed as well.

Enhanced ULF radiation observed by DEMETER two months around the strong 2010 Haiti earthquake

In this paper we study the energy of ULF electromagnetic waves that were recorded by the satellite DEMETER, during its passing over Haiti before and after a destructive earthquake. This earthquake occurred on 12 January 2010, at geographic Latitude 18.46° and Longitude 287.47°, with Magnitude 7.0 R. Specifically, we are focusing on the variations of energy of Ez-electric field component concerning a time period of 100 days before and 50 days after the strong earthquake. In order to study these variations, we have developed a novel method that can be divided in two stages: first we filter the signal, keeping only the ultra low frequencies and afterwards we eliminate its trend using techniques of Singular Spectrum Analysis (SSA), combined with a third-degree polynomial filter. As it is shown, a significant increase in energy is observed for the time interval of 30 days before the earthquake. This result clearly indicates that the change in the energy of ULF electromagnetic waves could be related to strong precursory earthquake phenomena. Moreover, changes in energy associated with strong aftershock activity were also observed 25 days after the earthquake. Finally, we present results concerning the comparison between changes in energy during night and day passes of the satellite over Haiti, which showed differences in the mean energy values, but similar results as far as the rate of the energy change is concerned.

Nonlinear Analysis of Structures Supported on Hysteric-Friction Isolation System with Elastic-Plastic Displacement-Constraint Device under Main Shock and Aftershock

The hysteric-friction isolation system with elastic-plastic displacement-constraint device is put forward. The action mechanism and restoring force model of the elastic-plastic displacement-constraint device are analyzed. The nonlinear seismic responses of structures supported on Hysteric-friction isolation system with elastic-plastic displacement-constraint device under main shock and aftershock are researched. The results indicate: the displacement-constraint device not only can ensure the upper structure safety, but also can effectively limit the displacement of the isolation layer, meanwhile can supply secondary protection under strong aftershock. The structure of the device is simply, which is convenient for production and installation. Meanwhile because the device is cheap, it can be widely used in isolation building.